Questions 5 to 9/XVIII - Quality of Service and performance of digital
networks including ISDNs

Preamble to Questions 5 to 9/XVIII

These Questions are concerned with studies related to the general
performance of digital networks, including ISDNs. In particular, studies
should embrace all of the network performance characteristics that are
observable at the ISDN user-network interface, encompassing
transmission, switching and signalling related performance aspects.

Due account should be taken of the progress made on this matter within
Study Group XVIII during the previous study period and of the work of
other CCITT Study Groups on other aspects of performance; in particular
Study Groups II, VII, XI, XV, XII and CCIR Study Group 4 and Study Group
9. The role of Study Group XVIII will therefore consist of coordination
of areas where relevant detailed study is being undertaken in the
specialist Study Groups. In the areas where detailed study is not being
undertaken, the role of Study Group XVIII should be to give direction as
required, and if necessary, progress the detailed study to completion.

Considering

(a) that there is a need to establish performance requirements for
ISDNs, taking account, for example, of broadband aspects (including
Asynchronous Transfer Mode), integration of mobile services, private
network issues and multipoint and broadcast services;

(b) that network performance requirements will influence the design of
systems (e.g., signalling systems, transmission systems);

(c) that general principles that govern the study of network performance
and Quality of Service are defined in Recommendation I.350;

(d) that certain performance objectives already studied need to be
expanded to cover bit rates other than those already the subject of
Recommendations (e.g., for broadband services, etc.);

(e) that there is a need to further clearly distinguish between the
network performance, and the Quality of Service of telecommunication
services offered to customers;

(f) that there is a need to establish a set of performance objectives
catering for a wide variety of services on fully integrated networks;

the following Questions 5 to 9/XVIII should be studied: