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TS 49.008
Application of the
Base Station System Application Part (BSSAP) on the
E-interface

Use "3GPP‑Page" to get the Word version, and "ETSI‑search" to get the PDF version
V16.0.0 (PDF)  2020/06  19 p.
V15.0.0  2018/06  19 p.
V14.0.0  2017/03  19 p.
V13.0.0  2015/12  18 p.
V12.0.0  2014/09  18 p.
V11.0.0  2012/09  18 p.
V10.0.0  2011/03  17 p.
V9.0.0  2009/12  17 p.
V8.1.1  2009/04  17 p.
V7.0.0  2007/06  17 p.
V6.1.0  2005/06  17 p.
V5.1.0  2003/03  16 p.
V4.1.0  2003/03  16 p.
GSM Rel-99 v8.2.0  2003/03  16 p.
GSM Rel-98 v7.2.0  1999/12  15 p.
GSM Rel-97 v6.0.0  1998/10  14 p.
GSM Rel-96 v5.1.0  1997/02  14 p.
GSM Phase-2 v4.1.1  1995/02  15 p.
Rapporteur:
Mr. Monrad, AtleEricsson LM

Content for  TS 49.008  Word version:  16.0.0

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1  ScopeWord‑p. 5

The present document describes the subset of Base Station System Application Part (BSSAP) messages and procedures, defined in TS 48.006 and TS 48.008, which is used on the E-interface. A general description can be found in TS 23.002 and TS 23.009.
For the initiation and execution of handover between MSCs a subset of BSSMAP procedures are used. For the subsequent control of resources allocated to the Mobile Station (MS) BSSMAP procedures are used. DTAP is used for the transfer of connection management and mobility management messages between the MS and the controlling MSC.
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2  References

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
  • References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
  • For a specific reference, subsequent revisions do not apply.
  • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
[1]  Void.
[1a]
TR 21.905: "Vocabulary for 3GPP Specifications".
[2]
TS 23.009: "Handover procedures".
[2a]
TS 23.002: "Network Architecture".
[3]
TS 48.006: "Signalling transport mechanism specification for the Base Station System Mobile services Switching Centre (BSS MSC) interface".
[4]
TS 48.008: "Mobile-services Switching Centre Base Station System (MSC BSS) interface; Layer 3 specification".
[5]
TS 29.002: "Mobile Application Part (MAP) specification".
[6]
TS 29.010: "Information element mapping between Mobile Station Base Station System (MS - BSS) and Base Station System Mobile services Switching Centre (BSS MSC); Signalling procedures and the Mobile Application Part (MAP)".
[7]
TS 23.172: "Technical realization of Circuit Switched (CS) multimedia service; UDI/RDI fallback and service modification; Stage 2)".
[8]
TS 25.413: "UTRAN Iu interface Radio Access Network Application Part (RANAP) signalling".
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3  AbbreviationsWord‑p. 6

For the purposes of the present document, the abbreviations defined in TR 21.905 and the following apply:
BSS
Base Station System
BSSAP
Base Station System Application Part
BSSMAP
Base Station System Management Application Part
CCCH
Common Control CHannel
DLCI
Data Link Connection Identifier
DTAP
Direct Transfer Application Part
MSC
Mobile services Switching Centre
MSC-A
Mobile services Switching Centre, Anchor (Anchor MSC)
MSC-I
Mobile services Switching Centre, Intermediate (Intermediate MSC)
MSC-T
Mobile services Switching Centre, Target (Target MSC)
SAPI
Service Access Point Identifier
SCCP
Signalling Connection Control Part
TCAP
Transaction Capabilities Application Part
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4  Principles for the use of BSSAP on the E interface

