7 Use of BSSAP-LE on the Ls Interface

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

7.1 Applicable Message Sets

The following BSSAP-LE messages are applicable to the Ls interface between an MSC and SMLC:

All DTAP-LE messages

All BSSMAP-LE positioning messages

All BSSMAP-LE LMU control messages

All BSSMAP-LE information messages

All BSSMAP-LE general messages

7.2 MTP Functions

SS7 signaling on the Ls interface may be supported using 56 kbps or 64 kbps digital signaling channels. These may be supported within either E1 or T1 physical links.

For E1 links or where CCITT/ITU SS7 signaling is applicable, the MTP functions as specified in CCITT Recommendations Q.702, Q.703, Q.704 and Q.707 are applicable. For T1 links or where ANSI SS7 signaling is applicable, the MTP functions as specified in ANSI T1.111 are applicable. For the SMLC, the requirements in these recommendations for a signaling end point are applicable. For the MSC, the requirements in these recommendations for both a signaling end point and signaling transfer point (STP) are applicable. MSC support of STP functions is only required for situations in which the SMLC has no signaling links to an STP and needs to access other network entities to which there are no direct point-to-point signaling links.

Where an SMLC supports direct signaling links to one or more MSCs only and has no signaling links to an STP, certain exceptions and modifications to normal CCITT and ANSI requirements may be applied within a PLMN administration.

7.3 SCCP functions

7.3.1 General

For E1 links or where CCITT/ITU SS7 signaling is applicable, the SCCP functions as specified in either CCITT Blue Book Recommendations Q.711, Q.712, Q.713 and Q.714 or ITU White Book Recommendations Q.711, Q.712, Q.713 and Q.714 are applicable, as amended by the exceptions and modifications defined here. For T1 links or where ANSI SS7 signaling is applicable, the SCCP functions as specified in ANSI T1.112 are applicable, as amended by the exceptions and modifications defined here.

Several functions of the SCCP are not used on the Ls interface: error detection, receipt confirmation, flow control.

The segmenting/reassembling function may be used if the total message length exceeds the maximum allowed message length that can be carried by the MTP.

7.3.2 Allowed Exceptions to CCITT Recommendations Q.711-714

Only the following SCCP messages are applicable to the Ls interface:

Connection Confirm (CC)

Connection Request (CR)

Connection Refused (CREF)

Data Form 1 (DT1)

Inactivity Test (IT)

Released (RLSD)

Release Complete (RLC)

Subsystem Allowed (SSA)

Subsystem Prohibited (SSP)

Subsystem Status Test (SST)

Unitdata (UDT)

Unitdata Service (UDTS)

Support of only SCCP protocol classes 0, 1 and 2 is required. For protocol class 2, the "credit" parameter field and the "sequencing/segmenting" parameter fields are not used, but the parameters must still be included in the Inactivity Test (IT) message for syntax reasons. Negotiation of protocol class and flow control is not required for protocol class 2.

The SCCP called party address in a CR or UDT may contain only the subsystem number (SSN) or a signaling point code (SPC) plus SSN or a global title. Use of a global title is not required for SMLC to MSC signaling within the same PLMN. SSN values applicable to the Ls interface are defined in 3GPP TS 03.03.

For protocol class 2, support of only a single connection section is required. Use of multiple connection sections is a national concern.

7.3.3 Allowed Exceptions to ANSI T1.112

Only the following SCCP messages are applicable to the Ls interface:

Connection Confirm (CC)

Connection Request (CR)

Connection Refused (CREF)

Data Form 1 (DT1)

Inactivity Test (IT)

Released (RLSD)

Release Complete (RLC)

Subsystem Allowed (SSA)

Subsystem Prohibited (SSP)

Subsystem Status Test (SST)

Unitdata (UDT)

Unitdata Service (UDTS)

Support of only SCCP protocol classes 0, 1 and 2 is required. For protocol class 2, the "credit" parameter field and the "sequencing/segmenting" parameter fields are not used, but the parameters must still be included in the Inactivity Test (IT) message for syntax reasons. Negotiation of protocol class and flow control is not required for protocol class 2.

