AGCH question.

Sylvain Munaut 246tnt at
Thu Feb 3 14:56:05 UTC 2011

> But I'm not sure whether the dissector already decodes them as it doesn't
> do it with normal bursts.

It doesn't dissect anything, just display the raw burst bits.

There is however a GSMTAP_CHANNEL_RACH channel type (using
GSMTAP_TYPE_UM) that could just carry the 8 encoded bits.
Not dissected either but much easier to read than the raw burst bits.

Neither is sent by osmocom thus far.

> But there is at least some kind of predictability. The assigned arfcn
> and time slot is usually the same until a certain load it reached and
> a second ts or even other arfcn/ts is used. The subchannel is hard to
> predict as I've never seen a stable pattern, it looks quite random.
> At least these are my observations with some live networks.

Well, it highly depends on the network ... and on channel types you want.
I've seen plenty of behaviors, some very predictable, some seemingly random.

Point is: You can't really rely on it.



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