ISO/IEC 17343:2007
(Main)Information technology — Telecommunications and information exchange between systems — Corporate telecommunication networks — Signalling interworking between QSIG and SIP — Basic services
Information technology — Telecommunications and information exchange between systems — Corporate telecommunication networks — Signalling interworking between QSIG and SIP — Basic services
ISO/IEC 17343:2007 specifies signalling interworking between QSIG and the Session Initiation Protocol (SIP) in support of basic services within a corporate telecommunication network (CN) (also known as enterprise network). 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 other Standards. 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 a type of multimedia session where just audio is exchanged. As the support of telephony within corporate networks evolves from circuit-switched technology to Internet technology, the two technologies will coexist in many networks for a period, perhaps several years. Therefore, there is a need to be able to establish, modify, and terminate sessions involving a participant in the SIP network and a participant in the QSIG network. Such calls are supported by gateways that perform interworking between SIP and QSIG. ISO/IEC 17343:2007 specifies SIP-QSIG signalling interworking for basic services that provide a bi-directional transfer capability for speech, DTMF, facsimile, and modem media between a PISN employing QSIG and a corporate IP network employing SIP. Other aspects of interworking, e.g., the use of RTP and SDP, will differ according to the type of media concerned and are outside the scope of ISO/IEC 17343:2007. Call-related and call-independent signalling in support of supplementary services is outside the scope of ISO/IEC 17343:2007, but support for certain supplementary services (e.g., call transfer, call diversion) could be the subject of future work. Interworking between QSIG and SIP permits a call originating at a user of a PISN to terminate at a user of a corporate IP network, or a call originating at a user of a corporate IP network to terminate at a user of a PISN. Interworking between a PISN employing QSIG and a public IP network employing SIP is outside the scope of ISO/IEC 17343:2007. However, the functionality specified in ISO/IEC 17343:2007 is in principle applicable to such a scenario when deployed in conjunction with other relevant functionality (e.g., number translation, security functions, etc.). ISO/IEC 17343:2007 is applicable to any interworking unit that can act as a gateway between a PISN employing QSIG and a corporate IP network employing SIP.
Technologies de l'information — Télécommunications et échange d'information entre systèmes — Réseaux de télécommunications d'entreprise — Signalisation d'interfonctionnement entre QSIG et SIP — Services de base
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INTERNATIONAL ISO/IEC
STANDARD 17343
Second edition
2007-11-15
Information technology —
Telecommunications and information
exchange between systems — Corporate
telecommunication networks —
Signalling interworking between QSIG
and SIP — Basic services
Technologies de l'information — Télécommunications et échange
d'information entre systèmes — Réseaux de télécommunications
d'entreprise — Signalisation d'interfonctionnement entre QSIG et SIP —
Services de base
Reference number
ISO/IEC 17343:2007(E)
©
ISO/IEC 2007
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ISO/IEC 17343:2007(E)
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ISO/IEC 17343:2007(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Conformance.2
3 Normative references .2
4 Terms and definitions .3
5 Abbreviated terms .3
6 Background and Architecture .4
7 General Requirements .6
8 Message Mapping Requirements.7
8.1 Message Validation and Handling of Protocol Errors.7
8.2 Call Establishment from QSIG to SIP .8
8.3 Call Establishment from SIP to QSIG .12
8.4 Call Clearing and Call Failure .16
8.5 Request to Change Media Characteristics.19
9 Number Mapping.19
9.1 Mapping from QSIG to SIP.20
9.2 Mapping from SIP to QSIG.21
10 Requirements for Support of Basic Services .23
10.1 Derivation of QSIG Bearer Capability Information Element .23
10.2 Derivation of Media Type in SDP.23
11 Security Considerations .24
11.1 General.24
11.2 Calls from QSIG to Invalid or Restricted Numbers .24
11.3 Abuse of SIP Response Code .24
11.4 Use of the To Header URI.24
11.5 Use of the From Header URI .25
11.6 Abuse of Early Media .25
11.7 Protection from Denial-of-Service Attacks .25
Annex A (normative) Implementation Conformance Statement (ICS) proforma .26
Annex B (informative) Example Message Sequences.34
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ISO/IEC 17343:2007(E)
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 17343 was prepared by Ecma International (as ECMA-339) 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 second edition cancels and replaces the first edition (ISO/IEC 17343:2004), which has been technically
revised.
