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%,%4%8)45G134G0G0RecommendationG0G0) (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommend
2、ation I.241.2 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 rem
3、ain 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 o
4、r by any means, electronic ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.7 - Rec. I.241.2 1Recommendation I.241.2Fascicle III.7 - Rec. I.241.2TELESERVICES SUPPORTED BY AN ISDN: TELETEX(Melbourne, 1988)2 TeletexThe prose description of the
5、 Teletex service is an extract of Recommendation F.200. If more detail is requiredthis Recommendation should be referred to. As such, this service description does not strictly follow step 1.1 of theservice description method. Further alignment with this description method requires further study.2.1
6、 DefinitionTeletex is an international service, enabling subscribers to exchange office correspondence in the form ofdocuments containing Teletex coded information on an automatic memory-to-memory basis via the ISDN.2.2 Description2.2.1 ScopeThe Teletex service provides communication between Teletex
7、 equipment1which are used for the preparation,editing and printing of correspondence containing text information using a standardized character set (seeRecommendation T.61).The basic element of the correspondence between users is the page which is the smallest unit of text treated asan entity. No re
8、strictions shall exist concerning the operator procedures for generation of the text or the positioning oftext within the printable area on a page.Note 1 - This does not necessarily imply that the characters used to construct a graphic symbol are transmittedin the same sequence as that in which they
9、 are keyed.Note 2 - This does not necessarily imply that the order in which text on a page is transmitted is the same as thatin which it was keyed.Note 3 - An exception to this rule is the application of the processable mode of operation for which the page, asa basic element of correspondence, canno
10、t be used. The processable mode of operation within the Teletex service isdefined in Recommendation F.220.2.2.2 Operation2.2.2.1 GeneralThe Teletex service in each country and the international interconnection between countries or networks shalluse automatic switching so that it is possible for any
11、Teletex subscriber to reach any other Teletex subscriber using fullyautomatic selection.It is a requirement to allow the through-connection of a call between a Teletex terminal connected to a privateautomatic branch exchange (or similar systems) and those connected to public exchanges used for the T
12、eletex service.A virtual dialogue mode of operation, which appears to the subscriber as an interactive mode, should bepossible, although this is not a basic requirement of the Teletex service.A virtual dialogue mode of operation, which appears to the subscriber as an interactive mode, may becomeposs
13、ible as a new standardized option within the Teletex service, allowing both communications between persons anddata base access (see Recommendation I.210).Processable mode of operation, as a standardized option within the Teletex service, allows the transfer of textcontaining information to permit co
14、nvenient further editing and processing by the recipient (see RecommendationF.220).Mixed mode of operation using the techniques of Telefax 4 for the transfer of facsimile-coded information andof Teletex for the transfer of character-coded text is described as a standardized option within the Teletex
15、 service inRecommendation F.230.1Teletex equipment may be a Teletex terminal or a system.2 Fascicle III.7 - Rec. I.241.2Two-way alternate (TWA) communication is a capability of the Teletex service, which also includes one-waycommunication (OWC); the calling subscriber will have full control of the T
16、eletex call.2.3 Procedures2.3.1 Provision/withdrawalThe national and international facilities of the Teletex service, including the Teletex/telex conversion facilities,shall be open continuously.Teletex subscriber equipment for which call numbers are published in the directories shall, in principle,
17、 beavailable to accept calls continuously.In order to facilitate the 24-hour duration of the service, it is permitted to use a centralized storage in thenetwork to realize the receiving memory capability of the terminal.2.3.2 Call phasesThe operations for each call may be divided into the following
18、three phases:a) Preparation preparation of the information in local mode; loading of the information into a memory,b) Transmission (in principle, automatic) call establishment; pre-information phase (see Note); information transfer from memory-to-memory (see Note); post information phase (see Note);
