Telecommunications -

Standards History

CCIR CCITT General International

International Secretariat Frequency

Radio Telegraph and Registration

Consultative Telephone Board

Committee Consultative (IFRB)


CCITT study groups

COM I Definition, operation and quality of service aspects of
telegraph, data transmission and telematic services
COM II Operation of telephone network and ISDN
COM III General tariff principles including accounting
COM IV Transmission maintenance of international lines, circuits and chains of circuits; maintenance of automatic and semi-automatic networks
COM V Protection against dangers and disturbances of electromagnetic origin
COM VI Outside plant
COM VII Data communication networks
COM VIII Terminal equipment for telematic services
COM IX Telegraph networks and terminal equipment
COM X Languages and methods for telecommunications applications
COM XI ISDN and telephone network switching and signaling
COM XII Transmission performance of telephone networks and terminals
COM XV Transmission systems
COM XVII Data transmission over the telephone network
COM XVIII Digital networks including ISDN

4 - Standards

The nature of packet switching means that the customers terminal (computer) equipment is deeply involved with the procedures for setting up calls, error correction and all aspects of running the link, the customers equipment almost becoming part of the network.

Such networks only become practical when there is a commonly accepted standard for the orderly exchange of data (known as the protocol)

The widely used standard for packet switching is known as X.25, this is defined by the CCITT (Consultative Committee International Telephony & Telegraphy).

X.25 is not specific enough in some parts and different packet switching networks and different suppliers of computer equipment sometimes interpret it differently.

The types of customers equipment which can be connected to an X.25 link into Public Network range from small microprocessor PADs to large mainframe computers (PAD = Packet Assembler/Dissesembler - described in Public Network-PAD).

CCITT standards available from:

International Telecommunication Union

CCITT standards

The X-series Recommendations, Volume VIII, are published in the Red Book

they can be ordered from


Sales Services


Place des Nations,


Geneva 20,


Volume VIII consists of the following seven fascicles:

VIII.1 Data communication over the telephone network.

Series V Recommendations

VIII.2 Data communications networks: services and facilities

Recommendations X.1 - X.15

VIII.3 Data communications networks: interfaces

Recommendations X.20 - X.32

VIII.4 Data communications networks: transmission, signaling and

switching, network aspects, maintenance and administrative


Recommendations X.40 - X.181

VIII.5 Data communications networks: Open Systems Interconnection (OSI),

system description techniques

Recommendations X.200 - X.250

VIII.6 Data communications networks: interworking between networks,

mobile data transmission systems

Recommendations X.300 - X.353

VIII.7 Data communications networks: Message Handling Systems

Recommendations X.400 - X.430

X series - applicable to public data networks.

X.1 international user classes of service in public data networks
X.2 international user facilities in public data networks.
X.3 Packet assembly/disassembly
X.4 General structure of signals of IA5 code for data transmission over public data networks
X.20 Interface between data terminal equipment and data circuit- terminating equipment for start-stop transmission services on public data networks.
X20 bis V21 compatible interface between DTE and DCE for start-stop transmission services on public data networks.
X.21 General purpose interface between DTE and DCE for synchronous operation on public data networks.
X21 bis use on public data networks of DTE which are designed for interfacing to synchronous V-series modems.
X22 Multiplex DTE/DCE Interface for user classes 3-6
X24 list of definitions of interchange circuits between DTE and DCE on public data networks
X.25 Interface between DTE and DCE for terminals operating in packet mode on public data networks.
X.26 Electrical characteristics for unbalanced double-current interchange circuits for general use with integrated circuit equipment in the field of data communications (identical to V10)
X.27 (identical to V.11)
X.28 DTE/DCE interface for a start/stop mode DTE accessing the PAD facility on a public data network situated in the same country.
X.29 Procedures for exchange of control information and user data between a packet mode DTE and a PAD
X.30 Support of X.21 and X.21bis based DTE's on the ISDN
X.31 Support of packet mode terminal equipment's on an ISDN
X.32 Interface between DTE and DCE for packet-mode terminals accessing a packet switched public data network through a public switched telephone network of a circuit switched public data network.
X.40 Standardization of frequency shift modulated transmission systems for the provision of telegraph and data channels by frequency division of a primary group
X.50 Fundamental parameters of a multiplexing scheme for the international interface between synchronous data networks
X.75 Terminal and transit call control procedures to data transfer on international circuits between public data networks operating in the packet mode.
X.92 hypothetical reference connections for public synchronous data networks
X.95 NETWORK parameters in public data networks
X.96 call progress signals in public data networks.
X.101 See X.150
X.110 Routing principles for international public data services through switched public data networks of the same type.
X.121 International numbering plan for public data networks.
X.150 DTE and DCE test loops for public data networks for X.21 for X.21bis interfaces (was X.101)
X.180 Administration arrangements for international closed user groups.
X.200 reference model of OSI
X.210 Layer service conventions of OSI for CCITT applications
X.211 Physical Layer service definition of OSI for CCITT applications
X.212 Data link layer service definition of OSI for CCITT applications
X.213 Network service definition of open systems Interconnection for CCITT applications.
X.214 (ISO DP 8072) Transport service of OSI
X.215 session layer service definition
X.216 Presentation Layer service definition of OSI for CCITT applications
X.217 Common application service elements definition of OSI for CCITT applications
X.224 (ISO DP 8073) Transport protocol specifications of open systems interconnection for CCITT applications.
X.225 session protocol specification
X.300 General principles and arrangement for interworking between public data networks, and between public data networks and other public networks.

