Cellular Network Infrastructure » cni-legacy » OpenBSC

the interesting question is: how does the format look on Abis? According to my reading of the specs:

• L3 Info TLV length given by TS 48.058 for SACCH FILLING is "22", where 1 byte is tag, and 2 bytes are length, i.e. 19 bytes left for actual payload
  • this indicates the full 19 bytes including pseudo-length are to be included
• The actual SI5 / SI6 definitions in TS 44.018 also include the L2 pseodo length as part of the SI message

I also found some old pcap files of a proprietary ip.access BSC, which confirms that assumption.

• OsmoBSC is lacking the L2 pseudo-length field as first byte of the L3 INFO
• the wireshark packet-rsl.c decoder is broken as it assumes no l2 plen
• we impleemnted our code to comply with wireshark, inheriting the bug
• the wireshark LAPDm decoder was "fixed" by me to also comply with that broken assumption

So now, wiershark RSL, wiershark GSMTAP/LAPDm and OsmoBSC are all broken. yay. :(

This appears to be the root of all evil:

commit 6f0e50c8337355eb59033903ede9ab6528890835
Author: Max <msuraev@sysmocom.de>
Date:   Wed Apr 12 15:30:54 2017 +0200

    Prepare for extended SI2quater support

as it overwrites the l2_plen just after it was written.

proposed (but yet untested) patch at https://gerrit.osmocom.org/7220

Just tested with this patch as well as https://gerrit.osmocom.org/#/c/7218/ (it's already merged to osmo-bts master, but let me mention that it was used in the test) and: YES! Finally the measurement reports survive a handover! No matter what I do, the neighbor lists are reliably populated. Excellent! Let me add a few percent there.

Hi Harald,

this is probably related to:

https://lists.osmocom.org/pipermail/openbsc/2017-December/011545.html

my plan is to revert the:

https://git.osmocom.org/osmocom-bb/commit/?id=1a8a80aeae4c2e5c870ae5b032d9a6ae60b67ac8

because I was referring an outdated spec version and the way of Osmocom stack.

ok, have merged the related patch now. Let's abuse this ticket until wireshark patches are written + tested.

openbsc.git fix submitted in https://gerrit.osmocom.org/#/c/7226/

My question was lost because the 7226 was merged, but anyway,
laforge, what do you think about introducing a new structure with l2_plen?

wireshark patch for RSL now proposed as https://code.wireshark.org/review/#/c/26797/

LAPDm patch submitted at https://code.wireshark.org/review/#/c/26798/1 - waiting for review.

both wireshark patches merged.