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Ryan HeatonDick Al-Bayaty

Wi-FiHow Wireless Communication works1

Overview What is Wi-FiHistoryEthernetIEEE standards 802.11(amendments a,b,g,n)2.4GHz /5GHz differences

2What is Wi-FiWi-Fi is a means which allows for electronic devices to talk to one another or exchange data through radio waves.Common devices utilizing Wi-Fi:ComputersSmartphonesVideo game consolesTablets

3The History1985: FCC releases ISM band

1991: Wi-Fi creates by NCR Corporation/AT&T

1992 & 1996: CISRO obtains patents for methods that were used to Unsmear the Wi-Fi signal

1999: Wi-Fi name trademarked

4The HistoryInitially meant for cashier systems, the first wireless products were brought on the market under the name WaveLAN with speeds of 1Mbps/2Mbps

It is continually advancing under IEEE amendments 802.11a 802.11b 802.11g 802.11n

5The History802.11Release DateFreq.BandwidthData rateper streamAllowableModulationApproximate indoor rangeApproximate outdoor rangeprotocol(GHz)(MHz)(Mbit/s)[7]MIMOstreams(m)(ft)(m)(ft)Jun-972.4201, 21DSSS,FHSS2066100330aSep-995206, 9, 12, 18, 24, 36, 48, 541OFDM351151203903.75,00016,000bSep-992.4201, 2, 5.5, 111DSSS35115140460gJun-032.4206, 9, 12, 18, 24, 36, 48, 541OFDM,DSSS38125140460nOct-092.4/5207.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.24OFDM702302508204015, 30, 45, 60, 90, 120, 135, 15070230250820ac (DRAFT)Nov. 2011520up to 87.6840up to 20080up to 433.3ISM BandISM stands for industrial, scientific, and medical.ISM bands are set aside for equipment that is related to industrial or scientific processes or is used by medical equipment.The ISM band is license-free, provided that devices are low-power.The 802.11 standard is contained by the ISM band.ISM Band

U-NII (Unlicensed National Information Infrastructure) Bands802.11n can operate at the 5G U-NII bands:

U-NII Low (U-NII-1): 5.15-5.25 GHz(indoor use only)

U-NII Mid (U-NII-2): 5.25-5.35 GHz.

U-NII Worldwide: 5.47-5.725 GHz.

U-NII Upper (U-NII-3): 5.725 to 5.825 GHz. 2.4GHz vs. 5GHz2.4 GHz band is divided into 11 overlapping channels spaced by 5 MHz.5GHz band is less likely to be congested. 2.4GHz is more prone to interference, commonly used.The 5GHz band offers much higherthroughput with the same channel width.

102.4GHz vs. 5GHz2.4GHz covers a substantially larger range than 5GHz.Higher frequency wireless signals of 5GHz networks do not penetrate solid objects nearly as well as 2.4GHz.In general, the higher the frequency of awireless signal, the shorter its range.

2.4GHz vs. 5GHz5GHz and 2.4GHz are simply different frequencies, each with its advantages and disadvantages. To get the best of both worlds, some recent routers have the capability for dual-band operation in both ranges simultaneously.

5GHz offers higherthroughputat a shorter distance, while 2.4GHz offers increased coverage and higher solid object penetration.

Protocol Stack

WiFi lives in the data link and physical layers underneath the Ethernet protocol stack13Wireless LAN Networks

Wireless LAN NetworksAd-HocPoint-to-pointMeshInfrastructureStar topologyWLAN ArchitectureAd Hoc Ad-Hoc mode: Peer-to-peer setup where clients can connect to each other directly.

Mobile stations communicate to each other directly.It is set up for a special purpose and for a short period of time. For example, the participants of a meeting in a conference room may create an ad hoc network at the beginning of the meeting and dissolve it when the meeting ends.

16WLAN Architecture Mesh Mesh: Every client in the network also acts as an access or relay point, creating a self-healing and (in theory) infinitely extensible network. Not yet in widespread use, unlikely to be implemented residentially.

Infrastructure network

There is an Access Point (AP), which becomes the hub of a star topology.Any communication has to go through AP. If a Mobile Station (MS), like a computer, a PDA, or a phone, wants to communicate with another MS, it needs to send the information to AP first, then AP sends it to the destination MSMultiple APs can be connected together and handle a large number of clients. Used by the majority of WLANs in homes and businesses.

18Comparison of Two StructuresInfrastructure Ad hocExpansionXFlexibilityXControlXRoutingXCoverageXReliabilityXHow does the RF propagate?AntennasWLAN equipment usually comes with a built-in omni-directional antenna, but some select products will let you attach secondary antennas that will significantly boost range.

AntennasAntennas come in many shapes and styles:Omni-directional:Vertical WhipCeiling mountDirectional:Yagi Pringles can Wall mounted panelParabolic dish

How Can Several Users Communicate Simultaneously?There is a difference between a network designed for voice conversation and one for data exchange.For voice conversations, like telephone and cell phone calls, each person has a dedicated channel during the entire conversation. For data exchange, many users can share one channel. A user sends information when no one else is sending.802.11e: QoS facilitates prioritization of data, voice, and video transmissions.

Share One Channel in Data CommunicationIn data communication, data are grouped into packets/frames. Each packet/frame contains a number of bits of information.

Devices (phones, computers, etc.) do not communicate simultaneously, similar to the concept of sharing a single connection (the air in this case); only one person can use it at one time.

Share One Channel in Data CommunicationSend RTS packetReceive CTS packetSend data packetsSend EOB packetReceive EOBC packetNo CTS packetGenerate random wait timeResend RTS

Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA)

Before an MS (mobile station) sends its packets, it checks to see if someone else is sending information. Only when the medium is free can an MS send packets.

If some station is sending or receiving a signal, the MS that intends to send will generate a random waiting time and wait for its turn. If several MSs are all waiting for their turns, since their waiting times are randomly generated and thus not equal, they will not start sending simultaneously. Thus collision (two or more MSs sending signals simultaneously) is avoided.

It is called Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA).

Image obtained from: http://www.freepatentsonline.com/6611521-0-large.jpg

25Security802.11i provides security enhancementsWEP Wired Equivalent PrivacyAdditional Security MeasuresWPA Wi-Fi Protected AccessWPA2Physical security is a major component of a wired LAN security solution. Wired networks equipment can be locked inside offices. Wireless networks cannot offer the same level of physical security, however, and therefore must depend on additional authentication routines to ensure that users accessing the network are authorized to do so. Authentication is a necessary prerequisite to association because only authenticated users are authorized to use the network. (In practice, though, many access points are configured for "open-system" mode and will authenticate any station.)

Deauthentication terminates an authenticated relationship. Because authentication is needed before network use is authorized, a side effect of deauthentication is termination of any current association.

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