ISO/IEC 23916:2005

INTERNATIONAL ISO/IEC
STANDARD 23916
First edition
2005-11-01
Information technology —
Telecommunications and information
exchange between systems — Corporate
Telecommunication Networks —
Signalling Interworking between QSIG
and SIP — Call Transfer
Technologies de l'information — Télécommunications et échange
d'information entre systèmes — Réseaux de télécommunications
d'entreprise — Interaction de signalisation entre QSIG et SIP —
Transfert d'appel
Reference number
©
ISO/IEC 2005
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©  ISO/IEC 2005
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ii © ISO/IEC 2005 – All rights reserved

Contents Page
Foreword .v
Introduction.vi
1 Scope.1
2 Normative references.1
3 Terminology.2
4 Definitions.3
4.1 External definitions .3
4.2 Other definitions.3
4.2.1 User A .3
4.2.2 User B .3
4.2.3 User C .3
4.2.4 Call transfer.3
4.2.5 Single step call transfer.4
4.2.6 Call transfer by join.4
4.2.7 Call transfer by rerouteing .4
4.2.8 Corporate telecommunication Network (CN).4
4.2.9 IP network.4
4.2.10 Private Integrated Services Network (PISN) .4
4.2.11 Private Integrated services Network eXchange (PINX) .4
5 Abbreviations and acronyms .4
6 Background and architecture .5
7 Procedures.5
7.1 Call transfers in QSIG .5
7.2 Call transfer in SIP.6
7.3 Scope of the interworking functions.6
7.3.1 QSIG side.6
7.3.2 SIP side.6
7.3.3 Discussion over transfer interworking functions .6
7.4 Mapping of numbers and URIs .9
7.5 UAC Processing .10
7.5.1 Receipt of a FACILITY message with callTransferComplete invoke APDU .10
7.5.2 Receipt of a FACILITY message with callTransferUpdate invoke APDU.10
7.5.3 Receipt of a FACILITY message with ssctInitiate invoke APDU.10
7.5.4 Receipt of a SETUP message with ssctSetup invoke APDU .11
7.5.5 Receipt of a FACILITY message with subaddressTransfer invoke APDU.12
7.6 UAS Processing.12
7.6.1 Receipt of a SIP REFER request .12
7.6.2 Receipt of a SIP INVITE request.17
7.6.3 Receipt of a SIP request with revised identity .18
8 Example message sequences.19
8.1 Call transfer by join where User B and C are SIP participants.19
8.2 Call transfer where User A is a SIP participant .20
8.3 Call transfer where User A is a SIP participant and where two gateways are used.21
8.4 Call transfer where User A and User B are SIP participants.22
8.5 Single step call transfer where User B is a SIP participant .23
8.6 Unsuccessful Single step call transfer where User A and User C are SIP participants .24
8.7 Single step call transfer where User A and User B are SIP participants.25
9 Security considerations . 25
© ISO/IEC 2005 – 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 23916 was prepared by Ecma International (as ECMA 361) 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.

iv © ISO/IEC 2005 – 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.
This International Standard specifies call transfer interworking between the Session Initiation Protocol
(SIP) and QSIG within corporate telecommunication networks (also known as enterprise networks). SIP
is an Internet application-layer control (signalling) protocol for creating, modifying, and terminating
sessions with one or more participants. These sessions include, in particular, telephone calls.
This International Standard is based upon the practical experience of member companies and the
results of their active and continuous participation in the work of ISO/IEC JTC1, ITU-T, IETF, ETSI and
other international and national standardization bodies. It represents a pragmatic and widely based
consensus.
© ISO/IEC 2005 – All rights reserved v

INTERNATIONAL STANDARD ISO/IEC 23916:2005(E)

Information technology — Telecommunications and information
exchange between systems — Corporate Telecommunication
Networks — Signalling Interworking between QSIG and SIP —
Call Transfer
1 Scope
This International Standard specifies call transfer interworking between the Session Initiation Protocol (SIP)
and “QSIG” within corporate telecommunication networks (CN), also known as enterprise networks.
"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 [1] (call control in support of
basic services), [2] (generic functional protocol for the support of supplementary services) and a number of
Standards specifying individual supplementary services. Transfer services are specified in [3], [6] and the
QSIG signalling protocol in support of these services is specified in [4], [7]. In particular, this signalling protocol
signals information about call transfer to the users who are involved.
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.
SIP is an application layer protocol for establishing, terminating and modifying multimedia sessions. It is
typically carried over IP. Telephone calls are considered as a type of multimedia session where just audio is
exchanged. SIP is defined in [10].
As the support of telephony within corporate networks evolves from circuit-switched technology to Internet
technology, the two technologies will co-exist in many networks for a period, perhaps several years. Therefore
there is a need to be able to establish, modify, terminate and transfer sessions involving participants in the
SIP network and participants in the QSIG network. Such calls are supported by gateways that perform
interworking between SIP and QSIG.
This specification specifies SIP-QSIG signalling interworking for transfer services between a PISN employing
QSIG and a corporate IP network employing SIP.
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.
[1] International Standard ISO/IEC 11572 "Information technology -- Telecommunications and information
exchange between systems -- Private Integrated Services Network -- Circuit mode bearer services -- Inter-
exchange signalling procedures and protocol" (also published by Ecma as Standard ECMA-143).
[2] International Stan
...