INTERNET-DRAFT                                            L. Coene
Internet Engineering Task Force                            Siemens
Issued:  8 may 2000                                    J. Loughney
Expires: 30 October 2000                                     Nokia
                                                         I. Rytina
                                                            L. Ong
                                                   Nortel Networks

      Stream Control Transmission Protocol Applicability Statement

Status of this Memo

   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 The list of Internet-
   Draft Shadow Directories can be accessed at


   This document describes the applicability of the Stream Control
   Transmission Protocol for general usage. A few general applications
   are described such as the transport of signalling information (SS7,
   DSS1/2 ...) over IP infrastructure. The use and specification of
   adaptation layers in conjunction with SCTP is described.

1 Introduction

   This document covers subject terminology and makes a overview of the
   solutions for transporting information over Internet Protocol
   infrastructure. The transport medium used is the Stream Control
   Transmission Protocol (SCTP). However some of the issues may also
   relate to the transport of information via TCP.

   SCTP provides the following services to its users:

   - acknowledged error-free non-duplicated transfer of user data

   - transport-level segmentation to conform to discovered MTU size

   - sequenced delivery of user datagrams within multiple streams, with
   an option for order-of-arrival delivery of individual datagrams

   - optional multiplexing of user datagrams into SCTP datagrams,
   subject to MTU size restrictions

   - enhanced reliability through support of multi-homing at either
    or both ends of the association.

   - Explicit indication in the message of the application protocol SCTP
   is carrying.

1.1 Terminology

   The following terms are commonly identified in related work:

   Port Number:  Indicates on the transport level which application
   needs to be reached in the layer above.  Transport Address:  An IP
   address and a port number forms a transport address which identifies
   a SCTP association.  Protocol Identifier:  Indicates the upper layer
   protocol that is using SCTP for the transport of its data.  Chunk:  a
   unit of information within an SCTP datagram, consisting of a chunk
   header and chunk-specific content. Each chunk can contain user or
   data information about the particular SCTP association.  Multihoming:
   Endpoint which uses more than one IP address for receiving SCTP
   datagrams on the same association.  NAT:  Network Address Translation
   SACK:  Selective Acknowledgement message, this is a response on the
   data msg acknowledging the receipt of it at the remote side.  TSN:
   Transaction Sequence Number, this is a number assigned by SCTP to
   assure reliable delivery of user data within an association.

2  Stream Control Transmission Protocol -- SCTP

2.1  Introduction

   The Stream Control Transmission Protocol (SCTP) provides a high
   reliable, redundant transport between two endpoints. The interface
   between SCTP and its applications is handled via adaptation layers
   which provide a intermediate layer so that the existing upper layer
   protocols do not have to change their interface towards the transport
   medium and internal functionality when they start using SCTP instead
   of an other transport protocol.

   The following function are provided by SCTP:  - Initialization of
   transport association - Synchronization of association state -
   Synchronization of sequence numbering - Reliable Data Transfer -
   Forward and backward sequence numbering - Timers for transmission and
   acknowledgement - Notification of out-of-sequence - Retransmission of
   lost messages - Support of multiple control streams - Separate
   sequence control and delivery of each stream - Congestion control -
   Window flow control - Congestion avoidance based on TCP methods, e.g.
    retransmission backoff, window reduction, etc.  - Detection of
   session failure by active means, e.g. heartbeat - Termination of
   association SCTP does support a number of functions that are not
   provided by current TCP:  - no head-of-line blocking, i.e. multiple
   streams - multilink failover for added reliability - keep-alive
   function for active rapid failure detection - message verses byte
   sequence numbering - tighter timer control (than standard TCP

   By defining the appropriate User adaptation module, a reliable
    transport mechanism can be provided:  - reliable transmission of
   packets with end-to-end congestion control provided using methods
   similar to TCP - choice between sequenced and unsequenced, reliable
   message delivery - keep-alive message

   Within a association between the two endpoints, 1 or more stream(s)
   may be available. These streams are visible to the adaptation layers
   but are invisible to any layer above the adaptation layer.

