ETSI ETS 300 079 ed.1 (1991-10)

Integrated Services Digital Network (ISDN); Syntax-based videotex End-to-end protocols, circuit mode DTE-DTE

DE/TE-01010

Digitalno omrežje z integriranimi storitvami (ISDN) – Protokoli za skladenjski sistem Videotex pri izvedbi konec-konec – Vodovni način za DTE-DTE

General Information

• Status: Published
• Publication Date: 20-Oct-1991
• Technical Committee: TE 1 - Telematics: Videotex and MultimediaInformation Retrieval Services
• Current Stage: 12 - Completion
• Due Date: 12-Jul-1991
• Completion Date: 21-Oct-1991
• Mandate: IT-149
• Ref Project: SIST ETS 300 079 E1:2003 - Integrated Services Digital Network (ISDN); Syntax-based videotex End-to-end protocols, circuit mode DTE-DTE

Standards Content (Sample)

SLOVENSKI STANDARD
01-december-2003
'LJLWDOQRRPUHåMH]LQWHJULUDQLPLVWRULWYDPL,6'1±3URWRNROL]DVNODGHQMVNL
VLVWHP9LGHRWH[SULL]YHGELNRQHFNRQHF±9RGRYQLQDþLQ]D'7('7(
Integrated Services Digital Network (ISDN); Syntax-based videotex End-to-end
protocols, circuit mode DTE-DTE
Ta slovenski standard je istoveten z: ETS 300 079 Edition 1
ICS:
33.080 Digitalno omrežje z Integrated Services Digital
integriranimi storitvami Network (ISDN)
(ISDN)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN ETS 300 079
TELECOMMUNICATION October 1991
STANDARD
Source: ETSI TC-TE Reference: DE/TE-01010
ICS: 33.080
ISDN; Videotex; End-to-end protocols; Circuit mode DTE - DTE
Key words:
Integrated Services Digital Network (ISDN);
Syntax-based Videotex end-to-end protocols
Circuit mode DTE - DTE
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
F-06921 Sophia Antipolis CEDEX - FRANCE
Postal address:
650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
Office address:
c=fr, a=atlas, p=etsi, s=secretariat - [e-mail]
X.400: Internet:
Tel.: [phone] - Fax: [phone]
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1991. All rights reserved.
New presentation - see History box

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ETS 300 079: October 1991
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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ETS 300 079: October 1991
Contents
Foreword.7
1 Scope .9
2 Normative references .9
3 Definitions and abbreviations.11
3.1 Definitions.11
3.2 Abbreviations.12
4 Overview .13
4.1 Direct selection of Videotex applications .13
4.2 Multi-communication .13
4.3 Multi-media communication .13
4.4 Distributed Videotex Application .14
4.5 ISDN supplementary services.14
4.6 Handling of incoming calls .14
5 Configurations.14
6 General model .15
6.1 Communication model.15
6.2 Terminal model .16
6.3 Access network scenario.20
6.4 Protocol pillar.21
7 Service definition .22
7.1 Introduction.22
7.2 Kernel services .23
7.2.1 SBV_Establish .23
7.2.2 SBV_Release .25
7.2.3 SBV_Reset.26
7.2.4 SBV_VTX_Data .26
7.2.5 X.3 [3] parameter manipulation services.26
7.2.5.1 SBV_Set_Param .26
7.2.5.2 SBV_Read_Param .27
7.2.5.3 SBV_Set_Read_Param.27
7.2.5.4 SBV_Param_Ind.27
7.2.6 SBV_TFI .28
7.2.7 SBV_TC_Error.28
7.3 Optional services .29
7.3.1 Communication channel management services.29
7.3.1.1 SBV_Channel_Open .29
7.3.1.2 SBV_Channel_Close.31
7.3.1.3 SBV_Channel_Error.32
7.3.2 Application selection services .33
7.3.2.1 SBV_Begin_Application.33
7.3.2.2 SBV_End_Application .33
7.3.3 Transparent processable data services.34
7.3.3.1 SBV_TPD_Begin .34
7.3.3.2 SBV_TPD_End.34
7.3.4 SBV_DFK.35
7.3.5 SBV_Escape .35

