[Nottingham] Bittorrent maths

[Michael Leuty]

Top marks to SUSE who are making the entire commercial distribution of 
version 10.0 immediately available for download. RC1 was very impressive, 
so Gold Master should glister nicely.

I'm downloading it via Bittorrent while waiting for the box to negotiate 
the Atlantic, which has got me wondering about the maths of BT swarms. 
Apologies if this sounds naïve but I haven't done any maths for 30 years.

My setup is downloading at around 100KB/s and uploading at a steady 
30KB/s. I can understand that once many people have downloaded the files 
and there are a large number of seeds, there is no shortage of supply. 
Ten seeds uploading at 30KB/s can provide a download of 300KB/s to a 
newcomer, who should then stay around long enough to repay the debt. But 
what happens at the early stage when there are relatively few seeds and 
lots of peers with partly downloaded files?

I'm currently in a swarm with 5 seeds and 72 peers. Assuming that everyone 
is uploading at 30KB/s, that makes a total upload of 2,310KB/s. But if 
the 72 peers are all downloading at roughly 100KB/s, that makes a total 
download of 7,200KB/s. There appears to be a gap of just under 5,000KB/s.

Presumably, either some people are uploading considerably faster than 
30KB/s, or there is some additional input into the system, or I have 
failed to understand something. (All three, perhaps?)

Mike

-- 
Michael Leuty
Nottingham, UK