Telephony Signalling Transport over Stream Control Transmission Protocol (SCTP) Applicability Statement
RFC 4166

Document Type RFC - Informational (February 2006; No errata)
Last updated 2013-03-02
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Network Working Group                                           L. Coene
Request for Comments: 4166                                       Siemens
Category: Informational                                 J. Pastor-Balbas
                                                                Ericsson
                                                           February 2006

                  Telephony Signalling Transport over
  Stream Control Transmission Protocol (SCTP) Applicability Statement

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document describes the applicability of the several protocols
   developed under the signalling transport framework.  A description of
   the main issues regarding the use of the Stream Control Transmission
   Protocol (SCTP) and an explanation of each adaptation layer for
   transport of telephony signalling information over IP infrastructure
   are given.

Coene & Pastor-Balbas        Informational                      [Page 1]
RFC 4166           Telephony Signalling over SCTP AS       February 2006

Table of Contents

   1. Introduction ....................................................2
      1.1. Scope ......................................................2
      1.2. Terminology ................................................3
      1.3. Contributors ...............................................3
   2. SIGTRAN Architecture ............................................3
   3. Issues for Transporting Telephony Signalling over SCTP ..........5
      3.1. Congestion Control .........................................5
      3.2. Detection of Failures ......................................6
           3.2.1. Retransmission TimeOut (RTO) Calculation ............6
           3.2.2. Heartbeat ...........................................7
           3.2.3. Maximum Number of Retransmissions ...................7
      3.3. Shorten End-to-End Message Delay ...........................7
      3.4. Bundling Considerations ....................................7
      3.5. Stream Usage ...............................................7
   4. User Adaptation Layers ..........................................7
      4.1. Access Signalling .........................................10
           4.1.1. IUA (ISDN Q.921 User Adaptation) ...................10
           4.1.2. V5UA (V5.2-User Adaptation) Layer ..................12
           4.1.3. DUA (DPNSS/DASS User adaptation) Layer .............13
      4.2. Network Signalling ........................................13
           4.2.1. MTP lvl3 over IP ...................................14
           4.2.2. M3UA (SS7 MTP3 User Adaptation) Layer ..............17
           4.2.3. SUA (SS7 SCCP User Adaptation) Layer ...............18
   5. Security Considerations ........................................20
   6. Informative References .........................................20

1.  Introduction

   This document is intended to describe how to transport telephony
   signalling protocols, used in classic telephony systems, over IP
   networks.  As described in [RFC2719], the whole architecture is
   called SIGTRAN (Signalling Transport) and is composed of a transport
   protocol (SCTP) and several User Adaptation Layers (UALs).  The
   transport protocol SCTP has been developed to fulfill the stringent
   requirements of telephony signalling networks [RFC3257].  The set of
   UALs has also been introduced to make it possible for different
   signalling protocols to use the SCTP layer.

1.1.  Scope

   The scope of this document is the SIGTRAN user adaptation layers and
   SCTP protocols and how they are used to transport telephony
   signalling information over IP networks.

Coene & Pastor-Balbas        Informational                      [Page 2]
RFC 4166           Telephony Signalling over SCTP AS       February 2006

1.2.  Terminology

   The following terms are commonly identified in related work:

   Association: SCTP connection between two endpoints.

   Stream:      A uni-directional logical channel established within an
                association, within which all user messages are
                delivered in sequence except for those submitted to the
                unordered delivery service.

   SPU:         Signalling protocol user, the application on top of the
                User adaptation layer.

   CTSP:        Classical Telephony Signalling Protocol (examples
                include: MTP level 2, MTP level 3, and SCCP).

   UAL:         User Adaptation Layer, the protocol that encapsulates
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