1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 ) TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2!4%$G0G03%26)#%3G0G0$)4!,G0G0.%47/2+G0 )3$.G93%26)#%G0G0#!0!“),)4)%34%,%3%26)#%3G0G03500/24%$G0G0“9G0G0!.G0G0)3$. 4%,%0(/.9)45G134G0G0RecommendationG0G0) (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recomme
2、ndation I.241.1 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 slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book version and copyright conditions r
3、emain unchanged (see below).2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be reproduced or utilized in any form
4、 or by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.7 - Rec. I.241.1 1Recommendation I.241.1Fascicle III.7 - Rec. I.241.1TELESERVICES SUPPORTED BY AN ISDN: TELEPHONY(Melbourne, 1988)1 Telephony1.1 DefinitionThe “tel
5、ephony service” provides users with the ability for real-time two-way speech conversation via thenetwork.1.2 Description1.2.1 General descriptionThe “telephony service” provides speech transmission at an audio bandwidth of 3.1 kHz. The communicationis bidirectional, with both directions continuously
6、 and simultaneously active during the speech phase. The network mayuse processing techniques appropriate for speech such as analogue transmission, echo cancellation and low bit-rateencoding.The digital signal at the S/T reference point follows the encoding laws for speech (according toRecommendation
7、 G.711), A-law or -law and the network may use digital signal processing techniques. It may also benecessary to use echo cancellation techniques in particular when interworking with other networks such as the PSTN.User information is provided over a B-channel, signalling is provided over the D-chann
8、el. Tones and announcements areprovided by the network, encoded according to Recommendation G.711, although terminals can generate tones or otherindications based on the messages received.1.2.2 Specific terminologya) Voice quality The required acoustic performance is described in terms of loudness r
9、atings, frequencyresponse, quantizing distortion, etc. Overall requirements are given in the Recommendations of the P-Series.b) Transmission delay The maximum delay is that specified for the general telephone network (cf.Recommendation G.114). The permissible variation of the actual delay is for fur
10、ther study.c) Retention timer This timer specifies the amount of time that the network retains the call information ofthe original call upon encountering busy or being released. It is a network provider option. The value forthis timer is greater than 15 seconds.1.3 Procedures1.3.1 Provision/withdraw
11、al1.3.1.1 Provision of this service will be by pre-arrangement with the Administration.1.3.1.2 The teleservice is offered with several subscription options which apply separately to each ISDN number orgroup of ISDN numbers on the interface. For each subscription option, only one value can be selecte
12、d. Subscriptionoptions for the interface are summarized below:2 Fascicle III.7 - Rec. I.241.1Subscription Option ValueMaximum number of information channelsavailable at user B m, where m is not greater than thenumber of information channels on theinterfaceMaximum number of total calls present atuser
13、 B n, where n is not greater than thenumber of information channels on theinterfaceUser B can be an ISDN number or group of ISDN numbers on the interface.Note - More than one ISDN number can be associated with the service/interface only as a part of asupplementary service such as multiple subscriber
14、 number. In the case of one ISDN number, the option given above forthe number of calls can only exceed the number of information channels in association with a supplementary service(e.g. call waiting). As a network provider option, separate values may be specified for incoming and for outgoing calls
15、for either or both of the limits.1.3.2 Normal proceduresa) Originating the service (call set-up)The service is originated by the originating user activating the terminal, performing service selection (ifapplicable) for the originating terminal, and terminating customer selection. During this process
16、 theoriginating user is given appropriate indications as to the state of the call.i) A service selection is required on a multi-service terminal.ii) Terminating customer selection is selecting the required termination (user/network interface) by anappropriate means for example, the use of direct-dia
17、lling-in (DDI), or multiple subscriber number.iii) Indications during call origination may include an indication that the network is ready to receive thenetwork address information (proceed indication) and an indication that the call is progressingthrough the network. It shall be possible to have au
18、dible indications which may be accompanied byother indications.b) Call acceptance (answer)Selection of the terminating customer is indicated to each user by appropriate indications (call arrivalindication and awaiting answer indication). The acceptance of the call by the terminating user, i.e. answe