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ETS 300 079: October 1991
8 Protocol.36
8.1 Introduction.36
8.2 Kernel services .37
8.2.1 SBV_Establish .37
8.2.2 SBV_Release.37
8.2.3 SBV_Reset.38
8.2.4 SBV_VTX_Data .38
8.2.5 X.3 [3] parameter manipulation services.38
8.2.5.1 SBV_Set_Param .38
8.2.5.2 SBV_Read_Param.39
8.2.5.3 SBV_Set_Read_Param.39
8.2.5.4 SBV_Param_Ind.39
8.2.6 SBV_TFI.40
8.2.7 SBV_TC_Error.40
8.3 Optional services.41
8.3.1 Communication channel management services.41
8.3.1.1 SBV_Channel_Open .41
8.3.1.2 SBV_Channel_Close.41
8.3.1.3 SBV_Channel_Error.42
8.3.2 Application selection services .42
8.3.2.1 SBV_Begin_Application .42
8.3.2.2 SBV_End_Application.42
8.3.3 Transparent processable data services.43
8.3.3.1 SBV_TPD_Begin .43
8.3.3.2 SBV_TPD_End.43
8.3.4 SBV_DFK .43
8.3.5 SBV_Escape.44
9 Coding.45
9.1 Introduction.45
9.2 Coding of the telematic commands .45
9.3 Coding structures.46
9.3.1 Basic coding structure.47
9.3.2 Extended coding structure.48
9.3.3 Coding of data types .48
9.3.3.1 Integers .48
9.3.3.2 Strings.48
9.3.3.3 Voids .48
9.3.3.4 Octet sequences .48
9.4 Coding of parameters.48
9.4.1 Coding of parameter fields as defined in other documents .48
9.4.2 Coding of User data fields as defined in other documents .49
9.4.3 Coding of user data fields using free format.49
9.4.4 Coding of user data fields using the coding structures .50
9.4.5 Service specific coding.52
9.4.5.1 Coding of the Error_Code parameter .52
9.4.5.2 Coding of the DDU_Fall-Back_Mode parameter.53
9.4.5.3 Coding of the Function_Keys parameter .53
10 Use of CCITT Recommendation X.3 [3] parameters.57
10.1 Selectable functions provided by ISDN syntax-based Videotex Terminals.57
10.1.1 Standard functions.57
10.1.2 Extended functions .57
10.1.2.1 Size of input field .57
10.1.2.2 End-of-frame signals.57
10.1.2.3 Extended data forwarding signals.57
10.2 List of CCITT Recommendation X.3 [3] parameters and possible values.57
10.2.1 Standard parameters.57
10.2.2 Extended parameters .57
10.2.2.1 Size of input field .58

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ETS 300 079: October 1991
10.2.2.2 End-of-frame signals.58
10.2.2.3 Extended data forwarding signals .58
10.2.3 Overview of supported CCITT Recommendation X.3 [3] parameters. 59
10.2.4 Other CCITT Recommendation X.3 [3] parameters.60
11 Lower Layers.61
11.1 Co-ordination between D-channel and B-channel .61
11.2 Layer 3 D-channel protocol .61
11.2.1 The access protocol. 61
11.2.2 Terminal selection and compatibility checking .61
11.2.3 Service specific use of supplementary services. 61
11.2.4 Call Progress signals.61
11.3 Layer 3 B-channel protocol .61
11.4 Layer 2 D-channel protocol .61
11.5 Layer 2 B-channel protocol .61
11.6 Layer 1 protocol.61
Annex A (informative): Examples of configurations . 62
A.1 Symbols . 62
A.2 Access to PSTN/PSPDN systems using a terminal adaptor .62
A.2.1 Analogue terminal adaptors.62
A.2.2 Rate adapting terminal adaptors.62
A.3 Connection to a VS.63
A.4 Access to a VS via a PSPDN .63
A.5 Access to a VS via an IVAP.64
A.5.1 Service selection after a dialogue with the IVAP . 64
A.5.2 Service selection using a VS identification .65
A.5.2.1 VS identified by a network address.65
A.5.2.2 VS identified by a name.65
A.5.3 Service selection using ISDN supplementary services .65
A.5.4 Distributed Videotex Application .66
A.5.4.1 Usage of a single VC between IVT and IVAP . 66
A.5.4.2 Establishment of the second VC by the IVT.67
A.5.4.3 Establishment of the second VC by the IVAP.67
A.6 Host to terminal call establishment.68
A.7 Terminal to terminal communication .68
Annex B (informative): Usage of supplementary services. 69
B.1 User-to-User Signalling (UUS) . 69
B.2 Supplementary services for addressing.69
B.2.1 Multiple Subscriber Number (MSN).69
B.2.2 Direct Dialling In (DDI). 69
B.2.3 Subaddressing (SUB).69
B.2.4 Call Deflection (CD).69
B.3 Supplementary services for identification.70
B.3.1 Calling Line Identification Presentation (CLIP).70
B.3.2 Calling Line Identification Restriction (CLIR) .70

