20CS2007 Computer Communication Networks
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This document provides information about local area networks (LANs), including their design, topologies, transmission media, and protocols. It discusses common LAN applications and topologies such as bus, star, ring, and mesh. Specific protocols covered include Ethernet, token ring, and spanning tree. Bridges are described as a way to interconnect multiple LANs. Factors in choosing a topology and transmission medium are also summarized.
20CS2007 Computer Communication Networks
- 1. 20CS2007 Computer Communication Networks Module 3 Local Area Networks Design Café and residential networks, Setup Wi-Fi networks, Traffic confinement with VLAN. LANs and Basic Topologies, LAN Protocols, MAC/IP Address Conversion Protocols, Wired LAN, Wireless LAN, Virtual LAN, IEEE 802.11 Wireless LAN Standard. Dr.A.Kathirvel, Professor, DCSE, KITS [email protected]
- 2. LAN and Basic Topologies 9/14/2021 2
- 3. Local Area Network Overview
- 4. LAN Applications (1) • Personal computer LANs —Low cost —Limited data rate • Back end networks —Interconnecting large systems (mainframes and large storage devices) • High data rate • High speed interface • Distributed access • Limited distance • Limited number of devices
- 5. LAN Applications (2) • Storage Area Networks — Separate network handling storage needs — Detaches storage tasks from specific servers — Shared storage facility across high-speed network — Hard disks, tape libraries, CD arrays — Improved client-server storage access — Direct storage to storage communication for backup • High speed office networks — Desktop image processing — High capacity local storage • Backbone LANs — Interconnect low speed local LANs — Reliability — Capacity — Cost
- 7. LAN Architecture • Topologies • Transmission medium • Layout • Medium access control
- 8. Topologies • Tree • Bus —Special case of tree • One trunk, no branches • Ring • Star
- 10. Bus and Tree • Multipoint medium • Transmission propagates throughout medium • Heard by all stations — Need to identify target station • Each station has unique address • Full duplex connection between station and tap — Allows for transmission and reception • Need to regulate transmission — To avoid collisions — To avoid hogging • Data in small blocks - frames • Terminator absorbs frames at end of medium
- 12. Ring Topology • Repeaters joined by point to point links in closed loop —Receive data on one link and retransmit on another —Links unidirectional —Stations attach to repeaters • Data in frames —Circulate past all stations —Destination recognizes address and copies frame —Frame circulates back to source where it is removed • Media access control determines when station can insert frame
- 14. Star Topology • Each station connected directly to central node —Usually via two point to point links • Central node can broadcast —Physical star, logical bus —Only one station can transmit at a time • Central node can act as frame switch
- 15. Choice of Topology • Reliability • Expandability • Performance • Needs considering in context of: —Medium —Wiring layout —Access control
- 16. Bus LAN Transmission Media (1) • Twisted pair —Early LANs used voice grade cable —Didn’t scale for fast LANs —Not used in bus LANs now • Baseband coaxial cable —Uses digital signalling —Original Ethernet
- 17. Bus LAN Transmission Media (2) • Broadband coaxial cable — As in cable TV systems — Analog signals at radio frequencies — Expensive, hard to install and maintain — No longer used in LANs • Optical fiber — Expensive taps — Better alternatives available — Not used in bus LANs • All hard to work with compared with star topology twisted pair • Coaxial baseband still used but not often in new installations
- 18. Ring and Star Usage • Ring —Very high speed links over long distances —Single link or repeater failure disables network • Star —Uses natural layout of wiring in building —Best for short distances —High data rates for small number of devices
- 19. 9/14/2021 19 Network: A network is a set of nodes (devices) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network. A network is two or more devices connected through links. A link is a communication pathway that transfers data from one device to another. There are two possible types of connections: point-to-point and multipoint Point-to-Point: A point-to-point connection provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between those two devices. Example : connection between the remote control and the television's control system.
- 20. 9/14/2021 20 Multipoint : A multipoint connection is connection in which more than two specific devices share a single link. In a multipoint environment, the capacity of the channel is shared, either spatially or temporally. If several devices can use the link simultaneously, it is a spatially shared connection. If users must take turns, it is a timeshared connection.
- 21. 9/14/2021 21 Station A Station B Communication Link Point –to-point Connection Mainframe Station 1 Station 2 Station 3 Station 4 Multipoint Connection
- 22. 9/14/2021 22 Benefits of Networks: The following are some of the benefits of networks. Provide convenience: Computers on a network can back up their files over the network. Allow sharing: Networked Computers can share resources such as printers and disks. Facilitate communication: Networks facilitate the communication such as sending and receiving email, transferring files and video conferencing. Generate savings: Networked computers can provide more computing power for less money. Since resources can be shared, not everyone need their own peripherals which can result in cost savings. Provide reliability : If one part of a network is down, useful work may be still possible using a different network path. Simplifying scalability : It is easy to add more computers to an existing network.
- 23. 9/14/2021 23 Network Topologies : Network topology refers to the way in which a network is laid out physically. The topology of a network is the geometric representation of the relationship of all the links and linking devices (nodes) to one another. There are four basic topologies Mesh Topology Star Topology Bus Topology Ring Topology
- 24. 9/14/2021 24 1. Mesh Topology : In a mesh topology, every device has a dedicated point-to-point link to every other device. The term dedicated means that the link carries traffic only between the two devices it connects. Example: connection of telephone regional offices in which each regional office needs to be connected to every other regional office. Advantages : 1. Eliminate the traffic problems that can occur when links shared by multiple devices. 2. Mesh topology is robust. 3. Privacy and Security 4. Point-to-point links make fault identification and fault isolation easy. Disadvantages: 1. More amount of cabling and the number of I/O ports required. 2. The hardware required to connect each link (I/O ports and cable) can be expensive.