2.2 Issues affecting deployment of SCTP

2.2.1   SCTP Multihoming

   Redundant communication between 2 SCTP endpoints is achieved by using
   multihoming where the endpoint is able to send/receive over more than
   one IP address.

   Under the assumption that every IP address will have a different path
   towards the remote endpoint, (this is the responsibility of the
   routing protocols or of manual configuration), if the transport to
   one of the IP address (= 1 particular path) fails then the traffic
   can migrate to the other remaining IP address (= other paths) within
   the SCTP association.

   As a practical matter, it is recommended that IP addresses in a
   multihomed endpoint be assigned IP endpoints from different TLV's to
   ensure against network failure.

   Multihoming provides redundant communication in SCTP by allowing
   communication between two endpoints to continue in the event of
   failure along a path between the endpoints.

   SCTP will always send its traffic to a certain transport address (=
   destination address + port number combination) for as long as the
   transmission is uninterrupted (= primary). The other transport
   addresses (secondary paths) will act as a backup in case the primary
   path goes out of service. The changeover between primary are backup
   will occur without packet loss and is completely transparent to the

   The port number is the same for all transport addresses of that
   specific association.

   Applications directly using SCTP may choose to control the
   multihoming service themselves. The applications have then to supply
   the specific IP address to SCTP for each datagram. This might be done
   for reasons of load-sharing and load-balancing across the different
   paths. This might not be advisable as the throughput of any of the
   paths is not known in advance and constantly changes due to the
   actions of other associations and transport protocols along that
   particular path, would require very tight feedback of each of the
   paths to the loadsharing functions of the user.

   Applications using adaptation layers to run over SCTP do not have
   that kind of control. The adaptation layers will have to take care of

   By sending a keep alive message on all the multiple paths that are
   not used for active transmission of messages across the association,
   it is possible for SCTP to detect whether one or more paths have
   failed. SCTP will not use these failed paths when a changeover is

   The transmission rate of sending keep alive message should be
   modifiable and the possible loss of keep alive message could be used
   for the monitoring and measurements of the concerned paths.

2.2.2 Fast retransmit of chunks

   The retransmission of a message is basically governed by the
   retransmission timer. So if no acknowledgement is received after a
   certain time, then the message is retransmitted. However there is a
   faster way for retransmitting which is not dependant on that timer.

   Every second message that a node received will be acknowledge to the
   remote peer. If gaps occur in the acknowledge message at the remote
   side, then the remote side will wait 3 further gap
   reports(acknowledgements) before it retransmit the message. As the
   gap occurs, the node must transmit a SACK on every datagram until
   there are no more gap. This retransmission will happen far sooner
   than with a timer. Especially if the traffic volume increases in
   SCTP, those retransmissions of the chunks would happen faster and
   faster (and hopefully, they would also be faster acknowledged). In
   any case if gaps occur, the node will certainly try to acknowledge
   them faster(irespective of the fact if the SACKs will get to the
   remote node, where, if received, they would speed up the
   retransmission of the chunks)

   See also the paragraph on congestion control and avoidance.

2.2.3 Use of SCTP in Network Address Translator (NAT) Networks

   When a NAT is present between two endpoints, the endpoint that is
   behind the NAT, i.e., one that does not have a publicly available
   network address, shall take one of the following options:

   A) Indicate that only one address can be used by including no
   transport addresses in the INIT message. This will make the endpoint
   that receives this Initiation message to consider the sender as only
   having that one address. This method can be used for a dynamic NAT,
   but any multi-homing configuration at the endpoint that is behind the
   NAT will not be visible to its peer, and thus not be taken advantage

   B) Indicate all of its networks in the Initiation by specifying all
   the actual IP addresses and ports that the NAT will substitute for
   the endpoint. This method requires that the endpoint behind the NAT
   must have pre-knowledge of all the IP addresses and ports that the
   NAT will assign.

   This requires the adaptation of NAT boxes to search within SCTP
   outgoing INIT and incoming INIT_ACK mesages for the addresses and
   replace them with the NAT internal address in addition to replacing
   the addresses in the IP header.

