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wolever/wifi_and_power.rst

Created November 8, 2011 02:57
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Wifi and power for medium sized tech events
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wifi_and_power.rst

This document is a practical checklist for anyone who needs to provide wifi and power for medium sized (10-100 attendants) tech events where attendees will expect to be able to plug in their laptops and get on a wireless network.

Full disclosure: I'm not an expert at this, but hopefully the things I've learned will be better than nothing.

General Notes

  • Don't trust the location's wifi. Unless it has been specifically designed to handle a large number of high-bandwidth clients it will almost certainly fall over. If the location only has wifi it's likely worth using a laptop (or other device) as a wireless-to-wired bridge, then plugging your own wireless APs in to that (almost any wifi equipment can handle a small number of high bandwidth clients - issues only come up when there are a large number of clients causing interference and competing for airtime). For more on setting up a wireless-to-wired bridge: Mac, Windows, Linux.
  • Wifi with WPA2 is just fine. At the two events I've done recently (total of about 150 people), only one person's device had persistent trouble connecting to the wifi (and luckily she was sitting next to the access point, so an ethernet cable fixed that).
  • Consumer grade APs are okay. At a recent Ladies Learning Code we had approximately 90 people sharing four WRT-54G APs. It wasn't perfect: some people had intermittent connection issues, and the WRTs would occasionally need to be rebooted, but overall connectivity was acceptable.

Week(s) Before the Event

  • Know your point of contact. While it is possible to CC all of the event organizers on all of your emails, it's much easier to have one single person who can answer your questions (or help you find the right person to answer them). You should have this person's email and phone number.
  • Confirm approximate number of attendees.
  • Confirm the official start and end times, and make sure that you'll have enough time for setup and tear down. If the event is in the morning it's ideal if you can setup the night before, but this isn't always possible. The exact amount of time that you'll need will depend on the help available, but consider that each power bar will take about a minute to a minute and a half to plug in and tape down, and each access point will take about five minutes to plug in and test.
  • Confirm your responsibilities. Will you also need to setup projectors? A sound system? Do software support?
  • Perform a site inspection. This will prevent surprises, and let you warn the organizers about potential issues ahead of time. Some things to check:
    • Location and number of power outlets, especially with relation to seating. Make note of approximately how many extension cords you will need, and how long they will need to be.
    • Location and number of ethernet drops. You will be plugging your wireless APs into these, so consider where the APs will be physically located, how they will get power, and how much ethernet cable you'll need.
    • The local network:
      • Is any authentication required to get online? (ex, MAC filtering, username/password, etc)
      • Can you trust the DHCP server? (hint: if it's giving out IP addresses with a 192.168 prefix you probably can't).
      • Does it have enough bandwidth? There probably isn't much that can be done about this except warn the event organizers.
    • Seating. It's helpful to double check that there's sufficient seating and table space.
  • Acquire the gear.
    • As I note above, my Linksys WRT-54G APs have been able to handle approximately 25 clients each, but we did have intermittent issues which might have been possible to alleviate with more. Older WRTs can be bought for ~$50 each, but it may also be possible to borrow some.
    • It may be possible to borrow enough power bars, but it is possible to buy them for less than $10 each if you are able to find the ones which don't have surge protection. Also remember that stupid Apple power bricks without an extension cord take up two spaces, so having ~25% more outlets then there are devices will help make sure that everyone can get a plug.
    • A few 25 or 50 foot lengths of ethernet cable in addition to the cabling you need for the APs will likely be useful if a drop turns out to be dead, or someone is having trouble with the wireless and needs to plug in.
    • Other miscellaneous things which will be useful: green painter's tape and a sharpie for labeling equipment and wires (green painters tape is good because it won't leave a sticky residue), duct tape for taping down wires (just be sure to take it off promptly so the wires don't get covered in sticky goop), and a pocket knife or multi tool for cutting tape which gets stuck to its self.
  • Organize per-table information sheets with the organizers. You want these because they will tell each table what wireless network they should be connecting to (along with the password), and the organizers will likely want to include things like sponsors, important URLs, Twitter hashtags, etc.

