[bittorrent] Choking based on network closeness?

Bill McGonigle bill at bfccomputing.com
Tue Jul 12 12:34:17 EDT 2005


On Jul 11, 2005, at 14:46, Justin Cormack wrote:

> It came up on the list before, and there were some uses for it. The 
> main problem is that no one seems to have enough information to 
> measure closeness, unless you actually work for a large ISP or run 
> BGP.

I've looked at a few different techniques that might apply - 
traceroute, pathchar, packet-tailgating.  Assuming 'closeness' is only 
one decision criterion I'm not seeing a reason why traceroute wouldn't 
be sufficient (but tell me otherwise).  You'd have to make some 
assumptions about how many hops are behind those * * * routers but the 
core internet routers seem to always respond properly, and that gets 
you most of the useful big-picture topology.

There are certainly broken routers, some edge routers that won't honor 
the ICMP packets, and probably an OS that won't allow the user to send 
ICMP packets.  But there is probably enough information most of the 
time to make a good guess.  And, you'd always fall back to the 'fastest 
peer' algorithm in the absence of other data.

-Bill

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