Network Working Group E. Zimmerer
Request for Comments: 3204 Rankom, Inc.
Category: Standards Track J. Peterson
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 (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.
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 ). 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
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