message handling systems

X.400 system model - service elements
X.401 basic service elements and optional user facilities
X.408 encoded information type conversion rules
X.409 presentation transfer syntax and notation
X.410 remote operations and reliable transfer server
X.411 message transfer layer
X.420 Inter=personal messaging user agent layer
X.430 access protocol for teletex terminals

F.200 The teletex service
S.60 Teletex terminal equipment
S.61 Character sets and coding for teletex
S.62 contol procedures for Teletex and Group 4 Facsimile
S.70 The teletex transport service

ISO standards

Information processing systems - open systems interconnection

ISO DP 7498 Basic reference model (was ISO TC97/SC16 N227)
ISO DP 8326 Session Services
ISO DP 8072 Transport service definition
646 7-bit coded character set for information processing exchange. (IS)
963 Guide for the definition of the 4-bit character set for information processing exchange. (IS)
2014 Writing of calendar dates in all numeric form. (IS)
2022 Code extension technique for use with the 7-bit coded character set. (IS)
2382/8 Information processing - vocabulary - data communications. (IS)
2382/18 Information exchange - vocabulary - distributed data processing. (IS)
3307 Information Interchange - representation of time of day. (IS)
3309 HDLC - Unbalanced class of procedures. (IS)
4073 8-bit coded character set for information interchange. (IS)
4335 HDLC - Balanced class of procedures. (IS)
6093 Representation of numeric values in character strings for information interchange. (IS)
6429 Additional control functions for character imaging devices.
7498 OSI - Basic reference model. (IS) (same as CCITT X200)
- dad 1: Connectionless mode. (ISO 8524).
- dad 2: Naming and addressing.
7776 HDLC - X25 link access procedures (1984 compatible).
8072 OSI - Transport service definition. (S)
- dad 1: Connectionless transport service.
8073 OSI - Connection oriented transport protocol. (IS)
- dad 1: Connectionless transport protocol.
- dad 2: Network connection management (network addressing).
8208 X25 - Packet mode protocol (1984 compatible).
8326 OSI - Connection oriented session service. (IS)
- dad 1: Symmetric synchronisation.
8327 OSI - Connection oriented session protocol. (IS)
- dad 1: Symmetric synchronisation.
8348 OSI - Network service definition.
- dad 1: Connectionless network service.
- dad 2: Network layer addressing.
8471 HDLC - Consolidation of elements of procedures.
8472 OSI - Network convergence protocol.
[For X25(1980); superseded by ISO 8878]
OSI - Connectionless network service protocl.
8509 OSI - Service conventions.
8524 OSI - Reference model - connectionless mode addendum.
8571 OSI - File transfer, access and manipulation (FTAM).
8571/1 - General description.
8571/2 - Virtual file store.
8571/4 - File protocol specification.
8602 OSI - Connectionless transport protocol.
8649 OSI - Common application service elements (CASE).
8649/1 - Introduction.
8649/2 - Basic kernel subset.
8649/3 - Commitment, concurrency and recovery (CCR).
8650 OSI - Protocols for common application service elements(In several parts; 8650/3 covers CCR).
8802 IEEE 802 compatible standards 8802/1 to 8802/5. (e.g. 8802/2 OSI - Data link layer).
8802/7 Slotted ring technique (i.e. Cambridge ring R-layer).
8807 LOTOS - A formal description technique.
8822 OSI - Connection oriented presentation service.
8823 OSI - Connection oriented presentation protocol.
8824 OSI - Specification of abstract syntax notation one ASN.1).
8831 OSI - Job transfer and manipulation (JTM) service.
8832 OSI - JTM basic class protocol
8871 OSI - Data link layer address resolution.
8878 OSI - Use of X25(1984) to provide connection oriented NS.
8880/1 General issues.
8880/2 In relation to X25(1984).
8880/3 In relation to ISO 8473.
8882 X25 DTE conformance testing.
8885 General-purpose XID I-field content and format.
8886 OSI - Data link service.
9065/60 Message oriented text interchange.
9074 ESTELLE - a formal description technique

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