19、 call clearing.Note - During these parts of the transmission phase the network must be transparent with respect tocontrol procedures.c) Output emptying the memory.Note - The information may consist of one or more Teletex documents each consisting of one or more Teletexpages.The control procedures as
20、 specified in Recommendation T.62 shall be used as end-to-end communicationprocedures between any Teletex equipment in the basic service.The lower layer protocols and the network independent basic transport protocol to be used for Teletex arespecified in Recommendations T.70 and T.90.The network-dep
21、endent control procedures for the Teletex are those that are defined for ISDN.2.3.3 Call identification lineThe Teletex procedures include the exchange of reference information prior to sending any document. Thisreference information includes identification of the parties to the call as well as the
22、date and time. Also, supplementaryreference information is exchanged during a call to allow reference to an individual document or page for error recoveryor other purposes.This reference information, taken together, is defined to be printable on a single line called the callidentification line. Use
23、of this information is a local decision except in recovering from an interrupted transmission.The call identification line is composed of four fields as follows (see Figure 1/I.241.2): Field 1: identification of the called Teletex equipment; Field 2: identification of the calling Teletex equipment;
24、Field 3: date and time; Field 4: supplementary reference information.Fascicle III.7 - Rec. I.241.2 3Field 1 - (identification of the called equipment) contains the identification of the called equipment. It is originated in thecontrol procedures by the called equipment.Field 2 - (identification of t
25、he calling equipment) contains the identification of the calling equipment. It is originated inthe control procedures by the calling equipment.Field 3 - (date and time) contains the date and time reference information showing the year, month, day, hour and minutein the fixed format of 14 characters
26、thus YY-MM-DD-HH:MM. This field is originated in the control procedures by thecalling equipment which obtains this information from the network. This time represents the local time at the callingequipment and is intended to represent the time of call origination.Field 4 - (supplementary reference in
27、formation) contains a document reference number, a hyphen (coding 2/13) as aseparator and a page reference number as number as defined in Recommendation T.62. This field has a fixed length ofseven character positions and is originated in the control procedures by the Teletex equipment that is sendin
28、g theassociated documents.FIGURE 1/I.241.2Format of the call identification line2.3.4 Error protectionWithin the Teletex service a high layer error detection and correction is provided in the session layer for allthose errors which are not corrected by the network layers.To ensure call integrity, er
29、ror protection will be provided by Teletex control procedures (seeRecommendations T.62, T.70 and T.90). The error rate on the pre-information, information and post-information phasesshould not exceed 1 in 106characters.2.4 Network capabilities for chargingThis Recommendation does not cover charging
30、principles. Future Recommendations in the D-Series areexpected to contain that information.It shall be possible to charge the subscriber accurately for the service.2.5 Interworking requirements2.5.1 Within the Teletex service, interworking between terminals connected to different networks is require
31、d. Real-time connection between terminals operating at different speeds has to be provided on the basis of at least 2.4 kbit/s.2.5.2 Intercommunication with other services2.5.2.1 The Teletex service will provide the ability for intercommunication in both directions with the telex service bymeans of
32、conversion facilities (see Recommendations F.201, U.201, T.390).2.5.2.2 Intercommunication between basic mode and mixed mode Teletex terminals and Classes I, II and III Group 4facsimile terminals is shown in Table 1/I.241.2 (see Recommendation F.184).4 Fascicle III.7 - Rec. I.241.22.5.2.3 The Telete
33、x service allows for intercommunication with telex and with the Interpersonal Messaging Service(IPM) (see Recommendations F.421, F.422).TABLE 1/I.241.2Current status of direct intercommunicationfor Teletex and Group 4 facsimile terminals on the same networkT: Basic Teletex document with character co
34、ded information only.F: Group 4 facsimile document with facsimile coded information only.MM: Mixed-mode document with character and facsimile coded information.PM1: Processable mode document with character coded information only.2.6 Interaction with supplementary servicesEach supplementary service d
