Additional Wireless Technologies

Cordless Phones

Cordless phones have been around as long as I can remember—or at least since I was in junior high. Cordless phones sometimes operate in the wireless spectrum as WLANs, which can cause interference issues. Visit an electronics store, and you’ll find some phones that operate at 2.4 GHz and others that operate at 5.8 GHz. This should be a consideration when you purchase cordless phones. If you have 802.11a deployed, a 2.4-GHz phone should suffice. If you have 802.11b/g, you should avoid a phone that operates in the 2.4- GHz range and go with a 5.8-GHz phone. With that said, let’s look at cordless phone technology in more detail.


To begin with,cordless phones canuse Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA). The Multiple Access technology is used to allow more than one handset to access the frequency band at the same time, as shown in Figure 8-1. As you can see, a cordless phone communicates with the base station. Multiple cordless phones can use the same base station at the same time by using TDMA or FDMA.


It’s common for cordless phones to use the Digital Enhanced Cordless Telecommunica- tions (DECT) standard. DECT is an ETSI standard for digital portable phones and is found in cordless technology that is deployed in homes and businesses. Currently, the DECT standard is a good alternative for avoiding interference issues with any 802.11 technolo- gies. The original DECT frequency band was 1880 to 1900 MHz. It’s used in all European countries. It is also used in most of Asia, Australia, and South America.

In 2005, the FCC changed channelization and licensing costs in the 1920 to 1930 MHz, or 1.9 GHz, band. This band is known as Unlicensed Personal Communications Services (UPCS). This change by the FCC allowed the use of DECT devices in the U.S. with few changes. The modified DECT devices are called DECT 6.0. This allows a distinction to be made between DECT devices used overseas and other cordless devices that operate at 900 MHz, 2.4 GHz, and 5.8 GHz.


Bluetooth

Bluetooth is a personal-area technology that was named after a king of Denmark, Harald “Bluetooth” Gormson. It is said that the use of his name is based on his role in unifying Denmark and Norway. Bluetooth technology was intended to unify the telecom and com- puting industries. Today, Bluetooth can be found integrated into cell phones, PDAs, lap- tops, desktops, printers, headsets, cameras, and video game consoles. Bluetooth has low power consumption, making it a good choice for mobile, battery-powered devices.

The Bluetooth Special Interest Group (SIG) was formed in 1998, and the name “Bluetooth” was officially adopted. In 1999, Bluetooth 1.0 and 1.0b were released, although they were pretty much unusable. Bluetooth 1.1 followed and was much more functional. Eventually, based on Bluetooth 1.1, the 802.15.1 specification was approved by the IEEE to conform with Bluetooth technology.

Bluetooth 1.2 was then adopted in 2003 with faster connections and discovery of devices as well as the use of adaptive Frequency Hopping Spread Spectrum technology. In 2004, Bluetooth 2.0 + Enhanced Data Rate (EDR), supporting speeds up to 2 Mbps, was adopted by the Bluetooth SIG. The IEEE followed with 802.15.1-2005, which is the speci- fication that relates to Bluetooth 1.2. After the 802.15-2005 standard, the IEEE severed ties to the Bluetooth SIG because the Bluetooth SIG wanted to pursue functionality with other standards.

Bluetooth technology might interfere with 802.11 LANs, because it operates in the 2.4- GHz range. However, because it is designed for a proximity of about 35 feet, has low transmit power, and uses Frequency Hopping Spread Spectrum, it is unlikely that Blue- tooth will interfere.

Bluetooth is considered a piconet; it allows eight devices (one master and seven slaves) to be paired, as shown in Figure 8-2. Although the figure is a little extreme, it shows you just how many devices can be paired with a laptop or desktop. You can download photos you’ve taken, while listening to music with your headphones, synchronizing your cell phone’s contacts and PDA calendar with Outlook, and using your mouse to print that new white paper on Cisco.com, all while playing a video game. Imagine the wire mess you would have without Bluetooth.


ZigBee

Many people have never heard of ZigBee, but it’s a technology that is well-designed and very useful. ZigBee was developed by the ZigBee Alliance. It consists of small, low-power digital radios based on the IEEE 802.15.4 standard for wireless personal-area networks (WPAN), such as wireless headphones connecting to cell phones via short-range radio. If you look at the ZigBee Alliance home page at http://www.zigbee.org, you’ll likely notice that ZigBee relates much of its use to control and monitoring. In fact, ZigBee is often used for monitoring, building automation, control devices, personal healthcare devices, and computer peripherals.

A Wireless Connection

Using Figures 7-11 through 7-18, you can step through a simple discovery and association process.

1. The AP sends beacons every 2 seconds, as shown in Figure 7-11.


2. Client A is passively scanning and hears the beacon. This enables the client to deter- mine whether it can connect. You can see this in Figure 7-12.

3. A new client (Client B) arrives. Client B is already configured to look for the AP, so in- stead of passive scanning, it sends a probe request for the specific AP (see Figure 7-13).


4. The AP sends a probe response, seen in Figure 7-14, which is similar to a beacon. This lets Client B determine if it can connect.


5. From this point on, the process would be the same for Client A and Client B. In Figure 7-15, Client B sends an authentication request.

6. Also seen in Figure 7-15, the AP returns an authentication response to the client.

7. The client then sends an association request, as seen in Figure 7-16.

8. Now the AP sends an association response, also seen in Figure 7-16.

9. When the client wants to send, it uses an RTS, assuming this is a mixed b/g cell. The RTS includes the duration, as you can see in Figure 7-17.

10. Also seen in Figure 7-17, the AP returns a CTS.

11. The client sends the data (see Figure 7-17).

12. The AP sends an ACK after each frame is received (Figure 7-17).

13. In Figure 7-18, the client sends a disassociation message.

14. The AP replies with a disassociation response (Figure 7-18).

15. The client returns and sends a reassociation message (Figure 7-18).

16. The AP responds with a reassociation response (Figure 7-18).


Again, this process has other variations, but this should give you a pretty good under- standing of how to manage a connection.