4.1  General

The mechanisms for the transfer of the BSSAP messages on the E-interface is defined in TS 29.002. The operation of the handover procedures between MSCs and the use of the BSSMAP messages for those procedures is described in TS 23.009 and TS 29.010.
In the same way as a SCCP signalling connection is used for the messages relating to one MS on the MSC-BSS interface a TCAP dialogue is used on the E-interface for messages relating to one MS. As no correspondence to the connectionless service on the MSC-BSS interface is used on the E-interface none of the global procedures (see TS 48.008, subclause 3.1) are applicable.
The management of the terrestrial circuits and IP connections between the MSCs is outside the scope of the E-interface (see TS 23.009), therefore all procedures, messages and information elements relating to terrestrial circuits or IP connections are also excluded from the BSSMAP procedures and messages used on the E-interface.
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4.2  Transfer of DTAP and BSSMAP layer 3 messages on the E interface

The BSSAP data which on the MSC-BSS interface is contained in the user data field of the exchanged SCCP frames (see TS 48.006) is on the E-interface transferred as the contents of the signalling info in a BSS APDU parameter as described in TS 29.002.
The BSSAP data consists of a BSSAP header and a DTAP or BSSMAP layer 3 message. The BSSAP header contains, as specified in TS 48.006, subclauses 6.3.1, 6.3.2 and 6.3.3, of a discrimination parameter, possibly a Data Link Connection Identification (DLCI) parameter, and a length indicator.
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4.3  Roles of MSC A, MSC I and MSC TWord‑p. 7

For the description in the present document, the MSC's functionality related to the handover between MSCs has been split into three logical parts, MSC-A, MSC-T and MSC-I. The different roles need not necessarily be performed by different MSCs.
MSC-A is the call/connection controlling part of the MSC where the call/connection was originally established and the switching point for handover between MSCs. (This corresponds to MSC-A as defined in TS 23.009 and TS 29.002). The MSC that is the MSC-A will not be changed during the duration of a call/connection.
MSC-T is the part relating to the transitory state during the handover for the MSC to which the MS is handed over when Basic handover or Subsequent handover (see TS 23.009) take place. (This corresponds, depending on the type of handover to MSC-A, MSC-B or MSC-B' in TS 23.009 and TS 29.002).
MSC-I is the part of an MSC through which the MSC-A, via an E-interface (or an internal interface) is in contact with the MS. (This corresponds, depending on the type of handover to MSC-A, MSC-B or MSC-B' in TS 23.009 and TS 29.002).
The MSC that is the MSC-A can also have the role of either the MSC-I or the MSC-T during a period of the call/connection.
The following is applicable for the involved MSCs concerning the exchange of BSSAP data on an E-interface before and after a successful inter MSC handover:
  1. At Basic handover, two MSCs are involved, one MSC being MSC-A and one being MSC-T. When this handover has been performed, the two MSCs interworking on the E-interface have the roles of MSC-A and MSC-I respectively, i.e. the MSC that is the MSC-T during the handover is now the MSC-I.
  2. At Subsequent handover back to MSC-A, two MSCs are involved. The MSC having the role of MSC-A has also the role of MSC-T. The other MSC involved has the role of MSC-I. When this handover has been completed, there is no exchange of BSS data on the E-interface, i.e. the MSC being the MSC-I before and during the handover is now no longer taking part.
  3. At subsequent handover to an MSC not being MSC-A, three MSCs are involved. The roles of these MSCs are MSC-A, MSC-I, and MSC-T respectively. When this handover has been performed, the two MSCs interworking on an E-interface have the roles of MSC-A and MSC-I respectively, i.e. the MSC that is the MSC-T during the handover is now the MSC-I and the MSC being MSC-I during the handover is now no longer taking part.
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5  Use of the BSSAP on the E interface

DTAP is used on the E-interface for the transfer of messages between the MSC-A and the MS.
The dedicated BSSMAP procedures (TS 48.008, subclause 3.1) used on the E-interface to some extent are:
  • assignment;
  • handover resource allocation;
  • handover execution;
  • internal handover indication;
  • release due to BSS generated reasons;
  • classmark handling;
  • cipher mode control;
  • trace invocation;
  • queuing indication;
  • data link control SAPI not equal to "0";
  • Location Acquisition;
  • LSA handling;
  • Common ID.
One dedicated BSSMAP procedure is used only on the E-interface:
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5.1  DTAPWord‑p. 8

For the exchange of the DTAP messages (TS 48.008, subclause 2.2), the involved MSCs shall act according to the following:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.

