diff --git a/common/chapters/bts.adoc b/common/chapters/bts.adoc index 6228310..2a8c83a 100644 --- a/common/chapters/bts.adoc +++ b/common/chapters/bts.adoc @@ -399,3 +399,50 @@ network timeslot 7 phys_chan_config PDCH ---- + +=== Tuning Access to the BTS + +OsmoBSC offers several configuration options to fine-tune access to the BTS. +It can allow only a portion of the subscribers access to the network. +This can also be used to ramp up access to the network on startup by slowly +letting in more and more subscribers. This is especially useful for isolated +cells with a huge number of subscribers. + +==== Load Management + +Every SIM card is member of one of the ten regular ACCs (0-9). Access to the +BTS can be restricted to SIMs that are members of certain ACCs. + +Since the ACCs are distributed uniformly across all SIMs allowing only ACCs +0-4 to connect to the BTS should reduce its load by 50%. + +The default is to allow all ACCs to connect. + +.Example: Restrict access to the BTS by ACC +---- +network + bts 0 + rach access-control-class 1 barred <1> + rach access-control-class 9 allowed <2> +---- +<1> Disallow SIMs with access-class 1 from connecting to the BTS +<2> Permit SIMs with access-class 9 to connect to the BTS. + + +Smaller cells with lots of subscribers can be overwhelmed with traffic after +the network is turned on. This is especially true in areas with little to no +reception from other networks. To manage the load OsmoBSC has an option to +enable one Access Class at a time so initial access to the network is +distributed across a longer time. + +.Example: Ramp up access to the BTS after startup +---- +network + bts 0 + access-control-class-ramping <1> + access-control-class-ramping-step-interval 30 <2> + access-control-class-ramping-step-size 1 <3> +---- +<1> Turn on access-control-class ramping +<2> Enable more ACCs every 30 seconds +<3> At each step enable one more ACC