1、1.255.4 INTEGRATED SERVICES DIGITAL NETWORK (ISDN) GENERAL STRUCTURE AND SERVICE CAPABILITIES PRIORITY SERVICE Recommendation 1.255.4 CCITT THE INTERNATIONAL TELEGRAPH AND TELEPHONE CONSULTATIVE COM M IlTEE PRIORITY SERVICE Recommendation I .255.4 CCITT RECMN*I-255- 4 90 m 48b259L 05bL200 T m FOREWO
2、RD The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCIIT is responsible for studying technical, operating and tariff questions and issuing Recornmendations on them with a view to standardizing telec
3、ommunications on a worldwide basis. The Plenary Assembly of CCITT 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 CCITT between Plenary Assemblies is covered by the procedure l
4、aid down in CCITT Resolution No. 2 (Melbourne, 1988). Recommendation 1.255.4 was prepared by Study Group I and was approved under the Resolution No. 2 procedure on 2 July 1990.: CCIT NOTE In this Recornmendation, the expression “Administration“ is used for shortness to indicate both a telecommunicat
5、ion Administration and a recognized private operating agency. O ITU 1990 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, without permission in writing from the ITU. Recommendat
6、ion 1.255.4 PRIORITY SERVICE 1 Definition The Priority service provides for preferential treatment in the network to calls originating from and/or addressed to certain numbers in the order of path selection. 2 Description 2.1 General description This service provides preferential treatment in the ne
7、twork for calls: a) b) originating from subscribers lines. This is designated as A-priority; and/or addressed to certain emergency numbers. This is designated as B-priority and concerns the order of path selection in the ISDN. For A-priority, subscribers lines are classified into two A-priority cate
8、gories which are: i) subscribers with first order priority (I) for all calls; ii) Only one B-priority category is envisaged. subscribers with first order priority (II) on a per call basis. 2.2 Specific terminology urgently at any time when the service is activated for his lines. also meets the needs
9、 of Administrations, communities and other organizations which provide this service. The A-priority service meets the needs of a subscriber for whom it is necessary to have calls completed The B-priority service meets the needs of subscribers for calling specified emergency numbers. This service 2.3
10、 Qiialijcations on the applicability to telecommirnication services The Priority supplementary service is applicable to all telecommunication services. 3 Procedures 3.1 Provisionlwithdrawal The provision of this service requires arrangements between the subscriber and the. Administration.The service
11、 can also be established unilaterally by the Administration for administrative reasons. The subscriber has to inform the Administration if he wants this service with A- or B-priority. The Administration can withdraw the service at the request of the subscriber or for administrative reasons. 3.2 Norm
12、al procedures 3.2.1 ActivationlJeactivationlinterrogationprocedures Priority will be given to the subscriber by the Administration, which has full control of the registration. All changes to priority information are made by the Administration. Recommendation 1.255.4 1 CCITT RECMN*I.255. 4 90 m 48b25
13、9L 0561Z02 3 m After provision .of the A-priority service, the subscriber may activate and deactivate the service by the use of a control procedure. B-priority is activated upon provision. 3.2.2 Invocation and operation When the servi waiting for a line on the route to become free. 3.3 Exceptional p
14、rocedures When a priority call is requested within an Administration that has no agreement to provide this service, the call will proceed as for a normal call. If the priority call is not connected due to congestion, the call will be cancelled after a time-out (e.g. five seconds). (Further study req
15、uired.) 3.4 Alternate procedures None identified 4 Network capabilities for c-arging This Recommendation does not cover charging principles. Future Recommendations in the D-Series are expected to contain that information. It shall be possible to charge the subscriber accurately for the service. 5 In
16、terworking consideration The service wilkbbe provided whenever there is an ISDN User Part (ISUP) available. 2 Recommendation 1.255.4 CCITT RECMN*I*255* 4 70 = 4862571 05b1203 5 In networks where there is no ISUP available or where priority service is not offered, the priority call will be handled as
17、 a normal call. If a B-priority call originates in a network that does not support the priority service, the priority will be assigned to the call upon entering the network supporting the priority service. 6 6.1 6.2 6.3 6.4 6.5 6.6 6-7 6.8 6.9 Interaction with other supplementary services Call Waiti
18、ng No impact, i.e. neither-supplementary service affects the operation of the other supplementary service. Call Transfer Priority service is restricted only to A-B connections. Connected Line Identification Presentation (COLP) No impact, i.e. neither supplementary service affects the operation of th
19、e other supplementary service. Connected Line Identification Restriction QCOLR) No impact, i.e. neither supplementary service affects the operation of the other supplementary service. Calling Line Identification Presentation (CLIP) No impact, i.e. neither supplementary service affects the operation
20、of the other supplementary service. Calling Line Identification Restriction (CLIR) No impact, Le. neither supplementary service affects the operation of the other supplementary service. Closed User Group No impact, i.e. neither supplementary service affects the operation of the other supplementary s
21、ervice. Conference Calling No impact, i.e. neither supplementary service affects the operation of the other supplementary service. Direct Dialling-In No impact, i.e. neither supplementary service affects the operation of the other supplementary service. Recommendation 1.255.4 3 CCITT RECNN*I.255- 4
22、YO m 4Bb2591 0563204 7 m 6.10 Diversion services Priority service is restricted to A-B connections. 6.1 1 Line Hunting No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.12 Three Party Service No impact, i.e. neither supplementary service affect
23、s the operation of the other supplementary service. 6.13 User-to-User Signalling No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.14 Multiple Subscriber Number No impact, Le. neither supplementary service affects the operation of the other sup
24、plementary service. 6.15 Call Hold No impact, Le. neither supplementary service affects the operation of the other supplementary service. 6.16 Advice of Charge No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.11 Multi-level precedence and pree
25、mption service (MLPP) No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.18 Priority service If at some point there is more than one priority connection waiting for service, “first in, first out“ principle is to be followed. 7 Overall SDL diagra
26、m The overall SDL Didgram is shown in Figures 1h.255.4 and 2b.255.4. 4 Recommendation 1.255.4 Call and sewice request I Assign free line Offer the call No I Yes Cancel the call 0 FIGURE 1h.255.4 Overall SDL diagram for the case of A-priority 5 - CCITT RECMN*I.255. 4 90 = 4862591 05b120b O Call request to B-priority number Offer the call a Start timer Active call No TO10090049 No Cancel the call ( Idle 6 FIGURE 2/1.255.4 Overall SDL diagram for the case of B-priority Recommendation 1.255.4
