What is Optimum Value of T200?
we like to know the optimum value for T200 on LAPDm. All vendors have different default values (Siemens 145 ms, Nokia 220 ms, Satellite Abis 400 ms etc.) for this timer - but which value is the best to reduce SDCCH drops and to keep the retransmissions at an acceptable level ?
Example: SDCCH/8
During a 51er multiframe the SDCCH/8 occupies four consecutive TDMA frames (four bursts are sent). Than the MS / BTS has to wait for the next 51er multiframe (i.e. 235 ms) before the next Layer 2 frame could be sent. 145 ms / 220 ms are shorter than the 51er multiframe (235 ms) so in case of an missing acknowledgement this is always a T200 expiry. The SDCCH drop will occur if T200 expired N200+1 times. If the T200 is increased (for example to 500 ms) we have two 51er multiframe to get the acknowledgement and the SDCCH drops are reduced.
The Qos Stats show a clear & strong corelation between the KPI and the parameter T200. That's amazing !
Regarding the Ack from the BTS, I'm not sure (and I'm tired to look in the 3GPP specs :) ). Take the subchannel "0" from the SDCCH ts.
in DL : the BTS sends SDCCH/0 on burst 0, 1, 2, 3 and the SACCH/0 on burst 32, 33, 34, 35
in UL : th MS sends SDCCH/0 on burst 15, 16, 17, 18
and the SACCH/0 on 47, 48, 49, 50
And I ***believe*** that the Lapdm acknowledgments can be sent on either the SACCH or the SDCCH, since both of them are sent over the same LapDm link. I'm not sure at all about this though, but it sounds logical.
The value of the SDCCH Drop due to Radio failures (in ALU) is usually around 1% in a fairly good network. The SDCCH Drop due to Radio Failures is a counter that encompasses both the Radio Link Timeout and the "T200*N200+1 times" failures.
I am not able to test your changes because I am not working on a live network (i am a gsm trainer, living in a world of theory...)
T200 = 220ms for sDCCH SAPI0
= 450ms for SDCCH SAPI3
= 900ms for SACCH associated to SDCCH
Thursday, May 13, 2010
What is difference between congestion and Blocking?
Congestion = time when all resources are occupied (no free TCH available)
Blocking = rejected (blocked) attempts over all attempts in %.
Also there is different formulas for TCH blocking. For example in subscriber perceived TCH Blocking all successful directed retries to another cell are removed from the nominator.
Answer2:
Blocking dives you the non served calls
congestion gives the time when no resource are available (it is possible that nobody needs them so no blocks)
there is a possiblity to have high blocking and low congestion - this means that you have a peak of the attempts.
Blocking = rejected (blocked) attempts over all attempts in %.
Also there is different formulas for TCH blocking. For example in subscriber perceived TCH Blocking all successful directed retries to another cell are removed from the nominator.
Answer2:
Blocking dives you the non served calls
congestion gives the time when no resource are available (it is possible that nobody needs them so no blocks)
there is a possiblity to have high blocking and low congestion - this means that you have a peak of the attempts.
what is TCH Blocking and Drop?
TCH call Blocking , it present how many subscriber asks for TCH channel and network reply with no available resource.
so it present how many subscriber request TCH channel to reject this request
TCH call drop
after subscriber get TCH and start converstion
during it the call is dropped for some reasons not related to the subscribers .
so it present how many subscriber request TCH channel to reject this request
TCH call drop
after subscriber get TCH and start converstion
during it the call is dropped for some reasons not related to the subscribers .
Handover failure due to protocol error
verify the ciphering algo used in both External Cells.this via DT.In case of ciphering issue, handover from one side to other should be happening. i.e. the side using higher ciphering algo will be able to transfer the call to cell with lower ciphering algo.
KPI Introduction
1. CSSR (CALL SETUP SUCCESS RATE)
Definition: Rate of calls going until TCH successful assignment
2. SCR (SUCCESSFULL CALL RATE)
Definition: Rate of calls going until normal release that is not interrupted by SDCCH DROP, neither by assignment failures, and neither by CALL DROP.
3. CALL DROP RATE (CDR)
Definition: Rate of all losses of TCH connections during a call in relation to the number of successful Call Setups
4. HOSR (HAND OVER SUCCESS RATE)
Definition: Successful internal and external outgoing handovers of total number of internal and external outgoing handover attempts
5. PSR (PAGING SUCCESS RATE)
Definition: Rate of successful paging attempts of total number of paging attempts.The formula is based on NSS point of view (based on MSC or LAC)
6. LOCATION UPDATE SUCCESS RATE
Definition: Successful location update
attempts of total number of location update attempts. The formula is based on NSS point of view.
7. SDCCH BLOCK RATE
Definition: SDCCH congestion of total number of SDCCH seizure attempts
8. SDCCH DROP RATE
Definition: Dropped SDCCH connections of total number of SDCCH connections without TCH congestion.
9. TCH ASSIGNMENT BLOCK RATE
Definition: Rate of TCH unsuccessful seizures during assignment procedure due to congestion
10. TCH Assignment Failure Rate (exclude blocking)
Definition: Rate of RTCH seizure failed (system + radio) during normal assignment procedure over the total amount of RTCH request for normal assignment procedure
11. EMD (Erlang Minute per Drop)
Definition: Total of Erlang minutes (TCH occupation) in one period measurement per drop call (after TCH Assignment).
12. TCH Availability
Definition: Available TCH of total number of defined TCH
13. RACH Success Rate
Definition : Rate of Successful RACH over the total number of channel required message received
Definition: Rate of calls going until TCH successful assignment
2. SCR (SUCCESSFULL CALL RATE)
Definition: Rate of calls going until normal release that is not interrupted by SDCCH DROP, neither by assignment failures, and neither by CALL DROP.
3. CALL DROP RATE (CDR)
Definition: Rate of all losses of TCH connections during a call in relation to the number of successful Call Setups
4. HOSR (HAND OVER SUCCESS RATE)
Definition: Successful internal and external outgoing handovers of total number of internal and external outgoing handover attempts
5. PSR (PAGING SUCCESS RATE)
Definition: Rate of successful paging attempts of total number of paging attempts.The formula is based on NSS point of view (based on MSC or LAC)
6. LOCATION UPDATE SUCCESS RATE
Definition: Successful location update
attempts of total number of location update attempts. The formula is based on NSS point of view.
7. SDCCH BLOCK RATE
Definition: SDCCH congestion of total number of SDCCH seizure attempts
8. SDCCH DROP RATE
Definition: Dropped SDCCH connections of total number of SDCCH connections without TCH congestion.
9. TCH ASSIGNMENT BLOCK RATE
Definition: Rate of TCH unsuccessful seizures during assignment procedure due to congestion
10. TCH Assignment Failure Rate (exclude blocking)
Definition: Rate of RTCH seizure failed (system + radio) during normal assignment procedure over the total amount of RTCH request for normal assignment procedure
11. EMD (Erlang Minute per Drop)
Definition: Total of Erlang minutes (TCH occupation) in one period measurement per drop call (after TCH Assignment).
12. TCH Availability
Definition: Available TCH of total number of defined TCH
13. RACH Success Rate
Definition : Rate of Successful RACH over the total number of channel required message received
Wednesday, May 12, 2010
Welcome telecom professionals
Welcome all the telecom professionals to my blog.
Please share the telecom releated articles.
Please share the telecom releated articles.
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