Internet Engineering Task Force Internet Draft Rajesh Kumar Document: draft-ietf-mmusic-sdp-atm-00.txt Mohamed Mostafa September 12, 2000 Cisco Systems Expires: March 12, 2001 Conventions for the use of the Session Description Protocol (SDP) for ATM Bearer Connections STATUS OF THIS DOCUMENT This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as work in progress. The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document describes conventions for using the Session Description Protocol (SDP) described in RFC2327 [1] for controlling ATM Bearer Connections, and any associated ATM Adaptation Layer (AAL). The AALs addressed are Type 1, Type 2 and Type 5. This list of conventions is meant to be exhaustive. Individual applications can use subsets of these conventions. Further, these conventions are meant to comply strictly with the SDP syntax as defined in rfc2327. 1. Introduction...............................................................2 2. Representation of Certain Fields within SDP description lines..............4 2.2 Representation of Parameter Values.....................................4 2.3 Directionality Convention..............................................4 2.4 Case convention.........................................................5 3. Capabilities Provided by SDP conventions..................................5 4. Format of the ATM Session Description......................................6 5.1 The Origin Line.........................................................8 5.2 The Session Name Line...................................................9 5.3 The Connection Information Line.........................................9 5.4 The Timestamp Line.....................................................10 5.5 Media Information Line for ATM connections.............................11 5.5.1 The Virtual Connection ID.........................................11 5.5.2 The Transport Parameter...........................................13 5.5.3 The Format List for AAL1 and AAL5 applications....................15 5.5.4 The Format List for AAL2 applications.............................15 Rajesh Kumar, Mohamed Mostafa. 1 Internet Draft ATM SDP September 2000 5.5.5 Media information line construction...............................15 5.6 The Media Attribute Lines..............................................18 5.6.1 The 'atmmap' attribute.......................................21 5.6.2 The 'eecid' attribute............................................24 5.6.3 The 'aalType' attribute............................................25 5.6.4 The 'silenceSupp' attribute........................................25 5.6.5 The 'ecanf' and 'ecanb' attributes.................................26 5.6.6 The 'gcf' and 'gcb' attributes.....................................27 5.6.7 The 'profileDesc' attribute........................................28 5.6.8 The 'vsel' attribute...............................................29 5.6.9 The 'dsel' attribute...............................................30 5.6.10 The 'fsel' attribute..............................................31 5.6.11 The 'capability' attribute.......................................32 5.6.12 The 'qosClass' attribute.........................................33 5.6.13 The 'bcob' attribute.............................................33 5.6.14 The 'stc' attribute..............................................33 5.6.15 The 'upcc' attribute.............................................34 5.6.16 The 'atmQOSfparms' and 'atmQOSbparms' attributes..................34 5.6.17 The 'aal2QOSfparms' and 'aal2QOSbparms' attributes...............35 5.6.18 The 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes..................35 5.6.19 The 'aal2FtrfcDesc' and 'aal2BtrfcDesc' attributes...............37 5.6.20 The 'abrFparms' and 'abrBparms' attributes.......................37 5.6.21 The 'clkrec' attribute............................................38 5.6.23 The 'prtfl' attribute.............................................38 5.6.24 The 'bearerType' attribute........................................39 5.6.25 The 'structure' attribute.........................................40 5.6.26 The 'sbc' attribute...............................................40 5.6.27 The 'fcpsSDUsize' and 'bcpsSDUsize' attributes....................40 5.6.28 The 'aal2CPS' attribute...........................................41 5.6.29 The 'aal2sscs3661' attribute......................................41 5.6.30 The 'aal2sscs3662' attribute......................................42 5.6.31 The 'aalApp' attribute............................................43 5.6.32 The 'lij' attribute...............................................44 5.6.34 The 'cache' attribute.............................................45 5.6.35 Specification of Higher-layer attributes......................46 5.6.36 Use of the second media-level part in H.323 Annex C applications46 5.6.37 Chaining SDP descriptors........................................47 5.6.38 Use of the eecid media attribute in call establishment procedures47 6.0 List of Parameters with Representations...............................50 7.0 Examples of ATM session descriptions using SDP.........................57 8.0 Representation of data media..........................................58 9.0 Security Considerations..................................................59 9.1 Bearer Security.......................................................59 9.2 Security of the SDP description.......................................59 1. Introduction SDP will be used in conjunction with a connection handling /device control protocol such as Megaco (H.248) [26], SIP [18] or MGCP [25] to communicate the information needed to set up ATM and AAL2 bearer connections. These connections include voice connections, voiceband data connections, clear channel circuit emulation connections, video connections and baseband data connections (such as fax relay, modem relay, SSCOP, frame relay etc.). These conventions use standard SDP syntax as defined in rfc2327 to describe the ATM-level and AAL-level connections, addresses and other parameters. In general, parameters associated with layers higher than the ATM adaptation layer are included only if they are tightly coupled to the ATM or AAL layers. Since the syntax conforms to rfc2327, standard SDP parsers should react in a well-defined and safe Rajesh Kumar, Mohamed Mostafa. 2 Internet Draft ATM SDP September 2000 manner on receiving session descriptions based on the SDP conventions in this document. This is done by extending the values of fields defined in rfc2327 rather than by defining new fields. This is true for all SDP lines except the of the media attribute lines, in which case new attributes are defined. The SDP protocol allows the definition of new attributes in the media attribute lines which are free-form. For the remaining lines, the fact that the <networkType> field in an SDP descriptor is set to "ATM" should preclude the misinterpretation of extended parameter values by rfc2327-compliant SDP parsers. These conventions are meant to address the following ATM applications: 1. Applications in which a new SVC is set-up for each service connection. These SVCs could be AAL1 or AAL5 SVCs or single-CID AAL2 SVCs. 2. Applications in which existing path resources are assigned to service connections. These resources could be: * AAL1/AAL5 PVCs, SPVCs or cached SVCs, * AAL2 single-CID PVCs, SPVCs or cached SVCs, * CIDs within AAL2 SVCs/PVCs/SPVCs that multiplex multiple CIDs. Note that the difference between PVCs and SPVCs is in the way the bearer virtual circuit connection is set up. SPVCs are a class of PVCs that use bearer signaling, as opposed to node-by-node provisioning, for connection establishment. This document is limited to the case when the network type is ATM. This includes raw RTP encapsulation [45] or voice sample encapsulation [46] over AAL5 with no intervening IP layer. It does not address SDP usage for IP, with or without ATM as a lower layer. In some cases, IP connection set-up is independent of lower layers, which are configured prior to it. For example, AAL5 PVCs that connect IP routers can be used for VoIP calls. In other cases, VoIP call set-up is closely tied to ATM-level connection set-up. This might require a chaining of IP and ATM descriptors, as described in section 5.6.37. This document makes no assumptions on who constructs the session descriptions (media gateway, intermediate ATM/AAL2 switch, media gateway controller etc.). This will be different in different applications. Further, it allows the use of one session description for both directions of a connection (as in SIP and MGCP applications) or the use of separate session descriptions for different directions. It also addresses the ATM multicast and anycast capabilities. This document makes no assumptions about how the SDP description will be coded. Although the descriptions shown here are encoded as text, alternate codings are possible: - Binary encoding such as ASN.1. This is an option (in addition to text encoding) in the Megaco context. - Use of extended ISUP parameters [36] to encode the information in SDP descriptors, with conversion to/from binary/text-based SDP encoding when needed. Rajesh Kumar, Mohamed Mostafa. 3 Internet Draft ATM SDP September 2000 2. Representation of Certain Fields within SDP description lines This document conforms to the syntactic conventions of standard SDP as defined in RFC2327 [1]. 2.1 Representation of Extension Attributes The SDP protocol [1] requires that non-standard attributes and codec names use an "X-" prefix. In this internet draft, the "X-" prefix is used consistently for codec names (Table 2) that have not been registered with IANA [31]. However, this prefix is not used for the extension SDP attributes defined in this document. This has been done to enhance legibility. This document suggests that parsers be flexible in the use of the "X-" prefix convention. They should accept codec names and attribute names with or without the "X-" prefix. 2.2 Representation of Parameter Values Parsers designed to this document should be flexible enough to accommodate decimal and hexadecimal representations. The former do not have a prefix. The latter should use a "0x" prefix if values other than hexadecimal are permitted by the application. Even though Section 6.0 of this document might allow both decimal and hexadecimal values, some applications might limit value representations to hexadecimal or decimal. If only hex values are permitted, then the "0x" prefix can be safely omitted. For both decimal and hex representations, if the underlying bit field is smaller or larger than the binary equivalent of the SDP representation, then leading 0 bits should be added or removed as needed. Thus, 3 and 0x3 translate into the following five-bit pattern: 0 0011. The SDP representations 0x12 and 18 translate into the following five-bit pattern: 1 0010. Both single-character and multi-character string values are enclosed in double quotes (i.e. "). By contrast, single quotes (i.e. ') are used for emphasizing keywords rather than to refer to characters or strings. 2.3 Directionality Convention This section defined the meaning of the terms 'forward' and 'backward' as used in this document. This is specially applicable to parameters that have a specific direction associated with them. In this document, 'forward' refers to the direction away from the ATM node under consideration, while 'backward' refers to the direction towards the ATM node. This convention must be used in all SDP-based session descriptions regardless of whether underlying bearer is an SVC, a dynamically allocated PVC/SPVC or a dynamically allocated CID. This is regardless of which side originates the service connection. If ATM SVC or AAL2 Q.2630.1 signaling is used, the directionality convention is independent of which side originates the SVC or AAL2 connection. This provides a simple way of identifying the direction in which a parameter is applicable, in a manner that is independent of the underlying ATM or AAL2 bearer. This simplicity comes at a price, described below. Rajesh Kumar, Mohamed Mostafa. 4 Internet Draft ATM SDP September 2000 The convention used by all ATM/AAL2 signaling specifications (e.g. Q.2931 Section 1.3.3 and Q.2630.1) mandates that forward direction is from the end initiating setup/establishment via bearer signaling towards the end receiving the setup/establishment request. The backward direction is in the opposite direction. In some cases, the 'forward' and 'backward' directions of the ATM signaling convention might be the exact opposite of the SDP convention described above, requiring the media gateway to perform the necessary translation. An example case in which this is needed is described below. Consider an SDP description sent by a media gateway controller to the gateway originating a service-level call. In the backward SVC call set-up model, this gateway terminates (rather than originates) an SVC call. The media gateway refers to the traffic descriptor (and hence the PCR) in the direction away from this gateway as the forward traffic descriptor and forward PCR. Clearly, this is at odds with ATM SVC signaling which refers to this very PCR as the backward PCR. The gateway needs to be able to perform the required swap of directions. In this example, the media gateway terminating the service level call (and hence originating the SVC call) does not need to perform this swap. 2.4 Case convention As defined in RFC2327 [1], SDP syntax is case-sensitive. Since these ATM conventions conform strictly with SDP syntax, they are case-sensitive. SDP line types (e.g. "c", "m", "o", "a") and fields in the SDP lines should be built according to the case conventions in [1] and in this document. It is suggested, but not required, that SDP parsers for ATM applications be case- tolerant where ignoring case does not result in ambiguity. 3. Capabilities Provided by SDP conventions To support these applications listed in section 1, the SDP conventions in this document provide the following session control capabilities: * Identification of the underlying bearer network type as ATM. * Identification by an ATM network element of its own address, in one of several possible formats. A connection peer can initiate SVC set-up to this address. A call agent or connection peer can select an pre-established bearer path to this address. * Identification of the ATM bearer connection that is to be bound to the service-level connection. This is either a VCC in AAL1/AAL2/AAL5 applications or a channel (identified by a CID) in AAL2 applications. * Identification of media type: audio, video, data. * In AAL1/AAL5 applications, declaration of a set of payload types that can be bound to the ATM bearer connection. RTP payload types that have been registered with IANA are re-used for AAL1 or AAL5 [31]. In the manner of standard SDP, unregistered payload types are mapped dynamically. * In AAL2 applications, declaration of a set of profiles that can be bound to the ATM bearer connection. A mechanism for dynamically defining custom profiles within the SDP session description is included. This allows the use of custom profiles for connections that span multi-network interfaces. Rajesh Kumar, Mohamed Mostafa. 5 Internet Draft ATM SDP September 2000 * A means of correlating service-level connections with underlying ATM bearer connections. The backbone network connection identifier or bnc-id specified in ITU Q.1901 [36] standardization work is used for this purpose. In order to provide a common SDP base for applications based on Q.1901 and SIP/SIP+, the neutral term 'eecid' is used in lieu of 'bnc-id' in the SDP session descriptor. * A means of mapping codec types and packetization periods into service types (voice, voiceband data and facsimile). This is useful in determining the encoding to use when the connection is upspeeded in response to modem or facsimile tones. * A means of describing the adaptation type, QoS class, ATM transfer capability/service category, broadband bearer class, traffic parameters, CPS parameters and SSCS parameters related the underlying bearer connection. * Means for enabling or describing special functions such as leaf- initiated-join, anycast and SVC caching. * For H.323 Annex C applications, a means of specifying the IP address and port number on which the node will receive RTCP messages. * A means of chaining consecutive SDP descriptors so that they refer to different layers of the same connection. 4. Format of the ATM Session Description The sequence of lines in the session descriptions in this document conforms to rfc2327 [1]. In general, a session description consists of a session-level part followed by zero or more media-level parts. ATM session descriptions consist of a session level part followed by one or two media-level parts. The only two media applicable are the ATM medium and RTCP control (where applicable). Session descriptor with one media-level part: v= (protocol version, zero or one line) o= (origin, zero or one line) s= (session name, zero or one line) c= (connection information, one line) t= (timestamp, zero or one line) m= (media information and transport address, one line) b= (bandwidth, zero or one line) k= (encryption key, zero or one line) a= (media attribute, zero or more lines) Session descriptor with two media-level parts (used in h.323 annex C applications): Session-level part v= (protocol version, zero or one line) o= (origin, zero or one line) s= (session name, zero or one line) c= (connection information, one line) t= (timestamp, zero or one line) Rajesh Kumar, Mohamed Mostafa. 