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CIS 1140 Network Fundamentals Chapter 8 Wireless Networking Collected and Compiled By JD Willard MCSE, MCSA, Network+, Microsoft IT Academy Administrator Computer Information Systems Instructor Albany Technical College 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 (case sensitive) • 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. • If you should click on the demo link and you are taken to the VTC.com web site page you should do a search in the search box for the CompTIA Network+ (2009 Objectives) Course and run the video from within that page. 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 WAN technologies, including 802.16 (WiMAX), HSPA+, LTE, 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 FCC oversees United States frequencies ITU oversees international frequencies – Air signals propagate across borders 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 Wireless Vs Wired Networks Demo – Signal transmission and reception – Same frequency required on each antenna Antennas • Radiation pattern – Relative strength over three-dimensional area • Of all electromagnetic energy that antenna sends, receives • Directional antenna – Issues wireless signals along single direction • Omnidirectional antenna – Issues, receives wireless signals • Equal strength, clarity in all directions • Range – Reachable geographical area • Generally about 100m Antennas Demo Wireless Antenna Types (3:09) 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 – Variation 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, very small frequency range • Broadband – Relatively wide wireless spectrum band – Higher throughputs than narrowband • Spread-spectrum – Multiple frequencies used to transmit signal – Offers security Wireless Transmission Methods Demo Narrowband, Broadband, and Spread-Spectrum Signals (cont’d.) • FHSS (frequency hopping spread spectrum) – Signal jumps between several different frequencies within band – Synchronization pattern known only to channel’s receiver, transmitter FHSS (frequency hopping spread spectrum) Narrowband, Broadband, and Spread-Spectrum Signals (cont’d.) • DSSS (directsequence spread spectrum) – Signal’s bits distributed over entire frequency band at once – Each bit coded • Receiver reassembles original signal upon receiving bits DSSS (direct sequence spread spectrum) Spread-Spectrum Signals Characteristic Frequency Hopping Spread Spectrum (FHSS) Direct-Sequence Spread Spectrum (DSSS) Description FHSS uses a narrow frequency band and 'hops' data signals in a predictable sequence from frequency to frequency over a wide band of frequencies. Because FHSS shifts automatically between frequencies, it can avoid interference that may be on a single frequency. Hopping between frequencies also increases transmission security by making eavesdropping and data capture more difficult. The transmitter breaks data into pieces and sends the pieces across multiple frequencies in a defined range. DSSS is more susceptible to interference and less secure then FHSS. 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 • Ad hoc WLAN – Wireless nodes transmit directly to each other – Use wireless NICs • No intervening connectivity device – Poor performance An ad-hoc WLAN • Many spread out users, obstacles block signals Ad hoc WLAN Topology Description An ad hoc network: Works in peer-to-peer mode without an access point (the wireless NICs in each host communicate directly with one another). Ad hoc Uses a physical mesh topology with a logical bus topology. Is cheap and easy to set up. Cannot handle a large number of hosts. Requires special modifications to reach wired networks. You will typically only use an ad hoc network to create a direct, temporary connection between two hosts. Wireless LAN Architecture • 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 Access point (WAP) – Accepts wireless signals from multiple nodes • Retransmits signals to network – Base stations, wireless routers, wireless gateways An infrastructure WLAN Infrastructure Mode WLAN Topology Description Wireless Topologies Demo An infrastructure wireless network employs an access point (AP) that functions like a hub on an Ethernet network. With an infrastructure network: The network uses a physical star topology with a logical bus topology. Infrastructure You can easily add hosts without increasing administrative efforts (scalable). The access point can be easily connected to a wired network, allowing clients to access both wired and wireless hosts. The placement and configuration of access points require planning to implement effectively. You should implement an infrastructure network for all but the smallest of wireless networks. Wireless Access Point •A Wireless Access Point: o Works as a wireless bridge o Connects wireless nodes to the wired network o Must be strategically located o The maximum number of stations each WAP can serve varies from 10 to 100 o Range of a WAP generally 300 feet or 100 meters Wireless Access Points Demo Access Point Placement (3:36) 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 • Notable Wi-Fi standards – 802.11b, 802.11a, 802.11g, 802.11n – Share characteristics • Half-duplexing, access method, frame format Radio Frequency Networking Demo Wireless Networking Standards Demo 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 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 Figure 8-9 CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance Courtesy Course Technology/Cengage Learning Characteristic Description Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) uses the following process: 1. The sending device listens to make sure that no other device is transmitting. If another device is transmitting, the device waits a random period of time (called a backoff period) before attempting to send again. 2. If no other device is transmitting, the sending device broadcasts a Request-tosend (RTS) message to the receiver or access point. The RTS includes the source and destination, as well as information on the duration of the requested communication. Media Access 3. The receiving device responds with a Clear-to-send (CTS) packet. The CTS also includes the communication duration period. Other devices use the information in the RTS and CTS packets to delay attempting to send until the communication duration period (and subsequent acknowledgement) has passed. 4. The sending device transmits the data. The receiving device responds with an acknowledgement (ACK). If an acknowledgement is not received, the sending device assumes a collision and retransmits the affected packet. 5. After the time interval specified in the RTS and CTS has passed, other devices can start the process again to attempt to transmit. 