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ETS 300 079: October 1991
Annex C (normative): Terminal Function basic state.71
C.1 CCITT Recommendation X.3 [3] parameter default values.71
C.2 SBV_DFK Default List.71
C.3 SBV_TPD default state.71
C.4 SBV_Escape default state .71
Annex D (informative): The SBV_Escape service .72
D.1 Service description .72
D.1.1 Bulk Update.72
D.2 Procedures.72
D.2.1 Bulk Update .72
D.3 Coding.73
Annex E (informative): Extended data forwarding signals.74
Annex F (informative): Bibliography.75
Annex G (informative): ETSI/CCITT cross-reference list .77
History .78

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ETS 300 079: October 1991
Foreword
This European Telecommunication Standard (ETS) has been produced by the Terminal Equipment (TE)
Technical Committee of the European Telecommunications Standards Institute (ETSI).
This ETS aims to meet the urgent requirements of network operators and equipment manufacturers who
are designing equipment to operate on an Integrated Services Digital Network (ISDN).
This ETS also has a close relationship to ETSs 300 072 [10] to 300 076 [14] inclusive and to other
proposed ETSs currently under development within the TE Technical Committee (draft prETS 300 177
[19], draft prETS 300 149 [18] and final draft prETS 300 080 [15]). Full details of these documents are
given in Clause 2 (Normative references) of this document.
NOTE: Abstract testing requirements for this ETS are to be developed by ETSI.

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ETS 300 079: October 1991
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ETS 300 079: October 1991
1 Scope
This standard specifies the end-to-end protocols for the ISDN syntax-based Videotex Service.
NOTE 1: This standard does not specify any service aspects of the ISDN syntax-based Videotex
Service.
This standard is applicable to devices supporting the ISDN syntax-based Videotex, to be attached at either
side of a T reference point or coincident S and T reference points when used as an access to the public
ISDN. In this context, a device is either an ISDN Videotex Terminal, an ISDN Videotex Service Centre, an
ISDN Videotex Access Point or an ISDN Videotex Host (cf. subclause 3.1).
For the lower layer protocols (layer 1 to layer 3), this standard makes use of final draft
prETS 300 080 [15] (based on CCITT Recommendation T.90) for demand circuit-switched calls using the
64 kbit/s unrestricted digital information bearer capability and the DTE/DTE case of the Network Layer
peer entities in B-channel connection.
NOTE 2: The end-to-end protocol specified in this ETS is intended to be applicable not only for
the DTE/DTE connection over an ISDN.
2 Normative references
This ETS incorporates by dated or undated reference, provisions from other publications. These normative
references are cited at the appropriate places in the text and the publications are listed hereafter. For
dated references subsequent amendments to, or revisions of, any of these publications apply to this ETS
only when incorporated in it by amendment or revision. For undated references the latest edition of the
publication referred to applies.
[1] CCITT Recommendation F.300 (1988): "Videotex Service".
[2] CCITT Recommendation T.51 (1988): "Coded character sets for telematic
services".
[3] CCITT Recommendation X.3: "Packet assembly/disassembly facility (PAD) in a
public data network".
[4] CCITT Recommendation X.25 (1988): "Interface between data terminal
equipment (DTE) and data circuit-terminating equipment (DCE) for terminals
operating in the packet mode and connected to public data networks by
dedicated circuit".
[5] CCITT Recommendation X.29: "Procedures for the exchange of control
information and user data between a packet assembly/disassembly (PAD)
facility and a packet mode DTE or another PAD".
[6] CCITT Recommendation X.75 (1984): "Packet-switched signalling system
between public networks providing data transmission services".
[7] CCITT Recommendation X.121 (1988): "International numbering plan for public
data networks".
[8] Draft prETS 300 011: "Integrated Services Digital Network (ISDN); Primary rate
user-network interface, Layer 1 specification and test principles (T/L 03-14)".
[9] Draft prETS 300 012: "Integrated Services Digital Network (ISDN); Basic user-
network interface, Layer 1 specification and test principles (T/L 03-07)".
[10] ETS 300 072 (1990): "Terminal Equipment (TE); Videotex Presentation Layer
protocol, Videotex presentation layer data syntax (T/TE 06-01)".

