1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU x.3 (03/00) SERIES X: DATA NETWORKS AND OPEN SYSTEM COM M U N I CAT I ON S Public data networks - Services and facilities Packet assembly/disassembly facility (PAD) in a public data network ITU-T Recommendati
2、on X.3 (Previously CCITT Recommendation) ITU-T X-SERIES RECOMMENDATIONS DATA NETWORKS AND OPEN SYSTEM COMMUNICATIONS PUBLIC DATA NETWORKS Services and facilities X.1-X.19 Interfaces Transmission, signalling and switching Network aspects Maintenance Administrative arrangements Model and notation Serv
3、ice definitions Connection-mode protocol specifications Connectionless-mode protocol specifications PICS proformas Protocol Identification Security Protocols Layer Managed Objects Conformance testing General Satellite data transmission systems MESSAGE HANDLING SYSTEMS DIRECTORY OS1 NETWORKING AND SY
4、STEM ASPECTS OPEN SYSTEMS INTERCONNECTION INTERWORKING BETWEEN NETWORKS Networking Efficiency Quality of service Naming, Addressing and Registration Abstract Syntax Notation One (ASN. 1) Systems Management framework and architecture Management Communication Service and Protocol Structure of Manageme
5、nt Information Management functions and ODMA functions OS1 MANAGEMENT SECURITY OS1 APPLICATIONS Cornmitment, Concurrency and Recovery Transaction processing Remote operations OPEN DISTRIBUTED PROCESSING X.20-X.49 X.50-X.89 X.90-X. 149 X.150-X. 179 X. 180-X. 199 X.200-X.209 X.2 1 0-X.2 19 X.220-X.229
6、 X.230-X.239 X.240-X.259 X.260-X.269 X.270-X.279 X.280-X.289 X.290-X.299 X.300-X.349 x.350-x.399 X.400-X.499 X.500-X.599 X.600-X.629 X.630-X.639 X.640-X.649 X.650-X.679 X.680-X.699 X.700-X.709 X.71 0-X.7 19 X.720-X.729 x.730-x.799 X.800-X.849 X.850-X.859 X.860-X.879 X.880-X.899 X.900-X.999 For furth
7、er details, please rer to ITD-T List of Recommendations. ITU-T RECOMMENDATION X.3 PACKET ASSEMBLY/DISASSEMBLY FACILITY (PAD) IN A PUBLIC DATA NETWORK Summary This Recommendation describes the functions performed by, and operational characteristics of, the PAD for the start- stop mode DTE. It provide
8、s the operation of the PAD depending on the possible values of PAD parameters. This revision includes a new parameter for the selection of the default packet size and additional PAD service and command signals for Chinese extended dialogue mode. Source ITU-T Recommendation X.3 was revised by ITU-T S
9、tudy Group 7 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on 3 1 March 2000. Recommendation X.3 (03/00) 1 FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommuni- cations. The ITU Telecommunication Standardiz
10、ation Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC
11、), 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 the procedure laid down in WTSC Resolution No. 1. In some areas of info
12、rmation technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating age
13、ncy. INTELLECTUAL PROPERTY RIGHTS The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual P
14、roperty Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. Howe
15、ver, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O ITU 2000 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, inc
16、luding photocopying and microfilm, without permission in writing fiom the ITU. Recommendation X.3 (03/00) 11 CONTENTS Scope 1 1.3 Functions of the PAD 1.4 User selectable functions which may be provided by the PAD . Characteristics of PAD parameters . 2.4 Determination of the values of PAD parameter
17、s . List of PAD parameters and possible values Description of the basic functions and user selectable functions of the PAD . 2 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26 3.27 3.28 3.29 3.30 PAD recall using a character .
18、 Echo Selection of data forwarding character(s) Selection of idle timer delay Control of PAD service signals and PAD command signals . Selection of operation of PAD on receipt of break signal fi-om the start-stop mode DTE Discard output . Padding after carriage return . Line folding . Binary speed F
19、low control of the PAD by the start-stop mode DTE Linefeed insertion after carriage return . Editing . Character delete . Line delete . Line display . Editing PAD service signals Echo mask . Ancillary device control Linefeed padding . Parity treatment . Page wait . Size of input field End-of-frame .
