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I work for a non-profit organization in a 4000 sf office with 30 staff. All laptops are connected to the network wirelessly. We have one switch (TP-Link TL-SF1008D Ethernet Switch) and three routers that function as AP (TP-Link TD-W891ND), with one of the routers functioning as the modem. Primary activities include e-mails, Dropbox, and downloading/uploading documents.

We have just recently upgraded our Internet package to 12 Mbps (as advertised), but the Internet connection is still very sluggish most of the time, even with less than half of the staff in the office. A lot of people can't connect to the APs, reliably, and even when they do, the connection is slow.

I have a feeling that the problem has more to do with network setup rather than bandwidth. Can anyone point me to the right direction on what I need to look for on troubleshooting?

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how many users are you trying to connect simultaneously? –  JamesRyan May 13 '13 at 11:13
    
@JamesRyan We have 30 staffs, but most of the time we only have 15-20 people at the office. Question edited. –  Khairul May 13 '13 at 16:10

4 Answers 4

up vote 7 down vote accepted

Setting up a wireless network in a 4000 square foot space requires either an extremely knowledgeable installer, or having someone who owns some proper testing equipment. You will need to do a survey of the room, including finding out what sort of background noise there is, and if there are other networks on the same spectrum. You will then have to plan the layout properly, as well as decide what sort of connectivity your users need, sitting at a desk wireless is a lot more simple to implement than one where users are roaming from AP to AP. The second situation would require central management of the APs, as seamless hand-offs require coordination.

Having 3 APs on the same channel will cause interference, having users that connect with 802.11b when everyone else is on 802.11n will slow down access considerably, as will many other types of incompatibilities.

The other option, if you do not want to consult with a professional, is to install ethernet cable, it is faster, more secure, and less likely to be influenced by outside signals, or interference.

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Hardwire ethernet defeats Wireless Magic any day of the week. It's why the FCC came into being with all those band plans. Too many unplanned signals in a limited area is the same as no connectivity at all. –  Fiasco Labs May 13 '13 at 16:50
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Amen to that, I like wifi, but not for anything work related. –  NickW May 14 '13 at 10:34

You should be able to do this yourself without a consultant and without special instruments as 4,000 square feet with 30 users isn't all that big. Test from the ground up:

  1. Make sure that the access points are configured to use different channels (Read the "Wireless- Advanced" section of the TP-Link Users Guide carefully and see "Wireless"->"Advanced" on the UI). With all of the access points off, verify that there are no other strong networks in the area using your channels.
  2. Test file transfer rates between workstations connected to identical access points. Do this for each access point. Note packet loss rates on transfers. You can use iperf for this. Do this test with only one AP working, two AP's, three AP's.
  3. Test file transfer rates between workstations connected to diferent access points (through the switch presumably). Note packet loss rates. Do the test when the office is full and when the office is relatively quiet.
  4. Test DNS name resolution times for outside sites on workstations without doing any file transfers or requests. The name resolution should be quick.
  5. When the traffic is low, before people come in for the day or at night, test the ping time from workstations to the inside interface of the modem. Repeat the test at peak traffic hours.
  6. Test ping times from workstations to the modem's default gateway, which is your ISP's nearest interface on the other side of your WAN connection.
  7. Test ping times from the modem to the modem's default gateway interface.
  8. Test ping times from the modem to a site inside/outside your country using dot-quad IP address, not name. Note any unusual packet loss. High packet loss could mean a routing mistake at your ISP, especially if you have a fixed IP address assigned to your modem line.
  9. Verify with the WAN line provider, if not the same as the ISP, that the line is conditioned for 16Mb. In some countries the DSL provider is a telco and the ISP is a separate company. Ask the DSL provider to perform a line conditioning test, during quiet hours at the office because this test stops traffic on the line.
  10. Ask the ISP for traffic statistics. Some ISP's can give you a link to an MRTG-like graph so that you can see the actual line usage.
  11. If you are using a fixed IP address on your outgoing modem interface, verify with the ISP that there aren't any routing mistakes.

Some colleagues perform these test in the opposite order, but if you suspect WiFi issues then you should use the above order. To isolate the fault you need to be methodical and record the results carefully. Same the records for future reference.

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Thank you for the detailed troubleshooting steps Jon! I definitely have a lot to learn before I could even perform half of this, but at least I know now where to start. –  Khairul May 15 '13 at 0:28
    
"without consultant". THis likely takes a week of his time - I would hire help for that without thinking, a consutlant likely can do that in a day. –  TomTom Aug 19 '13 at 5:06

Your primary challenge is simply that your three access points are very likely to be interfering with one another. Short of moving to an enterprise-grade solution, the best thing to do is take advantage of the only three non-overlapping channels in the 2.4GHz Wi-Fi spectrum:

  • Configure the first access point to use Channel 1.

  • Configure the second access point to use Channel 6.

  • Configure the third access point to use Channel 11.

Note that if you are in a dense office building shared with other organizations, this alone does not address likely interference from external sources, e.g. other companies' 2.4GHz access points located above and below you.

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We are in a dense office building shared other organizations, but thanks on the very specific suggestion. One thing that helped was setting the router (replaced it with Asus RT-N66U) to channel 1, and the signal had been stable, partially by other configurations as well. It was a bit odd since a lot of other networks are using channel 2 but much easier than keep changing it accordingly. –  Khairul Aug 19 '13 at 2:50

Among the things we've done to improve the Internet connection:

1) To avoid SSID clogging, we rename all three SSID with the same name and password, to avoid users clogging into just one SSID. This technique is called SSID roaming.

2) Make sure those three APs are set on a different channel, at least 3 channel apart from each other. (As suggested by Mike, the best setup would be on 1, 6, and 11)

3) When a user/device leave the office, their IP addresses are still visible from the router's dashboard. I'm uncertain if this actually affects the network, but I soft reboot the router every morning just to be safe.

4) Set wireless mode to only allow N type of connection.

5) With TP-Link TD-W891ND, one AP can only hold up to 30 clients in the dashboard before it slows down significantly. We changed to Asus RT-N66U and it can support up to 75 clients. (Note that these are only the amount of devices that are displayed on the router's dashboard. Some IP addresses stay even after leaving the network)

and perhaps the most important discovery was...

6) Our Internet package didn't actually get upgraded. We took a look at the modem's dashboard and very surprised to find out that it stayed at 8 Mbps. After calling our telco and having it upgraded, it still did not solve the problem (initially), but it was important to know that we get what we paid for.

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