Network Working Group W. Marshall Internet Draft AT&T Document:<draft-dcsgroup-sipping-proxy-proxy-00.txt> Category: Informational F. Andreasen Cisco Burcak Beser Juniper Networks June 6, 2002 Private SIP Proxy-to-Proxy Extensions for Supporting DCS Status of this Memo This document is an Internet-Draft and is in full compliance with all provisions of Section 10 of RFC 2026 [1]. 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. 1. Abstract In order to deploy a residential telephone service at very large scale across different domains, it is necessary for trusted elements owned by different service providers to exchange trusted information that conveys customer-specific information and expectations about the parties involved in the call. This document describes private extensions to the Session Initiation Protocol (RFC3261) for supporting the exchange of customer information and billing information between trusted entities in the architecture described in "Architectural Considerations for Providing Carrier Class Telephony Services Utilizing SIP-based Distributed Call Control Mechanisms" (RFCXXXX draft-dcsgroup-sipping-arch). 2. Table of Contents DCS Group Category Informational - Expiration 11/30/2002 1 SIP Proxy-to-Proxy Extensions May 2002 Status of this Memo................................................1 1. Abstract........................................................1 2. Table of Contents...............................................1 3. Applicability Statement.........................................3 4. Introduction....................................................3 5. Trust Boundary..................................................4 6. Conventions used in this document...............................5 7. P-DCS-TRACE-PARTY-ID............................................5 7.1 Syntax.........................................................6 7.2 Procedures at an Untrusted User Agent Client (UAC).............6 7.3 Procedures at a Trusted User Agent Client (UAC)................6 7.4 Procedures at a User Agent Server (UAS)........................6 7.6 Procedures at Proxy............................................6 7.6.1 Procedures at Originating Proxy..............................7 7.6.2 Procedures at Terminating Proxy..............................7 8. P-DCS-GATE......................................................7 8.1 Syntax.........................................................7 8.2 Procedures at an Untrusted User Agent Client (UAC).............8 8.3 Procedures at a Trusted User Agent Client (UAC)................8 8.4 Procedures at an Untrusted User Agent Server (UAS).............8 8.5 Procedures at a Trusted User Agent Server (UAS)................8 8.6 Procedures at Proxy............................................9 8.6.1 Procedures at Originating Proxy..............................9 8.6.2 Procedures at Terminating Proxy..............................9 9. P-DCS-OSPS.....................................................10 9.1 Syntax........................................................10 9.2 Procedures at an Untrusted User Agent Client (UAC)............10 9.3 Procedures at a Trusted User Agent Client (UAC)...............10 9.4 Procedures at an Untrusted User Agent Server (UAS)............11 9.5 Procedures at a Trusted User Agent Server (UAS)...............11 9.6 Procedures at Proxy...........................................12 10. P-DCS-BILLING-ID and P-DCS-BILLING-INFO.......................12 10.1 Syntax.......................................................13 10.2 Procedures at an Untrusted User Agent Client (UAC)...........14 10.3 Procedures at a Trusted User Agent Client (UAC)..............14 10.4 Procedures at an Untrusted User Agent Server (UAS)...........14 10.5 Procedures at a Trusted User Agent Server (UAS)..............15 10.6 Procedures at Proxy..........................................15 10.6.1 Procedures at Originating Proxy............................15 10.6.2 Procedures at Terminating Proxy............................16 11. P-DCS-LAES and P-DCS-REDIRECT.................................17 11.1 Syntax.......................................................17 11.2 Procedures at an Untrusted User Agent Client (UAC)...........18 11.3 Procedures at a Trusted User Agent Client (UAC)..............18 11.4 Procedures at an Untrusted User Agent Server (UAS)...........18 11.5 Procedures at a Trusted User Agent Server (UAS)..............18 11.6 Procedures at Proxy..........................................19 11.6.1 Procedures at Originating Proxy............................19 11.6.2 Procedures at Terminating Proxy............................21 12. Security Considerations.......................................21 13. IANA Considerations...........................................22 14. Notice Regarding Intellectual Property Rights.................23 15. Normative References..........................................23 DCS Group Category Informational - Expiration 11/30/02 2 SIP Proxy-to-Proxy Extensions May 2002 16. Informative References........................................23 17. Acknowledgements..............................................24 18. Editor's Addresses............................................24 Full Copyright Statement..........................................25 3. Applicability Statement The headers defined in this document are intended for use only within a single network where coordination of charging and other functions is required, according to the architecture presented in [4]. 4. Introduction In order to deploy a SIP[3]-based residential telephone service at very large scale across different domains, it is necessary for trusted elements owned by different service providers to exchange trusted information that conveys billing information and expectations about the parties involved in the call. There are many billing models used in deriving revenue from telephony services today. Charging for telephony services is tightly coupled to the use of network resources. It is outside the scope of this document to discuss the details of these numerous and varying methods. A key motivating principle of the DCS architecture described in [4] is the need for network service providers to be able to control and monitor network resources; revenue may be derived from the usage of these resources as well as from the delivery of enhanced services such as telephony. Furthermore, the DCS architecture recognizes the need for coordination between call signaling and resource management. This coordination ensures that users are authenticated and authorized before receiving access to network resources and billable enhanced services. DCS-Proxies, as defined in [4], have access to subscriber information and act as policy decision points and trusted intermediaries along the call signaling path. Edge routers provide the network connectivity and resource policy enforcement mechanism and also capture and report network connectivity and resource usage information. Edge routers need to be given billing information that can be logged