The SCCP called party address in a CR or UDT may contain only the subsystem number (SSN) or a signaling point code (SPC) plus SSN or a global title. Use of a global title is not required for SMLC to MSC signaling within the same PLMN. SSN values applicable to the Ls interface are defined in 3GPP TS 03.03.

For protocol class 2, support of only a single connection section is required. Use of multiple connection sections is a national concern.

7.3.4 Usage of Connectionless SCCP

Connectionless SCCP messages and procedures are used to transfer BSSMAP-LE Connectionless Information messages. Refer to 3GPP TS 03.71 for a description of the procedures in the SMLC and MSC. SCCP protocol class 1 shall be used when multiple BSSMAP-LE messages are transferred containing segments of a single fragmented LLP or SMLCPP message.

7.3.5 Usage of Connection Oriented SCCP

Connection oriented SCCP messages and procedures for SCCP protocol class 2 shall be used to transfer BSSMAP-LE positioning messages, BSSMAP-LE LMU control messages, BSSMAP-LE Connection Oriented Information messages and DTAP-LE messages. A separate dedicated SCCP connection shall be used to support either positioning for each target MS or signaling to each type A LMU. Connection establishment shall be instigated when the positioning attempt commences or when a signaling link to a type A LMU needs to be established. Connection release shall be instigated when the positioning attempt has been completed or has failed or when a signaling link to a type A LMU needs to be released. The MSC is normally expected to release the SCCP connection to the SMLC.

Transfer of BSSAP-LE messages within an SCCP connection is shown in the following figure. In particular, a BSSMAP-LE message shall be included in the data field of any SCCP CR and a BSSMAP-LE message may be included in the data fields of an SCCP CC, CREF or RLSD message.

Figure 7.3.5-1/09.31: SCCP Connection Oriented Signaling on Ls Interface

7.3.6 Contents of the SCCP Data Field

The contents of the SCCP data field for BSSMAP-LE and DTAP-LE messages are shown in the following figures.

8

7

6

5

4

3

2

1

Octet 1

0

0

0

0

0

0

0

D=0

Octet 2

Length indicator = n

Octet 3
to
Octet n+2

BSSMAP-LE Message Contents

Figure 7.3.6-1/3GPP TS 09.31: SCCP Data Field for a BSSMAP-LE Message

8

7

6

5

4

3

2

1

Octet 1

0

0

0

0

0

0

0

D=1

Octet 2

DLCI

Octet 3

Length indicator = n

Octet 4
to
Octet n+3

DTAP-LE Message Contents

Figure 7.3.6-2/3GPP TS 09.31: SCCP Data Field for a DTAP-LE Message

The Discrimination Indicator is coded in bit 1 of octet one and indicates the type of the BSSAP-LE message.

Discrmination Indicator

BSSAP-LE Message Type

0

BSSMAP-LE

1

DTAP-LE

The DLCI in octet 2 is applicable only to DTAP-LE messages and is coded as defined for the A interface in 3GPP TS 08.06 for DTAP. For signaling to a type A LMU using an SDCCH and SAPI=0, the value of the DLCI is 10000000.

The length indicator is coded in one octet, and is the binary representation of the number of octets of the subsequent BSSMAP-LE or DTAP-LE message parameter.

7.3.7 Content of DTAP-LE Messages

DTAP-LE messages transferred on the Ls interface are encoded as defined in 3GPP TS 04.71. In particular, in octet 1 of any DTAP-LE message, the Protocol discriminator shall indicate LCS and the transcation identifier (TI) shall indicate the transcation between the SMLC and type A LMU. The TI shall be assigned by the SMLC if the transcation is originated from the SMLC and by the LMU if the originator is the LMU. The MSC shall not change the value of the TI when transferring any DTAP-LE message from the SMLC to the LMU or from the LMU to the SMLC.

7.3.8 Abnormal Conditions

If a user-out-of-service information or signalling-point-inaccessible information is received by an MSC 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 MSC shall be terminated and, at an MSC, any associated SCCP connection or location service transaction to a BSC, or any associated signaling or circuit connection to an LMU, shall be released using appropriate signalling procedures.