Title: CWNA Guide to Wireless LANs, Second Edition
1CWNA Guide to Wireless LANs, Second Edition
- Chapter Two
- Wireless LAN Devices and Standards
2Objectives
- 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
3WLAN 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 computers internal data from parallel to
serial transmission - Divide data into packets and attach sending and
receiving computers address - Determine when to send packet
- Transmit packet
4WLAN Devices Wireless Network Interface Card
(continued)
Figure 2-1 Network interface card for a wired
network
5WLAN 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
6WLAN Devices Wireless Network Interface Card
(continued)
Figure 2-3 Wireless NICs for laptop computers
(a) CardBus card (b) Mini PCI card
7WLAN 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
8WLAN 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
9WLAN 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
10WLAN Devices Access Point (continued)
Figure 2-6 An access point acts as a bridge
between the wireless network and a wired network
11WLAN 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
12WLAN 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
13WLAN Devices Remote Wireless Bridge (continued)
Figure 2-8 Point-to-point remote wireless bridge
14WLAN Devices Remote Wireless Bridge (continued)
Figure 2-9 Point-to-multipoint remote wireless
bridge
15WLAN 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
16WLAN Devices Remote Wireless Bridge (continued)
Figure 2-10 Root and non-root modes
17WLAN Devices Remote Wireless Bridge (continued)
Figure 2-11 Repeater mode
18WLAN Devices Wireless Gateway
- Combines wireless management and security in
single appliance - Authentication
- Encryption
- Intrusion detection and malicious program
protection - Bandwidth management
- Centralized network management
19Understanding 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
20The 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
21Advantages and Disadvantages of Standards
Table 2-1 Advantages and disadvantages of
standards
22Types 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
23Types 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
organizations specific technology in little time
24Enforcing 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
25Wireless 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)
26Institute of Electrical and Electronics Engineers
(IEEE)
- Establishes standards for telecommunications
- Also covers wide range of IT standards
- Worlds 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
27Institute of Electrical and Electronics Engineers
(continued)
Table 2-2 Current IEEE 802 committees
28Wi-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
29Wi-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 Alliances Web site
30Federal 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
31FCC 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
32FCC Regulating the Radio Frequency Spectrum
(continued)
Table 2-3 Common radio frequency bands
33FCC 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
34FCC Regulating the Radio Frequency Spectrum
(continued)
Table 2-4 Unlicensed bands
35Types 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
36IEEE 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
37IEEE 802.11 (continued)
Figure 2-13 Directed transmission
38IEEE 802.11 (continued)
Figure 2-14 Diffused transmission
39IEEE 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
40IEEE 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
41IEEE 802.11b
- 802.11 standards 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
42IEEE 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
43IEEE 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
44Projected 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
45Summary
- 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
46Summary (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