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Wireless presentation-1
 

Wireless presentation-1

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    Wireless presentation-1 Wireless presentation-1 Presentation Transcript

    • Wireless LANs• Rat‟s nest of wires• Variety of power cords and adapters• Cables for modems, printers, scanner, mouse and keyboards• NEED OF CONNECTING COMPUTERS
    • Challenges• Radio and Infrared transmissions susceptible to noise and interference – Unreliable transmission• Strength varies in time and space – Fading• Finite Radio Spectrum – Shared with other systems• Radio spectrum regulated by different bodies
    • Wireless LANs• IEEE 802.11 Standards• Non IEEE Standards like – Bluetooth, HIPERLAN, HomeRF
    • What is IEEE 802.11?• IEEE: – Institute of Electrical and Electronics Engineers• 802.11: – Family of standards set forth by the IEEE to define the specifications for wireless LANs – Defines: • Medium Access Control (MAC) • Physical Layer (PHY) Specifications
    • IEEE 802.11 and the ISO stack
    • What is IEEE 802.11?• Local, high-speed wireless connectivity for fixed, portable and moving stations – stations can be moving at pedestrian and vehicular speeds• Standard promises interoperability – vendors products on the same physical layer should interoperate• Targetted for use in – inside buildings, outdoor areas, anywhere!
    • IEEE 802.11• Uses Direct Sequence spread spectrum (DSSS) technology – Frequency-Hopping spread spectrum (FHSS) can only be used for 1 or 2Mbps in US due to FCC regulations• Operates in unlicensed 2.4 GHz ISM band – ISM: Industrial, Scientific and Medical – ISM regulatory range: • 2.4 GHz to 2.4835 GHz for North America
    • IEEE 802.11• Supported Speeds and Distances – 1, 2, 5.5, 11 Mbps at distances of 150-2000 feet without special antenna – Greater distances can be achieved by using special antennas – Distance (or signal strength) greatly depends on obstructions such as buildings and other objects – Maximum speed obtained depends on signal strength
    • IEEE 802.11b• „b‟ in IEEE 802.11b – September 1999, 802.11b “High Rate” amendment was ratified by the IEEE – 802.11b amendment to 802.11 only affects the physical layer, basic architecture is the same • Added two higher speeds – 5.5 and 11 Mbps • More robust connectivity• 802.11b is the current „favorite‟ in 802.11 – also known as Wi-Fi (Wireless Fidelity)
    • IEEE 802.11a• “Fast Ethernet” standard of wireless LANs• Speeds of up to 54 Mbps• 5 GHz (U-NII band) instead of 2.4 GHz – Unlicensed National Information Infrastructure• OFDM instead of DSSS for encoding – Orthogonal Frequency Division Multiplexing
    • IEEE 802.11a• Advantages – higher speed – less RF interference than 2.4 GHz • 2.4 GHz used by Bluetooth, cordless/cellular phones, etc. – some interoperability, vendors currently have “dual-standard” 802.11a/b equipment• Disadvantages – shorter range, need to increase AP density or power 4X to compensate
    • IEEE 802.11g• Another high-speed standard• Viewed as a „step‟ towards 802.11a• Speeds of up to 54 Mbps – may be more like 20+ Mbps• Still works at 2.4 GHz – not in the 5 GHz range like 802.11a• Advantages – compatible with 802.11b – better range than 802.11a, for now
    • IEEE 802.11e• Another upcoming standard for WLANs – adds quality-of-service features to MAC layer of 802.11b compatible networks • error correction • better bandwidth management – significantly improves multimedia performance • works around RF interference – handles interference by moving away from it – i.e., moves to a new frequency when interference from a 2.4 GHz cordless phone is detected
    • IEEE 802.11 and the ISO stack
    • IEEE 802.11 Physical Layer• 802.11 Physical Layer Specifications – include FHSS, DSSS, IR• PLCP: Physical Layer Convergence Protocol – interface used by the other physical layer specs – maps data units into a suitable framing format• PMD system: Physical Medium Dependent – defines the characteristics/method of Tx/Rx data through a wireless medium between 2 or more stations
    • IEEE 802.11 Physical Layer• Spread Spectrum – spreads the transmitted signal over a wide range of spectrum – avoids concentrating power in a single narrow frequency band – noise makes this necessary so that receiver can accurately decode the transmitted signal – 2 major approaches to spread spectrum: • FHSS: Frequency Hopping Spread Spectrum • DSSS: Direct Sequence Spread Spectrum
