1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU OPERATIONS AND QUALITY OF SERVICE TELEMATIC SERVICE F.301 (1 0/95) FAST SPEED PSTN VIDEOTEX ITU-T Recommendation F.301 (Previously “CCITT Recommendation”) ITU-T RECflN*F*303 95 4862593 0605643 784 FOREWORD Th
2、e ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a world
3、wide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by
4、 the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation F.301 was prepared by ITU-T Study Group 1 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 3rd of October 1995. NOTE In this Recommendation, the expression “Administratio
5、n” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1996 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, wit
6、hout permission in writing from the ITU. ITU-T RECMN*F=303 95 H 4862593 Ob05644 bL0 m CONTENTS 1 Definition . 2 Description of the service . 2.1 General description . 2.3 Applications 3 Procedures 4 Network aspects . 5 Charging considerations . 6 Terminals 7 Quality of Service Interoperability with
7、other telematic services . Interoperability between videotex systems . 2.2 Specific terminology . 8 Interoperability . 8.1 8.2 Recommendation F.301 (10/95) Page 1 1 1 1 1 1 1 2 2 2 2 2 2 1 ITU-T RECPlN*F.301 95 = 4862593 0605b4.5 557 SUMMARY This Recommendation describes a high-speed terminal access
8、 to videotex services for use on the Public Switched Telephone Network (PSTN). It is equally applicable to any of the three defined regional data syntaxes. It provides not only for faster throughput, but also access to new capabilities that are not feasible at lower speeds. 11 Recommendation F.301 (
9、10/95) ITU-T RECMN*F*301 95 4862591 0605646 493 m Recommendation F.301 FAST SPEED PSTN VIDEOTEX (Geneva 1995) 1 Definition Fast-speed videotex is defined as the access to videotex services via the PSTN with a modem speed faster than 2400 bih in both ways (modems V.27 fer short train, V.29 short trai
10、n as defined by Recommendations T.104, V.32, V.32 bis, V.34). 2 Description of the service 2.1 General description Compared to existing videotex speeds (1200/75, 1200/1200, 2400/2400, 4800/75 bii/s), fast speed videotex provides a higher throughput and corresponding ease of use of existing alphamosa
11、ic, alphaphoto and alphageometric and file transfer services. It also meets new requirements such as the enhancement of text services with low resolution still pictures following JPEG-ISODIS 10.91 8 compression algorithm (Annex F/T. 101, describes the photographic syntax to be used in videotex servi
12、ces). Access to services is made with terminals that may or may not be dedicated to videotex use. Because of the higher cost of these terminals, the market for fast speed videotex is first seen to be professional users and then should progressively spread to the mass market. Implementation of fast-s
13、peed videotex should be upwards compatible with the traditional videotex systems as far as the terminals, the network and the service aspects are concerned. 2.2 Specific terminology See Blue Book, clause 2F.300, “Definition of terms” 2.3 Applications At present, there are three types of applications
14、 identified for fast-speed videotex: - Faster access of existing alphamosaic, alphaphoto and alphageometric services - This application concerns all the existing services and does not necessarily require any modification of those services. File transfer - This application concerns existing services
15、and does not necessarily require any modification of those services. - - Enhancement of text services with still pictures in various fields such as real estate, medicine, tourism, agriculture, shows, sports, etc. 3 Procedures If an end user introduces a request for a feature (i.e. photo) incompatibl
16、e with that users terminal, a service message should be sent to the user advising that that particular feature cannot be accessed from that type of terminal. 4 Network aspects The existing network infrastructure for current videotex is used with additional fast-speed ports. Recommendation F.301 (10/
17、95) 1 5 Charging considerations As far as the end user is concerned, fast-speed videotex does not necessarily imply any change in the existing billing system. The appropriate billing system will need to take into account the increased volume according to the scheme in use nationally: - flat rate; -
18、multirate; - charge dependent on the transmitted volume. When several transport classes (in terms of number of bytes per second) are available, the information provider or the videotex operator has to choose the most appropriate transport class, regarding the type of his service. The service provide
19、r may be charged for each overflow. For further details, see the D-Series Recommendations. 6 Terminals The terminal may be dedicated for videotex use or not. The use of multi-speed modems allows accessing high speed and photographic services, as well as current videotex services. Terminals based on
20、microcomputers may be able to use file transfer services. The compression with the PEG Standard allows the display of low resolution still images. The main body of Recommendation T.101 (1992) has defined a mechanism called “TFI: Terminal Facility Identifier” which could be used to determine the capa
21、bilities of the terminal (e.g. photographic profiles). NOTE - It should be noted that: - - this TFI mechanism is applicable to the three regional data syntaxes (Captain, CEPT and NAPLPS); the photographic profiles are common to the three regional syntaxes. 7 Quality of Service See Blue Book, clause
22、71F.300. 8 Interoperability 8.1 See Blue Book, clause 6lF.300. Interoperability with other telematic services 8.2 Interoperability between videotex systems1) The international interworking of the national fast-speed videotex systems is consistent with the principles described in clause 5F.300, “Inte
23、rnational interworking of videotex services”. In the case of transmitting still pictures, existing international gateways should be made transparent to photovideotex syntax, even if they have to transcode the data syntax. i) In the case of international fast-speed videotex, a bilateral agreement may be required to cover sharing of transportation costs between the two countries and the possibility of imposing overfiow surcharge. For further details, see the D-Series Recommendations. 2 Recommendation F.301 (10/95)