with Record Keeping or Billing servers. The DCS Proxy, as a central point of coordination between call signaling and resource management, can provide this information based on the authenticated identity of the calling and called parties. Since there is a trust relationship among DCS Proxies, they can be relied upon to exchange trusted billing information pertaining to the parties involved in a call. See [4] for a description of the trust boundary and trusted versus untrusted entities. DCS Group Category Informational - Expiration 11/30/02 3 SIP Proxy-to-Proxy Extensions May 2002 For these reasons, it is appropriate to consider defining SIP header extensions to allow DCS Proxies to exchange information during call setup. It is the intent that the extensions would only appear on trusted network segments, should be inserted upon entering a trusted network region, and removed before leaving trusted network segments. Significant amounts of information is retrieved by an originating proxy in its handling of a connection setup request from a user agent. Such information includes location information about the subscriber (essential for emergency services calls), billing information, and station information (e.g. coin operated phone). In addition, while translating the destination number, information such as the local-number-portability office code is obtained and will be needed by all other proxies handling this call. For Usage Accounting records, it is necessary to have an identifier that can be associated with all the event records produced for the call. Call-ID cannot be used as such an identifier since it is selected by the originating user agent, and may not be unique among all past calls as well as current calls. Further, since this identifier is to be used by the service provider, it should be chosen in a manner and in a format that meets the service provider's needs. Billing information may not necessarily be unique for each user (consider the case of calls from an office all billed to the same account). Billing information may not necessarily be identical for all calls made by a single user (consider prepaid calls, credit card calls, collect calls, etc). It is therefore necessary to carry billing information separate from the calling and called party identification. Furthermore, some billing models call for split- charging where multiple entities are billed for portions of the call. The addition of two SIP General Header Fields allows for the capture of billing information and billing identification for the duration of the call. It is the intent that the billing extensions would only appear on trusted network segments, and MAY be inserted by a DCS Proxy in INVITE requests and responses in a trusted network segment, and removed before leaving trusted network segments. 5. Trust Boundary The DCS architecture [4] defines a trust boundary around the various systems and servers that are owned, operated by, and/or controlled by the service provider. These trusted systems include the proxies and various servers such as bridge servers, voicemail servers, announcement servers, etc. Outside of the trust boundary lie the customer premises equipment, and various media servers operated by third-party service providers. DCS Group Category Informational - Expiration 11/30/02 4 SIP Proxy-to-Proxy Extensions May 2002 Certain subscriber-specific information, such as billing and accounting information, stays within the trust boundary. Other subscriber-specific information, such as endpoint identity, may be presented to untrusted endpoints or may be withheld based on subscriber profiles. The User Agent (UA) may be either within the trust boundary or outside the trust boundary, depending on exactly what function is being performed and exactly how it is being performed. Accordingly, the procedures followed by a User Agent are different depending on whether the UA is within the trust boundary or outside the trust boundary. The following sections giving procedures for User Agents therefore are subdivided into trusted user agents and untrusted user agents. 6. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [2]. The term "private-URL" used in this document refers to a SIP URL that is generated by a proxy, contains a "hostport" that identifies the proxy, and contains a "userinfo" string that is generated by the proxy. The "userinfo" typically contains (or points to) information that is not to be disclosed outside the trusted domain of the proxies, such as billing account numbers, electronic surveillance indication, electronic surveillance parameters, and call redirection information. This information is either stored locally by the proxy, or encrypted with a private key known only to the proxy and encoded in a character string in the "userinfo" portion of the URL. A checksum is included in the "userinfo" data to detect tampering. The mechanism by which a proxy recognizes a "userinfo" as a private- URL and decodes and recovers the original information is local to the proxy and is not subject to standardization. Some possible implementations include an initial magic cookie (e.g. z9hG4Bk followed by the pointer/information), or use of a reserved "user" name (e.g. "private") with the optional "password" containing the pointer/information. 7. P-DCS-TRACE-PARTY-ID In the telephone network, calling identity information is used to support regulatory requirements such as the Customer Originated Trace service, which provide the called party with the ability to report obscene or harassing phone calls to law enforcement. This service is provided independent of caller-id, and operates even if the caller requested anonymity. The calling party is here identified as the station originating the call. In order for this DCS Group Category Informational - Expiration 11/30/02 5 SIP Proxy-to-Proxy Extensions May 2002 service to be dependable, the called party must be able to trust that the calling identity information being presented is valid. To initiate a customer-originated-trace from an untrusted UAC, an additional header is defined for the INVITE request sent from the untrusted UAC to its proxy. This header is called P-DCS-Trace- Party-ID, and does not appear in any other request or response. The proxy receiving a properly formed INVITE request with this header performs the service-provider-specific functions of recording and reporting the caller identity for law enforcement action. The proxy then completes the call to either an announcement server or to the service-provider's business office to collect further information about the complaint. A trusted UAC does not use this header, as it initiates this action locally. 7.1 Syntax The BNF description of this header is: P-DCS-Trace-Party-ID = "P-DCS-Trace-Party-ID" HCOLON LAQUOT addr-spec RAQUOT Addr-spec contains a URL that identifies the remote endpoint. Addr- spec typically contains a tel: URL or SIP URI giving the identity of the remote endpoint, as provided in the signaling messages that established the previous session. 