1、ITU-T RECMN*Qm7b8 95 4862591 0635b02 ObT INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU DIGITAL SU BSC R I B ER SIGNALLING SYSTEM No. 1 (2.768 (1 0/95) SIGNALLING INTERFACE BETWEEN AN INTERNATIONAL SWITCHING CENTRE (ISC) AND AN ISDN SATELLITE SUBNETWORK I
2、TU-T Recommendation Q.768 (Previously “CCIlT Recommendation”) ITU-T RECMN*Q.ibfl 95 m YBb2591 Ob15b03 TTb m FOREWORD The IT-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The IT-T is responsible for studying technical, operating
3、and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the IT-T Study Groups which, in their turn
4、, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation 4.768 was prepared by ITU-T Study Group 11 (1993-1996) and was approved under the W
5、TSC Resolution No. 1 procedure on the 17th of October 1995. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1996 All rights reserved. No part of this publication may be r
6、eproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. ITU-T RECMN*Q.768 95 = 48625711 Ob115b04 732 CONTENTS Scope References Definitions Abbreviations . Architectural model for interworking Funct
7、ions of the signalling system . 6.1 Call Set-up . 6.2 Call release 6.3 Maintenance Signalling interface definition 7.1 Simplified Message Transfer Part . 7.2 Satellite ISDN User Part (SIUP) definition 8.1 Elements for layer to layer communication 8.2 Elements for peer-to-peer communications 8.3 Sate
8、llite ISDN User Pari . Specification of SiUP - SDL diagrams . Annex A . Figures on Basic Call Control Signalling Procedures . Recommendation Q.768 (10/95) Page 1 1 2 2 3 4 4 4 4 4 5 6 6 6 8 21 42 I SUMMARY This Recommendation describes the essential functions, procedures, and messages required for s
9、ignalling between an International Switching Centre (ISC) and a digital interface to an ISDN satellite subnetwork. This signalling allows and appropriately equipped ISDN satellite subnetwork to perform on-demand bandwidth allocation for 64 kbit/s unrestricted and multirate ISDN calls, and protocol c
10、onversion for those calls which contain protocols that would otherwise experience throughput degradation due to the transmission delay of a satellite link. The framework of this signalling interface allows for growth for the potential inclusion of future ISDN network capabilities at the internationa
11、l interface. INTRODUCTION This Recommendation describes the essential functions, procedures, and messages required for signalling between an International Switching Centre (ISC) and a digital interface (herein referred to as a Satellite Connection Manager (SCM) contained in an ISDN satellite subnetw
12、ork. This signalling can be used to facilitate the efficient support of existing and future ISDN services at the international interface, especially for 64 kbit/s unrestricted and multirate ISDN calls. Two representative functions supported by this signalling are on-demand connection management and
13、protocol conversion. This new signalling does not change the fixed mapping provided between outbound trunks at the ingress of the satellite subnetwork (at the outgoing international exchange) and inbound trunks at the egress of the subnetwork (at the incoming international exchange), i.e. the satell
14、ite subnetwork does not perform switching. 11 Recommendation Q.768 (10/95) - ITU-T RECMNwQ.768 95 m 486259L ObL560b 705 Recommendation Q.7S SIGNALLING INTERFACE BETWEEN AN INTERNATIONAL SWITCHING CENTRE (ISC) AND AN ISDN SATELLITE SUBNETWORK (Geneva, 1995) 1 Scope The procedures described in this Re
15、commendation are for a signalling relation between an International Switching Centre (ISC) and a digital interface to a satellite subnetwork, referred to as a Satellite Connection Manager (SCM). This Recommendation is specifically concerned with the transfer of signalling information between the ISC
16、 and the SCM, and with the procedures followed at the ISC for establishing and clearing calls routed through the satellite subnetwork. The signalling information transferred by the ISC is derived from Signalling System No. 7 signalling. The signalling information transferred by the SCM to the ISC is
17、 derived from control elements in the satellite subnetwork. This signalling supports the ISDN connection types of 64 kbiis unrestricted, 2 x 64 kbiis unrestricted, 384 kbitfs unrestricted, 1536 kbitfs unrestricted, and 1920 kbit/s unrestricted. This signalling is also defined to support the connecti
18、on types of speech, 3.1 kHz audio, and 64 kbitfs unrestricted preferred on a secondary basis: speech and 3.1 kHz connection types are only supported (uncompressed) in the case of fallback; the support of circuit multiplication functions within the SCM is for further study. Should speech and 3.1 kHz
