Question 6/VII - Further study on Recommendations for DTE/DCE interfaces
for circuit switched service (X.20, X.20bis, X.21, X.21bis, X.22) and
study on access to the CSPDN through telephone networks (continuation of
Question 6/VII studied in 1985-88)

considering

- that categories of access for data transmission services and
facilities will be modified or enhanced;

- that interworking between networks is requested;

- that access to CSPDN through telephone networks is requested;

- that the provision of the OSI-NS is requested;

- that for purposes of conformance testing a more formal protocol
description is required;

it is necessary to study the following:

- refinement of the DTE/DCE interface Recommendation for circuit
switched service following their implementation in public data networks;

- the enhancement/alignment of the DTE/DCE interface Recommendation for
circuit switched service of the OSI model;

- the separation of the network service functions between call control
phase and data transfer phase;

- implication of the provision of a V.25bis serial automatic dialling
function on X.20bis and X.21bis DTEs;

- the enhancement catering for reservation circuit switched service;
- the protocol aspects of management functions;

- further work on Annex 1 for access to a CSPDN through telephone
networks;

- the specification of the protocol using an FDT.

ANNEX 1

(to Question 6/VII)

Recommendation X.33

PROCEDURES AND ARRANGEMENTS FOR DATA TERMINAL

1.2 This Recommendation------------------------------------------

3. Timing problem-----------------------------------------------

3.2.2.2 Operation in PSTN DTE side

3.3.1.2 Operation in IWU------------------------------------

4.2.2 Circuit 106 (ready for sending) control

5.2.3 If the IWU---------------------------------------------

7.2.2 In order to use existing X.21----------------------------------

9. Modem type selection

APPENDIX 1

(to Recommendation X.33)

TABLE I-1/X.33

Examples of possible V-series interfaces