5.2  Assignment

The Assignment procedure (TS 48.008, subclause 3.1.1) is applied on the E-interface with following conditions:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.
The handling of terrestrial resources is not applicable.

5.3  Handover resource allocation

At Basic Inter MSC Handover (TS 23.009) the Handover resource allocation procedure (TS 48.008, subclause 3.1.5.2) is applied on the E-interface with the following conditions:
  • the MSC-A acts as the MSC;
  • the MSC-T acts as the target BSS.
At Subsequent Inter MSC Handover (TS 23.009) the Handover resource allocation procedure (TS 48.008, subclause 3.1.5.2) is applied on the E-interface with the following conditions:
  • the MSC-I acts as the MSC;
  • the MSC-T acts as the target BSS;
  • if the MSC that is the MSC-A is not also the MSC-T, then this MSC shall act as the target BSS towards the MSC-I and as the MSC towards the MSC-T.
The handling of terrestrial resources is not applicable.
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5.4  Handover execution

For the Handover execution procedure (TS 48.008, subclause 3.1.5.3) the applicable parts on the E-interface are the transfer of HANDOVER DETECT, HANDOVER COMPLETE and HANDOVER FAILURE messages at inter MSC handover. For those parts, the involved MSCs shall act according to the following:
  • the MSC that is the MSC-A, acts as the MSC;
  • the MSC that is the MSC-I, if it is not also the MSC-A, acts as the serving BSS;
  • the MSC that is the MSC-T, if it is not also the MSC-A, acts as the target BSS.
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5.5  Internal handover indicationWord‑p. 9

For the Internal handover indication (TS 48.008, subclauses 3.1.6 and 3.1.7), the involved MSCs shall act according to the following:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.
MSC internal handovers (inter BSS and intra BSS handover) at the MSC-I are decided and executed autonomously by that MSC together with the connected BSSs. At completion of the handover execution the MSC-I initiates the internal handover indication procedure.
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5.6  Release due to BSS generated reasons

For the Release due to BSS generated reasons procedure (TS 48.008, subclause 3.1.9.2) the involved MSCs shall act according to the following:
  • the MSC-I acts as the BSS;
  • no further action is taken by the MSC-A.
Additionally, at Basic Inter MSC Handover and at Subsequent Inter MSC Handover (TS 23.009), if the MSC that is the MSC-A is not also the MSC-T, the Release due to BSS generated reasons procedure (TS 48.008, subclause 3.1.9.2) is applied on the E-interface with the following conditions:
  • the MSC-T acts as the BSS;
  • no further action is taken by the MSC-A.
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5.7  Classmark handling

For the Classmark handling (TS 48.008, subclause 3.1.13), the involved MSCs shall act according to the following:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.

5.8  Cipher mode control

For the Cipher mode control (TS 48.008, subclause 3.1.14), the involved MSCs shall act according to the following:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.

5.9  Trace invocation

For the Trace invocation (TS 48.008, subclause 3.1.11), the involved MSCs shall act according to the following:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.
Additionally, at Basic Inter MSC Handover and at Subsequent Inter MSC Handover (TS 23.009), if the MSC that is the MSC-A is not also the MSC-T, the Trace invocation (TS 48.008, subclause 3.1.11) is applied on the E-interface with the following conditions:
  • the MSC-A acts as the MSC;
  • the MSC-T acts as the target BSS.
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5.10  Queuing indicationWord‑p. 10

For the Queuing Indication (TS 48.008, subclause 3.1.17), the involved MSCs shall act according to the following:
  • at Assignment and at Basic Inter MSC handover:
    • the MSC-A acts as the MSC;
    • the MSC-I acts as the BSS.
  • at Subsequent Inter MSC handover:
    • the MSC-I acts as the MSC;
    • the MSC-T acts as the BSS;
    • if the MSC that is the MSC-A is not also the MSC-T, then this MSC acts as the target BSS towards the MSC-I and as the MSC towards the MSC-T.
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5.11  Data link control SAPI not equal to "0"

For the Data Link Control SAPI not Equal to "0" (TS 48.008, subclause 3.1.18), the involved MSCs shall act according to the following:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.

