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Random thoughts regarding segmented downloading...


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Hi !

First a disclaimer: I really don't know anything about the ins & outs of BitTorrent or the protocols and other underlying technologies.

That said, I have often noticed that some contents are not completely available in the network, rather there are dozens of nodes having basically the same segments of a given file. So, for less popular contents there seems to be an availability issue.

So I was wondering what exactly are the underlying heuristics that determine which segments are downloaded (first) by a client?

As a programmer, but without any further background knowledge whatsoever, I would personally assume that there needs to be some sort of "attractivity" system in place in order to determine what shall be downloaded?

Something that is based on "how available" a file is (or rather its segments), so that those segments of a file that are least available are basically retrieved first, to ensure data/segment propagation across the network by using the concept of maximum redundancy?

I would expect something like this to be based on some sort of "availability score" for files and their segments, basically determining which segments are "most available" (i.e. widely shared by many users) and which ones aren't (yet).

Furthermore, it would probably make sense to consider the additional segment state of "currently being transferred", so that a file availability score would be based on segment availability being categorized into:

[*] completely available in network - shared by x>1 peers

[*] partially available in network - currently being downloaded by x>1 peers

[*] available only via x=1 peer

(for partially available segments it might also make sense to take their completion status into account)

Also, assuming that high content availability is a goal of bittorrent, wouldn't it make sense to consider honoring users sharing "less available" (underrepresented contents; lacking segments) by improving their allowable max download quota (i.e. marking such contents in the main window to illustrate lack of availability in the network and the resulting option to improve availability?)

As I said, I really don't know what's already done behind the scenes and what isn't- I would just appreciate some basic background information regarding the above mentioned points, I will be more than happy to be referred to a corresponding website or document.

Thank you & regards



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