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ETS 300 079: October 1991
[11] ETS 300 073 (1990): "Terminal Equipment (TE); Videotex presentation layer
syntax; Geometric Display (CEPT Rec. T/TE 06-02, Edinburgh 1988)".
[12] ETS 300 074 (1990): "Terminal Equipment (TE); Videotex Transparent Data
(CEPT Rec. T/TE 06-03, Edinburgh 1988)".
[13] ETS 300 075 (1990): "Terminal Equipment (TE); Videotex processable data
(T/TE 06-04)".
[14] ETS 300 076 (1990): "Terminal Equipment (TE); Videotex, Terminal Facility
Identifier (TFI) (T/TE 06-05)".
[15] Final draft prETS 300 080: "Integrated Services Digital Network (ISDN); ISDN
lower layer protocols for telematic terminals (T/TE 12-04)".
[16] ETS 300 102-1 (1990): "Integrated Services Digital Network (ISDN); User-
network interface layer 3, Specifications for basic call control".
[17] ETS 300 125 (1991): "Integrated Services Digital Network (ISDN); User-network
interface data link layer specifications, Application of CCITT Recommendations
Q.920/I.440 and Q.921/I.441".
[18] Draft prETS 300 149: "Terminal Equipment (TE); Videotex: Audio Syntax".
[19] Draft prETS 300 177: "Terminal Equipment (TE); Videotex, Photographic Syntax
(T/TE 06-06)".
[20] ISO 7776: "Information processing systems - Data communications - High-level
data link control procedures - Description of the X.25 LAPB-compatible DTE
data link procedures".
[21] ISO 8208: "Information processing systems - Data communications - X.25
Packet Level Protocol for Data Terminal equipment".

