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Paging capacity on Abis

Viewing 15 posts - 1 through 15 (of 15 total)
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  • #62834 Reply
    Guybrush
    Guest

    Hi,

    Is there a limit of number of paging messages that can be sent on Abis? How can this limit of capacity be calculated?

    Thanks,
    Guybrush

    #62835 Reply
    pix
    Guest

    hello,

    the pagings are sent on the RSL, and those channels are usually defined with a variable size. So the capacity cannot be calculated (or let’s say that i’m not aware of the method).

    However, the ABIS is probably never a limitation regarding paging. The limit comes from the radio PCH capacity, and also from the BSC processing. Deoending on your vendor, you might be able to find an indicator that measures the RSL load of the Abis.
    (RSL is alcatel specific : it is the channel on the Abis that carries all radio signalling for 1 TRX only)

    FYI, to further decrease the paging load on the Abis, you can activate a feature that aggregates multiple paging commands into one big paging message.

    #62836 Reply
    Rex
    Guest

    Hi,
    CCH_Paging_Command_Abis_discarded_cong_rate reached 5 percent. Is it to high? What’s the recommended threshold (ALU) and any solution to reduce it? Should we increase MFRS? MFRS is 5, BS_AG_BLKS_RES is 4. What’s the cause of high Paging_command_lost_Abis in some cells?
    BR,
    Rex

    #62837 Reply
    pix
    Guest

    rex,
    it is very high…
    could you share with us the full description of the counter ? what is the trigger event ?

    i’m not sure whether the congestion is in the abis link or on the radio interface. From the name of the indicator, of course, it looks like the abis is congested.
    So i’ll work on this assumption…

    You must either
    1- reduce the number of paging
    2- increase the RSL capacity

    1-
    (a) activate MULTIPLE PAGING feature (it will aggregate n paging requests into only one “Abis” paging message)
    (b) reduce the size of your LAC
    (c) ensure that the paging is done with TMSI (? huh… i don’t think that would help though)

    2-
    (a) use RSL Multiplexing “statistical 64kb/s” “NORMAL LOAD” (4 RSL / 64kbps)
    (b) if that’s already done, use “HIGH LOAD” (2 RSL / 64kbps). That means you’ll have to define more RSL timeslots on your Abis

    cheers
    pix

    #62838 Reply
    Rex
    Guest

    Hi Pix,
    the full description of the indicator is this:
    Rate of discarded “PAGING COMMAND” messages received by the BTS on Abis interface over the number of “48.058 PAGING COMMAND” messages received by the BTS on Abis and had to be sent for CS and PS traffic to the MS.

    Thanks for your solutions. By MULTIPLE PAGING feature, did you mean Multiple CCCH? I think it’s optional feature which we don’t have and need to pay I think. The only solution left is reduce the size of LAC, but, again I’m not sure because the mentioned LAC is in the big city. Dividing in 2 LACs will lead to high SDCCH congestion due to LU.
    All BTSs use statistical 64 kb/s multiplexing (Normal load). Using High Load, again, maybe we need secondary Abis for each BTS.
    Any comment on this?
    Thanks again,
    Regards,
    Rex.

    #62839 Reply
    Pix
    Guest

    Hi Rex,

    The indicator “CCH_Paging_Command_Abis_discarded_cong_rate” actually refers to Paging Cmd which are well received by the BTS (= the Abis is NOT congested), but cannot b forwarded on the Air interface because the PCH is congested.

    So forget about my previous post. The solutions are:
    1/ reduce your LAC size (still…)
    2/ increase the number of PCH blocks in the BCCH (= decrease AG_BLKS_RES by one, or rather set it to “1” and activate AG_PCH_PREEMPT = ENABLE)
    3/ activate the multiple CCCH feature 🙂

    The “multiple paging messages within one Paging Command” is not a commercial feature : it is just a way to reduce the RSL load on the Abis. It doesn’t impact the Air interface at all. It is free.

    Regards,
    pix

    #62840 Reply
    Rex
    Guest

    Thanks Pix,
    we’ll try with the solution under 2 and 3 first, and then see what happens.
    BR,
    Rex.

    #62841 Reply
    Rex
    Guest

    Hi Pix,
    1. In 6 cells (single cells) we changed AG_BLKS_RES from 4 to 3. As a result CCCH_Paging_Command_Abis_discarded_cong_rate for this object zone of 6 cells decreased from 5.5 % (aprox) to 1.8 %. The other indicator CCCH_AGCH_load_CS_Abis_max increased from 18% to 23% (that’s AGCH loading).

