Cordless phones sometimes operate in the wireless spectrum as WLANs, which can cause interference issues.. To begin with, cordless phones can useTime Division Multiple Access TDMA or Fre
Trang 12. DECT devices in the U.S use what designation to differentiate them from European DECT devices?
a. DECT 1.0
b. DECT 2.0
c. DECT 6.0
d. US-DECT
3. Bluetooth is designed to cover what type of area?
a. Metropolitan
b. Wide area
c. Local area
d. Personal area
4. How many Bluetooth devices can be paired?
a. Two
b. Four
c. Six
d. Eight
5. Bluetooth operates in which frequency band?
a. 2.4 GHz
b. 5.0 GHz
c. 900 MHz
d. 10 GHz
6. What is the current Bluetooth standard?
a. Bluetooth 2008
b. Bluetooth 2.1 + EDR
c. Bluetooth 2.0
d. Bluetooth 1.1
7. Which group is responsible for Bluetooth development?
a. IEEE
b. Bluetooth SIG
c. Bluetooth Forum
d. Bluetooth Inc
8. ZigBee is used for what common deployments? (Choose all that apply.)
a. Home automation
b. Monitoring
c. GPS location
d. Control systems
Trang 29. ZigBee operates in which frequency band?
a. 2.4 GHz
b. 5.0 GHz
c. 900 MHz
d. 10 GHz
10. True or false: WiMax interferes with 802.11 LANs because it operates on the same frequency band
a. True
b. False
11. WiMax is designed for what type of connections?
a. Last-mile access
b. Wireless mesh LANs
c. Point-to-multipoint WANs
d. Single-cell
12. WiMax is defined in which IEEE specification?
a. 802.15.1
b. 802.16e
c. 802.1
d. 802.3
13. Fixed line of sight (LOS) offers which data rate?
a. 40 Mbps
b. 100 Mbps
c. 1 Gbps
d. 10 Mbps
14. NLOS advertises which data rate?
a. 30 to 40 Mbps
b. 100 Mbps
c. 70 Mbps
d. 1 Gbps
15. Which of the following are potential sources of interference for WLANs? (Choose all that apply.)
a. Microwave
b. Fluorescent light
c. Magnet
d. Microphone
Trang 3Foundation Topics
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 5.8-2.4-GHz phone With that said, let’s look at cordless phone tech-nology in more detail
To begin with, cordless phones can useTime 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
Cordless Phone
2.4 GHz ISM
Cordless Phone on a Base Station
Figure 8-1 Standard Cordless Phone Usage
Key
Topic
Trang 4Bluetooth 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, desklap-tops, 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
As of July 26, 2007, the adopted standard according to the Bluetooth SIG is Bluetooth 2.1 + EDR One of the key features of the 2.1 standard is an improved quick-pairing process,
in which you simply hold two devices close together to start the quick-pairing process
Also, a new technology called “sniff subrating” increases battery life up to five times
Bluetooth 2.1 + EDR is backward-compatible with Bluetooth 1.1
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
Trang 5Slave 1
Slave 4
Bluetooth Master
2.4 GHz Piconet
Mouse
PDA
Game Controller Camera
Slave 3
Slave 7
Sla
ve 2
Slave 5
Figure 8-2 Bluetooth Piconet
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
The ZigBee website says:
“ZigBee was created to address the market need for a cost-effective, standards-based wireless networking solution that supports low data-rates, low-power consumption, security, and reliability
“ZigBee is the only standards-based technology that addresses the unique needs of most remote monitoring and control and sensory network applications
“The initial markets for the ZigBee Alliance include Energy Management and Effi-ciency, Home Automation, Building Automation and Industrial Automation.”1
Key
Topic
Trang 6You might be wondering how this technology relates to WLANs and how it might inter-fere The answer is that ZigBee operates in the ISM bands: 868 MHz in Europe, 915 MHz
in countries such as the U.S and Australia, and 2.4 GHz pretty much everywhere The 2.4 GHz operation range is where the issue lies, because that is the range in which 802.11b/g WLANs operate
Figures 8-3, 8-4, and 8-5 show some common ZigBee topologies Figure 8-3 shows the star topology, in which the center device is a network coordinator (NC) Every network has an NC Other devices can be full-function devices, and still others can be reduced-function devices Full-reduced-function devices can send, receive, and so on A reduced-reduced-function device doesn’t have as much capability and could do something like report the tempera-ture of a system back to a controller
The cluster topology shown in Figure 8-4 also has an NC, as well as some full-function de-vices and reduced-function dede-vices This cluster topology resembles an extended star in LAN terms
Reduced Function Device Full Function Device Coordinator (NC)
Figure 8-3 ZigBee Star Topology
Reduced Function Device Full Function Device Coordinator (NC)
Figure 8-4 ZigBee Cluster Topology
Key Topic
Key Topic
Trang 7Certain scenarios call for all devices to communicate with each other in a coordinated ef-fort to provide some sort of information This is where you find a mesh topology, as shown in Figure 8-5
WiMax
Worldwide Interoperability for Microwave Access (WiMax) is defined by the WiMax fo-rum and standardized by the IEEE 802.16 suite The most current standard is 802.16e According to the WiMax Forum:
“WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to wired broadband like cable and DSL WiMAX provides fixed, nomadic, portable and, soon, mobile wireless broadband connectivity without the need for direct line-of-sight with a base station In a typical cell radius deployment of three to ten kilometers, WiMAX Forum Certified systems can be ex-pected to deliver capacity of up to 40 Mbps per channel, for fixed and portable ac-cess applications
“This is enough bandwidth to simultaneously support hundreds of businesses with
T-1 speed connectivity and thousands of residences with DSL speed connectivity Mo-bile network deployments are expected to provide up to 15 Mbps of capacity within
a typical cell radius deployment of up to three kilometers It is expected that WiMAX technology will be incorporated in notebook computers and PDAs by 2007, allowing for urban areas and cities to become ‘metro zones’ for portable outdoor broadband wireless access.”2
You must understand a few aspects of WiMax; the first is the concept of being fixed line
of sight (LOS) or non-LOS (mobile) In non-LOS, mobile doesn’t mean mobile in the sense that most of us think WiMax mobility is more like the ability to travel and then set up shop temporarily When you are done, you pack up and move on A few service providers use this technology to provide end-user access as an alternative to DSL or cable modem Your signal range in this Non-LOS scenario is about 3 to 4 miles, and data rates are adver-tised at around 30 Mbps, but you can expect less—closer to 15 Mbps
Reduced Function Device Full Function Device Coordinator (NC)
Figure 8-5 ZigBee Mesh Topology
Key
Topic
Trang 8Other service providers are targeting business customers in a fixed LOS WiMax deploy-ment in which the topology most closely resembles that of a traditional T1, being a point-to-point type of topology and providing backhaul or backbone services This fixed LOS advertises 30 to 70 Mbps throughput, but you can expect around 40 Mbps
Note I know of a company in the Seattle area that advertises a 100-Mbps connection point-to-point with 10 Gbps of bandwidth per month at no additional charge If you go over the 10 Gbps limit, you are charged additional fees
As the IEEE standardizes WiMax technology, it has progressed from the original 802.16
to 802.16a, c, d, and finally 802.16e
As mentioned, the WiMax defines last-mile access Figure 8-6 shows a sample topology in which subscribers have a point-to-point connection back to a service provider and from there have access to the public Internet
WiMax operates on the 10- to 66-GHz frequency band, so it doesn’t interfere with 802.11 LANs So why is it discussed in this section? The school of thought here is that, with some planning, a device acting as a gateway can be deployed offering 802.11 LAN access with 802.16 last-mile access or upstream access to a service provider, thus removing the need for wires The question of how feasible this is lies in the hands of the vendors devel-oping the products and the standards committees ensuring interoperability Some vendors, however, have tested this technology in lab environments with much success
Subscriber
Subscriber
Base Station P2P
P2P
Public Internet
Figure 8-6 WiMax Deployment
Key Topic
Trang 9Other Types of Interference
Other types of interference can occur in the same frequency ranges These devices might not be the most obvious, but they should be considered They can include the following:
■ Microwaves (operate at 1 to 40 GHz)
■ Wireless X11 cameras (operate at 2.4 GHz)
■ Radar systems (operate at 2 to 4 GHz for moderate-range surveillance, terminal traffic control, and long-range weather and at 4 to 8 GHz for long-range tracking and air-borne weather systems)
■ Motion sensors (operate at 2.4 GHz)
■ Fluorescent lighting (operates at 20000 Hz or higher)
■ Game controllers and adapters (usually operate at 2.5 GHz) When dealing with wireless deployments, you can use tools to determine signal strength and coverage, but just knowing about these additional sources of interference will save you some time in determining where to place APs and clients
Trang 10Exam Preparation Tasks
Review All the Key Topics
Review the most important topics from this chapter, denoted with the Key Topic icon
Table 8-2 lists these key topics and the page number where each one can be found
Definition of Key Terms
Define the following key terms from this chapter, and check your answers in the Glossary:
Bluetooth, ZigBee, WiMax, Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Digital Enhanced Cordless Telecommunications (DECT), Spe-cial Interest Group (SIG), adaptive Frequency Hopping Spread Spectrum technology, En-hanced Data Rate (EDR), 802.15.1, 802.15.1-2005, sniff subrating, wireless personal-area network (WPAN), 802.16e, WiMax
Endnotes
1About ZigBee, http://www.zigbee.org/en/markets/index.asp
2About WiMax, http://www.wimaxforum.org/technology/
References in This Chapter
Digital Enhanced Cordless Telecommunications, Wikipedia.org, http://en.wikipedia.org/
wiki/Digital_Enhanced_Cordless_Telecommunications, December 2006 Bluetooth, Wikipedia.org, http://en.wikipedia.org/wiki/Bluetooth ZigBee, Wikipedia.org, http://en.wikipedia.org/wiki/Zigbee, February 2008
Table 8-2 Key Topics for Chapter 8