CWNA guide to wireless LANs 2nd ch02

WLAN Devices: Wireless Network Interface Card • Network interface card NIC: Connects computer to network so that it can send and receive data • Wireless NICs perform same function, but

CWNA Guide to Wireless LANs, Second Edition

Chapter Two

Wireless LAN Devices and Standards

• List WLAN devices and describe their basic

functions

• Explain the different types of communication

standards and why standards are important

• List the three major wireless standards and

regulatory agencies and their functions

• Describe the different IEEE WLAN standards

WLAN Devices: Wireless Network

Interface Card

• Network interface card (NIC): Connects computer

to network so that it can send and receive data

• Wireless NICs perform same function, but without wires

• When wireless NICs transmit:

– Change computer’s internal data from parallel to

serial transmission

– Divide data into packets and attach sending and

receiving computer’s address

– Determine when to send packet

– Transmit packet

WLAN Devices: Wireless Network

Interface Card (continued)

Figure 2-1: Network interface card for a wired network

WLAN Devices: Wireless Network

Interface Card (continued)

Figure 2-2: Wireless NICs for desktop computers: (a) PCI network interface card, (b) standalone USB device, (c) USB key fob

WLAN Devices: Wireless Network

Interface Card (continued)

Figure 2-3: Wireless NICs for laptop computers: (a) CardBus card; (b) Mini PCI card

WLAN Devices: Wireless Network

Interface Card (continued)

• For smaller devices, several options:

– CardBus or Type II PC Card

• May require a sled

– CompactFlash (CF) card: Consists of small circuit board containing flash memory chips and dedicated

controller chip

• Small and consume little power

– SDIO (Secure Digital I/O) or SDIO NOW! Card:

Provides high-speed data input/output with low

power consumption

WLAN Devices: Wireless Network

Interface Card (continued)

• A movement towards integrating wireless NICs

– Would eliminate need for external wireless NICs

• Software drivers necessary to allow wireless NIC

and operating system (OS) to interface

– Windows XP and PDA OSs have built-in drivers

WLAN Devices: Access Point

• Three major parts:

– Antenna and radio transmitter/receiver

– RJ-45 wired network interface

– Special bridging software

• To interface wireless devices to other devices

• Two basic function:

– Base station for wireless network

– Bridge between wireless and wired networks

WLAN Devices: Access Point

(continued)

Figure 2-6: An access point acts as a bridge between the wireless network and a wired network

WLAN Devices: Access Point

(continued)

• Range depends on several factors:

– Type of wireless network supported

– Walls, doors, and other solid objects

• Number of wireless clients that single AP can

support varies:

– Theoretically over 100 clients

– No more than 50 for light network use

– No more than 20 for heavy network use

• Power over Ethernet (PoE): Power delivered to

AP through unused wires in standard unshielded twisted pair (UTP) Ethernet cable

WLAN Devices: Remote Wireless

Bridge

• Bridge: Connects two network segments together

– Even if they use different types of physical media

• Remote wireless bridge: Connects two or more

wired or wireless networks together

– Transmit at higher power than WLAN APs

– Use directional antennas to focus transmission in

single direction

– Delay spread: Minimize spread of signal so that it

can reach farther distances

– Have software enabling selection of clearest

transmission channel and avoidance of noise and

interference

WLAN Devices: Remote Wireless

Bridge (continued)

Figure 2-8: Point-to-point remote wireless bridge

WLAN Devices: Remote Wireless

Bridge (continued)

Figure 2-9: Point-to-multipoint remote wireless bridge

WLAN Devices: Remote Wireless

Bridge (continued)

• Four modes:

– Access point mode: Functions as standard AP

– Root mode: Root bridge can only communicate with

other bridges not in root mode

– Non-root mode: Can only transmit to another bridge

in root mode

– Repeater mode: Extend distance between LAN

segments

• Placed between two other bridges

• Distance between buildings using remote wireless bridges can be up to 18 miles at 11 Mbps or 25

miles transmitting 2 Mbps

WLAN Devices: Remote Wireless

Bridge (continued)

