- This topic has 14 replies, 1 voice, and was last updated 9 years, 7 months ago by Fabio.
13th November 2009 at 11:32 #59634GURUGuest
CAN ANYONE GIVE SOME GYAN ON THIS13th November 2009 at 13:30 #59635BijoyGuest
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:-)13th November 2009 at 20:51 #59636pixGuest
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.
pix (ghost hunter)16th November 2009 at 05:17 #59637BijoyGuest
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.16th November 2009 at 10:54 #59638PixGuest
When you say :
“BTS fails to decode is a Phantom RACH”
That’s the problem… and I’m not sure you are meaning it ! 🙂
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.
pix16th November 2009 at 11:22 #59639BijoyGuest
My mistake Pix
I should have been careful while writing “BTS fails to decode”. This is actually MSC/BSC which fails to decode it.16th November 2009 at 11:30 #59640AliAsgherGuest
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.
Your reply looks more like from a Ghost rather than a Ghost Hunter 🙂16th November 2009 at 12:24 #59641BijoyGuest
I think I’ve already clarified myself.16th November 2009 at 12:48 #59642AliAsgherGuest
No you have not 🙂
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.16th November 2009 at 13:29 #59643PixGuest
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 !17th November 2009 at 05:50 #59644BijoyGuest
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:-(17th November 2009 at 10:48 #59645PixGuest
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 😉17th November 2009 at 10:54 #59646BijoyGuest
I already got tired trying to reply Krish.This erlang.com sometimes really get on your nerves17th November 2009 at 15:59 #59647AliAsgherGuest
Haha Pix. I think you are right. Perhaps I am watching National Geographic quite too often. 🙂
Sorry Bijoy to tire you brother. I was just having fun.13th September 2011 at 14:52 #59648FabioGuest
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.