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ETS 300 079: October 1991
3 Definitions and abbreviations
3.1 Definitions
For the purposes of this standard, the following definitions apply:
Access Function: the functional entity which gives access to the Videotex Service. This entity is an
integral part of the Videotex Service.
Access Network: the network which provides the link between the Terminal Function and the Access
Function.
Audio data: generic term for data which can be made audible (e.g. wave form encoded, phonemically
encoded).
Distributed Videotex Application: a Videotex Application which makes use of more than one Videotex
Host.
Host Access Network: the network which provides the link between the Access Function and the Host
Function(s). It is an integral part of the Videotex Service and may be void.
Host Function: the abstraction of the Videotex Applications available in a particular Videotex Service.
Multi-media communication: term used to indicate that both pictorial and audio data are exchanged.
Pictorial data: generic term for data which can be displayed (e.g. alphamosaic, geometric, photographic).
Telematic Command: In the scope of this ETS, a Telematic Command is a specific service element which
is carried in a complete packet sequence of X.25 PLP DATA packets with the Q-bit set to 1. The
first octet in the User Data field of the first packet of the complete packet sequence carries a
value which is reserved for videotex (cf. draft CCITT Recommendation X.29 (1992), "Telematic
service message, videotex").
Terminal Function: the abstraction of a functional entity which acts as a Videotex Terminal.
Videotex Access Point: see CCITT Recommendation F.300 [1].
Videotex Application: see CCITT Recommendation F.300 [1].
Videotex External Host: see CCITT Recommendation F.300 [1].
Videotex Host: this term describes a computer which offers one or more applications and/or facilities. It
can be represented through a Videotex Host Computer, an External Videotex Host or a Videotex
Service Centre.
Videotex Host Computer: see CCITT Recommendation F.300 [1].
Videotex Service: see CCITT Recommendation F.300 [1].
Videotex Service Centre: see CCITT Recommendation F.300 [1].
NOTE: According to CCITT Recommendation F.300, a Videotex Service Centre provides host
and/or access functions, i.e. it may also act as a Videotex Access Point.
Videotex Terminal: see CCITT Recommendation F.300 [1].

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ETS 300 079: October 1991
3.2 Abbreviations
For the purposes of this standard, the following abbreviations apply:
AU Access Unit
CCITT International Telegraph and Telephone Consultative Committee
CD Call Deflection
CLIP Calling Line Identification Presentation
CLIR Calling Line Identification Restriction
DCE Data Circuit-terminating Equipment
DDI Direct Dialling In
DDU Dialogue Data Unit
DFK Definable Function Key
DTE Data Terminal Equipment
ETS European Telecommunication Standard
HAN Host Access Network
IB In-Band
ISDN Integrated Services Digital Network
ISO International Organization for Standardization
ISPBX Integrated Services Private Branch eXchange
IVAP ISDN syntax-based VAP
IVT ISDN syntax-based VT
LSB Least Significant Bit
MSB Most Significant Bit
MSN Multiple Subscriber Number
OB Out-Band
PDN Public Data Network
PDU Protocol Data Unit
PH Packet Handler
PLP Packet Level Protocol
PSPDN Packet Switched Public Data Network
PSTN Public Switched Telephone Network
Rec Recommendation
SBV Syntax-Based Videotex
SUB Subaddressing
TDU Telesoftware Data Unit
TFI Terminal Facility Identifier
TPD Transparent Processable Data
UUI User-to-User Information
UUS User-to-User Signalling
VAP Videotex Access Point
VC Virtual Circuit
VH Videotex Host
VPDE Videotex Presentation Data Element
VS Videotex Service
VT Videotex Terminal
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ETS 300 079: October 1991
4 Overview
The main feature of an ISDN syntax-based Videotex Terminal (VT) is the capability to access those
Videotex Services which are defined for and used in a Public Switched Telephone Network (PSTN) or
Packet Switched Public Data Network (PSPDN) environment using an ISDN as an access network.
More advanced services can make use of additional features (specific for an ISDN), which are presented
in the following subclauses.
4.1 Direct selection of Videotex applications
The protocol allows the Videotex Terminal to shortcut the dialogue and welcome phase of the Videotex
Service and to be connected with a given Videotex Application identified by a network address or a
mnemonic.
4.2 Multi-communication
Multi-communication allows a terminal to establish several independent communication channels to one or
several independent Videotex Hosts or Videotex Applications.
The protocol supports multi-communication using virtual circuits on one B-channel.
NOTE: The handling of several independent communication channels may appear in any
configuration (cf. informative Annex A).
EXAMPLE: Assume that "ETSI" and "CCITT" are two Videotex Applications offering the
possibility to Videotex users to read texts of telecommunication standards. In
order to compare the text of a given ETS with an equivalent recommendation,
the terminal should establish a virtual circuit (VC) with each of the two
applications. The information from the two applications shall be simultaneously
displayed on the terminal using some windowing capability.
4.3 Multi-media communication
Multi-media information may contain pictorial data (i.e. alphamosaic, geometric, and photographic display
elements) and audio data. The audio data may be transmitted either in parallel or in serial with the pictorial
data.
When the audio data is transmitted in serial with the pictorial data, a single virtual circuit may be used to
carry both.
When the audio data has to be sent in parallel with the pictorial data, a second virtual circuit dedicated to
the transmission of audio data shall be set up.
The protocol supports multi-media communication using virtual circuits on one B-channel, providing for the
simultaneous reproduction of both pictorial and audio information, in addition to a serial transmission
already covered by the data syntax.
NOTE: The handling of several additional communication channels may appear in any
configuration (cf. informative Annex A).

