6.1 Description of PLMN connection types

3GPP43.010GSM Public Land Mobile Network (PLMN) connection typesRelease 16TS

The characterization of PLMN connection types is done by using a set of attributes. A PLMN connection type attribute is a specific characteristic of a PLMN connection type whose values distinguish it from another PLMN connection type. Particular values are assigned to each attribute when a given PLMN connection type is described and specified.

A list of definitions of attributes and values is contained in the annex A to this specification.

A PLMN connection type is partitioned into connection elements. This partitioning is based on the two most critical transitions of a connection, firstly, the change of signalling system, secondly, the type of transmission system. In a PLMN, the change in signalling and transmission between the radio interface and the A interface leads to two connection elements, the radio interface connection element and the A interface connection element. Subclause 6.3 describes the relationship between the attribute values of connection elements and connection types.

To complete the description of PLMN connection types, the definition of functions within the different entities of a PLMN which are involved in the realization of a PLMN Connection is needed. These functions will be used in subclauses 6.4 and 6.5 to describe the limited set of PLMN connection types.

The following functions have been identified:

– rate adaptation functions;

– the radio link protocol function;

– the forward error correction function;

– the Layer 2 relay function.

6.1.1 Rate adaptation

The RA0 rate adaptation is only used with asynchronous interfaces. Incoming asynchronous data is padded by the addition of stop elements to fit the same or nearest higher synchronous rate defined by 2 to the power n (where n 6) times 600 bit/s, 14.4 kbit/s or 28.8 kbit/s. Thus 300 bit/s user data signalling rate shall be adapted to a synchronous 600 bit/s stream. This function is described in 3GPP TS 44.021. The RA0 used in the PLMN is not identical to that described in ITU‑T Recommendation V.110 which converts the 14,4 and 28,8 kbit/s user rates to 19,2 and 38,4 kbit/s, respectively.

The intermediate rate adaptation function (RA1) is a rate adaptation function which turns either the output of the RA0 function or a synchronous user data stream into a data stream at 8, 16, or 32 kbit/s by bit repetition and frame addition. This function is described in 3GPP TS 48.020.

The adaptation of intermediate rates to 64 kbit/s (RA2) performs the final conversion from the intermediate rates generated by the RA1 function to 64 kbit/s.

The radio interface intermediate rate adaptation function (RA1′) is in the case of transparent data transmission a variant of the RA1 function and it adapts synchronous user data stream or the output of the RA0 function to one of the following data rates: 3.6, 6.0 or 12.0 or 14.5 kbit/s over the radio path. In case of a TCH/F28.8 channel two 14.5 kbit/s substreams produced by the RA1′ function are multiplexed into a 29.0 kbit/s air interface channel by an EDGE multiplexing function. For the non‑transparent case, the RA1′ function provides direct access to the 12.0 or 6.0 kbit/s data rates. This is achieved by allowing the V.110 frame status bits to be used as additional data bits. This function is described in 3GPP TS 44.021 and 3GPP TS 48.020. RA1’ is not applied in TCH/F14.4 or EDGE non-transparent operation.

For TCH/F14.4 channel coding five PLMN-specific adaptation functions are used: namely, RA1’/RAA’, RAA’, RA1’/RAA”, RAE and RAA’’ (3GPP TS 48.020). On the network side of the air interface, the 14.5 kbit/s substreams multiplexed into a 29.0 or 43.5 kbit/s air interface channel are transferred just as in a multislot connection of TCH/F14.4 substreams. RA1’/RAA’ adapts between the 14.5 kbit/s air-interface rate and the 16 kbit/s rate used across the Abis-interface. RAA’ adapts between the 16 kbit/s Abis Interface-rate and 16.0 kbit/s A-interface substream. (Up to four such A-interface substreams may be multiplexed into the 64kbit/s A-interface stream). RAA’’ converts between the A-interface data substream(s) and the overall synchronous stream. In non-transparent operation the RAA’’ converts between the A-interface stream and the 290-bit blocks containing bits M1, M2, and 288 data bits as described in 3GPP TS 44.021. The RA1’/RAA” function shall be used for channel codings TCH/F14.4 if the AIUR is equal to 64 kbit/s. It adapts between the 64 kbit/s data stream and the 14.5 kbit/s air-interface rate. For GERAN Iu mode exists another PLMN specific rate adaptation function, namely RAE. This function is the subsequent execution of RAA’ and RAA”, i.e., it adapts between the 16 kbit/s Abis Interface rate and the overall synchronous stream.

In multislot data configurations the intermediate rates 16, 32, and 64 kbit/s are supported on those sections of the network where the overall data stream is not split into multiple channels (3GPP TS 44.021 and 48.020). RA1-adaptation is not applied to rates higher than 38.4 kbit/s. Instead, a PLMN-specific rate adaptation function RA1’’ to user rates 48 and 56 kbit/s is applied; this function adapts between these rates and the 64 kbit/s "intermediate" rate. The RA2 function passes rate 64 kbit/s on as such.