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ISO/IEC 17343:2007(E)
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 defines the signalling protocol interworking for basic services between a Private
Integrated Services Network (PISN) and a packet-based private telecommunications network based on the
Internet Protocol (IP). It is further assumed that the protocol for the PISN part is QSIG and that the protocol for
the IP-based network is SIP. Compared with the first edition of ISO 17343, this second edition includes
numerous small changes arising during derived work in the IETF on RFC 4497. This second edition is in full
technical alignment with RFC 4497.
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 JTC 1, ITU-T, ETSI and other international and
national standardization bodies. It represents a pragmatic and widely based consensus.
In this International Standard, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in RFC 2119 [4] and indicate requirement levels for compliant SIP implementations.
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INTERNATIONAL STANDARD ISO/IEC 17343:2007(E)
Information technology — Telecommunications and information
exchange between systems — Corporate telecommunication
networks — Signalling interworking between QSIG and SIP —
Basic services
1 Scope
This International Standard specifies signalling interworking between QSIG and the Session Initiation Protocol
(SIP) in support of basic services within a corporate telecommunication network (CN) (also known as
enterprise network).
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 other Standards; in particular [2] (call control in
support of basic services), [3] (generic functional protocol for the support of supplementary services), 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.
SIP is an application-layer protocol for establishing, terminating, and modifying multimedia sessions. It is
typically carried over IP [15], [16]. Telephone calls are considered 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 coexist in many networks for a period, perhaps several years. Therefore,
there is a need to be able to establish, modify, and terminate sessions involving a participant in the SIP
network and a participant in the QSIG network. Such calls are supported by gateways that perform
interworking between SIP and QSIG.
This International Standard specifies SIP-QSIG signalling interworking for basic services that provide a bi-
directional transfer capability for speech, DTMF, facsimile, and modem media between a PISN employing
QSIG and a corporate IP network employing SIP. Other aspects of interworking, e.g., the use of RTP and
SDP, will differ according to the type of media concerned and are outside the scope of this International
Standard.
Call-related and call-independent signalling in support of supplementary services is outside the scope of this
International Standard, but support for certain supplementary services (e.g., call transfer, call diversion) could
be the subject of future work.
Interworking between QSIG and SIP permits a call originating at a user of a PISN to terminate at a user of a
corporate IP network, or a call originating at a user of a corporate IP network to terminate at a user of a PISN.
Interworking between a PISN employing QSIG and 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., number
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.
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ISO/IEC 17343:2007(E)
2 Conformance
In order to conform to this International Standard, a gateway shall satisfy the requirements identified in the
Implementation Conformance Statement (ICS) proforma in Annex A.