5.12  Location Acquisition

For the Location Acquisition procedure (TS 48.008, subclause 3.1.28), the involved MSCs shall act according to the following:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.

5.13  LSA handling

For the LSA handling (TS 48.008, subclause 3.1.27), the involved MSCs shall act according to the following:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.

5.14  Common ID

For the Common Id (TS 48.008), the involved MSCs shall act according to the following:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.

5.15  Service Change procedureWord‑p. 11

In the Service Change procedure for network-initiated SCUDIF (see TS 23.172), the MSC-I sends the CHANNEL MODIFY REQUEST message (see TS 48.008) to the MSC-A. The request was originally sent by the RNC using RAB MODIFY REQUEST to trigger execution of the alternative RAB configuration (see TS 25.413). For the CHANNEL MODIFY REQUEST message, the involved MSCs shall act according to the following:
  • the MSC-A acts as the MSC;
  • the MSC-I acts as the BSS.
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6  BSSMAP messages transferred on the E interface

The following BSSMAP messages, defined in TS 48.008, subclause 3.2.1, are transferred on the E-interface:
ASSIGNMENT REQUEST (MSC-A → MSC-I)
Excluded information elements: CIRCUIT IDENTITY CODE, AoIP Transport Layer Address (MGW), Call Identifier, Codec List (MSC Preferred)
ASSIGNMENT COMPLETE (MSC-I → MSC-A)
Excluded information elements: CIRCUIT POOL, CIRCUIT IDENTITY CODE, AoIP Transport Layer Address (BSS), Speech Codec (Chosen), Codec List (BSS Supported)
ASSIGNMENT FAILURE (MSC-I → MSC-A)
Excluded information elements: CIRCUIT POOL, CIRCUIT POOL LIST
*HANDOVER REQUEST (MSC-A → MSC-T and MSC-I → MSC-A)
Excluded information elements: CIRCUIT IDENTITY CODE, AoIP Transport Layer Address (MGW), Call Identifier, Codec List (MSC Preferred)
*HANDOVER REQUEST ACKNOWLEDGE (MSC-T → MSC-A and MSC-A → MSC-I)
Excluded information elements: CIRCUIT POOL, CIRCUIT IDENTITY CODE, AoIP Transport Layer Address (BSS), Speech Codec (Chosen), Codec List (BSS Supported)
*HANDOVER COMPLETE (MSC-T → MSC-A)
*HANDOVER FAILURE (MSC-T → MSC-A, MSC-A → MSC-I and MSC-I → MSC-A)
Excluded information elements: CIRCUIT POOL, CIRCUIT POOL LIST, Codec List (BSS Supported)
HANDOVER PERFORMED (MSC-I → MSC-A)
Excluded information elements: Speech Codec (Chosen), Codec List (BSS Supported)
*HANDOVER DETECT (MSC-T → MSC-A)
CLEAR REQUEST (MSC-I → MSC-A and MSC-T → MSC-A)
SAPI "n" REJECT (MSC-I → MSC-A)
CONFUSION (MSC-T → MSC-A, MSC-A → MSC-T,
MSC-I → MSC-A and MSC-A → MSC-I)
#MSC-INVOKE TRACE (MSC-A → MSC-I and MSC-A → MSC-T)
#BSS INVOKE TRACE (MSC-I → MSC-A and MSC-A → MSC-T)
CIPHER MODE COMMAND (MSC-A → MSC-I)
CIPHER MODE COMPLETE (MSC-I → MSC-A)
CIPHER MODE REJECT (MSC-I → MSC-A)
**QUEUING INDICATION (MSC-T → MSC-A, MSC-I → MSC-A, and MSC-A → MSC-I)
CLASSMARK UPDATE (MSC-I → MSC-A and MSC-A → MSC-T)
CLASSMARK REQUEST (MSC-A → MSC-I)
CONNECTION ORIENTED INFORMATION (MSC-I → MSC-A, MSC-A→MSC-I)
LSA INFORMATION (MSC-A → MSC-I)
PERFORM LOCATION REQUEST (MSC-I→MSC-A, MSC-A → MSC-I)
PERFORM LOCATION ABORT (MSC-I→MSC-A, MSC-A → MSC-I)
PERFORM LOCATION RESPONSE (MSC-I → MSC-A, MSC-A→MSC-I)
COMMON ID (MSC-A → MSC-I)
CHANNEL MODIFY REQUEST (MSC-I → MSC-A)
All other BSSMAP messages shall be considered as non existent on the E-interface.
Some of the messages above are qualified by *, ** or #. This signifies whether the message, when sent on the E-interface, is considered as:
  • handover related message (*);
  • handover related when sent as a response to HANDOVER REQUEST (**); or
  • trace related message (#).
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7  Exceptions for BSSMAP message contents and information element coding when transferred on the E interfaceWord‑p. 12

