1、 ECMA-355 3rdEdition / June 2008 Corporate Telecommunication Networks - Tunnelling of QSIG over SIP Ecma International Rue du Rhne 114 CH-1204 Geneva T/F: +41 22 849 6000/01 www.ecma-international.org IW ECMA-355.doc 6/24/2008 4:55:00 PM Corporate Telecommunication Networks - Tunnelling of QSIG over
2、 SIP Standard ECMA-355 3rdEdition / June 2008 . Introduction This Standard is one of a series of Ecma Standards defining the interworking of services and signalling protocols deployed in corporate telecommunication networks (CNs) (also known as enterprise networks). The series uses telecommunication
3、 concepts as developed by ITU-T and conforms to the framework of International Standards on Open Systems Interconnection as defined by ISO/IEC. This particular Standard specifies tunnelling of QSIG over the Session Initiation Protocol (SIP). This enables calls between “islands“ of circuit switched n
4、etworks that use QSIG signalling to be interconnected by an IP network that uses SIP signalling without loss of QSIG functionality. This standard facilitates the introduction of enhanced SIP and SDP functionality that was specified after publication of the early editions of this standard. These enha
5、ncements include payload encryption and mechanisms to negotiate SDP capabilities. The changes in this 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
6、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 Standard is based upon the practical experience of Ecma member companies and the results of their active
7、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. This Ecma Standard has been adopted by the General Assembly of June 2008. - i - Table of contents 1 Scope 1 2
8、 Normative references 1 3 Terms and definitions 2 3.1 External definitions 2 3.2 Other definitions 2 3.2.1 Corporate telecommunication Network (CN) 2 3.2.2 Egress gateway 2 3.2.3 Gateway 2 3.2.4 Ingress gateway 2 3.2.5 IP network 2 3.2.6 Media stream 2 3.2.7 Private Integrated Services Network (PISN
9、) 2 3.2.8 Private Integrated services Network eXchange (PINX) 3 4 Abbreviations and acronyms 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
10、 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 Reject
11、ing 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 - ii - 6.8 QSIG connectionless message ha
12、ndling 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 Changes fr
13、om early editions (informative) 17 - 1 - 1 Scope This Standard specifies tunnelling of “QSIG“ over the Session Initiation Protocol (SIP) within a corporate telecommunication network (CN). “QSIG“ is a signalling protocol that operates between Private Integrated services Network eXchanges (PINX) withi
14、n 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 servic
15、es) 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 1. SIP is an application layer protocol for establishing
16、, terminating and modifying multimedia sessions. It is typically carried over IP 4, 6. Telephone calls are considered as a type of multimedia session where just audio is exchanged. SIP is defined in 9. Often a CN comprises both PISNs employing QSIG and IP networks employing SIP. A call or call indep
17、endent 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
18、in 3. 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 cap
19、abilities across the IP network. It achieves this by tunnelling QSIG messages within SIP requests and responses in the context of a SIP dialog. The tunnelling of QSIG through a public IP network employing SIP is outside the scope of this specification. However, the functionality specified in this sp
20、ecification is in principle applicable to such a scenario when deployed in conjunction with other relevant functionality (e.g., address translation, security functions, etc.). This specification is applicable to any interworking unit that can act as a gateway between a PISN employing QSIG and a corp
21、orate IP network employing SIP, with QSIG tunnelled within SIP requests and responses. 2 Normative references 1 International Standard ISO/IEC 11572 “Information technology - Telecommunications and information exchange between systems - Private Integrated Services Network - Circuit mode bearer servi
22、ces - Inter-exchange signalling procedures and protocol“ (also published by Ecma as Standard ECMA-143). 2 International Standard ISO/IEC 11582 “Information technology - Telecommunications and information exchange between systems - Private Integrated Services Network - Generic functional protocol for
23、 the support of supplementary services - Inter-exchange signalling procedures and protocol “ (also published by Ecma as Standard ECMA-165). 3 International Standard ISO/IEC 17343 “Information technology - Telecommunications and information exchange between systems - Corporate telecommunication netwo
24、rks - Signalling interworking between QSIG and SIP - Basic services“ (also published by Ecma as Standard ECMA-339). 4 J. Postel, “Internet Protocol“, RFC 791. 5 Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels“, BCP 14, RFC 2119. 6 S. Deering, R. Hinden, “Internet Protocol, Ver
25、sion 6 (IPv6)“, RFC 2460. 7 Donovan, S., “The SIP INFO Method“, RFC 2976. - 2 - 8 Zimmerer, E., Peterson, J., Vemuri, A., Ong, L., Audet, F., Watson, M. and M. Zonoun, “MIME media types for ISUP and QSIG objects“, RFC 3204. 9 J. Rosenberg, H. Schulzrinne, et al., “SIP: Session initiation protocol“,
26、RFC 3261. 10 J. Rosenberg, H. Schulzrinne, et al., “An Offer/Answer Model with the Session Description Protocol (SDP)“, RFC 3264. 11 Rosenberg, J., “The Session Initiation Protocol (SIP) UPDATE message”, RFC 3311. 12 J. Rosenberg, H. Schulzrinne, P. Kyzivat, “Indicating User Agent Capabilities in th
27、e Session Initiation Protocol (SIP)”, RFC 3840. 3 Terms and definitions In this document, the key words “MUST“, “MUST NOT“, “REQUIRED“, “SHALL“, “SHALL NOT“, “SHOULD“, “SHOULD NOT“, “RECOMMENDED“, “MAY“, and “OPTIONAL“ are to be interpreted as described in 5 and indicate requirement levels for compl
28、iant SIP implementations. For the purposes of this document, the following definitions apply. 3.1 External definitions The definitions in 1 and 9 apply as appropriate. 3.2 Other definitions 3.2.1 Corporate telecommunication Network (CN) Sets of privately-owned or carrier-provided equipment that are
29、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. 3.2.2 Egress gateway A gateway handling a QSIG call or call-independent
30、signalling connection established in the direction IP network to PISN. 3.2.3 Gateway An entity that behaves as a QSIG Transit PINX with QSIG carried over a circuit-switched link within a PISN on one side and QSIG tunnelled over SIP within an IP network on the other side. 3.2.4 Ingress gateway A gate
31、way handling a QSIG call or call-independent signalling connection established in the direction PISN to IP network. 3.2.5 IP network A network, unless otherwise stated a corporate network, offering connectionless packet-mode services based on the Internet Protocol (IP) as the network layer protocol.
