Hello,
I have a question on tcp performance across WANs. For our two remote
offices, we have built a proxy architecture such that all tcp
connections from one office to the other are multiplexed over a single
tcp connection:-
Clients<--->Proxy 1<----WAN------>Proxy 2<---->Servers
TCP1 TCP TCP1
TCP2 TCP2
... ...
So a tcp connection from a client to a server is intercepted (through
nat) by proxy1. proxy 1 then multiplexes that tcp connection over its
single connection to proxy2. proxy 2 then demultiplexes the traffic.
Clients and proxy 1 are in one LAN, proxy2 and servers in another. The
WAN link is T3 with 100ms round trip time.
The question is would we be able to utilize our private T3 line better
by having more than 1 connection open between proxy 1 and proxy 2
instead of having just one.
Both proxy 1 and proxy 2 support large windows and SACKs so filling the
pipe is not a problem unless there is loss. The question really is
whether the congestion avoidance algorithms and slow start slow down a
single tcp connection very much. So if we had more than one connections,
only one of them would experience packet loss at a time so only one of
the connections would go slow. So with 5 connections carrying equal
traffic, 80% of traffic will still flow fast. So does using more than
one connection help? Should we do that? Or does it have other side
effects like each of the 5 connections competing with each other and
causing higher packet loss etc.?
I know eg. bbftp uses multiple connections to boost throughput but I am
not sure how much it helps when we already have large windows extension
and SACK. Also it makes sense for bbftp to use more than one connection
because over internet, using more connections is better - not sure
whether it is true for private lines as well.
Any ideas?
Thanks..
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