20、 Selection of extended data forwarding signals Display intemipt Confirmation of display intemipt Diacritic character editing . Extended echo mask Selection of the default packet size . Recommendation X.3 (03OO) Page 1 2 2 2 5 5 5 6 6 6 6 7 7 8 8 8 8 8 9 9 10 10 10 10 10 11 11 11 12 12 12 12 13 13 13
21、 14 14 1 111 Recommendation X.3 PACKET ASSEMBLY/DISASSEMBLY FACILITY (PAD) IN A PUBLIC DATA NETWORK (revised in 2000) Scope The establishment in various countries of public data networks providing packet switched data transmission services creates a need to produce standards to facilitate access fro
22、m the public telephone network, circuit switched public data networks and leased circuits. The ITU-T, considering a) that Recommendations X.l and X.2 define the user classes of service and user facilities in public data networks, Recommendation X.96 defines call progress signals, Recommendation X.29
23、 defiies the procedures between a packet assembly/disassembly facility (PAD) and a packet mode DTE or another PAD, Recommendation X.28 defines the DTEDCE interface for a start-stop mode DTE accessing the PAD; b) X.92, and that in particular Recommendation X.92 allows for the incorporation of a PAD;
24、that the logical control links for packet switched data transmission services are defined in Recommendation c) the urgent need to allow interworking between a start-stop mode DTE on a public switched telephone network, a public switched data network or leased circuit, and a packet mode DTE or anothe
25、r start-stop mode DTE using the virtual call facility of the packet switched data service; 4 information in the form of characters or the break signals; that DTEs operating in the start-stop mode will send and receive network control information and user e) information in the form of packets in acco
26、rdance with Recommendation X.25; that DTEs operating in the packet mode will send and receive network control information and user I) packet mode DTEs may wish to control specific functions of the PAD, that the packet mode DTE shall not be obliged to use the control procedures for PAD functions, but
27、 that some recommend 1) described below in clause 1 , Description of the basic functions and user selectable functions of the PAD; that the functions performed by, and operational characteristics of, the PAD for the start-stop mode DTE are 2) variables known as PAD parameters which are described bel
28、ow in clause 2, Characteristics of PADparameters; that the operation of the PAD for the start-stop mode DTE should depend on the possible values of internal 3) below in clause 3, List of PADparameters andpossible values; that the PAD parameters for the start-stop mode DTE and their possible values s
29、hould be those which are listed 4) with non packet mode DTEs other than start-stop mode DTEs. that the PAD features described in clauses 1 , 2 and 3 could be expanded by future studies to allow interworking Recommendation X.3 (03/00) 1 1 Description of the basic functions and user selectable functio
30、ns of the PAD 1.1 The PAD performs a number of functions and exhibits operational characteristics. Some of the functions allow either or both the start-stop mode DTE and the packet mode DTE (or remote PAD) to configure the PAD so that its operation is adapted to the start-stop mode DTE characteristi
31、cs, and possible to the application. 1.2 The operation of the PAD depends on the value of the set of internal variables called PAD parameters. This set of parameters exists for each start-stop mode DTE independently. The current value of each PAD parameter defines the operational characteristics of
32、its related function. 1.3 Functions of the PAD 1.3.1 Basic functions include: - - - - generation of service signals; - assembly of characters into packets; disassembly of the user data field of packets; handling of virtual call Set-up and clearing, resetting and interrupt procedures; a mechanism for
33、 forwarding packets when the proper conditions exist, e.g., when a packet is full or an idle timer expires; a mechanism for transmitting data characters, including start, stop and parity elements as appropriate to the start- stop mode DTE; a mechanism for handling a break signal fiom the start-stop
34、mode DTE; editing of PAD command signals; a mechanism for setting and reading the current value of PAD parameters. - - - - 1.3.2 Optional functions include: - - - a mechanism for the selection of a standard profile; automatic detection of data rate, code, parity and operational characteristics; a me
