Re: TCP congestion

[Iljitsch van Beijnum <iljitsch () muada com>]

On 12-jul-2007, at 22:27, Philip Lavine wrote:

> I just don't understand how if there is 1 segment that gets lost  
> how this could translate to such a catastrophic long period of slow- 
> start. How can I minimize the impact of  the inevitable segment  
> loss/out of order over a WAN. Is QoS the only option?

How exactly are you going to get out-of-order packets over a single  
link?

Is there perhaps a firewall somewhere in the communication path? In  
that case' it's entirely possible that packets that use certain TCP  
options are filtered because the firewall doesn't implement these  
options.

For instance, if there are selective acknowledgements, the firewall  
may not like that.

Also, if you use the window scale option the firewall probably  
doesn't understand that and may easily conclude that a packet which  
is in-window with the scale factor applied is out-of-window because  
the scale factor _isn't_ applied and drop it, so that you miss the  
packet with byte 1, then get the ones with everything upto 65535 and  
the rest is dropped, and so many dropped packets will stop TCP dead  
in its tracks.

Also note that minimal amounts of cell loss on ATM create huge  
amounts of packet loss at the IP layer.