7.2 Procedures at an Untrusted User Agent Client (UAC) The UAC MUST insert a P-DCS-Trace-Party-ID header into the initial INVITE message for a customer-originated-trace request. The UAC MUST use a SIP-URI in the Request-URI with userinfo set to "call- trace" and hostport identifying the provisioned proxy for the untrusted UA. 7.3 Procedures at a Trusted User Agent Client (UAC) A trusted UAC performs the customer-originated-trace in a manner similar to the originating proxy, described below. A trusted UAC MUST NOT include this header in any request. 7.4 Procedures at a User Agent Server (UAS) This header MUST NOT appear in any response sent by a UAS. 7.6 Procedures at Proxy Two sets of proxy procedures are defined: (1) the procedures at an originating proxy, and (2) the procedures at a terminating proxy. The originating proxy is a proxy that received the INVITE request from a non-trusted endpoint. DCS Group Category Informational - Expiration 11/30/02 6 SIP Proxy-to-Proxy Extensions May 2002 The terminating proxy is a proxy that sends the INVITE request to a non-trusted endpoint. A proxy that both receives the INVITE request from an untrusted endpoint, and sends the INVITE request to an untrusted endpoint, performs both sets of procedures. 7.6.1 Procedures at Originating Proxy If the P-DCS-Trace-Party-ID header is present in the initial INVITE request from the UAC, and the Request-URI of the INVITE has userinfo set to "call-trace" and hostport set to the originating proxy, the originating proxy MUST perform the service-provider-specific functions of recording and reporting the caller identity for law enforcement action. The proxy then MUST direct the call to either an announcement server or to the service-provider's business office to collect further information about the complaint. The originating proxy MUST remove the P-DCS-Trace-Party-ID header from the INVITE before sending the request to another proxy or UAS. 7.6.2 Procedures at Terminating Proxy This header MUST NOT appear in any request or response sent by a terminating proxy. 8. P-DCS-GATE The P-DCS-Gate header extension is used only on requests and responses between proxies and trusted user agents. It never is sent to, nor sent by, an untrusted UA. The proxy-proxy signaling establishes a synchronization path that may be required by the PacketCable Dynamic Quality of Service (D- QoS) specification [5] to coordinate the release of resources of the call. As per the D-QoS specification, the CMTS monitors the packet flow, and generates a Gate-Close message in response to either an explicit close request from the MTA/RGW, or when an equipment or facility failure causes the connection to be broken. This Gate-Close message is directed either to the local CMS/Agent (trusted UA), to the remote CMS/Agent (trusted UA), or to the CMTS serving the remote MTA, depending on the capabilities of the endpoints. When a CMS/Agent receives such a Gate-Close message, it considers it identical to a call termination request. The P-DCS-Gate header is used between proxies and trusted user agents, and conveys the location of the remote gate, identity of the gate, and the security key and ciphersuite to be used in gate coordination messages [5, 6]. 8.1 Syntax The BNF description of the DCS-Gate header is as follows: DCS Group Category Informational - Expiration 11/30/02 7 SIP Proxy-to-Proxy Extensions May 2002 P-DCS-Gate = "P-DCS-Gate" HCOLON hostport SLASH Gate-ID [SEMI Gate-Key SEMI Gate-CipherSuite] [SLASH Gate-strength-token] Gate-ID = 1*hex Gate-Key = 1*hex Gate-CipherSuite = token Gate-strength-token = "required" / "optional" Hostport gives the IP address or FQDN of the CMTS/EdgeRouter that enforces the QoS, or the trusted endpoint system (CMS/Agent) that simulates the gate coordination exchange on behalf of an edge router. Gate-ID is a token used at the system named in the hostport parameter to identify the particular session. For DCS systems, it is a 32-bit quantity encoded as an 8-character string. Gate-Key is a character string that provides keying information to the system named in the hostport parameter. The method of deriving the actual keys for the gate coordination messages, and the security procedures, are beyond the scope of this document. Gate-CipherSuite is a character string that gives the type of encryption algorithm that will be used to secure the gate coordination messages [6]. Gate-Strength-Token specifies whether the gate coordination is required or optional for the current session. Its use is described in the following sections. 8.2 Procedures at an Untrusted User Agent Client (UAC) This header MUST NOT be sent to an untrusted UAC, and MUST NOT be sent by an untrusted UAC. 8.3 Procedures at a Trusted User Agent Client (UAC) A UAC located within the trust boundary of the service provider MUST perform the functions given in section 8.6.1. 8.4 Procedures at an Untrusted User Agent Server (UAS) This header is never sent to an untrusted UAS, and is never sent by an untrusted UAS. 8.5 Procedures at a Trusted User Agent Server (UAS) A UAS located within the trust boundary of the service provider performs the functions given in section 8.6.2. DCS Group Category Informational - Expiration 11/30/02 8 SIP Proxy-to-Proxy Extensions May 2002 8.6 Procedures at Proxy The P-DCS-Gate header MUST NOT appear in any message other than the initial INVITE request, or in the first reliable non-100 response to that request. The proxy MUST remove the P-DCS-Gate header in any request or response sent to an untrusted endpoint. Two sets of proxy procedures are defined: (1) the procedures at an originating proxy, and (2) the procedures at a terminating proxy. The originating proxy is a proxy that receives the INVITE request from a non-trusted endpoint. The terminating proxy is a proxy that sends the INVITE request to a non-trusted endpoint. A proxy that both receives the INVITE request from an untrusted endpoint, and sends the INVITE request to a untrusted endpoint, performs both sets of proceduresDCS. A proxy that is neither an originating proxy nor a terminating proxy has no function in coordinating the commitment of resources. 8.6.1 Procedures at Originating Proxy The originating proxy MUST insert a P-DCS-Gate header in the initial INVITE message for a new call. The originating proxy MUST identify the system that will perform gate coordination on the originating side (either the proxy itself, or the CMTS controlling the media flow to the endpoint), and the identification token used at that system to identify the call. It MUST insert the IP address or FQDN of that system in the hostport parameter of the P-DCS-Gate header, and the identification token as the Gate-ID. The originating proxy MUST pick a security key and cipher suite for the gate coordination message exchange, and MUST insert these values in the P-DCS-Gate header. If the system that will perform gate coordination is a CMTS, the strength token MUST be given as required. If the system that will perform gate coordination is the proxy itself, the strength token MAY be given as optional, or omitted. Gate coordination procedures are described in [5]. 