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Is Teaching Wireless Networking in your Future?. Karl Dietrich – Lansing Community College Bill Saichek – Orange Coast College. Thanks to the book publishers. Cengage Sybex. Types of Wireless LANs. Since late 1990s, IEEE has approved five standards for wireless LANs: IEEE 802.11
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Is Teaching Wireless Networkingin your Future? Karl Dietrich – Lansing Community College Bill Saichek – Orange Coast College
Thanks to the book publishers • Cengage • Sybex
Types of Wireless LANs • Since late 1990s, IEEE has approved five standards for wireless LANs: • IEEE 802.11 • IEEE 802.11b • IEEE 802.11a • IEEE 802.11g • IEEE 802.11n
IEEE 802.11 • Specified that wireless transmission could take place via infrared (IR) or radio signals (RF) • Operated at 1 and 2 Mbps • WG formed in 1990
IEEE 802.11b • 802.11 standard’s 2 Mbps bandwidth not sufficient for most network applications • 802.11b amendment added two higher speeds to original 802.11 standard • 5.5 Mbps and 11 Mbps • 2.4-GHz band • Uses ISM band • Separated into 22-MHz channels • DSSS • Direct Sequence Spread Spectrum signaling
IEEE 802.11a • Released after 802.11b • 5-GHz frequency – UNII band • Not congested like 2.4-GHz band • Lower interference, requires more transmit power • Throughput • 54 Mbps theoretical • 11 and 18 Mbps effective • Attributable to higher frequencies and unique modulating data method • OFDM • Orthogonal Frequency Division Multiplexing
802.11g • Throughput • 54 Mbps theoretical • 20 to 25 Mbps effective • 2.4-GHz frequency band • Compatible with 802.11b networks • Operates in the ISM band • Data transfer range • 350 feet or 107 meters apart • Uses OFDM for transmission format • Same as 802.11a but different frequency
IEEE 802.11n • Finally ratified in September 2009 • Speed of 802.11n standard will be anywhere from 100 Mbps to 600 Mbps • 600 Mbps is theoretical not there yet • Standard defines that all 802.11n devices must contain two radios
802.11n • 2.4-GHz or 5-GHz frequency range • Backward compatible with 802.11a, b, g standards • Compared with 802.11a, 802.11g • Same data modulation techniques • Compared with three 802.11 standards • Manages frames, channels, encoding differently • Allows high throughput (HT) • Greenfield mode
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 • Still a one-to-one communication between devices
MIMO Signal Processing Techniques • Spatial Diversity: multiple redundant signals • Spatial Multiplexing creates separate data streams for each transmitting antenna • Maximal Ratio Combining can combine the signals of two antennas to increase the signal strength in a single stream • Transmit Beamforming(TxBF) allows a MIMO transmitter to focus the transmission and send in the direction of the receiving antenna
IEEE 802.11ac • IEEE 802.ac is in now in development • Also called Gigabit Wireless (Gigabit Wifi) • IEEE 802.11ac will be a game changer
IEEE 802.11ac • Some of the 802.11ac technologies include: • Spectrum: will operate in the less-crowded 5 GHz spectrum and not support 2.4 GHz • Roughly 8 times as many channels as 2.4 GHz • Increased channel bandwidth: uses channel bandwidths up to 80 MHz • Error correction coding: stronger processors can handle more internal instruction code • Beam forming: Transmit Beamforming (TxBF) is optional with 802.11n but will be standard for all ac devices
IEEE 802.11ac • A MU-MIMO device can transmit to multiple sources at the same time and it can transmit different data to each end source From Tech Republic – Cheat sheet: What you need to know about 802.11ac By Michael Kassner June 18, 2013
IEEE 802.11ac • Is there a downside to 802.11ac • There will be a significantly smaller coverage area • The 5 GHz range won’t go as far • Attenuation is directly proportional to the frequency • Will need multiple access points in large homes and buildings 802.11ac on the Horizon; Will You Be Ready? Posted on February 25, 2013 by Nick McLain
Access Points • Autonomous Access Points • Also called fat access points • These are quickly becoming obsolete with very limited usage • Lightweight Access Points • Also called thin access points • Does not contain management and configuration functions • Management features are contained in a central device called wireless LAN controller
Wireless LAN Controller • WLAN controller: used to manage devices from a central location • Devices are proprietary – all lightweight APs and WLCs must be from the same vendor • Cloud management: connecting wireless devices together using the Internet in order to remotely manage them • Because devices can be managed remotely there is no need for multiple support teams for each location
