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Versions: (draft-zimmerer-sip-isup-mime) 00 01 02 03 04 05 06 07 08 09 RFC 3204

Internet Engineering Task Force                     Eric Zimmerer
Internet Draft                                      ipVerse, Inc.
draft-ietf-sip-isup-mime-00.txt                     Aparna Vemuri
January 2000                               Level 3 Communications
Expires: July 2000                                         L. Ong
                                                        M. Zonoun
                                                        M. Watson
                                                  Nortel Networks

              MIME media types for ISUP and QSIG Objects

Status of this Memo

This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.  Internet-Drafts
are working documents of the Internet Engineering Task Force
(IETF), its areas, and its working groups.  Note that other
groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six
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in progress."

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The list of Internet-Draft Shadow Directories can be accessed at
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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
Optional parameters: version, compatibility, spec
Encoding scheme: binary
Security considerations: See section 5.

Note: It is mandatory for SoftSwitches 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 as a Media Gateway 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.

The 'spec' parameter provides more detailed identification of
the ISUP specification being sent, if this is available.  This
may be used, for example, to identify a particular national
specification.

The following is how a typical header would look:

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

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


  version           compatibility      protocol

  itu-t                   no          ITU-T Q.761-4 (1988)
  itu-t                   yes         ITU-T Q.761-4 (1992)
  ansi                    no          ANSI T1.113-1988
  etsi                    no          ETSI 300 121
  etsi                    yes         ETSI 300 356
  gr317                   no          BELLCORE GR-317

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.

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
        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
        Content-Transfer-Encoding: binary

        e1 f9 28 85 43 1e 05 44 1e 05 00 6e 0a 01 00
        00 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

ISUP and QSIG objects may have security considerations due to
customer-related information contained in the objects.  However,
the security mechanisms described in RFC 2543 (SIP - Session
Initiation Protocol) are sufficient to support security of the
encapsulated ISUP or QSIG information. No new security
considerations are thought necessary.

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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