Chapter 01

CÁC TỔ CHỨC VÀ TIÊU CHUẨN CỦA MẠNG KHÔNG

DÂY

2

Mục tiêu

Vai trò của các tổ chức

• FCC

• IEEE

• WIFI – Alliance

Mạng LAN không dây, PANs, MAN, WAN và

  Xác định vai trò công nghệ cho các công nghệ WLAN

  Ưu điểm và nhược điểm của mạng WLAN

3

Các tổ chức

The Federal Communications Commission (FCC)

Là một tổ chức phi chính phủ của Mỹ được thành lập vào năm 1934.

FCC tạo ra các văn bản pháp luật mà các thiết bị WLAN phải tuân thủ theo.

FCC qui định các phổ tần số vô tuyến mà WLAN có thể hoạt động, mức công suất cho phép,…

4

Các tổ chức

The Institute of Electrical and Electronics Engineers (IEEE)

The Wi-Fi Alliance.

5

FCC

Là một tổ chức phi chính phủ của Mỹ được thành lập vào năm 1934.

FCC tạo ra các văn bản pháp luật mà các thiết bị WLAN phải tuân thủ theo chẳng hạn như:

Các tần số sóng vô tuyến (Radio).

Mức công suất đầu ra.

Thiết bị sử dụng trong nhà (indoor) và ngoài trời (outdoor).

6

FCC

Radio Frequencies Available (Các tần số sóng vô tuyến)

FCC cung cấp 2 dãy băng tần miễn phí sau đây để giao tiếp trên sóng vô tuyến (radio):

- Industrial Scientific Medical (ISM) – dành cho công nghiệp, khoa học, y tế.

- Unlicensed National Information Infrastructure (U-NII) – hạ tầng thông tin quốc gia không cấp phép.

FCCIndustrial Scientific Medical (ISM)

900 MHz ISM Band– Từ 902 MHz đến 928 MHz or 915 MHz ± 13 MHz

2.4 GHz ISM Band– Được sử dụng cho các chuẩn 802.11, 802.11b và

802.11g. Hoạt động ở băng tần 2.4000 GHz and 2.5000 GHz (2.4500 GHz ± 50 MHz)

– Trong mạng WLAN, thường chỉ sử dụng ở các tần số 2.4000 - 2.4835 GHz .

5.8 GHz ISM Band– Băng tần này cũng được gọi là băng tần 5 GHz

ISM. Các thiết bị wireless hoạt động trong khoảng 5.725 GHz and 5.875 GHz

7

UNII bands are made up of three separate 100 MHz-wide bands.

The three bands are known as the lower, middle, and upper bands. Within each of these three bands, there are four non-overlapping DSSS channels, each separated by 5 MHz.

The FCC mandates that the lower band be used indoors, the middle band be used indoors or outdoors, and the upper band be allocated for outdoor use.

The 5 GHz UNII bands would allow for 8 non-overlapping access points indoors using both the lower and middle UNII bands.

8

FCCUnlicensed National Information Infrastructure (U-NII)

Lower Band

– Bound by 5.15 GHz and 5.25 GHz and is specified by the FCC to have a maximum output power of 50 mW by FCC and 40 mW by IEEE .

Middle Band

– Bound by 5.25 GHz and 5.35 GHz and is specified at:250 mW by FCC.200 mW by IEEE.

Upper Band

– Bound by between 5.725 GHz and 5.825 GHz

– Reserved for outdoor links and is limited by the FCC to 1 Watt (1000 mW ) of output power.

9

FCCUnlicensed National Information Infrastructure (U-NII)

10

FCCISM & UNII

11

FCC

Output Power Levels

The 2.4 GHz ISM band may be used indoors or outdoors, and the output power at the intentional radiator cannot exceed 1 watt and depending on whether the implementation is a point-to-multipoint or a point-to-point implementation.

FCC

Indoor and outdoor usage

- The FCC limits the 5.15–5.25 U-NII band to indoor-only usage.

- The other U-NII bands can be used indoors or outdoors; however, the 5.725–5.825 band is especially well suited for outdoor operations

12

13

IEEE

The Institute of Electrical and Electronics Engineers

The IEEE developed standards that impact and benefit wireless networking.

These standards include wireless specific standards as well as standards that have been implemented in the wired networking domain, which are now being utilized in the wireless networking domain.

14

IEEE 802.11 standards

IEEE 802.11

-The 802.11 standard was the first standard describing the operation of wireless LANs

-Contained all of the available transmission technologies including Direct Sequence Spread Spectrum (DSSS), Frequenc y Hopping Spread Spectrum (FHSS), and infrared .

