1、CCITT RECMN*E=L72 92 48b2591 0578575 523 I NTE R NAT I O N AL TE LECOM M U N I CAT I ON U N I ON CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COMMITTEE TELEPHONE NETWORK AND ISDN OPERATIONy NUMBERINGy ROUTING AND MOBILE SERVICE E.172 (1 0/92) ISDN ROUTING PLAN i Recommendation E.172
2、CCITT RECMN*E=L72 92 4862573 O578576 4bT FOREWORD The CCIT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCIT is responsible for studying technical, operating and tariff questions and issuing Recommendation
3、s on them with a view to standardizing telecommunications on a worldwide basis. The Plenary Assembly of CCIT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups, The approval of Recommendations by the members of CCIT between Plenar
4、y Assemblies is covered by tbe procedure laid down in CCIIT Resolution No. 2 (Melbourne, 1988). Recommendation E.172 was prepared by Study Group II and was approved under the Resolution No. 2 procedure on the 30th October 1992. CcI- NOTE In this Recommendation, the expression “Administration” is use
5、d for conciseness to indicate both a telecommunication administration and a recognized private operating agency. O IT 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, witho
6、ut permission in writing from the ITU. CCITT RECflN*E-L72 92 = 48b259L 0578577 3Tb M Recommendation E.172 ISDN ROUTING PLAN (I 992) 1 Introduction and scope 1.1 ISDN capabilities are currently being introduced into national and international networks. ISDN provides access to a wide range of services
7、, each of which must be supported by a minimum level of network capabilities. For each service requested by a user, the network must provide the appropriate switching, signalling and transmission capabilities required to successfully complete the call. In practical ISDN implementations some of the I
8、SDN functions will be implemented within the same network elements whereas other ISDN functions, such as those required for interworking, packet handling, etc. will be implemented in “special” network elements. 1.2 ensure that ISDN services can be routed effectively and efficiently by the various ne
9、tworks which support them. The purpose of this Recommendation is to provide network operators with the information necessary to 1.3 The Recommendation establishes basic principles on which to base network design and routing decisions. It provides detailed information on the mapping between ISDN bear
10、er services, ISDN connection types and network capabilities (e.g. transmission links, signalling systems, etc.) required to support a call. Guidance on the conveyance and use of routing information within network components is also included. Further information on the routing implications of network
11、 interworking is included at Annex C. 1.4 The Recommendation is intended to provide a single definitive reference Recommendation for ISDN routing. It supersedes earlier ISDN routing Recommendations, specifically Recommendation E.172 (1988) - Call routing in the ISDN era, and Recommendation 1.335 (19
12、88) - ISDN routing principles. 1.5 The scope of the Recommendation is limited to circuit and packet switched bearer services. It is further limited to services supported by Recommendation Q.767. Broadband services routing requirements are for further study. 2 References and related Recommendations T
13、he related Recommendations and their relationship to Recommendation E.172 are depicted below in Figure lE.172. 3 ISDN routing principles 3.1 customer satisfaction and network optimization. The following basic ISDN routing principles are recommended to assist in managing the trade-off between a) b) u
14、tilize network resources efficiently: complete as many calls as possible; - match network capability to service demand; minimize the use of “overmatching” network capability; minimize the number of links in a route; - - Recommendation E.172 (10/92) 1 2 I I ISDN basic description I.lOaSeries Recs. te
15、lecommunication services I .2-Series Recs. Recs. (2.931, Q.761, . . . . . . . . . . . . Recs. E.164, E.165, E.166, x.121 Recs. E.170, E.171, Reference connections Recs. G.801, To20223081 FIGURE 1E.172 c) adhere to network performance parameters: - - transmission quality; - error rates; delay (call s
16、et up delay, transfer delay, post-dialling delay); - throughput; - availability; d) minimize translation complexity; e) f) minimize digit analysis and manipulation; ensure efficient access to special network functionalities, such as: - signalling systems; - modems; - echo control devices; - mobile i
17、nterfaces; - databases; g) avoid “non-standard” arrangements. Recommendation E.172 (10192) 4 The concept of service defined network connections 4.1 In the Public Switched Telephone Network (PSTN) environment a single level of network performance is assured. That level of network performance ensures,
18、 within certain parameters, that services such as speech, facsimile and data will be supported. No standard means exists in the PSTN, on a call-by-call basis, to influence the type or Capability of network components which are selected by the network to establish a connection. Routing in the PSTN is
19、 basically performed through analysis of the called address to allow selection of the chain of physical trunk routes to the destination. Many techniques have been introduced to improve completion rates and efficiencies (see Recommendation E.170), and all are based on finding an available path to a d
20、estination using the called address, with no consideration given to service variables. 4.2 ISDN introduces the concept of customer selected service requirements on a call-by-call basis. Each telecommunication service demands a predefined minimum level of network capability to support the connection.
