[asterisk-users] Diagnosing poor call quality

[Chris Bagnall]

Eric said:
> This should be a FAQ. Set the RTP packet size on the SPAs to .2
> instead of .3

Thanks for the suggestion. I've logged into the offending devices and set
both to .2. I'll see how it goes for 48 hours or so.

I've looked at the Elmeg ip290's and they are set to 20ms from factory, so I
don't think that's the issue there.

Michael said:
> The advertised datarate (8mb/448k) are the speeds at which the
> circuit between the customer and the central office is clocked and
> has no relationship with *effective* throughput.

I have run a few speed tests from the sites in question (iperf to the
machine in the datacentre) and I'm consistently getting around 380k upstream
and 5.5mbit downstream, even during peak hours. Some distance away from the
quoted speeds, but still plenty enough to support 4 SIP devices using g729
(which should be about 30kbit/sec per device including packet overheads).

> So beware of VoIP over DSL.  Your users need to be aware of the
> tradeoffs between the cost of DSL vs. T1 and the effect on call
> quality.  

Alas, T1 for net traffic here in the UK is insanely expensive. DSL in its
various forms is about the best we get, and SDSL with low contention ratios
(1:1, 5:1, etc.) is only available in a few exchanges in major cities.

> Chris, if your customers are in the western US then please contact me
> about dedicated circuits. 

About 4500 miles away. :-) Thanks for the offer anyway though.

Any further thoughts would be gratefully appreciated, especially for the
site with the Elmegs.

Regards,

Chris
-- 
C.M. Bagnall, Director, Minotaur I.T. Limited
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