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Feature #3682

closed

Intra-domain connection of OsmoBSC to multiple MSCs

Added by laforge over 4 years ago. Updated over 2 years ago.

Status:
Resolved
Priority:
Normal
Assignee:
Category:
A interface
Target version:
-
Start date:
11/06/2018
Due date:
% Done:

100%

Spec Reference:
TS 23.236

Description

3GPP TS 23.236 specifies the "Intra-domain connection of
Radio Access Network (RAN nodes to multiple Core Network (CN) nodes".

This introduces two concepts:
  • a deviation from the strict hierarchy of classic GSM architecture where a BSC is always only served by one MSC
  • the introduction of "MSC pools" where a pool of multiple MSCs cover one geographic service area.

This appears to be functioning by dividing the TMSI range between different MSCs, using the higher-order TMSI bits to identify the MSC and the lower-order TMSI bits for the actual TMSI within that MSC.

Section 5.3 describes the functions required to be implemented in the BSC.
  • NAS Node Selection Function
    • investigate Initial L3 message at RR establishment
    • if TMSI is present, extract NRI and route requeest to MSC for that NRI
    • if only IMEI or IMSI is present, or no route for that NRI, send to 'ramdom' MSC (load distribution)
  • when any MSC sends a PAGING REQUEST, store the IMSI <-> MSC relation as long as the paging is active
    • any incoming response to that paging gets routed to the MSC that has issued the paging

Files

142217065-MSC-Pool.pdf View 142217065-MSC-Pool.pdf 605 KB description of MSC pool feature laforge, 09/04/2019 09:01 AM
success_first_msc_pooling.tgz success_first_msc_pooling.tgz 509 KB pcap and config files of first working MSC pooling neels, 05/26/2020 11:24 PM

Checklist

  • Function for deriving NRI from TMSI
  • storing of Global-CN-ID when receiving paging from MSC; routing paging response to that Global-CN-ID
  • VTY configuration of number of TMSI bits reserved for NRI
  • VTY configuration of NRI <-> MSC SCCP address mappings
  • ability to establish A to multiple MSCs simultaneously
  • NAS Node Selection Function
  • figure out how to test with multiple MSCs in ttcn-bsc-tests
  • ensure NULL-NRI config and behavior
  • add counters for MSC pooling
  • ttcn3 tests
  • code review and merge patches

Related issues

Related to osmo-gbproxy - Feature #4472: Intra-domain connection of OsmoGBPROXY to multiple SGSNs (pooling)Resolveddaniel03/29/2020

Actions
Related to OsmoBSC - Feature #3454: disable/constrain/hide "multiple msc" conceptRejectedneels08/08/2018

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