6 Internet Draft ATM SDP September 2000 media-level part (audio medium) m= (media information and transport address, one line) b= (bandwidth, zero or one line) k= (encryption key, zero or one line) a= (media attribute, zero or more lines) media-level part (control medium) m= (media information and transport address, one line) c= (connection information for control only, one line) In general, the 'v', 'o', 's', and 't' lines are mandatory. However, in the Megaco [26] context, these lines have been made optional. The 'o', 's', and 't' lines are omitted in most MGCP [25] applications. Note that SDP session descriptors for ATM can contain bandwidth (b=) and encryption key (k=) lines. Like all other lines, these lines should strictly conform to the SDP standard [1]. The bandwidth (b=) line is not necessarily redundant in the ATM context since, in some applications, it can be used to convey application-level information which does not map directly into the atmFtrfcDesc and atmBtrfcDesc media attribute lines. For instance, the 'b' line can be used in SDP descriptors in RTSP commands to describe content bandwidth. The encryption key line (k=) can be used to indicate an encryption key for the bearer, and a method to obtain the key. At present, the encryption of ATM and AAL2 bearers has not been conventionalized, unlike the encryption of RTP payloads. Nor has the authentication or encryption of ATM or AAL2 bearer signaling. In the ATM and AAL2 contexts, the term 'bearer' can include 'bearer signaling' as well as 'bearer payloads'. The order of lines in an ATM session description is exactly in the rfc2327-conformant order depicted above. However, there is no order of the media attribute ('a') lines with respect to other 'a' lines. The SDP protocol version for session descriptions using these conventions is 0. In conformance with standard SDP, it is strongly recommended that the 'v' line be included at the beginning of each SDP session description. In some contexts such as Megaco, the 'v' line is optional and may be omitted unless several session descriptions are provided in sequence, in which case the 'v' line serves as a delimiter. Depending on the application, sequences of session descriptions might refer to: - Different connections or sessions. - Alternate ways of realizing the same connection or session. - Different layers of the same session (section 5.6.37). The 'o', 's' and 't' lines are included for strict conformance with RFC2327. It is possible that these lines might not carry useful information in some ATM-based applications. Therefore, some applications might omit these lines, although it is recommended that they not do so. For maximum interoperability, it is preferable that SDP parsers not reject session descriptions that do not contain these lines. Rajesh Kumar, Mohamed Mostafa. 7 Internet Draft ATM SDP September 2000 5. Structure of the Session Description Lines 5.1 The Origin Line The origin line for an ATM-based session is structured as follows: o=<username> <sessionID><version> <networkType> <ATMaddressType> <ATMaddress> The <username> is set to "-". The <sessionID> can be set to one of the following: * an NTP timestamp referring to the moment when the SDP session descriptor was created. * a Call ID, connection ID or context ID that uniquely identifies the session within the scope of the ATM node. Since calls can comprise multiple connections (sessions), call IDs are generally not suitable for this purpose. NTP time stamps can be represented as decimal or hex integers. The part of the NTP timestamp that refers to an integer number of seconds is sufficient. Since this is a 32-bit field, the decimal or hex equivalent of a 32-bit field is adequate if NTP time stamps are used for this purpose. On the other hand, call IDs, connection IDs and context IDs can be represented in decimal or hex format, or as a string of alphanumeric characters. The MGCP connection ID can be 32 hex digits long. In general, to cover all cases, the <sessionID> can comprise of up to 34 alphanumeric characters. The additional two characters allow the inclusion of a "0x" prefix before 32 hex digits. The <version> refers to the version of the SDP session descriptor (not that of the SDP protocol). This is can be set to one of the following: * 0. * an NTP timestamp referring to the moment when the SDP session descriptor was modified. If the SDP session descriptor has not been modified by an intermediate entity (such as an MGC), then the <version> timestamp will be the same as the <sessionId> timestamp, if any. As with the <sessionId>, only the integer part of the NTP timestamp is used. It is adequate to allow up to 10 decimal or 8 hex digits for the <version>. This is enough to represent the integer part of an NTP timestamp. The <networkType> in SDP session descriptions for ATM applications should be assigned the string value "ATM". The <ATMaddressType> and <ATMaddress> parameters are identical to those for the connection information ('c') line. Each of these parameters can be set to a "-". However, it is not recommended that these fields be omitted without being set to a "-" since this is not explicitly allowed by standard SDP (rfc2327). It is recognized that some parser-builders follow this practice. Rajesh Kumar, Mohamed Mostafa. 8 Internet Draft ATM SDP September 2000 5.2 The Session Name Line In general, the session name line is structured as follows: s=<sessionName> For ATM-based sessions, the <sessionName> parameter is set to a "-". The resulting line is: s=- It is not recommended that the <sessionName> be omitted without being set to a "-" since this is not explicitly allowed by standard SDP (rfc2327). It is recognized that some parser-builders follow this practice. 5.3 The Connection Information Line The connection information line for ATM-based sessions is structured as follows: c=<networkType> <ATMaddressType> <ATMaddress> The <networkType> field in the 'c' line should be set to "ATM". When the SDP description is built by an ATM node such as a media gateway, the <ATMaddress> refers to the ATM address of the node building the SDP description. When this description is forwarded to another node, it still contains the original node's ATM address. When the media gateway controller builds part or all of the SDP description, the local descriptor can contain the ATM address of the local node, while the remote descriptor can contain the ATM address of the remote node. In most applications, the <ATM address> and <ATMaddressType> in the local descriptor are each set to "-". Additionally, in all contexts, the 'm' line can have an ATM address in the <virtualConnectionId> subparameter which, if present, is the remote address if the 'c' line address is local, and vice versa. The <ATMaddressType> can be NSAP, E164 or GWID (ALIAS). The <ATMaddress> format depends on the <ATMaddressType>. NSAP: If the ATMaddressType is NSAP, the ATMaddress is expressed as a string of 40 hex characters without the "0x" prefix. As an option, dots can be included after 16-bit fields, with the first dot following an 8-bit field (standard dotted hex NSAP format). The last octet of the NSAP address is the 'selector' field that is not used for ATM addressing and is available for non-standard use. For example: c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 E164: If the ATMaddressType is E164, the ATMaddress is expressed as a decimal number with up to 15 digits. For example: c=ATM E164 9738294382 The use of E.164 numbers in the B-ISDN context is defined in ITU E.191. There is a disparity between the ATM forum and the ITU in the use of E.164 numbers for ATM addressing. The ATM forum (e.g. UNI Rajesh Kumar, Mohamed Mostafa. 9 Internet Draft ATM SDP September 2000 Signaling 4.0) allows only International Format E.164 numbers, while the ITU (e.g. Q.2931) allows private numbering plans. Since the goal of this SDP specification is to interoperate with all bearer signaling protocols, it allows the use of numbers that do not conform to the E.164 International Format. However, to maximize overall consistency, network administrators can restrict the provisioning of numbers to the E.164 International Format. GWID (ALIAS): If the ATMaddressType is GWID meaning that the address is a Gateway Identifier or Node Alias. This may or may not be globally unique. In this case, the ATMaddress is expressed as alphanumeric string ("A"-"Z", "a"-"z", "0" - "9",".","-","_"). For example: c=ATM GWID officeABCmgx101vism12 Since these SDP conventions can be used for more than gateways, the string "ALIAS" can be used instead of "GWID" in the 'c' line. Thus, the example above is equivalent to: c=ATM ALIAS officeABCmgx101vism12 An example of a GWID (ALIAS)is the CLLI code used for telecom equipment. For all practical purposes, it should be adequate for the GWID (ALIAS) to be a variable length string with a maximum size of 32 characters. Some network administrations might restrict it to a smaller size (e.g. 15 characters). The connection information line is always present in an SDP session descriptor. However, if there is no address to transmit, this line can be represented in the following way: c=ATM - - This might be used when the address is known a priori. It is not recommended that <ATMaddressType> or <ATMaddress> be omitted without being set to a "-" since this is not explicitly allowed by standard SDP (rfc2327). It is recognized that some parser-builders follow this practice. 5.4 The Timestamp Line The timestamp line for an SDP session descriptor is structured as follows: t= <startTime> <stopTime> For ATM-based sessions, the <startTime>parameter can be made equal to the NTP timestamp (if any) used for the <sessionID> in the 'o' line. It can also be set to 0 indicating its irrelevance. If it made equal to the NTP timestamp in seconds, the fractional part of the NTP timestamp is omitted. In this case, it is adequate to allow the hex or decimal equivalent of a 32-bit field. Per Ref. [49], NTP time stamps use a 32 bit unsigned representation of seconds, and a 32 bit unsigned representation of fractional seconds. The <stopTime> parameter is set to 0 for ATM-based SDP descriptors. Rajesh Kumar, Mohamed Mostafa. 10 Internet Draft ATM SDP September 2000 5.5 Media Information Line for ATM connections The general format of the media information line adapted for AAL1 and AAL5 applications is: m=<media> <virtualConnectionId> <transport> <format list> The general format of the media information line adapted for AAL2 applications is: m=<media> <virtualConnectionId> <transport#1> <format list#1> <transport#2> <format list#2> ... <transport#M> <format list#M> Note that <virtualConnectionId> is equivalent to <port> in [1]. The subparameter <media> can take on all the values defined in [1]. These are: "audio", "video", "application", "data" and "control". When the <transport> parameter has more than one value in the 'm' line, the <transport> <format list> pairs can be arranged in preferential order. 5.5.1 The Virtual Connection ID The <virtualConnectionId> parameter can be in one of two basic formats: with explicit designation of subparameter types within the <virtualConnectionId> parameter, or with implicit inference of subparameter type from subparameter position in the <virtualConnectionId> parameter. In general, explicit designation is recommended for open, interoperable, large- scale applications. However, implicit designation is retained as a shortcut in smaller applications where the number of options is limited and the subparameter type can be inferred unambiguously from its position relative to slashes and hyphens, if any. This narrowing of options can be done on the basis of embedded defaults or prior provisioning. Likewise, in some cases of implicit designation, omitted ATM address types are known by default or through provisioning. With implicit inference of subparameter type from subparameter position, the AAL1 or AAL5 <virtualConnectionId> can be in one of the following formats (parameter definitions provided later): * <vcci> * <ATMaddressType>-<ATMaddress>/<vcci> * <ATMaddress>/<vcci> * <bcg>/<vcci> * <portId>/<vpi>/<vci> * <bcg>/<vpi>/<vci> * <vpci>/<vci> * <ATMaddressType>-<ATMaddress>/<vpci>/<vci> * <ATMaddress>/<vpci>/<vci> With implicit inference of subparameter type from subparameter position, the AAL2 <virtualConnectionId> can be in one of the following formats (parameter definitions provided later): * <vcci>/<cid> * <ATMaddressType>-<ATMaddress>/<vcci>/<cid> * <ATMaddress>/<vcci>/<cid> * <bcg>/<vcci>/<cid> * <portId>/<vpi>/<vci>/<cid> * <bcg>/<vpi>/<vci>/<cid> Rajesh Kumar, Mohamed Mostafa. 11 Internet Draft ATM SDP September 2000 * <vpci>/<vci>/<cid> * <ATMaddressType>-<ATMaddress>/<vpci>/<vci>/<cid> * <ATMaddress>/<vpci>/<vci>/<cid> With explicit designation of subparameter types, the <virtualConnectionId> in AAL1 and AAL5 applications can be in one of the following formats (parameter definitions provided later): * <ex_vcci> * <ATMaddressType>-<ATMaddress>/<ex_vcci> * <ATMaddress>/<ex_vcci> * <ex_bcg>/<ex_vcci> * <ex_portId>/<ex_vpi>/<ex_vci> * <ex_bcg>/<ex_vpi>/<ex_vci> * <ex_vpci>/<ex_vci> * <ATMaddressType>-<ATMaddress>/<ex_vpci>/<ex_vci> * <ATMaddress>/<ex_vpci>/<ex_vci> With explicit designation of subparameter types, the <virtualConnectionId> in AAL2 applications can be in one of the following formats (parameter definitions provided later): * <ex_vcci>/<ex_cid> * <ATMaddressType>-<ATMaddress>/<ex_vcci>/<ex_cid> * <ATMaddress>/<ex_vcci>/<ex_cid> * <ex_bcg>/<ex_vcci>/<ex_cid> * <ex_portId>/<ex_vpi>/<ex_vci>/<ex_cid> * <ex_bcg>/<ex_vpi>/<ex_vci>/<ex_cid> * <ex_vpci>/<ex_vci>/<ex_cid> * <ATMaddressType>-<ATMaddress>/<ex_vpci>/<ex_vci>/<ex_cid> * <ATMaddress>/<ex_vpci>/<ex_vci>/<ex_cid> Here, <ex_vcci> = VCCI-<vcci> <ex_vpci> = VPCI-<vpci> <ex_bcg> = BCG-<bcg> <ex_portId> = PORT-<portId> <ex_vpi> = VPI-<vpi> <ex_vci> = VCI-<vci> <ex_cid> = CID-<cid> The <vcci>, <portId>, <vpi>, <vci>, <vpci> and <cid> are decimal numbers or hexadecimal numbers. The <ATMaddressType> and <ATMaddress> are identical to their definitions above for the connection information line with the difference that this address refers to the remote peer in the media information line. The <vpi>, <vci> and <cid> have their usual ATM connotation. The <vpci> is a 16 bit field defined in Section 4.5.16 of ITU Q.2931 [Ref. 15]. The <vpci> is similar to the <vpi>,except for its width and the fact that it retains its value across VP crossconnects. In some applications, the size of the <vpci> is the same as the size of the <vpi> (8 or 12 bits). In this case, the most significant 8 or 4 bits are ignored. The <vcci> is a 16 bit field defined in ITU Recommendation Q.2941.2 [32]. The <vcci> is similar to the <vci>, except for the fact that it retains its value across VC crossconnects. Since <vpci> and <vcci> values are unique between a pair of nodes, they Rajesh Kumar, Mohamed Mostafa. 12 Internet Draft ATM SDP September 2000 need to be qualified, at any node, by the ATM address of the remote node. These parameters can be pre-provisioned or signaled. When signaled, the <vpci> is encapsulated in the connection identifier information element of SVC signaling messages. The <vcci> is encapsulated in the Generic Information Transport (GIT) information element of SVC signaling messages. In an ATM node pair, either node can assign <vcci> values and signal it to the other end via SVC signaling. A glare avoidance scheme is defined in [32] and [44].This mechanism works in SVC applications. A different glare avoidance technique is needed when a pool of existing PVCs/SPVCs is dynamically assigned to calls. One such scheme for glare reduction is the assignment of <vcci> values from different ends of the <vcci> range, using the lowest or highest available value as applicable. When <vpci> and <vcci> values are pre-provisioned, administrations have the option of provisioning them uniquely in a network or in a subnet. In this case, the ATM address of the far end is not needed to qualify these parameters. In the AAL2 context, the definition of a VCC implies that there is no CID-level switching between its ends. If either end can assign <cid> values, then a glare reduction mechanism is needed. One such scheme for glare reduction is the assignment of <cid> values from different ends of the <cid> range, using the lowest or highest available value as applicable. The <portId> parameter is used to identify the physical trunk port on a stand-alone ATM node or on a multiplexer into which the gateway is plugged as a tributary module. It can be represented as a decimal or hex number of up to 32 digits, or an alphanumeric string of up to 32 characters. In general, to cover all cases, the <portID> can consist of up to 34 alphanumeric characters. The additional two characters allow the inclusion of a "0x" prefix for hex digits. In some applications, it is meaningful to bundle a set of connections between a pair of ATM nodes into a bearer connection group. The <bcg> subparameter is an eight bit field that allows the bundling of up to 255 VPCs or VCCs. In some applications, it is necessary to wildcard the <virtualConnectionId> parameter, or some elements of this parameter. The "$" wildcard character can be substituted for the entire <virtualConnectionId> parameter, or some of its terms. A wildcarded <virtualConnectionId> can use the explicit or implicit formats described above. In the former, the constant strings that qualify the terms in the <virtualConnectionId> are retained. The concatenation <ATMaddressType>-<ATMaddress> can be wildcarded in the following ways: * The entire concatenation, <ATMaddressType>-<ATMaddress>, is replaced with a "$". * <ATMaddress> is replaced with a "$", but <ATMaddressType> is not. Examples of wildcarding the <virtualConnectionId> in the AAL1 and AAL5 contexts are: $, 62/$, 100/20/$, VCCI-$, BCG-100/VPI-20/VCI-$. Examples of wildcarding the <virtualConnectionId> in the AAL2 context are: $, 62/$, 100/20/$, VCCI-40/CID-$, BCG-100/VPI-20/VCI-120/CID-$. 5.5.2 The Transport Parameter The <transport> parameter indicates the method used to encapsulate the service payload. These methods are not defined in this document, which refers to existing ATMF and ITU-T standards, which, in turn, might Rajesh Kumar, Mohamed Mostafa. 