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ETS 300 079: October 1991
4.4 Distributed Videotex Application
It is recognized that, to accomplish some specific application, the application may be decomposed into
several sub-applications which may be implemented on more than one host. A communication channel from
the terminal to each of the sub-applications may exist. The incoming datastreams are combined in the
terminal to deliver the desired service to the user.
The protocol supports distributed videotex applications using virtual circuits on one B-channel.
EXAMPLE: Assume an application which serves PSTN terminals and ISDN terminals at the
same time. The PSTN application uses only alphamosaic information, while the
ISDN application additionally offers photographic pictures. The
"alphamosaic-host" is used for the dialogue with both PSTN and ISDN terminals.
When a specific picture has to be displayed, on request of the "dialogue-host" a
second VC is established between the ISDN terminal and the "picture-host".
4.5 ISDN supplementary services
The protocol allows for a use of several ISDN supplementary services (Multiple Subscriber Number (MSN),
Subaddressing (SUB), User-to-User Signalling 1 (UUS 1), Call Deflection (CD), Calling Line Identification
Presentation (CLIP) and Calling Line Identification Restriction (CLIR)), mainly to support ISDN-specific
Videotex Service selection mechanisms. For details on these supplementary services, refer to Annex B
(informative).
4.6 Handling of incoming calls
The protocol permits an ISDN syntax-based Videotex Terminal to be called by another terminal or a
Videotex Service.
In the case of a called ISDN syntax-based Videotex Terminal, the handling of ISDN supplementary services
is not within the scope of this ETS.
5 Configurations
Various configurations and topologies may be used, examples of which are given in Annex A (informative).
It shall be the responsibility of the Videotex Service providers to opt for the appropriate configuration(s) in
the definition of the ISDN syntax-based Videotex Service.