3 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] ISO/IEC 11571:1998, Information technology — Telecommunications and information exchange between
systems — Private Integrated Services Networks — Addressing
[2] 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
[3] 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
[4] RFC 2119, Key words for use in RFCs to Indicate Requirement Levels, BCP 14, S. Bradner
[5] RFC 793, Transmission Control Protocol, STD 7, J. Postel
[6] RFC 768, User Datagram Protocol, STD 6, J. Postel
[7] RFC 2246, The TLS Protocol Version 1.0, T. Dierks and C. Allen
[8] RFC 2327, SDP: Session Description Protocol, M. Handley and V. Jacobson
[9] RFC 2960, Stream Control Transmission Protocol, R. Stewart, Q. Xie, K. Morneault, C. Sharp,
H. Schwarzbauer, T. Taylor, I. Rytina, M. Kalla, L. Zhang, and V. Paxson
[10] RFC 3261, SIP: Session Initiation Protocol, J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston,
J. Peterson, R. Sparks, M. Handley, and E. Schooler
[11] RFC 3262, Reliability of Provisional Responses in the Session Initiation Protocol (SIP), J. Rosenberg and
H. Schulzrinne
[12] RFC 3264, An Offer/Answer Model with the Session Description Protocol (SDP), J. Rosenberg and
H. Schulzrinne
[13] RFC 3323, A Privacy Mechanism for the Session Initiation Protocol (SIP), J. Peterson
[14] RFC 3325, Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity within Trusted
Networks, C. Jennings, J. Peterson, and M. Watson
[15] RFC 791, Internet Protocol, STD 5, J. Postel
[16] RFC 2460, Internet Protocol, Version 6 (IPv6) Specification, S. Deering and R. Hinden
[17] ITU-T Recommendation E.164, The international public telecommunication numbering plan"
[18] RFC 3578, Mapping of Integrated Services Digital Network (ISDN), User Part (ISUP), Overlap Signalling
to the Session Initiation Protocol (SIP), G. Camarillo, A. Roach, J. Peterson, and L. Ong
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ISO/IEC 17343:2007(E)
[19] RFC 3311, The Session Initiation Protocol (SIP) UPDATE Method, J. Rosenberg
[20] RFC 3420, Internet Media Type message/sipfrag, R. Sparks
4 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 11572, RFC 3261 and the
following apply.
4.1
corporate telecommunication network
CN
sets of privately-owned or carrier-provided equipment that are located at geographically dispersed locations
and are interconnected to provide telecommunication services to a defined group of users
NOTE A CN can comprise a PISN, a private IP network (intranet), or a combination of the two.
4.2
gateway
entity that performs interworking between a PISN using QSIG and an IP network using SIP
4.3
IP network
network (unless otherwise stated, a corporate network) offering connectionless packet-mode services based
on the Internet Protocol (IP) as the network-layer protocol
4.4
media stream
audio or other user information transmitted in UDP packets, typically containing RTP, in a single direction
between the gateway and a peer entity participating in a session established using SIP
NOTE Normally a SIP session establishes a pair of media streams, one in each direction.
4.5
private integrated services network
PISN
CN or part of a CN that employs circuit-switched technology
4.6
private integrated services network exchange
PINX
PISN nodal entity comprising switching and call handling functions and supporting QSIG signalling in
accordance with ISO/IEC 11572:2000
5 Abbreviated terms
DNS Domain Name Service
IP Internet Protocol
PINX Private Integrated services Network eXchange
PISN Private Integrated Services Network
RTP Real-time Transport Protocol
SCTP Stream Control Transmission Protocol
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ISO/IEC 17343:2007(E)
SDP Session Description Protocol
SIP Session Initiation Protocol
TCP Transmission Control Protocol
TLS Transport Layer Security
TU Transaction User
UA User Agent
UAC User Agent Client
UAS User Agent Server
UDP User Datagram Protocol
6 Background and Architecture
During the 1980s, corporate voice telecommunications adopted technology similar in principle to Integrated
Services Digital Networks (ISDN). Digital circuit switches, commonly known as Private Branch eXchanges
(PBX) or more formally as Private Integrated services Network eXchanges (PINX) have been interconnected
by digital transmission systems to form Private Integrated Services Networks (PISN). These digital
transmission systems carry voice or other payload in fixed-rate channels, typically 64 Kbit/s, and signalling in
a separate channel. A technique known as common channel signalling is employed, whereby a single
signalling channel potentially controls a number of payload channels or bearer channels. A typical
arrangement is a point-to-point transmission facility at T1 or E1 rate providing a 64 Kbit/s signalling channel
and 23 or 30 bearer channels, respectively. Other arrangements are possible and have been deployed,
including the use of multiple transmission facilities for a signalling channel and its logically associated bearer
channels. Also, arrangements involving bearer channels at sub-64 Kbit/s have been deployed, where voice
payload requires the use of codecs that perform compression.