- 25. 9/14/2021 25 Device 1 Device 2 Device 3 Device 4 Device 5 Mesh Topology
- 26. 9/14/2021 26 2. Star Topology : In a star topology, each device has a dedicated point-to-point link only to a central controller, called a hub. The devices are not directly linked to one another. A star topology does not allow direct traffic between devices. The controller acts as an exchange. If one device wants to send data to another, it sends the data to the controller, which then relays the data to the other connected device. Example: The star topology is used in local-area networks (LANs). High-speed LANs often use a star topology with a central hub. Advantages: 1. A star topology is less expensive than a mesh topology. 2. Robustness 3. easy to install and reconfigure Disadvantages: 1. Star topology is dependent on hub . If the hub goes down, the whole system is dead.
- 27. 9/14/2021 27 Central Hub Device 1 Device 2 Device 3 Device 4 Star Topology
- 28. 9/14/2021 28 3. Bus Topology : A bus Topology is multipoint connection. One long cable acts as a backbone to link the devices in a network. Device 1 Device 2 Device 3 Tap Tap Tap Cable Drop Line Drop Line Drop Line
- 29. 9/14/2021 29 Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core. Advantages: Ease of installation Bus topology uses less cabling than mesh or star topologies. Disadvantages: Difficult reconnection and fault isolation Difficult to add new devices
- 30. 9/14/2021 30 4. Ring Topology: In a ring topology, each device has a dedicated point-to-point connection with only the two devices on either side of it. A signal is passed along the ring in one direction, from device to device, until it reaches its destination. Each device in the ring incorporates a repeater. When a device receives a signal intended for another device, its repeater regenerates the messages and passes them along path. Example : Token Ring. Advantages : Easy to install and reconfigure Fault isolation is simplified Disadvantages: Unidirectional traffic Break in the ring disable the entire network
- 31. 9/14/2021 31 Device 1 Device 2 Device 3 Device 4 Device 5 Device 6 Repeate r Repeat er Repeater Repeate r Repeater Repeat er Ring Topology
- 32. 32 Network Protocols Stack Application Transport Network Link Application protocol TCP protocol IP protocol Data Link IP Network Access IP protocol Data Link Application Transport Network Link
- 33. Types of Addresses in Internet • Media Access Control (MAC) addresses in the network access layer – Associated w/ network interface card (NIC) – 48 bits or 64 bits • IP addresses for the network layer – 32 bits for IPv4, and 128 bits for IPv6 – E.g., 128.3.23.3 • IP addresses + ports for the transport layer – E.g., 128.3.23.3:80 • Domain names for the application/human layer – E.g., www.purdue.edu 33
- 34. Routing and Translation of Addresses • Translation between IP addresses and MAC addresses – Address Resolution Protocol (ARP) for IPv4 – Neighbor Discovery Protocol (NDP) for IPv6 • Routing with IP addresses – TCP, UDP, IP for routing packets, connections – Border Gateway Protocol for routing table updates • Translation between IP addresses and domain names – Domain Name System (DNS) 34
- 35. Wired LAN • Constrained by LAN topology • Capacity • Reliability • Types of data supported • Environmental scope
- 36. Media Available (1) • Voice grade unshielded twisted pair (UTP) —Cat 3 —Cheap —Well understood —Use existing telephone wiring in office building —Low data rates • Shielded twisted pair and baseband coaxial —More expensive than UTP but higher data rates • Broadband cable —Still more expensive and higher data rate
- 37. Media Available (2) • High performance UTP — Cat 5 and above — High data rate for small number of devices — Switched star topology for large installations • Optical fiber — Electromagnetic isolation — High capacity — Small size — High cost of components — High skill needed to install and maintain • Prices are coming down as demand and product range increases
- 38. Protocol Architecture • Lower layers of OSI model • IEEE 802 reference model • Physical • Logical link control (LLC) • Media access control (MAC)
- 39. IEEE 802 v OSI
- 40. 802 Layers - Physical • Encoding/decoding • Preamble generation/removal • Bit transmission/reception • Transmission medium and topology
- 41. 802 Layers - Logical Link Control • Interface to higher levels • Flow and error control
- 42. Logical Link Control • Transmission of link level PDUs between two stations • Must support multiaccess, shared medium • Relieved of some link access details by MAC layer • Addressing involves specifying source and destination LLC users —Referred to as service access points (SAP) —Typically higher level protocol
- 43. LLC Services • Based on HDLC • Unacknowledged connectionless service • Connection mode service • Acknowledged connectionless service
- 44. LLC Protocol • Modeled after HDLC • Asynchronous balanced mode to support connection mode LLC service (type 2 operation) • Unnumbered information PDUs to support Acknowledged connectionless service (type 1) • Multiplexing using LSAPs
- 45. Media Access Control • Assembly of data into frame with address and error detection fields • Disassembly of frame —Address recognition —Error detection • Govern access to transmission medium —Not found in traditional layer 2 data link control • For the same LLC, several MAC options may be available
- 46. LAN Protocols in Context
- 47. Media Access Control • Where — Central • Greater control • Simple access logic at station • Avoids problems of co-ordination • Single point of failure • Potential bottleneck — Distributed • How — Synchronous • Specific capacity dedicated to connection — Asynchronous • In response to demand
- 48. Asynchronous Systems • Round robin — Good if many stations have data to transmit over extended period • Reservation — Good for stream traffic • Contention — Good for bursty traffic — All stations contend for time — Distributed — Simple to implement — Efficient under moderate load — Tend to collapse under heavy load
- 49. MAC Frame Format • MAC layer receives data from LLC layer • MAC control • Destination MAC address • Source MAC address • LLS • CRC • MAC layer detects errors and discards frames • LLC optionally retransmits unsuccessful frames
- 50. Generic MAC Frame Format
- 51. Bridges • Ability to expand beyond single LAN • Provide interconnection to other LANs/WANs • Use Bridge or router • Bridge is simpler —Connects similar LANs —Identical protocols for physical and link layers —Minimal processing • Router more general purpose —Interconnect various LANs and WANs —see later
- 52. Why Bridge? • Reliability • Performance • Security • Geography
