== CBSP Procedures

=== List of Procedures

The following tables list the CBSP procedures used by the OsmoBSC BSC-CBC interface,
grouped by their level of compliance with 3GPP TS 48.049.

==== Procedures Compliant With TS 48.049

Specific additions and limitations apply, see the linked sections.

.Procedures compliant with TS 48.049
[options="header",cols="10%,20%,40%,30%"]
|===
| TS 48.049 § | This document § | Procedure | Originated/Terminated by OsmoBSC
| 7.2 | <<PROC_WRITE_REPLACE>> | Write-Replace | Terminated
| 7.3 | - | Kill | Terminated
| 7.5 | - | Message Status Query | Terminated
| 7.7a | <<PROC_KEEP_ALIVE>> | Keep Alive | Terminated
| 7.8 | <<RESTART_IND>> | Restart Indication | Originated
|===


[[PROC_WRITE_REPLACE]]
===== Write-Replace

Procedures for _Write_ and _Replace_ of CBS messages as per 3GPP TS 48.049 Section 7.2.2.2
are fully supported.

Procedures for _Write_ and _Replace_ of ETWS messages as per 3GPP TS
48.059 Section 7.2.2.2 are fully supported.  Transmission of the ETWS
Primary Notification is implemented as follows, assuming related support
is present in the related BTS and PCU software (true for OsmoBTS >= 1.2.0
and OsmoPCU >= 0.8.0):

* broadcast to MS in idle mode / packet idle mode by sending a
  vendor-specific A-bis RSL message to each affected BTS.  A
  vendor-specific mechanism is needed as 3GPP TS 48.058 does not specify
  any standard message for this.  See the section on _Osmocom ETWS
  Command_ in <<osmobts-abis-spec>> for more details.
* broadcast to MS in dedicated mode by sending the ETWS PN via every
  currently active dedicated channel (SDCCH, FACCH) within the affected
  BTSs.

As an additional clarification to 3GPP TS 48.049, OsmoBSC rejects (via
WRITE-REPLACE FAILURE) any _write_ procedure for an emergency message if
there already is another emergency message active in a cell.  The
_replace_ procedure must be used (by specifying the _Old Serial Number
IE_) if the only existing emergency message of a cell shall be replaced.

[[PROC_KEEP_ALIVE]]
===== Keep-Alive

The Keep-Alive procedure is implemented only in as far as incoming
Keep-Alive requests are responded to.

The BSC currently does not use the _Keep Alive Repetition Period IE_.
This is permitted as 3GPP TS 48.049 states the information _may_ be used
by the BSC.

[[PROC_RESTART_IND]]
===== Restart Indication

Restart indications are currently only sent whenever any BSC-CBC link is
established.  They are not sent once subsequent cells become available
or are re-initialized due to A-bis link failure.

However, CBSP state for both CBS and Emergency messages is kept
persistent in the BSC and if cells reboot / restart during the duration
of a CBS / emergency message, they will resume broadcasts as expected.


==== Procedures Not Implemented by OsmoBSC

.3GPP TS 48.049 procedures not implemented by OsmoBSC
[options="header",cols="30%,40%,30%"]
|===
| TS 48.049 § | Procedure | Originated/Terminated by OsmoBSC
| 7.4 | Load Status Enquiry | Terminated
| 7.6 | Set DRX | Terminated
| 7.9 | Failure Indication | Originated
| 7.10 | Error Indication | Originated
|===