LCLS directly between BTSs
So far, we have implemented LCLS on the BSC level, i.e. in case of a local switch, the RTP stream still goes from BTS A to the BSC-colocated MGW and from there to BTS B. This removes the RTP/voice from A, but not from the Abis side.
In deployments where there are e.g. 3 BTS (A,B,C) at one site, back-hauled via Abis to a BSC in a remote data center, we want the voice to go directly between BTS A and BTS B, without going to the MGW at the BSC.
This basically means that we close the loop not inside our osmo-mgw via MGCP, but that we close it between the two involved BTSs.
Even in a single-remote-BTS use case, this helps in cases where both calling and called subscribers are attached to that same BTS.
On a related note: right now TTCN-3 TC_lcls_connect_clear() fails due to commit 6fe125294b219a519c77f7140de26870d17bf40a in OsmoBSC. Reverting just this commit doesn't fix it though so it's also affected by some changes in related commits as well.
The failing part in TC_lcls_connect_clear is probably
CONN_A.receive(tr_RSL_DATA_REQ(?, tr_RslLinkID_DCCH(0), l3_rr_chan_rel)) due to missing "DATA REQuest (DTAP) (RR) Channel Release" packet - see difference in .pcap from https://jenkins.osmocom.org/jenkins/view/TTCN3/job/ttcn3-bsc-test/369/ and https://jenkins.osmocom.org/jenkins/view/TTCN3/job/ttcn3-bsc-test/370/
- Checklist item add TTCN tests for RSL MDCX added
- Checklist item add RSL MDCX to BSC LCLS added
- Checklist item handle LCLS-MGW in handover added
- Checklist item handle LCLS-BTS in handover added
- Checklist item add TCCN test handover with LCLS-MGW added
- Checklist item add TCCN test handover with LCLS-BTS added
- % Done changed from 30 to 20
- % Done changed from 30 to 40
- LCLS break works as intended (needs corresponding MSC code)
- both variants work fine when closing the loop between phones connected to different BTS (using osmocom-bb "stick" feature to use explicit ARFCN)
Remaining patches: libosmocore 7, OsmoBSC 4.