Release Access Bearer Request


After Yesterday post on deletion of session and bearer in MME/SGW, later I am bit confused about Release Access Bearer Request, why again one more message to delete a bearer with a different name "release" :-) . So I have done some research to understand it which I am sharing with you below. Hope it will help you all.

. Release Access Bearer Request

What spec 29.274 says: 

The Release Access Bearers Request message shall sent on the S11 interface by the MME to the SGW as part of the S1
release procedure.

The message shall also be sent on the S4 interface by the SGSN to the SGW as part of the procedures:
- RAB release using S4
- Iu Release using S4
- READY to STANDBY transition within the network


List of RABs

Shall be present on S4 interface when this message is
used to release a subset of all active RABs according to
the RAB release procedure.
Several IEs with this type and instance values shall be
included as necessary to represent a list of RABs to be
released.

23.401 5.3.5 says

The MME sends a Release Access Bearers Request message to the S-GW that requests the release of all S1-U bearers for the UE. This message is triggered either by an S1 Release Request message from the eNodeB, or by another MME event.

The S-GW releases all eNodeB related information (address and TEIDs) for the UE and responds with a Release Access Bearers Response message to the MME. Other elements of the UE's S-GW context are not affected, means MME-HSS and MME-SGW interface is intact here and S-GW inside it retains the S1-U configuration that the S-GW allocated for the UE's bearers, SGW only removed the connection between SGW and serving ENB.

My Understanding:
Release Access Bearer Request used as part of S1-release procedure, it will remove all the active bearers (both default and dedicated) temporarily between SGW and ENB S1-U interface due to user inactivity(or due to some other reason) and session between S5/S8, S11, S6a will remain intact or you can say it is in preserve mode(not active). It is done to save some resource of the MME, so that MME can assign same user plane resource to other users(For network operators radio resource and user plane S1-U resource is very precious for them). So once UE context removed then Release Access Bearer Request will remove all the bearers between SGW and ENB. It is not dependent on any EBI or LBI and spec is also not telling to include any EBI or LBI value, but it can be vendor dependent. If you check any network side logs you may not get any IE related to EBI/LBI in Release Access Bearer Request messages.

After reading my post, please post your comment below, if still some doubt left in you ;-)





Comments

  1. Pilot-PoojaFebruary 3, 2021 at 1:43 PM

    what are the other MME events that can trigger it, please explain that too.
    USer inactivity in what sense, not clear?

    ReplyDelete
  2. uncesna-aMay 21, 2022 at 3:43 PM

    uncesna-a Jose Kadlecik Here
    inasruduf

    ReplyDelete

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