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David A. Burgess dburgess at jcis.netEven if two MS collide with the same random number at the same time, and one RACH burst overpowers the other enough to be detected and decoded, the L2 contention resolution procedure will usually prevent a complete failure, at lease for one of the MS. On Apr 18, 2010, at 11:14 PM, Dieter Spaar wrote: > Hello Holger, > > On Mon, 19 Apr 2010 12:37:12 +0800, "Holger Freyther" > <zecke at selfish.org> wrote: >> >> The other problem is with the 20 paging requests every two seconds >> I'm >> creating a RACH DoS for my BTS to a point that I think (didn't >> bother to >> do the easy math, and I don't have the spec here right now) we >> have two >> MS picking the same random number. At least the symptom is that >> even if >> we assign a channel, it gets closed down with a RF Failure. > > I wonder how frequently it happens with 20 MS that a RACH is sent > on the > same frame and with the same random number. There are at least 16 > possible > random numbers for the "Answere to Paging" Channel Request and > there are > 27 frames in the MF to chooses from (in the "Combined Configuration"). > Do you use the same phones for testing and does the RF Failure happen > frequently (this probably would mean a bad random number generator in > this phone firmware) ? Also I would expect that two RACH burst will > disturb each other, at least in a testing environment where all the > MS have the same distance to the BTS and send with the same power. > > Best regards, > Dieter > -- > Dieter Spaar, Germany > spaar at mirider.augusta.de David A. Burgess Kestrel Signal Processing, Inc.