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 SSID Management (2:39) 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 Components of a Wireless Network Component Description Station (STA) An STA is a wireless network card (NIC) in an end device such as a laptop or wireless PDA. STA often refers to the device itself, not just the network card. Access Point (AP) An access point (AP), sometimes called a wireless access point, is the device that coordinates all communications between wireless devices as well as the connection to the wired network. It acts as a hub on the wireless side and a bridge on the wired side. It also synchronizes the stations within a network to minimize collisions. A BSS, also called a cell, is the smallest unit of a wireless network. All devices in the BSS can communicate with each other. The devices in the BSS depend on the operating mode: Basic Service Set (BSS) In an ad hoc implementation, each BSS contains two devices that communicate directly with each other. In an infrastructure implementation, the BSS consists of one AP and all STAs associated with the AP. All devices within the BSS use the same radio frequency channel to communicate. Extended Service Set (ESS) Distribution System (DS) An ESS consists of multiple BSSs with a distribution system (DS). The graphic above is an example of an ESS. In an ESS, BSSs that have an overlapping transmission range use different frequencies. The distribution system (DS) is the backbone or LAN that connects multiple APs (and BSSs) together. The DS allows wireless clients to communicate with the wired network and with wireless clients in other cells. Frames • 802.11 networks overhead – ACKs, probes, beacons • 802.11 specifies MAC sublayer frame type • Multiple frame type groups – Control: medium access, data delivery • ACK and RTS/CTS frames Basic 802.11 data frame compared with an 802.3 (Ethernet) frame • – Management: association ad reassociation – Data: carry data sent between stations • • 802.11 data frame overhead – Four address fields • Source address, transmitter address, receiver address, and 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, and range 802.11b • 2.4-GHz band – Separated into 22-MHz channels – Uses Direct Sequence Spread Spectrum • Throughput – 11-Mbps theoretical – 5-Mbps actual typically • 100 meters node limit to access point • Oldest, least expensive • Being replaced by 802.11g 802.11b Demo 802.11a • Released after 802.11b • 5-GHz band – Not congested like 2.4-GHz band • Lower interference, requires more transmit power • Throughput – 54 Mbps theoretical – 11 and 18 Mbps effective • • • • • 20 meter node limit Requires additional access points Rarely preferred More expensive than either 802.11b or 802.11g Not compatible with either 802.11b and 802.11g 802.11a Demo 802.11g • Affordable as 802.11b • Throughput – 54 Mbps theoretical – 20 to 25 Mbps effective • 100 meter node range • 2.4-GHz frequency band – Compatible with 802.11b networks 802.11g Demo 802.11n • Standard ratified in 2009 • 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 • 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, and encoding differently • Allows high throughput 802.11n (cont’d.) • 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 (cont’d.) • Frame aggregation – Combine multiple frames into one larger frame – Advantage: reduces overhead Aggregated 802.11n frame • Maximum throughput dependencies – Number and 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 802.11n Demo Summary of WLAN Standards Wireless standards Wireless Standards (6:04) Wireless Compatibility (2:51) 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 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 Home or small office WLAN arrangement 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 • Access point CD-ROM or DVD – Guides through setup process • Variables set during installation – – – – – Administrator password SSID Whether or not DHCP is used Whether or not the SSID is broadcast Security options Configure WAP Demo Configuring Wireless Clients • Configuration varies from one client type to another • Linux and UNIX clients wireless interface configuration Configure Wireless client Demo – Use graphical interface – iwconfig command-line function • View, set wireless interface parameters 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 – 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 802.16 (WiMAX) • WiMAX (Worldwide Interoperability for Microwave Access) – – – – Most popular version: 802.16e (2005) Improved WiMAX version: 802.16m (2011) Functions in 2-11 or 11-66 GHz range Licensed or nonlicensed frequencies • Ability to transmit and receive signals up to 30 miles – With fixed antennas – About 10 miles when antennas are mobile • 802.16m – Positioned to compete favorably with cellular data services – Backwards compatible with 802.16e equipment • Maximum throughput – Downlink: 120Mbps – Uplink: 60Mbps – Future improvements could take to 1Gbps 802.16 (WiMAX) WiMAX network WiMAX residential antenna 45 Cellular • Initially designed for analog telephone service – Today deliver data and voice • Cellular technology generations – 1G: analog – 2G: digital transmission up to 240Kbps – 3G: data rates up to 384Kbps • Data communications use packet switching – 4G: all-IP, packet switched network for data and voice Cell Phone Technologies Demo Cellular (cont’d.) • Network infrastructure – Cells served by antenna and base station – Controller assigns mobile clients frequencies • Cell size depends on: – – – – • Network’s access method Region topology Population Amount of cellular traffic Basic infrastructure – HSPA+ (High Speed Packet Access Plus) • 3G technology – LTE (Long Term Evolution) • 4G technology Cellular network Satellite Internet Access • Used to deliver: – Digital television and radio signals – Voice and video signals – Cellular and paging signals – Data services to mobile clients in remote locations • Provides homes and businesses with Internet access • Most popular satellite orbit – Geosynchronous Earth orbit (GEO) • Satellites orbit at same rate Earth turns 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 • 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 • Satellite Internet services – Subscriber uses small satellite dish antenna, receiver – Exchanges signals with provider’s satellite network – Typically asymmetrical • Receives Internet data via downlink transmission • Sends data to satellite via analog modem connection – Bandwidth shared among many subscribers – Throughput controlled by service provider – Slower, more latency than other wireless WAN options Dial return satellite Internet service Summary • Wireless spectrum used for data and voice communications – Each type of service associated with specific frequency band • Wireless communication: fixed or mobile • Standards vary by frequency, signal method, and range – Notable wireless standards include 802.11 a/b/g/n • WiMAX 2: specified in IEEE’s 802.16m standard • Satellites can provide wireless data services The End