1、ITU-T RECMN*T=LOY 93 4862571 0593733 1Bb INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEMATIC SERVICES TERMINAL EQUIPMENTS AND PROTOCOLS FOR TELEMATIC SERVICES T.104 (03/93) PACKET MODE ACCESS FOR SYNTAX-BASED VIDEOTEX VIA PSTN ITU-T Recommendation T.
2、104 (Previously “CCITT Recommendation”) FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a vi
3、ew to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation T.1
4、04 was prepared by the ITU-T Study Group VI11 (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommun
5、ication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the text to references containing
6、the acronyms “CCITT, CCIR or IFRl3” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a recognized operating agency. In this Reco
7、mmendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1994 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
8、from the ITU. 1 2 3 4 5 6 7 8 9 10 11 12 13 CONTENTS Scope Normative references . Definitions and abbreviations . Overview Configurations., General Model Service Definition . 7.1 Introduction . 7.2 Kernel services 7.3 Optional services Coding . Use of Recommendation X.3 Parameters . Bearer Independe
9、nt Service (BIS) for Syntax-based Videotex Lower Layers . 12.1 Layer 3 protocols . . 12.2 Layer 2 . . 12.3 Layer 1 protocol . Asynchronous interface . Annexe A . Examples of configurations . A.l Symbols . A.2 Connection to a VH . A.3 Access to a VS via a VAP A.4 Host to terminal call establishment .
10、 A.5 Terminal to terminal communication Annexe B - Usage of supplementary services Annexe C - Terminal Function basic state . Annexe D - The SBV-Escape service Annexe E - Extended data forwarding signals Annexe F - Operating sequences for V.29 short turn around . F . 1 Turn-ON sequence at 9600/7200
11、bits per second . F.2 Turn-ON sequence at 48OO/2400 bit/s . F.3 Turn-OFF sequence . F.4 Circuit 109 F.5 Circuit 106 Page 1 1 2 2 2 2 3 3 3 4 4 4 5 5 5 5 5 5 6 6 6 6 7 10 10 11 11 11 11 11 11 12 13 13 13 Recommendation T.104 (03/93) 1 ITU-T RECMN*T*LOLI 93 W LIB62591 0593736 995 H Recommendation T.10
12、4 PACKET MODE ACCESS FOR SYNTAX-BASED VIDEOTEX VIA PSTN (Helsinki, i 993) 1 Scope This Recommendation aims to meet the requirements of network operators and equipment manufacturers who are designing equipment to operate with an increase speed on Videotex Services over the public switched telephone n
13、etwork (PSTN). This Recommendation has a close relationship to Annexes BiT.lO1, CiT.101, Dfl.101, EiT.101 and FE.101 2 describing the Videotex data syntaxes. This Recommendation specifies how to use the end-to-end protocols defined by Recommendation T.105 3 in case of “Packet mode access for Syntax-
14、based Videotex via PSTN. It - - - - identifies the parts of Recommendation T.105 3 which apply; defines the protocol pillar ; precises the difference of semantic of some parameters precises the lower layer elements which are applicable. It is applicable to devices supporting “Packet mode access for
15、Syntax-based Videotex via PSTN to be attached at the DTE side of a modem. In this context, a device is either a Videotex Terminal a Videotex Service Center, a Videotex Access point or a Videotex Host and a modem is a device providing an interface according to one of the V Series Recommendations cont
16、ained in the list given in clause 2. This Recommendation applies only for modems operating in “Synchronous interface” in both directions. For Videotex Services using modems operating in “Asynchronous interface”, the protocols to be used are those already defined by national Videotex Services. The fo
17、llowing principles apply for the use of Recommendation T.105 3 in case of “Packet mode access for Syntax- based Videotex via PSTN: - - - the term “S/T reference point” shall be read “Modem interface” the PSTN network shall be used instead of the ISDN network; in case of “Packet mode access for Synta
18、x-based Videotex via PSTN” there is no D-channel and/or B- channel ; the. communication and/or signalling is done via the protocol pillar described in clause 6; all parts of Recommendation T.105 3 related to the use of “ISDN Supplementary Services” do not apply for “Packet mode access for Syntax-bas
19、ed Videotex via PSTN a communication channel is equivalent to a virtual circuit (VC). - - Normative references CCIT Recommendation T.90 (199 i), Characteristics and protocols for terminals for telematic services in ISDN. CCITT Recommendation T. 1 01, International Interworking for Videotex Services.
