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Hello Pix,
In 2G HO case , is there any retry for HO command in case the target is congestionned or the request is just queued??
If ther’s a retry , what’s its occurence???S’bahir Slim 🙂
if the BSC detects the best candidate cell is congested, then the cell is put in a “black list” (this list is associated to one communication only and is not used for other HO for other MS).
The black list is emptied after T7 seconds.
Keep in mind that the HO COMMAND is not sent in case of congestion : the BSC knows that the target is congested, so it doesn’t send the HO COMMAND. It will just go to the 2nd candidate and check if that one too is also congested.
As long as the HO is detected for the call, the BSC will try to find the best candidate which is not congested.
Cheers
pixThanks a lot Pix,
My question is :
What’s failure HO cause congestion?there’s not another retry for HO for the best cell target which was detected as congestionned one?
And what’s the importance of Queuing then?hi pix have u ever worked in tunis??
good arabic!!campus,
salam 🙂
i went to tunis several times, for tunisana and tunisie telecom too… 😉slim,
ho failure due to congestion means :
1/ the BSC detects that 1 call shall do a HO.
2/ the BSC evaluates what would be the best candidate for this HO
3/the BSC detects this candidate is congested.In these 3 steps there were NO message sent (no msg to BTS, no msg to MS, no msg to MSC). It is all internal.
The BSC will then look for the 2nd best candidate, and so on. If 2nd is not congested, then the HO Execution is performed.
After T7 seconds, if HO preparation is still ongoing, then the list of “congesteed” cells is reset. The best candidate will be attempted again.The “request” is not queued at all. The only queuing is done for incoming EXTERNAL HO (means : coming from a different BSC). In this case, the incoming HO request is queued for T_QHO – IF THE TARGET CELL IS CONGESTED. At T QHO expiry, the target BSC will reply to the serving BSC, saying the target cell is congested.
During T QHO, the serving BSC just waits….
Cheers
pixThanks a lot Pix for the explanation
you are genious (“m3allem” in Arabic)slim,
haha, no no, i’m far from genious, just sharing what i’ve learnt from others 😉
pix
Hi Pix,
As mentioned by u when ms tries to handover to next best cell and if it is congested then it will not try to that cell (i mean will not give ho coomand) because bsc already knows that target cell is busy.
but how is it possible?because at a first time ms tries to attamept that target cell and once it shows busy bsc tries to next best cell is it ?
because in eric system ho success rate is not good then in it one of the reason which is ho failure due tch unavailblity is high..
hello,
you are making one mistake : the MS doesn’t try to do a HO at all. The BSC estimates the best target cell, and if the cell is not congested THEN ONLY it will send the HO CMD to the MS. At that point, the MS will try to access the new cell.
Please re-read all my previous post, because *all* the answers are there 🙂
hi Pix,
I have checked the case of a relation between A and B (in the same BSC) and for which fail HO cause congestion (shown by RNO) is 150/day
The counter is then incremented and considered as a fail even if the BSC tries to find another candidate cells not congestionned??)Slim,
Yes, 150 times, the best candidate is congested. But it doesn’t mean the HO itself is *failed* for the MS. It is highly probable the HO was sucessful towards another candidate.
So exactly, it works like this :
every time the BSC finds one “best” candidate, the HO REQUEST increments by 1.
every time the current candidate is “congested”, the HO rejected due to congestion increments by one… so the 2nd candidate will be counted as a new HO Request.
etc.
pix
Thanks Pix,
My question is :
There’s no retry for the same target?I mean if it’s intra BSC , it goes to the second, the third .., it doesn’t retry the best one??
And for the inter BSC , the request is considered congestionned after queuing (6 seconds in our network)or from the begining?No retry??Oh Pix,
You have already answered this question
SorryYours
Pix,
The definition of congestionned cell by the bsc is regardind the availibility of at least one TS or in other way??
Slim,
Yes : no timeslot to be allocated for the incoming HO. Usually it means that there are no free TCH available, but some (rare) cases where there are TCH left, but none of them can match the capability of the MS (for example : MS is only FULL RATE and the only TCH available are HALF RATE)
inter-BSC case : yes, the external target is congested after T QHO has expired. During 6 seconds, the “serving” BSC will not try to HO to another cell. It still hopes that the external target is available.
Cheers,
pix
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