Network Working Group E. Zimmerer

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.

Abstract

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.

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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).

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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
specified ISUP version is not supported. This specification places no
constraints on the values that may be used in 'version'; these are
left to the discretion of the network administrator.

This 'version' could, for example, be used to identify a network-
specific implementation of ISUP, e.g., X-NetxProprietaryISUPv3, or to
identify a well-known standard version of ISUP, e.g., itu-t or ansi.

A 'base' parameter can optionally be included in some cases (e.g., if
the receiver may not recognize the 'version' string) to specify that
the encapsulated ISUP can also be processed using the identified
'base' specification. Table 1 provides a list of 'base' values
supported by the 'application/ISUP' media type, including whether or
not the forward compatibility mechanism defined in ITU-T 1992 ISUP is
supported.

Table 1: ISUP 'base' values

base protocol compatibility

itu-t88 ITU-T Q.761-4 (1988) no
itu-t92+ ITU-T Q.761-4 (1992) yes
ansi88 ANSI T1.113-1988 no
ansi00 ANSI T1.113-2000 yes
etsi121 ETS 300 121 no
etsi356 ES 300 356 yes
gr317 BELLCORE GR-317 no
ttc87 JT-Q761-4(1987-1992) no
ttc93+ JT-Q761-4(1993-) yes

The Content-Disposition header [5] may be included to describe how
the encapsulated ISUP is to be processed, and in particular what the
handling should be if the received Content-Type is not recognized.
The default disposition-type for an ISUP message body is "signal".
This type indicates that the body part contains signaling information
associated with the session, but does not describe the session.

Supplementing the description of the Content-Disposition header in
[5], as well as any characterization of the Content-Disposition
header in the SIP standard, is the following BNF describing
disposition-types and disposition-params that may be used in the
header of ISUP and QSIG MIME bodies.

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RFC 3204 ISUP and QSIG MIME Objects December 2001

Content-Disposition = "Content-Disposition" ":"
disposition-type *( ";" disposition-param )
disposition-type = "signal" | disp-extension-token
disposition-param = "handling" "="
( "optional" | "required" | other-handling )
| generic-param
other-handling = token
disp-extension-token = token

A full definition of the use of the "handling" parameter is given in
the IANA Considerations section below. The following is how a
typical header would look ('base' may be omitted):

Content-Type: application/ISUP; version=nxv3; base=etsi121
Content-Disposition: signal; handling=optional

3.2 QSIG Media Type

The application/QSIG media type is defined by the following
information:

Media type name: application
Media subtype name: QSIG
Required parameters: none
Optional parameters: version
Encoding scheme: binary
Security considerations: See section 5.

The use of the 'version' parameter allows identification of different
QSIG variants. This enables the terminating Connection Server to
recognize and parse the message correctly, or (possibly) to reject
the message if the particular QSIG variant is not supported.

Table 2 is a list of protocol versions supported by the
'application/QSIG' media type.

Table 2: QSIG versions

version protocol
------- --------
iso ISO/IEC 11572 (Basic Call) and
ISO/IEC 11582 (Generic Functional Protocol)

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RFC 3204 ISUP and QSIG MIME Objects December 2001

The following is how a typical header would look (Content-Disposition
not included in this instance):

Content-Type: application/QSIG; version=iso

The default Content-Disposition disposition-type is "signal" as in an
ISUP body part. The "handling" parameter described above can also be
used for QSIG bodies.

4. Illustrative examples

4.1 ISUP

SIP message format requires a Request line followed by Header lines
followed by a CRLF separator followed by the message body. To
illustrate the use of the 'application/ISUP' media type, below is an
INVITE message which has the originating SDP information and an
encapsulated ISUP IAM.

Note that the two payloads are demarcated by the boundary parameter
(specified in RFC 2046 [4]) which in the example has the value
"unique-boundary-1". This is part of the specification of MIME
multipart and is not related to the

INVITE sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP den3.level3.com
From: sip:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 8348 INVITE
Contact: <sip:[email protected]>
Content-Length: 436
Content-Type: multipart/mixed; boundary=unique-boundary-1
MIME-Version: 1.0

--unique-boundary-1
Content-Type: application/SDP; charset=ISO-10646

v=0
o=jpeterson 2890844526 2890842807 IN IP4 126.16.64.4
s=SDP seminar
c=IN IP4 MG122.level3.com
t= 2873397496 2873404696
m=audio 9092 RTP/AVP 0 3 4
--unique-boundary-1
Content-Type: application/ISUP; version=nxv3;
base=etsi121
Content-Disposition: signal; handling=optional

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RFC 3204 ISUP and QSIG MIME Objects December 2001

01 00 49 00 00 03 02 00 07 04 10 00 33 63 21
43 00 00 03 06 0d 03 80 90 a2 07 03 10 03 63
53 00 10 0a 07 03 10 27 80 88 03 00 00 89 8b
0e 95 1e 1e 1e 06 26 05 0d f5 01 06 10 04 00
--unique-boundary-1--

Note: Since binary encoding is used for the ISUP payload, each byte
is encoded as a byte, and not as a two-character hex representation.
Hex digits were used in the document because a literal encoding of
those bytes would have been confusing and unreadable.