20、 CCITT Recommendation T. 105, Syntax-based Videotex Application Layer protocol. CCITT Recommendation V.22 bis (1988). 2400 bids duplex modem using the frequency division technique standardized for use on the general switched telephone network and on point Co point 2 wire leased telephone type circui
21、ts. Recommendation T.104 (03/93) 1 ITU-T RECMN*T*L04 93 4Bb259L 0573737 821 E CCIIT Recommendation V.26 bis (1988), 2400/1200 bids modem standardized for use in the general switched telephone network. CCITT Recommendation V.26 ter (1988), 2400 bids duplex modem using the echo cancellation technique
22、standardized for use on the general switched telephone network and on point to point 2 wire leased telephone type circuits. CCIlT Recommendation V.27 ter (1988), 4800/2400 bids modem standardized for use in the general switched telephone network. CCITT Recommendation V.29 (1988). 9600 bids modem sta
23、ndardized for use on point to point 4 wire leased telephone type circuits. CCITT Recommendation V.32 (1 988), A family of 2-wire, duplex modems operating at data signalling rates of up to 9600 bids for use on the general switched telephone network and on leased telephone type circuits. CCIIT Recomme
24、ndation V. 17 (1990). Recommendation for a 2-wire modem for facsimile applications with rates up to 14 400 bids. CCITT Recommendation V.42 (1988), Error correction procedures for DCE using asynchronous/synchronous converter. CCITT Recommendation X.3, Packet assembly disassembly facility (PAD) in a p
25、ublic data network. CCITT Recommendation X.32, (1988), Interface between data terminal equipment (DTE) and data-circuit terminating equipment (DCE) for terminals operating in the packet mode and accessing a packet switched public data network through a public switched telephone network or an integra
26、ted service digital network or a circuit switched public data network. CCITT Recommendation X.75, Packet-switched signalling system between public networks providing data transmission services. IS0 8208 standard (1990), Information processing systems - Data communications - X.25 Packet Level Protoco
27、l for Data Terminal Equipment. NOTE - The above list of modem Recommendations (V Series) might be extended if other types of modem will be standardized. 3 Definitions and abbreviations The definitions and abbreviations of Recommendation T.105 3 apply. Those related to ISDN are not used in this Recom
28、mendation. 4 Overview Clause 4f.105 3 applies except 4.5fl.105 3. 5 Configurations Clause 5fl.105 3 applies but examples of configurations are given in Annex A of this Recommendation. 6 General Model Clause 6f.105 3 applies with the following exceptions: - - the Access Network shall be the PSTN (see
29、 Figure 1) ; there are no “Channel-Management and “Coordination Function” for “Packet mode access for Syntax- based Videotex via PSTN; 2 Recommendation T.104 (03/93) ITU-T RECMN*T*LO4 73 4862573 0593738 768 X.75 14, X.32 13 (LAPX) 2 PSTN X.75 14 FIGURE l.104 Access Network scenario 1 Layer - the pro
30、tocol pillar is defined as follows V-Series Modem Recommendations Half Duplex Full Duplex FIGURE 2R.104 Protocol Pillar NOTE - Layers 4 and 5 are not used by “Packet mode access for Syntax-based Videotex via PSTN” Moreover, Note 2 of 6.3R.105 3, does not apply. 7 Service Definition 7.1 Introduction
31、Subclause 7.1R.105 3 applies. 7.2 Kernel services Subclause 7.2R. 105 3 applies with the following exceptions: Recommendation T.104 (03/93) 3 7.2.1 SBV-Establish The following parameters are not used by “Packet mode access for Syntax-based Videotex via PSTN”: - OB-Called-Address; - OBCalled-Subaddre
32、ss; - OB-Application-Address; - OB-Application-Selection; - OB-ApplicationData; - OB-User-Data; 7.2.2 SBV-Release The following parameter is not used by “Packet mode access for Syntax-based Videotex via PSTN”: - OBCause. 7.3 Optional services Subclause 7.3lT.105 3 applies with the following exceptio
33、ns: 7.3.1 SBVChannel-Open The following parameters are not used by “Packet mode access for Syntax-based Videotex via PSTN: - Req-OBCalled-Address ; - Req-OB-Called-Subaddress - OB-Application-Address; - OB-Application-Selection; - OB-Application-Data; - Req-OB-User -Data - Ind-OBCause. 7.3.2 SBV-Cha
34、nnel-Error The following parameter is not used by “Packet mode access for Syntax-based Videotex via PSTN: - Ind-OBCause. 8 Protocol Clause 8.105 3 applies. 9 Coding Clause 9/T. 105 3 applies. However, the following parameters shall not be used (see Table 40R.105 31): - Ind-OBCause; - OB-Application-