19、audio calls be carried across the satellite subnetwork, it is not the responsibility of the satellite subnetwork to provide echo control (i.e. follow normal ISUP procedures for placement of echo control. This Recommendation is not concerned with specifying the SCM, but on the signalling needed betwe
20、en an ISC and a SCM. This Recommendation is concerned with the international ISDN interface. The relationship of this Recommendation to national networks is for further study. 2 References The following Recommendations and other references contain provisions which, through reference in this text, co
21、nstitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision: all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of
22、 the Recommendation and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. - CCITT Recommendation Q.33 (1988), Protection against the effects of faulty transmission on groups of Circuits. - ITU-T Recommendation Q.50 (1993), Signalling between C
23、ircuit Multiplication Equipments (CME) and International Switching Centres (ISC). - IT-T Recommendation Q.704 (1993), Signalling System No. 7 - Signalling network functions and messages. - - CCITT Recommendation Q.710 (1988), Simplified MTP version for small systems. CCIIT Recommendation 4.724 (1988
24、), Specifications of Signalling System No. 7 - Signalling procedures. IT-T Recommendation Q.753 (1993). Signalling System No. 7 managementfunctions MRVT, SRVT and CVT and definition of the OMASE-user. 1T-T Recommendation Q.763 (19931, Formats and Codes of the ISDN User Part of Signalling System No.
25、7. - - Recommendation Q.768 (10/95) 1 ITU-T RECNN*Q=768 95 4862593 ObL.5607 643 - - ITU-T Recommendation 4.764 (1993), Signalling System No. 7 - ISDN User Part signalling procedures. ITU-T Recommendation 4.931 (1993), Digital subscriber Signalling System No. 1 (DSS I) - ISDN user- network interface
26、layer 3 specification for basic call control. 3 Definitions For the purposes of this Recommendation, the following definitions apply: 3.1 interworking: Interworking refers to the portion of the ISC call control that includes the transfemng of certain information elements from the ISDN-UP messages to
27、 the satellite subnetwork. The interworking enables a satellite subnetwork to efficiently manage its transmission resources or improve the transmission performance of certain services. 3.2 equipment at an earth station and an ISC, and which provides certain functions related to ISDN calls. satellite
28、 connection manager (SCM): A type of equipment which exists between the satellite access 3.3 trunks on a reduced number of transmission channels. circuit multiplication equipment (CME): A type of equipment which permits concentration of a number of 3.4 protocol conversion function (PCF): A specific
29、interworking function performed on a communications protocol for the purpose of replacing the protocol with a more appropriate protocol for a particular transmission channel. In a satellite context, PCF consists of terminating a user protocol at the source SCM and replacing it with a satellite- opti
30、mized protocol over the satellite link, and subsequently reintroducing the original user protocol at the destination SCM in a manner transparent to the end user. 3.5 channel: Used herein to refer to a 64 kbit/s digital circuit. 3.6 between the ISC and the SCM. Trunks are otherwise known as access ci
31、rcuits. trunk; access circuit: A bidirectional connection consisting of a forward channel and a backward channel 3.7 unit of corresponding earth stations. transmission channel; bearer circuit: One channel of the connection between the transmit unit and receive 3.8 Q.768: The signalling interface tha
32、t exists between the ISC and the SCM. 3.9 satellite subnetwork: A satellite network which exists transparent to the end (access) users on either side of the connection. The satellite subnetwork is bounded by two ISDNs in this case. In an ISDN context, a subnetwork may be transparent to or integrated
33、 with the SS No.7 signalling. 3.10 trunk subgroup; trunk group: A set of trunks, between two ISCs, that serves the same connection type(s). 4 Abbreviations For the purposes of this Recommendation the following abbreviations apply. NOTE - Signalling System No. 7 message abbreviations are described in
34、 Recommendations Q.763 and Q.704: CCH Continuity Check CIC Circuit Identification Code CME Circuit Multiplication Equipment HLC High Layer Compatibility IS c International Switching Centre ISC-DPC ISC Destination Point Code ISC-OPC ISC Originating Point Code ISUP ISDN User Part 2 Recommendation Q.76
35、8 (10/95) LLC MTP PCF SCM SJSJP SS No. 7 ITU-T RECNN*f2.768 95 D 4862591 Ob15bCl8 588 Low Layer Compatibility Message Transfer Part Protocol Conversion Function Satellite Connection Manager Satellite ISDN User Part Signalling System No. 7 5 Architectural model for interworking Figure 1 illustrates t
36、he interworking model for 4.768 signalling. Only signalling links are illustrated. The SCM exists within the satellite subnetwork, and is supported by the signalling across the 4.768 interface. Trunk groups (not shown) exist between the ISC and the SCM, and the SCM maps trunks to satellite transmiss
37、ion channels. Some 4.768 signalling elements are derived from the SS No. 7 messages. The reference configuration shown in Figure 1 corresponds closely to the reference configuration for ISDN-ISDN interworking via a transit network. The ISDN satellite subnetwork functions as a transit network and per
38、forms no switching (i.e. the correspondence between inter-ISC trunks is preserved). The SCMs function as access points to this transit network. Each SCM may have Q.768 signalling links to one or more ISCs; similarly, each ISC may have 4.768 signalling links to one or more SCMs. SS No. 7 ISDN Satelli
39、te Subnetwork ,-_-_ TI 166760-Wd01 FIGURE VQ.768 Architectural del for interworking Recommendation Q.768 (10/95) 3 ITU-T RECMN*Q.768 95 m 4862591 063560% 414 If a CME is deployed between the ISC and the satellite subnetwork, the Q.768 signalling system and the associated functions cannot be used for
40、 the trunks served by the CME. A different trunk group than that served by the CME is served by the SCM. At call Set-up time, the ISC makes the appropriate selection based on the bearer service required. The functions of the SCM are distinct from the CME. The CME and the SCM can coexist in the same
41、network, but they are served by separate channels. An implication of this is that speech and 3.1 kHz audio calls, if they are routed through the SCM (due to either a lack of CME capacity or the support of fallback), will be uncompressed through the satellite subnetwork. At some point, CME functions
42、may be included in SCM. It is for further study what protocol elements must be added to this Recommendation to support CME functions. In this case, the need for a separate Q.50 signalling interface and trunk separation between the two equipments would be removed. 6 Functions of the signalling system
43、 The signalling system comprises the ISC. the SCM, and a digital channel between the two. The basic signalling function is to support the on-demand establishment of physical connections within the satellite subnetwork. Another signalling function is the provision of information to the satellite subn
44、etwork for the purpose of performing protocol conversion on selected ISDN calls routed through the satellite subnetwork. 6.1 Call Set-up The signalling system provides for the following functions: a) on-demand call Set-up; b) fixed-assignment channel configuration (e.g. insertion of protocol convers
45、ion function); c) transfer of information elements from ISC to SCM; d) update of call parameters during call Set-up. This includes fallback initiated by either the terminal or the network (including HLC selection), and out-of-band LLC (see Annex J/Q.93 i) negotiation. 6.2 Call release The signalling
46、 system provides for call release of the satellite resources when the SS No. 7 network releases the call. 6.3 Maintenance The signalling system includes means to notify the ISC of call failures of active calls, and of any satellite subnetwork related or signalling related failures that prohibit the
47、use of the satellite subnetwork. The use of MRVT to verify MTP routing between an ISC and an SCM may be useful. However, since there will be limited routing, the addition of MRVT for MTP supporting SIUP is left as an implementation option. 7 Signalling interface definition This clause describes the
48、protocol architecture at the Q.768 interface. The protocol architecture to support the signalling functions is illustrated in Figure 2. Signalling System No. 7 is used in the national and international network at the ISC. The protocols operating over the Q.768 interface are 4.710 MTP and the Satelli
49、te ISDN User Part (SIUP). This protocol stack supports communication between the call control functions at the ISC and the SCM. 4 Recommendation Q.768 (10/95) ITU-T RECMN*Q-7b8 95 4862593 ObL5bLO L3b SIUP 1t I (2.710 I II I II I I I Ky MTP The SIUP, defined in clause 8, consists of signaling procedures for the Set-up and release of international ISDN connections over an on-demand ISDN satellite subnetwork, The SIW functions are similar to those of SS No. 7 ISUP (see Recommendation Q.764). A simplified Message Transfer Part (MTP), defined in Recommendation 4.710, i