21、 Networks are in a constant state of evolution, and consequently contain varying levels of capabilities. The matching between the telecommunication service request and network component capability is a new dimension of routing introduced by ISDN. 4.3 Telecommunication services must be viewed from tw
22、o perspectives: - feature capabilities as seen by the customer; - network, operational and commercial attributes as seen by the service providers. 4.4 From a network routing perspective, the physical requirements of a network connection may be determined through analysis of parameters (assessed in d
23、etail in 5 7). Bearer service definitions dictate the minimum capability for information transfer between ISDN access points. The service aspect of ISDN routing is based primarily on the bearer service requested by the customer. ISDN bearer services are defined in Recommendation 1.230. 4.5 routing p
24、rocess. This Recommendation provides guidance on the incoworation of service requirements into the network 5 Routing process 5.1 General 5.1.1 This subsection describes the ISDN routing process. Information generated and processed from the originating terminal equipment, signalling links and switchi
25、ng nodes is discussed. The basic reference for the ISDN architecture is taken from Recommendation 1.324. 5.1.2 terminal equipment and the terminating terminal equipment or network service node. The routing process is the sequence of functions required to establish a connection between the originatin
26、g 5.2 User-Network Interface 5.2.1 the terminai equipment the following information: The user initiates a request for service through ISDN capable terminal equipment. The user provides, through - service request details (including supplementary service); - called address: - calling address; - other
27、information required for call set up. 5.2.2 standard) call setup message which is ransmitted to the originating local exchange. The terminal equipment converts this information into a Recommendation Q.931 (network layer protocol Recommendation E.172 (10/92) 3 5.3 Originating local exchange 5.3.1 The
28、 originating local exchange performs the most critical function in ISDN call routing. That function is to assemble essential cail routing information, which is uniquely available to it, into an information package which will be used by all subsequent exchanges to make the required routing decisions.
29、 5.3.2 The originating locai exchange uses: - - - environmental and administrative conditions; cail specific information provided in the Recommendation Q.93 1 cail setup message; customer subscription profile data in exchange memory; to establish: - - the route treatment of that specific call (i.e.
30、route selection, block, etc.); the routing parameters which are associated with the call for use at subsequent exchanges in the connection. 5.3.3 The originating local exchange therefore defines the minimum network resources (switching, signalling, transmission) which are needed to support the servi
31、ce request. These cairouting parameters are transported through the network via SS No. 7. 5.3.4 contained in 0 7. Details of ISDN call routing parameters and their application andor generation at various exchanges are 5.4 Transit exchanges (national and international) 5.4.1 Each transit exchange in
32、the route sequence will receive the routing parameters generated by the previous exchange. These parameters will be used as the basis for selecting an appropriate outgoing route. In addition, routing parameters may be added to or modified to update such information as connection history. 5.4.2 condi
33、tions encountered in the network. This process continues until either the terminating local exchange is reached or the call is failed due to 5.4.3 may be used for routing purposes: The incoming and outgoing Initial Address Message (IAM) contains the following parameter fields which - nature of conne
34、ction indicators; - - calling party?s category; - transmission medium requirement (TMR); - calied party number; - user service information (USI); - forward call indicators (including ISUP preference indicator); transit network selection (for further study). 5.4.4 systems capability for the cail. The
35、se parameters are The IAM message may contain other parameters whose presence may influence the choice of signalling - call reference; - calling party number; - optional forward call indicators; - redirecting number; 4 Recommendation E.172 (10D2) CCITT RECMN*E.172 92 m 4862591 0578581 827 m National
36、 element Nodes Links 4 4 - CUG interlock code; International element National element Nodes Links Nodes Links 5 4 4 4 - connection request; - user-to-user information; - access transport. In the international network, the TMR is set to the value that represents the minimum network capability to 5.4.
