PDTCH and PTCCH activation

Max msuraev at sysmocom.de
Wed Jul 20 16:50:24 UTC 2016


Hi all.

I've noticed in osmo-bts logs several messages from L1:
238:<0006> oml.c:689 (bts=0,trx=0,ts=2,ss=0) MPH-ACTIVATE.conf (PDTCH TxDL)
243:<0006> oml.c:689 (bts=0,trx=0,ts=3,ss=0) MPH-ACTIVATE.conf (PDTCH TxDL)
246:<0006> oml.c:689 (bts=0,trx=0,ts=2,ss=0) MPH-ACTIVATE.conf (PDTCH RxUL)
251:<0006> oml.c:689 (bts=0,trx=0,ts=4,ss=0) MPH-ACTIVATE.conf (PDTCH TxDL)
254:<0006> oml.c:689 (bts=0,trx=0,ts=3,ss=0) MPH-ACTIVATE.conf (PDTCH RxUL)
260:<0006> oml.c:689 (bts=0,trx=0,ts=7,ss=0) MPH-ACTIVATE.conf (PDTCH TxDL)
263:<0006> oml.c:689 (bts=0,trx=0,ts=4,ss=0) MPH-ACTIVATE.conf (PDTCH RxUL)
274:<0006> oml.c:689 (bts=0,trx=0,ts=7,ss=0) MPH-ACTIVATE.conf (PDTCH RxUL)

Similarly, there are messages related to PTCCH:
257:<0006> oml.c:689 (bts=0,trx=0,ts=2,ss=0) MPH-ACTIVATE.conf (PTCCH TxDL)
266:<0006> oml.c:689 (bts=0,trx=0,ts=3,ss=0) MPH-ACTIVATE.conf (PTCCH TxDL)
277:<0006> oml.c:689 (bts=0,trx=0,ts=4,ss=0) MPH-ACTIVATE.conf (PTCCH TxDL)
288:<0006> oml.c:689 (bts=0,trx=0,ts=7,ss=0) MPH-ACTIVATE.conf (PTCCH TxDL)

Notice that while PDTCH is activated for both UL and DL, the PTCCH is
only activated for DL.

As far as I've understood continuous TA procedure I've got to have PTCCH
activated in both directions. The problem is that I have troubles
locating the code which triggers the activation above.

There is l1if_connect_pdch() in osmo-pcu src/sysmo_l1_if.c but it uses
GsmL1_PrimId_MphConnectReq while if I understood correctly
GsmL1_PrimId_MphActivateReq is necessary for channel activation. There
is mph_send_activate_req() in osmo-bts oml.c which uses it. It's called
from lchan_act_compl_cb() via sapi_queue_send() which is also in
mph_send_activate_req() - I have hard time understanding how this works
at all. Do we have this documented somewhere?

-- 
Max Suraev <msuraev at sysmocom.de> http://www.sysmocom.de/
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