4 General considerations

3GPP43.010GSM Public Land Mobile Network (PLMN) connection typesRelease 17TS

Low layer capabilities are defined in 3GPP TS 22.001 and characterized in 3GPP TS 22.002 for Bearer Services and 3GPP TS 22.003 for Teleservices. Apart from the short message service and GPRS, all Bearer Services and Teleservices are provided using low layer capabilities in the connection mode.

Network capabilities to support the short message services are defined in 3GPP TS 23.040 and 3GPP TS 24.011 for the point-to-point service, and in 3GPP TS 23.041 and 3GPP TS 24.012 for the cell broadcast service. Network capabilities to support GPRS are described in 3GPP TS 23.060.

4.1 Relationship between lower layer capabilities and radio traffic channels

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 3GPP 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 3GPP TS 24.011) or the cell broadcast service which uses the CBCH (see 3GPP TS 24.012). 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 3GPP 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 3GPP 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 3GPP 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 3GPP TS 45.003).

4.2 Transparent and non-transparent lower layer capabilities

Two classes of low layer capabilities have been identified (see 3GPP TS 22.002 and 3GPP 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 3GPP 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.

4.3 The PLMN environment

4.3.1 The hand-over procedure

The PLMN connection is heterogeneous and merges PCM links and radio path as a unit for the user.

One of the most specific characteristics of the mobile networks is the hand-over procedure (see 3GPP TS 23.009, 24.008, 45.008, 48.008) which result in a temporary break of the TCH, and consequently in a loss of information.

The PLMN makes it possible to use one TCH slot for signalling (frame stealing for FACCH) in one TDMA frame resulting in a loss of information.

For the transparent data calls, this will result in a period of highly errored stream. For the non-transparent services, the use of the ARQ procedure (3GPP TS 24.022) will overcome this problem.

After a hand-over, in case of loss of synchronization, the process to recover synchronization, as described in 3GPP TS 29.007 and 44.021 should apply. If data compression is used, V.42bis procedure should apply.

4.3.2 DTX procedure

For the full rate speech traffic channel, DTX function goes along with other procedures such as voice activity detection, generation of comfort noise, and is described in 3GPP TS 46.031.

For the non-transparent traffic channels, DTX apply according to 3GPP TS 48.020.