[82265] in North American Network Operators' Group
Re: London incidents
daemon@ATHENA.MIT.EDU (Iljitsch van Beijnum)
Mon Jul 11 06:22:42 2005
In-Reply-To: <OF38C066CB.D5AD9C93-ON8025703B.0034251C-8025703B.00352557@radianz.com>
Cc: nanog@merit.edu
From: Iljitsch van Beijnum <iljitsch@muada.com>
Date: Mon, 11 Jul 2005 12:19:10 +0200
To: Michael.Dillon@btradianz.com
Errors-To: owner-nanog@merit.edu
On 11-jul-2005, at 11:40, Michael.Dillon@btradianz.com wrote:
> I had moved the weekend before and my landline was not
> yet installed. Also, I live near a large hospital. I noticed
> that my mobile didn't function at all even late on Thursday
> unless I left home and travelled a kilometer or two from
> the hospital. Presumably, the cells in this suburban
> location had also been switched to emergency service.
A hospital using up "emergency mode" GSM capacity doesn't make much
sense to me. You're not supposed to use cell phones in many places in
hospitals, and the ones that I've seen have an ample supply of fixed
lines that are cheaper, more reliable and pose less risk of
interference with the equipment.
It's probably just congestion. Cellular networks don't come close to
being able to absorb the burstiness of the (potential) usage patterns
in situations like this. (The bean counters don't like cell towers
that are idle 99% of the time.) When all the time slots on all the
sites in range are filled up you can't get through with voice or
data, but SMS which just uses signalling still works. When it gets
really bad the random access channel gets clogged and all mobile-
intiated communication, including SMS, is dead in the water.
(The random access channel is the one not under control of the
network: handsets use it to signal their desire to communicate. As
such, it is very prone to collisions and congestion collapse under
heavy loads.)