- 53. Functions of a Bridge • Read all frames transmitted on one LAN and accept those address to any station on the other LAN • Using MAC protocol for second LAN, retransmit each frame • Do the same the other way round
- 54. Bridge Operation
- 55. Bridge Design Aspects • No modification to content or format of frame • No encapsulation • Exact bitwise copy of frame • Minimal buffering to meet peak demand • Contains routing and address intelligence — Must be able to tell which frames to pass — May be more than one bridge to cross • May connect more than two LANs • Bridging is transparent to stations — Appears to all stations on multiple LANs as if they are on one single LAN
- 56. Bridge Protocol Architecture • IEEE 802.1D • MAC level — Station address is at this level • Bridge does not need LLC layer — It is relaying MAC frames • Can pass frame over external comms system — e.g. WAN link — Capture frame — Encapsulate it — Forward it across link — Remove encapsulation and forward over LAN link
- 57. Connection of Two LANs
- 58. Fixed Routing • Complex large LANs need alternative routes —Load balancing —Fault tolerance • Bridge must decide whether to forward frame • Bridge must decide which LAN to forward frame on • Routing selected for each source-destination pair of LANs —Done in configuration —Usually least hop route —Only changed when topology changes
- 60. Spanning Tree • Bridge automatically develops routing table • Automatically update in response to changes • Frame forwarding • Address learning • Loop resolution
- 61. Frame forwarding • Maintain forwarding database for each port —List station addresses reached through each port • For a frame arriving on port X: —Search forwarding database to see if MAC address is listed for any port except X —If address not found, forward to all ports except X —If address listed for port Y, check port Y for blocking or forwarding state • Blocking prevents port from receiving or transmitting —If not blocked, transmit frame through port Y
- 62. Address Learning • Can preload forwarding database • Can be learned • When frame arrives at port X, it has come form the LAN attached to port X • Use the source address to update forwarding database for port X to include that address • Timer on each entry in database • Each time frame arrives, source address checked against forwarding database
- 63. Spanning Tree Algorithm • Address learning works for tree layout —i.e. no closed loops • For any connected graph there is a spanning tree that maintains connectivity but contains no closed loops • Each bridge assigned unique identifier • Exchange between bridges to establish spanning tree
- 64. Loop of Bridges
- 65. Layer 2 and Layer 3 Switches • Now many types of devices for interconnecting LANs • Beyond bridges and routers • Layer 2 switches • Layer 3 switches
- 66. Hubs • Active central element of star layout • Each station connected to hub by two lines — Transmit and receive • Hub acts as a repeater • When single station transmits, hub repeats signal on outgoing line to each station • Line consists of two unshielded twisted pairs • Limited to about 100 m — High data rate and poor transmission qualities of UTP • Optical fiber may be used — Max about 500 m • Physically star, logically bus • Transmission from any station received by all other stations • If two stations transmit at the same time, collision
- 67. Hub Layouts • Multiple levels of hubs cascaded • Each hub may have a mixture of stations and other hubs attached to from below • Fits well with building wiring practices — Wiring closet on each floor — Hub can be placed in each one — Each hub services stations on its floor
- 68. Two Level Star Topology
- 69. Buses and Hubs • Bus configuration —All stations share capacity of bus (e.g. 10Mbps) —Only one station transmitting at a time • Hub uses star wiring to attach stations to hub —Transmission from any station received by hub and retransmitted on all outgoing lines —Only one station can transmit at a time —Total capacity of LAN is 10 Mbps • Improve performance with layer 2 switch
- 70. Shared Medium Bus and Hub
- 71. Shared Medium Hub and Layer 2 Switch
- 72. Layer 2 Switches • Central hub acts as switch • Incoming frame from particular station switched to appropriate output line • Unused lines can switch other traffic • More than one station transmitting at a time • Multiplying capacity of LAN
- 73. Layer 2 Switch Benefits • No change to attached devices to convert bus LAN or hub LAN to switched LAN • For Ethernet LAN, each device uses Ethernet MAC protocol • Device has dedicated capacity equal to original LAN — Assuming switch has sufficient capacity to keep up with all devices — For example if switch can sustain throughput of 20 Mbps, each device appears to have dedicated capacity for either input or output of 10 Mbps • Layer 2 switch scales easily — Additional devices attached to switch by increasing capacity of layer 2
- 74. Types of Layer 2 Switch • Store-and-forward switch — Accepts frame on input line — Buffers it briefly, — Then routes it to appropriate output line — Delay between sender and receiver — Boosts integrity of network • Cut-through switch — Takes advantage of destination address appearing at beginning of frame — Switch begins repeating frame onto output line as soon as it recognizes destination address — Highest possible throughput — Risk of propagating bad frames • Switch unable to check CRC prior to retransmission
- 75. Layer 2 Switch v Bridge • Layer 2 switch can be viewed as full-duplex hub • Can incorporate logic to function as multiport bridge • Bridge frame handling done in software • Switch performs address recognition and frame forwarding in hardware • Bridge only analyzes and forwards one frame at a time • Switch has multiple parallel data paths — Can handle multiple frames at a time • Bridge uses store-and-forward operation • Switch can have cut-through operation • Bridge suffered commercially — New installations typically include layer 2 switches with bridge functionality rather than bridges
- 76. Problems with Layer 2 Switches (1) • As number of devices in building grows, layer 2 switches reveal some inadequacies • Broadcast overload • Lack of multiple links • Set of devices and LANs connected by layer 2 switches have flat address space — Allusers share common MAC broadcast address — If any device issues broadcast frame, that frame is delivered to all devices attached to network connected by layer 2 switches and/or bridges — In large network, broadcast frames can create big overhead — Malfunctioning device can create broadcast storm • Numerous broadcast frames clog network
