Make "waiting indicator" of IMMEDIATE ASSIGN REJECT dynamic.

The IMMEDIATE ASSIGN REJECT message contains a wait indicator which
tells an MS requesting a channel to wait for a specified amount of
time before trying to request a channel again, i.e. the wait indicator
controls the T3122 timeout value in the MS.

Previously, the wait indicator was fixed to 10 seconds.
This is not sufficient if there are a lot of MS requesting channels
because the MS will retry too soon. Instead of using a fixed value,
maintain a dynamic wait indicator value based on average channel load.

The load (used vs. available channels on a BTS) is sampled once per
second, and once 8 samples have been collected we update a BTS-specific
T3122 wait indicator based on the measured load.

While the wait indicator could go up to 255 seconds, this initial
implementation keeps it in the range from 10 to 128 seconds.

Further experimentation and testing will show whether higher wait
indicator values are desirable, if the sampling rate needs to change,
or if the function mapping the load measurement to a wait indicator
value should change (currently we map the load average linearly into
the range [10, 128] inclusive).

Change-Id: I57e38f6d6ba3b23cc6e1f9520b90261dbb1f1cec
Related: OS#2592

1 files changed, 3 insertions, 0 deletions

diff --git a/src/libcommon/gsm_data_shared.c b/src/libcommon/gsm_data_shared.c
index e4ec594f8..3afc67ebc 100644
--- a/src/libcommon/gsm_data_shared.c
+++ b/src/libcommon/gsm_data_shared.c
@@ -377,6 +377,9 @@ struct gsm_bts *gsm_bts_alloc(struct gsm_network *net, uint8_t bts_num)
 
 	bts->ho = ho_cfg_init(bts, net->ho);
 
+	/* timer overrides */
+	bts->T3122 = 0; /* not overriden by default */
+
 	return bts;
 }