Question 11/XI - Call control and bearer control protocols in Signalling
System No. 7 for the full range of ISDN telecommunication services

The following text was agreed for a new Question covering the study of
separated call and connection control protocols:

Considering

(a) that the increasing range of ISDN telecommunication services to be
provided in national and international networks;

(b) that existing ISDN User Part Recommendations have a field of
application for circuit switched services and associated supplementary
services;

(c) that the variety of network resources and transfer techniques
supported currently or in the future by the ISDN, such as:

- digital (and possibly analogue) circuit switching,

- packet switching,

- frame switching and relaying,

- asynchronous time division multiplex systems, etc.;

(d) that the increasing number of supplementary services to be supported
and the interest to unify the provision of supplementary services for
various types of bearer services;

(e) that the need to provide signalling to support multi-media,
asymmetric and multi-point calls;

(f) that an ISDN signalling protocol may be needed to support broadband
teleservices;

(g) that the desire that network signalling protocols should be designed
to allow independent evolution of service control and network resource
control;

(h) that the CCITT now recommends a service description based on a
three-stage approach, the definition of protocols (Stage 3) being based
on an abstract service description (Stage 2);

(i) that a great amount of technical problems for the 64 kbits circuit
control have been solved in existing Signalling System No. 7 protocols
and therefore there is no presently identified need to define procedures
to establish, monitor or release ISDN 64 kbits circuits different from
those defined in the ISDN User Part Recommendations;

(j) that some architecture and protocol analysis has already been made
in the 1984-1988 study period (see annex to the Question (note))
separating a generic Call Control Part (CCP) related to the control of
telecommunication services from several specific Bearer Connection
Control Parts (BCCPs) for the control of network resources, such as
circuit BCCP, new packet mode BCCP, etc., and that the principle of such
a full separation has been agreed;

(k) that there is an urgent need to study the separation of call control
from connection control;

(l) that the call control part may take advantage of application service
elements;

What Recommendations based on the principle of separation of the Call
Control and Bearer Connection Control Parts are necessary in Signalling
System No. 7 to meet present and future signalling and service
requirements in the evolving ISDN?

ANNEX 1

(to Question 11/XI)

Status on the studies on the separated ISDN User Part

(See Contribution COM XI-3)

ANNEX 2

(to Question 11/XI)

Proposed draft Recommendations texts for the
"Separated ISDN User Part (ISUP-S)"

(See Contribution COM IX-3)