MIME media types for ISUP and QSIG Objects
RFC 3204

Document Type RFC - Proposed Standard (December 2001; Errata)
Updated by RFC 5621, RFC 3459
Authors Mo Zonoun  , Francois Audet  , Jon Peterson  , Mark Watson  , Aparna Vemuri  , Lyndon Ong  , Eric Zimmerer 
Last updated 2020-01-21
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Network Working Group                                        E. Zimmerer
Request for Comments: 3204                                  Rankom, Inc.
Category: Standards Track                                    J. Peterson
                                                           Neustar, Inc.
                                                               A. Vemuri
                                                    Qwest Communications
                                                                  L. Ong
                                                          Ciena Networks
                                                                F. Audet
                                                               M. Watson
                                                               M. Zonoun
                                                         Nortel Networks
                                                           December 2001

               MIME media types for ISUP and QSIG Objects

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.


   This document describes MIME types for application/ISUP and
   application/QSIG objects for use in SIP applications, according to
   the rules defined in RFC 2048.  These types can be used to identify
   ISUP and QSIG objects within a SIP message such as INVITE or INFO, as
   might be implemented when using SIP in an environment where part of
   the call involves interworking to the PSTN.

1. Introduction

   ISUP (ISDN User part) defined in the ITU-T recommendations Q.761-4 is
   a signaling protocol used between telephony switches.  There are
   configurations in which ISUP-encoded signaling information needs to
   be transported between SIP entities as part of the payload of SIP
   messages, where the preservation of ISUP data is necessary for the
   proper operation of PSTN features.

Zimmerer, et al.            Standards Track                     [Page 1]
RFC 3204               ISUP and QSIG MIME Objects          December 2001

   QSIG is the analogous signaling protocol used between private branch
   exchanges to support calls within private telephony networks.  There
   is a similar need to transport QSIG-encoded signaling information
   between SIP entities in some environments.

   This document is specific to this usage and would not apply to the
   transportation of ISUP or QSIG messages in other applications. These
   media types are intended for ISUP or QSIG application information
   that is used within the context of a SIP session, and not as general
   purpose transport of SCN signaling.

   The definition of media types for ISUP and QSIG application
   information does not address fully how the non-SIP and SIP entities
   exchanging messages determine or negotiate compatibility.  It is
   assumed that this is addressed by alternative means such as the
   configuration of the interworking functions.

   This is intended to be an IETF approved MIME type, and to be defined
   through an RFC.  NOTE: usage of Q.SIG within SIP is neither endorsed
   nor recommended as a result of this MIME registration.

3. Proposed new media types

   ISUP and QSIG messages are composed of arbitrary binary data that is
   transparent to SIP processing. The best way to encode these is to use
   binary encoding. This is in conformance with the restrictions imposed
   on the use of binary data for MIME (RFC 2045 [3]). It should be noted
   that the rules mentioned in the RFC 2045 apply to Internet mail
   messages and not to SIP  messages. Binary has been preferred over
   Base64 encoding because the latter would only result in adding bulk
   to the encoded messages and possibly be more costly in terms of
   processing power.

3.1 ISUP Media Type

   This media type is defined by the following information:

   Media type name: application
   Media subtype name: ISUP
   Required parameters: version
   Optional parameters: base
   Encoding scheme: binary
   Security considerations: See section 5.

   The ISUP message is encapsulated beginning with the Message Type Code
   (i.e., omitting Routing Label and Circuit ID Code).

Zimmerer, et al.            Standards Track                     [Page 2]
RFC 3204               ISUP and QSIG MIME Objects          December 2001

   The use of the 'version' parameter allows network administrators to
   identify specific versions of ISUP that will be exchanged on a
   bilateral basis. This enables a particular client such as a
   SoftSwitch/Media Gateway Controller to recognize and parse the
   message correctly,  or (possibly) to reject the message if the
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