1、- ITU-T RECMN*E*220 96 YBb259L ObLb2Bb 231 = INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEPHONE NETWORK AND ISDN O PE RATION, NUMB E RING, ROUTING AND MOBILE SERVICE E.220 (02/96) INTERCONNECTION OF PUBLIC LAND MOBILE NETWORKS (PLMN) ITU-T Recommend
2、ation E.220 (Previously “CCITT Recommendation“) FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The -T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them wi
3、th 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, produce Recommendations on these topics. The approval of Re
4、commendations 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 E.220 was revised by -T Study Group 2 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 19th of February 1996. NOTE
5、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 reproduced or utilized in any form or by any means, electronic or
6、mechanical, including photocopying and microfilm, without permission in writing from the . . ITU-T RECMN*E-220 96 4B62-593 0636288 O04 = CONTENTS 1 Introduction 2 Scope 3 Related Recommendations . 4 General principles of interconnection 5 Network interconnection scenarios 6 Echo control . 6.1 Genera
7、l 6.2 Location of echo control devices 6.3 Network control 6.4 Implementation considerations . 7 Roaming . 8 Handover 9 History Annex A - Alphabetical list of abbreviations used in this Recommendation . Recommendation E.220 (02/96) Page 1 1 1 1 2 2 2 2 3 3 4 4 5 5 i ITU-T RECMN*E-220 96 W 4862591 Ob
8、Lb289 T40 ITU-T RECMN*E.220 96 4862591 Oblb290 7b2 Recommendation E.220 INTERCONNECTION OF PUBLIC LAND MOBILE NETWORKS (PLMN) (1 992; revised in 1996) 1 Introduction 1.1 The rapid advances in cellular radio technology have meant that Public Land Mobile Networks (PLMN) now have a significant role in
9、the provision of telecommunication services. The rapid growth of land mobile related traffic, and the proliferation of dedicated mobile networks has generated the need for guidelines to be established for interconnecting such networks to the fixed PSThVSDN. 1.2 This Recommendation identifies the pri
10、nciples to be adopted for interconnection of PLMNs with fixed networks. Various interconnection scenarios are developed and some issues relevant to mobile networks, and their impact on the fixed networks are addressed. 2 Scope 2.1 This Recommendation is applicable to those cases where the PLMN is a
11、separate entity from the fixed PSTNASDN. It does not cover the case where the mobile network switches are integrated within the fixed network. The mobile network and fmed network may be operated by separate companies (or Administrations) or by the same company. 2.2 This Recommendation does not cover
12、 the case of interconnection of PLMNs with the fixed network across an international boundary. Such interconnections are expected to allow for the connection of international calls to and from the PLMN. 2.3 PLMNs may be based on cellular, cordless or satellite systems. However, in this Recommendatio
13、n, the emphasis is on cellular systems, although the scope may be widened in the future. Interconnection of satellite mobile systems is for further study. 3 Related Recommendations 3.1 The following Recommendations are directly related to Recommendation E.220: - CCIT Recommendation E. 173 (1991), Ro
14、uting plan for interconnection between public land mobile networks andfied terminai networks. ITU-T Recommendation E.770 (1993), Land mobile and faed network interworking trafic grade of service concept. IT-T Recommendation E.771 (1993), Network grade of service parameters and target values for circ
15、uit-switched land mobile services. CCITT Recommendation F.111 (1991), Principles of service for mobile systems. - - - A complete list of mobile related Recommendations can be found in Recommendation E.201: Reference 3.2 Recommendation for mobile services. 4 General principles of interconnection 4.1
16、In general, the interconnection of a PLMN to the existing PSTNASDN, should not impose any requirement for additional functionality in the fixed network, nor any restriction in the normal operation of the fixed network. Any additional functionality should be provided in the mobile network, unless oth
17、erwise agreed between the operators of the mobile and fixed networks. The fixed network should not have to be specially engineered to compensate for possible performance degradation of services supported by the PLMN interconnected to it in order to match the performance of similar services fully sup
18、ported by the fixed network (see Recommendation E.770). 4.2 The interconnection should not result in any impairment to the quality of service provided on calls routed across the interconnection. Recommendation E.220 (02J96) 1 ITU-T RECMN*E.220 b = 48b25L ObLb27L bT7 m 4.3 In cases where more than on
