1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 ) TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2!4%$G0G03%26)#%3G0G0$)4!,G0G0.%47/2+G0 )3$.G93%26)#%G0G0#!0!“),)4)%3G0 G0“%!2%2G0G03%26)#%33500/24%$G0G0“9G0G0!.G0G0)3$.0!#+%4G13-/$%G0G0“%!2%2G0G03%26)#%#!4%/2)%3G0G0 G0G06)245!,G0G0#!,G0G0!.$0%2-!.%.4G
2、0G06)245!,G0G0#)2#5)4G0G0“%!2%23%26)#%G0G0#!4%/29)45G134G0G0RecommendationG0G0) (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation I.232.1 was published in Fascicle III.7 of the Blue Book. This file is an extract fromthe Blue Book. While the presentation and layout of the text might be slightl
3、y different from the Blue Book version, thecontents of the file are identical to the Blue Book version and copyright conditions remain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a reco
4、gnized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.7 - Rec. I.232.1 1Recommendation I
5、.232.1Fascicle III.7 - Rec. I.232.1PACKET MODE BEARER SERVICE CATEGORIES VIRTUAL CALL AND PERMANENTVIRTUAL CIRCUIT BEARER SERVICE CATEGORY(Melbourne, 1988)1 I.232.1 - Virtual call and permanent virtual circuit bearer service category1.1 DefinitionThis bearer service category provides the unrestricte
6、d transfer (without alteration) of user information in apacketized manner over a virtual circuit within a B- or D-channel at the S/T reference point. Signalling information forvirtual call and/or possibly OAM information for permanent virtual circuit services are transferred via B- or D-channelsas d
7、escribed in Recommendation I.462 (X.31).1.2 Description1.2.1 General descriptionThis packet-mode bearer service category allows users (e.g. terminals) in a point-to-point communicationconfiguration to communicate via the ISDN using X.25 encoding, by means of Recommendation I.462 (X.31)procedures ove
8、r either B- or D-channels, in both directions continuously and simultaneously for the duration of a call.1.2.2 Specific terminologyNot applicable.1.2.3 QualificationsNot applicable.1.3 ProceduresDetailed procedures for virtual calls appear in Recommendation I.462 (X.31), case B. The description belo
9、w isa synopsis of those procedures. For actual, complete procedures, refer to Recommendation I.462.1.3.1 Provision/withdrawalFor further study.1.3.2 Normal procedures1.3.2.1 Activation/deactivation/registrationNot applicable.2 Fascicle III.7 - Rec. I.232.11.3.2.2 Invocation and operation1.3.2.2.1 Vi
10、rtual call proceduresa) Call establishmentFor virtual calls, X.25 will be used on an active channel (B or D) to the packet handler. In order toestablish that channel and/or to negotiate the type of channel to be used, out-of-band signalling proceduresmay be used. Once connected to the packet handler
11、, remaining call information, including called useraddress, are signalled in the X.25 call request.b) Data transfer phaseOnce established, the virtual circuit is then available for unrestricted X.25 data transfer in both directionscontinuously and simultaneously. During the data transfer phase, info
12、rmation exchange occurs with thefollowing characteristics, among others:- packetized;- flow control;- delivery confirmation (optional);- reset/interrupt.c) Terminating the callThe call may be terminated by either or both of the users by indicating this to the network. In either case,an appropriate i
13、ndication is sent to the other user. The active channel may be released after the terminationof the last virtual call on that channel.1.3.2.2.2 Permanent virtual circuit proceduresFor permanent virtual circuits on B- or D-channels, there is no call set-up or clearing. For permanent virtualcircuits u
14、sing B-channel access, a semi-permanent connection of the channel to the packet handler must be in place. Theprocedures for the control of packets between user terminal equipment and network are covered by X.25 data transferphase.1.3.2.3 Interrogation/editingNot applicable.1.3.3 Exceptional procedur
15、es1.3.3.1 Activation/deactivation/registrationNot applicable.1.3.3.2 Invocation and operation1.3.3.2.1 Virtual callIn case of failure situations due to calling/called user error, user state, or network conditions, appropriate failureindications will be signalled from the network and the call set-up
