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5 Lan


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Unit 1 Of ACN

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5 Lan

  1. 1. LAN
  2. 2. What Is a LAN? <ul><li>A LAN is a high-speed data network that covers a relatively small geographic area. </li></ul><ul><li>It typically connects </li></ul><ul><ul><li>workstations, </li></ul></ul><ul><ul><li>personal computers, </li></ul></ul><ul><ul><li>printers, servers, </li></ul></ul><ul><ul><li>and other devices. </li></ul></ul><ul><li>LANs offer computer users many advantages, </li></ul><ul><ul><li>shared access to devices and applications, </li></ul></ul><ul><ul><li>file exchange between connected users, </li></ul></ul><ul><ul><li>communication between users via electronic mail and other applications. </li></ul></ul>
  3. 3. LAN Implementations
  4. 4. LAN Protocols & specifications <ul><li>LAN protocols function at the lowest two layers of the OSI reference model </li></ul><ul><ul><li>Between the physical layer and the data link layer </li></ul></ul><ul><li>Data link layer </li></ul><ul><ul><li>LLC sub layer </li></ul></ul><ul><ul><li>MAC sub layer </li></ul></ul><ul><li>LAN specifications </li></ul><ul><ul><ul><li>IEEE 802.2 (LLC) </li></ul></ul></ul><ul><ul><ul><li>IEEE 802.3 (Ethernet) </li></ul></ul></ul><ul><ul><ul><ul><li>10 BaseT,100BaseT </li></ul></ul></ul></ul><ul><ul><ul><li>Token Ring/802.5 </li></ul></ul></ul><ul><ul><ul><li>FDI </li></ul></ul></ul>
  5. 5. LAN Vs OSI
  6. 6. LAN media access methods <ul><li>Carrier Sense Multiple Access Collision Detect (CSMA/CD) </li></ul><ul><li>Token passing </li></ul><ul><li>Purpose </li></ul><ul><ul><li>to allow one device access to the network media at a time </li></ul></ul>
  7. 7. CSMA/CD <ul><li>When a device has data to send, it first listens to see if any other device is currently using the network </li></ul><ul><li>If not, it starts sending its data. </li></ul><ul><li>After finishing its transmission, it listens again to see if a collision occurred. </li></ul><ul><li>A collision occurs when two devices send data simultaneously. </li></ul><ul><li>When a collision happens, each device waits a random length of time before resending its data. </li></ul><ul><li>In most cases, a collision will not occur again between the two devices. </li></ul><ul><li>Because of this type of network contention, the busier a network becomes, the more collisions occur. </li></ul><ul><li>This is why performance of Ethernet degrades rapidly as the number of devices on a single network increases. </li></ul>
  8. 8. CSMA/CD <ul><li>For CSMA/CD networks, switches segment the network into multiple collision domains. </li></ul><ul><li>This reduces the number of devices per network segment that must contend for the media. </li></ul><ul><li>By creating smaller collision domains, the performance of a network can be increased significantly without requiring addressing changes. </li></ul>
  9. 9. CSMA/CD <ul><li>Normally CSMA/CD networks are half-duplex </li></ul><ul><ul><li>This is much like a walkie-talkie </li></ul></ul><ul><li>With switches full-duplex operation is possible </li></ul><ul><ul><li>works much like a telephone </li></ul></ul>
  10. 10. Token-passing <ul><li>In token-passing networks such as Token Ring and FDDI, a special network frame called a token is passed around the network from device to device. </li></ul><ul><li>When a device has data to send, it must wait until it has the token and then sends its data. </li></ul><ul><li>When the data transmission is complete, the token is released so that other devices may use the network media. </li></ul><ul><li>The main advantage of token-passing networks is that they are deterministic. </li></ul><ul><ul><li>In other words, it is easy to calculate the maximum time that will pass before a device has the opportunity to send data. </li></ul></ul><ul><li>This explains the popularity of token-passing networks in some real-time environments such as factories, where machinery must be capable of communicating at a determinable interval. </li></ul>
  11. 11. Token-passing <ul><li>Token-passing networks such as Token Ring can also benefit from network switches. </li></ul><ul><li>In large networks, the delay between turns to transmit may be significant because the token is passed around the network. </li></ul>
  12. 12. LAN Transmission Methods <ul><li>In LAN data transmission, a single packet is sent to one or more nodes </li></ul><ul><li>Three classifications: </li></ul><ul><ul><li>Unicast </li></ul></ul><ul><ul><ul><li>In a unicast transmission , a single packet is sent from the source to a destination on a network </li></ul></ul></ul><ul><ul><li>Multicast </li></ul></ul><ul><ul><ul><li>A multicast transmission consists of a single data packet that is sent to a specific subset of nodes on the network </li></ul></ul></ul><ul><ul><li>Broadcast </li></ul></ul><ul><ul><ul><li>A broadcast transmission consists of a single data packet that is sent to all nodes on the network </li></ul></ul></ul>
  13. 13. LAN Topologies <ul><li>Define the manner in which network devices are organized </li></ul><ul><li>Four common topologies exist: bus, ring, star, and tree </li></ul>Bus topology Ring topology Star/Tree topology
