02.023GPPBearer Services (BS) Supported by a GSM Public Land Mobile Network (PLMN)TS
All Bearer Service categories provide information transfer between R/S 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.
Provides an asynchronous connection to a PAD. This enables PLMN subscribers to access a packet network (PSPDN/ISDN). See GSM 09.05  for service and interworking specifications.
Provides a synchronous connection that enables PLMN subscribers to access a packet network (PSPDN/ISDN). See GSM 09.06  for service and interworking specifications.
– Alternate Speech/Data;
Provides the capability to swap between speech and data during a call.
If either the speech or data portion of the call requires a full rate channel, a full rate channel shall be used for the duration of the call.
– If the data portion of the call requires multiple full rate channels, the speech portion uses a single full rate channel.
The access interface at the mobile station for the data portion is assumed to be a standard data interface. Some means must be provided to select the speech/data capability.
– Speech followed by Data;
Provides a speech connection first and then at some time while the call is in progress, the user can switch to a data connection. The user cannot switch back to speech after the data portion.
If either the speech or data portion of the call requires a full rate channel, a full rate channel shall be used from the start of the call. The network may then change to a half rate channel for the data portion.
– If the data portion of the call requires multiple full rate channels, a single full rate channel shall be used from the start of the call.
– General Packet Radio Service (GPRS)
GPRS provides Internet (IP) and X.25 interworking with external networks. See GSM 02.60.