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AG_PREMPT_PCH parameter

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    The AG_PREMPT_PCH(pre-emption of PCH sub-channel for AGCCH) that parameter in alcatel cell. somebody can explain when we reserv AGCH = 1 and enable AG_PREMPT_PCH then how many maximum of AGCH stand for PCH and how minimum of PCH available.


    Hello NarChai,

    There is no information about the minimal number of PCH blocks in the frame, when using the AG_PREMPT_PCH = 1.

    So I guess the AGCH can be assigned on all the CCCH blocks when needed, even though i doubt the case will ever happened !

    (cf. PAGING AND ACCESS GRANT CONTROL B7 (or B9), p.50)

    “Each PCH occurrence, the BTS will use this order to search the waiting queue for a pending message.
    If there is a pending Access Grant message, and there is no PACKET DOWNLINK ASSIGNMENT in
    the Paging Group’s associated queue, the BTS will preempt this PCH block to sent the Access Grant



    Hi NarChai,
    From documentation : In cells where System Information 2bis and 2ter are used, or in cells where GSM to UMTS cell reselection is active and either of System Information 2bis or 2ter are used, it is recommended to setAGBLK=1 when GPRS/EGPRS is active in the cell. This is because System Information 13, which is sent when GPRS/EGPRS is active, will otherwise share resources with other System Information messages. This could impact cell selection/reselection performance.
    And my experiences is, that in special events (Christmas day) there was to many paging and nearly no AGCH seizures – in case of Comb Channel (number of reserved AGCH = 0)
    In case of channel configuration FCCH + SCH + BCCH + CCCH: uplink 800.000 RACH slots per hour and downlink 140 CCH block per hour. In case FCCH + SCH + BCCH + CCCH + SDCCH/4(0…3) + SACCH/C4(0…3): uplink 400.000 RACH slots per hour and downlink 46 CCH block per hour.
    1 RACH slot: 1 channel request message of 1 subscriber.
    1CCCH block (4 slots): 1 paging message for 1 ..4 subscribers or 1 access grant message for 1..2 subscribers.
    1 BCCH multiframe is 235.38 msec.
    BR Tomar


    Thanks Pix and Tomar


    Hello, all!

    Can someone explain for me AGCH/CCCH configurations or send documents if possible?

    Thank you,



    Dear All,
    I want to know that when we have AGCH Preemption Enabled(AG_PREMPT_PCH=1), then how do we calculate the Paging/CCCH load?
    We know that for Non-Combined configuration, lets say
    BS_AG_BLKS_RES = 4 (AGCH blocks) 9 – 4 = 5 PCH blocks (default configuration)

    5 PCH blocks/Multiframe * (3600s / 235 ms) = 76 594 PCH blocks/ hour

    2.5 paging per block due to average usage of the TMSI & IMSI paging methods:
    2.5 paging / Block x 76 594 Blocks =
    191 485 paging/hour at 100% load

    If 60 % engineering limit applied: 114 891 paging/hour
    or, 31.91 paging/sec.

    Now, if we use AGCH Premption, then the above mentioned equation shouldn’t hold true(as we dont know the number of AG Blocks). So, now how to calculate the CCCH Load/Capacity?



    well, that’s the whole point of dynamic capacity : you can’t compute the load 🙂 That’s the reason why operators do not care about this feature. They’d rather monitor the load precisely, because it should not congest that often anyway, using default parameters.

    But to monitor dynamic AGCH/PCH, you can now monitor the number of Immediate Assignment (resp. Pagings) which are rejected due to congestion. Those are new indicators in B10.


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