16、or established call may be terminated. For detailedprocedures, see Recommendation I.462.1.3.3.2.2 Permanent virtual circuitIn case of failure situations due to user error, user state, or network conditions, appropriate failure indicationswill be signalled from the network. For detailed procedures, s
17、ee Recommendation I.462.1.3.3.3 Interrogation/editingNot applicable.1.3.4 Alternative proceduresNot applicable.Fascicle III.7 - Rec. I.232.1 31.3.5 VerificationNot applicable.1.4 Network capabilities for chargingThis Recommendation does not cover charging principles. Future Recommendations in the D-
18、Series areexpected to contain that information.1.4.1 Virtual call chargingIt shall be possible to charge the subscriber accurately for the virtual call service.1.4.2 Permanent virtual circuit chargingIt shall be possible to charge the subscriber accurately for the permanent virtual circuit service.1
19、.5 Interworking requirementsGeneral interworking arrangements for this bearer service category are defined in Recommendation X.300.Specific interworking procedures are in Recommendation I.462.1.6 Interaction with supplementary servicesNot applicable.1.7 Attributes and values of attributes of the vir
20、tual call and permanent virtual circuit bearer service categoryInformation transfer attributes1. Information transfer mode: packet2. Information transfer rate: maximum throughput of a given virtual circuit is less than orequal to the maximum bit rate of the user information accesschannel and the thr
21、oughput class of the virtual circuit (Note)3. Information transfer capability: unrestricted4. Structure: service data unit integrity5. Establishment of communication: demand (virtual call)/permanent (permanent virtual circuit)6. Symmetry: bidirectional symmetric7. Communication configuration: point-
22、to-pointAccess attributes8. Access channel: user information over virtual circuit within B- or D-channel.When D-channel is used, maximum packet size and Quality ofService may be restricted. Signalling may be provided via D-channeland/or virtual circuit within B-channel9. Access protocol: as specifie
23、d in Recommendations I.440, I.450, I.451, I.462 andX.25 (layers 2 and 3)4 Fascicle III.7 - Rec. I.232.1General attributes10. Supplementary services provided: as listed in Recommendation X.2. Others are for further study11. Quality of Service Error! Reference source not found.12. Interworking possibi
24、lities Error! Reference source not found. for furtherstudy13. Operational and commercial aspects Note - The exact values of information transfer rates for the virtual call and permanent virtual circuit are forfurther study.1.8 Provision of virtual call and permanent virtual circuit bearer servicea)
25、Overall provision: Eb) Variations of secondary attributes:Establishment de Symmetry Communication Provisionof communication of configurationdemandpermanentbidirectional symmetricpt-ptpt-ptEEc) AccessL1, L2 and L3 Layer 1, layer 2 and layer 3Note 1 - The definition of other protocols for OAM is for f
26、urther study.Note 2 - The protocols listed in this column are for establishing communications with the packet handling function using out-of-band call control signals. This procedure does not apply in certain cases (for example, semi-permanent D-channel connection).Note 3 - The protocols listed in t
27、his column are for the establishment of a virtual circuit using X.25 procedures. Theseprocedures do not apply to permanent virtual circuits.Acces channel controlSignalling and OAM(Notes 1 and 2)Virtual call controlSignalling and OAM(Notes 1 and 3)User informationProvisionChanneland rateProtocols Cha
28、nneland rateProtocols Channeland rateProtocolsD(16) I.451I.441I.430B(64) X.25, L3X.25, L2I.430B(64) X.25, L3X.25, L2I.430AD(64) I.451I.441I.431B(64) X.25, L3X.25, L2I.431B(64) X.25, L3X.25, L2I.431AD(16) I.451I.441I.430D(16) X.25, L3I.441I.430D(16) X.25, L3I.441I.430AD(64) I.451I.441I.431D(64) X.25,
29、 L3I.441I.431D(64) X.25, L3I.441I.431AFascicle III.7 - Rec. I.232.1 51.9 Dynamic descriptionDynamic descriptions for the Recommendation I.462 procedures in the virtual call and permanent virtual circuitbearer service category are for future study. State transition diagrams for layer 3 of Recommendation X.25 (Annex B)apply for virtual call and permanent virtual circuit.