8.6.2 Procedures at Terminating Proxy The terminating proxy MUST identify the system that will perform gate coordination on the terminating side (either the proxy itself, or the CMTS controlling the media flow to the endpoint), and the identification token used at that system to identify the call. Gate coordination will be required for this call if (1) the strength token in the P-DCS-Gate header in the initial INVITE indicates DCS Group Category Informational - Expiration 11/30/02 9 SIP Proxy-to-Proxy Extensions May 2002 'required', or (2) the system that will perform gate coordination at the destination is a CMTS. If gate coordination is required for this call, the terminating proxy MUST include a P-DCS-Gate header in the first reliable non-100 response to the initial INVITE request. It MUST insert the IP address or FQDN of the system that will perform gate coordination in the hostport parameter of the DCS-Gate header, and the identification token as the Gate-ID. If gate coordination is not required for this call, the terminating proxy SHOULD NOT include a P-DCS-Gate header in the first non-100 response to the initial INVITE request. Gate coordination procedures are described in [5]. 9. P-DCS-OSPS Some calls have special call processing requirements that may not be satisfied by normal user agent call processing. For example, when a user is engaged in a call and another call arrives, such a call might be rejected with a busy indication. However, some PSTN operator services require special call processing. In particular, the Busy Line Verification (BLV) and Emergency Interrupt (EI) services initiated by an operator from an Operator Services Position System (OSPS) on the PSTN network have such a need. In order to inform the SIP user agent that special treatment should be given to a call, we use a new P-DCS-OSPS header field, which may be set to a value indicating when a special type of call processing is requested. We define two values in this header, namely "BLV" for busy line verification and "EI" for emergency interrupt. If the user agent decides to honor such a request, the response of the user agent to an INVITE with either "BLV" or "EI" will not be a busy indication. 9.1 Syntax P-DCS-OSPS = "P-DCS-OSPS" HCOLON OSPS-Tag OSPS-Tag = "BLV" / "EI" / token The OSPS-Tag value of "token" is defined for extensibility, and is reserved for future use. 9.2 Procedures at an Untrusted User Agent Client (UAC) The P-DCS-OSPS header MUST NOT be sent in a request from an untrusted UAC. 9.3 Procedures at a Trusted User Agent Client (UAC) This header is typically only inserted by a Media Gateway Controller [4] that is controlling a Media Gateway with special MF trunk DCS Group Category Informational - Expiration 11/30/02 10 SIP Proxy-to-Proxy Extensions May 2002 connections to a PSTN OSPS system. This trunk group is usually referred to as a BLV-trunk group and employs special signaling procedures that prevent inadvertant use. Calls originating at the PSTN OSPS system are sent over this trunk group, and result in an INVITE request with the OSPS header. This header MAY be sent in an INVITE request, and MUST NOT appear in any message other than an INVITE request. OSPS-Tag value "BLV" MUST NOT appear in any INVITE other than an initial INVITE request establishing a new dialog. OSPS-Tag value "EI" MUST NOT appear in any INVITE request other than a subsequent INVITE within a pre-existing dialog established with the OSPS-Tag value of "BLV". 9.4 Procedures at an Untrusted User Agent Server (UAS) If the UAS receives an INVITE request with an OSPS-Tag, dialog identification that matches an existing call, and the existing call was not established with the OSPS-Tag, it MUST reject the request with a 409-Conflict error code. If the UAS receives an INVITE request with an OSPS-Tag value of "EI", with dialog identification that does not match an existing dialog, it MUST reject the request with a 409-Conflict error code. If the UAS receives an INVITE that contains an OSPS-Tag value of "BLV" and is not willing to cooperate in offering this service, it MUST reject the request with a 403-Forbidden error code. The UAS SHOULD NOT reject an INVITE with a BLV OSPS-Tag due to a busy condition. The UAS MUST NOT respond with a 3xx-Redirect error code to an INVITE with a BLV OSPS-Tag. The UAS SHOULD NOT alert the user of the incomming call attempt if the BLV OSPS-Tag is present in the INVITE. If an INVITE with OSPS-Tag of "BLV" is accepted (meeting all QoS pre-conditions, etc.), the UAS MUST send an audio stream on this connection to the address and port given in the SDP of the INVITE. The UAS MAY perform a mixing operation between the two ends of an active call and send the resulting media stream to the address and port indicated. Alternatively, the UAS MAY send a copy of the local voice stream, and (if no activity on the local voice stream) send a copy of the received voice stream. If the state of the UAS is idle, the UAS SHOULD send a stream of silence packets to OSPS. If the state of the UAS is ringing or ringback, the UAS SHOULD send a ringback stream to OSPS. If an INVITE with OSPS-Tag of "EI" is accepted, the UAS MUST enable communication between the UAC and the local user. The UAS MAY put any existing call on hold, or initiate an ad-hoc conference. 9.5 Procedures at a Trusted User Agent Server (UAS) DCS Group Category Informational - Expiration 11/30/02 11 SIP Proxy-to-Proxy Extensions May 2002 The procedures at a trusted UAS MUST be identical to those described in 9.4. 9.6 Procedures at Proxy In the DCS architecture, the OSPS is considered a trusted UAC. If a proxy receives a P-DCS-OSPS header in a request from an untrusted source, it MUST reject the request. 10. P-DCS-BILLING-ID and P-DCS-BILLING-INFO There are many billing models used in deriving revenue from telephony services today. Charging for telephony services is tightly coupled to the use of network resources. It is outside the scope of this document to discuss the details of these numerous and varying methods. Proxies have access to subscriber information and act as policy decision points and trusted intermediaries along the call signaling path. Edge routers provide the network connection and resource policy enforcement mechanism and also capture and report network connection and resource usage information. Edge routers need to be given billing information that can be logged with Record Keeping or Billing servers. The proxy, as a central point of coordination between call signaling and resource management, can provide this information based on the authenticated identity of the calling and called parties. Since there is a trust relationship among proxies, they can be relied upon to exchange trusted billing information pertaining to the parties involved in a call. For Usage Accounting records, it is necessary to have an identifier that can be associated with all the event records produced for the call. Call-ID cannot be