[bittorrent] packet loss
andrew at bramp.freeserve.co.uk
Tue Apr 19 05:35:48 EDT 2005
I thought I'll go off on a tangent again to provoke discussion :)
I don't know typical numbers for packet loss, but I can tell you some
properties of it. Loss isn't constant over a length of time, its bursty .
So for 10 minutes you could have 0% then for the next 10 seconds you have
100% (losing in your example 20 packets).
This behaviour is important if you decide to recover from loss... Two simple
methods I know of solving loss is
Pre-emptive by using Forward Error Checking (FEC)  - This is where you
add 10% for example to each UDP packet containing redundant data that allows
you to re-construct ~10% of missing packets.
Re-transmission - You re-request any lost packets, this can be done by not
acking (this is what TCP does), or by explicitly re-requesting.
Now because of the bursty nature of internet loss, FEC doesn't perform well
in quickly recovering data, so in most cases its not very useful. However
re-transmission takes time so that is also not very quick but might be the
better option to guarantee complete delivery. However there are ways to
improve FEC in bursty conditions .
 PROMISE: Peer-to-Peer Media Streaming Using Collect Cast (2003), M.
Hefeeda and A. Habib and B. Boyan and D. Xu and B. Bhargava
 Theory and Practice of Error Control Codes, R. E. Blahut, Jan 1983
 Distributed Video Streaming with Forward Error Correction (2002), T.
Nguyen and A. Zakhor
----- Original Message -----
From: <larytet.8708132 at bloglines.com>
To: <bittorrent at lists.ibiblio.org>
Sent: Tuesday, April 19, 2005 3:57 AM
Subject: [bittorrent] packet loss
>i kept UDP session open for ~20 hours. 60 bytes of dummy payload was sent
> every 0.5s across two ISPs. Both ISPs are in the US. both connections are
> broadband. packet loss is under 0.5% (~600/130,000). probably real packet
> loss is ~1% because i measured packet loss according the number of missing
> Is this packet loss ratio typical for the modern networks ? or is
> it relatively low/high ?
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