Add support for Access Control Class ramping.

Access Control Class (ACC) ramping is used to slowly make the cell
available to an increasing number of MS. This avoids overload at
startup time in cases where a lot of MS would discover the new
cell and try to connect to it all at once.

Ramping behaviour can be configured with new VTY commands:

  [no] access-control-class-ramping
  access-control-class-ramping-step-interval (<30-600>|dynamic)
  access-control-class-ramping-step-size (<1-10>)

(The minimum and maximum values for these parameters are hard-coded,
but could be changed if they are found to be inadequate.)

The VTY command 'show bts' has been extended to display the
current ACC ramping configuration.

By default, ACC ramping is disabled.

When enabled, the default behaviour is to enable one ACC per
ramping step with a 'dynamic' step interval. This means the
ramping interval (time between steps) is scaled to the channel
load average of the BTS, i.e. the number of used vs. available
channels measured over a certain amount of time.

Below is an example of debug log output with ACC ramping enabled,
while many 'mobile' programs are concurrently trying to connect
to the network via an osmo-bts-virtual BTS. Initially, all ACCs
are barred, and then only one class is allowed. Then the current
BTS channel load average is consulted for scheduling the next
ramping step. While the channel load average is low, ramping
proceeds faster, and while it is is high, ramping proceeds slower:

(bts=0) ACC RAMP: barring Access Control Class 0
(bts=0) ACC RAMP: barring Access Control Class 1
(bts=0) ACC RAMP: barring Access Control Class 2
(bts=0) ACC RAMP: barring Access Control Class 3
(bts=0) ACC RAMP: barring Access Control Class 4
(bts=0) ACC RAMP: barring Access Control Class 5
(bts=0) ACC RAMP: barring Access Control Class 6
(bts=0) ACC RAMP: barring Access Control Class 7
(bts=0) ACC RAMP: barring Access Control Class 8
(bts=0) ACC RAMP: barring Access Control Class 9
(bts=0) ACC RAMP: allowing Access Control Class 0
(bts=0) ACC RAMP: step interval set to 30 seconds based on 0% channel load average
(bts=0) ACC RAMP: allowing Access Control Class 1
(bts=0) ACC RAMP: step interval set to 354 seconds based on 59% channel load average
(bts=0) ACC RAMP: allowing Access Control Class 2
(bts=0) ACC RAMP: step interval set to 30 seconds based on 0% channel load average
(bts=0) ACC RAMP: allowing Access Control Class 3
(bts=0) ACC RAMP: step interval set to 30 seconds based on 0% channel load average

Change-Id: I0a5ac3a08f992f326435944f17e0a9171911afb0
Related: OS#2591

1 files changed, 1 insertions, 0 deletions

diff --git a/src/libbsc/Makefile.am b/src/libbsc/Makefile.am
index bb1422762..805a7ee1f 100644
--- a/src/libbsc/Makefile.am
+++ b/src/libbsc/Makefile.am
@@ -26,6 +26,7 @@ libbsc_a_SOURCES = \
 	abis_om2000_vty.c \
 	abis_rsl.c \
 	a_reset.c \
+	acc_ramp.c \
 	bsc_rll.c \
 	bsc_subscriber.c \
 	paging.c \