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How I fixed my slow Gigabit network performance

My connection used to be fast when I first installed my TRENDnet TEW 672GR Wireless “N” Gigabit router. I have three computers that are connected using a wired GB connection. Things just seemed real slow when sending or receiving large files between the home server and my (or my wife’s) PC. For example, shutting down MS Money writes a backup to the server and this took several minutes. Copying a gigabyte .avi movie file would take a long time and copying a DVD would take hours.

So I needed some metrics to get a baseline. I decided on Jperf (tutorial) which is a graphical front-end to Iperf. With this tool, you run the client at one computer and the server on the other. The program easily connects between them and sends messages back and forth for several seconds and displays a graph of the performance.

imageThe graph shown on the left is the performance I was seeing which was about 376KB/sec.

Another tool I used to get some more data is WireShark. This is a complex tool to capture low-level packet data on the network. I viewed some tutorials on YouTube and captured a few seconds worth of data (that’s actually a lot of capture). It did confirm that gigabit throughput was happening by looking at the time between frames, but there were areas of re-transmissions due to failed acknowledgements, collisions or something. It takes a lot more networking experience to analyze these captures than I have or want to learn at this point.

So the first thing I tried was to replace the cat5 homemade cables with cat6 manufactured cables from Monoprice, a great place to get cheap inexpensive cables. This did not improve things at all.


I next tried a 7.25 GB DVD transfer and it would have completed in about 4 hours if I let it finish (see screen shot on right). The transfer rate is 556 KB/sec, a bit faster than the above graph. It also shows the network utilization at a fraction of a percent. The little graph at the bottom is a nice little utility called DUMeter, nice to keep at the bottom of your desktop.

My next test was to connect my PC and the Server with a 25’ cat6 cable port to port, bypassing the router altogether. This requires a crossover connection so the cable wire pairs are correctly flipped (normally done when connecting via a hub, router or switch. There’s no DHCP to assign IPs when connected this way so I had to assign static IPs to each site ( and .2).

The throughput jumped to what it should be when using Jperf. Now, instead of 4 hours, the file transfer would take about 7 minutes.


The transfer rate is about 23MB/sec and net utilization is 25%. That’s about 50 times faster.

So with the TRENDnet in the middle, the transfer is slow and without it, the transfer is fast. That tells me the router is the problem and that something is seriously wrong with the Gigabit part of it (the wireless part is fine).

I looked at the TRENDnet router configuration settings but there are very few related to the wired LAN and nothing performance-related. Most settings are for wireless. I checked the TRENDnet knowledgebase and forums and found nothing obvious. I started a trouble-ticket with TRENDnet and sent them a screen capture of the performance issue.

I continued thinking about the difference between the two tests and decided to try removing all the attached cables from the router to make sure none of theimage other devices was causing the problem. There are four ports on the router: 1) Server, 2) my PC, 3) wife’s PC and 4) connection to a 8-port cheapie switch (Zonet). Disconnecting one at a time quickly showed that the Zonet switch was the culprit. With it out of the mix, I had the fast network with the TRENDnet. Even if no connections were in any of the Zonet ports (the Tivos, etc.), it caused the slowness. So I told TRENDnet support that they could close the ticket, it was not their device’s fault.

This is the final Jperf graph for the fast network at 36372KB/sec. If the above graph was included in this graph, it would just be a straight line at hugging the bottom around 0.

Update: I tried a different switch (a TRENDnet 10/100 Wireless 4-port router, actually) and it had the same effect as the Zonet switch so the problem is not fixed as I thought. I will get a new Gigabit switch which should work, else I am back to blaming the TRENDnet Gig router.

Print | posted on Wednesday, July 29, 2009 12:00 AM | Filed Under [ Personal ]


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