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Phantom RACH

Viewing 15 posts - 1 through 15 (of 15 total)
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  • #59634 Reply
    GURU
    Guest

    CAN ANYONE GIVE SOME GYAN ON THIS

    #59635 Reply
    Bijoy
    Guest

    Phantom RACH is the RACH which BTS fails to decode.This may be due to co-bcch-bsic issue,poor path balance,low traffic cells,faulty MS,poor BTS sensitivity,ets ,etc.In simple words,corrupted RACH is Phantom RACH(ghost RACH)

    Got it:-)

    #59636 Reply
    pix
    Guest

    bijoy,

    i need to correct you on this one. Phantom RACH is a electromagnetic noise that looks like a CHANNEL REQUEST.
    The cell will allocate a SDCCH and reply with an immediate assignment. But because the channel request was NOT generated by a MS (..but by a ghost) the SDCCH is allocated for nothing.

    Cheers,
    pix (ghost hunter)

    #59637 Reply
    Bijoy
    Guest

    Pix
    The thing is whatever BTS fails to decode is a Phantom RACH,whether it is generated by MS or some other body,because BTS doesn’t comes to know the demarkation you suggested.Usually cells having very low traffic suffers from this phenomenon.

    #59638 Reply
    Pix
    Guest

    Bijoy,

    When you say :

    “BTS fails to decode is a Phantom RACH”

    That’s the problem… and I’m not sure you are meaning it ! ๐Ÿ™‚

    The phantom “Channel Request” on the RACH is **succesfully** decoded and leads to a SDCCH Allocation. All other noises which are not “looking like” a Channel Request are rejected by the BTS and do not lead to any QoS degradation. And they are not called “phantom”. Just noise.

    Whereas the Phantom RACH does lead to SDCCH Assignment Failure (the phantom does know seizes its SDCCH subchannel) and sometimes to SDCCH Congestion.

    Now, where does the Phantom comes from… it could be from random external noise, self-generated noise or army radar signals… Or by MS which are actually sending the channel requests (or ho access) to another cell with same frequency and same BSIC.

    Cheers,
    pix

    #59639 Reply
    Bijoy
    Guest

    My mistake Pix
    I should have been careful while writing “BTS fails to decode”. This is actually MSC/BSC which fails to decode it.

    #59640 Reply
    AliAsgher
    Guest

    Dear Bijoy,

    Pix is right. It is not a FAILED RACH. In fact it is just a narrow band noise which LOOKS LIKE a RACH attempt and is also successfully decoded and due to this attempt a SDCCH is also allocated for the ‘Ghost MS’. But as it was’t generated by a MS, the SDCCH will eventually be released.

    Dear Pix,
    Your reply looks more like from a Ghost rather than a Ghost Hunter ๐Ÿ™‚

    #59641 Reply
    Bijoy
    Guest

    Hi Ali
    I think I’ve already clarified myself.

    #59642 Reply
    AliAsgher
    Guest

    No you have not ๐Ÿ™‚
    It is not a case of MSC/BSC failing to decode the RACH attempt. They do decode it and also assign a SDCCH as a response.

    #59643 Reply
    Pix
    Guest

    Ali, sorry if I scared you with all my ghost stories :))

    You ar eright, the Channel Request is well decoded by every NE. Nobody knows that it is a ghost and it is processed as a regular channel request.

    Nobody can see it… Except a little boy, with a 6th sense, and who can see dead people…

    BOOOOH !

    #59644 Reply
    Bijoy
    Guest

    My Dear Ali
    It is OK that BTS assigns a SDCCH in response to the Ghost RACH.Then what happens??Who sends the SABM??Nobody.Does BTS sends UA??No.

    BTS waits till its T3101 expires and clear command comes from BSC to release the SDCCH.

    Complete decoding means establish indication must go to MSC from MS(DTAP).

    Oh!I’m getting tired:-(

    #59645 Reply
    Pix
    Guest

    Bijoy,

    Now, that is very correct.

    Your previous posts were confusing, you said that the BSC/MSC fails to decode the message…. It wasn’t correct, because (as you now write) BTS and BSC processes the message as usual.

    And the MSC won’t even see the message.

    And of course, after the IMMEDIATE ASSIGNMENT from the BSC to the MS, there is no answer… So the flow stops here.

    Sorry to tire you out, but Ali is a shark that just won’t let go ๐Ÿ˜‰

    #59646 Reply
    Bijoy
    Guest

    Pix
    I already got tired trying to reply Krish.This erlang.com sometimes really get on your nerves

    #59647 Reply
    AliAsgher
    Guest

    Haha Pix. I think you are right. Perhaps I am watching National Geographic quite too often. ๐Ÿ™‚

    Sorry Bijoy to tire you brother. I was just having fun.

    #59648 Reply
    Fabio
    Guest

    maybe you can help me, we are having high SDCCH DR due to Abis failure. We are using Abis over IP. I’ll apreciate the advise.

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