[p2p-hackers] UDP file transfer protocol peer review

[Alex Pankratov]

David Barrett wrote:

> In light of of my previous question on link speed identification of a 
> UDP file-transfer protocol, I'd like to share my overall protocol and 
> ask for feedback on how to improve it.  

Thanks, David. This is an interesting read.

> 5) Which option should I use to trigger decreases?

As Gregory P. Smith pointed out in a previous thread, using single
packet loss as an congestion indicator does not work well in lossy
networks. Like the wireless ones ... or certain Shaw cable segments
in Vancouver area :)

If your protocol allows for RTT estimation, you may try detecting
a congestion by looking at packet loss _and_ RTT value. If the
congestion is caused by the software which employs some sort of a
packet queueing, you will see a noticable increase in RTT at a rate
that immediately preceeds its maximum lossless value.

IIRC in a simple scenario with two directly-connected Linux boxes
RTT rapidly goes up 3-4 times before receiving box starts dropping
packets.

Alex

PS. My experience is purely empirical. If anyone is aware of any
formal research on RTT/congestion subject, I'd really like to hear
about it. Thanks.