Chapter 8 Wireless Networking Collected and Compiled By JD Willard MCSE, MCSA, Network+, Microsoft IT Academy Administrator Computer Information Systems.

Chapter 8 Wireless Networking

Collected and CompiledBy JD WillardMCSE, MCSA, Network+, Microsoft IT Academy AdministratorComputer Information Systems InstructorAlbany Technical College

CIS 1140 Network Fundamentals

Attention: Accessing Demos• This course presents many demos. • The Demos require that you be logged in to the Virtual

Technical College web site when you click on them to run. • To access and log in to the Virtual Technical College web site:

– To access the site type www.vtc.com in the url window– Log in using the username: CIS 1140 or ATCStudent1– *Enter the password: student

• If you should click on the demo link and you get an Access Denied it is because you have not logged in to vtc.com or you need to log out and log back in.

*Remember that passwords are case sensitive so enter it in all lower case letters.

Objectives• Explain how nodes exchange wireless signals• Identify potential obstacles to successful wireless

transmission and their repercussions, such as interference and reflection

• Understand WLAN (wireless LAN) architecture• Specify the characteristics of popular WLAN transmission

methods, including 802.11 a/b/g/n• Install and configure wireless access points and their

clients • Describe wireless MAN and WAN technologies, including

802.16 and satellite communications

Wireless Basics Demo

Wireless Transmission• Networks that transmit signals through the atmosphere via infrared or RF waves are

known as wireless networks or wireless LANs (WLANs)• Computers communicate using standard networking protocols, but without the use of

cabling to connect devices • The computers transmit data by means of wireless signals produced by infrared

(requiring equipment to be in a direct line of sight) or radio waves• Wireless networks require installation of NICs with built-in antennas and uses access

points as hubs• Wireless networks use the 2.4-2.4835 GHz frequency range

Introduction Demo

Wireless Hardware Overview Demo

The Wireless Spectrum• Continuum of

electromagnetic waves– Data, voice

communication– Arranged by

frequencies• Lowest to highest

– Spans 9 KHz and 300 GHz

• Wireless services associated with one area

• Most cordless telephones and many wireless LANs use frequencies around 2.4 GHz.

• FCC oversees United States frequencies

• ITU oversees international frequencies

– Air signals propagate across borders

Characteristics of Wireless Transmission

•Wireless signals originate from electrical current traveling along a conductor•The signal travels from the transmitter to an antenna, which emits the signal, as a series of electromagnetic waves, to the atmosphere•The signal propagates through the air until it reaches its destination•At the destination, another antenna accepts the signal, and a receiver converts it back to current

Characteristics of Wireless Transmission• Similarities with wired

– Layer 3 and higher protocols– Signal origination

• From electrical current, travel along conductor• Differences from wired

– Signal transmission• No fixed path, guidance

• Antenna– Signal transmission and reception– Same frequency required on each antenna

• Share same channel

Wireless Vs Wired Networks Demo

Characteristics of Wireless Transmission

Wireless transmission and reception

Antennas• Radiation pattern describes relative strength over

three-dimensional area of all electromagnetic energy the antenna sends or receives

• Directional antenna issues wireless signals along a single direction

• Omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions

• Range: geographical area an antenna or wireless system can reach, generally about 100m

Antennas Demo

Signal Propagation• LOS (line-of-sight)

– Signal travels• In straight line, directly from transmitter

to receiver• Obstacles affect signal travel

– Pass through them– Absorb into them– Subject signal to three phenomena

• Reflection: bounce back to source• Diffraction: splits into secondary waves• Scattering: diffusion in multiple

different directions• Multipath signals

– Wireless signals follow different paths to destination

– Caused by reflection, diffraction, scattering– Advantage

• Better chance of reaching destination– Disadvantage

• Signal delay

Multipath signal propagation

Signal Degradation

• Fading– Change in signal strength

• Electromagnetic energy scattered, reflected, diffracted

• Attenuation– Signal weakens

• Moving away from transmission antenna– Correcting signal attenuation

• Amplify (analog), repeat (digital)

• Noise– Significant problem

• No wireless conduit, shielding

Frequency Ranges• 2.4-GHz band (older)

– Frequency range: 2.4–2.4835 GHz– 11 unlicensed communications channels– Susceptible to interference