13 Internet Draft ATM SDP September 2000 refer to other standards. For ATM applications, the following <transport> values are defined: Table 1: List of Transport Parameter values used in SDP in the ATM context +---------------------------------------------------------------------+ | | Controlling Document for | | Transport | Encapsulation of Service Payload | +------------------------+--------------------------------------------+ | AAL1/ATMF | af-vtoa-0078.000 [7] | +------------------------+--------------------------------------------+ | AAL1/ITU | ITU-T H.222.1 [51] | +------------------------+--------------------------------------------+ | AAL5/ATMF | af-vtoa-0083.000 [46] | +------------------------+--------------------------------------------+ | AAL5/ITU | ITU-T H.222.1 [51] | +------------------------+--------------------------------------------+ | AAL2/ATMF | af-vtoa-0113.000 [44] and | | | af-vmoa-0145.000 [52] | +------------------------+--------------------------------------------+ | AAL2/ITU | ITU-T I.366.2 [13] | +------------------------+--------------------------------------------+ | AAL1/custom | Corporate document or | | AAL2/custom | application-specific interoperability | | AAL5/custom | statement. | +------------------------+--------------------------------------------+ | AAL1/<corporateName> | | | AAL2/<corporateName> | | | AAL5/<corporateName> | | | AAL1/IEEE:<oui> | Corporate document | | AAL2/IEEE:<oui> | | | AAL5/IEEE:<oui> | | +------------------------+--------------------------------------------+ | RTP/AVP | Annex C of H.323 [45] | +------------------------+--------------------------------------------+ In H.323 Annex C applications [45], the <transport> parameter has a value of "RTP/AVP". This is because these applications use the RTP protocol [2] and audio/video profile [3]. The fact that RTP is carried directly over AAL5 per [45] can be indicated explicitly via the aalApp media attribute. A value of "AAL1/custom", "AAL2/custom" or "AAL5/custom" for the <transport> parameter can indicate non-standard or semi-standard encapsulation schemes defined by a corporation or a multi-vendor agreement. Since there is no standard administration of this convention, care should be taken to preclude inconsistencies within the scope of a deployment. The use of <transport> values "AAL1/<corporateName>", "AAL2/<corporateName>", "AAL5/<corporateName>", "AAL1/IEEE:<oui>", "AAL2/IEEE:<oui>" and "AAL5/IEEE:<oui>" is similar. These indicate non-standard transport mechanisms or AAL2 profiles which should be used consistently within the scope of an application or deployment. The parameter <corporateName> is the registered, globally unique name of a corporation(e.g. Cisco, Telcordia etc.). The parameter <oui> is the hex representation of a three-octet field identical to the OUI maintained by the IEEE. Since this is always represented in hex, the "0x" prefix is not used. For example, "IEEE:00000C" is one of the <oui> values that refers to Cisco Systems, Inc. Rajesh Kumar, Mohamed Mostafa. 14 Internet Draft ATM SDP September 2000 5.5.3 The Format List for AAL1 and AAL5 applications In the AAL1 and AAL5 contexts, the <format list> is a list of payload types: <payloadType#1> <payloadType#2>...<payloadType#n> In most AAL1 and AAL5 applications, the ordering of payload types implies a preference (preferred payload types before less favored ones). The payload type can be statically assigned or dynamically mapped. Although the transport is not the same, SDP in the ATM context leverages the encoding names and payload types registered with IANA [31] for RTP. These are the statically assigned payload types. Encodings that are not statically mapped to payload types by IANA are to be dynamically mapped at the time of connection establishment to payload types in the decimal range 96-127. The SDP 'atmmap' attribute (similar to 'rtpmap') is used for this purpose. Table 2 lists a few key standard encoding names with their corresponding statically assigned payload types from Ref. 31. It also suggests encoding names for some other key codecs not addressed in [31]. For these, payload types are mapped dynamically via the 'atmmap' attribute. These lists of statically assigned and dynamically mapped codec names are not meant to be exhaustive. Ref. 31 should be considered the exhaustive list of statically assigned payload types. 5.5.4 The Format List for AAL2 applications In the AAL2 context, the <format list> is a list of AAL2 profile types: <profile#1> <profile#2>...<profile#n> In most applications, the ordering of profiles implies a preference (preferred profiles before less favored ones). The <profile> parameter is expressed as a decimal number in the range 1-255. 5.5.5 Media information line construction Using the parameter definitions above, the 'm' for AAL1-based audio media can be constructed as follows: m=audio <virtualConnectionId> AAL1/ATMF <payloadType#1> <payloadType#2>...<payloadType #n> Note that only those payload types, whether statically mapped or dynamically assigned, that are consistent with af-vtoa-78 [7] can be used in this construction. Backwards compatibility note: The transport value "AAL1/AVP" used in previous versions of this document should be considered equivalent to the value "AAL1/ATMF" defined above. "AAL1/AVP" is unsuitable because the AVP profile is closely tied to RTP. An example 'm' line use for audio media over AAL1 is: m=audio VCCI-27 AAL1/ATMF 0 This indicates the use of an AAL1 VCC with VCCI=24 to carry PCMU audio Rajesh Kumar, Mohamed Mostafa. 15 Internet Draft ATM SDP September 2000 that is encapsulated according to ATMF's af-vtoa-78 [7]. Another example of the use of the 'm' line use for audio media over AAL1 is: m=audio $ AAL1/ATMF 0 8 This indicates that any AAL1 VCC may be used. If it exists already, then its selection is subject to glare rules. The audio media on this VCC is encapsulated according to ATMF's af-vtoa-78 [7]. The encodings to be used are either PCMU or PCMA, in preferential order. In some applications, an "-" can be used in lieu of the <payloadType> and <transport>. This implies that the encoding scheme and encapsulation method are described elsewhere, or defaulted. For example: m=audio VCCI-234 - - a=aalType:AAL1 indicates the use of VCCI=234 with AAL1 adaptation and unspecified encoding. The 'm' for AAL5-based audio media can be constructed as follows: m=audio <virtualConnectionId> AAL5/ATMF <payloadType#1> <payloadType#2>...<payloadType #n> An example 'm' line use for audio media over AAL5 is: m=audio 2/6/$ AAL5/ITU 9 15 implies that any VCI on VPI= 6 of trunk port #2 may be used. The identities of the terms in the virtual connection ID are implicit in the application context. The audio media on this VCC is encapsulated according to ITU-T H.222.1 [51]. The encodings to be used are either ITU-T G.722 or ITU-T G.728 (LD-CELP), in preferential order. The 'm' for AAL5-based H.323 Annex C audio [45] can be constructed as follows: m=audio <virtualConnectionId> RTP/AVP <payloadType#1> <payloadType#2>...<payloadType #n> For example: m=audio PORT-9/VPI-3/VCI-$ RTP/AVP 2 96 a=rtpmap:96 X-G727-32 a=aalType:AAL5 a=aalApp:h323c implies that any VCI on VPI= 3 of trunk port #9 may be used. This VC encapsulates RTP packets directly on AAL5 per [45]. The 'rtpmap' (rather than the 'atmmap') attribute is used to dynamically map the payload type of 96 into the codec name X-G727-32 (Table 2). This name represents 32 kbps EADPCM. The 'm' for AAL5-based video media can be constructed as follows: m=video <virtualConnectionId> AAL5/ITU <payloadType#1> <payloadType#2>...<payloadType #n> Rajesh Kumar, Mohamed Mostafa. 16 Internet Draft ATM SDP September 2000 In this case, the use of AAL5/ITU as the transport points to H.222.1 as the controlling standard [51].An example 'm' line use for video media is: m=video PORT-9/VPI-3/VCI-$ AAL5/ITU 33 This indicates that any VCI on VPI= 3 of trunk port #9 may be used. The video media on this VCC is encapsulated according to ITU-T H.222.1 [51]. The encoding scheme is an MPEG 2 transport stream ("MP2T" in Table 1). This is statically mapped per [31] to a payload type of 33. The media information line for AAL5-based sessions with a "data" media type has the following format: m=data <virtualConnectionId> - - In this case, the adaptation type is known from the aalType attribute rather than the 'm' line. For example: m=data PORT-7/VPI-6/VCI-$ - - a=aalType:AAL5 a=aalApp:assuredSSCOP implies that any VCI on VPI= 6 of trunk port #7 may be used. This VC uses assured SSCOP on AAL5 to transport data. Using the parameter definitions in the previous subsections, the media information line for AAL2-based audio media can be constructed as follows: m=<media> <virtualConnectionId> <transport#1> <format list#1> <transport#2> <format list#2> ... <transport#M> <format list#M> where <format list#i> has the form <profile#i_1>...<profile#i_N> Unlike the 'm' line for AAL1 or AAL5 applications, the 'm' line for AAL2 applications can have multiple <transport> parameters, each followed by a <format list>. This is because it is possible to consider definitions from multiple sources (ATMF, ITU and non-standard documents) when selecting AAL2 profile to be bound to a connection. In most applications, the ordering of profiles implies a preference (preferred profiles before less favored ones). Therefore, there can be multiple instances of the same <transport> value in the same 'm' line. An example 'm' line use for audio media over AAL2 is: m=audio VCCI-27/CID-19 AAL2/ITU 7 AAL2/custom 100 AAL2/ITU 1 This indicates the use of CID #19 on VCCI #27 to carry audio. It provides a preferential list of profiles for this connection: profile AAL2/ITU 7 defined in [13], AAL2/custom 100 defined in an application-specific or interoperability document and profile AAL2/ITU 1 defined in [13]. Another example of the use of the 'm' line use for audio media over AAL2 is: m=audio VCCI-$/CID-$ AAL2/ATMF 6 8 This indicates that any AAL2 CID may be used, subject to any applicable glare avoidance/reduction rules. The profiles that can be bound to this Rajesh Kumar, Mohamed Mostafa. 17 Internet Draft ATM SDP September 2000 connection are AAL2/ATMF 6 defined in af-vtoa-0113.000 [44] and AAL2/ATMF 8 defined in af-vmoa-0145.000 [52]. These sources use non-overlapping profile number ranges. The profiles they define fall under the <transport> category "AAL2/ATMF". This application does not order profiles preferentially. This rule is known a priori. It is not embedded in the 'm' line. Another example of the use of the 'm' line use for audio media over AAL2 is: m=audio VCCI-20/CID-$ AAL2/xyzCorporation 11 AAL2 VCCs in this application are single-CID VCCs. Therefore, it is possible to wildcard the CID. The single-CID VCC with VCCI=20 is selected. The AAL2 profile to be used is AAL2/xyzCorporation 11 defined by xyzCorporation. In some applications, an "-" can be used in lieu of the <transport> and <profile#> fields. This is possible when the coding scheme is described elsewhere e.g. when 'aal2sscs3662' attribute indicates <faxDemod> = "on" and any other competing options as "off", and the <aalType> attribute indicates AAL2. An example of the use of the 'm' line in this case is: m=audio 123/5 - - a=aalType:AAL2 a=aal2sscs3662:audio off off on off on off off off - - - Besides indicating an audio medium, a VCCI of 123 and a CID of 5, the 'm' line indicates an unspecified profile. The media attribute lines indicate an adaptation layer of AAL2, and the use of the audio SAP [13] to carry demodulated facsimile. 5.6 The Media Attribute Lines In an SDP line sequence, the media information line 'm' is followed by one or more media attribute or 'a' lines. Media attribute lines are per the format below: a=<attribute>:<value> or a=<value> In general, media attribute lines are optional except when needed to qualify the media information line. This qualification is necessary when the "m" line for an AAL1 or AAL5 session specifies a payload type that needs to be dynamically mapped. The 'atmmap' media attribute line defined below is used for this purpose. In attribute lines, subparameters that are meant to be left unspecified are set to a "-". These are generally inapplicable or, if applicable, are known by other means such as provisioning. In some cases, a media attribute line with all parameters set to "-" carries no information and should be preferably omitted. In other cases, such as the 'lij' media attribute line, the very presence of the media attribute line conveys meaning. There are no restrictions placed by rfc2327 [1] regarding the order of 'a' lines with respect to other 'a' lines. However, these lines must not contradict each other or the other SDP lines. Inconsistencies Rajesh Kumar, Mohamed Mostafa. 18 Internet Draft ATM SDP September 2000 are not to be ignored and should be flagged as errors. Repeated media attribute lines can carry additional information. These should not be inconsistent with each other. Applications will selectively use the optional media attribute lines listed below. This is meant to be an exhaustive list for describing the general attributes of ATM bearer networks. However, it is recognized that this list might have overlooked some attributes, which particular applications might need. If these are common enough for general interoperability between vendors (as opposed to innovation and proprietary differentiation by particular vendors), then these should be brought to the attention of the IETF MMUSIC working group or the authors for incorporation into the RFC that will evolve out of this document. The following is a summary list of the SDP media attributes that can be used in the ATM context. Detailed descriptions of these attributes are to be found in subsequent sections. * The attributes defined in RFC2327 which allow indication of the direction in which a session is active. These are a=sendonly, a=recvonly, a=sendrecv, a=inactive. * The 'Ptime' attribute defined in RFC2327. It indicates the packet period. It is not recommended that this attribute be used in ATM applications since packet period information is provided with other parameters e.g. the profile type and number in the 'm' line, and the 'vsel', 'dsel' and 'fsel' attributes. Also, for AAL1 applications, 'ptime' is not applicable and should be flagged as an error. If used in AAL2 and AAL5 applications, 'ptime' should be consistent with the rest of the SDP description. * The 'atmmap' attribute. In the AAL1 and AAL5 contexts, this is used to dynamically map payload types into codec strings. * The 'eecid' attribute. This stands for 'end-to-end connection identifier'. It provides a means of correlating service-level connections with underlying ATM bearer connections. In the Q.1901 [36] context, the eecid is synonymous with the bnc-id (backbone network connection identifier). * The 'aalType' attribute. This is used to indicate the nature of the ATM adaptation layer (AAL). * The 'silenceSupp' attribute, used to indicate the use of of voice activity detection for silence suppression, and to optionally parameterize the silence suppression function. * The 'ecanf' and 'ecanb' attributes, used to indicate the use of of echo cancellation, and to parameterize the this function. * The 'gcf' and 'gcb' attributes, used to indicate the use of of gain control, and to parameterize the this function. * The 'profileDesc' attribute which can be used to describe AAL2 profiles. Although any AAL2 profile can be so described, this attribute is useful for describing, at connection establishment time, custom profiles that might not be known to the far end. This attribute applies in the AAL2 context only. * The 'vsel' attribute which indicates a prioritized list of 3-tuples for voice service. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it. * The 'dsel' attribute which indicates a prioritized list of 3-tuples for voiceband data service. Each 3-tuple indicates a codec, an optional packet length and an optional packetization Rajesh Kumar, Mohamed Mostafa. 19 Internet Draft ATM SDP September 2000 period. This complements the 'm' line information and should be consistent with it. * The 'fsel' attribute which indicates a prioritized list of 3-tuples for facsimile service. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it. * The 'capability' attribute which indicates the ATM transfer capability (ITU nomenclature), synonymous with the ATM Service Category (ATMF nomenclature). * The 'qosClass' attribute which indicates the QoS class of the ATM bearer connection. * The 'bcob' attribute which indicates the broadband connection oriented bearer class. * The 'stc' attribute which indicates susceptibility to clipping. * The 'upcc' attribute which indicates the user plane connection configuration. * The 'atmQOSfparms' and 'atmQOSbparms' attributes are used to describe certain key ATM QoS parameters in the forward and backward directions respectively. * The 'aal2QOSfparms' and 'aal2QOSbparms' attributes which are placeholders for AAL2-level impairments, yet to be defined. These attributes may be withdrawn if not needed. * The 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes which are used to describe ATM traffic descriptor parameters in the forward and backward directions respectively. * The 'aal2FtrfcDesc' and 'aal2BtrfcDesc' attributes which are placeholders for AAL2-level traffic descriptors, yet to be defined. These attributes may be withdrawn if not needed. * The 'abrFparms' and 'abrBparms' attributes which are used to describe ABR-specific parameters in the forward and backward directions respectively. These parameters are per the UNI 4.0 signaling specification [5]. * The 'clkrec' attribute which indicates the clock recovery method for AAL1 unstructured data transfer (UDT). * The 'fec' attribute which indicates the use of forward error correction. * The 'prtfl' attribute which indicates indicate the fill level of partially filled cells. * The 'bearerType' attribute is used to indicate whether the underlying bearer is an ATM PVC/SPVC, an ATM SVC, or an AAL2 CID connection within an existing ATM SVC/PVC/SPVC. * When present, the 'structure' attribute is used to indicate the presence or absence of AAL1 structured data transfer (SDT), and the size of the SDT blocks. * When present, the 'sbc' media attribute line denotes the subchannel count in the case of n x 64 clear channel communication. * When present, the 'fcpsSDUsize' and 'bcpsSDUsize' attributes are used to indicate the maximum size of the CPCS SDU payload in the forward and backward directions. * When present, the 'aal2CPS' attribute is used to indicate that an AAL2 CPS sublayer as defined in ITU I.363.2 [13] is associated with the VCC referred to in the 'm' line. Optionally, it can be used to indicate selected CPS options and parameter values for this VCC. * When present, the 'aal2sscs3661' attribute is used to indicate the presence of an AAL2 SSCS sublayer as defined in ITU I.366.1 [12]. Optionally, it can be used to indicate Rajesh Kumar, Mohamed Mostafa. 20 Internet Draft ATM SDP September 2000 selected options and parameter values for this SSCS. * When present, the 'aal2sscs3662' attribute is used to indicate the presence of an AAL2 SSCS sublayer as defined in ITU I.366.2. Optionally, it can be used to indicate selected options and parameter values for this SSCS. * When present, the 'aalApp' attribute is used to point to the controlling standard for an application layer above the ATM adaptation layer. * When present, the 'lij' attribute is used to indicate the presence of a connection that uses the Leaf-initiated-join capability described in UNI 4.0 [5], and to optionally describe parameters associated with this capability. * When present, the 'anycast' attribute line is used to indicate the applicability of the anycast function described in UNI 4.0 [5], and to optionally qualify it with certain parameters. * The 'fmtp' attribute line defined in the SDP standard can be used to describe higher-layer parameters. These pertain to layers higher than the ATM adaptation layer that are not closely coupled with the ATM or ATM adaptation layers. Examples are the B-HLI and B-LLI IEs specified in ITU Q.2931 [15], and the user-to-user information element described in ITU Q.2957 [48]. * The 'chain' attribute line is used to chain consecutive SDP descriptions. 