Dear Osmocom community,
About a year ago I published this specification:
https://www.freecalypso.org/specs/tw-ts-001-v010001.txt
TW-TS-001 is a spec, written in 3GPP language style, for enhanced RTP
transport of FR and EFR codec frames in an IP-based GSM RAN. I got
OsmoBTS support for this RTP extension on branch falconia/rtp_traulike,
but I never submitted it to Gerrit for mainlining: when I mentioned it
in OsmoDevCall in 2023-06, the feedback from Harald was that the
extension would need to be somehow requested from the CN via signaling,
rather than manually switched on via OsmoBTS local vty. Since then I
have familiarized myself with 3GPP specs for AoIP user place (TS 48.103
and TS 26.102 it refers to), and I see the problem with my initial
"brute force" method: when 3GPP specs explicitly call for standard RTP
formats at the AoIP interface, intentional deviations from that standard
need to be negotiated/signaled in some clean manner.
So here is my new solution:
https://www.freecalypso.org/specs/tw-ts-001-v010100.txt
https://www.freecalypso.org/specs/tw-ts-002-v010100.txt
https://www.freecalypso.org/specs/tw-ts-003-v010001.txt
There are 3 new specs in the above set:
* The new version of TW-TS-001 clarifies some deficiencies in the
original, and refers to TW-TS-003 for how the enhanced RTP format is
to be invoked at the AoIP interface.
* TW-TS-002 is a new spec that does for HRv1 codec what TW-TS-001 does
for FRv1 and EFR. The enhanced RTP payload format here is an
extension of RFC 5993, which I named super-5993.
* TW-TS-003 is an extension to BSSMAP for communicating the use of
enhanced RTP payload formats between MSC and BSS.
I will now be preparing some patches for TW-TS-003 support - see you
in Gerrit code review soon. :-)
With love and greetings from Themyscira,
Mother Mychaela