Question 32/XI - Enhancement and extension of the Q.550-Series of
Recommendations on the transmission performance of digital exchanges
(New Question)

Considering

(1) that the Q.550-Series of Recommendations on digital exchanges have
been developed over the last three CCITT study periods;

(2) that a large number of digital exchanges complying with these
Recommendations have already been supplied to administrations and RPOAs;

(3) that operational experience in an IDN environment of digital
exchanges complying with these Recommendations is rapidly building up,

and further considering

(4) that many national and international IDNs are already being evolved
to become ISDNs;

(5) that there is a need to develop these Recommendations in respect of
aspects arising from the requirement for digital exchanges to operate in
ISDNs, examples of which include:

-the impact on digital exchanges of the evolution of the
telecommunications management network concept with regard to
transmission performance,

-the impact on exchange transmission performance design objectives, O&M
objectives and measurements of packet mode services, supplementary
services etc.,

-the transmission requirements related to certain ISDN characteristics
e.g., to higher quality speech encoding, as well as to spectrum saving
low bit rate coding;

(6) that there is a need to develop these Recommendations in respect of
aspects arising from the requirement for digital exchanges to operate in
conjunction with both public land mobile networks and competing fixed
land networks;

(7) that broadband services will be introduced in ISDNs and may require
special interface and other functions within digital exchanges;

(8) that digital transmission technology will continue to evolve,
possibly at a different rate from exchanges and the latter may be
required to support more than one such technology;

(9) that connections other than bi-directional circuit switched
connections may be required to meet future service requirements,

What additions and modifications should be made to the existing
Q.550-Series of Recommendations on digital exchanges in order to promote
their updating and harmonization with the G.700-Series?

In particular the following points should be studied:

1. complete the items listed as "under study"
Recommendations Q.551-Q.554;

2. the use of the noise method for the measurements of quantizing
distortion and variation of gain with input level;

3. specific transmission requirements applicable to PABXs;

4. requirements for single frequency interference within the voice band;

5.specific transmission requirements applicable to ISDN;

6. conferencing (this point is of interest to Study Groups XII and XV);

7.conditions for establishing speech transmission during call setup;

8.a new Recommendation for exchange transmission measurements;

9.review of attenuation distortion problems;

10. effect of complex impedances and their tolerances, in particular
outside the voice band, on broadband measurements, e.g., noise;

11. longitudinal interference threshold measurement techniques;

12. sources and effects of impulsive noise in local digital exchanges;

13. effect of adaptive hybrids on digital exchange transmission
requirements;

14. transmission requirements related to higher quality speech encoding;

15. transmission requirements on customer premises equipment necessary
to ensure network compatibility;

16. the delay of and the impact of delay on services utilizing multislot
connections;

17. means for disabling devices such as 5 /A law converters, echo
control devices and digital pads for non speech calls requiring bit
integrity.

Information concerning some of these points can be found in Annex B.3.7
of COM XI-R 80 (1985-1988).


1 This temporal aspect is for further consideration.

2
It is recognized that certain aspects are being examined by other Study
Groups.