Author Topic: Identifying System Bottlenecks  (Read 17720 times)

Beyers Cronje

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Re: Identifying System Bottlenecks
« Reply #15 on: May 13, 2015, 02:32:05 PM »
The maximum throughput of a TCP session is expressed as:
Code: [Select]
TCP-Window-Size-in-bits / Latency-in-seconds = Bits-per-second-throughput
Without window scaling, the maximum window size is 64KB. Given a 15ms RTT and default 64KB window, the maximum TCP throughput is:

Code: [Select]
Window size = 64KB = 65536 Bytes.   65536 * 8 = 524288 bits
15ms RTT = 0.015 seconds
524288 / 0.015 = 34.95 Mbps

So the maximum throughput on a single TCP session over WAN link with 15ms RTT will be less than 34.95 Mbps
The throughput drops significantly the higher the RTT gets.

Some more information on TCP performance at

You run iperf on both ends on the LAN, so on a Windows or Linux box. One side runs as the client while the other runs as the server. iperf is just a command line tool, and is available for Windows, Linux and OSX. Using iperf you can manually set the TCP windows size as well as number of threads to run, or you can use it to send UDP stream at a given rate. This will help to see what the theoretical maximum throughput of your WAN link is.

Edit: to emphasize window scaling, which most stacks support.
« Last Edit: June 26, 2016, 06:03:42 PM by ahenning »


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Re: Identifying System Bottlenecks
« Reply #16 on: May 13, 2015, 03:35:42 PM »
Wanos by default bypasses UDP, so it could provide some useful stats on native traffic speeds, but its also useful to provide latency and packetloss stats. I can help with command line flags.

I think that because we see the throughput stabilize at 105 Mbps, it could mean that window scaling is relatively ok.

The test in 'low' cuts out the heavy computational and io tasks of dedup and it will tell us to focus there or look for bottlenecks somewhere else.

What was the average throughput on the 100 Mbps link before optimization or in other words while in bypass?
CCIE RS, CCIE SP, Mnet&sys

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Re: Identifying System Bottlenecks
« Reply #17 on: May 13, 2015, 05:20:06 PM »
OK so I have iperf loaded on a few endpoints and have played around with it a bit... very nice tool to have. I will probably need to run some tests during lunchtime to get accurate measurements when bandwidth utilization will be low.

I have a server at each location that can be bypassed in traffic policies so can test with and without optimization.

What flags would you like me to use to test? Thanks.