As a first step toward a Networking FAQ, I'm going to start posting some simple stuff that will help with a lot of problems.
1. How To Troubleshoot A Network
This is not as complex a task as it might seem. The first thing you need to do in troubleshooting anything is to figure out what's not working, versus what's working but can't do its job because something else is screwed up.
First, no matter what the problem is, it's a good idea to restart everything, starting with the modem. Turn it ALL off, and then turn things on one device at a time, begining with the first device in the building-usually the modem. Wait a TIMED two minutes from applying power to doing the next step, so that each device can properly power up. After the modem is on, turn on the router (whatever kind you have-and if you're in an area where "ADSL modem/routers" are common you'll have already done this when you turned the box back on). If your wireless network is based on a separate access point, turn it on next. LASTLY, turn on your computer.
In most cases the above will fix your problem, and it won't be important to know which device was at fault.
2. "My computer can't connect to the AirPort network after waking up."
This is common, and it's because of the way WiFi networks work. These networks "hop" from one frequency to another in a set, predetermined sequence. As these "hops" are precisely timed, if your AirPort card doesn't know that it's been asleep (and that's apparently exactly what happens), then it won't know that it's fallen out of sync with the network and that it needs to reacquire the pattern.
The fix here is simple: manually disconnect/reconnect when you wake your computer up.
The bad part about this issue is that it is not consistent enough for a straightforward "cure." Some computers have the problem and other, apparently identical computers don't. Sometimes there's a change when an AirPort update is installed, and sometimes there's no change...
More ideas about AirPort connections after waking up: according to MacOSX.com,
you might be able to fix this problem by simply deleting your AirPort entry in your Keychain. This will result in prompting you to re-enter the passphrase the next time you connect, but apparently it also changes the way the AirPort card handles lost connections, and it might
eliminate your connection problem.
3. Wireless Network Drop Outs-What can be the cause?
Lots of things! This applies to "WiFi" or IEEE 802.11B and G networks-I'm not addressing 802.11A, which works on a different frequency band, nor "draft N". WiFi networks work in the 2.4GHz frequency band, so anything else in the same frequency range (not even on the same exact frequency, just the same range) can interfere with the radio signals and either slow or cripple connections. That includes things like old microwave ovens and (the bane of WIFi networking) 2.4GHz cordless phones. If you notice that your network goes "BLOOIE" when you nuke your popcorn, or when the guy next door is gabbing cordlessly on his patio, you may have found your answer.
Another potential problem is another WiFi network nearby. Most wireless routers and access points come set for "channel 6" or "channel 7" from the factory. Why is this important? EVERYBODY's hardware is going to be on basically the same channel! That means that Joe next door is going to have his wireless network on the same channel as you, and Bob, the neighbor on the other side will too! If there's no cordless phone in the vicinity, change your wireless channel and see if that doesn't fix a lot of things fast!
Occasionally there is an oddity in the software that runs your router or access point-it's called the device's "firmware." Manufacturers sometimes upgrade these firmwares so they can provide new features, but they also release new versions to fix these glitches-and they won't always tell you "this is a bug fix to correct a reported problem with networks dropping for no apparent reason." If changing channels doesn't fix this kind of problem, you may want to change your firmware.
Finally, what about when ONE computer has problems like getting really poor signal strength even really close to the router or access point? With iBooks and PowerBooks (and maybe MacBooks and MacBook Pros), it could be that the antenna cable has worked loose. It's really that simple. Fixing this is a matter of finding the Apple knowledge base article on installing an AirPort card
in your particular laptop. These instructions tell you how to get at the spot the card is in, and show you where the antenna cable goes-all you have to do is plug that puppy back in and you're surfing again!
A nice description of computer networks in general is found in this Wikipedia entry.
More info on wireless networking standards can be found at this Wiki entry.