• Unlicensed– No FCC registration required

• 5-GHz band (newer)– Frequency bands

• 5.1 GHz, 5.3 GHz, 5.4 GHz, 5.8 GHz

– 24 unlicensed bands, each 20 MHz wide– Used by weather, military radar communications

Narrowband, Broadband, and Spread Spectrum Signals

• Narrowband: transmitter concentrates signal energy at single frequency or in very small range of frequencies

• Broadband: uses relatively wide band of wireless spectrum– Offers higher throughputs than narrowband

• Spread spectrum: use of multiple frequencies to transmit a signal which offers security

• FHSS (frequency hopping spread spectrum)– Signal jumps between several different frequencies within band– Synchronization pattern known only to channel’s receiver, transmitter

• DSSS (direct-sequence spread spectrum)– Signal’s bits distributed over entire frequency band at once– Each bit coded

• Receiver reassembles original signal upon receiving bits

Wireless Transmission Methods Demo

Fixed versus Mobile

• Fixed communications wireless systems– Transmitter, receiver locations do not move– Transmitting antenna focuses energy directly toward

receiving antenna• Point-to-point link results

– Advantage• No wasted energy issuing signals• More energy used for signal itself

• Mobile communications wireless systems– Receiver located anywhere within transmitter’s range

• Receiver can roam

Wireless LAN (WLAN) Architecture

An ad-hoc WLANWireless Topologies Demo

• Ad hoc WLAN– Wireless nodes

transmit directly to each other

– Use wireless NICs • No intervening

connectivity device

– Poor performance• Many spread out

users, obstacles block signals

• Access point (AP)– Accepts wireless signals

from multiple nodes• Retransmits signals to

network

– Base stations, wireless routers, wireless gateways

Wireless LAN Architecture

An infrastructure WLAN

• Infrastructure Mode WLAN– Stations communicate

with access point• Not directly with each

other

– Access point requires sufficient power, strategic placement

• WLAN may include several access points– Dependent upon number

of stations– Maximum number varies:

10-100

Wireless LAN Architecture

Wireless LAN interconnection

•A WAP works as a wireless bridge to connect the wireless nodes to the wired network•A WAP must be strategically located so that stations can communicate with it•The maximum number of stations each access point can server varies from 10 to 100•Stations must stay within the range of a WAP, generally 300 feet or 100 meters

Wireless Access Points Demo

WLAN Architecture• Mobile networking allows

roaming wireless nodes– Range dependent upon

wireless access method, equipment manufacturer, office environment

• Access point range: 300 feet maximum

• Can connect two separate LANs– Fixed link, directional

antennas between two access points

• Allows access points 1000 feet apart

• Support for same protocols, operating systems as wired LANs

– Ensures compatibility Wireless LAN interconnection

802.11 WLANs• Wireless technology

standard– Describes unique functions

• Physical and Data Link layers

– Differences• Specified signaling

methods, geographic ranges, frequency usages

– Developed by IEEE’s 802.11 committee

• Wi-Fi (wireless fidelity) standards– 802.11b, 802.11a, 802.11g,

802.11n (draft)– Share characteristics

• Half-duplexing, access method, frame format

Wireless Networking Standards Demo

Radio Frequency Networking Demo

Wireless Networks: 802.11

A WLAN with multiple access points

Access Method• 802.11 MAC services

– Append 48-bit (6-byte) physical addresses to frame• Identifies source, destination

• Same physical addressing scheme as 802.3– Allows easy combination

• Wireless devices– Not designed for simultaneous transmit, receive– Cannot quickly detect collisions– Use different access method

• CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)– Minimizes collision potential– Uses ACK packets to verify every transmission

• Requires more overhead than 802.3• Real throughput less than theoretical maximum

• RTS/CTS (Request to Send/Clear to Send) protocol– Optional– Ensure packets not inhibited by other transmissions– Efficient for large transmission packets– Further decreases overall 802.11 efficiency

Association• Packet exchanged between computer, access point

– Gain Internet access• Scanning

– Surveying surroundings for access point– Active scanning transmits special frame

• Probe– Passive scanning listens for special signal

• Beacon fame

• SSID (service set identifier)– Unique character string used to identify an access

point• In beacon fame information

– Configured in access point– Better security, easier network management

• BSS (basic service set)– Station groups sharing access point – BSSID (basic service set identifier)

• Station group identifier A network with a single BSS

Association• ESS (extended service set)