Figure 2-10: Root and non-root modes

WLAN Devices: Remote Wireless

Bridge (continued)

Figure 2-11: Repeater mode

WLAN Devices: Wireless Gateway

• Combines wireless management and security in

Understanding Standards

• Standards make it easier to purchase and use wide variety of products

• Wireless technology based on standards

– Standards help ensure different products from

different vendors function in same capacity

The Need for Standards

• Standards for telecommunications have been

essential since very beginning

– Without standards telecommunications would

• In reality, standards have proven to be more

beneficial than harmful

Advantages and Disadvantages of

Standards

Table 2-1: Advantages and disadvantages of standards

Types of Standards

• De facto standards: Common practices that the

industry follows for various reasons

– Ranging from ease of use to tradition to what

majority of users do

– Usually established by success in marketplace

• De jure standards: Official standards

– Controlled by organization or body that has been

entrusted with that task

– Process for creating these standards can be very

involved

Types of Standards (continued)

• One complaint against de jure standards is amount

of time it takes for a standard to be completed

• Consortia: Usually industry-sponsored

organizations that want to promote a specific

technology

– Goal is to develop a standard that promotes

organization’s specific technology in little time

Enforcing Standards

• Marketplace itself enforces some standards

– Standards created by consortia often regulated by marketplace

• De jure standards often enforced by outside

regulatory agency

– Ensure that participants adhere to prescribed

standards

– Must have power to enforce standards and

effectively punish those who refuse to abide by them

Wireless Standards Organizations and

Regulatory Agencies

• Three primary standard-setting and regulatory

bodies that play major role in wireless LAN

Institute of Electrical and Electronics

Engineers (IEEE)

• Establishes standards for telecommunications

– Also covers wide range of IT standards

• World’s largest technical professional society

– 37 Societies and Councils

– Publish technically focused journals, magazines, and proceedings

– Work on over 800 standards

• Best known for its work in establishing standards for computer networks

– Project 802

Institute of Electrical and Electronics

Engineers (continued)

Table 2-2: Current IEEE 802 committees

Wi-Fi Alliance

• Wireless Ethernet Compatibility Alliance

(WECA): Consortium of wireless equipment

manufacturers and software providers formed to

promote wireless network technology

– Three goals:

• Encourage wireless manufacturers to use IEEE 802.11 technologies

• Promote and market these technologies to consumers

at home, and in small and large organizations

• Test and certify that wireless products adhere to the IEEE 802.11 standards

Wi-Fi Alliance (continued)

• WECA changed name to Wi-Fi Alliance in 2002

– Reflected name of certification that it uses (Wi-Fi) to verify that products follow IEEE standards

– Only products that pass Wi-Fi Alliance tests may be referred to as Wi-Fi Certified

• Wi-Fi Alliance now allows businesses to apply to

be registered as a Wi-Fi ZONE

– Qualifies them to be placed in online database of

wireless hotspot locations

• Can be accessed through Alliance’s Web site

Federal Communications Commission

(FCC): Responsibilities

• Primary regulatory agency for wireless

communications in U.S and territorial possessions

– Independent government agency

– Directly responsible to Congress

• Broad range of responsibilities

– Develop and implement regulatory programs

– Process applications for licenses and other filings

– Analyze complaints

– Conduct investigations

– Take part in congressional hearings

FCC: Regulating the Radio Frequency

Spectrum

• FCC regulates radio frequency spectrum

– Entire range of all radio frequencies

– Spectrum divided into 450 different bands

– U.S obligated to comply with international spectrum allocations

• FCC license normally required to send and receive

on a specific frequency

– License-exempt spectrum or unregulated bands:

Bands that are available nationwide to all users

– Created to foster development of new devices

FCC: Regulating the Radio Frequency

Spectrum (continued)

