[VoiceOps] High Quality, Reliable Voice via the Internet / SIPNOC

Mark R Lindsey, ECG lindsey at e-c-group.com
Mon Jun 9 21:45:23 EDT 2014

On Mon, Jun 9, 2014 at 4:14 PM, Alex Balashov <abalashov at evaristesys.com>

> On 06/09/2014 02:50 PM, Mark R Lindsey wrote:
>> 2. Increase the ptime from 20 ms to 30-40 ms to reduce packet-drop
>> exposure
> Or does this thesis lean on countervailing tendencies, such as overall
> reduced PPS in a higher ptime scenario?

You're on the right track with ptime. The theory idea is that:

(A) Most packet loss is due to congestion

(B) When congestion occurs the router selects a packet to drop

(C) The routers pick a packet to discard more-or-less at random

(D) Therefore, A 180 byte packet is just as likely to be dropped as a 1500
byte packet.

(E) A ptime=20 generates twice the packets as ptime=40, and therefore
ptime=20 has twice the exposure to the discards

(F) You can reduce your exposure to discards by reducing the number of
packets you have in the queue.

(G) Reduced discards mean better audio quality.
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