7.1  Message contents

For the applicable BSSMAP messages transferred on the E-interface the following exceptions to the descriptions in TS 48.008, subclause 3.2.1 are valid:
Assignment request message:
  • excluded information elements:
    • circuit identity code;
    • AoIP Transport Layer Address (MGW);
    • Call Identifier;
    • Codec List (MSC Preferred).
  • if received, the information element shall be treated as an information element with an unrecognisable identifier.
Assignment complete message:
  • excluded information element:
    • circuit pool;
    • circuit identity code;
    • AoIP Transport Layer Address (BSS);
    • Speech Codec (Chosen);
    • Codec List (BSS Supported).
  • if received, the information element shall be treated as an information element with an unrecognisable identifier.
Assignment failure message:
  • excluded information elements:
    • circuit pool;
    • circuit pool list;
    • Codec List (BSS Supported).
  • if received, the information element shall be treated as an information element with an unrecognisable identifier.
Handover request message:
  • excluded information element:
    • circuit identity code;
    • AoIP Transport Layer Address (MGW);
    • Call Identifier;
    • Codec List (MSC Preferred).
  • if received, the information element shall be treated as an information element with an unrecognisable identifier.
Handover request acknowledge message:
  • excluded information element:
    • circuit pool;
    • circuit identity code;
    • AoIP Transport Layer Address (BSS);
    • Speech Codec (Chosen);
    • Codec List (BSS Supported).
  • if received, the information element shall be treated as an information element with an unrecognisable identifier.
Handover failure message:
  • excluded information elements:
    • circuit pool;
    • circuit pool list;
    • Codec List (BSS Supported).
  • if received, the information element shall be treated as an information element with an unrecognisable identifier.
Handover performed message:
  • excluded information elements:
    • Speech Codec (Chosen);
    • Codec List (BSS Supported).
  • if received, the information element shall be treated as an information element with an unrecognisable identifier.
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7.2  Information element codingWord‑p. 14

For the applicable BSSMAP information elements transferred on the E-interface the following exceptions to the description in TS 48.008, subclause 3.2.2.5 are valid:
Cause information element:
  • excluded causes:
    • call control;
    • CCCH overload;
    • handover successful;
    • requested terrestrial resource unavailable;
    • terrestrial circuit already allocated;
    • circuit pool mismatch;
    • switch circuit pool;
    • Call Identifier already allocated.
    The corresponding cause values shall be considered as reserved for national use.
Cell identifier information element:
  • excluded format:
    • Cell Identity.
    The corresponding cell identification discriminator value shall be considered as reserved.
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8  BSSAP message error handling when transferred on the E interface

The handling of abnormal events related to the BSSAP header (TS 48.008, subclause 2.4) and the BSSMAP error handling (TS 48.008, subclause 3.1.19) are applicable with exception of the following:
  • the handling of faults concerning the use of SCCP is not applicable.
The BSSMAP error messages sent on the E-interface shall only be sent as response to BSSAP messages received on the same interface.
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$  Change HistoryWord‑p. 15


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