Changes to the paging subsystem

[Holger Freyther]

Hi all,

I will implement the following changes on the on-waves/bsc-master branch
and if no one is screaming move them over to master shortly afterwards.

Right now I'm experiencing the following problem. When enabling the RF
on the BTS hordes of MS come to the network for Location Updating
Requests and the SDCCHs are close to 100% loaded, now I want to send a
SMS to every new Subscriber welcoming it (ideally one would do it during
the LU but... well... it does not). To deliver the SMS we need to page
the SMS and currently we are paging 20 MSs during 2 seconds.

The first problem is that the nanoBTS can not handle this load for a
long time, it is sending CPU Overload and as of GSM 08.58 we should
handle it by throttling the transfer but well that is not implemented.

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.

So here is my problem:
	- Remove the notion of paging slots... the nanoBTS is not
          even sending the load indication anyway.
	- Look at free channels (ignoring the requested channel at
          first... something we need to fix later) and have a config
          switch like.. only page if the cell is like 50% loaded or
          such. I will figure out the details while doing the changes.


The other reason to write this mail is, I think it is pretty interesting
to see how our experiments from the congress look different to what I
was seeing due way more paging going on.

regards
	holger