Question 30/VII - Support of X-Series interfaces in an ISDN and new
interface aspects for data services in ISDNs (continuation of Question
9/VII studied in 1985-1988)

Considering

(a) that user/network interface characteristics of the ISDN have been
defined in the I-Series Recommendations;

(b) that Recommendation X.30 defines the support of X.21, X.21bis and
X.20bis DTEs by means of terminal adaptors and that Recommendation X.31
defines the support of packet-mode terminals based on X.25 by an ISDN;

(c) that the need to align DTE/DCE interface protocols with the OSI
Model has been recognized;

(d) that the following four steps have been identified for the evolution
of the ISDN packet-mode services:

Step 1:The service defined by Recommendation X.31.

Step 2:Services as defined by Recommendation X.31 but with the addition
of a Layer 2 multiplexing capability.

Step 3:Additional packet-mode bearer services based on out-of-band call
control and Layer 2 multiplexing.

Step 4:Broadband Asynchronous Transfer Modes (ATM), which include
support for narrow-band services;

(e) that Question 31/VII deals with the further requirements and
arrangements to be met for the provisions of data services in ISDNs;

(f) that some administrations foresee the need for D-Channel access to
PSPDNs,

it is necessary to study the following:

1. What enhancements will be required to Recommendations X.30 and X.31
for the support of non-voice communication?

Study items of particular interest are:

a) impact of user facilities on the procedures of the TE interface;

b) fault isolation and maintenance.

2. What Recommendation, if any, will be required for the support of Step
2 of the evolutionary process?

3. What Recommendation, if any, will be required for the support Step 3
of the evolutionary process?

4. What Recommendation, if any, will be required for the support of Step
4 of the evolutionary process?

Note - Study of this Question should be closely coordinated with the
related study in this and other concerned Study Groups.