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Feature #4549

closed

Emergency Call Priority / Pre-Emption

Added by laforge over 2 years ago. Updated almost 2 years ago.

Status:
Resolved
Priority:
Normal
Assignee:
Category:
-
Target version:
-
Start date:
05/12/2020
Due date:
% Done:

100%

Spec Reference:

Description

This is entrely a BSC feature. The BSC
  1. notices there is a pending emergency call (RACH request with CHREQ_T_EMERG_CALL)
  2. notices it cannot allocate a suitable TCH/F or TCH/H channel
  3. must pick any random non-emergency TCH on he same cell and terminate it
  4. assign that TCH to the MS that has send the emrergency related RACH request

As OsmoBSC currently performs channel allocation "synchronously" (i.e. within the context of the received RACH request, without any delays), this must be extended. We need to introduce a queue for asynchronous processing of RACH requests, as we hav to wait for the deactivation/re-activation of the logical channel to complete at the BTS before being able to do the IMMEDIATE ASSIGNMENT.

manual testing sidenote: OsmoMSC may not be able to process Emergency Call without SIM (no IMSI, only IMEI). This is a layer3 feature and hence should be suppored by the regular operator MSC. There are no changes / extensions on the RAN side to support this. In some jurisdictions, like Germany, emergency calls without SIM/IMSI must be rejected by the operator anyway. I'm just mentioning this for testing of emergency calls: Make sure you test them with a SIM inserted.


Files


Checklist

  • BSC_Tests.ttcn case simulating fully loaded BTS with incoming emergency call RACH req
  • BSC logic pre-emption (see update 1)
  • manual end2end verification (with modem + coaxial cabling to BTS)
  • osmo-gsm-tester test (hand over to pespin?)

Related issues

Related to OsmoGSMTester - Feature #4543: Emergency call suport in osmo-gsm-testerResolveddexter05/12/2020

Actions
Related to libosmocore - Bug #4819: Wrong RLL ERR IND sent during LAPDm re-establishment proceduresResolvedpespin10/19/2020

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