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Unit 1 Of ACN

Unit 1 Of ACN

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