RAB and RRC establishment failures reasons after Admission Control

Timeout in the UE, RNC or RBS.

Invalid parameter settings.

TN failure reasons.

If the connection is suddenly lost with a RAB you will get a system RAB release

If it disconnects with RRC you may get an abnormal Disconnect message which is failure to setup a call.Know more on counter used to peg when

RRC and RAB fail after Admission Control pmNoFailedAfterAdm

Reasons & Solutions for Call Setup Failure Improvement

Reasons for Call Setup Failure are as given below:

1. Low Signal Strength

2. Interference3. High Congestion on SDCCH

4. High Congestion on TCH

5. Transmission Fault6. Faulty TRU/Hardware7. Central Processor Overload8. Software File Congestion9. Cell is not defined in MSC

Possible Solutions:

• Low signal strength

=> Signal strength analysis.

• Interference

=> Interference analysis.

• High Congestion on SDCCH:

==> Define more SDCCHs.==> Activate adaptive configuration of logical channel feature and immediate assignment to TCH.

• High Congestion on TCH:

==> Add capacity/Tune coverage array.==> Activate assignment to worse cell.

FACCH Call setup

When a MS requests a dedicated resource by sending a random access, the BSC tries to allocate an SDCCH for the MS. If thereare no SDCCHs available at that moment, the BSC tries to allocate a TCH instead of rejecting the resource request.If there are free TCHs, FACCH Call Set-up is used to assign the MS from the CCCH to the TCH - instead of the SDCCH - with

the immediate assignment procedure. The FACCH is used for call set-up signalling instead of the SDCCH. The TCH is used for

signalling

and thus no assignment procedure is needed in the radio interface. Instead, only the mode modify procedure is required to change

the channel mode from signalling to, for example, speech or data.

Note that circuit pool change is not supported with FACCH call setup.

SDCCH Study - Uses,Signalling Analysis,Drop Reasons and Solutions

Introduction:-

The signalling transported on the SDCCH channel is aimed at reaching the service requested by the Mobile Station; in some cases

this represents only the setup of the service, in other cases the service is completely performed on the SDCCH channel.

SDCCH usage:-

• User Requests (Mobile Originated Call, SMS, Supplementary Services)

• Answer To paging (Mobile Terminated Call)

• Call

- Re Establishment

• Location Update Procedure

• IMSI detach indication

Signalling Analysis:-

First of all the channel request message is sent from the MS on RACCH Channel to the BTS and the BTS sends the channelrequired message to the BSC.This is always the first step for accessing the network. This part of signalling is performed for every MS accessing a service,independently on the kind of service required, meaning that it is valid also for all the other services (not call) the MS can ask:SMS, Location Update, IMSI detach, Supplementary Service.This CR message consists of 8 bits 3 bits are reserved for the establishment cause and 5 bits for the random reference. Among the8 possible combinations of establishment cause's 3 bits, 5 are valid as establishment causes.the other 3 combinations are not valid and then refused by the network.Download to read More on Signalling Analysis

Reasons for SDCCH failures:-

Poor RF Condition

Path imbalance or sensitivity difference between MS and BTS

Co-BCCH & BSIC problem

Ghost random RACCH

Bursts of random accesses (HO access)

channel activation not acknowledgement message failure

Recommendations:-

• Modify the SDCCH formula:

- Remove the SDCCH fails due to Timer expiry T3101 from SDCCH abis failure counter

• SDCCH KPI could be improved by optimized use of cell parameters and removing the Co

-BCCH and Co-BSIC problems.

• Lower the Rx Lev min Access in urban area. Make cell boundary less by tilting and improvi

ng coverage area.

• It has been observed that SDCCH failures are in the cells between location area boundaries due to high location updates.It

isrecommended that use cell hysteresis value high for example like 10dbm in the cells at location boundary.

• Al

so increase the periodic location update counter to lower the no of location updates

Call Re-establishment feature in 3G Huawei System

By using call reestablishment feature in the 3G we can reduce the call drop in CS and PS domain. This feature enables us to successful reestablish the call after the abnormal release indication has been sent by the RNC.

Impact of Call Reestablishment on Network:By using call reestablishment feature in the WCDMA we can reduce the call drop in CS and PS domain. This feature enables us to successful reestablish the call after the abnormal release indication has been sent by the RNC.

The re-establishment procedure allows MS to resume a connection in progress after a radio link failure, possibly in a new cell or in a new location area (re-establishment in a new location area initiates no location updating).

The CS call drop analysis is as shown below the basic counter responsible for the call drops are as mentioned :

       VS.RAB.AbnormRel.CS.IuAAL2        VS.RAB.AbnormRel.CS.OLC        VS.RAB.AbnormRel.CS.OM        VS.RAB.AbnormRel.CS.Preempt        VS.RAB.AbnormRel.CS.RF        VS.RAB.AbnormRel.CS.RF.SRBReset        VS.RAB.AbnormRel.CS.RF.ULSync        VS.RAB.AbnormRel.CS.RF.UuNoReply        VS.RAB.AbnormRel.CS.UTRANgen

The call re-establishment details are transmitted in the SIB 4 and SIB 12 after the release indication has been received a counter N313 starts which repeats it self for the times T313 value is assigned.We need to increases these timers in order to provide UE the time for re-latching and making a call re attempt for the RAB new connection.