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Handover Congestion

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  • #51796 Reply
    CF
    Guest

    I am working with an Alcatel GSM system and we have been experiencing high handover congestion rate on the network; almost 70% of the total congestion is due to handover so I’d like to know if you have any recommendations to investigate and mitigate the problem.

    #51797 Reply
    BSSnik forever
    Guest

    Hello, CF!
    I have the same problem (where are you from? – if you don’t mind) indeed more then 80% of the total congestion is due to MC541a (external_HO_prep_fail due to cong), MC551 (internal_HO_prep_fail due to cong), MC 561 (intracel_HO_prep_fail due to cong), but MC812 (Normal_TCH_assign_fail due to cong) is only 5-7%.
    One of possibly cause, as we detected, is connected to GPRS and EDGE. Let’s imagine: cell has 3 carriers (21 TCHs) and at the certain moment we have 16 calls (MO, MT or HO) and 5 TS with packed data, so all of TS are busy. When the new normal TCH assignment request comes we have to reduce number of TS for packet data,but when HO reuest comes there is no GPRS downgrade – we have incoming HO failure due to congestion (MC541a, MC551 or MC561. We have no recommendations or solutions for this situation therefore I’ll be gratefull for your any comments.

    #51798 Reply
    CF
    Guest

    Thanks for your comments BSSnik forever. I was doing some test regarding this issue and I found sometimes the problem seems to be related with AMR-HR, that is, when I am handling a call in a sector using AMR-HR and I try to perform a handover to a neighbor cell that doesn’t have AMR_HR enable, a handover congestion event happens; I have to go deep on the investigation to be sure about it.

    #51799 Reply
    Pix
    Guest

    BSSnik forever,

    The management of the TCH vs. PDCH is more complex : it is managed by MAX PDCH, MAX PDCH HIGH LOAD and MIN PDCH.
    In your example, you are in high load, and i guess:
    MAX PDCH HIGH LOAD is set to 5
    like this, the 5 PDCH cannot be preempted for CS, either incoming HO or normal assignment.

    if MAX PDCH HIGH LOAD is set to 3, your situation is not possible : with 15 TCH, you’re already in high load. Therefore only 3 PDCH can be allocated by the MFS. So PDCH 4 and PDCH 5 are going to be deallocated (even though there is no CS that is going to be handled on those TS right now)

    You have a problem, but it should not be due to GPRS (what’s your value of max pdch high load ?)

    CF,

    I didn’t see any fault report about this. Can you raise this issue to the TAC ? I can’t say if this is due to AMR HR… maybe you can try to disable AMR for few hours, and see if it changes something ?

    **For further study**
    do you see the problem on all cells ?
    what type of cells especially ? (umbrella ? concentric ? micro ?)
    what type of handover is congested : internal, external, or intracell ?

    when did the problem starts ? Since B9 migration ? Since activation of a feature ?

    do you see a hourly correlation during the day between TCH HO Congestion and TCH NA Congestion ? What are those daily values ?
    what is the value of the timer T7?
    what is the value of T11, BTS_Q_LENGTH ?

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