19、e network operator is involved, a technical agreement could be drawn up by the operators of the two networks to formalize the interconnection arrangements. This agreement could cover the following areas: - network topology; - - provisioning procedures; - operations and maintenance procedures; - - -
20、charging and accounting arrangements. interface specifications, including signalling systems; performance monitoring (QOS, GOS, traffic measurement, etc.); growth management (forecasts, network planning, etc.); 5 Network interconnection scenarios 5.1 The following network scenarios are for guidance
21、only. In principle, the interconnection between the PLMN and the fixed network can be at any level in the fixed network hierarchy, e.g.loca1 exchange, transit exchange, international exchange, or a combination of these. 5.2 provided via digital facilities. Typically, this would be via digital transm
22、ission and common channel signalling. For interconnection of digital PLMNs (within national boundaries), the interconnection should ideally be 6 Echo control 6.1 General 6.1.1 In digital PLMNs electrical echo is eliminated through the use of 4-wire terminal sets. A PLMN can be regarded as having an
23、echo control device connected. Therefore, echo control devices need not be activated for calls within and between PLMNs with such terminal sets. “Guidance on how to connect to PSTNs for digital cellular designers can be found in Recommendation G.173 (transmission planning aspects of speech service i
24、n public land mobile networks) while guidance on 4-wire telephone sets can be found in Recommendation P.3 1 (transmission characteristics for digital telephones). Guidance on how to control echo control devices can be found in Recommendation Q.115.” 6.1.2 In a digital PLMN, a long propagation time c
25、an be caused by the speech processing devices at the radio access. For calls between such accesses and terminal equipments which generate echo, half-echo control devices (preferably echo cancellers) must be activated. Fixed networks, particularly on long intemational connections, also add propagatio
26、n delay which may require echo control. 6.2 Location of echo control devices 6.2.1 In principle, echo control devices should be connected as close to the echo generating source as possible, in order to be able to recognize and control the echo. Figure 1 shows the possible location of the echo contro
27、l devices for calls between PLMN and fixed networks. It should be noted that, if the requisite echo control and signalling capability does not exist in the PSTN, the PLMN must provide echo control. 6.2.2 The echo control devices may be located at the trunks between PLMN and the fixed network, either
28、 on the PLMN side or in the fixed network. In fixed networks, incoming half-echo control devices are normally associated at the incoming side of the exchange and outgoing half-echo control devices are associated at the outgoing side of the exchange. If the echo control devices are located in the PLM
29、N, the distance to the echo generating point is longer and the control of the echo may be more difficult. 6.2.3 the PLMN and fixed network operators and geographical considerations. The final decision on the location of echo control devices will depend on commercial arrangements between 2 Recommenda
30、tion E.220 (02496) ITU-T RECMN*E.220 96 = 4862591 0636292 535 Originating network PLMN PLMN Fixed network NOTE -The echo control device may also be located in the PSTN local exchange, transit exchange or international exchange. In such cases, if the signalling capability exists, the echo control dev
31、ice in the PUIN may be disabled. Half-echo control device activated Transit network Terminating network Fixed network Fixed network Yes Fixed network PLMN No Fixed network PLMN Yes FIGURE 1E.220 Location of echo cantmi devices 6.3 Network control 6.3.1 The following subclauses identify the ideal con
32、trol procedures for elimination of echo. It is recognized however that these procedures cannot easily be implemented in existing networks. Subclause 6.4 provides guidance on implementation. 6.3.2 echo control device due to interconnection between a fixed network and PLMN. Table 1 summarizes the call
33、 connection cases and identifies those cases that may require activation of a half- TABLE 1E.220 Activation of half-echo control device due to interconnection between a fued network and PLMN 6.3.3 For originating call from a PLMN, PLMN acts as if an outgoing half-echo control device is connected and
34、 request an incoming half-echo control device. If the PSTN has not connected the incoming echo control device, then PLMN should enablehnsert an incoming echo control device. 6.3.4 For terminating call to a PLMN, PLMN acts as if an incoming half-echo control device is connected and request an outgoin
