IP TTL support for localized peering and faster sharing

[tumu]

There might be benefit in supporting IP TTL field setting on making and accepting peer connections for torrents with large number of seeds and peers. As IP TTL directly controls the allowed network path length for connections (without any relation to IP address ranges or DNS names), it would allow prioritizing sharing for local peers and seeds first before trying ones further away.

The benefits from this kind of localizing would be:

1. Faster sharing speed amongst local peers

2. Less likely to be caught in traffic shaping/transparent proxy (as local connections usually are exempt)

3. Less packet loss due to reduced network congestion in slower ISP/international connections

The implementation probably should have global and torrent specific limits with relaxation based on current download/upload speeds in case of badly seeded or sparse torrents. Also having seperate upload speed limits for local peers might be useful.

Some technical documentation for the interested:

http://en.wikipedia.org/wiki/Time_to_live

http://www.sockets.com/ch16.htm#IP_TTL

http://msdn.microsoft.com/library/en-us/winsock/winsock/ipproto_ip_socket_options.asp