    • IEEE 802.11 Data Link Layer• 2 Sublayers – Logical Link Control (LLC) – Media Access Control (MAC)• 802.11 uses the same 802.2 LLC – same 48-bit addressing as other 802 LANs • MAC address is 6 bytes or 48 bits – allows for simple bridging to wired networks• MAC sublayer is unique in 802.11
    • IEEE 802.11 MAC Sublayer• MAC: Regulates access to the medium• Wired IEEE 802 LANs use CSMA/CD• 802.11 uses CSMA/CA• CSMA: carrier sense multiple access – CD: with collision detection – CA: with collision avoidance• Collision detection is not possible in 802.11 – near/far problem: can‟t transmit and “hear” a collision at the same time
    • IEEE 802.11 MAC Sublayer• CSMA/CA avoids collisions by explicit packet acknowledgment (ACK) – station wishing to transmit first senses the medium – if no activity detected, station waits an additional, random amount of time then transmits if the medium is still free – ACK packet is sent by receiving station to confirm the data packet arrived intact – collision assumed if sending station doesn‟t get ACK, data is retransmitted after a random time
    • IEEE 802.11 MAC Sublayer• Other unique features in 802.11 – IFS: Inter Frame Space • time interval between frames – Handling hidden stations (hidden-node problem) • virtual carrier sense – Power management functions – Data security (MAC address, WEP) • WEP: Wired Equivalent Privacy – Multirate support – Fragmentation / Defragmentation
    • Coordination Functions of MAC• Determine when a station in a BSS is allowed to transmit and when it may be able to receive PDUs over the wireless medium• Distributed Coordination Function (DCF) – Provides support for asynchronous data transfer of MAC SDUs on a best effort basis – Contention Mode for all station
    • Coordination Functions of MAC• Point Coordination Function – Optional and sits on top of DCF – May be implemented by an AP – Connection-oriented time bound transfer of MAC SDUs – Contention and contenion-free periods – Medium usage controlled by AP (synchronization and timing)
    • DCF• Basic access method• Contention services for fair service to all stations• All stations required to support DCF• Based on CSMA-CA protocol – All stations obliged to remain quiet for a certain minimum period after a transmission has been completed called the interframe space (IFS) – High priority frames: SIFS – PCF Priority access to the medium: PIFS – DCF Interframe Space: DIFS • Transmit data and management MPDUs
    • IEEE 802.11: A Closer Look
    • IEEE 802.11 Frame Types• Three types of frames – Control • RTS, CTS, ACK, Contention-Free (CF), PS-Poll • Used for handshaking and for positive acknowledgements during the data transfer – Management • Probe request/response • Station Association and Disassociation with the AP • Timing and Synchronization • Authentication / deauthentication • Announcement traffic indication message (ATIM) – sent after each frame – Data • Transmission of data
    • CSMA-CA operation• A station is allowed to transmit an initial MAC PDU under DCF if the station detects the medium idle for a period DIFS or greater. If the station detects medium busy, then it must calculate a random backoff time to schedule a reattempt. A station that has scheduled a reattempt monitors the medium and decrements a counter each time an idle contention slot expires. The station is allowed to transmit when its backoff timer expires during the contention period.• Idle period after a DIFS period called contention window (CW)
    • Handshaking in CSMA-CA• Required when there is hidden station problem. If a station A wants to send data frame to station B, station A first sends a request-to-send (RTS) frame. If station B receives the RTS frame, then B issues a clear-to-send (CTS) frame. All stations within range of B receive CTS frame and are aware that station A has been given permission to send, so they remain quiet while station A proceeds with its data frame transmission. If the data frame arrives without error, station B responds with an ACK. If two stations send RTS frames at the same time and they collide at B then the stations must execute a backoff to schedule a later attempt.
