Atmospheric Transmission Media - Wireless Networking
(Not to be confused with Asynchronous Transfer Mode, or even Automated Teller Machines
Intro and useless knowledge...
Wireless networking may seem like a hot new topic, but in fact, radio and television broadcasts have been using the atmosphere to transmit data for years. Radio and TV are analog signals, but remember your phone line sends analog signals, and your modem interprets them into digital data. Not only that, but the atmosphere is capable of transmitting digital signals as well... So don’t worry about analog signals (just a bit of spare knowledge).
A little free thinking...
Wireless networking used to be limited to companies with vast resources, and the government, who needed to let employees on the move stay connected to the network. But nowadays, wireless is moving into personal LANs as well. Just imagine waking up, opening your laptop, visiting a few sites, moving to the bathroom and brushing your teeth to the sounds of streaming radio, then maybe make some eggs while you connect to your favorite ftp. My biggest dream is to relax on my couch with my friends and watch TV with my laptop by my side. =)
Back to the info...
There are two main categories of wireless transmission:
Infrared- This type of wireless transmission uses infrared light to send data. You most likely use this kind of transmission technology everyday. TV remotes, automatic garage doors, and wireless speakers all use infrared as a transmission media.
Infrared is divided further into 2 subcategories:
Direct Infrared Transmission - This type of transmission is very limited in that it needs direct line of sight in order to transmit data. This also has a benefit in the field of security, because ease droppers cannot just sit outside the building and pick up all your data. Just as a note: cable media is not 100% safe either, it also can be tapped or sniffed just as wireless can. Fiber optic is pretty much secure in this respect.
One way companies are using direct infrared transmission, is in PDAs (palm pilots and such). This allows these mobile, handheld units to easily transmit data to other PDAs, printers, PCs, connect to a LAN, etc... This simple idea will make the future of PDAs much more interesting.
Indirect Infrared Transmission - This uses the same idea as the direct infrared, but the signal can bounce off walls, the floor, a person, or anything else. Just remember to close the doors, or all your data will escape out and bounce down the hallway. =) (Because this is a computer "security" site, I should mention that indirect is, of course, less secure than direct infrared transmission).
Radio Frequency Transmission (RF) - RF uses frequencies to broadcast data in the network. The Big advantage of RF over infrared is that since it uses frequencies as the transmission medium, like radio and television signals, it can go through objects. The FCC issues licenses for these frequencies so that no two networks end up using the same frequency and cause problems, such as frequent collisions for both networks.
I know what you are thinking, RF must be a huge security threat, right? However, predating the 1990s, the US Military came up with a technology called Spread Spectrum (or wideband), which uses smaller signal strengths sent over several different frequencies at the same time to transmit data. This along with solid encryption techniques can make RF a pretty secure transmission method. (Read up on the latest news about Public Key Encryption, link in the resources section at the end of the tutorial).
There is of course a less extreme method of transfer, this RF technology is known as narrowband. Narrowband is the typical, one frequency transmission type for radio frequency transmissions. This type of network can easily be intercepted, although you must always weigh your need for security in different situations. A spread spectrum network doesn’t make sense for most situations. The military may need to use spread spectrum, but does that mean your personal LAN has to?
Wireless Technologies
Bluetooth
Bluetooth is a standard for short distance infrared transmission. It came about due to a number of companies, each with their own wireless solutions, having conflicts between devices of the different venders. This incompatibility can be a real pain, as previous networking situations have proved. So a few large companies in the mobile communication and computing business made up the bluetooth technology. The greatest thing about bluetooth, and the reason you may be hearing a lot about it in the future, is that it is very cheap to integrate into a product and can be implemented into pretty much anything. In fact, it only costs around $5-$10 to put bluetooth into a device. Bluetooth works in the unlicensed 2.45 GHz band and can transfer up to 751KB/s in this range. It can withstand large amounts of noise and can even use frequency hopping to avoid interfering with other devices. Also, to ensure quality control, bluetooth uses FEC and automatic request repeat. Basically this means that you won't lose as many packets, and the packets you do lose will be resent. Each device has it's own, unique, 12 byte address. And for it's topology, bluetooth uses Piconet, which is a point-to-point topology with 1 master and up to 7 active slaves. Although, if the slaves are non-active, it can support over 250. Piconet use their own frequency to avoid other piconet's signals from colliding.
802.11
IEEE's standard for wireless networks covers the physical layer, and media access specifications. It runs on the unlicensed 2.4GHz band at up to 2GB/s. 802.11 networks have much of the same characteristics as the cellular phone networks. This is due to 802.11 using Basic Service Sets (BSS) which are cells of a networks (think of cells as a network segment). This enables wireless devices to join, leave, and even roam from cell to cell, like cell phones do. They use access points to control every BSS. When more than one access point is used in a network, they are known collectively as a distribution center. Now, when a wireless device wants to join an existing cell it needs to scan for an access point.
There are two different types of scanning: active and passive. In active scanning the device sends out probe request frames and waits for an access point to send probe response packets. In passive scanning the device waits for a beacon frame to be transmitted by an access point. When the device finds an access point it needs to sync with it. It sends it's authentication into the access point and receives the access point's authentication. Then they exchange a shared key. After this the access point allows authentication and gathers enough info to determine what best access point for the device is. Roaming is used in 802.11 when the device is likely to move from one cell to another. The way they tell if roaming will occur is simple. They sense if that the signal is getting weaker and they scan for a new access point with a stronger signal and try to sync with it.
The standard security for the 802.11 is WEP (Wired Equivalent Privacy). WEP has been under fire lately for it's insecurities. This is a reason why wireless security is such a hot topic as of late. We may see WEP get improved upon to use what many wireless networks are already using, 128 bit encryption as well as x.509 certificates in the future. 128 bit encryption uses 26 hexadecimal digits. Many wireless devices use 128 bit encryption are only sold in the US. Others with 40 bit encryption are offered worldwide.
And in conclusion...
I hope this gets at least a few of you interested in wireless networking, if so check out my resource links for some great links to further reading.
What else...
There is a great deal of talk lately about WAP, VoIP, and WEP... If you do not know what these mean I would suggest you visit ww*.slashdot.org, htt*://geeknews.net, and htt*://ww*.newsnow.co.uk/-NewsFeed.Tech.htm at least once a day to stay informed. =)