   C) Use RSIP [RFCRSIP] where the connection is tunneled from host
   until the NAT border and the host layers above IP network layer have
   no knowledge of the NAT internal addresses.

   D) Use the hostname feature and the DNS to resolve the addresses.
   (Ed note: have to figure out hows this precisely works)

2.2.4 MTU path discovery

   SCTP discovers the maximal length of the message that can be
   transported through the network to the final destination without
   having to fragment(=chop something in pieces) the message in IP
   network layer. This avoids using IP fragmenting. SCTP level
   segmentation is beneficial because if a packet is lost during network
   transmission, only that packet will need to be retransmitted.
   Contrasted with IP-level segmentation, where the whole unsegmented
   message will have to be retransmitted, this is a much more effective
   scheme [RFC1981].

2.2.5 Use of multiple streams

   A stream in a one-directional stream of bytes between 2 endpoints
   within a SCTP association. A association can have one or more streams
   in its association and the number of streams in one direction does
   NOT need to be the same as the number of streams in the opposite
   direction. The number of streams in both directions is thus

   The application can choose on which stream it can send it data.
   Streams may specify order of deliver or sequenced delivery.  Some
   application level protocols may reserve certain streams for certain
   media, for example sending graphical content (jpeg, gif, etc.) of a
   web page through a certain stream while text through others, and
   streaming content through others.  Any packet loss on one stream will
   not block packet transmission on others.

   Each stream within a association should be looked upon as a link
   between two points. If multiple streams are used then the application
   is dealing with multiple links towards the destination. Some
   applications require the use of sequenced delivery, which would
   require for them to select a certain link to send their message on.

2.2.6  Congestion control & avoidance

   Congestion control and/or avoidance is of primordial importance in
   any connectionless network. Congestion is the result of approaching
   or exceeding the processing capacity of the link, network,
   application and/or transport layers. If the processing capacity is
   exceeded, then the congestion can be avoided (example taking a other
   non-congested path towards the destination) or controlled (for
   example, reducing the rate of messages to that destination).

   The reaction of SCTP to congestion is detailed in the next

   Congestion can be controlled and/or avoided on  different levels:  -
   Transport: congestion control/avoidance within SCTP, TCP(fig 2.1.2) -
   Network : Congestion control/avoidance present in the network layers(
   example: SCCP, MTP ...)  - Link layer: flow control

   SCTP conforms to the model of end-to-end congestion control (Fig [RFCSALLY] while ISUP and SCCP model themselves on a link
   and network based congestion control/overload mechanism (Fig

     |                                                   |
     |         Application and/or transport layer        |
       |                                              A
       |                                              |
       |    +-------------------------------------+   |
       ---->|                                     |----
            |           Network layer             |
       ---->|                                     |----
       |    +-------------------------------------+   |
       |                                              |
       |                                              V
     |                                                   |
     |                    Link layer                     |

                Fig General Congestion model

     |               |
     |transport layer|       Congestion control present based on
     |     SCTP      |         windows
       |           A
       V           |
     |               |
     | Network layer |       No congestion control present
     |   IP(v4/v6)   |         in the IP layer
       |           A
       V           |
     |   Ethernet    |       No congestion control present
     |  Link layer   |         in the Ethernet link layer

                Fig End-to-End congestion control

     |                 |
     |Application layer|       Congestion control present for
     | TC + MAP, IN... |         specific applications
     +-----------------+          - MAP: No congestion control
       |             A            - IN: Call gapping
       V             |
     |                 |
     |  Network layer  |       Congestion control present in the
     |   SCCP & MTP    |         in MTP and SCCP based on link and
     +-----------------+         destination status
       |             A
       V             |
     |   MTP lvl 2     |       Congestion control present
     |   Link layer    |         in the link layer

                Fig Distributed congestion control

   By default, SCTP associations do not have a fixed capacity assigned
   to them unless other QoS mechanisms are employed. Thus congestion
   within SCTP association can and will be affected by all traffic using
   the same links including other SCTP, TCP, RTP, UDP ... traffic
   traveling on the same path followed by the SCTP association. 3-SACK rule in SCTP.

