[Freeswitch-users] FS-HA RTP state

Alex Balashov abalashov at evaristesys.com
Mon Aug 18 21:41:30 MSD 2014


Sorry for the newbie question. Regarding this:


How does FreeSWITCH pick up and resume RTP stream state in this 
scenario, vis-a-vis the RTP sequence numbers? Or does it not?

I don't really know how RTP works through the FreeSWITCH core. Based on 
the fact that this type of failover works, I am guessing that Freeswitch 
has several modes of RTP relay in a channel bridge:

(1) Where the RTP is regenerated/reoriginated with logically independent 
SSRC and sequence numbers, which would presumably be used in situations 
where invasive DSP work, transcoding and/or other heavy media 
involvement is required of the FreeSWITCH core. I assume this involves 
marshalling the audio payload onto some sort of generic internal audio 
frame bus, too.

(2) "Light" mode, analogous to Asterisk's "Packet2Packet" bridging, 
where the RTP is relayed more or less as-is between the endpoints, 
without this type of mediation. This would presumably pass through the 
endpoints' respective RTP stream properties.

Is it reasonable to assume that the call recovery functionality relies 
on #2, which would imply that the calls cannot be transcoded, use 
in-band DTMF signalling, etc?


-- Alex

Alex Balashov - Principal
Evariste Systems LLC
Tel: +1-678-954-0670
Web: http://www.evaristesys.com/, http://www.alexbalashov.com/

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