[cisco-voip] ATA - Late packets

[Mark R. Lindsey]

I'm not sure there's an official definition, per se. But, in case it 
helps, it's a common term: a late packet is one that arrived too late 
to be played back. Packets in a network suffer from end-to-end delay 
(latency), and this latency varies for each RTP packet. Each packet 
includes timing information, representing the time it was "recorded", 
relative to the beginning of the stream. If a packet arrives at the 
receiver (the playback device) after the latest time it could be 
played, it would be considered late.

Late packets represent a loss; usually this causes a brief moment of 
silence on the playback side. Late packets can also contribute to 
congestion collapse: they use resources in the network without doing 
any useful work.

Latency -- and in particular variation in latency (jitter) -- is 
usually the cause. Jitter buffers are used to allow packets to arrive 
late by a certain amount; a large jitter buffer allows for more jitter, 
but it causes more delay. The simplest is a fixed-length jitter buffer, 
which usually works, but can be susceptible to significant changes 
through the latency. A variable-length jitter buffer attempts to adapt 
to the latency-at-the-moment

Ketan Mayer-Patel's of UNC-CH has a fine course in Multimedia 
Networking; he goes into these issues in a lot of detail. 
http://www.cs.unc.edu/Courses/comp249-s05/

Mark R. Lindsey  |  ECG  |  +1-229-316-0013  |  lindsey at e-c-group.com

On Mar 8, 2005, at 3:33 AM, Vincent De Keyzer wrote:

> Hello,
>
>  
>
> does anybody know the exact definition of a “late packet” on the “RTP 
> Statistics” page of the web interface of ATA modules running version 
> 3.02?
>
>  
>
> Vincent
>
>  
>
>  
>
>  
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