Table 2-3: Common radio frequency bands

FCC: Regulating the Radio Frequency

Spectrum (continued)

• Two unregulated bands used for WLANs

• Industrial, Scientific, and Medical (ISM) band

• Unlicensed National Information Infrastructure (U-NII) band: Intended for devices that provide

short-range, high-speed wireless digital

communications

• Negative features of unregulated bands:

– Devices from different vendors may attempt to use same frequency

• Can cause interference and unpredictability

FCC: Regulating the Radio Frequency

Spectrum (continued)

Table 2-4: Unlicensed bands

Types of Wireless LANs

• Since late 1990s, IEEE has approved four

standards for wireless LANs:

IEEE 802.11

• Specified that wireless transmission could take

place via infrared (IR) or radio signals

• Infrared Transmissions:

– Can send data by the intensity of the infrared light

wave

– Light spectrum: All types of light

– Infrared light: Can be used for wireless

transmissions

• Invisible

– Emitter: Device that transmits a signal

– Detector: Device that receives a signal

IEEE 802.11 (continued)

Figure 2-13: Directed transmission

IEEE 802.11 (continued)

Figure 2-14: Diffused transmission

IEEE 802.11 (continued)

• Infrared Transmissions (continued):

– Advantages:

• Does not interfere with other communications signals

• Not affected by other signals

• Does not penetrate walls

– Disadvantages:

• Lack of mobility

• Limited range

• Confined to indoor use

• Slow transmission speed

IEEE 802.11 (continued)

• Radio Wave Transmissions:

– Radio waves can penetrate through objects

• Provides mobility

– Radio waves travel longer distances

– Can be used indoors and outdoors

– Radio waves can travel at much higher speeds than infrared transmissions

– IEEE 802.11 standard outlining radio wave

transmissions has become preferred method for

wireless LANs

IEEE 802.11b

• 802.11 standard’s 2 Mbps bandwidth not sufficient for most network applications

• 802.11b amendment added two higher speeds (5.5

Mbps and 11 Mbps) to original 802.11 standard

– Uses ISM band

• Supports wireless devices up to 115 meters (375 feet) apart

– Radio waves decrease in power over distance

– 802.11b standard specifies that, when devices out of range to transmit at 11 Mbps, devices drop

transmission speed to 5.5 Mbps

IEEE 802.11a

• IEEE 802.11a standard specifies maximum rated

speed of 54 Mbps

– Also supports 48, 36, 24, 18, 12, 9,and 6 Mbps

transmissions using U-NII band

• 802.11a and 802.11b published at same time

– 802.11a came to market later due to technical issues and high production cost

• Range of 802.11a is less than that of 802.11b

IEEE 802.11g

• Effort to combine best features of 802.11a and

802.11b

– Data transfer rates to 54 Mbps

– Support devices up to 115 meters apart

• 802.11g standard specifies that devices operate

entirely in ISM frequency

Projected IEEE 802.11n

• Currently in evaluation stage

• Top speed of 802.11n standard will be anywhere from 100 Mbps to 500 Mbps

• Ratification may not occur until 2006

– Devices based on standard may appear prior to that

• 802.11 pre-N

• Wireless LAN devices are in many respects similar

to those found in a wired network; the main

difference is that wireless devices use an antenna

or other means to send and receive signals instead

of a wired connection

• An access point (AP) is both the base station for the wireless network and a bridge to connect the wireless network with the wired network

• A remote wireless bridge is a wireless device

designed to connect two or more wired or wireless networks together

Summary (continued)

• Standards ensure that devices from one vendor will interoperate with those from other vendors, and

create competition between vendors

• There are three regulatory bodies that play a major role in wireless LAN technology: the IEEE, the Wi-

Fi Alliance, and the FCC

• There currently are three standards or types of

wireless LANs: IEEE 802.11b, IEEE 802.11a, and IEEE 802.11g