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New Member

Wan Optermiser / Accelarator

We have a T3 circuit between London & NY which there there appears to be a lot of latency and TCP overhead, we have been looking at the HP Wan Accelator and Riverbed. Please can you post your comments on this solution

many thanks


Re: Wan Optermiser / Accelarator

Before you venture into adding equipment, have you checked wither your end systems are configured for RFC1323? On such long links large TCP window is essential in order to get maximum performance out of your pipe. Latency here is noticible affected by the distance, you can't beat speed of light.

Another point - what's current avg. and peak utilisation of your link? If it's overloaded, latency could be due to buffering on the router. You could apply a service-policy that allocates appropriate amount of bandwidth to your critical application. It won't prioritise traffic as such, but it will have a chance to get on the line within predictable limits (determined by bandwidth of other classes).

TCP overhead will always be there unless you're doing TCP header compression. And for such link speed compression time might be bigger than simply sending packet away uncompressed.

Hope you'll find this info usefull.

New Member

Re: Wan Optermiser / Accelarator

What we have done so far is just copy files from one machine to another and also using ftp and established the file transfer is taking a lot longer than first expected from a DS3 link

Re: Wan Optermiser / Accelarator

Your files would have to be really large in order to get TCP window to size good enough to fill up such an LFN link with single session. What's RTT on your link? It's probably something similar you'd see on some small ADSL link. And it's RTT and not link speed that affects your TCP session setup time.

Try using iperf with large packets (important) and run some 10-20 sessions. This will give you slightly better view of what your link can deliver.

Meanwhile, in production you will have much more than single session none of them requiring 45Mbps to work unless you're doing transatlantic backups. With many sessions it's summary capacity of the link and RTT what play vital part and not max. transfer speed you can achieve with single session. You need to carefully evaluate what will be usage of this link and what requirements your applications set on network. After that you could probably configure some nice queuing policy and very likely to get most out of what your DS3 can deliver. If that's not enough, only then I'd look at adding more equipment and only if it's possible to get demo for couple days for evaluation.

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