- 77. Problems with Layer 2 Switches (2) • Current standards for bridge protocols dictate no closed loops — Only one path between any two devices — Impossible in standards-based implementation to provide multiple paths through multiple switches between devices • Limits both performance and reliability. • Solution: break up network into subnetworks connected by routers • MAC broadcast frame limited to devices and switches contained in single subnetwork • IP-based routers employ sophisticated routing algorithms — Allow use of multiple paths between subnetworks going through different routers
- 78. Problems with Routers • Routers do all IP-level processing in software —High-speed LANs and high-performance layer 2 switches pump millions of packets per second —Software-based router only able to handle well under a million packets per second • Solution: layer 3 switches —Implementpacket-forwarding logic of router in hardware • Two categories —Packet by packet —Flow based
- 79. Packet by Packet or Flow Based • Operates insame way as traditional router • Order of magnitude increase in performance compared to software-based router • Flow-based switch tries to enhance performance by identifying flows of IP packets —Same source and destination —Done by observing ongoing traffic or using a special flow label in packet header (IPv6) —Once flow is identified, predefined route can be established
- 80. Typical Large LAN Organization • Thousands to tens of thousands of devices • Desktop systems links 10 Mbps to 100 Mbps — Into layer 2 switch • Wireless LAN connectivity available for mobile users • Layer 3 switches at local network's core — Form local backbone — Interconnected at 1 Gbps — Connect to layer 2 switches at 100 Mbps to 1 Gbps • Servers connect directly to layer 2 or layer 3 switches at 1 Gbps • Lower-cost software-based router provides WAN connection • Circles in diagram identify separate LAN subnetworks • MAC broadcast frame limited to own subnetwork
- 82. Overview • A wireless LAN uses wireless transmission medium • Used to have high prices, low data rates, occupational safety concerns, and licensing requirements • Problems have been addressed • Popularity of wireless LANs has grown rapidly
- 83. Applications - LAN Extension • Saves installation of LAN cabling • Eases relocation and other modifications to network structure • However, increasing reliance on twisted pair cabling for LANs — Most older buildings already wired with Cat 3 cable — Newer buildings are prewired with Cat 5 • Wireless LAN to replace wired LANs has not happened • In some environments, role for the wireless LAN — Buildings with large open areas • Manufacturing plants, stock exchange trading floors, warehouses • Historical buildings • Small offices where wired LANs not economical • May also have wired LAN — Servers and stationary workstations
- 84. Single Cell Wireless LAN Configuration
- 86. Applications – Cross-Building Interconnect • Connect LANs in nearby buildings • Point-to-point wireless link • Connect bridges or routers • Not a LAN per se —Usual to include this application under heading of wireless LAN •
- 87. Applications - Nomadic Access • Link between LAN hub and mobile data terminal —Laptop or notepad computer —Enable employee returning from trip to transfer data from portable computer to server • Also useful in extended environment such as campus or cluster of buildings —Users move around with portable computers —May wish access to servers on wired LAN
- 89. Applications – Ad Hoc Networking • Peer-to-peer network • Set up temporarily to meet some immediate need • E.g. group of employees, each with laptop or palmtop, in business or classroom meeting • Network for duration of meeting
- 90. Add Hoc LAN
- 91. Wireless LAN Requirements • Same as any LAN — High capacity, short distances, full connectivity, broadcast capability • Throughput: efficient use wireless medium • Number of nodes:Hundreds of nodes across multiple cells • Connection to backbone LAN: Use control modules to connect to both types of LANs • Service area: 100 to 300 m • Low power consumption:Need long battery life on mobile stations — Mustn't require nodes to monitor access points or frequent handshakes • Transmission robustness and security:Interference prone and easily eavesdropped • Collocated network operation:Two or more wireless LANs in same area • License-free operation • Handoff/roaming: Move from one cell to another • Dynamic configuration: Addition, deletion, and relocation of end systems without disruption to users
- 92. Technology • Infrared (IR) LANs: Individual cell of IR LAN limited to single room —IR light does not penetrate opaque walls • Spread spectrum LANs: Mostly operate in ISM (industrial, scientific, and medical) bands —No Federal Communications Commission (FCC) licensing is required in USA • Narrowband microwave: Microwave frequencies but not use spread spectrum —Some require FCC licensing
- 93. Infrared LANs Strengths and Weaknesses • Spectrum virtually unlimited — Infrared spectrum is unregulated worldwide — Extremely high data rates • Infrared shares some properties of visible light — Diffusely reflected by light-colored objects • Use ceiling reflection to cover entire room — Does not penetrate walls or other opaque objects • More easily secured against eavesdropping than microwave • Separate installation in every room without interference • Inexpensive and simple — Uses intensity modulation, so receivers need to detect only amplitude • Background radiation — Sunlight, indoor lighting — Noise, requiring higher power and limiting range — Power limited by concerns of eye safety and power consumption
- 94. Infrared LANs Transmission Techniques • Directed-beam IR — Point-to-point links — Range depends on power and focusing • Can be kilometers • Used for building interconnect within line of sight — Indoor use to set up token ring LAN — IR transceivers positioned so that data circulate in ring • Omnidirectional — Single base station within line of sight of all other stations • Typically, mounted on ceiling — Acts as a multiport repeater — Other transceivers use directional beam aimed at ceiling unit • Diffused configuration — Transmitters are focused and aimed at diffusely reflecting ceiling
- 95. Spread Spectrum LANs Hub Configuration • Usually use multiple-cell arrangement • Adjacent cells use different center frequencies • Hub is typically mounted on ceiling — Connected to wired LAN — Connect to stations attached to wired LAN and in other cells — May also control access • IEEE 802.11 point coordination function — May also act as multiport repeater • Stations transmit to hub and receive from hub — Stations may broadcast using an omnidirectional antenna • Logical bus configuration • Hub may do automatic handoff — Weakening signal, hand off
- 96. Spread Spectrum LANs Peer-to-Peer Configuration • No hub • MAC algorithm such as CSMA used to control access • Ad hoc LANs •
