Bài giảng CWNA chương 01 giới thiệu về các tổ chức và tiêu chuẩn của mạng không dây

IEEE 802.11 standardsIEEE 802.11 -The 802.11 standard was the first standard describing the operation of wireless LANs -Contained all of the available transmission technologies includi

Chapter 01

CÁC TỔ CHỨC VÀ TIÊU

CHUẨN CỦA MẠNG KHÔNG

DÂY

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

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,…

 Các tần số sóng vô tuyến (Radio).

 Mức công suất đầu ra.

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

(outdoor).

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 NII) – hạ tầng thông tin quốc gia không cấp phép

– 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

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 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.

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

– 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.

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FCCUnlicensed National Information Infrastructure (U-NII)

ISM & UNII

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.

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

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.

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

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.

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

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

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.

15/9/2009

Data rate: 54-600Mbps

WECA Wireless 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

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.

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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.

Wireless LANs

There are three primary roles that wireless LANs play

in today’s enterprise organizations:

■ Access role

■ Distribution role

■ Core role

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

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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

Distribution role

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

Core role

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

Wireless PAN Network

WPAN

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.

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

Wireless LAN Technology Roles

Corporate Data Access and End-User Mobility

Wireless LAN Technology Roles

Network Extension to Remote Areas

Wireless LAN Technology Roles

Building-to-Building Connectivity: Bridging

Wireless LAN Technology Roles

Last-Mile Data Delivery: Wireless ISP

Small Office/Home Office (SOHO) Use

Wireless LAN Technology Roles

Mobile Office Networking

Educational/Classroom Use

Wireless LAN Technology Roles

Industrial: Warehousing and Manufacturing Health Care: Hospitals and Offices

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

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

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

direct sequence spread spectrum (DSSS) One of the original

Physical 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

Review Questions

 1 Which of the following organizations is

responsible for compatibility testing of

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

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

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

Review Questions

5 Which one of the following does a

wireless LAN provide that a wired network

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

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