• Association (cont’d.)• ESS with s

• Association (cont’d.)
• 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
• Frames
• Multiple frame types:
– Control: medium access and data delivery
• ACK and RTS/CTS frames
– Management: association and reassociation
– Data: carry data sent between stations
• Frames (cont’d.)
• 802.11 data frame overhead
– Four address fields
• Source address, transmitter address (AP), receiver address (AP), and destination address
– Sequence Control field
• How large a packet is fragmented (MAC sublayer of the Data Link layer
– On wired TCP/IP occurred at the Transport layer (segmentation)
– Frame Control field
• Holds information about the protocol in use, type of frame, and type of security the frame uses
• Channel Bonding
• Combines two non-overlapping 20 MHz channels into a single 40 MHz channel—results in slightly more than double the bandwidth
• 5.75 GHz Range
– 23 channels and 12 non-overlapping and 6 non-overlapping bonded (combined) channels
• 2.4 GHz Range
– 11 channels and 3 non-overlapped channels
– In the US it is recommended to use channels 1,6, & 11
– In the rest of the world 1, 5, 9, & 13 channels are recommended
– Allows for a maximum of 1 non-overlapping bonded channel and for this reason channel bonding is not practical when using 2.4 GHz
• 2.4 GHz Range
• 802.11b
• 2.4-GHz band
– Separated into 22-MHz channels
• Throughput
– 11-Mbps theoretical
– 5-Mbps actual
• 100 meters node limit
• Oldest, least expensive
• Being replaced by 802.11g
• 802.11a
• Released after 802.11b
• 5-GHz band
– Not congested like 2.4-GHz band
• Less likely to suffer interference from microwave ovens, cordless phones, motors, and other (incompatible) wireless LAN signals
• Require more power to transmit, and they travel shorter distances than lower frequency signals
• Throughput
– 54 Mbps theoretical
– 11 and 18 Mbps effective
• Rarely preferred
• 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
• 802.11n
• Standard ratified in 2009
• Primary goal
– Wireless standard providing much higher effective throughput
• Maximum throughput: 600 Mbps
– Threat to Fast Ethernet
• Mixed Mode--backward compatible with 802.11a, b, g standards
• 2.4-GHz or 5-GHz frequency range
• 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
– Enables devices to make multiple simultaneous connections
• 802.11n (cont’d.)
• Channel bonding
– Two adjacent 20-MHz channels bonded to make 40-MHz channel
• Devices use multiple radio signals simultaneously
• Higher modulation rates
– Orthogonal Frequency-Division Multiplexing (OFDM) modulation technique—like 802.11a & 802.11g
– Single channel subdivided into multiple, smaller channels
• More efficient use of smaller channels
• Different encoding methods
• 802.11n (cont’d.)
• Frame aggregation
– Combine multiple frames into one larger frame
– Advantage: reduces overhead
• Smaller data frames are combined into one larger frame
• 802.11n (cont’d.)
• 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
• Single MIMO antenna: is an antenna that has two or more antennas in a single physical packaged
• 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
• Small Office / Home Office (SOHO)
• One access point
– Contains switching and 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 and number of, between access point and clients
• Determining the Design (cont’d.)
• 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 a given area
• Determining the Design (cont’d.)
• Install access points
– Must belong to same ESS
• Enterprise-wide WLAN design considerations
– How wireless LAN portions will integrate with wired portions
– AP can participate in VLANs, allowing mobile clients to move from one AP’s range to another while belonging to the same virtual LAN
• Wireless Repeater & Extenders
• Devices that receive a transmitted signal, increases its gain (power), and rebroadcasts it to extend its range and coverage
– Original signal strength restored and, in most cases, with much of the noise removed
– Repeaters and extenders can add a small amount of delay (latency) to the signal
– Too many repeaters or extenders on a wireless system may cause timing issues on networks
• 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
• Configuring Wireless Clients
• Configuration varies from one client type to another
• Linux and UNIX clients wireless interface configuration
– Use graphical interface
– iwconfig command-line function
• View, set wireless interface parameters
• Avoiding Pitfalls
• Access point versus client configurations
– SSID mismatch (case sensitive)
– 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
• 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--using fixed antennas
– About 10 miles when antennas are mobile
• 802.16 (WiMAX) (cont’d.)
• 802.16m (A.K.A., WiMAX 2)
– Positioned to compete favorably with cellular data services
– Backwards compatible with 802.16e equipment
• Maximum throughput
– Downlink: 120Mbps
– Uplink: 60Mbps
– Future improvements may see higher throughput 1Gbps
• Cellular
• Initially designed for analog telephone service
– Today delivers 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 transmission

• Cellular (cont’d.)
• Cellular networks coverage areas are divided into cells
– Cells served by an antenna and its base station, or cell site
– At the base station, a controller assigns mobile clients frequencies and manages communication with them
– In network diagrams, cells are depicted as hexagons
– Multiple cells share borders to form a network in a honeycomb pattern
• Cellular (cont’d.)
• Basic infrastructure of a cellular network:
– HSPA+ (High Speed Packet Access Plus)
• 3G technology
– LTE (Long Term Evolution)
• 4G technology (currently the fastest wireless broadband service available in the U.S.)
• Cellular (cont’d.)
• AT&T, Verizon, and Sprint are behind LTE
– LTE could lead to the end of WiMAX
– Companies like Sprint & CLEAR who promoted early WiMAX technologies are focusing more on LTE
• Satellite
• Used to deliver:
– Digital television and radio signals
– Voice and video signals
– Cellular and paging signals
– Data services to mobile clients in remote locations
• Geosynchronous Earth orbit (GEO) are the type used by the most popular satellite data service providers
• GEO satellites orbit at same rate as the Earth turns
• Satellite (cont’d.)
• Downlink
– Satellite transponder transmits signal to Earth-based receiver
• Typical satellite
– Contains 24 to 32 transponders
– Each satellite uses unique frequencies for its downlink
• Satellite (cont’d.)
• Satellite 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 each band, frequencies used for uplink and downlink transmissions differ
• In North America, dish antennas are pointed toward the Southern Hemisphere (because the geosynchronous satellites travel over the equator)
• Satellite (cont’d.)
• Satellite Internet services
– Subscriber uses small satellite dish antenna and receiver, or satellite modem
– Typically asymmetrical
– Bandwidth shared among many subscribers
– Throughput controlled by service provider
– Slower, more latency than other wireless WAN options
• 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