- 97. Spread Spectrum LANs Transmission Issues • Licensing regulations differ from one country to another • USA FCC authorized two unlicensed applications within the ISM band: — Spread spectrum - up to 1 watt — Very low power systems- up to 0.5 watts — 902 - 928 MHz (915-MHz band) — 2.4 - 2.4835 GHz (2.4-GHz band) — 5.725 - 5.825 GHz (5.8-GHz band) — 2.4 GHz also in Europe and Japan — Higher frequency means higher potential bandwidth • Interference — Devices at around 900 MHz, including cordless telephones, wireless microphones, and amateur radio — Fewer devices at 2.4 GHz; microwave oven — Little competition at 5.8 GHz • Higher frequency band, more expensive equipment
- 98. Narrow Band Microwave LANs • Just wide enough to accommodate signal • Until recently, all products used licensed band • At least one vendor has produced LAN product in ISM band
- 99. Licensed Narrowband RF • Microwave frequencies usable for voice, data, and video licensed within specific geographic areas to avoid interference — Radium 28 km — Can contain five licenses — Each covering two frequencies — Motorola holds 600 licenses (1200 frequencies) in the 18-GHz range — Cover all metropolitan areas with populations of 30,000 or more in USA • Use of cell configuration • Adjacent cells use nonoverlapping frequency bands • Motorola controls frequency band — Can assure nearby independent LANs do not interfere • All transmissions are encrypted • Licensed narrowband LAN guarantees interference-free communication • License holder has legal right tointerference-free data channel
- 100. Unlicensed Narrowband RF • 1995, RadioLAN introduced narrowband wireless LAN using unlicensed ISM spectrum — Used for narrowband transmission at low power • 0.5 watts or less — Operates at 10 Mbps — 5.8-GHz band — 50 m in semiopen office and 100 m in open office • Peer-to-peer configuration • Elects one node as dynamic master — Based on location, interference, and signal strength • Master can change automatically as conditions change • Includes dynamic relay function • Stations can act as repeater to move data between stations that are out of range of each other
- 101. IEEE 802.11 - BSS • MAC protocol and physical medium specification for wireless LANs • Smallest building block is basic service set (BSS) — Number of stations — Same MAC protocol — Competing for access to same shared wireless medium • May be isolated or connect to backbone distribution system (DS) through access point (AP) — AP functions as bridge • MAC protocol may be distributed or controlled by central coordination function in AP • BSS generally corresponds to cell • DS can be switch, wired network, or wireless network
- 102. BSS Configuration • Simplest: each station belongs to single BSS —Within range only of other stations within BSS • Can have two BSSs overlap —Station could participate in more than one BSS • Association between station and BSS dynamic —Stations may turn off, come within range, and go out of range
- 103. Extended Service Set (ESS) • Two or more BSS interconnected by DS —Typically, DS is wired backbone but can be any network • Appears as single logical LAN to LLC
- 104. Access Point (AP) • Logic within station that provides access to DS —Provides DS services in addition to acting as station • To integrate IEEE 802.11 architecture with wired LAN, portal used • Portal logic implemented in device that is part of wired LAN and attached to DS —E.g. Bridge or router
- 106. Services Service Provider Category Association Distribution system MSDU delivery Authentication Station LAN access and security Deauthentication Station LAN access and security Dissassociation Distribution system MSDU delivery Distribution Distribution system MSDU delivery Integration Distribution system MSDU delivery MSDU delivery Station MSDU delivery Privacy Station LAN access and security Reassocation Distribution system MSDU delivery
- 107. Categorizing Services • Station services implemented in every 802.11 station — Including AP stations • Distribution services provided between BSSs — May be implemented in AP or special-purpose device • Three services used to control access and confidentiality • Six services used to support delivery of MAC service data units (MSDUs) between stations — Block of data passed down from MAC user to MAC layer — Typically LLC PDU — If MSDU too large for MAC frame, fragment and transmit in series of frames (see later)
- 108. Distribution of Messages Within a DS • Distribution is primary service used by stations to exchange MAC frames when frame must traverse DS — From station in one BSS to station in another BSS — Transport of message through DS is beyond scope of 802.11 — If stations within same BSS, distribution service logically goes through single AP of that BSS • Integration service enables transfer of data between station on 802.11 LAN and one on an integrated 802.x LAN — Integrated refers to wired LAN physically connected to DS • Stations may be logically connected to 802.11 LAN via integration service — Integration service takes care of address translation and media conversion
- 109. Association Related Services • Purpose of MAC layer transfer MSDUs between MAC entities • Fulfilled by distribution service (DS) • DS requires information about stations within ESS — Provided by association-related services — Station must be associated before communicating • Three transition types of based on mobility — No transition: Stationary or moves within range of single BSS — BSS transition: From one BSS to another within same ESS • Requires addressing capability be able to recognize new location • ESS transition: From BSS in one ESS to BSS in another ESS — Only supported in sense that the station can move — Maintenance of upper-layer connections not guaranteed — Disruption of service likely
- 110. Station Location • DS needs to know where destination station is — Identity of AP to which message should be delivered — Station must maintain association with AP within current BSS • Three services relate to this requirement: — Association: Establishes initial association between station and AP • To make identity and address known • Station must establish association with AP within particular BSS • AP then communicates information to other APs within ESS — Reassociation: Transfer established association to another AP • Allows station to move from one BSS to another — Disassociation: From either station or AP that association is terminated — Given before station leaves ESS or shuts • MAC management facility protects itself against stations that disappear without notification