37、5 provide the requested service and is not modified. 5.4.6 in the international network. The parameters listed within this sub-section contain all the signalling information needed to perform routing 5.4.7 In summary it should be noted that while many new parameters are potentially involved in selec
38、ting an ISDN route, most calls can be successfully completed by matching the service request with idle facilities which are capable of supporting it. 6 Network structure 6.1 Circuit switched services 6.1.1 In the ISDN era, it is suggested that a) b) the network stmcture should be non-hierarchical; f
39、or call routing purposes the network can be sub-divided into national and international connection elements; the national element being sub-divided into local and tmnk if appropriate; Administrations should be free to change their own call routing arrangements providing they are still within the gui
40、delines outlined in this plan; the routing concepts outlined in Recommendation E.170 can apply in any network element (e.g. local, national or international) but only by agreement should they be used across a connection element boundary. c) d) 6.1.2 The network structure for ISDN has been taken from
41、 Recommendation G.801 which provides a hypothetical reference connection for the digital environment. From that Recommendation the maximum allocations established for circuit switched services are as shown in Table 1E.172. TABLE 1E.172 Maximum allocation of nodes and links for circuit switched servi
42、ces in ISDN 6.1.3 assumed that ail special and manual nodes will be taken from the national links and node allocation. The limiting case on any routing configuration will be when an international extension is required. It is 6.2 Packet switched services 6.2.1 elements (or packet switched in the D-ch
43、annel) and three packet switched elements as shown in Table 2E.172. For international packet switched calls in ISDN the network structure consists of two circuit switched Recommendation E.172 (10/92) 5 CCITT RECMN*E.L72 92 W 4862573 0578582 7b3 National element International element TABLE uE.172 Nat
44、ional element Cicuit switched (Note) Packet Packet switched Packet Circuit switched switched switched (Note) Nore -Could be packet switched in the D-channel. National element Circuit switched packet (Note 1) Nodes Links Nodes Links 4 4 Further study (Note 3) 6.2.2 The network structure for the packe
45、t switched elements has been taken from Recommendation X.92, which provides a hypothetical reference connection for public synchronous data networks, and Recommendation G.801 for the national cicuit switched part of the connection. From these Recommendations the maximum allocations established are a
46、s shown in Table 3E. 172. Intemational National element element Circuit switched (Note 1) Packet switched Packet switched Nodes Links Nodes Links Nodes Links 5 4 Further study 4 4 (Note 2) (Note 3) TABLE 3E.172 Maximum allocation of nodes and links for packet switched services in ISDN Note I - Could
47、 be packet switched in the D-channel. Nofe2-The maximum allocation of nodes and links in the international element of PSPDN is 5 and 4 respectively. The allocation for ISDN is for further study. Note 3 -The maximum allocation of nodes and links in the national ISDN circuit switched element is 4. The
48、 allocation for packet switched calls is for futher study. 7 Information analysis The type of information that requires analysis for call routing purposes will vary depending on the progress of the cai1 through the network. Consequently this will place different requirements on the network nodes as
49、shown in Table 4E. 172. Ail the functions in Table 4E.172 need not be available at all network nodes, but a minimum set will be required to ensure efficient, and effective routing. 7.1 Calling party Depending on the calling partys service arrangement, a check of authorized and unauthorized service requests will be performed before the outgoing route is selected. 6 Recommendation E.172 (10/92) CCITT RECMN*E.L72 92 4862573 0578583 bTT = Originating exchange TABLE 4E.172 Application of routing information at network nodes National International transit exchange exchange (ISC) Infor
