45.1 OverviewThis provides the definition and describes the purposes of BSC local switching.
45.2 AvailabilityThis lists the NEs, software versions, and other support required for the implementation of BSClocal switching.
45.3 ImpactThis describes the impact of BSC local switching on system performance and other features.
45.4 Technical DescriptionThis describes the technical aspects of BSC local switching, consisting of start, recovery, andhandover of BSC local switching calls.
45.5 ImplementationThis describes how to configure and verify BSC local switching.
45.6 Maintenance InformationThis lists the alarms and performance counters related to BSC local switching.
45.7 ReferencesNone.
HUAWEI BSC6000 Base Station SubsystemBSS Feature Description 45 BSC Local Switching
45.1 OverviewThis provides the definition and describes the purposes of BSC local switching.
DefinitionBSC local switching refers to a process in which speech signals on the Abis interface loop backto the MS without passing through the NSS when the calling party and called party are servedby the same BSC, as shown in Figure 45-1. BSC local switching saves transmission resourcesof section C.
Figure 45-1 BSC local switching diagram
A B C D E
E
BTS
BTS
BTS
BSC
MGW
MGW
MSC
Speech signal flow of the BSClocal switching among differentBTSs controlled by one BSCService link
Signaling link
NOTE
BSC local switching is performed on the BSC side without involving the NSS. Speech signals do not passthrough the MSC. The transmission resources of section D and section E on the MSC side, however, arenot released.
PurposesBSC local switching saves transmission resources of the Ater interface.
45 BSC Local SwitchingHUAWEI BSC6000 Base Station Subsystem
Loopback Refers to local switching in this document.
BTS local switching When the calling party and called party are served by thesame BTS or BTS group, speech signals on the Abisinterface loop back to the MS in a BTS or BTS groupwithout passing through the BSC and MSC.
Loopback recovery Calls in the local switching state are recovered to theordinary conversation state.
Ater A transmission channel between the GMPS or GEPS andthe GTCS.
Speech version In the GSM communication system, the versions of thespeech coding/decoding algorithm are categorized intofull-rate speech versions 1, 2, and 3 and half-rate speechversions 1, 2, and 3.
Call completion supplementaryservice
This supplementary service enables a user to handle anongoing call. This supplementary service is categorizedinto two types: call hold and call waiting.
MPTY supplementary service This supplementary service enables a user to have a multi-connection call, that is, a simultaneous communicationwith more than one party. This supplementary service iscategorized into two types: three-party service andconference call.
Abbreviations
Abbreviation Full Spelling
ACS Active Coding Set
TFO Tandem Free Operation
AMR Adaptive Multi Rate
CIC Circuit Identity Code
GMPS GSM Main Processing Subrack
GEPS GSM Extended Processing Subrack
GTCS GSM TransCoder Subrack
HUAWEI BSC6000 Base Station SubsystemBSS Feature Description 45 BSC Local Switching
45.2 AvailabilityThis lists the NEs, software versions, and other support required for the implementation of BSClocal switching.
Network Elements Involved
Table 45-1 lists the NEs involved in BSC local switching.
Table 45-1 NEs involved in BSC local switching
MS BTS BSC MSC MGW SGSN GGSN HLR
– √ √ – – – – –
NOTE
l –: not involved
l √: involved
Software Versions
Table 45-2 describes the software versions of GBSS products that support BSC local switching.
Table 45-2 GBSS products and software versions
Product Version
BSC BSC6000 V900R003C01 and later releases
BTS BTS3012 V100R001C07 and later releases
BTS3012AE V100R001C07 and later releases
BTS3006C V100R001C07 and later releases
BTS3002E V100R001C07 and later releases
Miscellaneous
The other requirements for BSC local switching are as follows:
l A license is required for the use of BSC local switching.
l For a group of combined BTSs, if BTS versions support BSC local switching, but carrierversions of BTSs do not support this feature, BSC local switching cannot be enabled.
l Charging for local switching is controlled by the NSS.
45 BSC Local SwitchingHUAWEI BSC6000 Base Station Subsystem
45.3 ImpactThis describes the impact of BSC local switching on system performance and other features.
Impact on System Performance
The impact of BSC local switching on system performance is as follows:
l After BSC local switching is enabled, the success rate of handover may decrease, and thecall drop rate may increase. For details about the causes, refer to 45.4.3 Handover of BSCLocal Switching Calls.
l When the GTCS is locally configured, BSC local switching should not be enabled becausethe transmission line of the Ater interface is relatively short.
l When BSC local switching is enabled, a forced handover must be initiated. When the BSCrequests channels, it does not support a request to the PCU for TCH changeback and queuingpreemption. Enabling BSC local switching may fail because no radio resources areavailable.
l Enabling BSC local switching may cause discontinuous voice for a short time.