- 111. Access and Privacy Services - Authentication • On wireless LAN, any station within radio range other devices can transmit • Any station within radio range can receive • Authentication: Used to establish identity of stations to each other — Wired LANs assume access to physical connection conveys authority to connect to LAN — Not valid assumption for wireless LANs • Connectivity achieved by having properly tuned antenna — Authentication service used to establish station identity — 802.11 supports several authentication schemes • Allows expansion of these schemes — Does not mandate any particular scheme — Range from relatively insecure handshaking to public-key encryption schemes — 802.11 requires mutually acceptable, successful authentication before association
- 112. Access and Privacy Services - Deauthentication and Privacy • Deauthentication: Invoked whenever an existing authentication is to be terminated • Privacy: Used to prevent messages being read by others • 802.11 provides for optional use of encryption
- 113. Medium Access Control • MAC layer covers three functional areas • Reliable data delivery • Access control • Security —Beyond our scope
- 114. Reliable Data Delivery • 802.11 physical and MAC layers subject to unreliability • Noise, interference, and other propagation effects result in loss of frames • Even with error-correction codes, frames may not successfully be received • Can be dealt with at a higher layer, such as TCP — However, retransmission timers at higher layers typically order of seconds — More efficient to deal with errors at the MAC level • 802.11 includes frame exchange protocol — Station receiving frame returns acknowledgment (ACK) frame — Exchange treated as atomic unit • Not interrupted by any other station — If noACK within short period of time, retransmit
- 115. Four Frame Exchange • Basic data transfer involves exchange of two frames • To further enhance reliability, four-frame exchange may be used — Source issues a Request to Send (RTS) frame to destination — Destination responds with Clear to Send (CTS) — After receiving CTS, source transmits data — Destination responds with ACK • RTS alerts all stations within range of source that exchange is under way • CTS alerts all stations within range of destination • Stations refrain from transmission to avoid collision • RTS/CTS exchange is required function of MAC but may be disabled
- 116. Media Access Control • Distributed wireless foundation MAC (DWFMAC) —Distributed access control mechanism —Optional centralized control on top • Lower sublayer is distributed coordination function (DCF) —Contention algorithm to provide access to all traffic —Asynchronous traffic • Point coordination function (PCF) —Centralized MAC algorithm —Contention free —Built on top of DCF
- 118. Distributed Coordination Function • DCF sublayer uses CSMA • If station has frame to transmit, it listens to medium • If medium idle, station may transmit • Otherwise must wait until current transmission complete • No collision detection — Not practical on wireless network — Dynamic range of signals very large — Transmitting station cannot distinguish incoming weak signals from noise and effects of own transmission • DCF includes delays — Amounts to priority scheme • Interframe space
- 119. Interframe Space • Single delay known as interframe space (IFS) • Using IFS, rules for CSMA: 1. Station with frame senses medium • If idle, wait to see if remains idle for one IFS. If so, may transmit immediately 2. If busy (either initially or becomes busy during IFS) station defers transmission • Continue to monitor until current transmission is over 3. Once current transmission over, delay another IFS • If remains idle, back off random time and again sense • If medium still idle, station may transmit • During backoff time, if becomes busy, backoff timer is halted and resumes when medium becomes idle • To ensure stability, binary exponential backoff used
- 121. Priority • Use three values for IFS • SIFS (short IFS): — Shortest IFS — For all immediate response actions (see later) • PIFS (point coordination function IFS): — Midlength IFS — Used by the centralized controller in PCF scheme when issuing polls • DIFS (distributed coordination function IFS): — Longest IFS — Used as minimum delay for asynchronous frames contending for access
- 122. SIFS Use - ACK • Station using SIFS to determine transmission opportunity has highest priority — In preference to station waiting PIFS or DIFS time • SIFS used in following circumstances: • Acknowledgment (ACK): Station responds with ACK after waiting SIFS gap — No collision detection so likelihood of collisions greater than CSMA/CD • MAC-level ACK gives efficient collision recovery — SIFS provide efficient delivery of multiple frame LLC PDU • Station with multiframe LLC PDU to transmit sends out MAC frames one at a time • Each frame acknowledged after SIFS by recipient • When source receives ACK, immediately (after SIFS) sends next frame in sequence • Once station has contended for channel, it maintains control of all fragments sent
- 123. SIFS Use – CTS • Clear to Send (CTS): Station can ensure data frame will get through by issuing RTS —Destination station should immediately respond with CTS if ready to receive —All other stations hear RTS and defer • Poll response: See Point coordination Function (PCF)
- 124. PIFS and DIFS • PIFS used by centralized controller —Issuing polls —Takes precedence over normal contention traffic —Frames using SIFS have precedence over PCF poll • DIFS used for all ordinary asynchronous traffic
- 125. IEEE 802.11 MAC Timing Basic Access Method
- 126. Point Coordination Function (PCF) • Alternative access method implemented on top of DCF • Polling by centralized polling master (point coordinator) • Uses PIFS when issuing polls — PIFS smaller than DIFS — Can seize medium and lock out all asynchronous traffic while it issues polls and receives responses • E.g. wireless network configured so number of stations with time- sensitive traffic controlled by point coordinator — Remaining traffic contends for access using CSMA • Point coordinator polls in round-robin to stations configured for polling • When poll issued, polled station may respond using SIFS • If point coordinator receives response, it issues another poll using PIFS • If no response during expected turnaround time, coordinator issues poll
- 127. Superframe • Point coordinator would lock out asynchronous traffic by issuing polls • Superframe interval defined — During first part of superframe interval, point coordinator polls round- robin to all stations configured for polling — Point coordinator then idles for remainder of superframe — Allowing contention period for asynchronous access • At beginning of superframe, point coordinator may seize control and issue polls for given period — Time varies because of variable frame size issued by responding stations • Rest of superframe available for contention-based access • At end of superframe interval, point coordinator contends for access using PIFS • If idle, point coordinator gains immediate access — Full superframe period follows — If busy, point coordinator must wait for idle to gain access — Results in foreshortened superframe period for next cycle
