Network Plus Unit 4 Section 2: Wireless Networking

1/28/20101/28/2010Network PlusUnit 4 Section 2: Wireless Networking

Wireless Concepts

In this section we will discuss wireless concepts.AntennasFrequency rangesSignal types

AntennasAntennaOmnidirectional Common types of low-gain omnidirectional antennas are the whip antenna, "Rubber Ducky", ground plane antenna, vertically oriented dipole antenna, discone antenna, mast radiator, horizontal loop antenna (sometimes known colloquially as a 'circular aerial' because of the shape), and the halo antenna.Directional A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources. Directional antennas like Yagi-Uda antennas provide increased performance over dipole antennas when a greater concentration of radiation in a certain direction is desired.Network+ Guide to Networks, 5th Edition3

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Figure 8-3 Multipath signal propagation

Frequency Ranges2.4-GHz band Frequency range: 2.42.4835 GHz11 unlicensed communications channelsMost commonly used 1 6 - 11Susceptible to interferenceMicrowave, cordless phone, WAP compete5-GHz band Shorter distanceLess interference

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Network+ Guide to Networks, 5th Edition11Narrowband, Broadband, and Spread Spectrum SignalsDefines wireless spectrum use:NarrowbandTransmitter concentrates signal energy at single frequency, very small frequency rangeBroadbandRelatively wide wireless spectrum bandHigher throughputs than narrowbandSpread-spectrumMultiple frequencies used to transmit signalOffers security

Spread Spectrum Signals FHSS (frequency hopping spread spectrum)Signal jumps between several different frequencies within bandSynchronization pattern known only to channels receiver, transmitterUsed by Blue ToothDSSS (direct-sequence spread spectrum)Signals bits distributed over entire frequency band at onceUsed by 802.11xReceiver reassembles original signal upon receiving bits12

Network+ Guide to Networks, 5th Edition13WLAN (Wireless LAN) ArchitectureAd hoc WLANWireless nodes transmit directly to each otherUse wireless NICs No intervening connectivity devicePoor performanceMany spread out users, obstacles block signalsAccess point (AP)Accepts wireless signals from multiple nodesRetransmits signals to networkBase stations, wireless routers, wireless gateways

AdHoc An Ad Hoc network uses a connection between two or more devices without using a wireless access point: the devices communicate directly when in range. An Ad Hoc network is used in situations such as a quick data exchange or a multiplayer LAN game because setup is easy and does not require an access point. Due to its peer-to-peer layout, Ad Hoc connections are similar to Bluetooth ones and are generally not recommended for a permanent installation

14Ad Hoc Configuration

Figure 8-4 An ad hoc WLAN

Windows Ad Hoc Configuration

Network+ Guide to Networks, 5th Edition15Access Point ConfigurationInfrastructure Infrastructure WLANStations communicate with access pointNot directly with each otherAccess point requires sufficient power, strategic placementWLAN may include several access pointsDependent upon number of stationsMaximum number varies: 10-100

Network+ Guide to Networks, 5th Edition16WLAN Configuration

Figure 8-5 An infrastructure WLAN

Network+ Guide to Networks, 5th Edition18WLAN Bridged

Figure 8-6 Wireless LAN interconnection

Understanding 802.11x WAN TechnologyIn this section we will discuss the technologies behind the 802.11x standard.

802.11 WLANsWireless technology standardPhysical and Data Link layersUses CSMA/CA (Collision Avoidance)802.11b, 802.11a, 802.11g, 802.11n Share characteristicsHalfduplexing, access methodFrame contains 4 addresses2 for WAP and 2 for device

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Access Methods CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)Minimizes collision potentialUses ACK packets to verify every transmissionRequires more overhead than 802.3Real throughput less than theoretical maximumRTS/CTS (Request to Send/Clear to Send) protocolOptionalEnsure packets not inhibited by other transmissionsEfficient for large transmission packetsFurther decreases overall 802.11 efficiencyNetwork+ Guide to Networks, 5th Edition21