35、Address; - OB-Application-Data; - OB-ApplicationSelection; - OB-User-Data; - Req-OBCailed-Address; - Req-OBCalled-Subaddress; - ReqOB-User-Data. 4 Recommendation T.104 (03/93) ITU-T RECMN*T=LO4 93 = 4862591 0593740 316 U 10 Clause 10ir.105 3 applies with the following exception: In Table 43.105 3, t
36、he parameter i 1 may take one among the following values: 12 (2400 bids), 13 (4800 bids), i4 (9600 bids) and 15 (19200 bit/s) (see Recommendation X.3 12 for details). In that case, the Note 6 of Table 43. 1 O5 3 does not apply. Use of Recommendation X.3 121 Parameters 11 Clause 11/T.105 3 applies wi
37、th respect to the In-band procedures. Bearer Independent Service (BIS) for Syntax-based Videotex 12 Lower Layers This clause describes the lower layers (layer 1 to 3) for a ?Packet mode access for Syntax-based Videotex via PSTN? terminal. The description makes the difference between modems operating
38、 in half-duplex mode and those operating in full-duplex. This clause does not apply for modems operating in ?Asynchronous? interface. The protocols to be used for modems operating in ?Asynchronous? interface are described in clause 13. 12.1 Layer 3 protocols 12.1.1 Full-duplex mode The layer 3 proto
39、col to be used is described in Recommendation T.90 1 12.1.2 Half-duplex mode The layer 3 protocol to be used is described in Recommendation T.90 11 with the following supplementary rules: - NOTE - This default window size has been chosen because it allows a more efficient throughput in half-duplex.
40、the default packet window size is 3. 12.2 Layer2 12.2.1 Full-duplex mode The layer 2 protocol to be used is defined in Recommendation T.90 11. Alternatively, the layer 2 may also be embedded within the modem as described in Recommendation V.42 NOTE -The exact procedure for such a configuration needs
41、 further study. 12.2.2 Half-duplex mode The layer 2 protocol to be used is described in Recommendation T.90 I. The specific procedure (LAPX in case of half-duplex mode is described in 5.6X.32 13. 1 I. to be appiie? 12.3 Layer 1 protocol The layer 1 protocol to be used is the one described in the CCI
42、TT Recommendation, listed in clause 2 (V Series of Recommendations), related to the type of modem used. For V.29 8 modems, Annex F describes the operating sequences for V.29 short turn around. Recommendation T.104 (03/93) 5 ITU-T RECMN*T*LOq 93 LtBb2593 0593743 252 H 13 Asynchronous interface Videot
43、ex Services operating over the PSTN may wish to use different types of modems in “Asynchronous” interface, allowing an increase speed of communication, without modifying the lower layers protocols (error correction procedure by example) already used . For modems operating in the “Asynchronous” inter
44、face, the lower layers protocols to be used are those already defined by the different Videotex Services. Annex A Examples of configurations (This annex forms an integral part of this Recommendation) A.l Symbols See Figure A. 1. VideotexTerminal Videdex Access Point Hmt FIGURE A.lf.104 symbols A.2 C
45、onnection to a VH The Videotex Terminal is connected directly to a Videotex Host via the PSTN. At the protocol levei, one connection is estatblished between the terminal and host. See Figures A.2 and A.3. T080854O-91 /do3 FIGURE A.m.104 ConnectiontoaVH 6 Recommendation T.104 (03193) ITU-T RECMN*T*L0
46、4 93 W 4862.592 0593742 199 I 7 3 2 1 Terminai Application I 7 3 2 1 Application F FIGURE A.3T.104 Protocol stack for VT-VH connection A.3 Access to a VS via a VAP The terminal accesses a Videotex Service via a Videotex Access Point. The Host Access Network will be a PDN (generally a PSPDN). See Fig
47、ure A.4. FIGURE A.4n.104 Connection via a VAP The connection establishment with the host does not have any influence on the protocol stack between the terminal and the VAP. As far as the terminal is concerned, only a connection to the VAP exists. In terms of the protocol stack there is an end-to-end
48、 connection on layer 3 between the two sides, with an Application Layer on top. See Figure AS. A.3.1 Service selection after a dialogue with the VAP The terminal is connected to a VAP, which sets up a second connection to a server after some dialogue between the terminal and the VAP. This is basical
49、ly a refinement of the access to a VH. See Figure A.6. A.3.2 Service selection using a VS identification A connection is established between the terminal and the VAP. On this connection, layer 2 and layer 3 are set up. The layer 3 CALL REQUEST carries the address or the name of the requested application. This information is used by the VAP to establish an end-to-end dialogue between the terminal and the VH. See Figure A.7. Recommendation T.104 (03/93) 7 ITU-T RECNN*T.L04 93 4Bb259L 0593743