4.2 QSIG

To illustrate the use of the 'application/QSIG' media type, below is
an INVITE message which has the originating SDP information and an
encapsulated QSIG SETUP message.

Note that the two payloads are demarcated by the boundary parameter
(specified in RFC 2046 [4]) which in the example has the value
"unique- boundary-1". This is part of the specification of MIME
multipart and is not related to the 'application/QSIG' media type.

INVITE sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP sc10.nortelnetworks.com
From: sip:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 1234 INVITE
Contact: <sip:[email protected]>
Content-Length: 358
Content-Type: multipart/mixed; boundary=unique-boundary-1
MIME-Version: 1.0

--unique-boundary-1
Content-Type: application/SDP; charset=ISO-10646

v=0
o=audet 2890844526 2890842807 5 IN IP4 134.177.64.4
s=SDP seminar
c=IN IP4 MG141.nortelnetworks.com
t= 2873397496 2873404696
m=audio 9092 RTP/AVP 0 3 4

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RFC 3204 ISUP and QSIG MIME Objects December 2001

--unique-boundary-1
Content-type:application/QSIG; version=iso

08 02 55 55 05 04 02 90 90 18 03 a1 83 01
70 0a 89 31 34 30 38 34 39 35 35 30 37 32
--unique-boundary-1--

5. Security considerations

Information contained in ISUP and QSIG bodies may include sensitive
customer information, potentially requiring use of encryption.

Security mechanisms are provided in RFC 2543 (SIP - Session
Initiation Protocol) and should be used as appropriate for both the
SIP message and the encapsulated ISUP or QSIG body.

6. IANA considerations

This document registers the "application/ISUP" and "application/QSIG"
MIME media types.

Registrations for the 'version' symbols used within the ISUP and QSIG
MIME types must specify a definitive specification reference,
identifying a particular issue of the specification, to which the new
symbol shall refer. Identifying a definite specification reference
requires a review process; the authors recommend that a subject
matter expert be designated as described in RFC 2434 [6] under Expert
Review.

Note that where a specification is fully peer-to-peer backwards
compatible with a previous issue (i.e., the compatibility mechanism
is supported by both), then there is no need for separate symbols to
be registered. The symbol for the original specification should be
used to identify backwards-compatible upgrades of that specification
as well.

Symbols beginning with the characters 'X-' are reserved for non-
standard usage (e.g., cases in which a token other than a string
representing an issue of an ISUP specification is appropriate for
characterizing ISUP within an administrative domain). Such non-
standard version can only be transmitted between administrative
domains in accordance with a bilateral agreement. These symbols
should be administered under the Private Use policy described in RFC
2434.

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RFC 3204 ISUP and QSIG MIME Objects December 2001

This document registers a new disposition-type for the Content-
Disposition header, 'signal', to be used when a MIME body contains
supplemental signaling information (ISUP and QSIG as MIME bodies
being examples of this).

This document also defines a Content Disposition parameter,
"handling". The handling parameter, handling-parm, describes how the
UAS should react if it receives a message body whose content type or
disposition type it does not understand. If the parameter has the
value "optional", the UAS MUST ignore the message body; if it has the
value "required", the UAS MUST return 415 (Unsupported Media Type).
If the handling parameter is missing, the value "required" is to be
assumed.

7. Authors Addresses

Eric Zimmerer
Rankom Inc.
19500 Pruneridge Ave Suite #4303
Cupertino, CA 95014, USA
EMail: [email protected]

Aparna Vemuri
Qwest Communications
6000 Parkwood Pl
Dublin, OH 43016, USA
EMail: [email protected]

Jon Peterson
NeuStar, Inc
1800 Sutter Street, Suite 570
Concord, CA 94520, USA
EMail: [email protected]

Lyndon Ong
Ciena
Cupertino, CA, USA
EMail: [email protected]

Francois Audet
Nortel Networks
4301 Great America Parkway
Santa Clara, CA 95054, USA
EMail: [email protected]

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RFC 3204 ISUP and QSIG MIME Objects December 2001

Mo Zonoun
Nortel Networks
4301 Great America Parkway
Santa Clara, CA 95054, USA
EMail: [email protected]

M. Watson
Nortel Networks
Maidenhead, UK
EMail: [email protected]

8. References

[1] Freed, N., Klensin, J. and J. Postel, "Multipart Internet Mail
Extensions (MIME) Part Four: Registration Procedures", BCP 13,
RFC 2048, November 1996.

[2] Handley, M., Schulzrinne, H., Schooler, E. and J. Rosenberg,
"Session Initiation Protocol (SIP)", RFC 2543, March 1999.

[3] Freed, N. and N. Borenstein, "Multipart Internet Mail Extensions
(MIME) Part One: Format of Internet Message Bodies", RFC 2045,
November 1996.

[4] Freed, N. and N. Borenstein, "Multipart Internet Mail Extensions
(MIME) Part Two: Media Types", RFC 2046, November 1996.

[5] Troost, R., Dorner, S. and K. Moore, "Communicating Presentation
Information in Internet Messages: The Content-Disposition Header
Field", RFC 2183, August 1997.

[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

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RFC 3204 ISUP and QSIG MIME Objects December 2001

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Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

Zimmerer, et al. Standards Track [Page 10]