Day(s) Before the Event

  • Confirm the number of attendees, start and end time, and that you will be able to get in early to setup. Make sure you have a phone number to call if you show up and no one else is there.
  • Confirm that the per-table information sheets have been printed (or do it yourself).
  • Configure the wireless APs. For each AP:
    • Assign it a unique IP address in a range that won't clash with the site's network. Mine are 192.168.141.[1-4]. Even if the APs will be on different networks it's helpful to give them unique IPs so you can be sure of which one you're connecting to (ex, when you use the web UI).
    • Disable DHCP (with one exception, below).
    • Assign it a unique wireless channel. Because wifi channels have quite a bit of overlap (for example, a broadcast on "channel 6" may interfere with channels 3 through 9), try to keep the channels as far apart as possible. For example, the first AP should be on channel 1, the second on 11, the third on 6, the fourth on 9, the fifth on 4, etc. Of course, if you know that the site's wireless will be making heavy use of one channel you might want to avoid that channel, or if two routers will be very far apart they can run on the same channel.
    • Assign it a unique name. Including the channel in the name will make debugging easier, so EventName-<channel> might be a good template (just note that Windows truncates SSIDs to about 15 characters, so keep the names short).
    • Use WPA2 with a lower case, no-spaces password. No modern device has trouble with WPA2, and it's much easier to tell someone "the password is hello world, lower case, no spaces" than it is to tell someone "the password is 4fHJ9sAx8".
    • If possible and sensible, lower the AP's radio's power. If you're in a 50 foot room there's no point in running at full power (which is designed to cover an entire house) - it will just add to the noise.
    • Set the admin password (for the sake of sanity it should be the same on all devices).
    • Stick a label on the device (using the green painter's tape) which includes the IP address, wireless channel and possibly SSID.
    • Save its configuration so it can easily be re-loaded later. If all the APs are the same model, you can load the configuration from the first AP onto the subsequent APs to speed up configuration (just remember to change their IP addresses!).
  • If you aren't trusting the site's DHCP, setup one of the APs as a DHCP server. Make sure that's capable of giving out enough addresses (by default my WRTs will only give out 50 addresses).
  • Label all the things. The equipment, wires and power supplies. All of it. If the gear is borrowed, use the green painter's tape to put the owner's initials on it. Otherwise, just stick some green tape on everything. This makes cleanup easy, because you won't need to remember what's your and what's the site's - you (or your helpers) will just grab everything with green tape.
  • Pack everything. This may be obvious, but I'll often forget to pack the night before, forcing me to frantically stuffing things into my backpack the morning of the event. This is no fun. Everything includes:
    • Ethernet cables.
    • Extension cords.
    • Power bars.
    • Wireless APs + powers.
    • If you won't be present for the teardown, a bag or box that the gear can be put in.
    • Tape (duct + green).
    • Sharpie.
    • Pocket knife or multi tool.

Setup

  • Setup the wifi first. If worst comes to worst and you run out of time, attendees can plug in their own power bars, but they can't setup the wifi.
    • The locations of the APs is important. Try to keep them as far apart as possible (for example, by putting them at the edges of the room), and try to keep APs on similar channels as far apart as possible (for example, putting the channel 1 AP next to the channel 11 AP and far from the channel 4 AP). As with most of the wireless advice I'm giving this is in an attempt to reduce interference.
    • Plug in the APs one at a time, connecting to each one and testing it for connectivity as it comes up.`
    • If the APs are in a location where they might get jostled around, it might be a good idea to use a bit of green tape to secure the power and ethernet cables in the back. It's no fun trying to diagnose a connectivity issue only to find out it's because an ethernet cable is loose.
  • Run power to the tables. If you've got some time, it might be nice to put a bit of tape over the power switches to keep them in "on".
  • When possible, run cables up table legs and be concious of where chairs and chair legs will go.
  • When taping down cables, you'll need to decide if you want to tape down the whole length, or just at intervals along it. I tend to tape down the whole length when it's in a high traffic area, and at intervals when it's less trafficked. If you're taping the whole length, start by taping down one end, pull the cable tight, then tape down the other end. Now you'll have a nice straight line which you can cover with two or thee foot sections of tape.
  • Don't be shy about asking people for help. Things will go much faster if one or two people can help with the power while you're setting up the wireless.

During the Day

  • If you're curious, you can use tools like KisMAC (Mac) or Kismet (Linux) to monitor the network usage and make sure that load is roughly evenly distributed between the APs.
  • If you're getting strange connectivity errors, try rebooting the offending router. My WRTs occasionally act up (can't associate to them, the admin interface stops working, they stop routing packets, etc), but they are fine after a reboot.

Teardown

  • Make sure you're coiling your cables properly! It makes a huge difference. I won't describe the technique here, but Google has a bunch of good descriptions and videos.
  • When you're pulling up the cables which have been taped down, pull the tape up first, then pick up the cable; don't use the cable to pull up the tape. If you do, the tape will likely wrap around the cable and stick to its self, which is a huge pain.
  • Make sure you're ready to accept complements about how smoothly everything went.
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