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draft-ietf-sip-isup-mime-00.txt --> draft-ietf-sip-isup-mime-01.txt

MIME media types for ISUP and QSIG Objects

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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 [1]. 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 between legacy systems.

1. Introduction

ISUP (ISDN User part) defined in the ITU-T recommendations
Q.761-4 is a signaling protocol used between telephony switches.
There exists a need to transport ISUP-encoded signaling
information between SIP entities as part of the payload of SIP
[2] messages, in order to access ISUP-based legacy service
logic. For example, this may be implemented when using SIP to
control sessions between two systems that support legacy
telephony services or gateway between legacy systems.

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 to support legacy
services or gateway between legacy systems.

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Internet Draft ISUP and QSIG/MIME types Jan 2000

The following discussion 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 entities exchanging
messages determine or negotiate compatibility. It is assumed
that this is addressed by alternative means such as
configuration or routing protocols.

It is assumed in this document that the processing of ISUP and
QSIG information is in addition to the standard SIP processing,
and that no interworking of SIP and ISUP or QSIG signaling is
required.

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: none version
Optional parameters: version, compatibility, spec base
Encoding scheme: binary
Security considerations: See section 5.

Note: It is mandatory for SoftSwitches clients to specify the 'version'
of the ISUP message. Proxies, redirect servers, etc., have no
need to process/specify this information.

The use of the 'version' parameter allows differentiation
between different base ISUP variants. This enables the
SoftSwitch (also known a client
such as a Media SoftSwitch/Media Gateway Controller) Controller to

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Internet Draft ISUP and QSIG/MIME types Jan 2000

recognize and parse the message correctly, or (possibly) to
reject the message if the particular ISUP variant is not
supported. The idea here is to allow to specify a preference of
version, so that the following scenarios are possible: "I only
like application/isup;version=lcd" or "I accept application/isup
(but don't really know the details; I just pass them on to some
other tool that displays/munges them)". If not specified, the
default version is assumed to be ITU-T ISUP.

'compatibility' indicates whether or not the version of ISUP
supports the forward compatibility mechanism that is defined in
ITU-T White Book specifications and later issues of ISUP. If
present, its value is either yes or no. 1992.

The 'spec' 'base' parameter provides more detailed identification of a base regional
variant of ISUP that can be used to process the ISUP specification being sent, if this is available. body. This
may be used, for example, to identify a particular national
specification. that the message can be
processed using ITU-T 1992 ISUP processing, including support
of the forward compatibility mechanism.

The following is how a typical header would look:

Content-Type: application/ISUP; version=etsi;
compatibility=yes; spec=uk21 version=uk21;
base=etsi121
Content-Transfer-Encoding: binary

Table 1 is a partial list of protocol base versions supported by the
'application/ISUP' media type.

version type, and whether they support the forward
compatibility mechanism defined in later versions of ISUP.

base protocol

itu-t no compatibility

itu-t88 ITU-T Q.761-4 (1988)
itu-t yes no
itu-t92+ ITU-T Q.761-4 (1992)
ansi no yes
ansi88 ANSI T1.113-1988
etsi no ETSI
etsi121 ETS 300 121
etsi yes ETSI no
etsi356 ES 300 356 yes
gr317 no BELLCORE GR-317 no

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

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Internet Draft ISUP and QSIG/MIME types Jan 2000

recognize and parse the message correctly, or (possibly) to reject the
message if the particular QSIG variant is not supported.

The following is how a typical header would look:-

Content-Type: application/QSIG; version=iso
Content-Transfer-Encoding: binary

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

version protocol
------- --------
etsi93 ETSI 1993 version
iso ISO/IEC 11572 (equiv. to ETSI 1995)

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

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/ISUP' media type.

INVITE sip:13039263142@Den1.level3.com SIP/2.0
From: sip:13034513355@den3.level3.com
To: sip:13039263142@Den1.level3.com
Call-ID: DEN1231999021712095500999@Den1.level3.com
Content-Length: 448 420
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=ezimmerer 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

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Internet Draft ISUP and QSIG/MIME types Jan 2000

--unique-boundary-1
Content-type:application/ISUP; version=etsi;
compatibility=yes; spec=uk21 version=uk21;
base=etsi121
Content-Transfer-Encoding: binary

e1 f9 28 85 43 1e 05 44 1e 05 00 6e 0a

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 draft 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:14084955072@sc1.nortelnetworks.com SIP/2.0
From: sip:14085655675@sc10.nortelnetworks.com
To: sip:14084955072@sc1.nortelnetworks.com
Call-ID: 1231999021712095500999@sc12.nortelnetworks.com
Content-Length: 393
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

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

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--

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Internet Draft ISUP and QSIG/MIME types Jan 2000

5. Security considerations

Information contained in ISUP and QSIG objects bodies may have security considerations due to
customer-related information contained in the objects. However,
the security include
sensitive customer information, potentially requiring use of encryption.
Security mechanisms described are provided in RFC 2543 (SIP - Session Initiation
Protocol) are sufficient to support security of and should be used as appropriate for both the SIP message
and the encapsulated ISUP or QSIG information. No new security
considerations are thought necessary. body.

6. Authors

Eric Zimmerer L. Ong
ipVerse, Inc. M. Zonoun
1901 Landings Drive Nortel Networks
Mountain View, CA 94043, USA Santa Clara, CA 95054
Phone: 650-919-0648 long@nortelnetworks.com
Email: ericz@ipverse.com mzonoun@nortelnetworks.com

Aparna Vemuri M. Watson
Level 3 Communications Nortel Networks
Louisville, CO, USA Maidenhead, UK
Phone: 303-926-3768 mwatson@nortelnetworks.com
EMail: aparna.vemuri@level3.com

7. References

[1] Freed, Klensin, Postel, "Multipart Internet Mail Extensions
(MIME) Part Four: Registration Procedures" RFC 2048, Internet
Engineering Task Force, November 1996.

[2] Handley, Schulzrinne, Schooler and Rosenberg, "Session
Initiation Protocol (SIP)" RFC 2543, Internet Engineering Task
Force, March 1999.

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

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

This Internet Draft expires July 2000

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