   The Selective Acknowledgement (SACK) is one of the cornerstones of
   SCTP. It selectively Acknowledges datagrams that have been
   successfully received by the remote node. It serves 2 purposes:  - it
   indicates until a certain datagram that all previous datagrams have
   been received (without any holes in the sequence) and - it indicates
   the datagrams sequence ranges which have been received (and so does
   indicate the holes/gaps  between them). It provides us with a form of
   gap/hole report on messages that have been lost or delayed. A hole
   can consist of one or more messages.

               sender               Receiver

              -  |-----               |   -
    Emission  I  |                    |   I Link delay
      time    -  |----               |   I   time
                 |       ----------->|   -
              -  |---                |
              I  |      ------------>|
      Round   I  |--                 |
       trip   I  |     ------------->|
       time   I  |               /----|<-------- acknowledge sent
              I  |     -------- / --->|          after 3 data's
              I  |              /      |
              -  |<------------/       |

            Round trip Time  = RTT
            Windowsize       = Cwnd

   Fig Influence of Window Size/ Link Speed/ Round Trip Delay

   Fig is given here as a example where after receiving 3
   messages an advisory acknowledgement (SACK) is sent (in this case
   window = 6). Therefore the sender could be kept busy. The
   acknowledgement opens the window again. The total time (from first
   emission till the receiving of the acknowledgement) calculates as:
   (max. windowsize * emission time)/2 + round trip delay. If the round
   trip time(RTT) is large, the advisory acknowledgments (SACK) will
   enhance the throughput.

   The SACK is always generated and send back to the sender either -
   after every second message received (delayed ack).  - after at most
   200ms after receiving the last message.

   The reason for the holes may be diverse:  - simple message loss -
   different round trip times of messages being transmitted on different

   At the sender end, whenever the sender notices a hole in a SACK, it
   should wait for 3 further SACKs (identifying the same hole) before
   taking action. This is 3 strikes besides the first one, so that means
   4.  Thus after 4 SACK, the datagrams belonging to the hole should be
   retransmitted(and only those).

   If gaps occur, the receiver end will send SACKs on every data message
   received instead on being send on every second data message received.
   As the sender is waiting for the 3 SACK strikes and the receiver is
   increasing the SACK rate, that would mean that retransmission would
   be happening faster. Also the window should be opening up more than
   in the normal case (= transmission without gaps).

   The 3 SACKs rule might be relaxed in certain networks provided
   certain condition are met:

   - private IP network - closed networks - only a single type of
   application traffic is running on that network (the message in the
   network exhibit the same characteristics:
    example: signalling messages).

   The SACK rule might be configurable in such a networks, if the
   network operator felt confident in the correctness of the network.
   This would mean that in case of packet loss, retransmission could be

   SACK will also report duplicate message arrival. See paragraph Congestion Control

   The number of messages in flight is determined by the Congestion
   window (Cwnd).  Every time a message is SACK, a new message might be
   send to the remote side(up till the Cwnd), even if gaps exists which
   might ultimately lead to retransmissions.

   The value of the Cwnd is dependant on the slow start and/or
   congestion avoidance/control.

   If messages are getting lost, then it is assumed by SCTP that they
   are lost according to congestion, not that they are lost due to error
   on the link(such as cable cutthrough ...).

   When messages are lost then the rate of messages sending is reduced,
   till no messages are lost. Use of Explicit Congestion notification (ECN)

   Explicit Congestion control is a experimental method for
   communicating congestion back to the end node.  SCTP does not support
   the use of ECN, but specific recommendations for using ECN with SCTP
   might be forthcoming. Duplicated messages

   SACKs can get lost. The receiving node would then received duplicated
   packets. A reason for such a behavior is imbalance between the 2
   traffic direction, use of different up and down path.