used as such an identifier since it is selected by the originating user agent, and may not be unique among all past calls as well as current calls. Further, since this identifier is to be used by the service provider, it should be chosen in a manner and in a format that meets the service provider's needs. Billing information may not necessarily be unique for each user (consider the case of calls from an office all billed to the same account). Billing information may not necessarily be identical for all calls made by a single user (consider prepaid calls, credit card calls, collect calls, etc). It is therefore necessary to carry billing information separate from the calling and called party identification. Furthermore, some billing models call for split- charging where multiple entities are billed for portions of the call. The addition of two SIP General Header Fields allows for the capture of billing information and billing identification for the duration of the call. DCS Group Category Informational - Expiration 11/30/02 12 SIP Proxy-to-Proxy Extensions May 2002 It is the intent that the billing extensions would only appear on trusted network segments, and MAY be inserted by a proxy in INVITE requests in a trusted network segment, and removed before leaving trusted network segments. The P-DCS-Billing-ID and P-DCS-Billing- Info header extensions are used only on requests and responses between proxies and trusted User Agents. They are never sent to, nor sent by, an untrusted UA. 10.1 Syntax The DCS-Billing-ID and DCS-Billing-Info headers are defined by the following BNF: P-DCS-Billing-ID = "P-DCS-Billing-ID" HCOLON Billing-Correlation-ID SLASH FEID P-DCS-Billing-Info = "P-DCS-Billing-Info" HCOLON [hostport] Acct-Entry *(COMMA Acct-Entry) Acct-Entry = Acct-Charge-URI SLASH Acct-Calling-URI SLASH Acct-Called-URI [SLASH Acct-Routing-URI SLASH Acct-Loc-Routing-URI] Acct-Charge-URI = LAQUOT URI RAQUOT Acct-Calling-URI = LAQUOT URI RAQUOT Acct-Called-URI = LAQUOT URI RAQUOT Acct-Routing-URI = LAQUOT URI RAQUOT Acct-Loc-Routing-URI = LAQUOT URI RAQUOT Billing-Correlation-ID = 1*hex FEID = 1*hex "@" host The P-DCS-billing-ID extension contains an identifier that can be used by an event recorder to associate multiple usage records, possibly from different sources, with a billable account. P-DCS- billing-ID is chosen to be globally unique within the system for a window of several months. This header is only used between proxies and trusted User Agents. The Billing-Correlation-ID is specified in other PacketCable documents as a 24-byte binary structure, containing 4 bytes of NNTP timestamp, 8 bytes of the unique identifier of the network element that generated the ID, 8 bytes giving the timezone, and 4 bytes of monotonically increasing sequence number at that network element. This MUST be encoded in the P-DCS-Billing-ID header as a hex string of up to 48 characters. Leading zeroes may be suppressed. The Financial Entity ID (FEID) is specified in other PacketCable documents as an 8-byte structure, containing the financial identifier for that domain, followed by a domain name. FEID can be associated with a type of service and could be assigned to multiple domains by the same provider. A domain could contain multiple assigned FEIDs. This 8-byte structure MUST be encoded in the P-DCS- DCS Group Category Informational - Expiration 11/30/02 13 SIP Proxy-to-Proxy Extensions May 2002 Billing-ID header as a hex string of up to 16 characters. Trailing zeroes may be suppressed. The P-DCS-billing-info extension identifies a subscriber account number of the payer, and other information necessary for accurate billing of the service. The hostport, if present, specifies a record keeping server for event messages relating to this call. If not present, event messages will be sent to the default record keeping server for each network element. Acct-Entry contains the information needed by the Gate Controller to give to the CMTS for generation of event message records. Acct- Charge-URI, Acct-Calling-URI, Acct-Called-URI, Acct-Routing-URI, and Acct-Location-Routing-URI are each defined as URLs; they should all contain tel: URLs with E.164 formatted addresses. 10.2 Procedures at an Untrusted User Agent Client (UAC) This header is never sent to an untrusted UAC, and is never sent by an untrusted UAC. 10.3 Procedures at a Trusted User Agent Client (UAC) The UAC MUST generate the Billing-Correlation-ID for the call, and insert the P-DCS-Billing-ID header into the initial INVITE message sent to the terminating proxy. If the response to the initial INVITE is a 3xx-Redirect, the UAC generates a new initial INVITE request to the destination specified in the Contact: header, as per standard SIP. If a UAC receives a 3xx-Redirect response to an initial INVITE, the new INVITE generated by the UAC MUST contain the P-DCS-Billing-Info headers from the 3xx- Redirect response. A UAC that includes a Refer-to header in a REFER request MUST include a P-DCS-Billing-Info header in the Refer-to's URL. This P- DCS-Billing-Info header MUST include the accounting information of the initiator of the REFER. A UAC that sends a mid-call REFER request including a Refer-to header MUST include a P-DCS-Billing-ID header and one or more P- DCS-Billing-Info headers attached to the Refer-to. The P-DCS- Billing-Info headers MUST include the complete set of P-DCS-Billing- Info headers associated with the current call, and MUST include one additional P-DCS-Billing-Info header (for the segment from the initiator) with accounting information of the initiator. 10.4 Procedures at an Untrusted User Agent Server (UAS) This header is never sent to an untrusted UAS, and is never sent by an untrusted UAS. DCS Group Category Informational - Expiration 11/30/02 14 SIP Proxy-to-Proxy Extensions May 2002 10.5 Procedures at a Trusted User Agent Server (UAS) The UAS MAY include a P-DCS-Billing-Info header in the first reliable non-100 response to an initial INVITE message if it wishes to override the billing information that was present in the INVITE (e.g. for a toll-free call). The decision to do this and the contents of the resulting P-DCS-Billing-Info header MUST be determined by service provider policy provisioned in the UAS. The UAS MUST add P-DCS-Billing-Info headers to a 3xx-redirect response to an initial INVITE. All P-DCS-Billing-Info headers present in the initial INVITE MUST be copied to the 3xx-redirect response. In addition, the UAS MUST add an additional P-DCS- Billing-Info header, for the segment from the destination to the forwarded-to destination, giving the accounting information for the call forwarder. 