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GR/EIL/E K. Sivarajah
2004-02-04
Reference
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ANALYSIS OF SDCCH DROP
1
Purpose This Document gives a brief about the SDCCH, flow of various signals for SDCCH establishment, SDCCH drop and how to do traces for the SDCCH Drop.This document is valid for R9.1.
2
RNSDCCH
Signal flow for SDCCH establishment
RNLCT
RMSCS
RMHBI
RCLCCH
RNCHREQUIRED
BTS Channel request on RACH
RMCHANNELREQ RNALLOCCH CCALLS RNGETNOSDCCH RNGRTNOSDCCHACK (1) CCONG RNALLOCCHR RMCHACTIVATE ABIS MSG RMCHACTIVATER
RMESTINDIC CMESTAB (2)
Note: 1) CCONG will be increased if there is no deblocked channel individual is available.
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2) CNDROP will only be increased after establishment of SDCCH i.e. after increment of the counter CMESTAB. 2.1
CNRELCONG If CCONG is network perceived congestion then CNRELCONG would be the subscriber perceived congestion. The Released Connections on SDCCH due to Radio Resource Congestion counter is incremented when a connection on SDCCH is released due to radio resource congestion, that is when there is congestion on TCH or congestion on transcoder resources. The counters are stepped when a CLEAR COMMAND message with cause 'No radio resource available' (Cause value 33) is received. The counter (CNDROP) is also stepped at the same time. The counters are not incremented if CLEAR REQUEST has been sent by BSC previously Actually CCONG will be increased due to SDCCH congestion in a cell but in case of CNRELCONG it is due to TCH congestion and call will get drop on SDCCH.The counter value of CNRELCONG increased when block RMCNT received signal RMRELCNT (with counter indicator 3)from block RMHBI RMRELCNT RMHBI ------------------------------------------------------------>> RMCNT
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Analysis of SDCCH drop Call setup, Paging, location Updating,authentication,ciphering, SMS and IMEI check are the main functions of SDCCH. So it is equally required to check MSC part also while analyzing the SDCCH drop. There could be the following reasons for SDCCH drop
Signal strength Quality Timing Advance (TA) Other reasons Our experience from field says that if SDCCH drop is due Signal strength or Quality or TA, then it is not very difficult to find out the valid cause but the “Other Reasons” is the area which is really difficult to point out as there could be various possibilities of the same. There is list of some possibilities that has to be taken care while analysing the SDCCH drop:
3.1
Hardware Fault at BTS For BTS, HW fault should be the prime and preliminary point to be concentrated. This can be seen by collecting The OMT Logs of CF,TRX, ECU etc.This type of fault could also be intermittent in nature.
Ericssonwide Internal INTERNAL Prepared (also subject responsible if other)
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3.2
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Definition of Parameter Wrong definition or parameter in the BSC could lead to this type of fault. Few important ones are as follows
The MS power control and BTS power control : As the MS and BTS powers are regulated in order to decrease battery consumption of the MS and not to saturate the multicoupler of the BTS as well as decreasing the interference in the system. So the fine tuning of the control parameters are very important in accordance with R&D recommendation.
Activation of Adaptive configuration : This could also be the reason for the SDCCH drop. So proper R&N consultation is needed before activating the same, if required . It is advisable to use of this only in those cells which are really needing the same not the entire BSC area.
3.3
DIP Status DIP with poor quality may lead to drop call problem in different cells. Poor quality may implicate High BER or Frame Loss in the DIP connected to a site. DIP Quality Supervision tools should be initiated for the suspected connecting Digital Path. Mismatch of DIP could be another reason behind drop call occurrence in some of the cell.
3.4
Frequency Interference Problem Interference is generally related with Quality Drop, but sometimes it may provoke Sudden Drop as per situation.
3.5
C7 link
The C7 link between BSC to MSC should be properly dimensioned and check the command C7ERP for SCCP information.
4
Stability of C7 link
USEFUL TRACES FOR TROUBLESHOOTING There is a signal RMCONRELINIT2 which can be very useful for finding out the reasons for call release. RMCONRELINIT2 RMCC ------------------------------------------------------------>> RMCR
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To find the cause of SDCCH Drops, we use the trace on RMCONRELINIT2
BMCH1BE91001/018/040000 AT-20 TIME 040102 1107 PAGE
1
PROGRAM TRACING (1) ON OUTSIG RMCC BUFSIG SSP=H'0E8 RMCONRELINIT2 ON THL TO RMCR WITH DR2 DR4 H'00 0BC1 H'0000, H'0011, H'0003, H'0020, H'0009, H'0001, H'843B, H'1618, H'0900, H'1D80, H'0A11, H'A572, H'0000, H'0000, H'1618, H'0010, H'00E9, H'000D, H'0000, H'0000, H'0000, H'FFF0, H'FFFF, H'0000 DR6 END
DR16
< WO
BMCH1BE91001/018/040000 AT-20 TIME 040102 1224 PAGE
1
PROGRAM TRACING (1) ON OUTSIG RMCC BUFSIG SSP=H'0E8 RMCONRELINIT2 ON THL TO RMCR WITH H'00 0564 H'0000, H'0002, H'0004, H'0020, H'XXXX, H'0001, H'843B, H'1618, H'0900, H'1D80, H'0A11, H'F171, H'0000, H'0000, H'1618, H'0010, H'00E9, H'0020, H'0000, H'0000, H'0000, H'FFF0, H'FFFF, H'0000 END It important to see the value of DR2 and DR4 which shows the release cause. From above trace the important observations are as follows
Ericssonwide Internal INTERNAL Prepared (also subject responsible if other)
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1. In first case value of DR2=H’0003 and DR4=H’0009 then this is normal SDCCH release. 2. In second case DR2=4 , that is the indication of fault and further investigation is required . There could mainly be following two possibilities when DR2=4 :
DR2=4, DR3=8, DR4=1 (usually) and it indicates “T200 expired (N200+1) times, abnormal release”. Generally in this case problematic part is BTS.
DR2=4,DR3 is other than H’ 0008 then the value of DR4 is not valid and in this case problematic area could be anyone described in section 3 i.e. “Analysis of SDCCH drop”.