    • DIFS Contention Window PIFS SIFSDIFS Busy Medium Next Frame Wait for Time Defer Access reattempt time Basic CSMA-CA operation
    • IEEE 802.11 Topologies• Three basic topologies for WLANs – IBSS: Independent Basic Service Set – BSS: Basic Service Set – ESS: Extended Service Set• Independent of type of PHY chosen
    • IEEE 802.11 IBSS• IBSS: Independent Basic Service Set – Peer-to-peer or ad-hoc network – Wireless stations communicate directly with one another – Generally are not connected to a larger network – No Access Point (AP)
    • IEEE 802.11 BSS• BSS: Basic Service Set – Infrastructure mode – An AP connects clients to a wired network
    • BSS• Defined as group of stations that coordinate their access to the medium under a given instance of the medium access control• Area covered by BSS called Basic Service Area (BSA) – Analogous to a cell in cellular network – Upto a diameter of tens of meters
    • BSS and Adhoc Wireless Network• Adhoc Network consists of group of stations within range of each other• Typically temporal in nature• Can be formed spontaneously anywhere• Disbanded after a limited period of time
    • IEEE 802.11 ESS• ESS: Extended Service Set – A set of BSSs interconnected by a distribution system – Consists of overlapping BSSs (each with an AP) • DS connects APs together, almost always Ethernet • ESS allows clients to seamlessly roam between APs
    • Access Point• Similar in functionality to base station in a cellular system• ESS can also provide gateway access for wireless users into a wired network such as Internet – Such access accomplished via a device called portal• Infrastructure network refers to combination of BSSs, a distribution system and portals
    • Access Points (APs)• To join an infrastructure BSS, a station must select an AP and establish an association with it• This establishes mapping between station and the AP• Station can then send and receive data messages via the AP• Reassociation and Dissociation services
    • Access Points (APs)• Usually connects wireless and wired networks – if not wired • acts as an extension point • Creation of ESS by overlapping AP coverage – allows roaming operation – APs should be on different channels
    • Access Points (APs)• Capacity and Bandwidth – Possible to keep these higher by using these techniques • Reducing size of coverage areas • Reducing client-to-AP ratio • Using bandwidth aggregation – AP-to-client ratio – load balancing
    • Access Points (APs)• Roaming – More than 1 AP provides signals to a single client – Client is responsible for choosing the best AP • first, signal strength. second, network utilization. – When signal in use degrades, client tries to find another AP • if found, tries to authenticate and associate
    • Access Points (APs)• Configuration – Management usually done via • HTTP, Telnet, SNMP, serial interface – Configuring Security Settings • SSID: Service Set Identifier • WEP: Wired Equivalent Privacy • EAP: Extensible Authentication Protocol – Configuring Network Settings • DHCP: Dynamic Host Configuration Protocol • NAT: Network Address Translation
    • Access Points (APs)• How to setup a secure access point – Enable WEP or EAP – Change SSID and disable broadcast – Change the management password of your AP • some have 2: read-only as well as read-write – Use MAC address filtering – Consider not using DHCP • instead use fixed IP addresses for wireless NICs – Consider other mechanisms for privacy • PPTP, VPN, SSL, SSH
    • IEEE 802.11 Security• Authentication – Open system – Shared key• Authorization – MAC address• Privacy – WEP: Wired Equivalent Privacy
    • Overview of the Bluetooth technology
    • Bluetooth• Bluetooth must be able to:• Recognize any other Bluetooth device in radio range• Permit easy connection of these devices• Be aware of the device types• Support service discovery• Support connectivity aware applications• Examples of Bluetooth uses:• Briefcase email: access email while the PC is still in the briefcase; when PC receives an email, you are notified thru the mobile phone. Use the mobile phone to browse the email.• Cordless desktop: connect your desktop/laptop cordlessly to printers, scanner, keyboard, mouse, etc.
    • Bluetooth• Bluetooth radio modules operate in the unlicensed ISM band centered at at 2.45GHz. RF channels:2420+k MHZ, k=0..78.• Bluetooth devices within 10m of each other can share up to 720kbps of capacity• Projected cost for a Bluetooth chip is ~$5. Plus its low power consumption, means you could literally place one anywhere.• Can operate on both circuit and packet switching modes, providing both synchronous and asynchronous data services• It is intended to support an open-ended list of applications, including data, audio, graphics and even video.
    • Bluetooth Architecture• Up to 8 devices can communicate in a small network, called piconet.• 10 piconets can coexist in the same coverage range of the Bluetooth radio.• Each piconet has 1 MASTER and the rest serve as SLAVES. SLAVES within a piconet only have links to the MASTER.• Multi-hop communication is obtained thru the scatternet.
