6.1 Generic Signalling Model for LCS

03.713GPPFunctional descriptionLocation Services (LCS)Release 1999Stage 2TS

6.1.1 Protocol layering

Figure 6 shows the generic signalling model applicable to LCS for any signalling interaction in which an SMLC forms at least one of the signalling end points.

Figure 6: Generic Model for LCS Signalling to an SMLC

The functions performed by each protocol layer are as follows:

a) LCS application protocol – this depends on the other signaling end point (e.g. whether a target MS or LMU) and may be absent if supported in the BSSAP-LE layer. The application protocol supports specific LCS functions (e.g. positioning measurements, assistance measurements) and is independent of lower protocol layers.

b) BSSAP-LE – this is an extension of BSSAP and carries the LCS application protocol signaling units. Necessary functions include identification of the LCS application protocol and identification, where not provided by the network layer, of the two end points. This layer can be relayed by an intermediate entity or mapped into an equivalent layer 3 protocol used by the other signaling end point. This layer supports segmentation of LCS application layer protocols.

c) Network Layer – provides signaling transport between the SMLC and either the other end point or some intermediate entity at which the BSSAP-LE layer is relayed or mapped. The network layer may support connection oriented or connectionless signaling. For second generation circuit oriented applications, the network layer is provided using MTP and SCCP. For third generation and packet oriented applications, other protocols may be used. This layer supports segmentation of LCS application layer protocols.

d) Physical Layer – for second generation circuit oriented applications, SS7 signaling links are supported by the physical layer.

e) L3 – a protocol layer compatible with or the same as BSSAP-LE.

f) L2 – logical link layer for the other endpoint

g) L1 – physical layer for the other end point.

6.1.2 Message Segmentation

Message segmentation is needed to transport any large LCS message that exceeds the message size limitation supported by any GSM interface over which transport is needed. Intermediate Level Segmentation

The segmentation of SMLCPP (GSM 08.31) and BSSLAP (GSM 08.71) messages is supported by segmentation mechanisms defined in GSM 08.08, GSM 04.08 and GSM 09.31. The sending, receiving and all intermediate entities supporting segmentation shall ensure reliable and sequenced delivery of the message segments by appropriate use of the capabilities supported by lower transport and network level protocols. Network Level Segmentation

Segmentation and reassembly of large SMLCPP and BSSLAP messages at the network (e.g. SCCP) level may be supported. For message transfer over any interface where network level segmentation is not supported (e.g. Abis interface, Um interface), segmentation at the application level shall be used. This may require support of both network and intermediate level segmentation by certain intermediate entities.