In multislot data connections, the rate adaptation functions are performed per TCH/F between the Split/Combine-functions. On the A-interface up to four TCH/Fs are multiplexed into one 64 kbit/s channel according to the procedures defined in 3GPP TS 48.020. However, multiplexing is not applied to those user rates which make use of more than four TCH/Fs; for such rates the Split/Combine-function is located at the BSS.

The splitting and recombining of the data flow into/from TCH/Fs takes place at the RA1-function or RAA“ function (transparent service) at the MSC/IWF and at the MS’s RA1’-function, or between the RLP and RA1’ (RA1’ not applied to TCH/F14.4) (non-transparent service) at the MS and between RA1 or RAA” and RLP at MSC/IWF (figures 6 and 7). The TCH/Fs are treated as independent channels between the Split/Combine-functions.

For user rates requiring more than four TCH/Fs (transparent only) the Split/Combine-function is located at the RA1’-function at the MS and at the RA1’/RA1” or RA1’/RAA”-function at the BSS (figures 6 and 7). The rate adaptation functions for the various user data rates are summarized in tables 1 to 3. It should be noted that in the case of synchronous data transmission, the RA0 is not present.

For 56 and 64 kbit/s connections using a 2TCH/F32.0 channel configuration across the radio interface, no rate adaptation is applied as the PLMN offers a ’64 kbit/s pipe’ between TE and an external network.

For 32 kbit/s connections using a 1TCH/F32.0 channel configuration across the radio interface, the ITU-T I.460 rate adaptation is applied as described in 3GPP TS 44.021.

Table 1: Rate adaptation functions for the support of TE2 in the transparent case

R I/F

RA0

RA1′

Radio I/F

async

<——>

sync

≤ 2.4

<——>

≤ 2.4

<————————————————->

3.6

4.8

<——>

4.8

<————————————————->

6.0

9.6

<——>

9.6

<————————————————->

12.0 or 2  6.0

14.4

<——>

14.4

<————————————————->

14.5 or 2  12.0 or 3  6.0

19.2

<——>

19.2

<————————————————->

2  12.0 or 4  6.0

28.8

<——>

28.8

<————————————————->

1 x 29.0 or 2 x 14.5 or 3  12.0

32

<————————————————->

1  32

38.4

<——>

38.4

<————————————————->

3 x 14.5 or 4  12.0

48.0

<————————————————->

4 x 14.5 or 5  12.0

56.0

<————————————————->

2 x 32.0 or 4 x 14.5 or 5  12.0 note 1

64.0

<————————————————->

2 x 32.0 or 5 x 14.5 or 6  12.0 note 1

NOTE 1: AIUR of 11.2 kbit/s per 12.0 kbit/s air interface channel (3GPP TS  44.021).

Table 2: Void.

Void

Table 3: RA1′ function in the non-transparent case

RA1′

6.0

<——>

6.0

12.0

<——>

12.0

NOTE: RA1’ not applicable to TCH/F14.4, TCH/F28.8, or TCH/F43.2

6.1.2 Radio Link Protocol

The Radio Link Protocol (RLP) is a layer 2 LAPB based protocol which performs grouping of user data for the purpose of implementing error control and retransmission mechanisms in the case of non-transparent low layer capabilities. The RLP layer is in charge of the transmission of the data compression parameters to the peer RLP entity and to the L2R layer, when those parameters have to be negotiated. The function that realizes the implementation of the protocol (described in 3GPP TS 24.022) takes place at both ends of the PLMN connection in the MT and the IWF/MSC.

6.1.3 Layer 2 Relay function

The Layer 2 Relay function (L2R) performs protocol conversion between the user data structure (e.g. characters or X.25 Layer 2 frames) and a structure more adapted to the radio link protocol. This function is described in the relevant 3GPP TS 27-series specifications.

The L2R function includes the data compression function.

6.1.4 Resources allocated by the PLMN network

Part of the PLMN connection concerns the resources allocated by the PLMN network on the basis of the attribute values of the connection elements.

For the speech calls, the PLMN codec is allocated.

For data calls, resources are provided at the IWF/MSC such as:

– V.110 based rate adaptation for such channel codings as TCH/F 4.8 and TCH/F9.6 and PLMN specific rate adaption for channel codings TCH/F14.4, TCH/F28.8, TCH/F43.2 (3GPP TS 44.021, 48.020);

– filtering of status bits (TS 27.001);

– RLP for non-transparent services (TS 24.022);

– Data compression (TS 24.022, 27.002).

These are sufficient for data services such as:

– asynchronous circuit (bearer service series 20), used with unrestricted digital information transfer capability;

– synchronous circuit (bearer service series 30), used with unrestricted digital information transfer capability when interworking with circuit switched digital networks.

In addition to the above listed resources, further resources are allocated in the other cases:

– modems for asynchronous circuit (bearer service series 20) or synchronous circuit (bearer service series 30) used with 3.1 kHz information transfer capability;

– fax adaptor for the fax group 3 (teleservice series 60);