RTS/CTS ModeCTS Mode - CTS (Clear To Send)Function used to minimize collisions among wireless devices on a wireless local area network (WLAN). CTS will make sure the wireless network is clear before a wireless client attempts to send wireless data. Enabling CTS will add overhead and may lower wireless throughput.SettingsAuto - CTS will monitor the wireless network and automatically decide whether to implement CTS based on the amount of traffic and collisions that occur on the wireless network.Always - CTS will always be used to make sure the wireless LAN is clear before sending data.None - Typically used in a pure 802.11g environment. If CTS is set to None in a mixed mode environment populated by 802.11b clients, wireless collisions may occur frequently.If you have a mixed environment, both 802.11b and 802.11g clients, the recommended setting is Auto. Auto is the default setting. Note: If you are in a pure 802.11g environment (802.11g devices only), you can optimize the performance by setting the CTS to None.

Network+ Guide to Networks, 5th Edition22Association ProcessProcess that connects to WAP

ScanningSurveying surroundings for access pointActive scanning transmits special frameProbePassive scanning listens for special signal called a Beacon fame

Network+ Guide to Networks, 5th Edition23Association (contd.)SSID (service set identifier)Unique character string identifying access pointIn beacon fame informationConfigured in access pointCan turn broadcast off for increased securityBSS (basic service set)Station groups sharing access point BSSID (basic service set identifier)Station group identifier

Basic Service SetThe basic service set (BSS) is the basic building block of an 802.11 wireless LAN. In infrastructure mode, a single access point (AP) together with all associated stations (STAs) is called a BSS.[1] This is not to be confused with the coverage of an access point, which is called basic service area (BSA). [2] An access point acts as a master to control the stations within that BSS. In ad hoc mode a set of synchronized stations, one of which acts as master, forms a BSS. Each BSS is identified by a BSSID. The most basic BSS consists of one access point and one station

Network+ Guide to Networks, 5th Edition24Extended Service SetESS (extended service set)Access point group connecting same LANShare ESSID (extended service set identifier)Allows roamingStation moving from one BSS to another without losing connectivityRe-associationSeveral access points detectedSelect strongest signal, lowest error ratePoses security riskPowerful, rogue access point

Extended Service SetAn extended service set (ESS) is a set of one or more interconnected BSSs and integrated local area networks that appear as a single BSS to the logical link control layer at any station associated with one of those BSSs.The set of interconnected BSSs must have a common service set identifier (SSID). They can work on the same channel, or work on different channels to boost aggregate throughputThe Extended Service Set Identification (ESSID) is one of two types of Service Set Identification (SSID). In an ad hoc wireless network with no access points, the Basic Service Set Identification (BSSID) is used. In an infrastructure wireless network that includes an access point, the ESSID is used, but may still be referred to as SSID.An SSID is a 32-character (maximum) alphanumeric key identifying the name of the wireless local area network. Some vendors refer to the SSID as the network name. For the wireless devices in a network to communicate with each other, all devices must be configured with the same SSID.

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Figure 8-7 A network with a single BSS

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Figure 8-8 A network with multiple BSSs forming an ESS

Switching between WAPsQuestion:I'd like to add wireless to my network, and I need multiple access points to cover the whole area. I'd like to set them up so that there's only one "wireless network" that the clients see, and it switches them as seamlessly as possible between access points as they wander around (if that's not possible, then at least have it so that they don't need to set up the security by hand on each one the first time, if possible).Answer:The last time I did this, I setup the same SSID and WPA keys on two access points and set them to different channels. I've been told that due to overlapping frequencies, the channels 1, 6, and 11 are the best ones to use. I set mine up on 1 and 6. So far everything seems to be working well. My Windows-based clients connect to either one seamlessly, and the software will normally choose the one with the strongest signal automatically.

