6 Usage of BSSAP-LE and BSSAP on the Lb Interface

09.313GPPBase Station System Application Part LCS Extension (BSSAP-LE)Location Services (LCS)Release 1999TS

6.1 Applicable Message Sets

The following BSSAP-LE message sets are applicable to the Lb interface between an SMLC and BSC:

All DTAP-LE messages

All BSSMAP-LE positioning messages

All BSSMAP-LE information messages

All BSSMAP-LE general messages

The following BSSMAP messages defined in 3GPP TS 08.08 are applicable to the Lb interface to support signaling to a Type A LMU using an SDCCH:

Cipher Mode Command (SMLC to BSC)

Cipher Mode Complete (BSC to SMLC)

Cipher Mode Reject (BSC to SMLC)

Classmark Update (BSC to SMLC)

Clear Command (SMLC to BSC)

Clear Complete (BSC to SMLC)

Clear Request (BSC to SMLC)

Complete Layer 3 Information (BSC to SMLC)

Confusion (BSC to SMLC)

Handover Required (BSC to SMLC)

Handover Required Reject (SMLC to BSC)

Handover Performed (BSC to SMLC)

Paging (SMLC to BSC)

The following additional BSSMAP messages defined in 3GPP TS 08.08 are applicable to the Lb interface to support signaling to a Type A LMU using a TCH:

Assignment Request (SMLC to BSC)

Assignment Complete (BSC to SMLC)

Assignment Failure (BSC to SMLC)

Block (bothway)

Blocking Acknowledge (bothway)

Unblock (bothway)

Unblocking Ack. (bothway)

Unequipped circuit (bothway)

The following DTAP messages defined in 3GPP TS 04.08 are applicable to the Lb interface to support signaling to a Type A LMU using an SDCCH:

RR Paging Response

All MM Messages

The following additional CM level DTAP messages defined in 3GPP TS 04.08 are applicable to the Lb interface to support signaling to a Type A LMU using a TCH.

Call Confirmed (LMU to SMLC)

Connect (LMU to SMLC)

Connect Acknowledge (SMLC to LMU)

Setup (SMLC to LMU)

Disconnect (bothway)

Release (bothway)

Release Complete (bothway)

6.2 MTP Functions

Except where defined otherwise in this specification, MTP requirements on the Lb interface for the BSC are the same as those defined for the A interface in 3GPP TS 08.06 for the BSC. MTP requirements on the Lb interface for the SMLC are the same as those defined for the A interface in 3GPP TS 08.06 for the MSC. STP functions are not required in the SMLC and a single signaling link set may be used between the BSC and SMLC. The BSC shall be homed to a single SMLC and shall only use the Lb signaling interface for signaling communication with the SMLC.

6.3 SCCP Functions

6.3.1 General

Except where defined otherwise in this specification, SCCP requirements on the Lb interface for the BSC are the same as those defined for the A interface in 3GPP TS 08.06 for the BSC. SCCP requirements on the Lb interface for the SMLC are the same as those defined for the A interface in 3GPP TS 08.06 for the MSC. Requirements concerning support of a type A LMU are the same as those in 3GPP TS 08.06 regarding support of a normal MS. In particular, usage of SCCP to transfer DTAP-LE messages between a type A LMU and SMLC are the same as those regarding transfer of other DTAP messages.

6.3.2 Modifications for Connectionless SCCP

Connectionless SCCP messages and procedures are used to transfer BSSMAP-LE Connectionless Information messages and those BSSMAP messages applicable to the Lb interface for which connectionless SCCP transfer is defined in 3GPP TS 08.08. Refer to 3GPP TS 03.71 for a description of the procedures in the SMLC and BSC. SCCP protocol class 1 shall be used when multiple BSSMAP-LE messages are transferred containing segments of a single fragmented LLP or SMLCPP message.

6.3.3 Modifications for Connection Oriented SCCP

Use of connection oriented SCCP messages and procedures on the Lb interfaces to support signaling access to a type A LMU using DTAP-LE, DTAP and BSSMAP messages is the same as that defined in 3GPP TS 08.06 on the A interface to support access to a normal MS.

To support positioning of a target MS, connection oriented SCCP messages and procedures using protocol class 2 shall be used to transfer BSSMAP-LE positioning messages and BSSMAP-LE Connection Oriented Information messages over the Lb interface. A separate dedicated SCCP connection shall be used to support positioning for each target MS. Connection establishment shall be instigated by the BSC when the positioning attempt commences. Connection release shall be instigated by either the BSC or SMLC when the positioning attempt has been completed or has failed.

Transfer of BSSMAP-LE messages using an SCCP connection to support positioning of a particular target MS is shown in the following figure. In particular, a BSSMAP-LE message shall be included in the data field of the SCCP CR and a BSSMAP-LE message may be included in the data field of an SCCP CC, CREF or RLSD message.

Figure 6.3.3/09.31: SCCP Connection Oriented Signaling on Lb Interface for Positioning

6.3.4 Contents of the SCCP Data Field

The contents of the SCCP data field are the same as that defined for the A interface in 3GPP TS 08.06 for MSC-BSC signaling. In particular, the same conventions are used to transfer and discriminate between any BSSAP and DTAP message contained within the SCCP data field. Since all BSSAP-LE messages applicable to the Lb interface use the same encoding as for the A interface, the conventions used to discriminate a BSSMAP message are applicable to any BSSMAP-LE message on the Lb interface, while the conventions for a DTAP message apply to any DTAP-LE message.

6.3.5 Abnormal Conditions

If a user-out-of-service information or signalling-point-inaccessible information is received by a BSC or SMLC, no new attempt to establish SCCP connections towards the affected point code shall be started until the corresponding user-in-service information or signalling-point-accessible information is received.

When a user-out-of-service information or signalling-point-inaccessible is received, an optional timer may be started. If the timer expires all the SCCP connections towards the affected point code shall be released. When the user-in-service or signalling-point-accessible is received, the timer is stopped.

If an SCCP connection is released, the optional timer expires or a connection refusal is received, any dependent BSSAP-LE procedure between the SMLC and BSC shall be terminated and, at a BSC, any associated SCCP connection or location service transaction to an MSC, or any associated signaling or circuit connection to an LMU, shall be released using appropriate signalling procedures.