For the purposes of the present document, the following definitions apply. (DIGITAL) connection: PLMN connection: PLMN connection type: EDGE channels:

Abbreviations used in this specification are listed in TR 21.905.

The realization of low layer capabilities for the provision of telecommunication services will make use of a physical medium consisting of a traffic channel TCH (refer to TS 44.004) or a combination of several full rate traffic channels (Multislot configuration for data) except for the short message point-to-point which uses a dedicated control channel DCCH (see TS 24.011) or the cell broadcast service which uses the CBCH (see 3GPP TS 24.012 [21]). No multiplexing of data connections on one TCH is allowed. Either a full rate or a half rate channel may be used depending on the requirements of the individual service. User data rates below or equal to 4 800 bit/s may be supported either on a full rate channel or on a half rate channel. Single slot configurations of 9.6Kbit/s and above are always supported on a full rate channel. Multislot configurations for data use combinations of 4.8 kbit/s or 9.6 kbit/s or 14.4 kbit/s full rate traffic channels only. Technically every MS, regardless of whether it uses a half or a full rate TCH for speech transmission, should be able to use both half and full rate TCHs for data transmission and telematic services. However, particular designs of MS may only provide access to a limited set of services and therefore only use limited options. For the alternate speech and group 3 facsimile teleservice, when a full rate traffic channel is required for the speech or data portion of the service, a full rate traffic channel will be used for the duration of the call, see TS 22.002. Within a PLMN, the transport of user data and access interface status information (if present) will use a rate adaptation method based on ITU-T Recommendation V.110 except on TCH/F14.4 or EDGE channels for which PLMN specific rate adaption is used between the mobile station and the interworking function. For the access interface, the rate adaptation schemes used are referenced in the 3GPP TS 27-series. On the radio path, rate adaptation leads to rates of 43.5, 32.0, 29.0, 14.5, 12.0, 6.0 and 3.6 kbit/s per TCH (see TS 44.021). However, in multislot configurations for data the 3.6 kbit/s per TCH/F rate is excluded. At the BSS to MSC interface, the rate adaptation scheme used is described in TS 48.020. Protection of information from errors on the radio path (i.e. between MS and BSS) will be implemented by use of FEC techniques (see TS 45.003).

Two classes of low layer capabilities have been identified (see TS 22.002 and TS 22.003):

• a transparent class which is characterized by constant throughput, constant transit delay and variable error rate;
• a non-transparent class for which an ARQ technique is used (see TS 24.022) on the radio path and extended to an appropriate interworking function. This class is characterized by improved error rate with variable transit delay and throughput. Data compression can optionally be used in combination of non-transparent lower layer capability, to increase the data rate on the DTE/DCE interface (or the equivalent interface depending on the TE type).

The considerations described above provide the basis for the definition of a limited set of connection types to be implemented by a GERAN PLMN.