Status update / layer23

Harald Welte laforge at
Wed Mar 3 15:37:03 UTC 2010


I'm pleased to report that the current master branch in osmocom-bb.git
has initial support for bi-directional communication, and handles
messages all the way up from L1 to L3 and back.

The architecture is as follows:
L1 events (such as received 23byte mac blocks) are encapsulated in L1CTL
messages, which are sent over HDLC/rs232 to the PC.  'osmocon' then
demultiplexes the L1CTL from the console messages and sends it via unix
domain socket to the layer23 program.

Inside layer23, L1CTL is decapsulated and passed into the LAPDm code, from
where the data is encapsulated in RSLms (RSL for mobil station, my invention)
and handed off to L3.

Messages from L3 take the opposite way L3->RSLms->LAPDm->L1CTL->HDLC->L1

So far, we still only support IMMEDIATE ASSIGNments to SDCCH/4 on a 
combined CCCH.  But if you are on a BTS with that channel configuration,
layer23 will now happily send a LOCATION UPDATE REQUEST to the BTS :)

Dieter has indicated he will be looking into supporting TCH/F as well as
frequency hopping during the next week(s).

I myself desperately need to get some real work done at this point,
so don't expect any major developments for some time.

- Harald Welte <laforge at> 
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)

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