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Many a times I have seen while downloading a .torrent file the other client either snubs or not interested. Does anybody know why this happens? The possible reasons for it ? I have seen this both in small and large swarms so it doesn't seem to have anything either with the swarm size or how many seeders vs leechers it has (or does it ? )

Now AFAIK, the upload speed is directly symmetrical to your download speed (at least in some clients) so if you give 50 KB/s as your upload ratio then you would get the same or better download speeds and vice-versa. Does that also play into the decision-making of both the clients?

AFAIK after the tracker has made the hand-shakes with both the clients (as a broker in-between the number of seeders vis-a-vis the leecher the rest is to the individual clients.) its work is over and it's upto the clients to negotiate with each other.

Any explanation to what goes on as a negotiation between the clients and what factors are at play would be nice, mostly when one of them has pieces and is either choked or not interested - this is in public tracker where ratios don't really have a role to play.

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The question was edited. This is an answer to the original question:

Chokes, not interested peers in bittorrent, why does it happen?

If another peer is not interested, it's because your peer doesn't have any pieces that the other peer want.

If another peer is choked that means either that it's not interested, or that your peer have one or more pieces that the other peer is interested of and want to download from your client, but your client is busy uploading to some other clients.

From the BitTorrent Protocol Specification:

Connections contain two bits of state on either end: choked or not, and interested or not. Choking is a notification that no data will be sent until unchoking happens. The reasoning and common techniques behind choking are explained later in this document.

Data transfer takes place whenever one side is interested and the other side is not choking. Interest state must be kept up to date at all times - whenever a downloader doesn't have something they currently would ask a peer for in unchoked, they must express lack of interest, despite being choked. Implementing this properly is tricky, but makes it possible for downloaders to know which peers will start downloading immediately if unchoked.

Connections start out choked and not interested.

AFAIK, the upload speed is directly symmetrical to your download speed

No, that is not correct.
In some cases the tit for tat mechanism will make it appear to be somewhat symmetrical. If you upload more to others, they will upload more to you. If your upload is very slow the other peer may temporary snub you until you improve your upload speed.

From the µTorrent User Manual:

Snubbed
This word describes the state of a BitTorrent connection. A connection is marked as snubbed when the client has not received anything over the connection for an extended period of time.

AFAIK after the tracker has made the hand-shakes with both the clients (as a broker in-between the number of seeders vis-a-vis the leecher the rest is to the individual clients.) its work is over and it's upto the clients to negotiate with each other.

That is correct.

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    just modified the question, I was more interested in the snubbing part, thought choking was the same, now I understand that the term has a different meaning altogether.
    – shirish
    Mar 5, 2015 at 21:23
  • Also keeping the question a day or two before accepting your answer in the hopes that somebody else also answers it.
    – shirish
    Mar 5, 2015 at 21:40
  • @shirish, you should mark the answer straight away, as I'm about to close the question!
    – Dave
    Mar 6, 2015 at 9:29

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