    • Bluetooth Limitations• Does not address routing, most network functions are pushed into the link layer• Does not support multi-hop multicasting• Does not address how to cope with mobility !• The MASTER node is the bottleneck• No. of nodes in piconet is limited• Does not address power-saving methods done at upper layers, above the link-layer
    • NS : Network SimulatorAny kind of network simulationIncluding mobile and wireless network simulation
    • Outlines Use NS to simulate wireless networkExtend NS to support mobile and wirelessapplication: Internal implementation
    • ns-2 overview•Collection of various protocols at multiple layers TCP(reno, tahoe, vegas, sack) MAC(802.11, 802.3, TDMA) Ad-hoc Routing (DSDV, DSR, AODV, TORA) Sensor Network (diffusion, gaf) Multicast protocols, Satellite protocols, and many others•Codes are contributed from multiple researchcommunities Good: Large set of simulation modules Bad: Level of support and documentation varies•The source code and documentation is currentlymaintained by VINT project at ISI
    • Introduction•ns-2 is an discrete event driven simulation Physical activities are translated to events Events are queued and processed in the order of their scheduled occurrences Time progresses as the events are processed Time: 1.5 sec Time: 1.7 sec 1 2 Time: 2.0 sec Time: 1.8 sec
    • Event Driven Simulation RX Ack Event TX Pkt Event @ 1.5sec 2.0sec Node 1 Module Event Queue RX Ack Event TX Pkt Event TX @ 1.5sec 2.0sec 1.8sec 1.7secSimulation Finished! Node 2 Module TX Ack Event RX Pkt @ 1.7sec 1.8sec
    • Network Components inside amobile node Link Layer ARP Interface Queue Mac Layer: IEEE 802.11 Network Interface Radio Propagation Model 2 Friss-space attenuation(1/ r ) at near distance 2  Two ray Ground (1/ r ) at far distance
    • Mobile Node Modules•Agent Responsible for packet generations and receptions Can think of it as an Application layer CBR(Constant Bit Rate), TCP, Sink, FTP, etc.•RTagent(DSDV, TORA, AODV) or DSR Ad-hoc network routing protocols Configure multi hop routes for packets•LL (Link Layer) Runs data link protocols Fragmentation and reassembly of packet Runs Address Resolution Protocol(ARP) to resolve IP address to MAC address conversions
    • Mobile Node Modules (Continued)•IFq (Interface Queue) PriQueue is implemented to give priority to routing protocol packets Supports filter to remove packets destined to specific address•Mac Layer IEEE 802.11 protocol is implemented Uses RTS/CTS/DATA/ACK pattern for all unicast pkts and DATA for broadcast pkts
    • Mobile Node Modules (Continued)•NetIF (Network Interfaces) Hardware interface used by mobilenode to access the channel Simulates signal integrity, collision, tx error Mark each transmitted packet with transmission power, wavelength etc.•Radio Propagation Model Uses Friss-space attenuation(1/r2) at near distance and Two ray ground (1/r4) at far distance Decides whether the packet can be received by the mobilenode with given distance, transmit power and wavelength Implements Omni Directional Antenna module which has unity gain for all direction
    • Wireless Simulation in ns-2 (Mobile NodeDiagram - DSDV) Agent (Src/Sink) Demux Port Demux Addr RTagent (DSDV) LL ARP IFq MAC Radio Propagation NetIF Model Channel
    • Wireless Simulation in ns-2 (Mobile NodeDiagram - DSR) Agent (Src/Sink) Demux Port DSR LL ARP IFq MAC Radio Propagation NetIF Model Channel
    • Abstract the real mobile world intoyour simulation Node Packets Wireless channel and channel access Forwarding and routing Radio propagation model Trace/Visualization Event scheduler to make everything running
    • Implementing mobile node byExtending “standard” NS node Node Classifier:Forwarding Agent: Protocol Entity Routing Node Entry LL ARP LL LL:Link layer object IFQ:Interface queue MAC Radio Propagation PHY Model MAC MAC:Mac object MobileNode PHY PHY:Net interface CHANNEL
    • ReferencesAnand Trivedi‟s IEEE 802.11 Page – http://alpha.fdu.edu/~anandt/introduction.html• IEEE 802.11 Working Group Page – http://www.ieee802.org/11/ – Can download the 802 standards here for FREE – Has links to all the latest 802.11 developments• O‟Reilly – http://oreilly.wirelessdevnet.com/• http://wireless.telerama.com
    • THAT‟S ALL