Question 29/XII - Transmission plan aspects of the interworking between
PSTN and ISDN in the evolving network
(continuation of Question 29/XII studied during the 1985-1988 study
period; new wording)

Considering

(a) that digital telephones, PBXs, remote line concentrators, local and
main exchanges are either already in service or are planned for the
PSTN;

(b) that intense planning is underway for ISDNs and trials are occurring
in some administrations;

(c) that the mixed analogue/digital PSTNs must interwork with ISDNs to
preserve the objectives of the overall transmission plan,

The CCITT has decided to study the following Questions:

What new Recommendations or changes to existing Recommendations must be
made concerning PSTNs or connections to PSTNs to ensure that voice and
voice band data interconnection between mixed analogue/digital PSTNs and
ISDNs comply with the objectives of the transmission plan?

Voice or voice band data connections may be established from digital
telephones or modems in the ISDN and terminate in the conventional
manner in a PSTN or in a private network subtending the PSTN. On an end-
to-end basis the objectives of the transmission plan must be satisfied
with regard to loss/level and the control of stability and echo.

Specific points for study are:

a) For digital interconnection below a digital local exchange in a PSTN,
what should be the location, means of control and range of values of
loss insertion devices taking into account interworking with ISDNs?

b) What special considerations concerning noise and level must be taken
into consideration in interconnecting PSTN and ISDN or in providing
voice service on ISDN?