Subject: [ledbat] Impact of Ledbat on BitTorrent completion time

From: Dario Rossi <[email-masked]>
Date: Fri, 17 Jun 2011 14:42:39 +0200

Dear all,

we want to share on the list some recent results (though not necessarily 
useful to finalize the draft, hence in a separate mail)

we have been doing some ns2 simulation on  swarm scenarios, where peers 
implementing the BitTorrent protocol are running Ledbat (or TCP) 
congestion control, focusing on the completion time of individual peers 
-- instead of fairness, for once ;)

we used the ns2 BitTorrent implementation provided in [1] and our own 
ns2 Ledbat implementation (which is not uptodate with the latest draft 
specification), emulating reasonable settings of the 
bt.transp_disposition flag (i.e., peer accept both incoming TCP and 
Ledbat for downlink, but only use TCP xor Ledbat in uplink)

results of our investigation are available in [2], shortly:
*  no difference can be seen in homogeneous swarm (i.e., all peers run 
TCP,  or all peers run Ledbat)
*  in heterogeneous swarm (i.e., half TCP, half Ledbat), peers running 
Ledbat in their uplink have a shorter completion time.
    We argue  this to be due to a shorter queuing delay in the Ledbat 
case w.r.t TCP, so that signaling of Ledbat peers is
    faster and they can opportunistically "steal" download slots (by 
hitting earlier the  request queue of other peers)  to
    self-congested peers using TCP in uplink.

We hope these findings are of interest for the wg;  if you have any 
comment, or are aware of similar studies, please do not hesitate to 
share them on the list

Best regards,
D.

[1] K. Eger, T. Hoßfeld, A. Binzenhofer, and G. Kunzmann,
"Efficient simulation of large-scale p2p networks: packet-level vs. 
flow-level simulations,"
in ACM UPGRADE-CN, Monterey, CA, Jun 2007.

[2] C. Testa and D. Rossi,
*The impact of uTP on BitTorrent completion time* 
<http://www.enst.fr/%7Edrossi/paper/rossi11p2p.pdf> .
In /IEEE Peer to Peer (P2P'11)/, Kyoto, Japan, September 2011.

-- 
  Oo    Associate Professor
   >     TELECOM ParisTech
  ~     (formerly ENST)

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