QSIG is the internationally-standardized message-based signalling protocol for use in networks as described
above. It runs in a signalling channel between two PINXs and controls calls on a number of logically
associated bearer channels between the same two PINXs. The signalling channel and its logically associated
bearer channels are collectively known as an inter-PINX link. QSIG is independent of the type of transmission
capabilities over which the signalling channel and bearer channels are provided. QSIG is also independent of
the transport protocol used to transport QSIG messages reliably over the signalling channel.
QSIG provides a means for establishing and clearing calls that originate and terminate on different PINXs. A
call can be routed over a single inter-PINX link connecting the originating and terminating PINX, or over
several inter-PINX links in series with switching at intermediate PINXs known as transit PINXs. A call can
originate or terminate in another network, in which case it enters or leaves the PISN environment through a
gateway PINX. Parties are identified by numbers, in accordance with either [17] or a private numbering plan.
This basic call capability is specified in [2]. In addition to basic call capability, QSIG specifies a number of
further capabilities supporting the use of supplementary services in PISNs.
More recently, corporate telecommunications networks have started to exploit IP in various ways. One way is
to migrate part of the network to IP using SIP. This might, for example, be a new branch office with a SIP
proxy and SIP endpoints instead of a PINX. Alternatively, SIP equipment might be used to replace an existing
PINX or PINXs. The new SIP environment needs to interwork with the QSIG-based PISN in order to support
calls originating in one environment and terminating in the other. Interworking is achieved through a gateway.
Interworking between QSIG and SIP at gateways can also be used where a SIP network interconnects
different parts of a PISN, thereby allowing calls between the different parts. A call can enter the SIP network at
one gateway and leave at another. Each gateway would behave in accordance with this International
Standard.
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ISO/IEC 17343:2007(E)
Another way of connecting two parts of a PISN would be to encapsulate QSIG signalling in SIP messages for
calls between the two parts. This is outside the scope of this International Standard but could be the subject of
future work.
This International Standard specifies signalling protocol interworking aspects of a gateway between a PISN
employing QSIG signalling and an IP network employing SIP signalling. The gateway appears as a PINX to
other PINXs in the PISN. The gateway appears as a SIP endpoint to other SIP entities in the IP network. The
environment is shown in Figure 1.
SIP IP network PISN
PINX
Proxy
PINX
Gateway
SIP SIP
PINX
End- End-
point point
Figure 1 — Environment
In addition to the signalling interworking functionality specified in this International Standard, it is assumed that
the gateway also includes the following functionality:
⎯ one or more physical interfaces on the PISN side supporting one or more inter-PINX links, each link
providing one or more constant bit rate channels for media streams and a reliable layer 2 connection
(e.g., over a fixed rate physical channel) for transporting QSIG signalling messages; and
⎯ one or more physical interfaces on the IP network side supporting, through layer 1 and layer 2 protocols,
IP as the network layer protocol and UDP [6] and TCP [5] as transport layer protocols, these being used
for the transport of SIP signalling messages and, in the case of UDP, also for media streams;
⎯ optionally the support of TLS [7] and/or SCTP [9] as additional transport layer protocols on the IP network
side, these being used for the transport of SIP signalling messages; and
⎯ a means of transferring media streams in each direction between the PISN and the IP network, including
as a minimum packetization of media streams sent to the IP network and de-packetization of media
streams received from the IP network.
NOTE: [10] mandates support for both UDP and TCP for the transport of SIP messages and allows optional support
for TLS and/or SCTP for this same purpose.
The protocol model relevant to signalling interworking functionality of a gateway is shown in Figure 2.
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ISO/IEC 17343:2007(E)
Interworking
function
SIP QSIG
layer 3
SIP
QSIG
IP network PISN
UDP/TCP/TLS/SCTP
IP
IP network PISN lower
lower layers layers
Figure 2 — Protocol model
In Figure 2, the SIP box represents SIP syntax and encoding, the SIP transport layer, and the SIP transaction
layer. The Interworking function includes SIP Transaction User (TU) functionality.
The gateway maps received QSIG messages, where appropriate, to SIP messages and vice versa and
maintains an association between a QSIG call and a SIP dialog.
A call from QSIG to SIP is initiated when a QSIG SETUP message arrives at the gateway. The QSIG SETUP
message initiates QSIG call establishment, and an initial response message (e.g., CALL PROCEEDING)
completes negotiation of the bearer channel to be used for that call. The gateway then sends a SIP INVITE
request, having translated the QSIG called party number to a URI suitable for inclusion in the Request-URI.
The SIP INVITE request and the resulting SIP dialog, if successfully established, are associated with the
QSIG call. The SIP 2xx response to the INVITE request is mapped to a QSIG CONNECT message, signifying
answer of the call. During establishment, media streams established by SIP and SDP are connected to the
bearer channel.
A call from SIP to QSIG is initiated when a SIP INVITE request arrives at the gateway. The gateway sends a
QSIG SETUP message to initiate QSIG call establishment, having translated the SIP Request- URI to a
number suitable for use as the QSIG called party number. The resulting QSIG call is associated with the SIP
INVITE request and with the eventual SIP dialog. Receipt of an initial QSIG response message completes
negotiation of the bearer channel to be used, allowing media streams established by SIP and SDP to be
connected to that bearer channel. The QSIG CONNECT message is mapped to a SIP 200 OK response to
the INVITE request.
Annex B gives examples of typical message sequences that can arise.
7 General Requirements
In order to conform to this International Standard, a gateway SHALL support QSIG in accordance with [2] as a
gateway and SHALL support SIP in accordance with [10] as a UA. In particular, the gateway SHALL support
SIP syntax and encoding, the SIP transport layer, and the SIP transaction layer in accordance with [10]. In
addition, the gateway SHALL support SIP TU behaviour for a UA in accordance with [10] except where stated
otherwise in 8, 9, and 10 of this International Standard.
NOTE 1 [10] mandates that a SIP entity support both UDP and TCP as transport layer protocols for SIP messages.
Other transport layer protocols can also be supported.
The gateway SHALL also support SIP reliable provisional responses in accordance with [11] as a UA.
NOTE 2 [11] makes provision for recovering from loss of provisional responses (other than 100) to INVITE requests
when using unreliable transport services in the IP network. This is important for ensuring delivery of responses that map to
essential QSIG messages.
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ISO/IEC 17343:2007(E)
The gateway SHALL support SDP in accordance with [8] and its use in accordance with the offer/answer
model in [12].
Clause 9 also specifies optional use of the Privacy header in accordance with [13] and the P-Asserted-Identity
header in accordance with [14].
The gateway SHALL support calls from QSIG to SIP and calls from SIP to QSIG.
SIP methods not defined in [10] or [11] are outside the scope of this International Standard but could be the
subject of other standards for interworking with QSIG, e.g., for interworking in support of supplementary
services.
As a result of DNS lookup by the gateway in order to determine where to send a SIP INVITE request, a
number of candidate destinations can be attempted in sequence. The way in which this is handled by the
gateway is outside the scope of this International Standard. However, any behaviour specified in this
International Standard on receipt of a SIP 4xx or 5xx final response to an INVITE request SHOULD apply only
when there are no more candidate destinations to try or when overlap signalling applies in the SIP network
(see 8.2.2.2).
8 Message Mapping Requirements
8.1 Message Validation and Handling of Protocol Errors
The gateway SHALL validate received QSIG messages in accordance with the requirements of [2] and
SHALL act in accordance with [2] on detection of a QSIG protocol error. The requirements of this Clause for
acting on a received QSIG message apply only to a received QSIG message that has been successfully
validated and that satisfies one of the following conditions:
⎯ the QSIG message is a SETUP message and indicates a destination in the IP network and a bearer
capability for which the gateway is able to provide interworking; or
⎯ the QSIG message is a message other than SETUP and contains a call reference that identifies an
existing call for which the gateway is providing interworking between QSIG and SIP.
The processing of any valid QSIG message that does not satisfy any of these conditions is outside the scope
of
...
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