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Hello Oga,
This failure is VERY strange, it’s very difficult to identify the problem.
Does it happen on all cells of the BSC? Or only on cells with external neighbours ? (from other BSC)Try to reduce the size of TCH queues (T11 less than 6 seconds, BTS Q LENGTH less than 5), try to disable Forced Directed Retry (EN FDR = Disable), try to disable Fast Traffic HO (En_Fast_Traffic_HO = disable), try to forbid external directed retry (EN_EXT_DR = disable). Attempt those actions only one by one. Don’t rush 🙂 The External Directed Retry and Queuing could generate BSS errors if it is not understood by MSC correctly.
If you still have failures, then it’s perhaps a discrepancy between NSS and BSS. Check that your NSS have the latest patches… (that happened to me… NSS update fixed the problem)
Also, check BSC Radio parameters are in line with MSC configuration. For example, below, there are some parameters set in BSC that must be checked by MSC team, so that both sides are using the same timers, same messages, etc.
EDR_ASSIGN_FAIL_CAUSE
EDR_MSG_ORDER
EDR_QUEUING_MAINTAINED
EDR_SEND_ASSIGN_FAIL
EN_EXT_DR
EN_SEND_CM3
EN_SEND_OLD_CHAN_MODE
EN_TCH_PREEMPT
MSCR
QUEUE_ANYWAY
T(iar) & T(ias)
T_qho
T11 & T11_FORCED (T11 forced Must be < assignment timer in the MSC (trr1)) T9110 etc...what are the major causes of tch assignment failures in GSM
how to find feeder swap in drive test
There r 2 kinds of swapped feeders or sectors u may detect when making a drive test.
1- cross sectors, feeders (TX, RX) of sector 1 are used for sector 2 and Vice versa.
U detect this when u r in the coverage area of S1 but u find you are served by the frequencies of sector 2 and when u need to make a HO to the other sector, it occurrs in an opposite way.2- cross feeders, feeders(TX,RX) are connected in the place of each other in a certain antenna.
There will be no coverage transmitted by this sector.
When u make a DT. U will find that sector is not serving.
U may suspect the sector us down or crossed sectors.how we can reduce call drop
To reduce the call drop resulted by the swapped feeders, just reconnect the feeders in a correct way.
You may go after the feeders starting from the BTS to the antennas to ensure correctly connection.CDR Sequence error in seimens vendor
what is tch assignment failur
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