5.6.1 The 'atmmap' attribute The 'atmmap' attribute is defined on the basis of the 'rtpmap' attribute used in RFC2327. a=atmmap:<payloadType> <encodingName> The 'atmmap' attribute is used to dynamically map encoding names into payload types. This is necessary for those encoding names which have not been assigned a static payload type through IANA [31]. Payload types and encoding techniques that have been registered with IANA for RTP are retained for AAL1 and AAL5. AAL5. The range of statically defined payload types is in the range 0-95. All static assignments of payload types to codecs are listed in [31]. The range of payload types defined dynamically via the 'atmmap' attribute is 96-127. Table 2 lists standard encoding names with their corresponding statically mapped payload types [31]. It also suggests encoding names for codecs not addressed in [31]. For these, payload types are mapped dynamically via the 'atmmap' attribute. Table 2 is not meant to be an exhaustive list of codec names. Rajesh Kumar, Mohamed Mostafa. 21 Internet Draft ATM SDP September 2000 Table 2: Encoding Names and Payload Types |---------------------|--------------|---------------------------| | Encoding Technique | Encoding Name| Payload type | |---------------------|--------------|---------------------------| | PCM - Mu law | "PCMU" | 0 (Statically Mapped) | |---------------------|--------------|---------------------------| | 32 kbps ADPCM | "G726-32" | 2 (Statically Mapped) | |---------------------|--------------|---------------------------| |Dual rate 5.3/6.3kbps| "G723" | 4 (Statically Mapped) | |---------------------|--------------|---------------------------| | PCM- A law | "PCMA" | 8 (Statically Mapped) | |---------------------|--------------|---------------------------| | 7 KHz audio coding | "G722" | 9 (Statically Mapped) | | within 64 kbps | | | |---------------------|--------------|---------------------------| | LD-CELP | "G728" | 15 (Statically Mapped) | |---------------------|--------------|---------------------------| | CS-ACELP | "G729" | 18 (Statically Mapped) | |(normal/low-complexity) | | |---------------------|--------------|---------------------------| | Low-complexity | "X-G729a" | None, map dynamically | | CS-ACELP | | | |---------------------|--------------|---------------------------| |Normal | "X-G729b" | None, map dynamically | |CS-ACELP w/ ITU | | | |defined silence | | | |suppression | | | +---------------------+--------------+---------------------------+ |Low-complexity | "X-G729ab" | None, map dynamically | |CS-ACELP w/ ITU | | | |defined silence | | | |suppression | | | |---------------------|--------------|---------------------------| | 16 kbps ADPCM | "X-G726-16" | None, map dynamically | |---------------------|--------------|---------------------------| | 24 kbps ADPCM | "X-G726-24" | None, map dynamically | |---------------------|--------------|---------------------------| | 40 kbps ADPCM | "X-G726-40" | None, map dynamically | |---------------------|--------------|---------------------------| | Dual rate 5.3/6.3 |"X-G7231-H" | None, map dynamically | | kbps - high rate | | | |---------------------|--------------|---------------------------| | Dual rate 5.3/6.3 |"X-G7231-L" | None, map dynamically | | kbps - low rate | | | |---------------------|--------------|---------------------------| | Dual rate 5.3/6.3 |"X-G7231a-H" | None, map dynamically | | kbps - high rate w/ | | | | ITU-defined silence | | | | suppression | | | |----------------------------------------------------------------| | Dual rate 5.3/6.3 |"X-G7231a-L" | None, map dynamically | | kbps - high rate w/ | | | | ITU-defined silence | | | | suppression | | | |---------------------|--------------|---------------------------| | 16 kbps EADPCM | "X-G727-16" | None, map dynamically | |---------------------|--------------|---------------------------| Rajesh Kumar, Mohamed Mostafa. 22 Internet Draft ATM SDP September 2000 +---------------------+--------------+---------------------------+ | 24 kbps EADPCM | "X-G727-24" | None, map dynamically | |---------------------|--------------|---------------------------| | 32 kbps EADPCM | "X-G727-32" | None, map dynamically | |---------------------|--------------|---------------------------| |n x 64 kbps Clear | "X-CCD" | None, map dynamically | |Channel without CAS | | | |per af-vtoa-78 [7] | | | |---------------------|--------------|---------------------------| |n x 64 kbps Clear | "X-CCD-CAS" | None, map dynamically | |Channel with CAS | | | |per af-vtoa-78 [7] | | | |---------------------|--------------|---------------------------| |GSM Full Rate | "GSM" | 3 (Statically Mapped) | |---------------------|--------------|---------------------------| |GSM Half Rate | "X-GSM-HR" | None, map dynamically | |---------------------|--------------|---------------------------| |GSM-Enhanced Full Rate "X-GSM-EFR" | None, map dynamically | |---------------------|--------------|---------------------------| |GSM-Enhanced Half Rate "X-GSM-EHR" | None, map dynamically | |---------------------|--------------|---------------------------| |Group 3 fax demod. "X-FXDMOD-3" | None, map dynamically | |---------------------|--------------|---------------------------| |Group 3 fax demod. "X-FXDMOD-3" | None, map dynamically | |---------------------|--------------|---------------------------| | Federal Standard | "1016" | 1 (Statically Mapped) | | FED-STD 1016 CELP | | | |---------------------|--------------|---------------------------| | DVI4, 8 KHz [3] | "DVI4" | 5 (Statically Mapped) | |---------------------|--------------|---------------------------| | DVI4, 16 KHz [3] | "DVI4" | 6 (Statically Mapped) | |---------------------|--------------|---------------------------| | LPC [3], Linear | "LPC" | 7 (Statically Mapped) | | Predictive Coding | | | |---------------------|--------------|---------------------------| | L16 [3], Sixteen | "L16" | 10 (Statically Mapped) | | Bit Linear PCM, | | | | Double channel | | | |---------------------|--------------|---------------------------| | L16 [3], Sixteen | "L16" | 11 (Statically Mapped) | | Bit Linear PCM, | | | | Single channel | | | |---------------------|--------------|---------------------------| | QCELP [3] | "QCELP" | 12 (Statically Mapped) | |---------------------|--------------|---------------------------| | MPEG1/MPEG2 audio | "MPA" | 14 (Statically Mapped) | |---------------------|--------------|---------------------------| | DVI4, 11.025 KHz[3] | "DVI4" | 16 (Statically Mapped) | |---------------------|--------------|---------------------------| | DVI4, 22.05 KHz [3] | "DVI4" | 17 (Statically Mapped) | |---------------------|--------------|---------------------------| | MPEG1/MPEG2 video | "MPV" | 32 (Statically Mapped) | |---------------------|--------------|---------------------------| | MPEG 2 audio/video | "MP2T" | 33 (Statically Mapped) | | transport stream | | | |---------------------|--------------|---------------------------| Rajesh Kumar, Mohamed Mostafa. 23 Internet Draft ATM SDP September 2000 |---------------------|--------------|---------------------------| | ITU H.261 video | "H261" | 31 (Statically Mapped) | |---------------------|--------------|---------------------------| | ITU H.263 video | "H263" | 33 (Statically Mapped) | |---------------------|--------------|---------------------------| | ITU H.263 video |"H263-1998" | None, map dynamically | | 1998 version | | | |---------------------|--------------|---------------------------| | MPEG 1 system stream| "MP1S" | None, map dynamically | |---------------------|--------------|---------------------------| |MPEG 2 program stream| "MP2P" | None, map dynamically | |---------------------|--------------|---------------------------| 5.6.2 The 'eecid' attribute The 'eecid' attribute is synonymous with the 4-byte'bnc-id' parameter used by T1SI, the ATM forum and the ITU (Q.1901) standardization effort. The term 'eecid' stands for 'end-to-end connection identifier', while 'bnc-id' stands for 'backbone network connection identifier'. The name "backbone" is slightly misleading since it refers to the entire ATM network including the ATM edge and ATM core networks. In Q.1901 terminology, an ATM "backbone" connects TDM or analog edges. While the term 'bnc-id' might be used in the bearer signaling plane and in an ISUP (Q.1901) call control plane, SDP session descriptors use the neutral term 'eecid'. This provides a common SDP baseline for applications that use ISUP (Q.1901) and applications that use SIP/SIP+. Section 5.6.38 depicts the use of the eecid in call establishment procedures. In these procedures, the eecid is used to correlate service-level calls with SVC set-up requests. In the forward SVC establishment model, the call-terminating gateway selects an eecid and transmits it via SDP to the call-originating gateway. The call originating gateway transmits this eecid to the call terminating gateway via the bearer set-up message (SVC set-up or Q.2630.1 establish request). In the backward SVC establishment model, the call-originating gateway selects an eecid and transmits it via SDP to the call-terminating gateway. The call terminating gateway transmits this eecid to the call originating gateway via the bearer set-up message (SVC set-up or Q.2630.1 establish request). The value of the eecid attribute values needs to be unique within the node terminating the SVC set-up but not across multiple nodes. Hence, the SVC-terminating gateway has complete control over using and releasing values of this parameter. The eecid attribute is used to correlate, one-to-one, received bearer set-up requests with service-level call control signaling. Within an SDP session description, the eecid attribute is used as follows: a=eecid:<eecid> where <eecid> consists of up to 8 hex digits (equivalent to 4 octets). Rajesh Kumar, Mohamed Mostafa. 24 Internet Draft ATM SDP September 2000 This SDP document does not specify how the eecid (synonymous with bnc-id) is to be communicated through bearer signaling (Q.931, UNI, PNNI, AINI, IISP, proprietary signaling equivalent, Q.2630.1). This is a task of these bearer signaling protocols. However, the following informative statements are made to convey a sense of the interoperability that is a goal of current standardization efforts: - ITU Q.2941.3 and the ATMF each recommend the use of the GIT IE for carrying the eecid (synonymous with bnc-id) in the set-up message of ATM signaling protocols (Q.2931, UNI 4.0, PNNI, AINI, IISP). The coding for carrying the eecid (bnc-id) in the GIT IE is defined in ITU Q.2941.3 and accepted by the ATM forum. - Another alternate method is to use the called party subaddress IE. In some networks, this might be considered a protocol violation and is not the recommended means of carrying the eecid (bnc-id). The GIT IE is the preferred method of transporting the eecid (bnc-id) in ATM signaling messages. - The establish request (ERQ) message of the Q.2630.1 [37] signaling protocol can use the SUGR (Served User Generated Reference) IE to transport the eecid (bnc-id). The node assigning the eecid can release and re-use it when it receives a Q.2931 [15] set-up message or a Q.2630.1 [37] establish request message containing the eecid. However, in both cases (backward and forward models), it is recommended that this eecid be retained until the connection terminates. Since the eecid space is large enough, it is not necessary to release it as soon as possible. 5.6.3 The 'aalType' attribute When present, the 'aalType' attribute is used to indicate the ATM adaptation layer. If this information is redundant with the 'm' line, it can be omitted. The format of the 'aalType' media attribute line is as follows: a=aalType: <aalType> Here, <aalType> can take on the following string values: "AAL1", "AAL1_SDT", "AAL1_UDT", "AAL2", "AAL3/4", "AAL5" and "USER_DEFINED_AAL". Note that "AAL3/4" and "USER DEFINED AAL" are not addressed in this document. 5.6.4 The 'silenceSupp' attribute When present, the 'silenceSupp' attribute is used to indicate the use or non-use of silence suppression. The format of the 'silenceSupp' media attribute line is as follows: a=silenceSupp: <silenceSuppEnable> <silenceTimer> <suppPref> <sidUse> <fxnslevel> Rajesh Kumar, Mohamed Mostafa. 25 Internet Draft ATM SDP September 2000 If any of the parameters in the silenceSupp media attribute line is not specified, is inapplicable or is implied, then it is set to "-". The <silenceSuppEnable> can take on values of "on" or "off". If it is "on", then silence suppression is enabled. The <silenceTimer> is a 16-bit field which can be represented in decimal or hex. Each increment (tick) of this timer represents a millisecond. The maximum value of this timer is between 1 and 3 minutes. This timer represents the time-lag before silence suppression kicks in. Even though this can, theoretically, be as low as 1 ms, most DSP algorithms take more than that to detect silence. Setting <silenceTimer> to a large value (say 1 minute> is equivalent to disabling silence suppression within a call. However, idle channel suppression between calls on the basis of silence suppression is still operative in non-switched, trunking applications if <silenceSuppEnable> = "on" and <silenceTimer> is a large value. The <suppPref> specifies the preferred silence suppression method that is preferred or already selected. It can take on the string values of "standard" and "custom". If its value is "standard", then a standard method (e.g. ITU-defined) is preferred to custom methods if such a standard is defined. Otherwise, a custom method may be used. If <suppPref> is set to "custom", then a custom method, if available, is preferred to the standard method. The <sidUse> indicates whether SIDs (Silence Insertion Descriptors) are to be used, and whether they use fixed comfort noise or sampled background noise. It can take on the string values of "No SID", "Fixed Noise", "Sampled Noise". If the value of <sidUse> is "Fixed Noise", then <fxnslevel> provides its level. It can take on integer values in the range 0-127, as follows: +-----------------------+---------------------+ | <fxnslevel> value | Meaning | +-----------------------+---------------------+ | 0-29 | Reserved | | 30 | -30 dBm0 | | 31 | -31 dBm0 | | . . . | . . . | | 77 | -77 dBm0 | | 78 | -78 dBm0 | | 79-126 | reserved | | 127 | Idle Code (no noise)| +-----------------------+---------------------+ A hex representation, preceded by a 0x prefix, of <fxnslevel> is allowed. 5.6.5 The 'ecanf' and 'ecanb' attributes When present, the 'ecanf' and 'ecanb' attributes are used to indicate the use or non-use of echo cancellation in the forward and backward directions respectively. See Section 2.3 for a definition of the terms 'forward' and 'backward'. Rajesh Kumar, Mohamed Mostafa. 26 Internet Draft ATM SDP September 2000 The format of the 'ecanf' and 'ecanb' media attribute lines is as follows: a=ecanf: <ecanEnable> <ecanType> a=ecanb: <ecanEnable> <ecanType> If any of the parameters in the ecanf and ecanb media attribute lines is not specified, is inapplicable or is implied, then it is set to "-". If the 'ecanf' or 'ecanb' media attribute lines is not present, then means other than the SDP descriptor must be used to determine the applicability and nature of echo cancellation in that direction. Examples of such means are MIB provisioning, the local connection options structure in MGCP etc. The <ecanEnable> parameter can take on values of "on" or "off". If it is "on", then echo cancellation is enabled. If it is "off", then echo cancellation is disabled. The <ecanType> parameter can take on the string values "G165" and "G168" respectively. When SDP is used with some media gateway control protocols such as MGCP and Megaco [26], there exist means outside SDP descriptions to specify the echo cancellation properties of a connection. Nevertheless, this media attribute line is included for completeness. As a result, the SDP can be used for describing echo cancellation in applications where alternate means for this are unavailable. 5.6.6 The 'gcf' and 'gcb' attributes When present, the 'gcf' and 'gcb' attributes are used to indicate the use or non-use of gain control in the forward and backward directions respectively. See Section 2.3 for a definition of the terms 'forward' and 'backward'. The format of the 'gcf' and 'gcb' media attribute lines is as follows: a=gcf: <gcEnable> <gcLvl> a=gcb: <gcEnable> <gcLvl> If any of the parameters in the gcf and gcb media attribute lines is not specified, is inapplicable or is implied, then it is set to "-". If the 'gcf' or 'gcb' media attribute line is not present, then means other than the SDP descriptor must be used to determine the applicability and nature of gain control in that direction. Examples of such means are MIB provisioning, the local connection options structure in MGCP etc. The <gcEnable> parameter can take on values of "on" or "off". If it is "on", then gain control is enabled. If it is "off", then gain control is disabled. The <gcLvl> parameter is represented as the decimal or hex equivalent of a 16-bit binary field. A value of 0xFFFF implies automatic gain control. Otherwise, this number indicates the number of decibels of inserted loss. The upper bound, 65,535 dB (0xFFFE) of inserted loss, is an absurdly large number and is a Rajesh Kumar, Mohamed Mostafa. 27 Internet Draft ATM SDP September 2000 carryover from Megaco [26]. In practical applications, the inserted loss is much lower. When SDP is used with some media gateway control protocols such as MGCP and Megaco [26], there exist means outside SDP descriptions to specify the gain control properties of a connection. Nevertheless, this media attribute line is included for completeness. As a result, the SDP can be used for describing gain control in applications where alternate means for this are unavailable. 