10.6 Procedures at Proxy Two sets of proxy procedures are defined: (1) the procedures at an originating proxy, and (2) the procedures at a terminating proxy. The originating proxy is a proxy that received the INVITE request from a non-trusted endpoint. The terminating proxy is a proxy that sends the INVITE request to a non-trusted endpoint. For purposes of mid-call changes, such as call transfers, the proxy that receives the request from a non-trusted endpoint is considered the initiating proxy; the proxy that sends the request to a non- trusted endpoint is considered the recipient proxy. Procedures for the initiating proxy are included below with those for originating proxies, while procedures for the recipient proxy are included with those for terminating proxies. A proxy that both receives the INVITE request from an untrusted endpoint, and sends the INVITE request to a non-trusted endpoint, performs both sets of procedures. A proxy that is neither an originating proxy nor a terminating proxy has no function in manipulating existing calls. 10.6.1 Procedures at Originating Proxy The originating proxy MUST generate the Billing-Correlation-ID for the call, and insert the P-DCS-Billing-ID header into the initial INVITE message sent to the terminating proxy. Any such header present from an untrusted UA MUST be removed. If the Request-URI contains a private-URL, and the decoded username contains billing information, the originating proxy MUST generate a P-DCS-Billing-Info header with that decrypted information. DCS Group Category Informational - Expiration 11/30/02 15 SIP Proxy-to-Proxy Extensions May 2002 Otherwise, the originating proxy MUST determine the accounting information for the call originator, and insert a P-DCS-Billing-Info header including that information. If the response to the initial INVITE is a 3xx-Redirect, received prior to a 18x-Ringing, the originating proxy generates a new initial INVITE request to the destination specified in the Contact: header, as per standard SIP. If an originating proxy receives a 3xx-Redirect response to an initial INVITE prior to a 18x-Ringing response, the INVITE generated by the proxy MUST contain the P-DCS- Billing-Info headers from the 3xx-Redirect response. Based on local billing policy, the new INVITE MAY contain the same value of P-DCS- Billing-ID, or it MAY contain a newly generated value. If the response to the initial INVITE is a 3xx-Redirect, received after a 18x-Ringing, the originating proxy generates a private-URL and places it in the Contact header of a 3xx-Redirect response sent to the originating endpoint. This private-URL MUST contain (or contain a pointer to) the sequence of P-DCS-Billing-Info values, which indicate the complex charging arrangement for the new call, and an expiration time very shortly in the future, to limit the ability of the originator to re-use this private-URL for multiple calls. An originating proxy that processes a REFER request from an untrusted UA MUST include a P-DCS-Billing-Info header in the Refer- to's URL. This P-DCS-Billing-Info header MUST include the accounting information of the initiator. An initiating proxy that sends a REFER request including a Refer-to header MUST include a P-DCS-Billing-ID header and one or more P-DCS- Billing-Info headers in the Refer-to's URL. The P-DCS-Billing-Info headers MUST include the complete set of P-DCS-Billing-Info headers associated with the current call, and MUST include one additional P- DCS-Billing-Info header (for the segment from the initiator) with accounting information of the initiator. Based on local billing policy, the proxy MAY include a P-DCS-Billing-ID header in the Refer-to's URL. 10.6.2 Procedures at Terminating Proxy The terminating proxy MUST NOT send the P-DCS-Billing-ID nor the P- DCS-Billing-Info headers to a untrusted destination. The terminating proxy MAY include a P-DCS-Billing-Info header in the first reliable non-100 response to an initial INVITE message if it wishes to override the billing information that was present in the INVITE (e.g. for a toll-free call). The decision to do this and the contents of the resulting P-DCS-Billing-Info header MUST be determined by service provider policy provisioned in the terminating proxy. DCS Group Category Informational - Expiration 11/30/02 16 SIP Proxy-to-Proxy Extensions May 2002 The terminating proxy MUST add P-DCS-Billing-Info headers to a 3xx- redirect response to an initial INVITE. All P-DCS-Billing-Info headers present in the initial INVITE MUST be copied to the 3xx- redirect response. In addition, the terminating proxy MUST add an additional P-DCS-Billing-Info header, for the segment from the destination to the forwarded-to destination, giving the accounting information for the call forwarder. A proxy receiving a mid-call REFER request that includes a Refer-to header generates a private-URL and places it in the Refer-to header sent to the endpoint. This private-URL MUST contain the value of P- DCS-Billing-ID, the sequence of P-DCS-Billing-Info values, which indicate the complex charging arrangement for the new call, and an expiration time very shortly in the future, to limit the ability of the endpoint to re-use this private-URL for multiple calls. 11. P-DCS-LAES and P-DCS-REDIRECT The P-DCS-Laes extension contains the information needed to support Lawfully Authorized Electronic Surveillance. This header contains the address and port of an Electronic Surveillance Delivery Function for delivery of a duplicate stream of event messages related to this call. The header may also contain an additional address and port for delivery of call content. Security key information is included to enable pairs of Delivery Functions to securely exchange surveillance information. This header is only used between proxies and trusted User Agents. The P-DCS-Redirect extension contains call identifying information needed to support the requirements of Lawfully Authorized Electronic Surveillance of redirected calls. This header is only used between proxies and trusted User Agents. 11.1 Syntax The format of the P-DCS-Laes header is given by the following BNF. P-DCS-LAES = "P-DCS-LAES" HCOLON Laes-sig [SLASH Laes-content] SEMI Laes-key Laes-sig = hostport Laes-content = hostport Laes-key = token P-DCS-Redirect = "P-DCS-Redirect" HCOLON Called-id Redirector Num-redir Called-id = LAQUOT URI RAQUOT Redirector = LAQUOT URI RAQUOT Num-redir = 1*DIGIT The values of Laes-sig and Laes-content are addresses of the Electronic Surveillance Delivery Function, and used as the destination address for call-identifying information and call- content, respectively. DCS Group Category Informational - Expiration 11/30/02 17 SIP Proxy-to-Proxy Extensions May 2002 Laes-key is a string generated by the proxy that is used by the Delivery Function to securely transfer information between them [6]. 