Access Points - PoE • Power over Ethernet (PoE) • Power delivered to AP through unused wires in standard unshielded twisted pair (UTP) Ethernet cable • IEEE 802.3af – up to 15.4 watts • Only 12.95 watts of power is used • PoE+ or PoE Plus • IEEE 802.3at – up to 25.5 watts • Multiple radio APs need additional power
Radio Signal Characteristics • Wavelength • Frequency • Amplitude • Phase • The higher the frequency the smaller the wavelength • Phase is measured in distance, time, or degrees
Wavelength • Wavelength • Distance between the wave’s peaks • Can also be measured from anywhere in the wave as long as it is at the same point in each cycle
Frequency • Frequency: Rate at which an event occurs • Number of times that a wave completes a cycle within a given amount of time • When wave completes trip and returns back to starting point it has finished one cycle
Amplitude • Amplitude: the magnitude of change of the wave • Is measured by how high or how deep the wave is • Is essentially a measure of the strength of an electromagnetic wave’s signal
Phase • Phase: the relationship between at least two signals that share the same frequency yet have different starting points
Analog vs. Digital Transmissions • Analog signals are continuous • Digital signals are discrete • WLANs use digital transmissions Analog signal Digital signal
RF Modulation • In order for an electromagnetic wave to transmit information it must be modified • Three types of modulations enable carrier signals to carry information • Amplitude modulation - Height of the signal • Frequency modulation – Frequency of the signal • Phase modulation – change the starting point of the signal
Radio Frequency Behavior: Loss • Loss: Negative difference in amplitude between signals • Attenuation: loss of signal strength due to wave propagation and multipath • Propagation behaviors • FSPL - Natural loss of signal strength through space
Wave Propagation Loss • Reflection • Refraction • Scattering • Diffraction • Absorption
Amplification • Gain: Positive difference in amplitude between two signals • Technically, gain is measure of amplification • Power – a constant measured in mW (milliwatts) • Gain/Loss – a relative figure measured in dB • Combined to become dBm • Active Gain • Intentionally boosting the signal • Passive Gain • Using the antenna to strengthen the signal
Types of Antennas • Three basic categories of antennas: • Omnidirectional • Semidirectional • Highly directional • Each category includes multiple types, each with different characteristics
Omni-directional rod antenna Dipole Antenna
How is the data prepared for transmission • Segments to Packets to Frames • Frames are dependent upon the standard being used to send the data • Wired vs. Wireless • Each wireless standard frames the data differently • Are they compatible?
IEEE 802.11Physical Layer Standards Data Link sublayers
IEEE 802.11Physical Layer Standards PHY sublayers
MAC Frame Formats SDUs and PDUs
MAC Frame Formats – 802.11n A-MSDU and A-MPDU
MAC Frame Types • Three categories of MAC frame types • Management Frames • Used to manage access to wireless networks and to move associations between APs • Control Frames • Used to assist with the delivery of data frames • Data Frames • The actual carriers of application level data
WLAN Service Sets • Service set: all of the devices that are associated with an 802.11 WLAN • Three different WLAN service set configurations: • Basic service set • Extended service set • Independent basic service set
Basic Service Set • Basic Service Set – BSS • One AP with one or more client stations • Infrastructure Mode • Service Set Identifier – SSID • A logical name used to identify an 802.11 wireless network • Comparable to a Windows Workgroup name • Up to 32 characters and is case sensitive
Basic Service Set • Basic Service Area (BSA) • The physical area of coverage provided by an access point in a BSS • Power settings affect the coverage area
Extended Service Set • Extended Service Set (ESS) • One or more BSSs connected by a distribution system medium • An overlap of 15 to 25% is needed to achieve seamless roaming between cells
Independent Basic Service Set • Independent Basic Service Set (IBSS): Wireless network that does not use an AP • Peer-to-peer or ad hoc mode
MAC Operations • MAC layer WLAN functions: • Discovering a WLAN • Joining the WLAN • Transmitting on a WLAN • Remaining connected to WLAN
Discovering the WLAN: Scanning • Two types of scanning • Passive scanning - Wireless device simply listens for beacon frame. The station will determine the AP with the best signal (RSSI) • Active scanning - Wireless device first sends out a management probe request frame then waits for probe response frame • The difference between passive scanning and active scanning is which device initiates the discovery
Joining the WLAN:Authentication and Association • Once a wireless device discovers the WLAN, it next requests to join the network • Authentication • Association • A client must authenticate before it can associate