Late Assignment in MSC2D

nh gi nh hng ca fearture Late Assignment-SR12 ca MSC Siemens ti CSSR ca h thng v tuyn

Hin tng Siemens thc hin nng cp SW cho MSC2D_CTO t SR10 ln SR12 ngy 27/01/2007.

4 BSC kt ni vo MSC2D: BSC_207S_CTO; BSC_228M_CTO; BSC_230M_CTO v BSC_232M_AGG.

CSSR ca 3 BSC Motorola gim khong 6% mc BSC (tt c cc cell cng gim tng t); lu lng v tuyn gim 3k Erlang/1 ngy.

CSSR ca BSC Siemens khng gim; lu lng v tuyn gim 2k Erlang/ngy.

CSSR v Traffic trc/sau nng cpCSSR: Thi im 9h->10h ( so snh 2 ngy 25/01 v 31/01)Traffic: Thi im 9h->10h ( so snh 2 ngy 25/01 v 31/01)

3GPPOACSU may be implemented in PLMNs in order to increase the call handling capacity of the PLMN.OACSU may be implemented in PLMNs on an optional basis subject to the following conditions:i) OACSU should not be used for calls to an international number;

ii) OACSU should not be used for incoming international calls, except where bilateral agreement has been reached to allow such an application of OACSU. For the avoidance of doubt, OACSU shall not be applied to calls where the call type or originating network is not known by the PLMN

iii) foreign MSs not supporting the OACSU procedure should be allowed to access the PLMNs where OACSU is used;

iv) MSs supporting OACSU should be capable of operating in PLMNs where OACSU is not implemented;v) OACSU should only be used for telephone calls.OACSU: Off-Air Call Setup = Late Assignment

The benefits of OACSU are that you increase the call handling capacity of the PLMN by delaying the allocation of the traffic channels until you are sure that the B party has answered the call . This feature will reduce the congestion on the A-interface because a CIC will not be allocated to the A-party until the switch make sure the B-party is available. If OACSU works properly, with correct billing, and minimal side effects, then it would be a beneficial feature for most operators to use. Just imagine the number of failed call attempts, Why use 10s of TCH capacity waiting for a call to be answered if you can stay on the SDCCH instead. If we had never allocated the traffic channels YET, as in OACSU, we could have saved a lot of extra signalling and resources. As you observed, it will increase SDCCH usage, but the bright side is that it will decrease TCH usage. Thus when enabling this feature, it would be worth converting a single TCH to an additional 8 SDs. Of course you want to be confident of minimal TCH blocking else when the Called party answers, there might not be a free TCH to use which would be very annoying to both parties.

Siemens once estimated that they saved 10% of TCH capacity using OACSU. When this feature was enabled, the following has been observed and traced: 4 seconds delay in setup SDCCH congestion (because the BSC has to wait for the assignment command from the MSC and thus the MS is waiting)Call success rate dropped by 20% C7 messages ordering has changed which is obvious

3GPP TS 04.08 7.3.2.Mobile originating call establishment a) Non-OACSU option (early assignment)b) OACSU option (late assignment)c) Very early assignment

without OACSU (Early Assignment):- MS nhn c bn tin Alerting sau khi gi bn tin Assignment complete n NetworkMobile Station Network +- -+ CHANNEL REQUEST RR connection -------------------------> establishment IMMEDIATE ASSIGNMENT (MO) Service request +- -++- -+ AUTHENTICATION REQUEST Authentication +- -++- -+ CIPHER MODE COMMAND +- -++- -+ SETUP --------------------------> Call initiation CALL PROCEEDING

Mobile Station Network+- -+ CHANNEL REQUEST RR connection -------------------------> establishment IMMEDIATE ASSIGNMENT (MO) +- -++- -+ AUTHENTICATION REQUEST Authentication +- -++- -+ CIPHER MODE COMMAND +- -++- -+ SETUP --------------------------> Call initiation CALL PROCEEDING

Siemens SpecificationOACSU l mt feature c lp vi Late Assigment, tuy nhin v hot ng th n gn ging vi Late Assigment ch c mt s bn tin internal l khc nhau, cn cc giao tip bn ngoi ti BSC th ging nhau. V Late Assigment l mcnh trong SR12, trong khi OACSU c thkch hot trong cc version trc (v d SR10).