   (Ed note: something more has to be put here, still thinking on the
    right words and reading a couple of RFCs on the subject :-) SCTP in high throughput delivery networks

   The TSN is associated with a message, not with the number of bytes(as
   is the sequence number of TCP) in the message. So the TSN will wrap
   around less frequently but has a dependency on the length of each
   message. Use of short messages will lead to a faster wrapping around
   of the TSN. So in high throughput networks, it is advised to make the
   messages as long as possible so that the wrap around will be less

   SCTP already has a larger window than TCP does even when TCP is using
   the "large windows" option. SCTP in long delay/Fat networks (LFN)

   Long delay(Fat) Networks consists of network paths which have a high
   "bandwidth*delay product"(such as satelite links(high delay) or high
   capacity fiber(high bandwith)). There the 3-SACK rule would lead to
   enhanced throughput, if the initial windowsize is set higher than
   2(which is the default value for non-LFNs).

   The initial windowsize should be set to a higher value (4 or 8) as
   that would mean that 4 messages would be injected in the network and
   the first sack would come back at about the same time as the last
   message before the window is full, is injected.

   Thus to have the most of the 3 sack rule immediatly, the initial
   window size should at least be set at 4 (and possible at 8 if we are
   dealing with really very long delays).

   The drawback of this is that it makes SCTP more aggressive to begin
   with(certainly when faced with TCP).

   For a more precise description of the issues associated with this,
   refer to [RFC123], [RFC2001] and [RFC2018] SCTP in Long Thin Networks(LTN)

   Long thin networks consists of network paths that traverse "very low
   bit-rate" links(such as 56 Kbit modem links). This means that a
   single host can very easy saturate such a link(= pushing the link
   into congestion).

2.2.7  Use of the protocol identifier in SCTP

   Indicates the the upper layer protocol that is using the
   associations. The protocol identifier is available to the application
   and is included in each chunk. 0 is the unknown protocol. This
   protocol id can be used by firewalls for filtering out certain
   protocols. If firewalls drops certain protocol id then then
   association will fail in the end because the TSN will be lost. If the
   chunk(without its user data) is simulated with the TSN in it, then
   the user data will be dropped, but the association is preserved.

   The protocol identifier is administered by IANA[IANA].

2.2.8  Use of QoS methods

   SCTP is a end-to-end protocol which cannot guarantee the quality-of-
   service along the complete path(s) taken by the messages of that
   particular association. If more guarantees are required for improving
   the reliability of the transport, some form of QoS mechanism may be

   The possible schemes are as follows. Over-provisioning

   Over-provisioning of the links so that the total traffic running over
   the link never exceeds the link capacity.  In practice, this may be
   difficult to ensure reliably. Private Internets

   Use of a private network solely for transport purposes. Private
   networks may allow better control and monitoring of resources
   available. Differentiated services

   By providing a certain code point in the Type-of-service field (TOS),
   certain Differential services can be selected. [RFC2597, RFC2598]

   Setting the code point for transport requires some thought. It is
   dependant on the kind of differentiate service selected. Also the use
   of traffic is important: example signalling info should have a higher
   priority than the user data traffic for which the signalling is
   responsible(and that relation does not always exist). Integrated services

   By use of integrated services [RFC2208], resources are reserved for
   signaling transport.

   If resources are unavailable for to initiate a new signaling
   transport, that request will be denied.  RSVP may not scale well and
   this solution may prove to be unfeasible.

   An example is Multi Protocol Label Switching.

2.2.9  SCTP Checksum

   SCTP uses the Adler-32 checksum algorithm. This algorithm will
   perform better than a 16 bit (CRC or not) checksum or even a 32 bit
   CRC checksum.

   The message can also be protected by IPSEC which is much stronger. In
   that case, the checksum should still be computed.

2.2.10  Tunneling of SCTP association over UDP

   The basic operation of SCTP is to run directly on top of IP. However,
   due to restrictions placed on implementers by Operating Systems, not
   all implementations may be able to run over IP directly. Therefore an
   alternative is given which might circumvent some or all of the

   The STCP messages are transported over UDP instead. The following
   issues must be observed:  - the port number in the UDP header should
   be the port number assigned to SCTP. The port number in the SCTP
   common header should be the one assigned to the user adaptation layer
   or to the application of SCTP. This means that port numbers
   previously used in UDP and/or TCP can be reused for the same
   application using SCTP. SCTP DOES NOT change the semantics of the
   port number just because the protocol identifier is added to the SCTP
   message.  - the checksum field might be used as a additional guard
   against errors(particular errors in the UDP header). However, the
   SCTP checksum employed is far better at catching errors, but does not
   take the UDP header into account.