5.6.7 The 'profileDesc' attribute There is one 'profileDesc' media attribute line for each AAL2 profile that is intended to be described. The 'profileDesc' media attribute line is structured as follows: a=profileDesc: <transport> <profile> <uuiCodeRange#1> <encodingName#1> <packetLength#1> <packetTime#1> <uuiCodeRange#2> <encodingName#2> <packetLength#2> <packetTime#2>... <uuiCodeRange#N> <encodingName#N> <packetLength#N> <packetTime#N> Here, <transport> and <profile> are identical to their definition, above, for the 'm' line. The profile elements (rows in the profile tables of ITU I.366.2 or AF-VTOA-0113) are represented as four-tuples following the <profile> parameter in the 'profileDesc' media attribute line. If a member of one of these four-tuples is not specified or is implied, then it is set to "-". The <uuiCodeRange> parameter is represented by D1-D2, where D1 and D2 are decimal integers in the range 0 through 15. The <encodingName> parameter can take one of the values in column 2 of Table 2. Additionally, it can take on the following descriptor strings: "PCMG", "SIDG" and "SID729". These stand for generic PCM, generic SID and G.729 SID respectively. The <packetLength> is a decimal integer representation of the AAL2 packet length in octets. The <packetTime> is a decimal integer representation of the AAL2 packetization interval in ms. For instance, the 'profileDesc' media attribute line below defines the AAL2/custom 100 profile. This profile is reproduced in the Table 3 below. For a description of the parameters in this profile such as M and the sequence number interval, see ITU I.366.2 [13]. a=profileDesc:AAL2/custom 100 0-7 PCMG 40 5 0-7 SIDG 1 5 8-15 G726-32 40 10 8-15 SIDG 1 5 If the <packetTime> parameter is to be omitted or implied, then the same profile can be represented as follows: a=profileDesc:AAL2/custom 100 0-7 PCMG 40 - 0-7 SIDG 1 - 8-15 G726-32 40 - 8-15 SIDG 1 - If a gateway has a provisioned or hard coded definition of a profile, then any definition provided via the 'profileDesc' line Rajesh Kumar, Mohamed Mostafa. 28 Internet Draft ATM SDP September 2000 overrides it. The exception to this rule is with regard to standard profiles such as ITU-defined profiles and ATMF-defined profiles. In general, these should not be defined via a 'profileDesc' media attribute line. If they are, then the definition needs to be consistent with the standard definition else the SDP session descriptor should be rejected with an appropriate error code. Table 3: Example of a custom AAL2 profile |---------------------------------------------------------------| | UUI | Packet |Encoding | | |Packet|Seq.No. | | Code | Length |per ITU |Description of | M |Time |Interval| |point |(octets)|I.366.2 | Algorithm | |(ms) |(ms) | |Range | | 2/99 | | | | | | | | version | | | | | |---------------------------------------------------------------| | 0-7 | 40 | Figure | PCM, G.711-64,| 1 | 5 | 5 | | | | B-1 | generic | | | | |------|--------|---------|---------------|-----|------|--------| | 0-7 | 1 | Figure | Generic SID | 1 | 5 | 5 | | | | I-1 | | | | | |------|--------|---------|---------------|-----|------|--------| | 8-15 | 40 | Figure | ADPCM, | 2 | 10 | 5 | | | | E-2 | G.726-32 | | | | |------|--------|---------|---------------|-----|------|--------| | 8-15 | 1 | Figure | Generic SID | 1 | 5 | 5 | | | | I-1 | | | | | |------|--------|---------|---------------|-----|------|--------| 5.6.8 The 'vsel' attribute The 'vsel' attribute indicates a prioritized list of one or more 3-tuples for voice service. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it. The 'vsel' line is structured as follows: a=vsel:<encodingName #1> <packetLength #1><packetTime #1> <encodingName #2> <packetLength #2><packetTime #2> ... <encodingName #N> <packetLength #N><packetTime #N> where the <encodingName> parameter can take one of the values in column 2 of Table 2. The <packetLength> is a decimal integer representation of the packet length in octets. The <packetTime> is a decimal integer representation of the packetization interval in ms. The parameters <packetLength>and <packetTime> can be set to "-" when not needed. Also, the entire 'vsel' media attribute line can be omitted when not needed. For example, a=vsel:G729 10 10 G726-32 40 10 indicates first preference of G.729 or G.729a (both are interoperable) as the voice encoding scheme. A packet length of 10 octets and a packetization interval of 10 ms are associated with this codec. G726-32 is the second preference stated in this line, with an associated packet length of 40 octets and a packetization interval of 10 ms. If the packet length and packetization interval are intended to be omitted, then this media attribute line becomes Rajesh Kumar, Mohamed Mostafa. 29 Internet Draft ATM SDP September 2000 a=vsel:G729 - - G726-32 - - The media attribute line a=vsel:G726-32 40 10 indicates preference for or selection of 32 kbps ADPCM with a packet length of 40 octets and a packetization interval of 10 ms. This media attribute line can be used in the AAL1, AAL2 and AAL5 contexts. The <packetLength> and <packetTime> are not meaningful in the AAL1 case and should be set to "-". In the AAL2 case, this line determines the use of some or all of the rows in a given profile table. If multiple 3-tuples are present, they can indicate a hierarchical assignment of some rows in that profile to voice service e.g. row A preferred to row B etc. If multiple profiles are present on the 'm' line, the profile qualified by this attribute is the first profile. If a single profile that has been selected for a connection is indicated in the 'm' line, the 'vsel' attribute qualifies the use, for voice service, of codecs within that profile. 5.6.9 The 'dsel' attribute The 'dsel' attribute indicates a prioritized list of one or more 3-tuples for voiceband data service. The <fxIncl> flag indicates whether this definition of voiceband data includes fax ("on" value) or not ("off" value). If <fxIncl> is "on", then the 'dsel' line must be consistent with any 'fsel' line in the session description. In this case, an error event is generated in the case of inconsistency. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it. The 'dsel' line is structured as follows: a=dsel:<fxIncl> <encodingName #1> <packetLength #1><packetTime #1> <encodingName #2> <packetLength #2><packetTime #2> ... <encodingName #N> <packetLength #N><packetTime #N> where the <encodingName> parameter can take one of the values in column 2 of Table 2. The <packetLength> and <packetTime> parameters are per their definition, above, for the 'vsel' media attribute line. The parameters <packetLength>and <packetTime>) can be set to "-" when not needed. The <fxIncl> flag is presumed to be "off" if it is set to "-". Also, the entire 'dsel' media attribute line can be omitted when not needed. For example, a=dsel:- G726-32 20 5 PCMU 40 5 indicates that this line does not address facsimile, and that the first preference for the voiceband data codes is 32 kbps ADPCM, while the second preference is PCMU. The packet length and the packetization interval associated with G726-32 are 20 octets and 5 ms respectively. For PCMU, they are 40 octets and 5 ms respectively. Rajesh Kumar, Mohamed Mostafa. 30 Internet Draft ATM SDP September 2000 This media attribute line can be used in the AAL1, AAL2 and AAL5 contexts. The <packetLength> and <packetTime> are not meaningful in the AAL1 case and should be set to "-". In the AAL2 case, this line determines the use of some or all of the rows in a given profile table. If multiple 3-tuples are present, they can indicate a hierarchical assignment of some rows in that profile to voiceband data service e.g. row A preferred to row B etc. If multiple profiles are present on the 'm' line, the profile qualified by this attribute is the first profile. If a single profile that has been selected for a connection is indicated in the 'm' line, the 'dsel' attribute qualifies the use, for voiceband data service, of codecs within that profile. 5.6.10 The 'fsel' attribute The 'fsel' attribute indicates a prioritized list of one or more 3-tuples for facsimile service. If an 'fsel' line is present, any 'dsel' line with <fxIncl> set to "on" in the session description must be consistent with it. In this case, an error event is generated in the case of inconsistency. Each 3-tuple indicates a codec, an optional packet length and an optional packetization period. This complements the 'm' line information and should be consistent with it. The 'fsel' line is structured as follows: a=fsel:<encodingName #1> <packetLength #1><packetTime #1> <encodingName #2> <packetLength #2><packetTime #2> ... <encodingName #N> <packetLength #N><packetTime #N> where the <encodingName> parameter can take one of the values in column 2 of Table 2. The <packetLength> and <packetTime> parameters are per their definition, above, for the 'vsel' media attribute line. The parameters <packetLength>and <packetTime> can be set to "-" when not needed. Also, the entire 'fsel' media attribute line can be omitted when not needed. For example, a=fsel:FXDMOD-3 - - indicates demodulation and remodulation of ITU-T group 3 fax at the gateway. a=fsel:PCMU 40 5 G726-32 20 5 indicates a first and second preference of Mu-law PCM and 32 kbps ADPCM as the facsimile encoding scheme. The packet length and the packetization interval associated with G726-32 are 20 octets and 5 ms respectively. For PCMU, they are 40 octets and 5 ms respectively. This media attribute line can be used in the AAL1, AAL2 and AAL5 contexts. The <packetLength> and <packetTime> are not meaningful in the AAL1 case and should be set to "-". In the AAL2 case, this line determines the use of some or all of the rows in a given profile table. If multiple 3-tuples are present, they can indicate a hierarchical assignment of some rows in that profile to facsimile service e.g. row A preferred to row B etc. If multiple profiles are present on the 'm' line, the profile Rajesh Kumar, Mohamed Mostafa. 31 Internet Draft ATM SDP September 2000 qualified by this attribute is the first profile. If a single profile that has been selected for a connection is indicated in the 'm' line, the 'fsel' attribute qualifies the use, for facsimile service, of codecs within that profile. 5.6.11 The 'capability' attribute When present, the 'capability' attribute indicates the ATM Transfer Capability described in ITU I.371 [28], equivalent to the ATM Service Category described in the UNI 4.1 Traffic Management specification [6]. The 'capability' media attribute line is structured in one of the following ways: a=capability:<asc> <subtype> a=capability:<atc> <subtype> Possible values of the <asc> are enumerated below: "CBR", "nrt-VBR", "rt-VBR", "UBR", "ABR", "GFR" Possible values of the <atc> are enumerated below: "DBR","SBR","ABT/IT","ABT/DT","ABR" Some applications might use non-standard <atc> and <asc> values not listed above. Equipment designers will need to agree on the meaning and implications of non-standard transfer capabilities / service capabilities. The <subtype> field essentially serves as a subscript to the <asc> and <atc> fields. In general, it can take on any integer value, or the "-" value indicating that it does not apply or that the underlying data is to be known by other means, such as provisioning. The following combinations are recognized in the ATMF and ITU specifications: <asc>/<atc> <subtype> Meaning nrt-VBR 1 nrt-VBR.1 nrt-VBR 2 nrt-VBR.2 nrt-VBR 3 nrt-VBR.3 rt-VBR 1 rt-VBR.1 rt-VBR 2 rt-VBR.2 rt-VBR 3 rt-VBR.3 UBR 1 UBR.1 UBR 2 UBR.2 GFR 1 GFR.1 GFR 2 GRR.2 SBR 1 SBR1 SBR 2 SBR2 SBR 3 SBR3 It is beyond the scope of this specification to examine the equivalence of some of the ATMF and ITU definitions. These need to be recognized from the ATMF and ITU source specifications and exploited, as much as possible, to simplify ATM node design. When the bearer connection is a single AAL2 CID connection within a Rajesh Kumar, Mohamed Mostafa. 32 Internet Draft ATM SDP September 2000 multiplexed AAL2 VC, the 'capability' attribute does not apply. 5.6.12 The 'qosClass' attribute When present, the 'qosClass' attribute indicates the QoS class specified in ITU I.2965.1 [34]. The 'qosClass' media attribute line is structured as follows: a=qosClass:<qosClass> Here, <qosClass> is an integer in the range 0 - 5. <qosClass> Meaning 0 Default QoS 1 Stringent 2 Tolerant 3 Bi-level 4 Unbounded 5 Stringent bi-level 5.6.13 The 'bcob' attribute When present, the 'bcob' attribute represents the broadband connection oriented bearer class defined in ITU Q.2961.2 [33]. The 'bcob' media attribute line is structured as follows: a=bcob:<bcob> Here, <bcob> is the decimal or hex representation of a 5-bit field. Currently, all values are unused and reserved with the following exceptions: <bcob> Meaning 1 BCOB-A 3 BCOB-C 16 BCOB-X 24 BCOB-VP (transparent VP service) 5.6.14 The 'stc' attribute When present, the 'stc' attribute represents susceptibility to clipping. The 'stc' media attribute line is structured as follows: a=stc:<stc> Here, <stc> is the decimal equivalent of a 2-bit field. Currently, all values are unused and reserved with the following exceptions: <stc> value Binary Equivalent Meaning 0 00 Not susceptible to clipping 1 01 Susceptible to clipping Rajesh Kumar, Mohamed Mostafa. 33 Internet Draft ATM SDP September 2000 5.6.15 The 'upcc' attribute When present, the 'upcc' attribute represents the user plane connection configuration. The 'upcc' media attribute line is structured as follows: a=upcc:<upcc> Here, <upcc> is the decimal equivalent of a 2-bit field. Currently, all values are unused and reserved with the following exceptions: <upcc> value Binary Equivalent Meaning 0 00 Point to point 1 01 Point to multipoint 5.6.16 The 'atmQOSfparms' and 'atmQOSbparms' attributes When present, the 'atmQOSfparms' and 'atmQOSbparms' attributes are used to describe certain key ATM QoS parameters in the forward and backward directions respectively. See Section 2.3 for a definition of the terms 'forward' and 'backward'. The 'atmQOSfparms' and 'atmQOSbparms' media attribute lines are structured as follows: a=atmQOSfparms: <cdvType><acdv><ccdv><actd><cctd><aclr> a=atmQOSbparms: <cdvType><acdv><ccdv><actd><cctd><aclr> The <cdvType> parameter can take on the string values of "PP" and "2P". These refer to the peak-to-peak and two-point CDV as defined in UNI 4.0 [5] and ITU Q.2965.2 [35] respectively. The CDV parameters, <acdv> and <ccdv>, refer to the acceptable and cumulative CDVs respectively. These are expressed in units of microseconds and represented as the decimal or hex equivalent of 24-bit fields. These use the cell loss ratio, <aclr>, as the "alpha" quantiles defined in the ATMF TM 4.1 specification [6] and in ITU I.356 [47]. The CTD parameters, <actd> and <cctd>, refer to the acceptable and cumulative CTDs respectively in milliseconds. These are represented as the decimal or hex equivalent of 16-bit fields. These parameters are equivalent to the maximum end-to-end transit delay defined in ATMF TM 4.1 specification [6] and Q.2965.2 [35]. The <aclr> parameter refers to forward and backward acceptable cell loss ratios. This is the ratio between the number of cells lost and the number of cells transmitted. It is expressed as the decimal or hex equivalent of an 8-bit field. This field expresses an order of magnitude n, where n is an integer in the range 1-15. The Cell Loss Ratio takes on the value 10 raised to the power of minus n. If any of these parameters is not specified, is inapplicable or is implied, then it is set to "-". An example use of these attributes for an rt-VBR, single-CID AAL2 voice VC is: a=atmQOSfparms:pp 8125 3455 32000 - 11 Rajesh Kumar, Mohamed Mostafa. 34 Internet Draft ATM SDP September 2000 a=atmQOSbparms:pp 4675 2155 18000 - 12 This implies a forward acceptable peak-to-peak CDV of 8.125 ms, a backward acceptable peak-to-peak CDV of 4.675 ms, forward cumulative peak-to-peak CDV of 3.455 ms, a backward cumulative peak-to-peak CDV of 2.155 ms, a forward acceptable maximum cell transfer delay of 32 ms, a backward acceptable maximum cell transfer delay of 18 ms, an unspecified forward cumulative cell transfer delay, an unspecified backward cumulative cell transfer delay, a forward cell loss ratio of 10 raised to minus 11 and a backward cell loss ratio of 10 to the minus 12. In certain applications (such as SIP-based applications), an SDP descriptor might have both the atmQOSfparms and atmQOSbparms attributes. In other applications (such as Megaco-based applications), the remote descriptor can have the atmQOSfparms attribute while the local descriptor can have the atmQOSbparms attribute. 5.6.17 The 'aal2QOSfparms' and 'aal2QOSbparms' attributes It is recognized that means of characterizing impairments in AAL2 packet streams are not clearly defined at this time. These AAL2 media attributes lines will constructed along the line of the 'atmQOSfparms' and 'atmQOSbparms' attribute lines. At present, their names serve as placeholders. 5.6.18 The 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes When present, the 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes are used to indicate ATM traffic descriptor parameters in the forward and backward directions respectively. See Section 2.3 for a definition of the terms 'forward' and 'backward'. The 'atmFtrfcDesc' and 'atmBtrfcDesc' media attribute lines are structured as follows: a=atmFtrfcDesc:<clpLvl> <pcr><scr><mbs><cdvt><mcr><mfs><fd><te> a=atmBtrfcDesc:<clpLvl> <pcr><scr><mbs><cdvt><mcr><mfs><fd><te> If any of these parameters in these media attribute lines is not specified, is inapplicable or is implied, then it is set to "-". The <clpLvl> (CLP level) parameter indicates whether the rates and bursts described in these media attribute lines apply to CLP values of 0 or (0+1). It can take on the following string values: "0", "0+1" and "-". If rates and bursts for both <clpLvl> values are to be described, then it is necessary to use two separate media attribute lines for each direction in the same session descriptor. If the <clpLvl> parameter is set to "-", then it implies that the CLP parameter is known by other means such as default, MIB provisioning etc. Rajesh Kumar, Mohamed Mostafa. 