– Access point group connecting same LAN• Share ESSID (extended service set identifier)

– Allows roaming• Station moving from one BSS to another without

losing connectivity

• Several access points detected– Select strongest signal, lowest error rate– Poses security risk

• Powerful, rogue access point

• ESS with several authorized access points– Must allow station association with any access

point• While maintaining network connectivity

• Reassociation– Mobile user moves from one access point’s range

into another’s range– Occurs by simply moving, high error rate

• Stations’ scanning feature– Used to automatically balance transmission loads

• Between access points

A network with multiple BSSs forming an ESS

Frames• 802.11 networks overhead

– ACKs, probes, beacons• 802.11 specifies MAC sublayer frame type• Multiple frame type groups

– Control: association and reassociation• Probe, beacon frames

– Management: medium access, data delivery• ACK and RTS/CTS frames

– Data: carry data sent between stations• 802.11 data frame overhead

– Four address fields• Source address, transmitter address, receiver address, destination address

– Sequence Control field• How large packet fragmented

– Frame Control field• Wi-Fi share MAC sublayer characteristics• Wi-Fi differ in modulation methods, frequency, usage, ranges

Basic 802.11 data frame

802.11b• 802.11b also know as Wi-Fi for Wireless Fidelity• The oldest and least expensive wireless standard• Compatible with 802.11g and being replace by 802.11g• Uses Direct Sequence Spread Spectrum signaling in the 2.4-GHz band• Theoretical maximum throughput of 11Mbps; actual throughput

typically around 5Mbps• Nodes must stay within 100 meters of an access point • 802.11b Wireless Local Area Networks (WLANs) support three non-

overlapping or non-interfering channels that can be used in a single area

• The Wireless Access Points or bridges must use non-adjacent, non-overlapping radio channels to prevent interference from the adjacent bridge or Access Point

• When using multiple bridges to cover a large area, you should ensure that the channels are configured in such a way that there is no overlapping

802.11b Demo

802.11a• Released after 802.11b• 802.11a differs from 802.11b and 802.11g in that it uses

multiple frequency bands in the 5GHz range• Not congested like 2.4-GHz band

– Lower interference, requires more transmit power • Provides a maximum theoretical throughput of 54Mbps,

though its effective throughput falls generally between 11 and 18Mbps

• Attributable to higher frequencies, unique modulating data method, more available bandwidth

• The average geographic range for an 802.11a antenna is 20 meters, or approximately 66 feet

• As a result, 802.11a networks require a greater density of access points between the wire-bound LAN and wireless clients to cover the same distance that 802.11b networks cover

• More expensive than either 802.11b or 802.11g• Not compatible with either 802.11b and 802.11g802.11a Demo

802.11g• 802.11g is just as affordable as 802.11b • A maximum theoretical throughput of 54Mbps

through different encoding techniques • The effective throughput ranges generally from 20 to

25 Mbps • Its geographic range is 100 meters or 328 feet • 802.11b and 802.11g NICs and WAPs can be mixed

into the same network • 802.11g uses the 2.4-GHz frequency band making it

compatible with 802.11b networks

802.11g Demo

802.11n• Draft: expected ratification in late 2009• Manufacturers

– Selling 802.11n-compatible transceivers• Primary goal

– Wireless standard providing much higher effective throughput• Maximum throughput: 600 Mbps

– Threat to Fast Ethernet• Backward compatible with 802.11a, b, g standards• May use either the 2.4-GHz or 5-GHz frequency range.• Compared with 802.11a, 802.11g

– Same data modulation techniques• Compared with three 802.11 standards

– Manages frames, channels, encoding differently• Allows high throughput

802.11n Demo

802.11n• MIMO (multiple input-multiple output)

– Multiple access point antennas may issue signal to one or more receivers

– Increases network’s throughput, access point’s range• Channel bonding

– Two adjacent 20-MHz channels bonded to make 40-MHz channel

• Doubles the bandwidth available in single 20-MHz channel

• Bandwidth reserved as buffers assigned to carry data

• Higher modulation rates– Single channel subdivided into multiple, smaller

channels• More efficient use of smaller channels• Different encoding methods

802.11n access point with three antennas

802.11n• Frame aggregation

– Combine multiple frames into one larger frame– Advantage: reduces overhead

Aggregated 802.11n frame

• Maximum throughput dependencies– Number, type of strategies used– 2.4-GHz or 5-GHz band– Actual throughput: 65 to 600 Mbps

• Backward compatible– Not all 802.11n features work

• Recommendation– Use 802.11n-compatible devices

Bluetooth• Bluetooth is a short-range radio technology aimed at creating a very easy to set up, small in nature, wireless

network. It’s normally used for mobile devices sharing a close proximity. Wireless mice and keyboards commonly use Bluetooth.

