[BitTorrent] Seeds and downloader free-riding problem in BT.

Vitenka vitenka at ntlworld.com
Wed Mar 9 13:07:52 EST 2005

>  Is there any other difference between seeds and downloaders? 

No.  A seed is just a peer who happens to have a full copy of the file(s).

However some clients use slightly different logic when deciding which 
peers to send to whilst seeding than while downloading.

>  We are considering the free-riding part of bittorrent. How could 
> seeds decide which peer to upload(unchoke) because no peer have a 
> download rate to the seeds? In contrast downloader (peer A) will 
> unchoke the fifth peer depending on the downloading rate to Peer A 
> every 30 seconds. 

Seeds optimistically unchoke random peers.  They CAN choose to do more 
(eg. send out pieces which are rare in the swarm, or send to peers with 
few pieces)

>  Does the tracker site discriminate the seeds and downloader?

Yes, but only for stats purposes.

> What kind of strategy for the seeds to decide which peer to upload to? 

By default, random selection amongst all peers the tracker has told you 

> As we know it is not necessary for other peers to 
> download sth to the seeds and it seemed that it is good idea for the 
> free-rider to take advantage of that fact and they prefer to be 
> served by the seeds and wait in that kind of queue( If they can 
> select other peer to download). If the free-rider is denied by other 
> peers continusly (they have 20% chance to be served of course), most 
> of free-rider will like to turn to seeds to continue their free-
> riding because the success chance is larger than 20%. Am I right? 

Yes - if you do not upload then you will (in the limit) only be able to 
download from seeds.  There are usually less seeds than normal peers - 
so a 'free rider' will get a slower download rate than a normal peer.

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