35、g half-echo control device. If the PSTN has not connected the outgoing echo control device then PLMN should enablelinsert an outgoing echo control device. 6.3.5 proper echo control. The routing must be performed in such a way that sufficient signalling and analysing capability is achieved for 6.4 Im
36、plementation considerations 6.4.1 In principle it is desirable that the originating exchange which can identify the originating terminal set type and call destination, should determine on a per call basis whether echo control should be included. However it is recognized that this will not always be
37、possible and therefore an assumption must be made on whether to include echo control, Recommendation E.220 (02/96) 3 ITU-T RECMN*E.220 96 48b259L Oblb293 471 either at the originating exchange or interconnection point. This decision may be changed later on in the network when more knowledge about th
38、e routing and terminating equipment is achieved, such that echo control devices are properly connected when they are needed. This will require enhanced signalling capabilities in the network. 6.4.2 As network modernization proceeds consideration should be given to providing functionality to enable a
39、dequate control of echo through enhanced signalling Capabilities. For example, if procedures to determine the total propagation delay for a connection were available, the result could be used for the decision by ail exchanges whether to include echo control devices in the connection and also to avoi
40、d speech manipulation devices (DCME, etc.) for mobile calls. In this case, the PLMN would set the appropriate value for the radio access. 7 Roaming 7.1 retaining the service. Roaming could be implemented automatically or manually (e.g. via an operator). Automatic roaming allows a mobile subscriber t
41、o move from one service area to another area while still 7.2 Two kinds of roaming may impact on the interconnection of fixed networks with PLMNs: a) b) intra-network roaming, Le. roaming from one location area to another within the same network; and inter-network roaming, i.e. roaming from one PLMN
42、to another, possibly in different countries. 7.3 The interconnection arrangements may provide for: - circuit interconnection to facilitate the routing of calls to roamed mobile stations (see also Recom- mendation E. 173); and - signalling interconnection, to facilitate the routing of signalling mess
43、ages between PLMNs, for location updating, etc. (e.g. using SS No. 7 SCCP). 7.4 unavailability of circuits in the target network. In all situations, consideration should be given to unsuccessful roaming due to fixed network blocking, and the 7.5 In order to route calls to roamed mobile stations, the
44、 PLMN may translate the dialled number into a Mobile Station Roaming Number (MSRN) as defined in Recommendation E.213. It is desirable for a call to the roaming number originating from an ordinary subscriber, to be rejected by the network (either the fixed network or the PLMN). The method of achievi
45、ng this would be by bilateral agreement. 7.6 In order to avoid trombone routing of calls to roamed mobile stations it may be desirable for the fixed network to have the capability to interrogate the location registers in the PLMN. This will depend on the volume of calls requiring this facility, and
46、the commercial arrangements between the fixed network operators and the PLMNs. 7.7 example, due to signalling failures and consequent loss of location registration information. Provision should also be made to avoid loss of location information for roamers in a visiting location area, for 7.8 arrang
47、ements between the fixed network and PLMN operators. Provision of limited roaming ability based upon lower rental and call charges will be subject to commercial 8 Handover 8.1 In a cellular system, handover occurs when, for a call in progress, the current channel cannot maintain the target quality o
48、f the connection and another channel takes over, whether in the same or in a different base station. In some cases, handover is required between base stations connected to different Mobile Switching Centres (MSC), which means that a new connection has to be established from the original (controlling
49、) MSC to another. Where this connection between the MSCs is provided via the fixed network, consideration must be given to the overall number of links, particularly where more than one such handover occurs during the same call. Consideration should also be given to the engineered fixed network blocking loss, and the possibility that a handover will be unsuccessful, due to non-availability of the fixed network circuits. “Grade of service standards for the probability of unsuccessful handover are given in Recommendation E.77 1 .” 4 Recommendation E.220 (02/96) ITU-T R
