TCP Window Scaling in IOS

[subbarao.s]

What is the advantage of this feature? Referred to RFC1323 but dont understand it fully!

Does this improves performance of end hosts if I enable this feature on intermediate hosts (Cisco Router), while using high bandwidth link like Metro Ether?

My problem, when I tested two PCs back to back and do FTP I get almost 70Mbps throughput where as If I perform the same test across the WAN/MAN link (Metro Ether), I am not getting more than 8Mbps~10Mbps. I am able to get the same rate with multiple PCs (I mean if I connect 4 PCs I am getting 35~40Mbps aggregated throughput almost), so from this test it is clear that WAN/MAN is not causing bottle neck but end hosts does.

I could not get the chance to sniff the packets during the test, so no idea on Window size they are using. However I think problem is something to do with TCP Window size, Am I right? I don’t see any long delay also across the link, I got an SLA from the SP for 40msec RTT delay (Currently I am getting only 19~24msec RTT). So where exactly is problem lying?

I appreciate if someone can help.

Thanks in advance.

[pkokhan]

You may want to check the TCP window size on the end systems (not on the routers). There is a theoretical limit of the transfer

Speed = Receiver Window Size / RTT.

If TCP window size set to maximum 64K, then try enabling windows scaling (on both the receiver and tramsmitter).

If this does not help then the bottleneck may be the ftp application itself (uses small buffers).