GPRS, EDGE support

historical

On Sat, Jan 25, 2014 at 12:39:39PM +0100, Sipos Csaba wrote:

Hi again,

> So there is only GPRS support at the moment, no EDGE. Do you guys have
> a plan for EDGE? To be clear I am not demanding anything, just kindly
> asking :-)

The answer is complicated. The current PCU code is not really good and
we at sysmocom are the only ones changing that. I am keeping a TODO in
the osmo-pcu code and post status reports to the PCU mailinglist from
time[1] to time.

The current agenda is:
 * Re-factor code so it can be unit-tested and write tests
 * Optimize bandwidth usage
 * Dynamic CS mode switch

After this we will support EDGE (in a non-mixed mode config). The
structure will not change that much when EDGE is added. The window
handling is more dynamic (dl/ul size can be dynamically decided),
more codec schemes, new CSN1 messages.

> Can someone enlighten me about the current limitations of the GPRS
> stack?

Please have a look here[2].

> 
> For example: what are the slot configuration (or GPRS class) limitations? I am not
> interested in voice calls so my plan is to configure one (or maybe
> more than one) TRX with just PDCH channels to gain as much PD
> bandwidth as much as possible.

> Can I use more than one downlink or uplink channels if my terminal is capable of
> doing that?

The current allocator can assign multiple downlink slots. It will
assign only a single uplink though. The bad part is that the same
uplink slot will be assigned for all phones. The more phones you
have the more problems you will get. E.g. to ACK the TCP frame all
phones compete for the same uplink resource.. while all other PDCHs
have no uplink usage...

It is just one example of the problem space one has to deal with in
GPRS/EDGE PCU.

cheers
	holger

[1] http://lists.osmocom.org/pipermail/osmocom-pcu/2014-January/thread.html
[2] http://openbsc.osmocom.org/trac/wiki/osmo-pcu#Status