11.2 Procedures at an Untrusted User Agent Client (UAC) This header MUST NOT be sent to an untrusted UAC, and MUST NOT be sent by an untrusted UAC. 11.3 Procedures at a Trusted User Agent Client (UAC) The UAC checks for an outstanding lawfully authorized surveillance order for the originating subscriber, and, if present, includes this information in the Authorization for Quality of Service or signals this information to the device performing the intercept (e.g. a Media Gateway). If the P-DCS-LAES header is present in the first reliable non-100 response (indicating surveillance is required on the terminating subscriber, but that the terminating equipment is unable to perform that function), the UAC MUST include this information in the Authorization for Quality of Service, or MUST signal this information to the device performing the intercept (e.g. a Media Gateway). If a 3xx-Redirect response is received to the initial INVITE request, and if a P-DCS-LAES header is present in the 3xx response, the UAC MUST include that header unchanged in the reissued INVITE. The UAC MUST also include a P-DCS-Redirect header containing the original dialed number, the new destination number, and the number of redirections that have occurred. A UAC that includes a Refer-to header in a REFER request, when the originating subscriber has an outstanding lawfully authorized surveillance order, MUST include a P-DCS-Laes header attached to the Refer-to. The P-DCS-LAES header MUST include the address and port of the local Electronic Surveillance Delivery Function for a copy of the call's event messages, MUST include the address and port of the local Electronic Surveillance Delivery Function for the copy of call content if call content is to be intercepted, and MUST include a random string for use as a security key between the Delivery Functions. The trusted UAC MUST NOT send the P-DCS-Laes and P-DCS-Redirect headers to an untrusted entity. 11.4 Procedures at an Untrusted User Agent Server (UAS) This header MUST NOT BE sent to an untrusted UAS, and MUST NOT Be sent by an untrusted UAS. 11.5 Procedures at a Trusted User Agent Server (UAS) DCS Group Category Informational - Expiration 11/30/02 18 SIP Proxy-to-Proxy Extensions May 2002 The UAS checks for an outstanding lawfully authorized surveillance order for the terminating subscriber. If present, the UAS includes this information in the authorization for Quality of Service. If the terminating equipment is unable to perform the required surveillance (e.g. if the destination is a voicemail server), the UAS MUST include a P-DCS-LAES header in the first reliable non-100 response requesting the originating proxy to perform the surveillance. The P-DCS-LAES header MUST include the address and port of the local Electronic Surveillance Delivery Function for a copy of the call's event messages, MUST include the address and port of the local Electronic Surveillance Delivery Function for the copy of call content if call content is to be intercepted, and MUST include a random string for use as a security key between the Delivery Functions. If the response to the initial INVITE request is a 3xx-Redirect response, and there is an outstanding lawfully authorized surveillance order for the terminating subscriber, the UAS MUST include a P-DCS-Laes header in the 3xx-Redirect response, with contents as described above. The trusted UAS MUST NOT send the P-DCS-Laes and P-DCS-Redirect headers to an untrusted entity. 11.6 Procedures at Proxy Two sets of proxy procedures are defined: (1) the procedures at an originating proxy, and (2) the procedures at a terminating proxy. The originating proxy is a proxy that received the INVITE request from a non-trusted endpoint. The terminating proxy is a proxy that sends the INVITE request to a non-trusted endpoint. For purposes of mid-call changes, such as call transfers, the proxy that receives the request from a non-trusted endpoint is considered the initiating proxy; the proxy that sends the request to a non- trusted endpoint is considered the recipient proxy. Procedures for the initiating proxy are included below with those for originating proxies, while procedures for the recipient proxy are included with those for terminating proxies. A proxy that both receives the INVITE request from an untrusted endpoint, and sends the INVITE request to a non-trusted endpoint, MUST NOT generate P-DCS-Laes nor P-DCS-Redirect headers. A proxy that is neither an originating proxy nor a terminating proxy has no function in manipulating existing calls. 11.6.1 Procedures at Originating Proxy DCS Group Category Informational - Expiration 11/30/02 19 SIP Proxy-to-Proxy Extensions May 2002 The Originating Proxy MUST remove any P-DCS-Laes and P-DCS-Redirect headers in requests or responses to or from an untrusted proxy or UA. The originating proxy checks for an outstanding lawfully authorized surveillance order for the originating subscriber, and, if present, includes this information in the Authorization for Quality of Service or signals this information to the device performing the intercept (e.g. a Media Gateway). If the P-DCS-LAES header is present in the first reliable non-100 response (indicating surveillance is required on the terminating subscriber, but that the terminating equipment is unable to perform that function), the originating proxy MUST include this information in the Authorization for Quality of Service, or MUST signal this information to the device performing the intercept (e.g. a Media Gateway). If the Request-URI in an initial INVITE request contains a private- URL, the originating proxy MUST decrypt the userinfo information to find the real destination for the call, and other special processing information. If electronic surveillance information is contained in the decrypted userinfo, the originating proxy MUST generate a P-DCS- LAES header with the surveillance information. If a 3xx-Redirect response is received to the initial INVITE request prior to a 18x-Ringing, and if a P-DCS-LAES header is present in the 3xx response, the originating proxy MUST include that header unchanged in the reissued INVITE. The originating proxy MUST also include a P-DCS-Redirect header containing the original dialed number, the new destination number, and the number of redirections that have occurred. If a 3xx-Redirect response is received to the initial INVITE request after a 18x-Ringing, the originating proxy generates a private-URL and places it in the Contact header of a 3xx-Redirect response sent to the originating endpoint. If a P-DCS-Laes header is present in the 3xx response, this private-URL MUST contain (1) the electronic surveillance information from the 3xx-Redirect response, (2) the original destination number, (3) the identity of the redirecting party, and (4) the number of redirections of this call. An originating proxy that processes a REFER request from an untrusted UA, when the originating subscriber has an outstanding lawfully authorized surveillance order, MUST include a P-DCS-Laes header in the Refer-to's URL. The P-DCS-LAES header MUST include the address and port of the local Electronic Surveillance Delivery Function for a copy of the call's event messages, MUST include the address and port of the local Electronic Surveillance Delivery Function for the copy of call content if call content is to be intercepted, and MUST include a random string for use as a security key between the Delivery Functions. DCS Group Category Informational - Expiration 11/30/02 20 SIP Proxy-to-Proxy Extensions May 2002 An initiating proxy that sends a mid-call REFER request including a Refer-to header, when the initiating subscriber has an outstanding lawfully authorized surveillance order, MUST include a P-DCS-Laes header in the Refer-to's URL. The originating proxy MUST NOT send the P-DCS-Laes and P-DCS- Redirect headers to an untrusted entity. 