- 128. IEEE 802.11 MAC Timing PCF Superframe Construction
- 129. IEEE 802.11 MAC Frame Format
- 130. MAC Frame Fields (1) • Frame Control: — Type of frame — Control, management, or data — Provides control information • Includes whether frame is to or from DS, fragmentation information, and privacy information • Duration/Connection ID: — If used as duration field, indicates time (in s) channel will be allocated for successful transmission of MAC frame — In some control frames, contains association or connection identifier • Addresses: — Number and meaning of address fields depend on context — Types include source, destination, transmitting station, and receiving station
- 131. MAC Frame Fields (2) • Sequence Control: —4-bit fragment number subfield • For fragmentation and reassembly —12-bit sequence number —Number frames between given transmitter and receiver • Frame Body: —MSDU (or a fragment of) • LLC PDU or MAC control information • Frame Check Sequence: —32-bit cyclic redundancy check
- 132. Control Frames • Assist in reliable data delivery • Power Save-Poll (PS-Poll) — Sent by any station to station that includes AP — Request AP transmit frame buffered for this station while station in power-saving mode • Request to Send (RTS) — First frame in four-way frame exchange • Clear to Send (CTS) — Second frame in four-way exchange • Acknowledgment (ACK) • Contention-Free (CF)-end — Announces end of contention-free period part of PCF • CF-End + CF-Ack: — Acknowledges CF-end — Ends contention-free period and releases stations from associated restrictions
- 133. Data Frames – Data Carrying • Eight data frame subtypes, in two groups • First four carry upper-level data from source station to destination station • Data — Simplest data frame — May be used in contention or contention-free period • Data + CF-Ack — Only sent during contention-free period — Carries data and acknowledges previously received data • Data + CF-Poll — Used by point coordinator to deliver data — Also to request station send data frame it may have buffered • Data + CF-Ack + CF-Poll — Combines Data + CF-Ack and Data + CF-Poll
- 134. Data Frames – Not Data Carrying • Remaining four data frames do not carry user data • Null Function —Carries no data, polls, or acknowledgments —Carries power management bit in frame control field to AP —Indicates station is changing to low-power state • Other three frames (CF-Ack, CF-Poll, CF-Ack + CF-Poll) same as corresponding frame in preceding list (Data + CF-Ack, Data + CF-Poll, Data + CF-Ack + CF-Poll) but without data
- 135. Management Frames • Used to manage communications between stations and Aps • E.g. management of associations —Requests, response, reassociation, dissociation, and authentication
- 136. 802.11 Physical Layer • Issued in four stages • First part in 1997 — IEEE 802.11 — Includes MAC layer and three physical layer specifications — Two in 2.4-GHz band and one infrared — All operating at 1 and 2 Mbps • Two additional parts in 1999 — IEEE 802.11a • 5-GHz band up to 54 Mbps — IEEE 802.11b • 2.4-GHz band at 5.5 and 11 Mbps • Most recent in 2002 — IEEE 802.g extends IEEE 802.11b to higher data rates
- 137. Original 802.11 Physical Layer - DSSS • Three physical media • Direct-sequence spread spectrum —2.4 GHz ISM band at 1 Mbps and 2 Mbps —Up to seven channels, each 1 Mbps or 2 Mbps, can be used —Depends on bandwidth allocated by various national regulations • 13 in most European countries • One in Japan —Each channel bandwidth 5 MHz —Encoding scheme DBPSK for 1-Mbps and DQPSK for 2-Mbps
- 138. Original 802.11 Physical Layer - FHSS • Frequency-hopping spread spectrum — 2.4 GHz ISM band at 1 Mbps and 2 Mbps — Uses multiple channels — Signal hopping from one channel to another based on a pseudonoise sequence — 1-MHz channels are used — 23 channels in Japan — 70 in USA • Hopping scheme adjustable — E.g. Minimum hop rate forUSA is 2.5 hops per second — Minimum hop distance 6 MHz in North America and most of Europe and 5 MHz in Japan • Two-level Gaussian FSK modulation for 1-Mbps — Bits encoded as deviations from current carrier frequency • For 2 Mbps, four-level GFSK used — Four different deviations from center frequency define four 2-bit combinations
- 139. Original 802.11 Physical Layer – Infrared • Omnidirectional • Range up to 20 m • 1 Mbps used 16-PPM (pulse position modulation) — Each group of 4 data bits mapped into one of 16-PPM symbols — Each symbol a string of 16 bits — Each 16-bit string consists of fifteen 0s and one binary 1 • For 2-Mbps, each group of 2 data bits is mapped into one of four 4-bit sequences — Each sequence consists of three 0s and one binary 1 — Intensity modulation • Presence of signal corresponds to 1
- 140. 802.11a • 5-GHz band • Uses orthogonal frequency division multiplexing (OFDM) — Not spread spectrum • Also called multicarrier modulation • Multiple carrier signals at different frequencies • Some bits on each channel — Similar to FDM but all subchannels dedicated to single source • Data rates 6, 9, 12, 18, 24, 36, 48, and 54 Mbps • Up to 52 subcarriers modulated using BPSK, QPSK, 16- QAM, or 64-QAM — Depending on rate — Subcarrier frequency spacing 0.3125 MHz — Convolutional code at rate of 1/2, 2/3, or 3/4 provides forward error correction
- 141. 802.11b • Extension of 802.11 DS-SS scheme • 5.5 and 11 Mbps • Chipping rate 11 MHz — Same as original DS-SS scheme — Same occupied bandwidth — Complementary code keying (CCK) modulation to achieve higher data rate in same bandwidth at same chipping rate — CCK modulation complex • Overview on next slide — Input data treated in blocks of 8 bits at 1.375 MHz • 8 bits/symbol 1.375 MHz = 11 Mbps • Six of these bits mapped into one of 64 code sequences • Output of mapping, plus two additional bits, forms input to QPSK modulator
- 143. 802.11g • Higher-speed extension to 802.11b • Combines physical layer encoding techniques used in 802.11a and 802.11b to provide service at a variety of data rates
- 144. Required Reading • Stallings chapter 17 • Web sites on 802.11
- 145. Virtual LANs
- 146. VLAN introduction VLANs logically segment switched networks based on the functions, project teams, or applications of the organization regardless of the physical location or connections to the network. All workstations and servers used by a particular workgroup share the same VLAN, regardless of the physical connection or location.