• Ericson’s original goals– Wireless technology compatible with multiple devices– Require little power– Cover short ranges

• Aim of Bluetooth Special Interest Group (SIG) – Refine and standardize technology– Result: Bluetooth

• Mobile wireless networking standard using FHSS (frequency hopping spread spectrum) RF signaling in 2.4-GHz band

• Version 1.1– Maximum theoretical throughput: 1 Mbps– Effective throughput: 723 Kbps– 10 meter node difference– Designed for PANs (personal area networks)

• Version 2.0 (2004)– Different encoding schemes

• 2.1-Mbps throughput– communicating nodes can be as far as 30 meters apart– Usage: cellular telephones, phone headsets, computer peripherals, PDAs

Overview of Bluetooth Demo

Summary of WLAN Standards

Wireless standards

Implementing a WLAN

• Designing a small WLAN– Home, small office

• Formation of larger, enterprise-wide WANs• Installing and configuring access points and

clients• Implementation pitfalls

– Avoidance• Material applies to 802.11b and 802.11g

– Most popular

Determining the Design• One access point

– Combine with switching, routing functions

– Connects wireless clients to LAN

– Acts as Internet gateway• Access point WLAN

placement considerations– Typical distances between

access point and client– Obstacles

• Type, number between access point and clients

Determining the Design• Larger WLANs

– Systematic approach to access point placement

• Site survey– Assesses client requirements, facility

characteristics, coverage areas– Determines access point

arrangement ensuring reliable wireless connectivity

• Within given area

– Proposes access point testing• Testing wireless access from farthest

corners

• Install access points– Must belong to same ESS, share

ESSID• Enterprise-wide WLAN design

considerations– How wireless LAN portions will

integrate with wired portions

Enterprise-wide WLAN

Site Survey & Design Demo

Configuring Wireless Connectivity Devices

• Netgear WGR614 (v7)– Popular, low-cost access point– Four switch ports, routing capabilities– Supports 802.11b, 802.11g transmission

• Configuration steps on other small wireless connectivity devices– Differ somewhat– Follow similar process, modify same variables

Configure WAP Demo

The Netgear router Basic Settings page

Netgear router Wireless Settings page

The Netgear router Advanced Wireless Settings page

The Netgear router LAN IP Setup page

The Netgear router Router Status page

Wireless Router Re-Configuration• If something goes awry during your wireless router

configuration, you can force all of the variables you changed to be reset.

• Wireless routers feature a reset button on their back panel. • To reset the wireless router, first unplug it. • Then, using the end of a paperclip, depress the reset button

while you plug it in. • Continue holding down the button for at least 30 seconds

(this time period varies among manufacturers; check your wireless router’s documentation for the duration yours requires).

• At the end of this period, the wireless router’s values will be reset to the manufacturer’s defaults.

Configuring Wireless Clients• Configuration varies from one client type to

another• Windows XP client WLAN configuration

– Use graphical interface• Linux and UNIX clients wireless interface

configuration– Use graphical interface– iwconfig is a command-line function for viewing

and setting wireless interface parameters and it is common to nearly all versions of Linux and UNIX

Configuring Wireless Clients

Windows XP Wireless Network Connection Properties dialog box

Windows XP Wireless network properties dialog box

Configure Wireless client Demo

Configuring Wireless Clients

Output from iwconfig command

Avoiding Pitfalls• Access point versus client configurations

– SSID mismatch– Incorrect encryption– Incorrect channel, frequency– Standard mismatch (802.11 a/b/g/n)

• Incorrect antenna placement– Verify client within 330 feet

• Interference– Because wireless signals cannot depend on a conduit or shielding to

protect them from extraneous EMI, they are more vulnerable to noise. – The extent of interference depends partly on the density of signals

within a geographical area.– If intermittent and difficult-to-diagnose wireless communication errors

occur, interference might be the culprit.– Check for EMI sources

Wireless WANs and Internet Access

• Wireless broadband– Latest wireless WAN technologies– Specifically designed for:

• High-throughput, long-distance digital data exchange

802.11 Internet Access• Access points: 802.11b or 802.11g access methods• Hot spots

– Places with publicly available wireless Internet access– Free or subscription

• Hot spot subscription Internet access– Log on via Web page– Client software managing client’s connection

• Network log on, secure data exchange• Added security: accept connection based on MAC address

• Accept user’s connection based on MAC address

802.16 (WiMAX) Internet Access• WiMAX (Worldwide Interoperability for Microwave Access)

– Current version: 802.16e (2005)• Improved mobility, QoS characteristics• Digital voice signals, mobile phone users

• Functions in 2 and 66 GHz range– Licensed, nonlicensed frequencies

• line-of-sight paths between antennas– Throughput potential maximized

• Non-line-of-sight paths– Exchange signals with multiple stations at once

• Two distinct advantages over Wi-Fi– Much greater throughput (70 Mbps)– Much farther range (30 miles)

• Appropriate for MANs and WANs• Highest throughput achieved over shortest distances between transceivers• Possible uses

– Alternative to DSL, broadband cable– Well suited to rural users– Internet access to mobile computerized devices– Residential homes

Residential WiMAX Installation• In residential WiMAX the carrier installs a

small antenna on the homeowner’s roof or chimney or even inside the house. – This antenna is connected to a device

similar to a cable or DSL modem for clients to access the LAN.

– The connectivity device could be incorporated along with the antenna in the same housing or might be separate.

– If separate, the device typically attaches to the antenna with coaxial cable.

– It’s often combined with a router. • The homeowner’s antenna communicates

in a non-line-of-sight fashion with the service provider’s antenna. – If the service provider’s facility is far away, it

might use multiple antennas on towers that communicate in a line-of-sight manner. WiMAX

residential antenna

802.16 (WiMAX) Internet Access

WiMAX service provider’s antenna

• Metropolitan area installation– Home antenna, connectivity device

eliminated

• WiMAX MANs– Extensive connectivity– Download data rates faster than home

broadband connection– Shared service

• Apportioned bandwidth

• Drawback– Expensive

Satellite Internet Access

• Used to deliver:– Digital television and radio signals– Voice and video signals– Cellular and paging signals

• Provides homes and businesses with Internet access

Satellite Orbits• Geosynchronous orbit

– Geosynchronous orbiting satellites are the type used by the most popular satellite Internet access service providers

– Satellites orbit the Earth at the same rate as the Earth turns

– Downlink• Satellite transponder

transmits signal to Earth-based receiver

– Typical satellite• 24 to 32 transponders• Unique downlink

frequencies• LEO (low Earth orbiting)

satellites– Orbit Earth with altitude 100

miles to 1240 miles– Not positioned over equator

• MEO (medium Earth orbiting) satellites– Orbit Earth 6000 to 12,000 miles above surface– Not positioned over equator

• Latitude between equator and poles– Advantage

• Cover larger Earth surface area than LEO satellites

• Less power, less signal delay than GEO satellites

• Geosynchronous orbiting satellites most popular for satellite Internet access

Satellite Frequencies

• Five frequency bands– L-band—1.5–2.7 GHz– S-band—2.7–3.5 GHz– C-band—3.4–6.7 GHz– Ku-band—12–18 GHz– Ka-band—18–40 GHz

• Within bands– Uplink, downlink transmissions differ

• Satellite Internet access providers typically use frequencies in the C- or Ku- bands.– Ka-band (future)

Satellite Internet Services• Subscriber

– Small satellite dish antenna, receiver– Exchanges signals with provider’s

satellite network• Satellite Internet access service

– Dial return arrangement (asymmetrical)

• Receives Internet data via downlink transmission

• Sends data to satellite via analog modem connection

– Satellite return arrangement (symmetrical)

• Send, receive data to and from Internet using satellite uplink and downlink

• Upstream and downstream throughputs are advertised to reach 400–500 Kbps.

– In reality, throughputs are often higher

Dial return satellite Internet service

Summary

• WLAN Architecture characteristics• Popular WLAN Physical, Data Link layer standards• Wireless signal exchange• Small WLAN considerations• Larger, enterprise-wide WAN formation• Installing, configuring access points, clients• WLAN Pitfalls• MANs, WANs wireless transmission• Satellite Internet Access characteristics