11.6.2 Procedures at Terminating Proxy The Terminating Proxy MUST remove any P-DCS-Laes and P-DCS-Redirect headers in requests or responses to or from an untrusted proxy or UA. The terminating proxy checks for an outstanding lawfully authorized surveillance order for the terminating subscriber. If present, the terminating proxy includes this information in the authorization for Quality of Service. The terminating proxy MUST NOT send the P-DCS-Laes and P-DCS- Redirect headers to an untrusted entity, either as headers in the request or response, or as headers attached to URIs in the request or response. If the terminating equipment is unable to perform the required surveillance (e.g. if the destination is a voicemail server), the terminating proxy MUST include a P-DCS-LAES header in the first reliable non-100 response requesting the originating proxy to perform the surveillance. The P-DCS-LAES header MUST include the address and port of the local Electronic Surveillance Delivery Function for a copy of the call's event messages, MUST include the address and port of the local Electronic Surveillance Delivery Function for the copy of call content if call content is to be intercepted, and MUST include a random string for use as a security key between the Delivery Functions. If the response to the initial INVITE request is a 3xx-Redirect response, and there is an outstanding lawfully authorized surveillance order for the terminating subscriber, the terminating proxy MUST include a P-DCS-Laes header in the 3xx-Redirect response, with contents as described above. A proxy receiving a mid-call REFER request that includes a Refer-to header with a P-DCS-Laes header attached MUST generate a private-URL and place it in the Refer-to header sent to the endpoint. This private-URL MUST contain the P-DCS-Laes information from the attached header. 12. Security Considerations Billing information is often considered sensitive and private information to the customers. It is therefore necessary that the Proxies take precautions to protect this information from DCS Group Category Informational - Expiration 11/30/02 21 SIP Proxy-to-Proxy Extensions May 2002 eavesdropping and interception. Use of IPSec between Proxies is recommended. 13. IANA Considerations This document defines a number of SIP extension headers, which should be included in the registry of SIP headers defined in [3]. Registration information for new headers is as follows: Header Field Name: P-DCS-Trace-Party-ID RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: DCS-Trace-Party-ID Note: Not yet specified, only reserved RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: P-DCS-Gate RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: DCS-Gate Note: Not yet specified, only reserved RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: P-DCS-OSPS RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: DCS-OSPS Note: Not yet specified, only reserved RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: P-DCS-Billing-ID RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: DCS-Billing-ID Note: Not yet specified, only reserved RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: P-DCS-Billing-Info RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: DCS-Billing-Info Note: Not yet specified, only reserved RFC Number: XXXX [number of this document] Compact Form: none DCS Group Category Informational - Expiration 11/30/02 22 SIP Proxy-to-Proxy Extensions May 2002 Header Field Name: P-DCS-Laes RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: DCS-Laes Note: Not yet specified, only reserved RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: P-DCS-Redirect RFC Number: XXXX [number of this document] Compact Form: none Header Field Name: DCS-Redirect Note: Not yet specified, only reserved RFC Number: XXXX [number of this document] Compact Form: none 14. Notice Regarding Intellectual Property Rights The IETF has been notified of intellectual property rights claimed in regard to some or all of the specification contained in this document. For more information consult the online list of claimed rights. 15. Normative References 1. Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. 2. Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 3. Rosenberg, J, et al, "The Session Initiation Protocol", RFC 3261, June 2002. 16. Informative References 4. DCS Group, "Architectural Considerations for Providing Carrier Class Telephony Services Utilizing SIP-based Distributed Call Control Mechanisms", draft-dcsgroup-sipping-arch-00.txt, June 2002. 5. PacketCable Dynamic Quality of Service Specification, pkt-sp- dqos-i03-020116. January, 2002. 6. PacketCable Security Specification, pkt-sp-sec-i05-020116. January, 2002. DCS Group Category Informational - Expiration 11/30/02 23 SIP Proxy-to-Proxy Extensions May 2002 17. Acknowledgements The Distributed Call Signaling work in the PacketCable project is the work of a large number of people, representing many different companies. The authors would like to recognize and thank the following for their assistance: John Wheeler, Motorola; David Boardman, Daniel Paul, Arris Interactive; Bill Blum, Jon Fellows, Jay Strater, Jeff Ollis, Clive Holborow, Motorola; Doug Newlin, Guido Schuster, Ikhlaq Sidhu, 3Com; Jiri Matousek, Bay Networks; Farzi Khazai, Nortel; John Chapman, Bill Guckel, Michael Ramalho, Cisco; Chuck Kalmanek, Doug Nortz, John Lawser, James Cheng, Tung- Hai Hsiao, Partho Mishra, AT&T; Telcordia Technologies; and Lucent Cable Communications. Previous versions further acknowledged, as co-authors, several people for providing the text of this document. They are: K. K. Ramakrishnan (kk@teraoptic.com), TeraOptic Networks; Ed Miller (edward.miller@terayon.com), Terayon; Glenn Russell (G.Russell@Cablelabs.com), CableLabs; Mike Mannette (Michael- Mannette@3com.com) and Kurt Steinbrenner (Kurt_ Steinbrenner@3com.com), 3Com; Dave Oran (oran@cisco.com), Cisco Systems; John Pickens (jpickens@com21.com), Com21; Poornima Lalwaney (poornima.lalwaney@nokia.com), Nokia; Jon Fellows (jfellows@coppermountain.com), Copper Mountain Networks; Doc Evans (n7dr@arrl.net) D. R. Evans Consulting, and Keith Kelly (keith@netspeak.com), NetSpeak. 18. Editor's Addresses Bill Marshall AT&T Florham Park, NJ 07932 Email: wtm@research.att.com Flemming Andreasen Cisco Edison, NJ Email: fandreas@cisco.com Burcak Beser Juniper Networks Sunnyvale, CA Email: burcak@juniper.net DCS Group Category Informational - Expiration 11/30/02 24 SIP Proxy-to-Proxy Extensions May 2002 Full Copyright Statement "Copyright (C) The Internet Society (2002). 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." This memo is filed as <draft-dcsgroup-sipping-proxy-proxy-00.txt>, and expires November 30, 2002. DCS Group Category Informational - Expiration 11/30/02 25