ISO/IEC 22535:2009

INTERNATIONAL ISO/IEC
STANDARD 22535
Third edition
2009-04-15
Information technology —
Telecommunications and information
exchange between systems — Corporate
telecommunication networks —
Tunnelling of QSIG over SIP
Technologies de l'information — Télécommunications et échange
d'information entre systèmes — Réseaux de télécommunications
d'entreprise — Tunnellisation de QSIG sur SIP

Reference number
©
ISO/IEC 2009
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©  ISO/IEC 2009
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ii © ISO/IEC 2009 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Normative references .1
3 Terms and definitions .2
4 Abbreviated terms .3
5 Background and architecture.3
5.1 Architecture.3
5.2 Basic operation.4
5.3 QSIG connectionless transport.5
5.4 Late availability of SDP parameters at the egress gateway .5
6 Procedures .5
6.1 General.5
6.2 Encapsulation of QSIG messages in SIP messages.5
6.3 QSIG SETUP message handling at an ingress gateway.6
6.3.1 Sending a SIP INVITE request .6
6.3.2 Receipt of responses to the INVITE request.6
6.4 QSIG SETUP message handling at an egress gateway.7
6.4.1 Receiving a SIP INVITE request .7
6.4.2 Rejecting a QSIG message in an INVITE request.8
6.5 Subsequent QSIG messages.8
6.6 Terminating the SIP dialog .8
6.7 QSIG connectionless message handling at an ingress gateway .9
6.7.1 Sending a SIP INVITE request .9
6.7.2 Receipt of responses to the INVITE request.9
6.8 QSIG connectionless message handling at an egress gateway.10
7 Example message sequences.10
7.1 Call establishment .10
7.2 Call clearing.11
7.3 QSIG connectionless message .12
7.4 Call establishment with port=0 in first SDP answer.13
7.5 Backwards compatibility with early editions .14
8 Security considerations .16
Annex A (informative) Changes from early editions.17
Bibliography .19

© ISO/IEC 2009 – All rights reserved iii

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members of
ISO or IEC participate in the development of International Standards through technical committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC 22535 was prepared by Ecma International (as ECMA-355) and was adopted, under a special “fast-
track procedure”, by Joint Technical Committee ISO/IEC JTC 1, Information technology, in parallel with its
approval by national bodies of ISO and IEC.
This third edition cancels and replaces the second edition (ISO/IEC 22535:2006), which has been technically
revised.
iv © ISO/IEC 2009 – All rights reserved

Introduction
This International Standard is one of a series of Standards defining the interworking of services and signalling
protocols deployed in corporate telecommunication networks (CNs) (also known as enterprise networks). The
series uses telecommunication concepts as developed by ITU-T and conforms to the framework of
International Standards on Open Systems Interconnection as defined by ISO/IEC.
"QSIG" is a signalling protocol that operates between Private Integrated services Network eXchanges (PINX)
within a Private Integrated Services Network (PISN). A PISN provides circuit-switched basic services and
supplementary services to its users. QSIG is specified in Standards, in particular ISO/IEC 11572,
ISO/IEC 11582 and a number of Standards specifying individual supplementary services.
NOTE The name QSIG was derived from the fact that it is used for signalling at the Q reference point. The Q
reference point is a point of demarcation between two PINXs (ISO/IEC 11572).
SIP is an application layer protocol for establishing, terminating and modifying multimedia sessions. It is
typically carried over IP (RFC 791), (RFC 2460). Telephone calls are considered as a type of multimedia
session where just audio is exchanged. SIP is defined in RFC 3261.
Often a CN comprises both PISNs employing QSIG and IP networks employing SIP. A call or call independent
signalling can originate at a user connected to a PISN and terminate at a user connected to an IP network or
vice versa. In either case, a gateway provides interworking between QSIG and SIP at the boundary between
the PISN and the IP network. Basic call interworking at a gateway is specified in ISO/IEC 17343. Another case
is where a call or call independent signalling originates at a user connected to a PISN, traverses an IP
network using SIP, and terminates at a user connected to another (or another part of the same) PISN. This
document addresses this last case in a way that preserves all QSIG capabilities across the IP network. It
achieves this by tunnelling QSIG messages within SIP requests and responses in the context of a SIP dialog.
This International Standard specifies tunnelling of QSIG over the Session Initiation Protocol (SIP). This
enables calls between "islands" of circuit switched networks that use QSIG signalling to be interconnected by
an IP network that uses SIP signalling without loss of QSIG functionality. This International Standard facilitates
the introduction of enhanced SIP and SDP functionality that was specified after publication of the early
editions of this International Standard. These enhancements include payload encryption and mechanisms to
negotiate SDP capabilities.
The changes in this International Standard comprise a mandatory payload renegotiation with reversed
direction of the offer/answer exchange compared with early editions. In order to achieve backward
compatibility with early editions an indicator for the changed signalling procedures is introduced. This indicator
is used to dynamically detect if fallback to signalling procedures compliant to early editions is necessary.
This International Standard is based upon the practical experience of Ecma member companies and the
results of their active and continuous participation in the work of ISO/IEC JTC 1, ITU-T, IETF, ETSI and other
international and national standardization bodies. It represents a pragmatic and widely based consensus.
© ISO/IEC 2009 – All rights reserved v

INTERNATIONAL STANDARD ISO/IEC 22535:2009(E)

Information technology — Telecommunications and information
exchange between systems — Corporate telecommunication
networks — Tunnelling of QSIG over SIP
1 Scope
This International Standard specifies tunnelling of "QSIG" over the Session Initiation Protocol (SIP) within a
corporate telecommunication network (CN).
The tunnelling of QSIG through a public IP network employing SIP is outside the scope of this International
Standard. However, the functionality specified in this International Standard is in principle applicable to such a
scenario when deployed in conjunction with other relevant functionality (e.g. address translation, security
functions, etc.).
This International Standard is applicable to any interworking unit that can act as a gateway between a PISN
employing QSIG and a corporate IP network employing SIP, with QSIG tunnelled within SIP requests and
responses.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO/IEC 11572:2000, Information technology — Telecommunications and information exchange between
systems — Private Integrated Services Network — Circuit mode bearer services — Inter-exchange signalling
procedures and protocol
ISO/IEC 11582:2002, Information technology — Telecommunications and information exchange between
systems — Private Integrated Services Network — Generic functional protocol for the support of
supplementary services — Inter-exchange signalling procedures and protocol
RFC 2119, Key words for use in RFCs to Indicate Requirement Levels, BCP 14, S. Bradner, March 1997
RFC 2976, The SIP INFO Method, S. Donovan, October 2000
RFC 3204, MIME media types for ISUP and QSIG Objects, E. Zimmerer et al., December 2001
RFC 3261, SIP: Session Initiation Protocol, J. Rosenberg et al., June 2002
RFC 3264, An Offer/Answer Model with the Session Description Protocol (SDP), J. Rosenberg,
H. Schulzrinne, June 2002
RFC 3840, Indicating User Agent Capabilities in the Session Initiatio
...