cwna guide to wireless lan's second edition - chapter 2

CWNA Guide to Wireless LANs, Second Edition

Chapter TwoWireless LAN Devices and Standards

CWNA Guide to Wireless LANs, Second Edition 2

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


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



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



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



• 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



• 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



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



• 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



Figure 2-10: Root and non-root modes



Figure 2-11: Repeater mode


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


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

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


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 technology– Institute of Electrical and Electronics Engineers

(IEEE)– Wi-Fi Alliance– U.S. Federal Communications Commission (FCC)


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



• 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



Table 2-4: Unlicensed bands


Types of Wireless LANs

• Since late 1990s, IEEE has approved four standards for wireless LANs: – IEEE 802.11– IEEE 802.11b– IEEE 802.11a– IEEE 802.11g

• IEEE 802.11n expected to be approved by 2006


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



Figure 2-14: Diffused transmission



• 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



• 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


Summary

• 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

cwna guide to wireless lan's second edition - chapter 2

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