35 Internet Draft ATM SDP September 2000 The meaning, units and applicability of the remaining parameters are per the ATMF TM 4.1 specification [6] and are reiterated below: PARAMETER MEANING UNITS APPLICABILITY <pcr> PCR Cells/ CBR, rt-VBR, nrt-VBR, second ABR, UBR, GFR; CLP=0,0+1 <scr> SCR Cells/ rt-VBR, nrt-VBR; second CLP=0,0+1 <mbs> MBS Cells rt-VBR, nrt-VBR, GFR; CLP=0,0+1 <cdvt> CDVT Microsec. CBR, rt-VBR, nrt-VBR, ABR, UBR, GFR; CLP=0,0+1 <mcr> MCR Cells/ ABR,GFR; second CLP=0+1 <mfs> MFS Cells GFR; CLP=0,0+1 <fd> Frame "on"/"off" CBR, rt-VBR, nrt-VBR, Discard ABR, UBR, GFR; Allowed CLP=0+1 <te> CLP "on"/"off" CBR, rt-VBR, nrt-VBR, tagging ABR, UBR, GFR; Enabled CLP=0 <fd> indicates that frame discard is permitted. It can take on the string values of "on" or "off". Note that, in the GFR case, frame discard is always enabled. Hence, this subparameter can be set to "-" in the case of GFR. Since the <fd> parameter is independent of CLP, it is meaningful in the case when <clpLvl> = "0+1". It should be set to "-" for the case when <clpLvl> = "0". <te> (tag enable) indicates that CLP tagging is allowed. These can take on the string values of "on" or "off". Since the <te> parameter applies only to cells with a CLP of 0, it is meaningful in the case when <clpLvl> = "0". It should be set to "-" for the case when <clpLvl> = "0+1". An example use of these media attribute lines for an rt-VBR, single-CID AAL2 voice VC is: a=atmFtrfcDesc:0+1 200 100 20 - - - on - a=atmFtrfcDesc:0 200 80 15 - - - - off a=atmBtrfcDesc:0+1 200 100 20 - - - on - a=atmBtrfcDesc:0 200 80 15 - - - - off This implies a forward and backward PCR of 200 cells per second all cells regardless of CLP, forward and backward PCR of 200 cells per second for cells with CLP=0, a forward and backward SCR of 100 Rajesh Kumar, Mohamed Mostafa. 36 Internet Draft ATM SDP September 2000 cells per second for all cells regardless of CLP, a forward and backward SCR of 80 cells per second for cells with CLP=0, a forward and backward MBS of 20 cells for all cells regardless of CLP, a forward and backward MBS of 15 cells for cells with CLP=0, an unspecified CDVT which can be known by other means, and an MCR and MFS which are unspecified because they are inapplicable. Frame discard is enabled in both the forward and backward directions. Tagging is not enabled in either direction. In certain applications (such as SIP-based applications), an SDP descriptor might have both the atmFtrfcDesc and atmBtrfcDesc attributes. In other applications (such as Megaco-based applications), the remote descriptor can have the atmFtrfcDesc attribute while the local descriptor can have the atmBtrfcDesc attribute. 5.6.19 The 'aal2FtrfcDesc' and 'aal2BtrfcDesc' attributes It might be meaningful to construct descriptors for traffic at the AAL2 packet (subcell) level. These can tentatively be named the 'aal2FtrfcDesc' and 'aal2BtrfcDesc' attributes When constructed, these can be similar in some aspects to the 'atmFtrfcDesc' and 'atmBtrfcDesc' attributes. Until then, these names serve as placeholders. 5.6.20 The 'abrFparms' and 'abrBparms' attributes When present, the 'abrFparms' and 'abrBparms' attributes are used to indicate the 'additional' ABR parameters specified in the UNI 4.0 signaling specification [5]. These refer to the forward and backward directions respectively. See Section 2.3 for a definition of the terms 'forward' and 'backward'. The 'abrFparms' and 'abrBparms' media attribute lines are structured as follows: a=abrFparms:<nrm><trm><cdf><adtf> a=abrBparms:<nrm><trm><cdf><adtf> These parameters are mapped into the ABR service parameters in [6] in the manner described below. These parameters can be represented in SDP as decimal integers, with fractions permitted for some. Details of the meaning, units and applicability of these parameters are in [5] and [6]. If any of these parameters in the 'abrFparms' or 'abrBparms' media attribute lines is not specified, is inapplicable or is implied, then it is set to "-". In SDP, these parameters are represented as the decimal or hex equivalent of the binary fields mentioned below. Rajesh Kumar, Mohamed Mostafa. 37 Internet Draft ATM SDP September 2000 +-----------+----------------------------------+-----------------------+ | PARAMETER | MEANING | FIELD SIZE | +-----------+----------------------------------+-----------------------+ | <nrm> | Maximum number of cells per | 3 bits | | | forward Resource Management cell | | +-----------+----------------------------------+-----------------------+ | <trm> | Maximum time between | 3 bits | | | forward Resource Management cells| | +-----------+----------------------------------+-----------------------+ | <cdf> | Cutoff Decrease Factor | 3 bits | +-----------+----------------------------------+-----------------------+ | <adtf> | Allowed Cell Rate Decrease | 10 bits | | | Time Factor | | +-----------+----------------------------------+-----------------------+ In certain applications (such as SIP-based applications), an SDP descriptor might have both the abrFparms and abrBparms attributes. In other applications (such as Megaco-based applications), the remote descriptor can have the abrFparms attribute while the local descriptor can have the abrBparms attribute. 5.6.21 The 'clkrec' attribute When present, the 'clkrec' attribute is used to indicate the clock recovery method. This attribute is meaningful in the case of AAL1 unstructured data transfer (UDT). The format of the 'clkrec' media attribute line is as follows: a=clkrec:<clkrec> The <clkrec> field can take on the following string values: "NULL", "SRTS" or "ADAPTIVE". SRTS and adaptive clock recovery are defined in ITU I.363.1 [10]. "NULL" indicates that the stream (e.g. T1/E1) encapsulated in ATM is synchronous to the ATM network or is retimed, before AAL1 encapsulation, via slip buffers. 5.6.22 The 'fec' attribute When present, the 'fec' attribute is used to indicate the use of forward error correction. Currently, there exists a forward error correction method defined for AAL1 in ITU I.363.1 [10]. The format of the 'fec' media attribute line is as follows: a=fec:<fecEnable> The <fecEnable> flag indicates the presence of absence of Forward Error Correction. It can take on the string values of "NULL", "LOSS_SENSITIVE" and "DELAY_SENSITIVE". An "NULL" value implies disabling this capability. FEC can be enabled differently for delay-sensitive and loss-sensitive connections. 5.6.23 The 'prtfl' attribute When present, the 'prtfl' attribute is used to indicate the fill level of cells. When this attribute is absent, then other means (such as provisionable defaults) are used to determine the presence and level of partial fill. This attribute indicates the number of non-pad payload octets, not including any AAL SAR or convergence sublayer octets. For example, in some AAL1 applications that use partially filled cells with Rajesh Kumar, Mohamed Mostafa. 38 Internet Draft ATM SDP September 2000 padding at the end, this attribute indicates the number of leading payload octets not including any AAL overhead. The format of the 'prtfl' media attribute line is as follows: a=prtfl:<partialFill> Here, <partialFill> can be expressed as a decimal or a hex integer. In general, permitted values are integers in the range 1 - 48 inclusive. However, this upper bound is different for different adaptations since the AAL overhead, if any, is different. If the specified partial fill is greater than or equal to the maximum fill, then complete fill is used. Using a 'partial' fill of 48 always disables partial fill. In the AAL1 context, this media attribute line applies uniformly to both P and non-P cells. In AAL1 applications that do not distinguish between P and non-P cells, a value of 47 indicates complete fill (i.e. the absence of partial fill). In AAL1 applications that distinguish between P and non-P cells, a value of 46 indicates no padding in P-cells and a padding of one in non-P cells. If partial fill is enabled (i.e there is padding in at least some cells), then AAL1 structures must not be split across cell boundaries. These shall fit in any cell. Hence, their size shall be less than or equal to the partial fill size. Further, the partial fill size is preferably an integer multiple of the structure size. If not, then the partial fill size stated in the SDP description shall be truncated to an integer multiple (e.g. a partial fill size of 40 is truncated to 36 to support six 6 x 64 channels). 5.6.24 The 'bearerType' attribute When present, the 'bearerType' attribute is used to indicate whether the underlying bearer is an ATM PVC/SPVC, an ATM SVC, or an AAL2 CID connection within an existing ATM PVC/SPVC. Additionally, for ATM SVCs and AAL2 CID connections, the 'bearerType' attribute can be used to indicate whether the media gateway initiates connection set-up via bearer signaling (Q.2931-based or Q.2630.1 based). The format of the 'bearerType' media attribute line is as follows: a=bearerType: <bearerType> <localInititiation> The <bearerType> field can take on the following string values: "PVC", "SVC", "CID", with semantics as defined above. Here, "PVC" includes both the PVC and SPVC cases. In the case when the underlying bearer is a PVC/SPVC, or a CID assigned by the MGC rather than through bearer signaling, the <localInititiation> flag can be omitted or set to "-". In the case when bearer signaling is used, this flag can be omitted when it is known by default or by other means whether the media gateway initiates the connection set-up via bearer signaling. Only when this is to be indicated explicitly that the <localInititiation> flag takes on the values of "on" or "off". An "on" value indicates that the media gateway is responsible for initiating connection set-up via bearer signaling (SVC signaling or Q.2630.1 signaling), an "off" value indicates otherwise. Rajesh Kumar, Mohamed Mostafa. 39 Internet Draft ATM SDP September 2000 5.6.25 The 'structure' attribute This attribute applies to AAL1 connections only. When present, the 'structure' attribute is used to indicate the presence or absence of structured data transfer (SDT), and the size in octets of the SDT blocks. The format of the 'structure' media attribute line is as follows: a=structure: <structureEnable> <blksz> where the <structureEnable> flag indicates the presence of absence of SDT. It can take on the values of "on" or "off". An "on" value implies AAL1 structured data transfer (SDT), while an "off" value implies AAL1 unstructured data transfer (UDT). The block size field, <blksz>, is an optional 16-bit field (Q.2931) that can be represented in decimal or hex. It can be omitted or set to a "-" when not applicable, as in the case of unstructured data transfer (UDT). For SDT, it can be omitted or set to a "-" when <blksz> is known by other means. For instance, af-vtoa-78 [7] fixes the structure size for n x 64 service, with or without CAS. The theoretical maximum value of <blksz> is 65,535, although most services use much less. 5.6.26 The 'sbc' attribute The 'sbc' media attribute line denotes the subchannel count and is meaningful only in the case of n x 64 clear channel communication. A clear n x 64 channel can use AAL1 (ATM forum af-vtoa-78) or AAL2 adaptation (ITU I.366.2). Although no such standard definition exists, it is also possible to use AAL5 for this purpose. An n x 64 clear channel is represented by the encoding names of "X-CCD" and "X-CCD-CAS" in Table 2. The format of the 'sbc' media attribute line is as follows: a=sbc:<sbc> Here, <sbc> can be expressed as a decimal or hex integer. This attribute indicates the number of DS0s in a T1 or E1 frame that are aggregated for transmitting clear channel data. For T1-based applications, it can take on integral values in the inclusive range [1...24]. For E1-based applications, it can take on integral values in the inclusive range [1...31]. When omitted, other means are to be used to determine the subchannel count. 5.6.27 The 'fcpsSDUsize' and 'bcpsSDUsize' attributes When present, the 'fcpsSDUsize' and 'bcpsSDUsize' attributes are used to indicate the maximum size of the CPCS SDU payload in the forward and backward directions respectively. See section 2.3 for a definition of the terms 'forward' and 'backward'. The format of these media attribute lines is as follows: a=fcpsSDUsize: <cpcs> a=bcpsSDUsize: <cpcs> The <cpcs> fields is a 16-bit integer that can be represented in decimal or in hex. The meaning and values of these fields are as follows: Rajesh Kumar, Mohamed Mostafa. 40 Internet Draft ATM SDP September 2000 Application Field Meaning Values AAL5 <cpcs> Maximum CPCS-SDU size 1- 65,535 AAL2 <cpcs> Maximum CPCS-SDU size 45 or 64 In certain applications (such as SIP-based applications), an SDP descriptor might have both the fcpsSDUsize and bcpsSDUsize attributes. In other applications (such as Megaco-based applications), the remote descriptor can have the fcpsSDUsize attribute while the local descriptor can have the bcpsSDUsize attribute. 5.6.28 The 'aal2CPS' attribute When present, the 'aal2CPS' attribute is used to indicate describe parameters associated with the AAL2 CPS layer. The format of the 'aal2CPS' media attribute line is as follows: a=aal2CPS:<cidCount> <timerCU> Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor. The <cidCount> integer can take on values between 1 and 255. It represents the number of channels (CIDs) multiplexed into the AAL2 VCC. It can be represented in decimal or in hex. Although the <cidCount> can take on values in the range 1-255, current applications do not allocate more than 248 CIDs per VC. This is because of reserved CID values [11]. The larger range is permitted in the SDP to allow future and proprietary applications. The <timerCU> integer represents the "combined use" timerCU defined in ITU I.363.2. This timer is represented as an integer number of microseconds. 5.6.29 The 'aal2sscs3661' attribute When present, the 'aal2_SSCS_3661' attribute is used to indicate the options that pertain to the SSCS defined in ITU I.366.1 [12]. This SSCS can be selected via the aalApp attribute defined below or through the 'aal2_SSCS_3661' attribute. The format of this media attribute line is as follows: a=aal2sscs3661:<adt> <ted> <fsssar> <bsssar> Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor. The <adt> flag indicates the presence of absence of assured data transfer as defined in I.366.1. The <ted> flag indicates the presence of absence of transmission error detection as defined in I.366.1. Each of these flags can take on the values of "on" or "off". An "on" value indicates presence of the capability. The <fsssar> and <bsssar> fields are 16-bit integers that can be represented in decimal or in hex. The meaning and values of the <fsssar> and <bsssar> fields are as follows: Rajesh Kumar, Mohamed Mostafa. 41 Internet Draft ATM SDP September 2000 Field Meaning Values <fsssar> Maximum SSSAR-SDU size 1- 65,535 forward direction <bsssar> Maximum SSSAR-SDU size 1- 65,535 backward direction In certain applications (such as SIP-based applications), an SDP descriptor might have an 'aal2sscs3661' media attribute line with the <fsssar> and <bsssar> subparameters. In applications (such as Megaco-based applications), the remote descriptor can have the <fsssar> subparameter while the local descriptor can have the <bsssar> subparameter. 5.6.30 The 'aal2sscs3662' attribute When present, the 'aal2sscs3662' attribute is used to indicate the options that pertain to the SSCS defined in ITU I.366.2 [13]. This SSCS can be selected via the aalApp attribute defined below or through the 'aal2sscs3662' attribute. The format of this media attribute line is as follows: a=aal2sscs3662: <sap> <circuitMode> <frameMode> <faxDemod> <cas> <dtmf> <mfall> <mfr1> <mfr2> <PCMencoding> <fmaxFrame> <bmaxFrame> Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor. Additionally, the values of these fields need to be consistent with each other. For instance, <circuitMode> = on is inconsistent with <frameMode> = on. Inconsistencies should be flagged as errors. The <sap> field can take on the following string values: "AUDIO" and "MULTIRATE". These correspond to the audio and multirate Service Access Points (SAPs) defined in ITU I.366.2. The <circuitMode> flag indicates whether the transport of circuit mode data is enabled or disabled, corresponding to the string values of "on" and "off" respectively. The <frameMode> flag indicates whether the transport of frame mode data is enabled or disabled, corresponding to the string values of "on" and "off" respectively. The <faxDemod> flag indicates whether facsimile demodulation and remodulation are enabled or disabled, corresponding to the string values of "on" and "off" respectively. The <cas> flag indicates whether the transport of Channel Associated Signaling (CAS) bits in AAL2 type 3 packets is enabled or disabled, corresponding to the string values of "on" and "off" respectively. The <dtmf> flag indicates whether the transport of DTMF dialled digits in AAL2 type 3 packets is enabled or disabled, corresponding to the string values of "on" and "off" respectively. The <mfall> flag indicates whether the transport of MF dialled digits in AAL2 type 3 packets is enabled or disabled, corresponding to the string values of "on" and "off" respectively. This flag Rajesh Kumar, Mohamed Mostafa. 42 Internet Draft ATM SDP September 2000 enables MF dialled digits in a generic manner, without specifying type (e.g. R1, R2 etc.). The <mfr1> flag indicates whether the transport, in AAL2 type 3 packets, of MF dialled digits for signaling system R1 is enabled or disabled, corresponding to the string values of "on" and "off" respectively. The <mfr2> flag indicates whether the transport, in AAL2 type 3 packets, of MF dialled digits for signaling system R2 is enabled or disabled, corresponding to the string values of "on" and "off" respectively. The <PCMencoding> field indicates whether PCM encoding, if used, is based on the A-law or the Mu-law. This can be used to qualify the 'generic PCM' codec stated in some of the AAL2 profiles. The <PCMencoding> field can take on the string values of "PCMA" and "PCMU". The <fmaxFrame> and <bmaxFrame> fields are 16-bit integers that can be represented in decimal or in hex. The meaning and values of the <fmaxFrame> and <bmaxFrame> fields are as follows: Field Meaning Values <fmaxFrame> Maximum length of a 1- 65,535 frame mode data unit, forward direction <bmaxFrame> Maximum length of a 1- 65,535 frame mode data unit, backward direction In certain applications (such as SIP-based applications), an SDP descriptor might have an 'aal2sscs3662' media attribute line with the <fmaxFrame> and <bmaxFrame> subparameters. In applications (such as Megaco-based applications), the remote descriptor can have the <fmaxFrame> subparameter while the local descriptor can have the <bmaxFrame> subparameter. 