agch: Recalculate length limit of AGCH queue

This patch adds a function bts_update_agch_max_queue_length()
to compute a limit of the AGCH queue. This is based on the idea,
that the AGCH queue has a limited drain rate and that CHANNEL
REQUESTs must be answered within a certain time frame, given
by the minimum value of T3126 (see GSM 04.08). When the AGCH queue
reaches that limit, the last message would be delivered in time if
there were no other delays involved (which is not the case).

The calculation is based on the ratio of the number RACH slots and
CCCH blocks per time:
  Lmax = (T + 2*S) / R_RACH * R_CCCH
where
  T3126_min = (T + 2*S) / R_RACH
  R_RACH is the RACH slot rate (e.g. RACHs per multiframe)
  R_CCCH is the CCCH block rate (same time base like R_RACH)

The value depends control_channel_desc.ccch_conf and
rach_control.tx_integer (both from SYSINFO_TYPE_3) and should
therefore by called at least each time after one of these is changed.
For this reason, a signal callback is registered under
SS_GLOBAL/S_NEW_SYSINFO which invokes bts_update_agch_max_queue_length().

Sponsored-by: On-Waves ehf
Based-On: "bts: Calculate length of agch queue" by Ivan Kluchnikov
  <kluchnikovi@gmail.com>

0 files changed, 0 insertions, 0 deletions