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Feature #6095

closed

Feature #5759: Support for Mobility between SGSN (2G/3G) and S-GW (4G)

osmo-sgsn: Use/validate RIM Routing Address (Discriminator) IE from RAN Information Relay msg

Added by pespin 8 months ago. Updated 4 months ago.

Status:
Resolved
Priority:
Normal
Assignee:
Category:
GTP interface
Target version:
-
Start date:
07/12/2023
Due date:
% Done:

100%

Spec Reference:
TS 29.060

Description

Relevant spec section: TS 29.060 7.5.14 RAN Information Management Messages

Also interesting:
  • 3GPP TS 23.401, sections "5.6 Network Assisted Cell Change" and "5.15 RAN Information Management (RIM) procedures", "Annex D"

osmo-sgsn is currently ignoring the "RIM Routing Address" and "RIM Routing Address Discriminator" IEs when handling "RAN Information Relay" coming from GTPv1C (peer MME).
Instead, it is parsing the "RAN Transparent Container" and using the content inside it to always find out the destination of the message in order to relay it.
This is unexpected, since the "RAN Transparent Container" should in theory not be looked at.

Hence, we should be instead looking at "RIM Routing Address" and "RIM Routing Address Discriminator" IEs to know the destination address and hence know if we have to drop the message, or forward it to a specific PCU.
Since those IEs are optional, if not providing then we can keep the logic to look inside the container.

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