[bittorrent] Choking based on network closeness?

Justin Cormack justin at street-vision.com
Tue Jul 12 12:52:03 EDT 2005


On 12 Jul 2005, at 17:34, Bill McGonigle wrote:

>
> 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.

Even Linux requires root to send ICMP which is a bit of a pain  
(though you can open a raw socket and drop privs). Would latency give  
a good enough answer? It would penalize slow hosts too I suppose, but  
it would be easier to measure...

Justin




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