Computer Voodoo logo

wireless networking

hardware | security | complicated stuff

hardware

Make sure you buy the correct equipment for what you want to do. Remember that your network is only as good as your weakest piece of equipment.

speed

Wireless network speeds can vary. If you buy a wireless networking card you'll probably see 802.11b or 802.11g. That letter trailing the 802.11 tells you about the network functions. B transmits at 11Mbps while G is up to 54Mbps. A higher letter alphabetically does not mean an increase in speed. 802.11a is faster than 802.11b, but 802.11a has a far shorter transmission range.

distance

For 802.11b and g the typical range is 300 feet (100 meters) outdoors and 150 feet (50 meters) indoors. The more obstacles between your router and computer the shorter the distance will become. Always work with line-of-sight to gain the best range. If the signal has to go through walls and floors your signal will be weak. If your signal is weak you can add more powerful antennae or signal boosters to your router. You can also use repeaters to pick up the decaying signal and retransmit from the placement point of the repeater. On the computer end you can replace your current network card with one more powerful. Engenius Tech sells laptop cards with 200mW (milliwatt) transmit power for the same price of a Linksys with a 32mW transmit power.

Remember that even though the router signal is reaching you does not mean that the signal will reach from your computer to the router. This is when you would require a stronger wireless card in your computer. In order for everything to work you need to complete the loop. The signal is sent from the router to your computer. Your computer then has to send a signal back to the router to tell it what you want to do (e.g. grab a web page, send/receive e-mail, etc.)

Here's a useful page that explains how to gain wireless range in simple terms.

adding wireless access points to a network

If you have a leftover router and you want to extend your network you can connect wireless routers together. You can use wireless range extenders, but connecting routers via a network cable creates a backbone. Otherwise the wireless throughput degrades due to half the bandwidth being dedicated to communicating between the wireless access points. The following are basic instructions and will vary depending upon your router.

  1. Set a static IP for the LAN portion of the router. The IP should be on the same subnet as the primary router. For example, if your primary router's IP address is 192.168.1.1 then set the LAN IP address of the secondary router to something like 192.168.1.2.
  2. Disable the DHCP server for the LAN. The DHCP server on the primary router will hand out IP addresses.
  3. Set the ESSID (wireless network name), the encryption type, and encryption password to the same as the primary router. This will allow you to seamlessly roam between wireless access points. Different ESSIDs means you'll have to possibly switch manually between access points.
  4. Connect the two routers together using a network cable. Make sure you plug into a LAN port on the secondary router and NOT the WAN port. Plugging into the WAN port would create another network and lead to double-NATing. Also remember that the maximum length of a network cable is 100 meters (roughly 328ft).

security

If you're going to set up a wireless network in your home or anywhere make sure you secure it. Read the manual for your wireless router before you start doing anything. Combining the following methods together will make your network that much more fortified. Remember that nothing is impenetrable, just measured in level of difficulty.

firewall

First you'll want to make sure that your router has a firewall activated. This will deter the malicious portions of the internet from seeping into your network from your DSL or cable connection.

encryption

Now that you've got a wall between you and your internet connection you'll want to scramble the transmissions between your computer and the wireless router. Why do this? If your neighbor lives close to you he has the ability to watch what data goes between your computer and the router. Encryption turns those transmissions into secret code that you have the decoder to. The encryption types you'll probably see are WEP, WPA, and WPA2. WPA2 using AES is the best, but older equipment may not be able to implement it. For all encryption types you'll need to type in a pass code on each computer that attempts to access the network.

WEP encryption is easily crackable, but at least you'll have proof that someone is intentionally attempting to attack your network. No encryption is like living in an invisible house. Everyone can see what's going on.

MAC filtering

Assigned to every piece of networking equipment is something called a MAC address. It typically looks something like 01:23:45:67:89:AB composed of hexadecimal numbers. Take a look on a wireless card or router and you'll probably find a sticker on it listing the MAC address. You can find the MAC address of network equipment in your computer by opening a DOS or command prompt (type cmd in the Run.. dialogue) and typing ipconfig /all. With MAC filtering you can tell your wireless router to only allow certain network devices to connect to it. If you have two computers in the house and add the MAC address of each wireless card to the filter the router will deny everyone else access except for those two computers. You can also do it the other way around denying those two computers but allowing everyone else.

MAC spoofing (impersonating another MAC address) is extremely simple so don't count on it as good security.

change the defaults

Change the ESSID (network name). Make sure to also change the login password for the equipment.

When looking for an easy target the first place to look is for wireless network names like linksys, netgear, default, etc. These are common default network names. There are also default passwords for logging into the router.

complicated stuff

interference

Every 3dB increase/decrease means double/halve the power level. Here's a listing of materials and the signal loss caused in decibels:

A quick and sloppy way to find out the percentage of signal you'll be left with: take the dB loss (window: 3dB), move the decimal one spot to the left (0.3), raise 10 to that power (100.3=2), now throw a 1 over that answer and convert to a percentage (1/2 = 50%). This percentage is how strong the signal will be compared to the original full power when it arrives at the destination. A 2dB loss means the signal will be arriving with around 63% of its original power.

calculating path loss

L[dB]=Ptx[dBm]+Gtx[dBi]-Prx[dBm]+Grx[dBi]+Gdv[dBi]-M[dB]

Useful pages regarding the math involved: