7.7 Common Procedures to Support Positioning

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

The procedures described in this section enable an SMLC to obtain positioning related information or instigate positioning for a particular target MS. The procedures are applicable to all positioning methods after an SMLC receives a BSSMAP-LE Perform Location request for a target MS until a BSSMAP-LE Perform Location response is returned to the originator.

7.7.1 Information Transfer between an NSS based SMLC and a Target MS

An NSS based SMLC uses the procedure shown in Figure 34 in order to obtain positioning information from a target MS or transfer location assistance information to a target MS after a request has been received from the VMSC. More details of the location information transfer procedure between the BSC and MS can be found in GSM 04.08.

Figure 34: Information Transfer between an NSS based SMLC and a Target MS

1) The SMLC passes a BSSMAP-LE Connection Oriented Information message to the VMSC containing an embedded BSSLAP MS Position Command with an RRLP message parameter. The message is transferred using the SCCP connection established between the SMLC and VMSC for positioning the target MS. If the BSSLAP message is too large to fit in a single BSSMAP-LE Connection Oriented Information message, it may be segmented and transferred inside a sequence of BSSMAP-LE messages with the last BSSMAP-LE message containing a last segment indication and the last BSSLAP segment. The SMLC shall indicate in the BSSLAP MS Position Command whether the embedded RRLP message contains a positioning command. versus positioning assistance data.

2) The VMSC forwards the BSSMAP message(s) to the serving BSC for the target MS.

3) The BSC transfers the embedded RRLP message to the target MS inside an RR Application Information message. If the BSSLAP message was segmented by the SMLC, onward transfer to the MS shall be deferred until all segments have arrived and the complete BSSLAP message is reassembled. The embedded RRLP message shall then be re-segmented if necessary with each RRLP segment transferred in a separate RR Application Information message with the last RR message indicating the last RRLP segment. No later than when the last RR Application Information message has been transferred, the BSC shall start a positioning supervision timer if none is already in progress or restart this if already in progress. If the timer expires before the final response in step 4 is received, the BSC shall return a BSSMAP-LE Connection oriented Information message to the SMLC containing a BSSLAP Abort with a cause of BSC timeout.

4) When the target MS has positioning information to return to the SMLC, it sends an RR Application Information message to the BSC containing an embedded RRLP message. If the RRLP message is too large to fit in a single RR Application Information message, it may be segmented and carried in a sequence of RR Application Information messages with the last message indicating the last RRLP segment. The last RR LCS Information message shall indicate if this is the final response from the MS.

5) If the timer started in step 3 has already expired, the BSC discards the RRLP message received in step 4. Otherwise, the BSC forwards the RRLP message to the VMSC inside a BSSLAP MS Positioning Response message contained in a BSSMAP Connection Oriented Information message. If the RRLP message was segmented onward transfer to the MSC shall be deferred until all segments have arrived and the complete RRLP message is reassembled. If the resulting BSSLAP message is too large to fit into a single BSSMAP Connection Oriented Information message (e.g. if the RRLP message was segmented), it shall be segmented. Each segment is then transferred in a separate BSSMAP message with the last message containing the last BSSLAP segment. If the SMLC indicated a positioning command in step 1 and the MS has indicated a final response, the BSC may add additional measurement information to the BSSLAP MS Position Response in the last BSSMAP message – if necessary, creating a new BSSMAP message if message size limitations would be exceeded. The BSC shall stop the supervision timer started in step 3 when the final segment of the final response from the MS has been transferred.

6) The VMSC forwards the received BSSMAP messages as corresponding BSSMAP-LE message(s) to the SMLC using the SCCP connection previously established for positioning the target MS. If the MS did not indicate a final response in step 3, the SMLC may transfer a further RRLP message to the MS (e.g. containing assistance data) according to steps 1 to 3 and the MS may return a subsequent response according to steps 4 to 6.

7.7.2 Information Transfer between a BSS based SMLC and a Target MS

A BSS based SMLC uses the procedure shown in Figure 35 in order to obtain positioning measurements from a target MS or transfer location assistance information to a target MS after a request has been received from the BSC serving the target MS. More details of the location information transfer procedure between the BSC and MS can be found in GSM 04.08.

Figure 35: Information Transfer between a BSS based SMLC and a Target MS

1) The SMLC passes a BSSMAP-LE Connection Oriented Information message to the serving BSC containing an embedded BSSLAP MS Position Command with an RRLP message parameter. The message is transferred using the SCCP connection established between the SMLC and BSC for positioning the target MS If the BSSLAP message is too large to fit in a single BSSMAP-LE Connection Oriented Information message, it may be segmented and transferred inside a sequence of BSSMAP-LE messages with the last BSSMAP-LE message containing a last segment indication and the last RRLP segment. The SMLC shall indicate in the first BSSLAP MS Position Command whether the embedded RRLP message contains a positioning command. versus positioning assistance data.

