[[smscb]]
== SMSCB (Cell Broadcast)

OsmoBSC supports SMS Cell Broadcast (SMSCB) services (CBS).  This
includes the CBSP protocol to interact with a CBC (Cell Broadcast
Centre) such as OsmoCBC, as well as the scheduling of SMSCB messages on
both the BASIC and EXTENDED CBCH and transmission of related RSL
messages to the attached BTS.

More high-level information can be found at
https://en.wikipedia.org/wiki/Cell_Broadcast and the related
specification is <<3gpp-ts-23-041>>.

In order to use SMSCB with OsmoBSC, you will need to

* Configure the CBSP server and/or client
* Use a channel combination including a CBCH on the BTSs

=== Enabling a CBCH channel combination

On the Um interface, SMSCB are transmitted via the CBCH (Cell Broadcast
Channel).  The CBCH is a separate downlink-only logical channel which
must be activated on any of the BTSs requiring CBSP support.

The channel combination is configured in the `timeslot` node of each TRX.

The two `phys_chan_config` supporting CBCH are `CCCH+SDCCH4+CBCH` and
`SDCCH/8+CBCH`.  Please note that the CBCH steals one of the SDCCH, so
a SDCCH/4 will only have three remaining SDCCH, and a SDCCH/8 will
have only seven remaining SDCCH.

=== Configuring the CBSP connection

CBSP is the protocol between BSC and CBC.  It operates over TCP.

According to 3GPP TS 48.049, a BSC typically operates as a TCP server,
and the CBC connects as TCP client.  This would require the CBC to have
out-of-band knowledge of all the BSCs in the network (and their IP
addresses).

In order to comply with the specifications, OsmoBSC supports this mode
of operation as CBSP TCP server.  However, to make network operation and
configuration more simple, it also can operate in TCP client mode,
connecting to the CBC.  This way the all the BSCs need to know is the CBC IP
address, but not vice-versa.

The BSC can operate both CBSP TCP server and CBSP TCP client mode in
parallel.

The CBC related configuration of OsmoBSC can be found in the `cbc` configuration
node of the VTY interface.

.Example: Configure CBSP TCP client to connect to CBC at 1.2.3.4:48049
----
OsmoBSC> enable
OsmoBSC# configure terminal
OsmoBSC(config)# cbc
OsmoBSC(config-cbc)# remote-ip 1.2.3.4
OsmoBSC(config-cbc)# remote-port 48049
OsmoBSC(config-cbc)# end
----

.Example: Disable CBSP TCP client
----
OsmoBSC> enable
OsmoBSC# configure terminal
OsmoBSC(config)# cbc
OsmoBSC(config-cbc)# no remote-ip
OsmoBSC(config-cbc)# end
----

.Example: Configure CBSP TCP server to listen for CBC at 127.0.0.2:9999
----
OsmoBSC> enable
OsmoBSC# configure terminal
OsmoBSC(config)# cbc
OsmoBSC(config-cbc)# listen-ip 127.0.0.2
OsmoBSC(config-cbc)# listen-port 9999
OsmoBSC(config-cbc)# end
----

For more details on the available configuration commands, please check the OsmoBSC VTY Reference.