28 Jan
2014
28 Jan
'14
12:11 p.m.
Ralph -
On Jan 27, 2014, at 17:07, Ralph A. Schmid, dk5ras <ralph(a)schmid.xxx> wrote:
Hi,
There is a hold-off timer sent in the immediate assignment reject message, but it is still
possible for the RACH to be so congested that only a small fraction of bursts are
decodable. And it is possible for the AGCH to be so congested that it is impossible to
respond to any significant fraction of the requests anyway. Once this happens, you get a
kind of live-lock on the air interface. If you are the only BTS in the area, this locked
condition can persist for hours. You can either turn down the power and reduce the number
of phones in the coverage area and serve that reduced population, or stay in the live-lock
condition and not serve anyone.
Yes, you ramp up power on startup. We just automated that process. And unless the BTS
falls into this kind of live-lock condition, because of the sudden failure of a neighbor
cell or some other overlapping network, this mechanism does not take any action.
Then, there is an issue with OsmoBTS when there
are too many phones are
trying to connect to it for LUR. I described this a while ago, but we haven't
had time to look more into it yet. So far we just used various workarounds to
solve it. We're looking into writing a BS power reduction algorithm, similar to
the one used in OpenBTS - If there is a severe congestion for LU's, BS will
reduce its power until the load doesn't stabilize. Then it'll slowly increase
the
power again, until it hits the LU congestion or hits the maximum specified
power.
Sure that this is a good idea? It will throw out all users at the edge of the coverage
area, maybe cause even more load, when those show up again with their accumulated
requests like call attempts, SMS, additional LU, and in fact I have never seen that
commercial networks do something like that.
Is there not some waiting queue defined in the standards, with some timers,
commanding the location updaters to wait for some period of time? Has
been a long time when I looked into this, but I mean to remember that even
OpenBTS does it this way.
Or am I totally wrong?
It’s not normal operation. It is an emergency measure that takes effect with the network
is in a hopeless congestion condition. And in my experience, this approach changes the
recovery time from several hours to several minutes.
From my point of view slowly increasing TX power
is OK for booting a new cell into
operation, but during normal operation?! --
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru
Ralph.