Question 7/VII - Further study of DTE/DCE interfaces for terminals
operating in the packet-mode (continuation of Question 7/VII studied in
1985-88)

considering

(a) that Recommendation X.25 specifies the DTE/DCE interface for
terminals operating in the packet mode and connected to a public data
network by dedicated circuits;

(b) that Recommendation X.10 specifies the different methods of
accessing a packet-switched data transmission service;

(c) that Recommendation X.32, in addition to Recommendation X.25,
defines the DTE/DCE interface for terminals operating in the packet mode
and accessing a Packet-Switched Public Data Network through the Public
Switched Telephone Network or a Circuit-Switched Public Data Network, or
an Integrated Services Digital Network;

(d) that Recommendation X.31 (support of packet mode terminals in an
ISDN) includes the use of the X.25 protocol for packet mode operation
through the ISDN;

(e) that ISO/IEC JTC 1/SC 6 has developed standards at link and packet
layers which are compatible with Recommendation X.25;

(f) that networks and DTEs conforming to Recommendation X.25 have been
in operation for several years, and that their number is increasing;

(g) that Recommendation X.25 provides the Network Service defined by ISO
and CCITT (Recommendation X.213);

(h) that Recommendation X.223 describes the use of X.25 to provide the
OSI connection mode network service,

1. What enhancements and additions to Recommendation X.25 should be
defined, keeping in mind points e), f), g), and h) above?

Aspects to be covered include:

1.1 Inclusion of procedures for additional user facilities defined (or
which may be defined) in Recommendation X.2. In particular, direct call
for packet mode terminals is for further study in X.2.

1.2 Consideration of the inclusion of an asynchronous mode of
delimitation for X.25 and X.32, as an alternative to the current
synchronous mode. This study should be conducted in liaison with Study
Group XVII.

1.3 Consideration of the accommodation of throughput classes higher than
those presently defined in X.25, that would be needed for access to
PSPDNs or other applications of the X.25 Packet Layer Protocol.

2. What additions and changes to Recommendation X.32 should be required?

In particular, the security aspects of X.32 should be further
investigated, in relation with work on security and authentication
undertaken in CCITT and ISO.

3. What enhancements to existing Recommendations (e.g. X.25, X.32) are
needed to define the DTE/DCE interface at reference point R on the ISDN
for a terminal in the packet mode accessing a packet switched data
transmission service?

This study should be based on the input from Questions 30 and 31/VII and
carried in cooperation with Question 30/VII during the study period
1989-1992.

Alignment should be aimed between the various ways of accessing a packet
switched data transmission service (i.e. through PSTN, CSPDN or the
ISDN).

4. What additions and changes to Recommendation X.223 should be
required?

In particular, this study should be based on the input from Question
27/VII on the enhancements of the OSI Network Service. Close cooperation
with ISO/IEC JTC 1/SC6 on this point is required.

5. A potential addition to X.223 is attached as Annex 1 to this
Question. Close cooperation with ISO/IEC JTC 1/SC6 and with Questions 30
and 31/VII on the provision of the OSI network service by packet mode
terminal equipment connected to an ISDN for CCITT applications is
required, to ensure compatibility with Recommendation X.223.

6. The feasibility of producing a standard set of procedures to test the
conformances at a DTE with Recommendation X.25 should be studied with
the view toward creating a Recommendation. This work should be conducted
in close cooperation with ISO/IEC JTC 1/SC6.

7. The feasibility of producing a Recommendation describing X.25 data
terminal equipment procedures for CCITT applications should be studied.
This work should be conducted in close cooperation with other CCITT
Study Groups and with ISO/IEC JTC 1/SC6.

8. What additional protocol or protocol elements, if any, are necessary
in packet switched public data networks (PSPDNs) to support the
addressing aspects of the OSI network service?

In particular, it is for further study (see Question 27/VII) how to
derive an address by which PSPDNs route from an OSI NSAP address. Work
is to be done, based on input from and in cooperation with Question
27/VII, on the definition of any additional protocols or protocol
elements to be used by the DTE and either supported by or carried
transparently by PSPDNs for the above derivation.