Impact on Other Features
The impact of BSC local switching on other features is as follows:
l After BSC local switching is enabled, call completion supplementary services and MPTYsupplementary services are not supported.
l After BSC local switching is enabled, the announcement and lawful interception servicesof the MSC are not supported.
45.4 Technical DescriptionThis describes the technical aspects of BSC local switching, consisting of start, recovery, andhandover of BSC local switching calls.
45.4.1 Start of BSC Local Switching CallsThis describes the requirements for the start of BSC local switching calls. To initiate a BSC localswitch call, the call must meet the relevant conditions, pass the BSC local switch call check,comply with the relevant initiation policies, and select the correct speech version for the callingand called parties.
45.4.2 Recovery of BSC Local Switching CallsThis describes the recovery of BSC local switching calls. When a handover occurs during a BSClocal switching call, the target cell may not support local switching or the outgoing BSC handoverfails. In this case, the BSC local switching call must be recovered to an ordinary call.
45.4.3 Handover of BSC Local Switching CallsThis describes the handover of BSC local switching calls. The intra-BSC handover and outgoingBSC handover of BSC local switching calls are different from the common handovermechanism.
HUAWEI BSC6000 Base Station SubsystemBSS Feature Description 45 BSC Local Switching
45.4.1 Start of BSC Local Switching CallsThis describes the requirements for the start of BSC local switching calls. To initiate a BSC localswitch call, the call must meet the relevant conditions, pass the BSC local switch call check,comply with the relevant initiation policies, and select the correct speech version for the callingand called parties.
1. After the called party answers or the incoming BSC handover of speech service is complete,the BSC checks the conditions for starting BSC local switching. The conditions for startingBSC local switching are as follows:l Whether the license supports BSC local switching.
l Whether BSS General Strategy supports BSC local switching.
l Whether the conditions in Options for BSC Local Switch are met.
2. If these conditions are met, the BSC starts local switching call detection to detect whetherthe calling and called parties are served by the same BSC.
3. If the calling and called parties are located under the same BSC, proceed with the followingsteps:l If Options for BSC Local Switch is set to Prefix Number, and one party meets the
start conditions, BSC local switching is started.l If Avoid Number for BSC is set, and one party meets the closing conditions, BSC local
switching is not started.
When starting BSC local switching, ensure that the voice coding rates of the calling and calledparties are the same. The same voice coding rate must be used by the calling and called parties.In addition, the rate is fixed. If different voice coding rates are used, the BSC adjusts the differentrates to the same rate through a forcible handover. If the adjustment fails, BSC local switchingis suspended.
During the selection of speech version, the BSC must calculate to acquire the intersection ofspeech versions that both parties support. If there is an intersection of speech version, and thespeech versions used by both parties are in the intersection, select speech version by referringto the policy for selecting speech versions in Table 45-3.
l If only one speech version that is being used belongs to the intersection, select the speechversion as the target speech version.
l If neither the speech version currently used by the calling party nor the speech versioncurrently used by the called party belongs to the intersection, select the speech version ofthe highest version from the intersection. Full rate is preferred when both full rate and halfrate are supported.
NOTE
As the same rate set is used for a call when the call uses Adaptive MultiRate (AMR), AMR is not selectedwhen neither the speech version used by the calling party nor the speech version used by the called partybelongs to the intersection.
45 BSC Local SwitchingHUAWEI BSC6000 Base Station Subsystem
Table 45-3 Policies for selecting a speech version for local switching
AMR Whether theACS IsConsistentand Uses theSame Rate
Full- or Half-Rate Channel
SpeechVersion
AdjustmentPolicy
Both the callingand calledparties useAMR.
Yes Not involved Not involved The conditionsfor local switchare met. There isno need foradjustment.
No Not involved Not involved Both the callingand calledparties need tobe adjusted.
AMR is used byeither the callingparty or calledparty of a call.
Not involved Not involved Not involved Change an MSusing AMR to anon-AMR MS.Ensure that thespecific rate andspeech versionof one party areconsistent withthose of theother party.
Neither thecalling party northe called partyuses AMR.
Not involved Inconsistent Not involved Change a half-rate MS to a full-rate MS. Ensurethat the specificrate and speechversion of oneparty areconsistent withthose of theother party.
Consistent Same The conditionsfor local switchare met. There isno need foradjustment.
Different Change thespeech versionof a high-rateMS to thespeech versionof a low-rateMS.
HUAWEI BSC6000 Base Station SubsystemBSS Feature Description 45 BSC Local Switching
When the speech versions used by both parties are consistent, the BSC sets up speech signallinks, and both parties perform TDM switching in the BSC. After the TDM switching issuccessful, the call enters the BSC local switching state, and the redundant resources on the Aterinterface are released.
