ITU-T X.81 PDF

Scope and field of application

The purpose of this Recommendation is to describe the detailed arrangements for the interworking between CSPDNs and ISDNs (CS) for the provision of data transmission services. These arrangements are applicable only to the interworking involving transmission capabilities, and not to interworking involving communication capabilities as described in Recommendation X.300.

a) within the scope of interworking between an ISDN using circuit-switched connection types and a CSPDN the following cases of network interworking can be identified:

i) where the terminals connected to the interworking networks use identical data transmission services and have identical high layer capabilities. The identity of data transmission services in both networks assumes that both terminals involved in a communication belong to the same user class of service;

ii) where the terminals connected to the interworking networks use non-identical data transmission services but have identical high layer capabilities. In this case two terminals involved in a communication may belong to different user classes of service, e.g. user classes of service 4 and 30.

b) Not within the scope of this Recommendation is asynchronous mode of operation at the network-tonetwork interface (ISDN-to-CSPDN interface). In the case, that the ISDN supports the connection of asynchronous mode terminals via an appropriate terminal adaptor (TA) (see Recommendation X.30) and that interworking has to be provided to asynchronous terminals connected to a CSPDN, then the interworking arrangements as for synchronous mode operation will be used. Asynchronous to synchronous conversion may be provided within the TA for ISDN-connected terminals and at the terminal or at the CSPDN for CSPDN-connected terminals.

Note - The typing of subnetworks in this Recommendation is based on the support for the OSI connectionmode Network Service and is therefore only valid in this context.