-IEEE 802.11 standard describes DSSS systems that operate at 1 Mbps and 2 Mbps only

15

IEEE 802.11 standards

IEEE 802.11b-1999 (amended slightly in 2001)

Sử dụng trải phổ chuổi trực tiếp với tần số cao (high-rate direct-sequence spread spectrum - HR/DSSS) thay vì DSSS.

Cung cấp tốc độ truyền dữ liệu (data rates) 11 Mbps.

Uses the 2.4 GHz ISM band (2400 GHz – 24835 GHz).

Có khả năng tương thích ngược với DSSS.

16

IEEE 802.11a - 1999

-Hoạt động ở băng tần 5 GHz UNII.

-Hổ trợ các tốc độ (data rates) 6, 9, 12, 18, 24, 36, 48, and 54 Mbps.

IEEE 802.11 standards

17

IEEE 802.11g-2003

-Hổ trợ trải phổ chuổi trực tiếp (DSSS) và HR/DSSS đồng thời tương thích với điều chế OFDM tại băng tần 2.4 GHz ISM.

-Tốc độ trao đổi dữ liệu: 54 Mbps.

-Có khả năng tương thích ngược (backwards compatibility) với các thiết bị chuẩn 802.11b.

IEEE 802.11 standards

18

IEEE 802.11n (2009)

-Sửa đổi theo IEEE 802.11 tại tầng PHY và MAC.

-Điều này cho phép các thiết bị mạng WLAN có thể truyền thông với thông lượng (throughput) cao hơn và có thể đạt tối đa 100Mbps hoặc cao hơn.

-Điều này được thực hiện nhờ công nghệ MIMO (multiple-input-multiple-output)-

IEEE 802.11 standards

19

IEEE 802.11 standards

IEEE 802.11n (2009)Công nghệ MIMO: Thiết bị phát WLAN chia gói dữ liệu ra thành nhiều phần, mỗi phần được gọi là chuỗi dữ liệu (Spatial Stream) và phát từng chuỗi dữ liệu qua các anten riêng rẽ đến các anten thu.15/9/2009Data rate: 54-600Mbps

WECAWireless Ethernet Compatibility Alliance

Nhiệm vụ WECA là xác nhận khả năng tương tác của các sản phẩm Wi-Fi ™ (IEEE 802. 11 ) và thúc đẩy Wi-Fi như các tiêu chuẩn mạng WLAN trên tất cả các phân khúc thị trường của toàn cầu.

Có 6 công ty bao gồm Intersil, 3Com, Nokia, Aironet (về sau được Cisco sáp nhập), Symbol và Lucent liên kết với nhau để tạo ra Liên minh tương thích Ethernet không dây WECA 

The website for WECA is : www.wirelessethernet.org

20

Wi-Fi Alliance

Khi một sản phẩm đáp ứng được yêu cầu về tính tương thích do WECA kiểm tra tì WECA sẽ gán cho sản phẩm đó một chứng nhần về tính tương thích và cho phép nhà sản xuất sử dụng logo wifi trong việc quảng cáo và đóng gói sản phẩm.

Logo này nói lên rằng thiết bị đó có thể giao tiếp được với các thiết bị khác có logo Wi-Fi.

21

22

Spread Spectrum Technology

Spread spectrum technology is used in multiple ways that can be organized within four primary categories: wireless LANs, wireless PANs (WPANs), wireless MANs (WMANs) and wireless WANs.

23

Wireless LANs

There are three primary roles that wireless LANs play in today’s enterprise organizations:

■ Access role

■ Distribution role

■ Core role

24

In the access role, the wireless network is used to provide wireless clients with access to wired resources. The access point remains fixed while the clients may move.

The access point is usually connected to an Ethernet network where other resources, such as file servers, printers,…, reside.

Access role

25

26

In the distribution role, wireless bridges provide a backhaul connection between disconnected wired networks.

In this case, each network is connected to the Ethernet port of a wireless bridge and the wireless bridges communicate with each other using the IEEE 802.11 standard.

Once these connections are made, network traffic can be passed across the bridge link so that the two previously disconnected networks may act as one.

Distribution role

27

Distribution role

28

In the core role, the wireless LAN is the network. This

may be suitable for small networks built on-the-fly, such

as those built at construction sites or in disaster areas.

However, the limited data throughput will prohibit the

wireless LAN from being the core of the network in a

large enterprise installation.

Core role

29

Core role

30

Wireless PANs

A wireless PAN (personal area network) provides hands-free connectivity and communications within a confined range and limited throughput capacity.

Bluetooth is a perfect example of a wireless PAN technology that is both beneficial and in widespread use.