    2. In 11 cells (micro cells and some single cells with 2 TRXs) we changed AG_BLKS_RES from 4 to 1 and activated AG_PCH_PREEMPT. Results for the object zone of these 11 cells: CCCH_Paging_Command_Abis_discarded_cong_rate decreased from around 6% to around 0.57 %.

    Questions:
    Did we do a good thing, since paging congestion decreased?
    Is the AGCH loading to much? I think better a bit increase in loading (AGCH) than an increase in paging congestion.
    What do you think if we continue the same with all cells in the LAC?.
    And, what if we activate AG_PCH_PREEMPT for the cells with AG_BLKS_RES=3?

    There is an indicator CCCH_Paging_Multiple_Paging_Command_received_Abis (nb) and is around 660000. Is that mean we already have activated multiple CCCH feature. How to check that, I can’t see it among Cell or BSS parameters.
    Best Regards,
    Rex

    #62842 Reply
    Pix
    Guest

    Hi,

    First of all, thanks a lot for sharing your results so precisely, this is very important to me.

    1. Max AGCH load = 23%, I think this is totally acceptable. I believe that it can increase up to 60% without negative impact on the call setup.

    2. You cannot activate AG PCH PREEMPT if BLKS = 3. It can be activated only if BLKS = 0 or 1. However, you didn’t share your AGCH Load after activating the PREEMPTION. Was it still OK ?

    I know the preemption looks fantastic, but there is something I don’t like about preemption : I am not sure the “PCH Load” and the “AGCH Load” indicators are correctly computed.
    If I were you, I’d set:
    BLKS = 1
    PREEMPT = enable

    And I would monitor MC925f very closely (Number of IMMEDIATE ASSIGN COMMAND messages received by the BTS on Abis and discarded due to congestion).

    3. The Multiple CCCH : I am afraid your eyes are not going past the word “multiple” 🙂 “Multiple CCCH” and “Multiple Pagings” are different features !
    The “Multiple Pagings Commands on Abis” mean that the BSC aggregates several paging requests into 1 Abis message, insttead of 1 request for 1 Abis msg.
    There are two parameters to control this feature :
    NB_MAX_MSG_MULTIPLE_PAGING_CMD (5)
    T_SEND_MULTIPLE_PAGING_CMD (50ms)

    Defaults values indicates that this feature is activated by default. This is a new B10 feature, which is (therefore) activated during the migration. Keep it enable 🙂

    Cheers
    pix

    #62843 Reply
    Rex
    Guest

    Hi Pix,
    sorry I forgot to mention that about AGCH load with BLKS=1 and PREEMPT activated. It was increased to around 30%.
    Immediate_assign_command discarded due to congestion it remains in 0%.
    What you think to not go directly to blks=1, first blks=2 see what happens. If it’s still OK then to go to blks=1.
    Thank you very much for your proffesional suggestions,
    Regards,

    #62844 Reply
    Pix
    Guest

    Rex,

    The problem is that with blks = 2, the PCH preemption cannot be activated. Therefore, the AGCH might congest.

    I am not saying it *will*, but it *could*.
    Therefore, it is safer to try “BLKS = 1 with Preemption” rather than “BLKS = 2 without Preemption”

    Anyway, just try it out, if there is congestion, just change the settings… Let me know what happens.

    BR,
    Pix

    #62845 Reply
    Rex
    Guest

    Hi Pix,
    Yes, I know about preemption should activate only when blks=1. But, I wanted to see how it looks without preemption with blks=2. Anyway, we’ll change to blks=1 and with preempt after that.
    Thanks Pix, you really helped me.
    Best regards,
    Rex

    #62846 Reply
    Pix
    Guest

    no problem, you’re welcome 🙂

    #62847 Reply
    Ayat
    Guest

    Hello all
    we are going to swap a part of our network with 6 LACs replaced by 2 LACs…….

    info

    CCCH and SDCCH=not combine
    Reserved AGCH blocks (BS-AG-BLK-RES) BSAGBLKRES = 2
    Number of multi-frames of the PCH (BS_PA_MFRAMS) BSPAMFRAMS = 5

    So could you help me to know the imprtant notice about this swap

    #62848 Reply
    pix
    Guest

    ayat,

    look for the AGCH congestion rate and the PCH congestion rate. You can’t miss them, they are available per cell in the NPO.
    Then, you can also monitor the AGCH radio load and PCH radio load. They should not exceed 60% (in theory), to avoid any possible blocking.

    Finally, check the RSL load on the Abis : it is the physical channel that carries all those pagings. Look for : LAPD Congestion, in BTS object, or in Lapd object, I forgot.

    Keeping only 2 AGCH blocks is rather low, focus especially on hourly AGCH radio load & congestion.

    Regards
    pix

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