CWNA guide to wireless LANs 2nd ch02

CWNA Guide to Wireless
LANs, Second Edition
Chapter Two
Wireless LAN Devices and Standards


Objectives
• 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

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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
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WLAN Devices: Wireless Network
Interface Card (continued)

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

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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

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WLAN Devices: Wireless Network
Interface Card (continued)

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

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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
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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

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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

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WLAN Devices: Access Point
(continued)

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

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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
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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

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WLAN Devices: Remote Wireless
Bridge (continued)

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

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WLAN Devices: Remote Wireless
Bridge (continued)

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

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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
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WLAN Devices: Remote Wireless
Bridge (continued)

Figure 2-10: Root and non-root modes

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WLAN Devices: Remote Wireless
Bridge (continued)

Figure 2-11: Repeater mode

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WLAN Devices: Wireless Gateway
• Combines wireless management and security in
single appliance
–
–
–
–
–

Authentication

Encryption
Intrusion detection and malicious program protection
Bandwidth management
Centralized network management

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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

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The Need for Standards
• Standards for telecommunications have been
essential since very beginning
– Without standards telecommunications would
essentially be impossible

• Some IT professionals believe that standards have
stifled growth in the field

– Waiting for standards to catch up to changes slows
down process of change and development

• In reality, standards have proven to be more
beneficial than harmful
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Advantages and Disadvantages of
Standards

Table 2-1: Advantages and disadvantages of standards

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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
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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

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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

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Wireless Standards Organizations and
Regulatory Agencies
• Three primary standard-setting and regulatory
bodies that play major role in wireless LAN
technology
– Institute of Electrical and Electronics Engineers
(IEEE)
– Wi-Fi Alliance
– U.S. Federal Communications Commission (FCC)

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