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ETS 300 079: October 1991
6 General model
In order to describe all configurations, the following reference models are used:
- a communication model;
- a terminal model;
- an access network scenario.
The communication model describes the relationships between the functional entities involved in the
communication. It models the communication between a user and a Videotex Service in terms of terminal
functions, access network functions and service functions.
The terminal model defines, in an abstract way, the terminal aspects which are relevant for the protocol.
The access network scenario describes the use of an ISDN as the Access Network.
6.1 Communication model
In describing the communication model, the following entities can be identified:
- a User;
- a Terminal Function;
- an Access Network;
- an Access Function;
- a Host Access Network;
- a Host Function.
In all videotex configurations, the User employs a terminal to communicate with a Videotex Service. The
abstraction of the terminal is named Terminal Function.
The Access Network provides the link between the Terminal Function and the Videotex Service. It may
consist of one or several networks of different types. The Access Network shall be an ISDN within the
scope of this ETS.
NOTE 1: For an overview of possible Access Network architectures for the DTE/DCE case of
connection over an ISDN refer to DE/TE-01012.
The Access Function is the functional entity which gives access to the Videotex systems. It is an integral
part of the Videotex Service.
The Host Access Network, which is an optional functional entity, is the abstraction of the function, which
connects the Access Function to one or more Host Functions. Depending on the actual topology used in a
specific service, it may be void.
The Host Function is the abstraction of the collection of Videotex Applications.
The interfaces and protocols defined between the functional entities are:
(1) User interface;
(2) Terminal-Access Network interface;
(3) Access Function-Access Network interface;
(4) Access Function-Host Access Network interface;
(5) Host Function-Host Access Network interface;
(6) Terminal-Access Function protocol;
(7) Host Access protocol.
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ETS 300 079: October 1991
Figure 1 shows the relationships between the entities:
�˝˝˝˝˝˝˝˝˝˝»
”  Host  ”
”     ”˜¿
” Function ” |
¨˝˝˝˝˝˝˝˝˝˝… |
ø   |
øøøøøøøøø   |
ø    ø   |
ø    ˝(5)  |
ø    ø   |
�˝˝˝˝˝˝˝˝˝˝»              ø �˜˜˜˜˜˜˜˜˜¿ |
”     ”              ø ‡ Host  ‡ |
”  User  ”              ø ‡ Access ‡ |(7)
”     ”              ø ‡ Network ‡ |
¨˝˝˝˝˝�˝˝˝˝…              ø �˜˜˜˜˜˜˜˜˜� |
|                ø    ø   |
|                ø    ˝(4)  |
�(1)               ø    ø   |
|                øøøøøøøøø   |
|                    ø   |
�˝˝˝˝˝ˇ˝˝˝˝»  (2)  �˜˜˜˜˜˜˜˜˜¿  (3)  �˝˝˝˝˝˝˝˝˝˝» |
” Terminal ”     ‡ Access ‡     ” Access ” |
”     ˙˜˜˜˜�˜˜˜˜·     ˆ˜˜˜˜�˜˜˜˜¶     ”˜�
” Function ”     ‡ Network ‡     ” Function ”
¨˝˝˝˝˝�˝˝˝˝…     �˜˜˜˜˜˜˜˜˜�     ¨˝˝˝˝˝�˝˝˝˝…
‡                    ‡
�˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜�
(6)
Figure 1: Communication Model
Of these interfaces and protocols, only items (2), (3) and (6) are within the scope of this ETS.
The Terminal-Access Network interface (2) and the Access Function-Access Network interface (3) are
covered by the layer 1 to layer 3 protocol specified in this ETS. For the DTE/DTE case of connection, it
shall be based on draft prETS 300 080 [15].
The Terminal-Access Function protocol (6), the end-to-end protocol between Terminal and Access
Function, specifies the features of a Videotex Terminal which can be used for the ISDN syntax-based
Videotex Service.
NOTE 2: The same end-to-end protocol may be used between two terminals, whereas one of
the terminals acts as an Access Function (cf. subclause 7.1 and informative Annex A,
clause A.7).
6.2 Terminal model
The terminal model is the reference model which is used throughout the document. This model describes
the relationships between functions of an ISDN syntax-based Videotex Terminal.
The Application layer is decomposed into the following components:
- communication channel manager;
- layer 7 protocol machine;