Operating in the 2.4 GHz ISM band, Bluetooth technologies can cause interference with wireless LAN technologies like DSSS, HR/DSSS, and ERP. However, the newer adaptive frequency hopping technology helps to reduce this interference if not completely remove it. Adaptive frequency hopping is a new feature found in Bluetooth 1.2 devices and higher.

31

Wireless PAN Network

32

WPAN

33

Wireless MANs

WiMAX is the most commonly referenced wireless MAN technology.

WiMAX is based on the IEEE 802.16 standard and provides expected throughput of approximately 40 Mbps for fixed, line of sight connections and approximately 15 Mbps for mobile, non–line of sight connections.

In addition to the throughput speeds, WiMAX incorporates QoS mechanisms that help to provide greater throughput for all users and important applications using the network.

34

Wireless WANs

Wide area networks (WANs) are usually used to connect LANs together. If the LANs are separated by a large distance, WAN technologies may be employed to connect them. These technologies include Frame Relay, analog dial-up lines, Digital Subscriber Line (DSL), ISDN, and others.

Free Space Optics is an example of wireless WAN technologies.

The key differentiator of wireless WAN technologies from WLAN, WPAN, and WMAN is that the wireless WAN link aggregates multiple communications channels together (multiplexing) and passes them across the single WAN link.

35

Wireless LAN Technology Roles

Corporate Data Access and End-User Mobility

36

Wireless LAN Technology Roles

Network Extension to Remote Areas

37

Wireless LAN Technology Roles

Building-to-Building Connectivity: Bridging

38

Wireless LAN Technology Roles

Last-Mile Data Delivery: Wireless ISP

39

Small Office/Home Office (SOHO) Use

Wireless LAN Technology Roles

40

Mobile Office Networking

Educational/Classroom Use

Wireless LAN Technology Roles

Industrial: Warehousing and Manufacturing

Health Care: Hospitals and Offices

41

Advantages of WLAN

Mobility is primary advantage of wireless technology

Easier and Less Expensive Installation: Installing network cabling in older buildings difficult and costly

Increased Reliability

– Eliminates certain types of cable failures and increases overall network reliability

42

Disadvantages of WLAN

Security: Wireless signals broadcast in open air

– Security for wireless LANs is the prime concern

Unauthorized users might access network

Attackers might view transmitted data

Employees could install rogue access points

Attackers could easily crack existing wireless security Radio Signal Interference: Signals from other devices can

disrupt wireless transmissions

Health Risks: Wireless devices emit RF energy

43

Glossary

FCC The Federal Communications Commission (FCC) is responsible for defining limitations and allowances for radio frequency communications—among other things—in the United States and its territories. They define the regulations that are then implemented in IEEE and other standards.

IEEE The Institute of Electrical and Electronics Engineers specifies standards based on regulations defined by regulatory bodies.

Wi-Fi Alliance An organization that certifies equipment to be interoperable with other equipment in the WLAN industry based on their certification standards.

44

Summarise

direct sequence spread spectrum (DSSS) One of the originalPhysical layer technologies specified in the IEEE 802.11 standard that provides instantaneous data rates of 1 or 2 Mbps and operates in the 2.4-GHz frequency band.

HR/DSSS Originally specified in the IEEE 802.11b amendment, the high-rate/direct-sequence spread spectrum Physical layer specifies data rates up to 11 Mbps.

45

Review Questions

1. Which of the following organizations is responsible for compatibility testing of 802.11 hardware?

A. IEEE

B. ETSI

C. Wi-Fi Alliance

D. FCC

46

Review Questions

2. You want to read the 802.11 standard so that you can better understand the details of the MAC and PHY layer functionality in wireless LANs. Which organization’s web site should you visit?

A. IEEE

B. ETSI

C. Wi-Fi Alliance

D. FCC

47

Review Questions

3. Which of the following technologies are not wireless WAN solutions? (Choose all that apply.)

A. Zigbee

B. Free Space Optics

C. Wi-Fi Access Points

D. Bluetooth

48

Review Questions

4. What are the two types of wireless bridge links that can be created? (Choose two.)

A. Point-to-point

B. Building-to-building

C. Point-to-multipoint

D. Remote-to-local

49

Review Questions

5. Which one of the following does a wireless LAN provide that a wired network does not?

A. Mobility

B. Centralized security

C. Reliability

D. VPN security

50

Review Questions

6. Which one of the following would not be an appropriate use of a wireless LAN?

A. Connecting two buildings together that are on opposite sides of the street

B. Connecting two computers together in a small office so they can share a printer

C. Connecting a remote home to a WISP for Internet access

D. Connecting two rack-mounted computers together

51

Review Questions

7. Wireless ISPs provide which one of the following services?

A. Small office/home office services

B. Connectivity for large enterprises

C. Last mile data delivery

D. Building-to-building connectivity