19、r,causes the indications to be removed and bidirectional communication paths to be provided. The call isnow termed in the “speech phase”.c) Call releaseA request to terminate the service may be generated by either user. If one user terminates the service theother user is given an appropriate indicat
20、ion as to the state of the call.d) Failure situations due to user errorThe following failure situations may occur due to user error:i) user taking too long to input the network address information will be given a failure indication, e.g.during overlap sending (see Recommendations I.451 and I.220);ii
21、) user inputting a non valid network address, e.g. an unallocated address, will be given a failureindication.e) Failure indications due to terminating termination statei) User attempting to set up a call to a termination where no free B-channels are available will receive abusy indication unless cal
22、l waiting or another supplementary service is in operation.Note - In support of some supplementary services (e.g. call waiting, line hunting), it may optionallybe necessary for the subscriber to register some additional parameters (e.g. destination number usedto distinguish PSTN telephony calls) wit
23、h the network to allow the network to know when a channelis busy with telephony.Fascicle III.7 - Rec. I.241.1 3ii) User attempting to set up a call to a termination where the call is not accepted, i.e. no responseindicating call acceptance is received, will, after a defined period, be given a call f
24、ailure indication(see Recommendations I.451 and I.220).f) Failure situations due to network conditionsUser attempting to set up a call but meeting problems in the network (e.g. congestion) will be given asuitable indication.1.4 Network capabilities for chargingThis Recommendation does not cover char
25、ging principles. Future Recommendations in the D-Series areexpected to contain that information.It shall be possible to charge the subscriber accurately for the service.1.5 Interworking requirements1.5.1 Interworking is required between the ISDN and PSTN.1.6 Interaction with supplementary servicesNo
26、t applicable. Each supplementary service description identifies the applicability with this teleservice.1.7 Attributes and values of attributes of the telephony servicea) LOW LAYER ATTRIBUTESInformation transfer attributes1. Information transfer mode: circuit2. Information transfer rate: 64 kbit/s3.
27、 Information transfer capability: speech4. Structure 8 kHz integrity5. Establishment of communication: on demand6. Symmetry: bidirectional symmetric7. Communication configuration point-to-pointAccess attributes8. Access channel (and rate): B(64) for user information, D for signalling (Note)9. Access
28、 protocol9.1 Signalling access protocol layer 1: I.430/I.4319.2 Information access protocol layer 2: I.440/I.4419.3 Signalling access protocol layer 3: I.450/I.4519.4 Information access protocol layer 1: I.430/I.431; G.7119.5 Signalling access protocol layer 2: not applicable9.6 Information access p
29、rotocol layer 3: not applicableb) HIGH LAYER ATTRIBUTES10. Type of user information: speech11. Layer 4 protocol functions: not applicable12. Layer 5 protocol functions: not applicable13. Layer 6 protocol functions: Recommendation G.71114. Layer 7 protocol functions: not applicablec) GENERAL ATTRIBUT
30、ES15. Supplementary services provided: further study16. Quality of Service: further study17. Interworking possibilities: to and from PSTN18. Operational and commercial: further studyNote - For reserved/permanent services, the operational, administrative and maintenance messages (OAM)related to these
31、 services may be conveyed over the D-channel.4 Fascicle III.7 - Rec. I.241.11.8 Recommended support of telephony by an ISDNa) Overall support1: E/ANote - It is anticipated that ISDNs will offer telephony as a basic telecommunication service. Somenetworks will offer this as a teleservice. However, du
32、e to national regulation policies, some networks willoffer telephony as a bearer service rather than as a teleservice.b) Variations of non-dominant attributes :1) Information transfer mode Circuit : E2) Establishment Symmetry Communication Support1of communication configuration_demand pt-pt Ereserve
33、d bidirectional pt-pt FSpermanent symmetric pt-pt Ademand multipt Areserved bidirectional pt-pt FSpermanent symmetric multipt A3) AccessSignalling and OAM(Note 1)User informationSupportChannel and rate Protocols Channel and rate ProtocolsD(16) I.430, I.440, I.441,I.450, I.451(Note 2)B(64) I.430, G.7
34、11 ED(64) I.431, I.440, I.441,I.450, I.451(Note 2)B(64) I.431, G.711 ENote 1 - Definition of protocols for OAM is for further study.Note 2 - Demand services only. Others are for further study.1.9 Dynamic descriptionThe circuit-mode dynamic description appears in Recommendation I.220.1The definition of E (essential) and A (additional) can be found in Recommendation I.240.
