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Causes
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BSC
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Cell-Level
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Troubleshooting Burst Traffic
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None.
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A3030A: Call Setup Indications (MOC Non SMS) (SDCCH)
A3030B: Call Setup Indications (MOC SMS) (SDCCH)
A3030C: Call Setup Indications (MTC) (SDCCH)
A3030D: Call Setup Indications (Emergency Call) (SDCCH)
A3030E: Call Setup Indications (Call Re-establishment) (SDCCH)
A3030F: Call Setup Indications (Location Updating) (SDCCH)
A3030G: Call Setup Indications (IMSI Detach) (SDCCH)
A3030H: Call Setup Indications (PS Service) (SDCCH)
A3030I: Call Setup Indications (SS) (SDCCH)
A3030J: Call Setup Indications (LCS) (SDCCH)
A3030K: Call Setup Indications (Others) (SDCCH)
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3.2.3Checking Data Configuration
The SDCCH congestion relates to the parameter settings of the BSC. If the parameters are set correctly, the SDCCH congestion can be relieved.
1. LAC planning: The LAC setting is very important to the network performance. If the LAC is too great, the signaling flow increases during the paging in the BTSs within the LA, and thus the network load increases. If the LAC is too small, the number of MS location updating increases, and thus the signaling flow of the system increases, which may lead to the SDCCH congestion. Therefore, proper planning of LA can reduce the SDCCH congestion. SDCCH Congesiton Caused by Improper Configuration of LAC
2. SDCCH dynamic allocation: Enabling the SDCCH dynamic allocation function reduces the SDCCH congestion, but also decreases the utilization of the TCH resources. To prevent this problem, set the relevant counters according to the actual situations.
3. Set relevant timers such as T3101 and T3212 properly.
Setting the T3101 to a small value can effectively reduce the congestion caused by double SDCCH allocation. If the T3101 is set to an over-great value, the signaling resources are occupied for a long period, which leads to a waste of resources. To optimize the utilization of the signaling resources, set T3101 to a small value, especially when enabling the queuing function.
Setting T3212 to a great value can decrease the SDCCH load caused by periodical location updating. If the T3212 is too great, the MS possibly sends no request for location updating. In this case, the MS is identified as implicit off-line, and the system displays "The subscriber you dial is power off" even though the called MS is on.
The setting of RACH Min.Access Level may cause SDCCH congestion. If this parameter is set too small, the interference signal access increases and excessive SDCCH requests are initiated, thus leading to the SDCCH congestion. If the parameter is set too great, call failures may occur though there are signals. Therefore, set the parameter according to the actual BTS sensitivity, the lowest MS access level and the interference.
5. In the assignment procedure, if the late assignment is enabled, the calling MS always occupies the SDCCH during the period of waiting for the called party to pick up the phone. Therefore, the time of the SDCCH occupation increases and other MSs may fail to request the SDCCH, thus leading to the SDCCH congestion.
6. The setting of RXLEV_ACCESS_MIN also causes the SDCCH congestion. If the RXLEV_ACCESS_MIN is set too small, the number of MSs that access the network increases. When the MS requests MOC or location updating, the SDCCH congestion may occur.
7. The setting of MS MAX Retrans also causes the SDCCH congestion. To increase the paging success rate, MS MAX Retrans is increased. The BSC may assign multiple SDCCHs to a single MS. Thus, the SDCCH congestion rate increases.
8. Improper setting of power also causes the SDCCH congestion. If the power of the main BCCH is set normal but the power of the TCH on the non-main BCCH TRX is set too small, a power difference band forms. When an MS requests the SDCCH successfully in the power difference band, the TCH cannot be occupied and the time of the SDCCH occupation increases, thus leading to congestion. For details, see section 5.1 "Congestion Caused by Improper Configuration of Power"
3.2.4Checking the Um Interface
Interference on the Um interface also causes congestion. In the network with small space between BTSs and tight BCCH frequency reuses, the system may receive many random interference signals and assign each random access signal a SDCCH. Thus, the congestion occurs. If the immediate assignment success rate and the paging success rate decrease, the RACH during the performance measurement may be overloaded. The traffic measurement counters related to the interference include the number of idle TCHs in interference bands 4 and 5, the rate of bad quality handovers and the TCH seizure failures in the measurement of the call drop performance. The interference of GSM is classified into inter-network interference and intra-network interference. The methods of eliminating the interference are as follows:
a. Inter-network Interference
For inter-network interference, query the number of idle TCHs in interference bands 4 and 5 to determine whether the uplink interference exists. To eliminate the interference, use a spectrum analyzer and check the network parameters to locate the interference source. Then, adjust or close the interference source.
b. Intra-network Interference
If the frequency planning and antenna tilt planning are improper, the network cannot achieve high Carrier-to-Interference Ratios (CIRs), which causes intra-frequency or inter-frequency interferences or the SDCCH congestion.
The UL frequency and DL frequency are paired, so we can query the interference band to find out the cells with high mean number of SDCCHs in interference band four and five. Then check the frequency planning of the network. Find out the faulty cell, and modify the frequency planning to eliminate the interference. For intra-network interference, perform drive tests. Check the actual distribution of signals to determine whether the interference exists. Then, modify the antenna planning or frequency planning.
For detailed methods of checking interference, refer to the G-Guide to Eliminate Interference.
The following tables lists some KPIs related to the BSC6000 interference.
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