WPCL 2BJ|x HH Hp P X`h!(#  X  6p&6p&  c4 P   H8NFOREWORD  H Ё The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCITT is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.  H  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 laid down in CCITT Resolution No. 2 (Melbourne, 1988).  Recommendation I.255.4 was prepared by Study Group I and was approved under the Resolution No. 2 procedure on 2 July 1990. P___________________  HT c4 P CCITT NOTE  c4 P   c4 P   In this Recommendation, the expression "Administration" is used for shortness to indicate both a telecommunication Administration and a recognized private operating agency. UMITU1990  H ЁAll 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. PAGE BLANCHE c4 P    HH  c4 P   c4 P Recommendation I.255.4  c4 P  PAGE5 c4 P    HH  c4 P PAGE6  c4 P Recommendation I.255.4  X   c4 P Recommendation I.255.4 Q c4 P PRIORITY SERVICE  c4 P 1X Definition  H Ё 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. 2X Description 2.1h  General description  H  This service provides preferential treatment in the network for calls:  H   a)poriginating from subscribers' lines. This is designated as Apriority; and/or  H   b)paddressed to certain emergency numbers. This is designated as Bpriority and concerns the order of path selection in the ISDN.  H  For Apriority, subscribers' lines are classified into two Apriority categories which are:   i)psubscribers with first order priority (I) for all calls;  H   ii)psubscribers with first order priority (II) on a per call basis.  HH  Only one Bpriority category is envisaged. 2.2h  Specific terminology  H  The Apriority service meets the needs of a subscriber for whom it is necessary to have calls completed urgently at any time when the service is activated for his lines.  The Bpriority service meets the needs of subscribers for calling specified emergency numbers. This service also meets the needs of Administrations, communities and other organizations which provide this service. 2.3h  Qualifications on the applicability to telecommunication services  H  The Priority supplementary service is applicable to all telecommunication services. 3X Procedures 3.1h  Provision/withdrawal  H  The provision of this service requires arrangements between the subscriber and the Administration.The service 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 Bpriority.  The Administration can withdraw the service at the request of the subscriber or for administrative reasons. 3.2h  Normal procedures  H3.2.1 Activation/deactivation/interrogation procedures  H  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.  H  After provision of the Apriority service, the subscriber may activate and deactivate the service by the use of a control procedure.  Bpriority is activated upon provision.  H3.2.2 Invocation and operation  When the service is provided for all calls, it will automatically be invoked by the network at the call setup.  H  For a call based request, it will be invoked by the user using a service code as a part of a call setup. For this service option, invocation is possible only for the calling terminal in A-priority, category II.  H  For calls to Bpriority numbers, this service may automatically be invoked by the network depending on the address dialled, i.e. calls to fire, rescue and ambulance services.  H  Calls originating from subscribers' lines with the appropriate Apriority category will be treated as priority calls at the sending exchange as well as at the transit and the incoming exchange. This means that a priority call will have preferential access to all network units necessary for a call setup. When a priority call meets congestion in the network the call is not released, but waits for the first line to be free.  This supplementary service does not give priority in accessing a busy subscriber. For this purpose other supplementary services may be used.  H  The preferential treatment of priority calls within the network should include the following functions:  - extended waiting time before timeout of network units;  - waiting for a line on the route to become free.  HH 3.3h  Exceptional procedures  H  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.  H  If the priority call is not connected due to congestion, the call will be cancelled after a timeout (e.g. five seconds).  (Further study required.) 3.4h  Alternate procedures  None identified. 4X Network capabilities for charging  This Recommendation does not cover charging principles. Future Recommendations in the DSeries are expected to contain that information.  H  It shall be possible to charge the subscriber accurately for the service. 5X Interworking consideration  H Ё The service will be provided whenever there is an ISDN User Part (ISUP) available.  H  In networks where there is no ISUP available or where priority service is not offered, the priority call will be handled as a normal call.  H  If a Bpriority 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. 6X Interaction with other supplementary services 6.1h  Call Waiting  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.2h  Call Transfer  Priority service is restricted only to AB connections. 6.3h  Connected Line Identification Presentation (COLP)  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.4h  Connected Line Identification Restriction (COLR)  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.5h  Calling Line Identification Presentation (CLIP)  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.6h  Calling Line Identification Restriction (CLIR)  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.7h  Closed User Group  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.8h  Conference Calling  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.9h  Direct DiallingIn  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service.  6.10 Diversion services  HH  Priority service is restricted to AB connections. 6.11  Line Hunting  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.12  Three Party Service  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.13  UsertoUser Signalling  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.14  Multiple Subscriber Number  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.15  Call Hold  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.16  Advice of Charge  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.17  Multilevel precedence and preemption service (MLPP)  H  No impact, i.e. neither supplementary service affects the operation of the other supplementary service. 6.18  Priority service  H  If at some point there is more than one priority connection waiting for service, "first in, first out" principle is to be followed. 7X Overall SDL diagram  The overall SDL Diagram is shown in Figures 1/I.255.4 and 2/I.255.4. S c4 P Fig.1 = 24cm  c4 P  c4 P  RFig. 2 = 24 cm  c4 P