5.6.31 The 'aalApp' attribute When present, the 'aalApp' attribute is used to point to the controlling standard for an application layer above the ATM adaptation layer. The format of the 'aalApp' media attribute line is as follows: a=aalApp: <aalApp> The <aalApp> field can take on the string values listed below, along with their meaning. Note that most applications which are specified to run on AAL5 can also run on one or more of the AAL2 SSCS variants (TED and ADT) specified in I.366.1. This list is not exhaustive. Other values are possible. If used, these need to be defined consistently across an application. Rajesh Kumar, Mohamed Mostafa. 43 Internet Draft ATM SDP September 2000 <aalApp> Meaning "itu_h323c" Annex C of H.323 which specifies direct RTP on AAL5 [45]. "af83" af-vtoa-0083.001, which specifies variable size AAL5 PDUs with PCM voice and a null SSCS [46]. "assuredSSCOP" SSCOP as defined in ITU Q.2110 [43], assured operation. "nonassuredSSCOP" SSCOP as defined in ITU Q.2110 [43], non-assured operation. "itu_i3661" SSCS per ITU I.366.1 [12]. "itu_i3662" SSCS per ITU I.366.2 [13]. "itu_i3651" Frame relay SSCS per ITU I.365.1 [39]. "itu_i3652" Service-specific coordination function, as defined in ITU I.365.2, for Connection Oriented Network Service (SSCF-CONS) [40]. "itu_i3653" Service-specific coordination function, as defined in ITU I.365.3, for Connection Oriented Transport Service (SSCF-COTS) [41]. "FRF5" Use of the FRF.5 frame relay standard [53]. "FRF8" Use of the FRF.8 frame relay standard [54]. "FRF11" Use of the FRF.11 frame relay standard [55]. "itu_h2221" Use of the ITU standard H.222.1 for audiovisual communication over AAL5 [51]. 5.6.32 The 'lij' attribute When present, the 'lij' attribute is used to indicate the presence of a connection that uses the Leaf-initiated-join capability described in UNI 4.0 [5], and to optionally describe parameters associated with this capability. The format of the 'lij' media attribute line is as follows: a=lij: <sci><lsn> The <sci> (screening indication) is a 4-bit field expressed as a decimal or hex integer. It is defined in the UNI 4.0 signaling specification [5]. It is possible that the values of this field will be defined later by the ATMF and/or ITU. Currently, all values are reserved with the exception of 0, which indicates a 'Network Join without Root Notification'. The <lsn> (leaf sequence number) is a 32-bit field expressed as a decimal or hex integer. Per the UNI 4.0 signaling specification [5], it is used by a joining leaf to associate messages and responses during LIJ (leaf initiated join) procedures. Each of these fields can be set to a "-" when the intention Rajesh Kumar, Mohamed Mostafa. 44 Internet Draft ATM SDP September 2000 is to not specify them in an SDP descriptor. 5.6.33 The 'anycast' attribute When present, the 'anycast' attribute line is used to indicate the applicability of the anycast function described in UNI 4.0 [5]. Optional parameters to qualify this function are provided. The format of the 'anycast' attribute is: a=anycast: <atmGroupAddress> <cdStd> <conScpTyp> <conScpSel> The <atmGroupAddress> is per Annex 5 of UNI 4.0 [5]. Within an SDP descriptor, it can be represented in one of the formats (NSAP, E.164, GWID/ALIAS) described elsewhere in this document. The remaining subparameters mirror the connection scope selection information element in UNI 4.0 [5]. Their meaning and representation is as shown below: PARAMETER MEANING REPRESENTATION <cdStd> Coding standard for the Decimal or hex connection scope selection IE equivalent of Definition: UNI 4.0 [5] 2 bits <conScpTyp> Type of connection scope Decimal or hex Definition: UNI 4.0 [5] equivalent of 4 bits <conScpSel> Connection scope selection Decimal or hex Definition: UNI 4.0 [5] equivalent of 8 bits Currently, all values of <cdStd> and <conScpTyp> are reserved with the exception of <cdStd> = 3 (ATMF coding standard) and <conScpTyp> = 1 (connection scope type of 'organizational'). Each of these fields can be set to a "-" when the intention is to not specify them in an SDP descriptor. 5.6.34 The 'cache' attribute This attribute is used to enable SVC caching. This attribute has the following format: a=cache:<cacheEnable><cacheTimer> The <cacheEnable> flag indicates whether caching is enabled or not, corresponding to the string values of "on" and "off" respectively. The <cacheTimer> indicates the period of inactivity following which the SVC is to be released by sending an SVC release message into the network. This is specified as the decimal or hex equivalent of a 32-bit field, indicating the timeout in seconds. As usual, leading zeros can be omitted. For instance, a=cache:on 7200 implies that the cached SVC is to be deleted if it is idle for 2 hours. Rajesh Kumar, Mohamed Mostafa. 45 Internet Draft ATM SDP September 2000 The <cacheTimer> can be set to "-" if it is inapplicable or implied. 5.6.35 Specification of Higher-layer attributes This conventions in this ATM SDP document are limited to the ATM and adaptation layers. Parameters associated with layers higher than the ATM adaptation layer are addressed only if these are tightly coupled to the ATM or adaptation layers. ATM signaling standards provide 'escape mechanisms' to represent, signal and negotiate higher-layer parameters. Examples are the B-HLI and B-LLI IEs specified in ITU Q.2931 [15], and the user-to-user information element described in ITU Q.2957 [48]. SDP, as described in rfc2327, has a similar mechanism to describe higher-layer parameters. This is the 'fmtp' or the format-specific parameters attribute. This attribute is expressed in the following manner: a=fmtp:<format><format specific parameters> It is suggested that applications use this attribute, described in detail in rfc2327 [1], to express higher-layer parameters. Conventions for the use of the 'fmtp' attribute to describe higher-layer information are beyond the scope of the present document. However, it is recognized that in some applications it is necessary to describe higher-layer information within the same SDP descriptor as the ATM and AAL information. 5.6.36 Use of the second media-level part in H.323 Annex C applications Section 4 mentions that H.323 annex C applications have a second media level part for the ATM session description. This is used to convey information about the RTCP stream. Although the RTP stream is encapsulated in AAL5 with no intervening IP layer, the RTCP stream is sent to an IP address and RTCP port. This media level part has the following format: m= control <rtcpPortNum> H323c - c= IN IP4 <rtcpIPaddr> Consistency with rfc2327 is maintained in the location and format of these lines. The <fmt list> in the 'm' line is set to "-". The 'c' line in the second media-level part pertains to RTCP only. The <rtcpPortNum> and <rtcpIPaddr> subparameters indicate the port number and IP address on which the media gateway is prepared to receive RTCP packets. Any of the subparameters on these lines can be set to "-" if they are known by other means. The range and format of the <rtcpPortNum> and <rtcpIPaddr> subparameters is per [1]. The <rtcpPortNum> is a decimal number between 1024 and 65535. It is an odd number. If an even number in this range is specified, the next odd number is used. The <rtcpIPaddr> is expressed in the usual dotted decimal IP address representation, from 0.0.0.0 to 255.255.255.255, resulting in an alphanumeric string of 7 to 15 characters. Rajesh Kumar, Mohamed Mostafa. 46 Internet Draft ATM SDP September 2000 5.6.37 Chaining SDP descriptors The start of an SDP descriptor is marked by a 'v' line. In some applications, consecutive SDP descriptions are alternative descriptions of the same session. In others, these describe different layers of the same connection (e.g. IP, ATM, frame relay). This is useful when these connectivity at these layers are established at the same time e.g. an IP-based session over an ATM SVC. To distinguish between the alternation and concatenation of SDP descriptions, a 'chain' attribute can be used in the case of concatenation. When present, the 'chain' attribute binds an SDP description to the next or previous SDP description. The next or previous description is separated from the current one by a 'v' line. It is not necessary that this description also have a 'chain' media attribute line. Chaining averts the need to set up a single SDP description for a session that is simultaneously created at multiple layers. It allows the SDP descriptors for different layers to remain simple and clean. Chaining is not needed in the Megaco context, where it is possible to create separate terminations for the different layers of a connection. The 'chain' media attribute line has the following format: a=chain:<chainPointer> The <chainPointer> field can take on the following string values: "next", "previous" and "NULL". The value "NULL" is not equivalent to omitting the chain attribute from a description since it expressly precludes the possibility of chaining. If the 'chain' attribute is absent in an SDP description, chaining can still be realized by the presence of a chain media attribute line in the previous or next description. 5.6.38 Use of the eecid media attribute in call establishment procedures This informative section supplements the definition of the eecid attribute (Section 5.6.2) by describing example procedures for its use. These procedures assume a bearer-signaling mechanism for connection set-up that is independent of service-level call control. These procedures are independent of the media gateway control protocol (MGCP, Megaco, SIP etc.), the protocol used between media gateway controllers (ITU Q.1901, SIP etc.) and the protocol used for bearer connection set-up (Q.2931, UNI, PNNI, AINI, IISP, Q.2630.1 etc.). Inter-MGC +---------+ Protocol +---------+ | MGC |------------------| MGC | +---------+ +---------+ | | |Media Gateway |Media Gateway |Control Protocol |Control Protocol | | +------------+ (ATM Network) +------------+ |Originating |------------------|Terminating | |Media | Bearer Setup |Media | |Gateway | Protocol |Gateway | +------------+ +------------+ In the diagram above, the originating media gateway originates the service- level call. The terminating media gateway terminates it. In the forward call Rajesh Kumar, Mohamed Mostafa. 47 Internet Draft ATM SDP September 2000 model, the originating media gateway initiates bearer connection set-up. In the backward call model, the terminating gateway initiates bearer connection set- up. Example use of the Backward Call Model: (1) The originating media gateway controller (OMGC) initiates service-level call establishment by sending the appropriate control message to the originating media gateway (OMG). (2) The originating media gateway (OMG) provides its NSAP address and an eecid value to the OMGC, using the following SDP description: v=0 o=- 2873397496 0 ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 s=- c=ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 t=0 0 m=audio $ AAL2/ITU 8 a=eecid:B3D58E32 (3) The originating media gateway controller (OMGC) signals the terminating media gateway controller (TMGC) through the appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.). It provides the TMGC with the NSAP address and the eecid provided by the OMG. (4) The TMGC sends the appropriate control message to the TMG. This includes the session descriptor received from the OMG. This descriptor contains the NSAP address of the OMG and the EECID assigned by the OMG. Additionally, the TMGC instructs the TMG to set up an SVC to the OMG. It also requests the TMG to notify the TMGC when SVC set-up is complete. Depending on the control protocol used, this can be done through a variety of means. In the Megaco context, the request to set-up an SVC (not the notification request for the SVC set-up event) can be made through the following local descriptor: v=0 o=- 2873397497 0 ATM - - s=- c=ATM - - t=0 0 m=audio $ - - a=bearerType:SVC on The 'bearerType' attribute indicates that an SVC is to be used and that the <localInititiation> flag is on i.e. the SVC is to be set up by the TMG. (5) The TMG acknowledges the control message from the TMGC. It returns the following SDP descriptor with the acknowledge: Rajesh Kumar, Mohamed Mostafa. 48 Internet Draft ATM SDP September 2000 v=0 o=- 2873397498 0 ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 s=- c=ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 t=0 0 m=audio $ AAL2/ITU 8 The NSAP address information provided in this descriptor is not needed. It can be omitted (by setting it to "- -"). (6) The TMG sends an SVC set-up message to the OMG. Within the GIT information element, it includes eecid (B3D58E32) received from the OMG. (7) The OMG uses the eecid to correlate the SVC set-up request with service-level control message received before from the OMGC. (8) The OMG returns an SVC connect message to the TMG. On receiving this message, the TMG sends an event notification to the TMGC indicating successful SVC set-up. Note that, for this example, the "v=", "o=", "s=" and "t=" lines can be omitted in the Megaco context. Example use of the Forward Call Model: (1) The originating media gateway controller (OMGC) initiates service-level call establishment by sending the appropriate control message to the originating media gateway (OMG). (2) The originating media gateway (OMG) provides its NSAP address to the OMGC, using the following SDP description: v=0 o=- 2873397496 0 ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 s=- c=ATM NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00 t=0 0 m=audio $ AAL2/ITU 8 The NSAP address information provided in this descriptor is not needed. It can be omitted (by setting it to "- -"). (3) The originating media gateway controller (OMGC) signals the terminating media gateway controller (TMGC) through the appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.). Although this is not necessary, it can provide the TMGC with the NSAP address provided by the OMG. (4) The TMGC sends the appropriate control message to the TMG. This includes the session descriptor received from the OMG. This descriptor contains the NSAP address of the OMG. (5) The TMG acknowledges the control message from the TMGC. Along with the acknowledgement, it provides an SDP descriptor with a locally assigned eecid. Rajesh Kumar, Mohamed Mostafa. 49 Internet Draft ATM SDP September 2000 v=0 o=- 2873397714 0 ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 s=- c=ATM NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00 t=0 0 m=audio $ AAL2/ITU 8 a=eecid:B3D58E32 (6) The terminating media gateway controller (TMGC) signals the originating media gateway controller (OMGC) through the appropriate mechanism (ISUP with Q.1901 extensions, SIP etc.). It provides the OMGC with the NSAP address and the eecid provided by the TMG. (7) The OMGC sends the appropriate control message to the OMG. This includes the session descriptor received from the TMG. This descriptor contains the NSAP address of the TMG and the EECID assigned by the TMG. Additionally, the OMGC instructs the OMG to set up an SVC to the TMG. It also requests the OMG to notify the OMGC when SVC set-up is complete. Depending on the control protocol used, this can be done through a variety of means. In the Megaco context, the request to set-up an SVC (not the notification request for the SVC set-up event) can be made through the following local descriptor: v=0 o=- 2873397874 0 ATM - - s=- c=ATM - - t=0 0 m=audio $ - - a=bearerType:SVC on The 'bearerType' attribute indicates that an SVC is to be used and that the <localInititiation> flag is on i.e. the SVC is to be set up by the TMG. (8) The OMG acknowledges the control message from the OMGC. (9) The OMG sends an SVC set-up message to the TMG. Within the GIT information element, it includes eecid (B3D58E32) received from the TMG. (10)The TMG uses the eecid to correlate the SVC set-up request with the service-level control message received before from the TMGC. (11)The TMG returns an SVC connect message to the OMG. On receiving this message, the OMG sends an event notification to the OMGC indicating successful SVC set-up. Note that, for this example, the "v=", "o=", "s=" and "t=" lines can be omitted in the Megaco context. 6.0 List of Parameters with Representations This section provides a list of the parameters used in this document, and the formats used to represent them in SDP descriptions. In general, a "-" value can be used for any field that is not specified, is inapplicable or is implied. Rajesh Kumar, Mohamed Mostafa. 50 Internet Draft ATM SDP September 2000 PARAMETER MEANING REPRESENTATION <username> User name Constant "-" <sessionID> Session ID Up to 34 alphanumeric characters. <version> Version of 10 decimal or 8 hex SDP descriptor digits <networkType> Network type Constant "ATM" <ATMaddressType> ATM address type String values: "NSAP", "E164", "GWID", "ALIAS" <ATMaddress> ATM address "NSAP": 40 hex digits, optionally dotted "E164": up to 15 decimal digits "GWID": up to 32 characters "ALIAS": up to 32 characters <sessionName> Session name Constant "-" <startTime> Session start 10 decimal or 8 hex time digits <stopTime> Session stop Constant "0" time <vcci> Virtual Circuit Decimal or hex equivalent Connection of 16 bits Identifier <ex_vcci> Explicit "VCCI-" prefixed to <vcci> representation of <vcci> <bcg> Bearer Connection Decimal or hex equivalent Group of 8 bits <ex_bcg> Explicit "BCG-" prefixed to <bcg> representation of <bcg> <portId> Port ID Up to 34 alphanumeric characters. <ex_portId> Explicit "PORT-" prefixed to <portId> representation of <portId> <vpi> Virtual Path Decimal or hex equivalent Identifier of 8 or 12 bits <ex_vpi> Explicit "VPI-" prefixed to <vpi> representation of <vpi> Rajesh Kumar, Mohamed Mostafa. 51 Internet Draft ATM SDP September 2000 <vci> Virtual Circuit Decimal or hex equivalent Identifier of 16 bits <ex_vci> Explicit "VCI-" prefixed to <vci> representation of <vci> <vpci> Virtual Path Decimal or hex equivalent Connection of 16 bits Identifier <ex_vpci> Explicit "VPCI-" prefixed to <vpci> representation of <vpci> <cid> Channel Decimal or hex equivalent Identifier of 8 bits <ex_cid> Explicit "CID-" prefixed to <cid> representation of <cid> <payloadType> Payload Decimal integer 0-127 Type <transport> Transport String values listed in Table 1. <profile> Profile Decimal integer 1-255 <eecid> End-to-end Up to 8 hex digits Connection Identifier <aalType> AAL type String values: "AAL1","AAL1_SDT","AAL1_UDT", "AAL2", "AAL3/4", "AAL5", "USER_DEFINED_AAL" <silenceSuppEnable> Silence suppression String values: Enable "on", "off" <silenceTimer> Kick-in timer Decimal or hex representation for silence of 16-bit field suppression <suppPref> Preferred Silence String values: Suppression Method "standard", "custom" <sidUse> SID Use String values: Method "No SID", "Fixed Noise", "Sampled Noise" <fxnslevel> Fixed Noise Decimal or hex representation Level of a 7-bit field <ecanEnable> Enable Echo String values: Cancellation "on", "off" <ecanType> Type of Echo String values: Rajesh Kumar, Mohamed Mostafa. 