NOTE
l The MSC cannot obtain BSC local switching information because speech signals do not pass throughthe MSC. During a BSC local switching call, the MSC does not support announcement, lawfulinterception, or supplementary services.
l To ensure the consistency of circuit resources on the MSC and BSC sides, the BSC does not releasethe CIC circuit.
45.4.2 Recovery of BSC Local Switching CallsThis describes the recovery of BSC local switching calls. When a handover occurs during a BSClocal switching call, the target cell may not support local switching or the outgoing BSC handoverfails. In this case, the BSC local switching call must be recovered to an ordinary call.
The BSC sets up the Ater interface transmission channel between the GMPS or GEPS and theGTCS. The speech signals are sent to the MSC through the BSC and then are switched to theMS.
The recovery of BSC local switching calls is determined by the BSC without manual interventionand configuration parameters.
45.4.3 Handover of BSC Local Switching CallsThis describes the handover of BSC local switching calls. The intra-BSC handover and outgoingBSC handover of BSC local switching calls are different from the common handovermechanism.
Intra-BSC Handover
The difference between the intra-BSC handover of BSC local switching calls and the commonhandover is that the speech version cannot be changed during the handover of BSC localswitching calls. That is, the speech version before the handover must be consistent with thatafter the handover. Therefore, the success rate of handover may decrease, and the call drop ratemay increase.
l After the intra-BSC handover succeeds, the BSC local switching call may be maintainedor switched to a BTS local switching call and then recovered to an ordinary call dependingon the local switching support capability of the target channel.
l If the intra-BSC handover fails, the BSC local switching call is kept in the BSC localswitching state.
Outgoing BSC Handover
The outgoing BSC handover process for BSC local switching calls is as follows:
1. The BSC decides to initiate an outgoing BSC handover through the handover decisionalgorithm and sends a handover request to the MSC.
45 BSC Local SwitchingHUAWEI BSC6000 Base Station Subsystem
2. Upon receipt of the handover request, the MSC sends a handover command to the BSC.l After receiving the handover command from the MSC, the BSC instructs the MS to
recover the call to an ordinary call to ensure that the outgoing BSC handover issuccessful and the voice quality is sound.
l If the BSC does not receive the handover command, the BSC local switching call ismaintained.
l If the MS reports a handover failure message, the BSC local switching call is recoveredto an ordinary call at the party that initiates the handover.
45.5 ImplementationThis describes how to configure and verify BSC local switching.
45.5.1 Configuring BSC Local SwitchingThis describes how to configure BSC local switching on the BSC6000 Local MaintenanceTerminal.
45.5.2 Verifying BSC Local SwitchingThis describes how to verify BSC local switching on the BSC6000 Local MaintenanceTerminal.
45.5.1 Configuring BSC Local SwitchingThis describes how to configure BSC local switching on the BSC6000 Local MaintenanceTerminal.
Procedure
Step 1 Apply for a license and activate it.1. When you apply for a license for BSC local switching, ensure that in the
BSC6000V900R003 (None) Commercial License Application Template, the Number ofresources corresponding to the Number of the TRX supporting BSC local switching inthe Resource control items column is not 0 and input the actual number of TRXs thatsupport BSC local switching.
2. Activate the license on the BSC6000 Local Maintenance Terminal. For details, refer toActivating the BSC License.
Step 2 Configure BSC local switching on the BSC.1. On the Management Tree tab page of the BSC6000 Local Maintenance Terminal, right-
click BSC6000 and choose Configure BSS Local Switching from the shortcut menu. Adialog box is displayed, as shown in Figure 45-2.
HUAWEI BSC6000 Base Station SubsystemBSS Feature Description 45 BSC Local Switching
5. Click the BSC Local Switching Prefix Close tab, as shown in Figure 45-4.l If BSC Close Based on Number in Figure 45-2 is set to Yes, set Avoid Number for
BSC and Number. Go to Step 2.6.l If BSC Close Based on Number in Figure 45-2 is set to No, go to Step 2.6.
HUAWEI BSC6000 Base Station SubsystemBSS Feature Description 45 BSC Local Switching
6. Click Finish to complete the configuration of BSC local switching.
----End
45.5.2 Verifying BSC Local SwitchingThis describes how to verify BSC local switching on the BSC6000 Local MaintenanceTerminal.
Procedure
Step 1 On the BSC6000 Local Maintenance Terminal, choose BSC Maintenance > Maintain UserResource > Query Call Resources . A dialog box is displayed, as shown in Figure 45-5.
45 BSC Local SwitchingHUAWEI BSC6000 Base Station Subsystem