- input buffer;
- output buffer;
- echo handler;
- forwarding condition handler;
- processable data unit;
- escape function units.
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ETS 300 079: October 1991
Figure 2 introduces these functions and their relationship:
�˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝»
”œœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœ     ”
”œ    �˜˜˜˜˜˜˜˜˜˜¿ �˜˜˜˜˜˜˜˜˜˜˜¿œ     ” �˜˜˜˜˜˜˜˜˜˜¿
”œ    ‡Forwarding‡ ‡      ‡œ     ” ‡  Co-  ‡
”œ    ‡Condition ˆ˜·      ‡œ     ” ‡ordination‡
”œ    ‡ Handler ‡ ‡      ‡œ     ” ‡ Function ‡
”œ    �˜˜˜˜´˜˜˜˜˜� ‡      ‡œ     ” �˜˜˜˜´˜˜˜˜˜�
”œ       ‡    ‡      ‡œ�˜˜˜˜˜˜˜¿” �˜˜˜˜`˜˜˜˜˜¿
”œ�˜˜˜˜˜˜¿�˜˜˜˜`˜˜˜˜˜¿ ‡      ‡œ‡    ‡” ‡     ‡
”œ‡ User ‡‡ Input  ‡ ‡      ‡œ‡    ‡” ‡     ‡
”œ‡   ˆ·     ˆ˜· Layer 7 ‡œ‡Commun.‡” ‡Layer 1-3 ‡
”œ‡Input ‡‡ Buffer ‡ ‡      ‡œ‡    ‡” ‡     ‡ ”
”œ�˜˜˜˜˜˜��˜˜˜˜´˜˜˜˜˜� ‡ Protocol ˆ˜·Channelˆ�˜· Protocol ˆ˜�˜
”œ    �˜˜˜˜`˜˜˜˜˜¿ ‡ Machine ‡œ‡    ‡” ‡ Machine ‡ ”
”œ    ‡  Echo  ‡ ‡      ‡œ‡Manager‡” ‡     ‡
”œ    ‡     ˆ˜·      ‡œ‡    ‡” ‡     ‡S/T
”œ    ‡ Handler ‡ ‡      ‡œ‡    ‡” ‡     ‡
”œ    �˜˜˜˜´˜˜˜˜˜� ‡      ‡œ�˜˜˜˜˜˜˜�” �˜˜˜˜˜˜˜˜˜˜�
”œ�˜˜˜˜˜˜¿�˜˜˜˜`˜˜˜˜˜¿ ‡      ‡œ     ”
”œ‡ User ‡‡ Output ‡ ‡      ‡œ     ”
”œ‡   ˆ·     ˆ˜·      ‡œ     ”
”œ‡Output‡‡ Buffer ‡ ‡      ‡œ     ”
”œ�˜˜˜˜˜˜��˜˜˜˜˜˜˜˜˜˜� �´˜˜˜˜´˜˜˜˜˜�œ     ”
”œ     �˜˜˜˜˜˜˜˜˜˜˜˜�  ‡   œ     ”
”œ�˜˜˜˜˜˜˜˜`˜˜˜˜˜˜˜¿  �˜˜˜˜˜`˜˜˜˜˜¿œ     ”
”œ‡        ˆ¿ ‡Processable‡œ     ”
”œ‡Escape Functions‡ˆ¿ ‡      ‡œ     ”
”œ‡        ‡‡‡ ‡  Data  ‡œ     ”
”œ�´˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜�‡‡ ‡      ‡œ     ”
”œ �´˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜�‡ ‡  Unit  ‡œ     ”
”œ �˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜˜� �˜˜˜˜˜˜˜˜˜˜˜�œ     ”
”œœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœœ     ”
¨˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝˝…
NOTE: For every communication channel, one separate independent instance of each of the functional
entities inside the dotted rectangle exists.
Figure 2: Functional entities of the terminal model
The protocol machine handling layers 1-3 of the protocol and the co-ordination function are integral parts of
the Network layer entity and do not require further refinement in the model.
NOTE 1: The co-ordination function may also be empty.
In the context of this ETS, a communication channel is equivalent to a virtual circuit (VC) on an
established B-channel.
NOTE 2: For other cases of connections, a communication channel might be defined differently.
The communication channel manager supervises the handling of related communication channels. The
protocol allows for the definition of a hierarchical relationship between communication channels. An
application can request the establishment of further dependent communication channels via an already
established communication channel. The requesting communication channel shall be named a "Master"-
channel and the requested communication channels shall be named "Slave"-channels.
NOTE 3: The handling of more than one communication channel is optional. Therefore, the
communication channel manager may also be empty.
This relationship is maintained during the lifetime of a communication channel implying that existing "Slave"-
channels have to be closed implicitly when the "Master"-channel is closed. The communication channel
manager takes care of this implicit closure and keeps track of related communication channels.
For each established communication channel, one separate independent (virtual) instance of the following
functional entities exists (regardless of whether it is an independent or a linked communication channel).

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ETS 300 079: October 1991
The layer 7 protocol machine supports the procedures as defined in the Application layer protocol. It
conveys information to the output buffer (display data), the echo handler (parameter settings, related to
echoing), the forwarding condition handler (parameter settings, related to forwarding and function key
information), the communication channel manager (related communication channels) or the processable
data or escape modules.
The input buffer rece
...