Siemens SpecificationWhat are the advantages of Late Assignment?

The allocation time for TCH resources (which are expensive) will be reduced and the allocation time for SDCCH resources (cheaper than TCH resources) will be longer.the feature 2G3G directed retry intersystem-handover can only be supported with Late AssignmentFaults on B-side will not lead to unnecessary TCH allocation on A-side.

Siemens SpecificationWhat are the impacts of Late Assignment on MS call processing and traffic analysis?

The call setup time (between CM_SERV_REQ and ALERT) remains unchangedAdditional time between CM_SERV_REQ and ASS_REQ is compensated by reduced time between ASSIGNMENT_COMPLETE and ALERT.The aborts from CM_Serv_REQ until ASS_COM shows now also how good the networks are and make them easily visible. Aborts from B-side (e.g. less trunks to other MSCs) can be better detected and configured accordingly.The assignment procedure is executed in a later call state and failures are now counted in a later phase. Therefore, there are counters which have previously been counted on the incoming side but are now counted on the outgoing side.

Voi SR10:BSC (A) MSC BSC (B)CM_SERV_REQUEST----------------------->.....DT1(SETUP)-------------------------------------->.......

............ DT1(SETUP)- ------------------------------------------> DT1(TMSI_REALLOC_CMD)------------------->

BSC (A) MSC BSC (B)CM_SERV_REQUEST----------------------->.....DT1(SETUP)-------------------------------------->....... DT1(SETUP)- ------------------------------------------> DT1(TMSI_REALLOC_CMD)------------------->

CSSR Formula in BSS side

CSSR_Siemens = (1-Number of lost radio links while using an SDCCH/ Number of successful SDCCH seizures in a period)* ( 1 - Total Number of TCH Assignment Failures/Total Number of TCH Assignment Attempts)*100 CSSR=(1-SDCCH Drop Rate)*(1- Assignment Fail Rate).CSSR_Motorola_new=(1-(RF_LOSSES_SD/ (ALLOS_SDCCH - CHAN_REQ_MS_FAIL_ROLL))) * (MA_COMPLETE_TO_MSC/MA_REQ_FROM_MSC) *100.

CSSR_Motorola

Phn tch kt qu t s liu thng kCSSRTraffic_carriedSDCCH_mean_holding_timeTCH_mean_holding_timeRaw_counter

Phn tch kt qu o bng my Nettest MPA 7400QLM + OMC-S s dng my MPA 7400 o bo hiu trn A-interface i vi 2 BSC Motorola v 1 BSC Huawei.BSC_230M_CTO kt ni vo MSC_2D_Siemens (SR12)BSC_236H_CTO kt ni vo MSC_2D_Siemens (SR12)BSC_205M_KGG kt ni vo MSC_2B_Siemens (SR10)Thi gian o: 9h->11h ngy 19/04/2007 10h->12h ngy 20/04/2007.

S liu t kt qu oCMS_Distribution (Connection management service)BSS Cause

Call_Interrupted_cause: User busy; User alerting, no answer.;Unassigned (unallocated) number; No user responding; Call rejected ....Call_fail_system_cause: Network failure ; Temporary failure ; No radio resource available; No circuit/channel available; Resource unavailable, unspecified ...v.vCall_fail_radio_cause: Radio interface message failure; Radio interface failure ; Call control; Radio interface failure, reversion to old channel ....

Call Flow t kt qu oBSC_205M_KGG ( No Late Assignment, no OACSU)A-number- Gi bn tin CM_Service_request t 11:18:39.058- Gi bn tin Setup lc: 11:18:39.999- Nhn bn tin ASGREQ lc: 11:18:40.152 Gi li bn tin ASGCPL lc:11:18:40.877 ( gn xong TCH/CIC cho A). Nhn c bn tin Alerting lc: 11:18:46.872B-number- Gi bn tin PAGRES lc: 11:18:43.739 Nhn bn tin Setup lc: 11:18:44.504- Nhn bn tin ASGREQ lc: 11:18:45.878 Gi li bn tin ASGCPL lc:11:18:46.496 ( gn xong TCH/CIC cho B). Gi bn tin Alerting lc: 11:18:46.603Sau khi gn xong TCH/CIC cho A-side th mi paging/authen/assign TCH cho B-side. Sau khi nhn c bn tin Alerting t B-side th mi gi alerting cho A. ASR_MOC_A-side khng lin quan n B-side.