35、escription identifies the applicability with this teleservice.For the ISDN, the international supplementary services which may be used for Teletex in the circuit modeusing a B-Channel are:i) closed user group;ii) multiple subscriber number;iii) user-to-user signalling;iv) calling line identification
36、 presentation;v) calling line identification restriction;vi) connected line identification presentation;vii) connected line identification restriction;viii) direct-dialling-in.The use of other supplementary services is for further study.Supplementary services for Teletex with a packet-mode of operat
37、ion are for further study.ToFromFacsimileGroup 4,Class IFacsimileGroup 4,Class IIFacsimileGroup 4,Class IIITeletexbasic modeTeletexmixed modeTeletexprocessablemode 1Facsimile Group 4,Class IFFFFacsimile Group 4,Class IIFFFFacsimile Group 4,Class IIIF T, F, MM T, F, MM T T, MM TTeletex basic mode T T
38、 T T TTeletex mixed mode T, MM T, MM T T, MM TTeletex processablemode 1T T T T T, PM1Fascicle III.7 - Rec. I.241.2 52.7 Attributes and values of attributes of the Teletex servicea) LOW LAYER ATTRIBUTESInformation transfer attributesCircuit-mode bearer capability Packet-mode bearer capability1. Infor
39、mation transfer mode circuit packet2. Information transfer rate 64 kbit/s maximum throughput of a givenvirtual circuit is less than or equalto the maximum bit rate of theuser information access channeland the throughput class of thevirtual circuit3. Information transfer capability unrestricted (Note
40、 1) unrestricted4. Structure unstructured (Note 2) service data unit integrity5. Establishment ofcommunicationdemand demand (VC), permanent (PVC)6. Symmetry bidirectional symmetric bidirectional symmetric7. Communication configuration point-to-point point-to-pointAccess attributesCircuit-mode bearer
41、 capability Packet-mode bearer capability8. Access channel: B for user informationD for signallinguser information over virtualcircuit within B- or D-channel.When D-channel is used,maximum packet size and qualityof service may be restricted.Signalling may be provided via D-channel and/or virtual cir
42、cuitwithin B-channel.9. Access protocol9.1 Signalling access protocollayer 1:Rec. I.430/I.431 Rec. I.430/I.4319.2 Signalling access protocollayer 2:Rec. I.440/I.441 Rec. I.440/I.441, X.319.3 Signalling access protocollayer 3:Rec. I.450/I.451 Rec. I.450/I.451, X.319.4 Information access protocollayer
43、 1:Rec. I.430/I.431 Rec. I.430/I.4319.5 Information access protocollayer 2:Rec. X.75 (SLP) Rec. X.25 (LAPB)9.6 Information access protocollayer 3:ISO 8208 Rec. X.25 (PLP)6 Fascicle III.7 - Rec. I.241.2b) HIGH LAYER ATTRIBUTES10. Type of user information : Teletex11. Layer 4 protocol functions: T.701
44、2. Layer 5 protocol functions: T.6213. Layer 6 protocol functions: T.6114. Layer 7 protocol functions: T.60c) GENERAL ATTRIBUTES15. Supplementary services provided: see 2.616. Quality of service: for further study17. Interworking possibilities: see 2.518. Operational and commercial: for further stud
45、ySLP Single link protocolPLP Packet layer protocolVC Virtual circuitPVC Permanent virtual circuitNote 1 - The interworking arrangements with networks having a restricted 64 kbit/s information transfercapability require further study.Note 2 - Even if no structure is required the network may provide 8
46、 kHz integrity.2.8 Recommended support of Teletex by an ISDNa) Overall support2: Ab) Variations of non-dominant attributes:1) Information transfer modeNote - In the interim period, the circuit mode method of operation is preferred circuit: A packet: A2) Establishment Symmetry Communication Support2o
47、f communication configuration_demand bidirectional pt-pt Esymmetric2The definition of E (essential) and A (additional) can be found in Recommendation I.240.Fascicle III.7 - Rec. I.241.2 73) AccessNote 1 - Definition of protocols for OAM is for further study.Note 2 - Demand services only. Others are
48、for further study.2.9 Dynamic descriptionThe circuit-mode dynamic description appears in Recommendation I.220.Signalling and OAM(Note 1)User informationSupportChannel and rate Protocols Channel and rate ProtocolsCircuit modeD(16) I.430, I.440, I.441,I.450, I.451(Note 2)B(64) I.430,X.75 (SLP),ISO 820
49、8AD(64) I.431, I.440, I.441,I.450, I.451(Note 2)B(64) I.431,X.75 (SLP),ISO 8208APacket modeD(16) I.430, I.440, I.441,I.450, I.451, X.31B(64) or D (16) I.430,X.25 LAPB,X.25 (PLP)AD(64) I.431, I.440, I.441,I.450, I.451, X.31B(64) I.431,X.25 LAPB,X.25 (PLP)FSVC in B(64) for further study B(64) for further study FS
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