GSM Public Land Mobile Network (PLMN) Connection Types
A GSM PLMN may be described by a limited set of access interfaces (refer to 3GPP TS  04.02 and 02.01) and a limited set of GSM PLMN connection types to support the telecommunication services described in the 3GPP 02-series of specifications. This Global System for Mobile communications Technical Specification (TS) identifies and defines these connection types in so far as they relate to the particular network capabilities for a GSM PLMN.
The basic lower layer capabilities of a GSM PLMN are represented by a set of GSM PLMN connection types. The definition of a set of GSM PLMN connection types provides the necessary input to identify network capabilities of a GSM PLMN. In addition to describing network capabilities of a GSM PLMN, the identification of connection types facilitates the specification of network-to-network interfaces. It may also assist in the allocation of network performance parameters.
This specification should be considered in conjunction with other 3GPP specifications with particular reference to 3GPP TS  01.02, 02.01, 22.002, 02.03, 03.01, 23.002, 04.02 and 04.03.
This specification provides a bridge between the service specification in the 3GPP TS 02 and 22-series of specifications and the more detailed specifications such as the 3GPP TS 03, 04, 23, 24, 27 and 29 series. As such, it establishes a framework for the specification and understanding of the more detailed specifications. It is therefore not a specification against which detailed conformance testing can be performed. However, it shall be considered mandatory for the understanding of the more detailed specifications and used to resolve issues of conflict in these specifications.
From GSM R99 onwards the following services are no more required to be provided by a GSM PLMN:
• the dual Bearer Services “alternate speech/data” and “speech followed by data”
• the dedicated services for PAD and Packet access
• the single asynchronous and synchronous Bearer Services (BS 21..26, BS 31..34)
If a PLMN network still provides these services it has to fulfil the specification of GSM R98.