35、chanism for the remote DTE to request a virtual call between the start-stop mode DTE and another DTE. 1.4 A number of packet-switched data network facilities may be available either on a subscription basis or on a per call basis, to start-stop mode DTEs as described in Recommendation X.2 for user cl
36、asses of service 20 to 22. In addition, the following features may be available on a subscription basis: - - - User selectable functions which may be provided by the PAD selection of an initial profile; modem type, speed, code and parity to be used by the PAD; other operational characteristics of th
37、e DTE. As defined in this Recommendation, parameters provide for functions which concern: - - - - management of the procedure between the start-stop mode DTE and the PAD; management of the assembly and disassembly of packets; a number of additional functions related to the operational characteristic
38、s of the start-stop mode DTE; a number of additional functions related to videotex applications. The method for the control of these functions is specified in Recommendation X.28 for the start-stop mode DTE and in Recommendation X.29 for the packet mode DTE or for another PAD. Table 1 shows details
39、of the valid values and combination of values of PAD parameters standardized by ITU-T. Other values and combinations of values are for further study. 2 Recommendation X.3 (03/00) 1.4.1 This function allows the start-stop mode DTE to initiate an escape from the data transfer state or the connection i
40、n progress state in order to send PAD command signals. PAD recali using a character 1.4.2 Echo This function provides for characters received from the start-stop mode DTE to be transmitted back to the start-stop mode DTE as well as being interpreted by the PAD. 1.4.3 This function allows the selecti
41、on of defined sets of character(s) received from the start-stop mode DTE to be recognized by the PAD as an indication to complete the assembly and forward a complete packet sequence as defined in Recommendation X.25. Selection of the data forwarding characters 1.4.4 Selection of idle timer delay Thi
42、s function allows the selection of the duration of an interval between successive characters received from the start- stop mode DTE which, when exceeded, will cause the PAD to terminate the assembly of a packet and to forward it as defined in Recommendation X.25. 1.4.5 Ancillary device control This
43、function allows for flow control between the PAD and the start-stop mode DTE. The PAD indicates whether it is ready or not to accept characters from the start-stop mode DTE by transmitting special characters. These characters are those which in International Alphabet No. 5 (IA5) are used to switch a
44、n ancillary transmitting device on and off. 1.4.6 This function provides the start-stop mode DTE with the ability to decide whether or not and in what format PAD service signals are transmitted. Control of PAD service signals 1.4.7 Selection of operation of the PAD on receipt of the break signal Thi
45、s function allows the selection of the operation of the PAD after the receipt of a break signal from the start-stop mode DTE. 1.4.8 Discard output This function provides for a PAD to discard the content of user sequences in packets upon request rather than disassembling and transmitting these to the
46、 start-stop mode DTE. 1.4.9 Padding after carriage return This function provides for the automatic insertion by the PAD of padding characters in the character stream transmitted to the start-stop mode DTE after the occurrence of a carriage return character. This allows for the printing mechanism for
47、 the start-stop mode DTE to perform the carriage return function correctly. 1.4.10 Line folding This function provides for the automatic insertion by the PAD of appropriate format effectors in the character stream transmitted to the start-stop mode DTE. The predetermined maximum number of graphic ch
48、aracters per line may be set. 1.4.11 This function allows for flow control between the start-stop mode DTE and the PAD. The start-stop mode DTE indicates whether it is ready or not to accept characters from the PAD by transmitting special characters. These characters are those which in IA5 are used
49、to switch an ancillary transmitting device on and off. Flow control of the PAD by the start-stop mode DTE 1.4.12 This function provides for the automatic insertion by the PAD of a linefeed character in the character stream to or from the start-stop mode DTE or after each of each carriage return character. This function applies only in the data transfer state. Linefeed insertion after carriage return Recommendation X.3 (03/00) 3 1.4.13 Padding after linefeed This function provides for the automatic insertion by the PAD of padding characters in the character stream transmitted to the start-s