- 147. VLAN introduction A workstation in a VLAN group is restricted to communicating with file servers in the same VLAN group.
- 148. VLAN introduction VLANs function by logically segmenting the network into different broadcast domains so that packets are only switched between ports that are designated for the same VLAN. Routers in VLAN topologies provide broadcast filtering, security, and traffic flow management.
- 149. VLAN introduction VLANs address scalability, security, and network management. Switches may not bridge any traffic between VLANs, as this would violate the integrity of the VLAN broadcast domain. Traffic should only be routed between VLANs.
- 150. Broadcast domains with VLANs and routers A VLAN is a broadcast domain created by one or more switches.
- 151. Broadcast domains with VLANs and routers Layer 3 routing allows the router to send packets to the three different broadcast domains.
- 152. Broadcast domains with VLANs and routers Implementing VLANs on a switch causes the following to occur: The switch maintains a separate bridging table for each VLAN. If the frame comes in on a port in VLAN 1, the switch searches the bridging table for VLAN 1. When the frame is received, the switch adds the source address to the bridging table if it is currently unknown. The destination is checked so a forwarding decision can be made. For learning and forwarding the search is made against the address table for that VLAN only.
- 153. VLAN operation Each switch port could be assigned to a different VLAN. Ports assigned to the same VLAN share broadcasts. Ports that do not belong to that VLAN do not share these broadcasts.
- 154. VLAN operation Users attached to the same shared segment, share the bandwidth of that segment. Each additional user attached to the shared medium means less bandwidth and deterioration of network performance. VLANs offer more bandwidth to users than a shared network. The default VLAN for every port in the switch is the management VLAN. The management VLAN is always VLAN 1 and may not be deleted. All other ports on the switch may be reassigned to alternate VLANs.
- 155. VLAN operation Dynamic VLANs allow for membership based on the MAC address of the device connected to the switch port. As a device enters the network, it queries a database within the switch for a VLAN membership.
- 156. VLAN operation In port-based or port-centric VLAN membership, the port is assigned to a specific VLAN membership independent of the user or system attached to the port. All users of the same port must be in the same VLAN.
- 157. VLAN operation Network administrators are responsible for configuring VLANs both manually and statically.
- 158. Benefits of VLANs The key benefit of VLANs is that they permit the network administrator to organize the LAN logically instead of physically.
- 159. VLAN types There are three basic VLAN memberships for determining and controlling how a packet gets assigned: - Port-based VLANs MAC address based Protocol based VLANs The frame headers are encapsulated or modified to reflect a VLAN ID before the frame is sent over the link between switches. Before forwarding to the destination device, the frame header is changed back to the original format.
- 160. VLAN types Port-based VLANs MAC address based VLANs Protocol based VLANs
- 161. Membership by Port
- 163. VLAN types The number of VLANs in a switch vary depending on several factors: Traffic patterns Types of applications Network management needs Group commonality
- 164. VLAN types An important consideration in defining the size of the switch and the number of VLANs is the IP addressing scheme. Because a one-to-one correspondence between VLANs and IP subnets is strongly recommended, there can be no more than 254 devices in any one VLAN. It is further recommended that VLANs should not extend outside of the Layer 2 domain of the distribution switch.
- 165. VLAN types There are two major methods of frame tagging, Inter-Switch Link (ISL) and 802.1Q. ISL used to be the most common, but is now being replaced by 802.1Q frame tagging.
- 166. Bluetooth Technology
- 167. Introduction • What is Bluetooth? • Why is it useful? • Governing Standard – Large Consortium
- 168. History • 1998 - Bluetooth technology is officially introduced and the BLUETOOTH SIG is formed. Bluetooth technology's intended basic purpose is to be a wire replacement technology in order to rapidly transfer voice and data. • 1999 - Bluetooth 1.0 Specification is introduced. • 2003 - The BLUETOOTH SIG overhauls the Bluetooth Core Specification with the announcement of Version 2.1. • 2004 - Bluetooth Version 2.0 + EDR (Enhanced Data Rate) is introduced. • 2005 - Devices using Version 2.0 + EDR begin to hit the market in late 2005. • 2007 - Bluetooth Core Specification Version 2.1 + EDR is adopted by the BLUETOOTH SIG. • 2009 - Bluetooth Core Specification Version 3.0 + HS (High Speed) is adopted by the BLUETOOTH SIG.
- 169. How it works? • Short range wireless connectivity. • Low power consumption • Automatic recognition.
- 170. Privacy/Security • Very Important. • Don’t want data to be shared. • Security not great. —Pairing security.
- 171. Reliability • What it really means? • Which device are you connecting to? • How large is the file? • Which version are you using? • Have the two devices been connected before?
- 172. Support of Community
- 173. Devices • Laptops • Gaming Consoles • Headsets • Cell Phones • Printers
- 174. Ease of Use • Very easy to use. • Connection is fast and simple. • More devices are Bluetooth capable. • Auto recognition.
- 175. Future • Diverse applications with Bluetooth. • Faster transfer rate. • Stronger connection. • Longer distance.
- 176. Conclusion • Few flaws —Security • Good for short transfers —Limitations on file size —Limitations on distance • Convenient —Faster —More simple than flash drive
- 177. References • 1.http://www.bluetooth.com/English/Experience /Pages/On_The_Cutting_Edge.aspx • 2. http://electronics.howstuffworks.com/bluetooth 2.htm • 3.http://www.bluetomorrow.com/about- bluetooth-technology/history-of- bluetooth/bluetooth-history.html • 4.http://www.bluetooth.com/English/SIG/Pages /default.aspx • 5. http://en.wikipedia.org/wiki/Bluetooth • 6. http://www.allbusiness.com/technology/67826 6-1.html
- 178. Questions?