22.0023GPPCircuit Bearer Services (BS) supported by a Public Land Mobile Network (PLMN)TS
All Bearer Service categories provide information transfer between the reference points and allow the use of sub-rate information streams which are rate-adapted.
The Bearer Services can be grouped into the following categories:
– Unrestricted Digital Information (UDI);
Provides the transfer of unrestricted digital information.
– 3,1 kHz (External to the PLMN);
Used to select a "3,1 kHz audio" interworking function at the MSC. This service category is used when interworking with the ISDN or PSTN "3,1 kHz audio" service and includes the capability to select a modem at the interworking function. "External to the PLMN" indicates that the "3,1 kHz audio" service is only used outside of the PLMN, in the ISDN/PSTN. The connection within the PLMN, user access point to the interworking function, is an unrestricted digital connection.