2) The BSC transfers the embedded RRLP message to the target MS inside an RR Application Information message. If the BSSLAP message was segmented by the SMLC, onward transfer to the MS shall be deferred until all segments have arrived and the complete BSSLAP message is reassembled. The embedded RRLP message shall then be re-segmented if necessary with each RRLP segment transferred in a separate RR Application Information message with the last RR message indicating the last RRLP segment. No later than when the last RR Application Information message has been transferred, the BSC shall start a positioning supervision timer if none is already in progress or restart this if already in progress. If the timer expires before the final response in step 3 is received, the BSC shall return a BSSMAP-LE Connection oriented Information message to the SMLC containing a BSSLAP Abort with a cause of BSC timeout.

3) When the target MS has positioning information to return to the SMLC, it sends an RR Application Information message to the BSC containing an embedded RRLP message. If the RRLP message is too large to fit in a single RR Application Information message, it may be segmented and carried in a sequence of RR Application Information messages with the last message indicating the last RRLP segment. The last RR Application Information message shall indicate if this is the final response from the MS.

4) If the timer started in step 2 has already expired, the BSC discards the RRLP message received in step 3. Otherwise, the BSC forwards the RRLP message to the SMLC inside a BSSLAP MS Positioning Response message contained in a BSSMAP-LE Connection Oriented Information message. If the RRLP message was segmented, onward transfer to the SMLC shall be deferred until all segments have arrived and the complete RRLP message is reassembled. If the resulting BSSLAP message is too large to fit into a single BSSMAP-LE Connection Oriented Information message (e.g. if the RRLP message was segmented), it shall be segmented. Each segment is then transferred in a separate BSSMAP-LE message with the last message containing the last BSSLAP segment. If the SMLC indicated a positioning command in step 1 and the MS has indicated a final response, the BSC may add additional measurement information to the BSSLAP MS Position Response in the last BSSMAP-LE message – if necessary, creating a new BSSMAP-LE message if message size limitations would be exceeded. The BSC shall stop the supervision timer started in step 2 when the final segment of the final response from the MS has been transferred. If the MS did not indicate a final response in step 2, the SMLC may transfer a further RRLP message to the MS (e.g. containing assistance data) according to steps 1 and 2 and the MS may return a subsequent response according to steps 3 and 4.

7.7.3 Information Transfer between an NSS based SMLC and a BSC

An NSS based SMLC uses the procedure shown in Figure 36 in order to obtain positioning related information for a particular target MS from the BSC after a positioning request has been received from the VMSC.

Figure 36: Information Transfer between an NSS based SMLC and a BSC

1) The SMLC passes a BSSMAP Connection Oriented Information message to the VMSC containing an embedded BSSLAP message. The BSSMAP message is transferred using the SCCP connection previously established between the SMLC and MSC when the positioning request for the target MS was initially sent to the SMLC.

2) The VMSC forwards the BSSMAP-LE message to the BSC serving the target MS. The BSC recognizes that it is the final destination due to the presence of the embedded BSSLAP message.

3) When the BSC has positioning information for the target MS to return to the SMLC, it sends a BSSMAP-LE Connection Oriented Information message to the VMSC containing an embedded BSSLAP message.

4) The VMSC forwards the BSSMAP message to the SMLC using the SCCP connection previously established for positioning the target MS.

7.7.4 Information Transfer between a BSS based SMLC and a BSC

A BSS based SMLC uses the procedure shown in Figure 37 in order to obtain positioning related information from the BSC serving a particular target MS after a positioning request has been received from the BSC.

Figure 37: Information Transfer between a BSS based SMLC and a BSC

1) The SMLC passes a BSSMAP-LE Connection Oriented Information message to the BSC containing an embedded BSSLAP message. The BSSMAP-LE message is transferred using the SCCP connection previously established between the SMLC and BSC when the positioning request for the target MS was initially sent to the SMLC. The BSC recognizes that it is the final destination due to the presence of the embedded BSSLAP message.

2) When the BSC has positioning information for the target MS to return to the SMLC, it sends a BSSMAP-LE Connection Oriented Information message to the SMLC containing an embedded BSSLAP message. The message is sent using the SCCP connection previously established for positioning the target MS.