T200 , N200 and call drop rate

Publication Date:  2011-08-08 Views:  916 Downloads:  18
Issue Description


BSC6900V12 which include BTS 3900 & 3900A & DBS3900 after swapping Siemens BSC RU10




  • T200 :


    1. T200 timers are used to avoid deadlock during data transfer on the data link layer.
       

    2. On the LAPDm layer, every time a message is sent, the opposite end is requested to acknowledge the reception. If this message is lost for unknown reasons, it will occur that both ends keep waiting, leading to system deadlock.
       

    3. Therefore, a timer should be started when the sender sends a message. If the timer times out, the sender will regard that the receiver has not received the message and will resend the message.
       


  • N200


    1. The maximum resend times are determined by N200.
       

    2. Different timer values should be set for different LAPDm channels such as SDCCH, FACCH and SACCH. This is because these channels have different transmission rate.
       


  • Command: SET GCELLCCTMR / LST GCELLCCTMR
     


Use LAPDm N200




  • Range: Yes, No
     

  • Description: Determines whether BSC delivers LAPDm N200 parameters to BTS. If it configured as Yes, then LPADm N200 parameters will be delivered to BTS, otherwise not.
     

  • Command: SET GCELLCCTMR / LST GCELLCCTMR
     


 



 






in this case there is no alarm indicated.



 


Alarm Information
验证
Handling Process


For Huawei the LAPDm N200 is set it to No that’s mean we switch off N200 that mean losing the times and make n200 equal to 0



but after checking the N200 on Siemens side I found that they had a fixed value and match 3GPP standardized as the attached photo



 




a trial test was done on one cluster and set the value as before swap to be:



Parameter ID



Parameter Name



Meaning



Value



N200



N200



System parameter in the LAPD protocol. The value of this parameter specifies the maximum number of times when a frame is retransmitted.



3



N200PARASWITCH



Use LAPDm N200



Whether the RNC sends the LAPDm N200 parameter to the BTS.

If this parameter is set to YES, the BSC sends the LAPDm N200 parameter. If this parameter is set to NO, the RNC does not send the LAPDm N200 parameter.



ON



N200ESTAB



N200 of Establish



Error control is performed on the I frame sent over the LAPDm layer between the BTS and MS. If the MS detects errors in an I frame, the BTS should resend the I frame. This parameter indicates the maximum number of retransmissions of the I frame.

For the function of N200 and the effect of the parameter, see the description of "T200 SDCCH".



5



N200REL



N200 of Release



Error control is performed on the I frame sent over the LAPDm layer between the BTS and MS. If the MS detects errors in an I frame, the BTS should resend the I frame. This parameter indicates the maximum number of retransmissions of the I frame during the multi-frame release.

For the function of N200 and the effect of the parameter, see the description of "T200 SDCCH".



5



N200SACCH



N200 of SACCH



Error control is performed on the I frame sent over the LAPDm layer between the BTS and MS. If the MS detects errors in an I frame, the BTS should resend the I frame. This parameter indicates the maximum number of retransmissions of the I frame on the SACCH.

For the function of N200 and the effect of the parameter, see the description of "T200 SDCCH".



5



N200SDCCH



N200 of SDCCH



Error control is performed on the I frame sent over the LAPDm layer between the BTS and MS. If the MS detects errors in an I frame, the BTS should resend the I frame. This parameter indicates the maximum number of retransmissions of the I frame on the SDCCH.

For the function of N200 and the effect of the parameter, see the description of "T200 SDCCH".



23



N200FHALF



N200 of FACCH/Half Rate



Error control is performed on the I frame sent over the LAPDm layer between the BTS and MS. If the MS detects errors in an I frame, the BTS should resend the I frame. This parameter indicates the maximum number of retransmissions of the I frame on the FACCH (a half-rate channel).

For the function of N200 and the effect of the parameter, see the description of "T200 SDCCH".



29



N200FFULL



N200 of FACCH/Full Rate



Error control is performed on the I frame sent over the LAPDm layer between the BTS and MS. If the MS detects errors in an I frame, the BTS should resend the I frame. This parameter indicates the maximum number of retransmissions of the I frame on the FACCH (a full-rate channel).

For the function of N200 and the effect of the parameter, see the description of "T200 SDCCH".



34



 



 



 



 



After applying these values , the cells on this cluster were monotire for one week and you can find below the statistic for top Ncells before and after



On general view the total number of call drops due to (T200 expired) decrease after activate N200



 



Root Cause

T200 N200 setting.

Solution

Change T200 N200.

Suggestions


Need to follow the old configuration for N200 and set the values for the previous parameters



On all Huawei BSCs


END