2.2.11  How to define and Use adaptation layers

   Many different applications may use SCTP for different purposes. They
   go from File transfer over HTTP transport to signalling information

   Some applications might want preserve the existing interface with its
   lower layer (in this case SCTP) while for other applications, this
   does not pose a problem. A narchitecture has been devised to let the
   application choose whether they want to run over SCTP directly (just
   a many applications run over TCP) or let application run on top of a
   adaptation layer over SCTP.

   The basic architecture is as in Figure 2.11.1 :

                   User/Application level Protocols
                            |    |    |
                |        User Adaptation modules     |
                |Stream Control Transmission protocol|
                |       Standard IP Transport        |
                         Network Layer (IP)

          Figure 2.11.1:  Transport Components

   The three components of the transport protocol are :  Adaptation
   modules that support specific primitives, e.g. management
   indications, required by a particular user/ application protocol. The
   use of a adaptation protocol is optional. It is only used in case in
   which the application protocol does not want to change its interface
   with the underlying layer.

   the Stream Control Transmission Protocol itself that supports a
   common set of reliable transport functions.

   a standard IP transport/network protocol  provided by the operating
   system. In some network scenarios, it has been recognized that TCP
   can provide limited (but sufficient) reliable transport functionality
   for some applications.

2.2.12 Security considerations

   The following aspects of security are :


   Information is sent/received from a known and/or trusted partner.


   Information may not be modified while in transit. The integrity of a
   message in a public network is not guaranteed.


   Confidentiality of the user data must be ensured.  User data can not
   be examined by unauthorized users.


   The communicating endpoint must remain in service in all
   circumstances. Some services have very high availability
   requirements: for example, all SS7 nodes have to remain active for
   the 99.999% of the time. General Considerations

   SCTP only tries to increase the availability of a network. SCTP does
   not contain any protocol elements in its messages which are directly
   related to Authentication, Integrity and Confidentiality functions.
   It depends for such a features on the IPSEC protocols and

   The only function which has some bearing on security of SCTP is the
   integrity of message in SCTP, which is guarded by a Checksum. This
   checksum is mandatory if IPSEC is NOT used. If IPSEC is used then the
   SCTP checksum becomes optional.  The use of IPSEC in the SCTP
   association must in this case be END-TO-END. The use of IPSEC on a
   part of a path of a SCTP association does NOT relieve SCTP from using
   the checksum(as this ain't end-to-end transport)

   The general rule is that IPSEC should be turned on unconditionally.

   The description of the internet security architecture and the use of
   it is described in [RFC2401]. The cookie mechanism and Denial-of-Service (DOS) attacks

   The cookie mechanism in SCTP is a measure against Denial-of-Service
   (DOS) attacks. In a DOS attack, a lot of init chunks are send towards
   a single terminating node (the source is a bogus node = a invalid
   source address in the datagram), so that very quickly all resources
   are used up and that normal users are rejected due to resource

   When a INIT chunk is received, the TCB info is encoded and put into
   the cookie and send to the initiating node via the INIT_ACK. No TCB
   is allocated at the receiving node as all info is encoded in the
   cookie and the cookie will return in the COOKIE_ACK (at that time the
   TCB will be really allocated with the info from the cookie and a full
   association is set up). As the INIT_ACK will be send back to a bogus
   address, no COOKIE_ACK will come back and no resources will be tied
   up in the terminating node. Initiate Tag considerations

   As the tag is fixed during the whole lifetime of the association, the
   initiate Tag values should be selected as random as possible to help
   protect against "man in the middle" and "sequence number" attacks. It
   is suggested that RFC 1750 [RFC1750] be used for the Tag
   randomization. A new tag is only assigned if a new association is set
   up. Fingerprinting of SCTP

   Different implementations may show a certain fingerprint in their
   messages when they have to answer to certain messages send to them.
   It is advisabel to send only the basic required information back
   according to the SCTP protocol. The ACK-Splitting attack

   (Ed note : something need to be provided here)

3 Recommendations

   To be provided.