52 Internet Draft ATM SDP September 2000 Cancellation "G165", "G168" <gcEnable> Enable Gain String values: Control "on", "off" <gcLvl> Level of inserted Decimal or hex equivalent Loss of 16-bit field <uuiCodeRange> UUI code range Decimal integer 0-15 <encodingName> Encoding name String values: "PCMG", "SIDG", "SID729", any value from column 2 of Table 2 <packetLength> Packet length Decimal integer 0-45 <packetTime> Packetization Decimal integer 1-500 Interval <fxIncl> Facsimile included String values: "on", "off" <asc> ATM service String values: category defined "CBR", "nrt-VBR", "rt-VBR", by the ATMF "UBR", "ABR", "GFR" <atc> ATM transfer String values: capability "DBR","SBR","ABT/IT","ABT/DT", defined by the "ABR" ITU <subtype> <asc>/<atc> Decimal integer subtype <qosClass> QoS Class Decimal integer 0-5 <bcob> Broadband Bearer Decimal or hex representation Class of 5-bit field <stc> Susceptibility Decimal equivalent of to clipping a 2-bit field <upcc> User plane Decimal equivalent of connection a 2-bit field configuration <cdvType> CDV type String values: "PP", "2P" <acdv> Acceptable CDV Integer or hex equivalent of 24-bit field <ccdv> Cumulative CDV Integer or hex equivalent of 24-bit field <actd> Acceptable CTD Integer or hex equivalent of 16-bit field <cctd> Cumulative CTD Integer or hex equivalent of 16-bit field Rajesh Kumar, Mohamed Mostafa. 53 Internet Draft ATM SDP September 2000 <aclr> Acceptable Integer or hex equivalent Cell Loss Ratio of 8-bit field <clpLvl> CLP level String values: "0", "0+1" <pcr> Peak Cells/second Cell Rate <scr> Sustained Cells/second Cell Rate <mbs> Maximum Cells Burst Size <cdvt> CDVT Decimal integer or fraction, range determined by application. <mcr> Minimum Cells/second Cell Rate <mfs> Maximum Cells Frame Size <fd> Frame Discard String Values: Allowed "on", "off" <te> CLP tagging String Values: Enabled "on", "off" <nrm> NRM Decimal/hex equivalent of 3 bit field <trm> TRM - ditto- <cdf> CDF -ditto- <adtf> ADTF Decimal/Hex equivalent of 10 bit field <clkrec> Clock Recovery String values: Method "NULL", "SRTS", "ADAPTIVE" <fecEnable> Forward Error String values: Correction Enable "NULL", "LOSS_SENSITIVE" "DELAY_SENSITIVE" <partialFill> Partial Fill Decimal integer 1-48 or hex equivalent <bearerType> Bearer Type String Values: "PVC", "SVC", "CID" <structureEnable> Structure Present String values: "on", "off" <blksz> Block Size Decimal or hexadecimal equivalent of 16 bits Rajesh Kumar, Mohamed Mostafa. 54 Internet Draft ATM SDP September 2000 <sbc> Subchannel Count T1: Decimal integer 1-24 or hex equivalent E1: Decimal integer 1-31 or hex equivalent <cpcs> Maximum AAL5: Decimal or hex CPCS SDU size equivalent of 16 bits AAL2: 45 or 64 <cidCount> Number of Decimal integer 1-255 subcell channels or hex equivalent <timerCU> Timer, combined use Integer decimal; range determined by application <adt> Assured Data String values: Transfer Enable "on", "off" <ted> Transmission Error String values: Detection Enable "on", "off" <fsssar> Maximum SSSAR-SDU Decimal or hex size, forward equivalent of 16-bit direction field <bsssar> Maximum SSSAR-SDU Decimal or hex size, backward equivalent of 16-bit direction field <sap> Service Access String values: Point "AUDIO", "MULTIRATE" <circuitMode> Circuit Mode String values: Enable "on", "off" <frameMode> Frame Mode String values: Enable "on", "off" <faxDemod> Fax Demodulation String values: Enable "on", "off" <cas> Enable CAS transport String values: via Type 3 packets "on", "off" <dtmf> Enable DTMF transport String values: via Type 3 packets "on", "off" <mfall> Enable MF transport String values: via Type 3 packets "on", "off" <mfr1> Enable MF (R1) String values: transport via "on", "off" Type 3 packets <mfr2> Enable MF (R2) String values: transport via "on", "off" Type 3 packets <PCMencoding> PCM encoding String values: "PCMA", "PCMU" Rajesh Kumar, Mohamed Mostafa. 55 Internet Draft ATM SDP September 2000 <fmaxFrame> Maximum length of a Decimal or hex frame mode data unit, equivalent of forward direction 16-bit field <bmaxFrame> Maximum length of a -ditto- frame mode data unit, backward direction <aalApp> Application specification String values: "itu_h323c","af83", "assuredSSCOP", "nonassuredSSCOP", "itu_i3661", "itu_i3662", "itu_i3651", "itu_i3652", "itu_i3653", "FRF11", "FRF5", "FRF8", "itu_h2221" <sci> Screening Indication Decimal or hex equivalent of 4 bits. <lsn> Leaf Sequence Number Decimal or hex equivalent of 32 bits. <cdStd> Coding standard for the Decimal or hex connection scope selection equivalent of IE 2 bits Definition: UNI 4.0 [5] <conScpTyp> Type of connection scope Decimal or hex Definition: UNI 4.0 [5] equivalent of 4 bits <conScpSel> Connection scope selection Decimal or hex equivalent Definition: UNI 4.0 [5] of 8 bits <cacheEnable> Enable SVC caching String values: "on", "off" <cacheTimer> Timer for cached SVC Decimal or hex equivalent deletion of 32-bit field <rtcpPortNum> RTCP port number for Odd decimal in range 1,024 to H.323 Annex C applications 65,535. Preferred: Odd number in the range 49,152 to 65,535 <rtcpIPaddr> IP address for receipt Dotted decimal, 7-15 chars of RTCP packets <chainPointer> Chain pointer String values: "next", "previous", "NULL" Rajesh Kumar, Mohamed Mostafa. 56 Internet Draft ATM SDP September 2000 7.0 Examples of ATM session descriptions using SDP An example of a complete AAL1 session description in SDP is: v=0 o=- A3C47F21456789F0 0 ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 s=- c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 t=0 0 m=audio $ AAL1/AVP 18 0 96 a=atmmap:96 X-G727-32 a=eecid:B3D58E32 An example of a complete AAL2 session description in SDP is: v=0 o=- A3C47F21456789F0 0 ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 s=- c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 t=0 0 m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1 a=eecid:B3E32 The AAL2 session descriptor below is the same as the one above except that it states an explicit preference for a voice codec, a voiceband data codec and a voiceband fax codec. Further, it defines the profile AAL2/custom 100 rather than assume that the far-end is cognizant of the elements of this profile. v=0 o=- A3C47F21456789F0 0 ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 s=- c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 t=0 0 m=audio $ AAL2/ITU 8 AAL2/custom 100 AAL2/ITU 1 a=eecid:B3E32 a=profileDesc:AAL2/custom 100 0-7 PCMG 40 5 0-7 SIDG 1 5 8-15 G726-32 40 10 8-15 SIDG 1 5 a=vsel:G726-32 40 10 a=dsel:off PCMU - - a=fsel:G726-32 40 10 Rajesh Kumar, Mohamed Mostafa. 57 Internet Draft ATM SDP September 2000 An example of an SDP session descriptor for an AAL5 switched virtual circuit for delivering MPEG-2 video: v=0 o=- A3C47F21456789F0 0 ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 s=- c=ATM NSAP 47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00 t=0 0 m=video $ AAL5/ITU 33 a=eecid:B3E32 a=aalType:AAL5 a=bearerType:SVC on a=atmFtrfcDesc:0+1 7816 - - - - - off - a=atmBtrfcDesc:0+1 0 - - - - - on - a=fcpsSDUsize:20680 a=aalApp:itu_h2221 An example of an SDP session descriptor for an AAL5 permanent virtual circuit for delivering MPEG-2 video: v=0 o=- A3C47F21456789F0 0 ATM - - s=- c=ATM - - t=0 0 m=video PORT-$/VPI-0/VCI-$ AAL5/ITU 33 a=bearerType:PVC - a=atmFtrfcDesc:0+1 7816 - - - - - off - a=atmBtrfcDesc:0+1 0 - - - - - on - a=fcpsSDUsize:20680 a=aalApp:itu_h2221 8.0 Representation of data media The following encoding names in Table 2 can refer to data as well as audio media: X-CCD and X-CCD-CAS in Table 2. The following encoding names in Table 2 refer to data media: X-FXDMOD-3 in Table 2. In the AAL1 context, X-CCD and X-CCD-CAS can be represented as "audio" codecs that are dynamically mapped into payload types. This is done through the 'atmmap' attribute, as described earlier. For example: m=audio 27 AAL1/AVP 98 a=atmmap:98 X-CCD implies that AAL1 VCCI=27 is used for n x 64 transmission. Currently, AAL1 in unsuitable for transmitting demodulated facsimile because it lacks the bearer plane mechanisms (equivalent to AAL2 type 3 messages) for transmitting control information. In the AAL2 context, these "codecs" can be assigned profile types and numbers. Even though it is not possible to construct profile tables as described in ITU I.366.2 for these "codecs", it is preferable to adopt the common AAL2 profile convention in their case. An example AAL2 profile mapping for these could be as follows: Rajesh Kumar, Mohamed Mostafa. 58 Internet Draft ATM SDP September 2000 PROFILE TYPE PROFILE NUMBER "CODEC" (ONLY ONE) "custom" 200 X-CCD "custom" 201 X-FXDMOD-3 The profile does not identify the number of subchannels ('n' in nx64). This is known by other means such as the 'sbc' media attribute line. Currently, there is no definition of n x 64 trunking with CAS for AAL2. For example, the media information line: m=audio $ AAL2/custom 200 a=sbc:6 implies a 384 kbps n x 64 circuit using AAL2 adaptation. In the case of fax demodulation and remodulation (ITU I.366.2), parameters such as information type, image data size and control type are negotiated in the 'bearer plane' via type 3 messages. There is no need to define several encoding names for these control streams. 9.0 Security Considerations 9.1 Bearer Security At present, standard means of encrypting ATM and AAL2 bearers are not conventionalized in the same manner as means of encrypting RTP payloads. Nor has the authentication of ATM or AAL2 bearer signaling. The SDP encryption key line (k=) defined in rfc2327 can be used to represent the encryption key and the method of obtaining the key. In the ATM and AAL2 contexts, the term 'bearer' can include 'bearer signaling' as well as 'bearer payloads'. 9.2 Security of the SDP description The SDP session descriptions might originate in untrusted areas such as equipment owned by end-subscribers or located at end-subscriber premises. SDP relies on the security mechanisms of the encapsulating protocol or layers below the encapsulating protocol. Examples of encapsulating protocols are the Session Initiation Protocol (SIP), MGCP and Multimedia Gateway Control Protocol (MEGACO). No additional security mechanisms are needed. SIP, MGCP and MEGACO can use IPSec authentication as described in RFC1826 [Ref. 27]. IPSec encryption can be optionally used with authentication to provide an additional, potentially more expensive level of security. IPSec security associations can be made between equipment located in untrusted areas and equipment located in trusted areas through configured shared secrets or the use of a certificate authority. References [1] IETF RFC 2327, 'SDP: Session Description Protocol', April '98, Mark Handley and Van Jacobson. [2] IETF RFC 1889, 'RTP: A Transport Protocol for Real-Time Applications', Jan. 1996. RFC1889 will be obsoleted, in a substantially backwards compatible manner, by the RFC that evolves out of draft-ietf-avt-rtp-new-08.txt. [3] IETF RFC 1890, 'RTP Profile for Audio and Video Conferences Rajesh Kumar, Mohamed Mostafa. 59 Internet Draft ATM SDP September 2000 with Minimal Control', Jan. 1996. RFC1890 will be obsoleted, in a fully backwards compatible manner, by the RFC that evolves out of draft-ietf-avt-profile-new-09.txt. [4] ATMF UNI 3.1 Specification, af-uni-0010.002. Of special interest for this document is Section 5.4.5.5, ATM Adaptation Layer Parameters. [5] ATMF UNI 4.0 Signaling Specification, af-sig-0061.000. [6] ATMF Traffic Management Specification, Version 4.1, af-tm- 0121.000. [7] ATMF Circuit Emulation Service (CES) Interoperability Specification, version 2.0, af-vtoa-0078.000, Jan. 97. [8] ATMF Voice and Telephony over ATM - ATM Trunking using AAL1 for Narrowband Services, version 1.0, af-vtoa-0089.000, July 1997. [9] ATMF Specifications of (DBCES) Dynamic Bandwidth Utilization - in 64kbps Timeslot Trunking over ATM - using CES, af-vtoa- 0085.000, July 1997. [10] ITU-T I.363.1, B-ISDN ATM Adaptation Layer Specification: Type 1 AAL, August 1996. [11] ITU-T I.363.2, B-ISDN ATM Adaptation Layer Specification: Type 2 AAL, Sept. 1997. [12] ITU-T I.366.1, Segmentation and Reassembly Service Specific Convergence Sublayer for AAL Type 2, June 1998. [13] ITU-T I.366.2, AAL Type 2 Reassembly Service Specific Convergence Sublayer for Trunking, Feb. 99. [14] Draft ietf-avt-telephone-tones-05.txt, RTP payloads for Telephone Signal Events, S.B.Petrack, Nov. 17, 1998. [15] ITU-T Q.2931, B-ISDN Application Protocol for Access Signaling. [16] Amendment 1, 2, 3 and 4 to ITU-T Q.2931, B-ISDN Application Protocol for Access Signaling. [17] SAP: Session Announcement Protocol , draft-ietf-mmusic-sap-v2- 04.txt, Mark Handley, Colin Perkins and Edmund Whelan . [18] rfc2543, Handley, M., H. Schulzrinne , Schooler, E. and Rosenberg, J., "Session Initiation Protocol (SIP)", March 1999. [19] rfc1349, Type of Service in the Internet Protocol Suite. P. Almquist. July 1992. [20] rfc2474, Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers. K. Nichols, S. Blake, F. Baker, D. Black. December 1998. [21] ITU-T I.363.5, B-ISDN ATM Adaptation Layer Specification: Type 5 AAL, Aug. 1996. Rajesh Kumar, Mohamed Mostafa. 60 Internet Draft ATM SDP September 2000 [22] ATMF PNNI 1.0, af-pnni-0055.000, March 1996. [23] ietf-avt-rtp-new-05.txt, Oct. 21, 1999, RTP: A Transport Protocol for Real-Time Applications. [24] ietf-avt-profile-new-07.txt, Oct. 21, 1999, RTP Profile for Audio and Video Conferences with Minimal Control. [25] Media Gateway Control Protocol (MGCP), Mauricio Arango, Isaac Elliott, Christian Huitema, Scott Pickett, Version 1.0, RFC2705. [26] draft-ietf-Megaco-merged-00.txt, April, 2000, Media Gateway control (Megaco) protocol, Fernando Cuervo, Nancy Greene, Christian Huitema, Abdallah Rayhan, Brian Rosen, John Segers. [27] IP Authentication Header, R. Atkinson, August 1995, RFC1826. [28] ITU I.371, Traffic Control and Congestion Control in the BISDN. [29] ITU E.191, BISDN Numbering and Addressing. [30] ATM Forum Addressing: Reference Guide, af-ra-0106.000. [31] http://www.isi.edu/in-notes/iana/assignments/rtp-parameters for a list of codecs with static payload types. [32] ITU Q.2941-2, Digital Subscriber Signalling System No. 2 (DSS 2): Generic identifier transport extensions. [33] ITU Q.2961, Digital subscriber signalling system no.2 (DSS 2) - additional traffic parameters. Also, Amendment 2 to Q.2961. [34] ITU Q. 2965.1, Digital subscriber signalling system no.2 (DSS 2) - Support of Quality of Service classes. [35] ITU Q. 2965.2, Digital subscriber signalling system no.2 (DSS 2) - Signalling of individual Quality of Service parameters. [36] ITU Q.1901, Bearer Independent Call Control Protocol. [37] ITU Q.2630.1, AAL type 2 signaling protocol - capability set 1. [38] ITU I.363.5, B-ISDN ATM Adaptation Layer specification: Type 5 AAL. [39] I.365.1,Frame relaying service specific convergence sublayer (FR-SSCS). [40] I.365.2, B-ISDN ATM adaptation layer sublayers: service specific coordination function to provide the connection oriented network service. [41] I.365.3, B-ISDN ATM adaptation layer sublayers: service specific coordination function to provide the connection-oriented transport service. [42] I.365.4, B-ISDN ATM adaptation layer sublayers: Service specific convergence sublayer for HDLC applications. [43] Q.2110, B-ISDN ATM adaptation layer - service specific connection Rajesh Kumar, Mohamed Mostafa. 61 Internet Draft ATM SDP September 2000 oriented protocol (SSCOP). [44] af-vtoa-0113.000, ATM trunking using AAL2 for narrowband services. [45] H.323-2, Packet-based multimedia communications systems. [46] af-vtoa-0083.000, Voice and Telephony Over ATM to the Desktop. [47] I.356, BISDN ATM layer cell transfer performance. [48] ITU Q.2957, Digital Subscriber Signaling System No. 2, User to user signaling. [49] rfc1305, Network Time Protocol, version 3. [50] TIA/EIA/IS-J-STD-025-A, Lawfully Authorized Electronic Surveillance, May 2000. [51] ITU-T H.222.1, Multimedia multiplex and synchronization for audiovisual communication in ATM environments. [52] af-vmoa-0145.000, Voice and Multimedia over ATM, Loop Emulation Service using AAL2. [53] FRF.5, Frame Relay/ATM PVC Network Interworking Implementation Agreement. [54] FRF.8, Frame Relay/ATM PVC Service Interworking Implementation Agreement. [55] FRF.11, Voice over Frame Relay Implementation Agreement. Acknowledgements The authors wish to thank several colleagues at Cisco and in the industry who have contributed towards the development of these SDP conventions, and who have reviewed, implemented and tested these constructs. Valuable technical ideas that have been incorporated into this internet draft have been provided by Hisham Abdelhamid, David Auerbach, Robert Biskner, Bruce Buffam, Steve Casner, Alex Clemm, Bill Foster, Snehal Karia, Raghu Thirumalai Rajan, Joe Stone, Bruce Thompson, Dan Wing and Ken Young of Cisco, Michael Brown, Rade Gvozdanovic, Graeme Gibbs, Tom-PT Taylor, Mark Watson and Sophia Scoggins of Nortel Networks, Brian Rosen, Tim Dwight and Michael Mackey of Marconi, Ed Guy and Petros Mouchtaris of Telcordia, Christian Groves of Ericsson, Charles Eckel of Vovida Networks, Tom Jepsen and Chris Gallon of Fujitsu, Mahamood Hussain of Hughes Software Systems, Sean Sheedy of nCUBE Corporation and Narendra Tulpule of Trillium Digital systems. The authors also wish to thank the ISC device control group, and the MMUSIC and MEGACO subgroups of the IETF, especially Bill Foster, Jeorg Ott, Sean Sheedy and Brian Rosen for their help in the preparation of this document. Authors' Addresses Rajesh Kumar Cisco Systems, Inc. M/S SJC01/3 170 West Tasman Drive San Jose, CA 95134-1706 Phone: 1-800-250-4800 Email: rkumar@cisco.com Mohamed Mostafa Rajesh Kumar, Mohamed Mostafa. 62 Internet Draft ATM SDP September 2000 Cisco Systems, Inc. M/S SJC01/3 170 West Tasman Drive San Jose, CA 95134-1706 Phone: 1-800-250-4800 Email: mmostafa@cisco.com Full Copyright Statement Copyright (C) The Internet Society (March 2, 2000). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." Rajesh Kumar, Mohamed Mostafa. 63
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