Question 31/VII - Requirements and arrangements for the provision of
data services in ISDNs (continuation of Question 46/VII studied in 1985-
1988)

Considering

(a) that characteristics and features of circuit and packet switched
data services and corresponding customer interfaces are defined in
XSeries Recommendations and that new Recommendations may emerge from
further studies;

(b) that Study Group VII defined Recommendation X.30 specifying the
support of X.21, X.21bis and X.20bis on an ISDN, and Recommendation X.31
for the support of packet mode terminals based on X.25 by an ISDN;

(c) that Recommendations X.1 and X.10 have been already defined in order
to take into account provision of data transmission services by the
ISDN;

(d) that the intention of many administrations is that customers
connected to the ISDN will have access to a wide range of services
including telephony and data services as those mentioned above;

(e) that there is a further need to define, in a common framework,
coherent standards for customer access to different services provided by
the ISDN;

(f) that such standards have to allow various network architectures,
taking into account the varying conditions in different countries, for
example, provision of some services through the ISDN by means of
interworking with specialized networks;

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

Step 1:Services 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;

(h) that Question 30/VII deals with studies on the interface aspects,

it is necessary to study the following:

1. What further requirements and arrangements are to be established for
the provision of data services on an ISDN?

2. What new Recommendation or enhancements or existing ones are needed?

Annex 1 to this Question contains a list of items which will be studied
under the Question. Annex 2 contains a draft Recommendation to be
finalized concerning the provision of the Connection-mode Network
Service in ISDN (Step 1).

Note - A close liaison should be maintained with other Study Groups, in
particular Study Groups II, XI, XVII and XVIII.

ANNEX 1

(to Question 31/VII)

The following subjects will be studied under this Question:

a) Definition of the service and technical implication of the proposed
evolutionary step identification of interest of new data services
exploiting information transfer, access and general attributes offered
by the ISDN circuit and packet bearer services. Relevant study items are
for example use of Recommendation X.31 procedures for data services at
rates higher than 64 kbit/s (e.g., H-channel rate) assessment of need
for and subsequently technical options and requirements for the support
of step 2 services.

b) Technical options and requirements for the support of step 3 services
based on the service characteristics developed by this and other Study
Groups.

In both studies of a) and b), the relationship with the OSI network
service should be considered for data services operated within an ISDN.

c) Requirements to be established for the provision of packet mode data
services steps 1, 2 and 3 with view to interworking situations to be
studied in close cooperation with related studies in concerned Study
Groups.

d) Definition of compatibility requirements for ISDN DTEs in their
operation through either a circuit switched connection type or a packet
switched connection type.

e) Definition of ISDN operational requirements for the support of data
services, e.g., maintenance aspects.

f) The alignment between the representation for access unit (AU)/packet
handler (PH)/interworking function (IWF) in Recommendation X.31 and the
drawing conventions in Recommendation X.300.

ANNEX 2

(to Question 31/VII)

Provision of the OSI connection-mode network service
by packet mode terminal equipment connected to an
integrated services digital network (ISDN)
for CCITT applications

Recoup

Recoup

Recoup

Recoup

"call-offering procedure" which, when present, takes place
before the conveyance of INCOMING CALL packets. The
procedures of Recommendation Q.931 enable terminal
identification and a determination of which channel (D or B)
a specific INCOMING CALL packet is to be conveyed on. The
following limitations apply:

1) The maximum User Data field length of DATA packets shall
not exceed 256 octets.

2) The Recommendation X.25 Throughput Class used shall not
exceed 16 kbit/s on a basic interface.