4 Adaptation Layers

   Currently, there are four adaptation layers, to support carrying of
   SS7 application protocols over IP.  These adaptation layers are being
   developed for different purposes, and there is no assumption that
   they should interwork - i.e. - M2UA carries M3UA.  They should be
   thought of as individual protocols for specific uses.

4.1 IUA

   There is a need for Switched Circuit Network (SCN) signaling protocol
   delivery from an ISDN Signaling Gateway (SG) to a Media Gateway
   Controller (MGC).  The delivery mechanism should meet the following

   *  Support for transport of the Q.921 / Q.931 boundary primitives *
   Support for communication between Layer Management modules on SG and
   MGC *  Support for management of active associations between SG and

   This draft supports both ISDN Primary Rate Access (PRA) as well as
   Basic Rate Access (BRA) including the support for both point-to-point
   mode and point-to-multipoint modes of communication.  QSIG adaptation
   layer requirements do not differ from Q.931 adaptation layer, hence
   the procedures described in this draft are also applicable to QSIG
   adaptation layer.

4.2 M2UA

   There is a need for SCN signaling protocol delivery from an Signaling
   Gateway (SG) to a Media Gateway Controller (MGC) or IP Signaling
   Point (IPSP).  The delivery mechanism should meet the following

   *  Support for MTP Level 2 / MTP Level 3 interface boundary *
   Support for communication between Layer Management modules on SG and
   MGC *  Support for management of active associations between the SG
   and MGC

   In other words, the Signaling Gateway will transport MTP Level 3
   messages to a Media Gateway Controller (MGC) or IP Signaling Point
   (IPSP).  In the case of delivery from an SG to an IPSP, the SG and
   IPSP function as traditional SS7 nodes using the IP network as a new
   type of SS7 link. This allows for full MTP Level 3 message handling
   and network management capabilities.

4.3 M3UA

   There is a need for SCN signaling protocol delivery from an SS7
   Signaling Gateway (SG) to a Media Gateway Controller (MGC) or IP-
   resident Database as described in the Framework Architecture for
   Signalling Transport [11].  The delivery mechanism should meet the
   following criteria:

   *  Support for transfer of all SS7 MTP3-User Part messages (e.g.,
   ISUP, SCCP, TUP, etc.)  *  Support for the seamless operation of
   MTP3-User protocol peers *  Support for the management of SCTP
   transport associations and traffic between an SG and one or more MGCs
   or IP-resident Databases *  Support for MGC or IP-resident Database
   failover and loadsharing *  Support for the asynchronous reporting of
   status changes to management

   In simplistic terms, the SG will terminate SS7 MTP2 and MTP3
   protocols and deliver ISUP, SCCP and/or any other MTP3-User protocol
   messages over SCTP transport associations to MTP3-User peers in MGCs
   or IP-resident Databases.

4.4 SUA

   This document details the delivery of SCCP-user messages (MAP & CAP
   over TCAP, RANAP, etc.) over IP.  The architecture may be from from
   an SS7 Signaling Gateway (SG) to an IP-based signaling node (such as
   an IP-resident Database) as described in the Framework Architecture
   for Signaling Transport [RFC2719], or between two endpoints located
   completely within an IP network. The delivery mechanism SHOULD meet
   the following criteria:

   *  Support for transfer of SS7 SCCP-User Part messages (e.g., TCAP,
   RANAP, etc.)  *  Support for SCCP connectionless service.  *  Support
   for SCCP connection oriented service.  *  Support for the seamless
   operation of SCCP-User protocol peers *  Support for the management
   of SCTP transport associations between an SG and one or more IP-based
   signaling nodes).  *  Support for distributed IP-based signaling
   nodes.  *  Support for the asynchronous reporting of status changes
   to management

5 References and related work

   [SCTP] Stewart, R. R., Xie, Q., Morneault, K., Sharp, C. , ,
   Schwarzbauer, H. J., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and
   Paxson, V."Stream Control Transmission Protocol", <draft-ietf-
   sigtran-sctp-09.txt>, April 2000.  Work In Progress.

