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Bug #5852

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osmo-sgsn: Keep TLLI<->NSEI+BVCI relation knowledge in BSSGP layer

Added by pespin about 1 year ago. Updated about 1 year ago.

Status:
New
Priority:
Normal
Assignee:
-
Category:
Gb interface
Target version:
-
Start date:
01/11/2023
Due date:
% Done:

0%

Spec Reference:

Description

Related specs:
BSSGP = 3GPP TS 48.018
LLC = 3GPP TS 44.064
SNDCP = 3GPP TS 44.065

Right now we are passing BVCI and NSEI knowledge BSSGP<->LLC<->SNDCP<->processing, and updating the relation TLLI<->{NSEI,BVCI} really high in the stack (mmctx.gb.bvci/nsei).
According to specs, it seems the knowledge of the relation of an MS and its current NSEI+BVCI should be kept in the SGSN before reaching the LLC layer processing.

<pespin> I'm trying to understand better how the BVCI/NSEI are supposed to be tracked by the SGSN.
<pespin> Right now we are passing BVCI and NSEI in msgb_bvci() and msgb_nsei() up to the GMM layer, but that looks wrong from what I read on the specs
<pespin> since I don't see anywhere that BVCI and NSEI should even be passed to LLC layer
<pespin> so my understanding is that the good thing to do would be to track BVCI and NSEI based on TLLI in the BSSGP layer itself? As in a hashmap of TLLI->{NSEI,BVCI} which is updated everytime we receive a BSSGP pdu and looked up every time we need to send a message to a given TLLI on downlink
<pespin> TS 48.018 6.2 "he SGSN shall obtain the BVCI, the NSEI, and in the case of an IP sub-network may obtain
<pespin> the LSP and the NS Change IP endpoint, from the underlying network service; the BVCI and the NSEI are not visible in
<pespin> the UL-UNITDATA PDU." 
<pespin> in BSSGP spec the equivalent primitives (BSSGP-{U,D}L-UNITDATA contain BVCI and NSEI, but there's a note in TS 48.018 5.3:
<pespin> "NOTE: The parameters in the BSSGP-DL-UNITDATA and BSSGP-UL-UNITDATA primitives that are not
<pespin> included in the corresponding primitives in 3GPP TS 44.064 are provided or extracted by some
<pespin> intermediate function out of the scope of the present document." 
<pespin> so sounds like we need to cache the BVCI and NSEI in between BSSGP and LLC as I suggested?
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