[asterisk-users] Meaning of RTT in channelstats

[Joshua C. Colp]

On Sat, May 16, 2020 at 10:58 AM Michael Maier <m1278468 at mailbox.org> wrote:

> On 15.05.20 at 14:31 Doug Lytle wrote:
> > Google says Round Trip Time
> >
> > https://www.voip-info.org/asterisk-rtcp/
>
> That doesn't answer my question (I know the abbreviation RTT). Therefore
> I'm trying again:
>
> I'm just wondering what the RTT *exactly* means. Where are the exact
> measuring points located?
>
> => How are the RTT values exactly calculated? Which values are actually
> used for?
>

The value is calculated according to the logic in the RFC[1]. Specifically
using embedded timestamps in the RTCP packets and calculated delays. The
value is presented in seconds I believe in the output.


> => What about the processing time between the inbound leg and the outbound
> leg (transcoding, ...)?
>

That has no impact within this, since it's calculated using the RTCP
traffic which is not used for media. It's really just for round trip time
of a UDP packet, not for end to end time of a single audio packet/frame
through the system.

[1] https://tools.ietf.org/html/rfc3550

-- 
Joshua C. Colp
Asterisk Technical Lead
Sangoma Technologies
Check us out at www.sangoma.com and www.asterisk.org
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