BSC_230M_CTO (SR12 Late Assignment without OACSU)A-number- gi bn tin CM_Service_request t 09:52:23.231- Gi bn tin Setup lc: 09:52:24.494 (sau ch B, vn SDCCH)- Nhn bn tin ASGREQ lc: 09:52:28.204 Gi li bn tin ASGCPL lc:09:52:28.706 ( gn xong TCH/CIC cho A). Nhn c bn tin Alerting lc: 09:52:29.871-> Thi gian chim knh SDCCH tng thm khong 4s/1 cuc tng ng vi thi gian chim TCH gim 4s.B-number- Gi bn tin PAGRES lc: 09:52:26.419Nhn bn tin Setup lc: 09:52:26.967- Nhn bn tin ASGREQ lc: 09:52:28.821Gi li bn tin ASGCPL lc:09:52:29.617 ( gn xong TCH/CIC cho B). Gi bn tin Alerting lc: 09:52:29.712

nh gi nh hng ca Late assignment ti gi tr CSSR v TrafficCng thc CSSR ca Motorola hin ti ph thuc ch yu vo 2 tham s: CM_SER_REQ v Total_calls (= Ass_complete). SR10, qu trnh asignment cho A-side (MOC) khng ph thuc vo B-side. Sau khi gn knh thnh cng cho A-side mi thc hin IN_dialog/digit processing/paging/authen/assignment cho B-side. SR12, qu trnh assignment cho A-side ph thuc vo B-side, n ch xy ra khi paging/authen B thnh cng. Nu khng thnh cng th s khng c AssCPL cho A-side trong khi vn c tnh l 1 ln CM_SER_REQ.-> CSSR_Motorola_SR12 < CSSR_Motorola_SR10.Tuy nhin, kt qu o A-interface cho thy t l Assignment_Success_rate 2 BSC_205M v BSC_230M l tng i nh nhau (0.93 v 0.94) -> t pha MS s khng c s khc bit no trong vic thc hin cuc gi.

-Cng thc CSSR ca Siemens/Alcatel/Ericsson/Huawei BSS ang s dng ph thuc ch yu 2 tham s: ASS_REQ v ASS_CPL ( A-side).- Cng thc ny ch phn nh cht lng v tuyn A-side m khng quan tm n cc vn thuc v MSC or BSC khc (ca B-side).Gi tr CSSR ca cc h thng ny khng ph thuc vo thay i ca MSC/Core.S liu thc t chng minh CSSR ca BSC_207S_CTO khng thay i sau khi MSC2D nng cp ln SR12.Vn gim Traffic ca h thng BSS sau khi nng cp SR12Nh kt qu o thc nghim cho thy, thi gian chim TCH ca 1 cuc gi (MOC) SR12 gim trung bnh khong 4s.TCH_mean_holding_time ca h thng BSS hin ti khong 40s.- T l MOC/Total_Call khong t 55->62%. (tnh da trn kt qu o)Do , sau khi nng cp ln SR12, lu lng s b gim khong 5.5%->6.2%..Note: Traffic trn SDCCH cng s tng ln tng ng.

Khuyn nghS dng cng 1 cng thc tnh KPI cho 5 h thng v tuyn ( Metrica cng so snh cc h thng v tuyn khc nhau da trn 1 cng thc chung).Xem xt s dng tnh nng Dynamic SDCCH ti u ha vic s dng SDCCH v TCH (do khi nng cp SR12 s lm tng ti SDCCH).D bo trc vic gim lu lng ca cc h thng kt ni vo MSC Siemens sau khi nng cp SR12 ( ty thuc vo % MOC).Kch hot OACSU MSC Siemens.

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Late Assignment in MSC2D