do_lchan_free() timer

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Holger Freyther holger at freyther.de
Mon May 23 17:15:59 UTC 2016


> On 23 May 2016, at 18:46, Neels Hofmeyr <nhofmeyr at sysmocom.de> wrote:
> 
> On openbsc master, in do_lchan_free(), a T3111 timer is started in case
> the lchan is in an error state. Why?


we received a connection failure indication (e.g. LAPDm retransmissions missed N200+1(?) times with T200 for the timeout). Now just because the BTS gave up does not mean the MS stopped broadcasting. It might continue to send it SACCH and cause interference. So we wait a bit before re-using the channel.


> Also, I'm not sure whether we want the defragmentation feature at this
> time. It seems to be orthogonal, not related to dynamic reassignment of
> TCH <-> PDCH per se.

I just guess. For GPRS some channel combinations are better for multi-slot assignments than others. So the defrag can be beneficial for some MS classes and some configurations. I don't remember out of my head which classes and which patterns are wanted.

holger


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