Probable Reasons of SDCCH Congestion
Low Availability
Action: Check SDCCH Availability. Check if the channels are manual, control or automatic blocked.
Solution: Change and repair faulty equipment. Review the O&M procedures.
Increasing Traffic Demand
The high traffic could be related to an occasional event or due to a long term growth.
Action: Check if short term traffic growth. Make trend comparisons. Check if combined SDCCH is used. Check SDCCH dimensioning.
Solution: Increase the number of SDCCH channels. Note, that an increase may lead to the need for new transceivers. If combined SDCCH is used, non-combined channel configuration should be introduced.
Bad use of Adaptive configuration of Logical Channels
By using the Adaptive configuration of logical channels feature, the basic SDCCH configuration in a cell will be under-dimensioned. If this feature is not used correctly, it will cause SDCCH congestion.
Action: Check if ACSTATE is on. Check parameters related to Adaptive configuration of logical channels
Solution: If ACSTATE is off, it is suggested to switch on.
Long Mean Holding Time
If the mean holding time is long, this generates a higher traffic load.
Action: Check SDCCH Mean Holding Time
Too Frequent Periodic Registration
Action: Check Random Access Distribution. Check the timer T3212 in the BSC and the parameters
BTDM and GTDM in the MSC
Solution: Decrease the periodic registration.
Location Area Border Cell
If the cell is situated on a misplaced Location Area border, this means that unnecessary many normal LUs are performed.
Action: Check site position and location area border. Check Location Update Performance. Check parameter CRH etc.
Solution: If the site is located close to major road or railway, consider to move the Location Area border. Increase the hysteresis CRH. The CRH is the hysteresis value used when the MS in idle mode crosses a LA border. The default value for this parameter is 4. If a high number of Location Updatings occurs in a Location Area border cell, a higher CRH can be set in order to reduce the number of LUs.
Extensive SMS Usage
Extensive SMS usage increases the SDCCH traffic and could cause congestion if badly dimensioned SDCCH channels.
Action: Check SMS activity.
Solution: Re-dimension the SDCCH channels with consideration taken to SMS usage.
Cell Broadcast Used
Action: Check if Cell Broadcast is active. .If active, check if it is used by the operator.
Solution: Remove Cell Broadcast if not used.
IMSI Attach/Detach in Use.
An introduction of IMSI attach/detach will increase the traffic on SDCCH. However, the benefits are that the paging success rate will increase. The recommendation is to use Attach/Detach.
Cell Software File Congestion
Action: Check SAE setting. High Ratio of Random Accesses
Action: Check Random Access performance
Low Availability
Action: Check SDCCH Availability. Check if the channels are manual, control or automatic blocked.
Solution: Change and repair faulty equipment. Review the O&M procedures.
Increasing Traffic Demand
The high traffic could be related to an occasional event or due to a long term growth.
Action: Check if short term traffic growth. Make trend comparisons. Check if combined SDCCH is used. Check SDCCH dimensioning.
Solution: Increase the number of SDCCH channels. Note, that an increase may lead to the need for new transceivers. If combined SDCCH is used, non-combined channel configuration should be introduced.
Bad use of Adaptive configuration of Logical Channels
By using the Adaptive configuration of logical channels feature, the basic SDCCH configuration in a cell will be under-dimensioned. If this feature is not used correctly, it will cause SDCCH congestion.
Action: Check if ACSTATE is on. Check parameters related to Adaptive configuration of logical channels
Solution: If ACSTATE is off, it is suggested to switch on.
Long Mean Holding Time
If the mean holding time is long, this generates a higher traffic load.
Action: Check SDCCH Mean Holding Time
Too Frequent Periodic Registration
Action: Check Random Access Distribution. Check the timer T3212 in the BSC and the parameters
BTDM and GTDM in the MSC
Solution: Decrease the periodic registration.
Location Area Border Cell
If the cell is situated on a misplaced Location Area border, this means that unnecessary many normal LUs are performed.
Action: Check site position and location area border. Check Location Update Performance. Check parameter CRH etc.
Solution: If the site is located close to major road or railway, consider to move the Location Area border. Increase the hysteresis CRH. The CRH is the hysteresis value used when the MS in idle mode crosses a LA border. The default value for this parameter is 4. If a high number of Location Updatings occurs in a Location Area border cell, a higher CRH can be set in order to reduce the number of LUs.
Extensive SMS Usage
Extensive SMS usage increases the SDCCH traffic and could cause congestion if badly dimensioned SDCCH channels.
Action: Check SMS activity.
Solution: Re-dimension the SDCCH channels with consideration taken to SMS usage.
Cell Broadcast Used
Action: Check if Cell Broadcast is active. .If active, check if it is used by the operator.
Solution: Remove Cell Broadcast if not used.
IMSI Attach/Detach in Use.
An introduction of IMSI attach/detach will increase the traffic on SDCCH. However, the benefits are that the paging success rate will increase. The recommendation is to use Attach/Detach.
Cell Software File Congestion
Action: Check SAE setting. High Ratio of Random Accesses
Action: Check Random Access performance
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