  14. 14. LAN Devices <ul><li>Devices commonly used in LANs include </li></ul><ul><ul><li>Repeaters, </li></ul></ul><ul><ul><li>Hubs, </li></ul></ul><ul><ul><li>LAN extenders, </li></ul></ul><ul><ul><li>Bridges, </li></ul></ul><ul><ul><li>LAN switches </li></ul></ul><ul><ul><li>Routers. </li></ul></ul>
  15. 15. Repeater <ul><li>A repeater is a physical layer device ( Layer 1) </li></ul><ul><li>Used to interconnect the media segments of an extended network. </li></ul><ul><li>A repeater essentially enables a series of cable segments to be treated as a single cable. </li></ul><ul><li>Repeaters receive signals from one network segment and amplify, retime, and retransmit those signals to another network segment. </li></ul><ul><li>These actions prevent signal deterioration caused by long cable lengths and large numbers of connected devices. </li></ul><ul><li>Repeaters are incapable of performing complex filtering and other traffic processing. </li></ul><ul><li>In addition, all electrical signals, including electrical disturbances and other errors, are repeated and amplified. </li></ul><ul><li>The total number of repeaters and network segments that can be connected is limited due to timing and other issues. </li></ul>
  16. 16. HUB <ul><li>A hub is a physical layer device that connects multiple user stations, each via a dedicated cable. </li></ul><ul><li>Electrical interconnections are established inside the hub. </li></ul><ul><li>Hubs are used to create a physical star network while maintaining the logical bus or ring configuration of the LAN. </li></ul><ul><li>In some respects, a hub functions as a multiport repeater. </li></ul>
  17. 17. LAN extender <ul><li>A LAN extender is a remote-access multilayer switch that connects to a host router. </li></ul><ul><li>LAN extenders forward traffic from all the standard network layer protocols (such as IP, IPX, and AppleTalk) and filter traffic based on the MAC address or network layer protocol type. </li></ul><ul><li>LAN extenders scale well because the host router filters out unwanted broadcasts and multicasts. </li></ul><ul><li>However, LAN extenders are not capable of segmenting traffic or creating security firewalls. </li></ul>
  18. 18. LAN extender
  19. 19. Bridges & Switches <ul><li>They are data communications devices that operate principally at Layer 2 of the OSI reference model </li></ul><ul><li>As such, they are widely referred to as data link layer devices </li></ul><ul><ul><li>Controls data flow, handles transmission errors, provides physical (as opposed to logical) addressing, and manages access to the physical medium. </li></ul></ul><ul><li>Bridges provide these functions by using various link layer protocols </li></ul><ul><ul><li>Examples of popular link layer protocols include Ethernet, Token Ring, and FDDI. </li></ul></ul>
  20. 20. Bridges & Switches <ul><li>Transparent bridging is found primarily in Ethernet environments </li></ul><ul><li>source-route bridging occurs primarily in Token Ring environments. </li></ul><ul><li>Translational bridging provides translation between the formats and transit principles of different media types (usually Ethernet and Token Ring). </li></ul><ul><li>Source-route transparent bridging combines the algorithms of transparent bridging and source-route bridging to enable communication in mixed Ethernet/Token Ring environments. </li></ul>
  21. 21. Bridges & Switches <ul><li>Upper-layer protocol transparency is a primary advantage of both bridging and switching </li></ul><ul><li>Bridges are capable of filtering frames based on any Layer 2 fields </li></ul><ul><li>Divide large networks into self-contained units </li></ul>
  22. 22. Bridges & Switches <ul><li>Bridges are generally used to segment a LAN into a couple of smaller segments. </li></ul><ul><li>Switches are generally used to segment a large LAN into many smaller segments. </li></ul><ul><li>Bridges generally have only a few ports for LAN connectivity, whereas switches generally have many. </li></ul><ul><li>Switches can also be used to connect LANs with different media—for example, a 10-Mbps Ethernet LAN and a 100-Mbps Ethernet LAN can be connected using a switch. </li></ul><ul><li>Some switches support cut-through switching, which reduces latency and delays in the network </li></ul><ul><li>Bridges support only store-and-forward traffic switching. </li></ul><ul><li>Switches reduce collisions on network segments because they provide dedicated bandwidth to each network segment. </li></ul>
  23. 23. Routers <ul><li>A router is a computer networking device that forwards data packets across a network toward their destinations, through a process known as routing. </li></ul><ul><li>Routing occurs at layer 3 (the Network layer e.g. IP) of the OSI seven-layer protocol stack. </li></ul><ul><li>A router acts as a junction between two or more networks to transfer data packets among them. </li></ul><ul><li>A router is different from a switch. </li></ul><ul><li>A switch connects devices to form a Local area network (LAN). </li></ul>
  24. 24. Routers <ul><li>A router connects the Internet Service Provider's (ISP) network to a LAN </li></ul><ul><li>The switch connects devices together to form the LAN. </li></ul><ul><li>Sometimes the switch and the router are combined together in one single package sold as a multiple port router. </li></ul><ul><li>In order to route packets, a router communicates with other routers using routing protocols and using this information creates and maintains a routing table </li></ul>