32、 3.2.6 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 directi
33、on. 3.2.7 Private Integrated Services Network (PISN) A CN or part of a CN that employs circuit-switched technology and QSIG signalling. - 3 - 3.2.8 Private Integrated services Network eXchange (PINX) A PISN nodal entity comprising switching and call handling functions and supporting QSIG signalling
34、in accordance with 1. 4 Abbreviations and acronyms CN corporate telecommunication network IP Internet Protocol PINX Private Integrated services Network eXchange PISN Private Integrated Services Network QSIG Signalling system for the Q reference point RTP Real-time Transport Protocol SDP Session Desc
35、ription Protocol SIP Session Initiation Protocol TCP Transmission Control Protocol TLS Transport Layer Security UA User Agent UAC User Agent Client UAS User Agent Server UDP User Datagram Protocol URI Universal Resource Identifier 5 Background and architecture 5.1 Architecture This document concerns
36、 the case of a call or call independent signalling that originates at a user connected to a PISN employing QSIG, traverses an IP network employing SIP, and terminates at a user connected to another (or another part of the same) PISN. This can be achieved by employing a gateway at each boundary betwe
37、en a PISN employing QSIG and an IP network employing SIP, as shown in Figure 1. Figure 1 Call from QSIG via SIP to QSIG Each gateway can provide interworking as specified in 3. This provides a basic call capability. However, 3 only specifies interworking for QSIG basic call, as specified in 1. Many
38、of the other capabilities of QSIG (support for supplementary services and additional network features) as specified in other standards and in vendor-specific specifications are not covered. Some of these additional capabilities of QSIG are suitable for interworking with SIP and might be the subject
39、of future Standards or other specifications. Other capabilities of QSIG are unsuitable for interworking with SIP because corresponding capabilities do not exist in SIP or are achieved in ways that are - 4 - incompatible with QSIG. Therefore interworking at a gateway between QSIG and SIP will be limi
40、ted to those QSIG capabilities that have sufficiently compatible equivalents in SIP. Each capability requires special implementation in the gateway, and therefore a typical gateway might provide interworking for only a subset of capabilities for which interworking is feasible.The result of this is t
41、hat there will be a loss of capability on a call or call independent signalling from QSIG to SIP or vice versa. For a case similar to that shown in Figure 1 there will likewise be a loss of capability. This can be compounded if the two gateways are of different types, since only those capabilities c
42、ommon to both gateways will survive end-to-end.The solution is to tunnel QSIG messages through the IP network within SIP messages so that no end-to-end QSIG capabilities are lost. One of the two gateways originates a SIP dialog to the other gateway. SIP messages within the dialog are used to tunnel
43、QSIG messages. Through the use of SDP 10, the dialog also establishes a session in which media streams carry user information (e.g., speech) between the two QSIG gateways, if required. The two gateways act as QSIG Transit PINXs, which relay QSIG messages with little or no modification. In a conventi
44、onal PISN employing QSIG, two PINXs are connected by means of an inter-PINX link, which comprises a signalling channel (carrying QSIG messages) and one or more user information channels carrying speech, modem information or data. With the tunnelling solution, the IP network provides the inter-PINX l
45、ink between the two gateways acting as Transit PINXs. The tunnel provided by SIP for QSIG messages acts as the signalling channel and the media streams act as the user information channels. This document covers the case where a single dialog between two gateways is used for a single QSIG call or cal
46、l independent signalling connection, as specified in 2. This means that the dialog is established when the QSIG call or call independent signalling connection is established and cleared down when the QSIG call or call independent signalling connection is cleared down. An enhanced scenario in which a
47、 single SIP dialog is maintained long term and used to tunnel a multiplicity of QSIG calls or call independent signalling connections, with the possibility of multiple QSIG calls or call independent signalling connections being in progress at any one time, is outside the scope of this document. This
48、 document also covers call-independent connectionless transport. 5.2 Basic operation When a gateway (the ingress gateway) receives a QSIG call or call-independent signalling connection establishment request (QSIG SETUP message) from the PISN, it needs to generate a SIP INVITE request using a Request
49、-URI that will route the request to an appropriate egress gateway. The Request-URI must be derived in some way from the required destination of the QSIG call or call-independent signalling connection (as indicated in the Called party number information element of the QSIG SETUP message). The Request-URI can explicitly identify the egress gateway or it can simply identify the required destination. The first case is likely to require some sort of look-up capability in the ingress gateway, the configuration of which is o
