[82323] in North American Network Operators' Group
Re: London incidents
daemon@ATHENA.MIT.EDU (Petri Helenius)
Tue Jul 12 13:22:40 2005
Date: Tue, 12 Jul 2005 20:20:18 +0300
From: Petri Helenius <pete@he.iki.fi>
To: Francesco Usseglio Gaudi <cecco@ica-net.it>
Cc: NANOG <nanog@merit.edu>
In-Reply-To: <42D3DCAA.1040006@ica-net.it>
Errors-To: owner-nanog@merit.edu
Francesco Usseglio Gaudi wrote:
>
> My little experience is that cell phones are in the most of cases
> nearly congenstion: a simple crow of people calling all together can
> shut down or delay every calls and sms
GSM networks running TFR or EFR audio codecs have 8 timeslots on a cell.
Usual 900MHz frequency allocation plans allow for 4-5 usable cells but
most handsets try only the two with best reception to get an available
timeslot. If you happen to be in a neighborhood with 850/1900 or
900/1800 service, the odds of having more capacity available are better.
This translates to 16 people with the same network dialing
simultaneously can congest the two local cells.
Almost all GSM networks implement emergency priority where a call with
the bit set will pre-empt capacity in the primary cell. Some handset
firmware can be modified to set the neccessary bit on demand. Not sure
how long one would get away with it or if the BTS firmware would check
the number dialed before granting pre-emption.
Pete
