BTS support for generating ETWS primary notifications
ETWS (Earthquake and Tsunami Warning System) doesn't only use SMSCB, but also contains parts that ensure notification of all MS as quickly as possible. Specifically, this means
- there's a special PAGING REQUEST TYPE 1 sent on all sub-channels of the PCH
- there's a PACKET APPLICATION INFO message sent over PACCH to all MS with TBF established
This ticket is about implementing the required features in the BTS. One of the problems is that TS 48.058 (RSL) doesn't appear to have been updated for support of ETWS.
The paging messages are not encoded by the BSC but by the BTS; RSL PAGING COMMAND contains only the MS Identity, so there's no way to send a pre-encoded message with the ETWS bits in the rest octets.
- PAGING REQUEST TYPE 1 with ETWS primary notification
- handing ETWS primary notification to PCU for transmission over PACCH
- segmentation of primary notification message
- Checklist item segmentation of primary notification message added
- % Done changed from 0 to 10
The RSL PAGING CMD is not suitable for ETWS primary notification, as it only transfers a single identity to be paged, while the ETWS primary notification is more something like "background traffic" on the PCH. It fills the PCH PAGING CMD1 rest octets with (segments of) the ETWS primary notification.
So as a result, the best option is to have a vendor-specific Abis RSL message for enabling/disabling ETWS primary notification broadcasting in the BTS downlink PCH.
The primary notification message is 56 bytes long, while the respective Paging Message Type 1 Rest Octets can only accomodate up to 127 bits in each message. As a result, the primary notification needs to be segmented (protocol supports for up to 15 segments).
We have to make sure to broadcast all segments of the primary notification message on all paging groups, for as long as requested by the BSC.
- Checklist item PAGING REQUEST TYPE 1 with ETWS primary notification set to Done
- Checklist item segmentation of primary notification message set to Done
- Status changed from New to In Progress
- % Done changed from 10 to 70
- https://gerrit.osmocom.org/c/osmo-bts/+/15417 for the main change implementing this feature
- https://gerrit.osmocom.org/c/libosmocore/+/15415 and https://gerrit.osmocom.org/c/libosmocore/+/15416 for required libosmocore changes
- https://gerrit.osmocom.org/c/osmo-ttcn3-hacks/+/15411 for the TTCN-3 functional tests covering this feature
- Checklist item handing ETWS primary notification to PCU for transmission over PACCH set to Done
- Status changed from In Progress to Resolved
- % Done changed from 70 to 100
Last bit implemented as https://gerrit.osmocom.org/#/c/osmo-bts/+/15420/, tested by https://gerrit.osmocom.org/#/c/osmo-ttcn3-hacks/+/15421/