   [Q1400] SG11, ITU-T Recommendation Q.1400, " architecture framework
   for the development of signaling and OA&M protocols using OSI
   concepts ",1993

   [HUITEM] Huitema, C., "Routing in the Internet", Prentice-Hall, 1995.

   [RFC2373] Hinden, R. and Deering, S., "IP Version 6 Addressing
   Architecture", RFC 2373, July 1998.

   [RFC2460] Hinden, R. and Deering, S., "Internet Protocol, Version 6
   (IPv6) Specification", RFC 2460, December 1998.

   [RFC814] Clark, D.D., "Names, addresses, ports and routes", RFC 0814,
   July 1982.

   [RFC2401] Kent, S., and Atkinson, R., "Security Architecture for the
   Internet Protocol", RFC 2401,  November 1998.

   [RFC1981] McCann, J., Deering, S., and Mogul, J., "Path MTU Discovery
   for IP version 6", RFC 1981, August 1996.

   [RFC2208] Mankin, A. Ed., Baker, F., , Braden, B., Bradner, S.,
   O`Dell, M., Romanow, A., Weinrib, A. and Zhang, L., "Resource
   ReSerVation Protocol (RSVP) -- Version 1 Applicability Statement Some
   Guidelines on Deployment" , RFC 2208, September 1997.

   [RFC2597] Heinanen, J., Baker, F., Weiss, W. and Wroclawski, J.,
   "Assured Forwarding PHB Group", RFC2597, June 1999

   [RFC2598] Jacobson, V., Nichols, K. and Poduri, K., "An Expedited
   Forwarding PHB", RFC2598, June 1999

   [RFC2719] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene,
   L., Lin, H., Juhasz, I., Holdrege, M., Sharp, C., "Framework
   Architecture for Signaling Transport", RFC2719, October 1999

   [IANA] Internet Assigned Numbers Authority,,
   April 2000

   [RFCRSIP] Borella, M., Grabelsky, D., Lo, J., Tuniguchi, K. "Realm
   specific IP",RFCxxxx, xxxx 2000

   [RFCSALLY] Floyd, S. Ed., "Congestion Control Principles", <draft-
   floyd-cong-02.txt> RFCxxxx, April 2000

   [RFC1750] Eastlake, 3rd, D., Crocker, S., Schiller, J., "Randomness
   Recommendations for Security", RFC1750, December 1994

   [RFC1323] Jacobson, V., Braden, R., Borman, D., "TCP Extensions for
   High Performance", RFC1323, May 1992

   [RFC2001] Stevens, W., "TCP Slow Start, Congestion Avoidance, Fast
   Retransmit, and Fast Recovery Algorithms ", RFC2001, Januarey 1997

   [RFC2018] Mathis, M., Mahdavi, J., Floyd, S.,  Romanow, A., "TCP
   Selective Acknowledgement Options ", RFC2018, October 1996

6 Acknowledgments

   The authors wish to thank Renee Revis, R.R. Stewart, Q. Xie, H.J.
   Schwarzbauer, M. Tuexen, J.P. Martin-Flatin and many others for their
   invaluable comments.

7  Author's Address

   Lode Coene
   Siemens Atea
   Atealaan 34
   B-2200    Herentals

   Phone: +32-14-252081

   John Loughney
   Nokia Research Center
   Itamerenkatu 11-13
   FIN-00180    Helsinki

   Phone: +358-9-43761

   Ian Rytina
   Ericsson Australia
   37/360 Elizabeth Street
   Melbourne, Victoria 3000

   Phone : -

   Lyndon Ong
   Nortel Networks
   4401 Great America Parkway
   Santa Clara, CA 95054

   Phone: -

   Expires: October 30, 2000

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