Windows WAP Settings

Network+ Guide to Networks, 5th Edition31802.11bDSSS (direct-sequence spread spectrum) signaling2.4-GHz bandSeparated into 22-MHz channelsThroughput11-Mbps theoretical5-Mbps actual100 meters node limitOldest, least expensiveBeing replaced by 802.11g

802.11aReleased after 802.11b5-GHz bandNot congested like 2.4-GHz bandLower interference, requires more transmit powerThroughput54 Mbps theoretical11 and 18 Mbps effectiveAttributable to higher frequencies, unique modulating data method, more available bandwidth20 meter node limitMore expensive, least popularNetwork+ Guide to Networks, 5th Edition32

Network+ Guide to Networks, 5th Edition33802.11gAffordable as 802.11bThroughput54 Mbps theoretical20 to 25 Mbps effective100 meter node range2.4-GHz frequency bandCompatible with 802.11b networks

Network+ Guide to Networks, 5th Edition34802.11nDraft: expected ratification in late 2009ManufacturersSelling 802.11n-compatible transceiversPrimary goalWireless standard providing much higher effective throughputMaximum throughput: 600 MbpsBackward compatible with 802.11a, b, g standards2.4-GHz or 5-GHz frequency range

Network+ Guide to Networks, 5th Edition36802.11n (contd.)MIMO (multiple input-multiple output) page 380Multiple access point antennas may issue signal to one or more receiversIncreases networks throughput, access points range

Figure 8-10 802.11n access point with three antennas

Bluetooth Networks Version 1.1Maximum theoretical throughput: 1 MbpsEffective throughput: 723 Kbps10 meter node differenceDesigned for PANs (personal area networks)Version 2.0 (2004)Different encoding schemes2.1-Mbps throughput30 meters node differenceUsage: cellular telephones, phone headsets, computer peripherals, PDAsNetwork+ Guide to Networks, 5th Edition41

Network+ Guide to Networks, 5th Edition42Summary of WLAN Standards

Table 8-1 Wireless standards

WAP ConfigurationIn this section we will discuss basic Wireless Access configuration using a Linksys router running the dd-wrt firmware.

Network+ Guide to Networks, 5th Edition49Configuring Wireless Connectivity DevicesSet SSIDDetermine if beacon on or offSecurityWPA2 is bestSecure passwordVerify DHCP settingsOptional Port forwardingdd-wrt Configuration

dd-wrt Configuration - SSID

dd-wrt Configuration - DHCP

dd-wrt Configuration - DynDNS

dd-wrt ConfigurationPort Forwarding

802.16 (WiMAX) Internet AccessWiMAX (Worldwide Interoperability for Microwave Access)Current version: 802.16e (2005)Improved mobility, QoS characteristicsDigital voice signals, mobile phone usersFunctions in 2 and 66 GHz rangeLicensed, nonlicensed frequenciesline-of-sight paths between antennasThroughput potential maximizedNon-line-of-sight pathsExchange signals with multiple stations at onceNetwork+ Guide to Networks, 5th Edition62802.16 (WiMAX) Internet Access (contd.)Two distinct advantages over Wi-FiMuch greater throughput (70 Mbps)Much farther range (30 miles)Appropriate for MANs and WANsHighest throughput achieved over shortest distances between transceiversPossible usesAlternative to DSL, broadband cableWell suited to rural usersInternet access to mobile computerized devicesResidential homesNetwork+ Guide to Networks, 5th Edition63Network+ Guide to Networks, 5th Edition64802.16 (WiMAX) Internet Access (contd.)

Figure 8-22 WiMAX residential service installationSatellite Internet AccessUsed to deliver:Digital television and radio signalsVoice and video signalsCellular and paging signalsProvides homes and businesses with Internet accessNetwork+ Guide to Networks, 5th Edition67Network+ Guide to Networks, 5th Edition68Satellite OrbitsGeosynchronous orbitSatellites orbit the Earth at the same rate as the Earth turnsDownlinkSatellite transponder transmits signal to Earth-based receiverTypical satellite24 to 32 transpondersUnique downlink frequenciesLEO (low Earth orbiting) satellitesOrbit Earth with altitude 100 miles to 1240 milesNot positioned over equatorNetwork+ Guide to Networks, 5th Edition69Satellite Orbits (contd.)

Figure 8-25 Satellite communicationNetwork+ Guide to Networks, 5th EditionNetwork+ Guide to Networks, 5th EditionThe End