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Bug #5688

open

osmo-bts-sysmo and osmo-bts-trx use different GSM-HR RTP packet format

Added by dexter 15 days ago. Updated 14 days ago.

Status:
New
Priority:
Normal
Assignee:
Category:
-
Target version:
-
Start date:
09/20/2022
Due date:
% Done:

0%

Spec Reference:

Description

When comparing the RTP packet format that is used by osmo-bts-sysmo and osmo-bts-trx it becomes obvious that osmo-bts-trx uses RFC5993 (35 byte payload), while osmo-bts-sysmo uses TS 101.318 (34 byte payload). The reason for this is that osmo-bts-trx is using the encoding function in libosmocore gsm0503_coding.c, while osmo-bts-sysmo uses the encoder and decoder functions of its DSP.

We should make sure that all osmo-bts versions always use the same format. For osmo-bts-sysmo that would mean that we need to convert to RFC5993. The conversion is simple, we just need to prepend one byte ToC at the beginning of each RTP packet we emit.

In the receiving path we should make sure that both formats are accepted. Since the BTS knows when GSM-HR is in use we could just check the length of the packets to distinguish which of the two formats we receive

Optionally it might also make the format configurable. Preferably using a proprietary RSL IE so that the config value can be in the osmo-bsc.cfg.

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