== Configuring OsmoGbProxy

OsmoGbProxy requires very little configuration, most of it being the
configuration of the NS links.
Most config options specific to OsmoGbProxy are related to SGSN pooling and
telling the proxy which NSE(s) it should use to talk to the SGSN(s).

=== Configure the Network Service (NS)

A detailed description of the NS configuration can be found in <<libosmogb>>.
The following config snippets assume the SGSN(s) (NSEI 101 and 102) are using
IP-SNS and listen on 10.0.1.1:23000 and 10.0.1.2:23000 respectively.

This would be the NS config for the SGSN(s):

.Example: NS configuration example (SGSN)
----
ns
 bind udp local
  listen 10.0.0.1 23000 <1>
 nse 101 <2>
  ip-sns 10.0.1.1 23000 <3>
 nse 102
  ip-sns 10.0.1.2 23000
----
<1> Define the local IP/port from which to connect
<2> Define an NSE with NSEI
<3> Use IP-SNS to connect to the SGSN

=== Configure an SGSN

Configuration of a single (non-pooling) SGSN is rather simple.

.Example: SGSN configuration example
----
sgsn 101 <1>
 name Main SGSN <2>
----
<1> Each SGSN is identified by its NSEI (same as in the NS configuration)
<2> An SGSN can optionally have a name. If none is set a default name will be used.

=== SGSN pool support

In a SGSN pool, osmo-gbproxy is facing the problem of dividing the downlink
capacity of a cell towards the SGSN.  The BSS advertises the per-BVC capacity
by means of the BSSGP FLOW-CONTROL-BVC messages, but as there are multiple
SGSN in a pool, they all have to share / divide that total capacity.

By default, osmo-gbproxy advertises the full capacity to _each_ of the SGSN
pool members, which results in significant over-provisioning and can lead to
overload situations.

The administrator can configure the _percentage_ of the overall BSS-advertised
capacity that shall be reported to each pool member SGSN using the
`pool bvc-flow-control-ratio <1-100>` configuration command.

A setting of 100 means that each pool member is informed of 100% of the
BSS side capacity.

A setting of 25 means that each pool member is informed of 25% of the
BSS side capacity.  This would make most sense in a set-up with four
SGSN of equal share.

More complex capacity division schemes are so far not supported by
osmo-gbproxy.