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Lecture 4b Data Link Layer

Lecture 4b Data Link Layer. Objectives: Explain the role of the data link layer in supporting communications across data networks. Compare media access control techniques and logical topologies used in networks. Purpose of the Data Link Layer The Data Link Layer.

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Lecture 4b Data Link Layer

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  1. Lecture 4bData Link Layer Objectives: • Explain the role of the data link layer in supporting communications across data networks. • Compare media access control techniques and logical topologies used in networks.

  2. Purpose of the Data Link LayerThe Data Link Layer The Data Link layer is responsible for • logical link control (for upper-layer processes) and • media access control (for the Physical layer )

  3. Purpose of the Data Link LayerData Link Layer Terminology

  4. Purpose of the Data Link LayerData Link Sublayers

  5. Purpose of the Data Link LayerData Link Sublayers 802.3 Ethernet 802.11 Wi-Fi 802.15 Bluetooth

  6. Satellite link Wireless link Ethernet link Purpose of the Data Link LayerMedia Access Control • In any exchange of Network layer packets, there may be numerous Data Link layer and media transitions • Without the Data Link layer, a Network layer protocol would have to make provisions for connecting to every type of media that exists along a delivery path

  7. Purpose of the Data Link LayerProviding Access to Media

  8. Data Link LayerLayer 2 Frame Structure • The Data Link layer prepares a packet for transport across the local media by encapsulating it with a header and trailer to create the frame • header – contains control information, such as addressing, and is located at the beginning of the protocol data unit (PDU) • data – the packet from the Network Layer • trailer – contains control information added to the end of the PDU

  9. TopologiesPhysical and Logical Topologies Physical topologyis the physical layout of the components on the network Logical topologydetermines how the hosts access the medium to communicate across the network

  10. WAN TopologiesCommon Physical WAN Topologies

  11. WAN TopologiesPhysical and LogicalPoint-to-Point Topology Physical point-to-point connection

  12. WAN TopologiesHalf and Full Duplex • Half-duplex communication means that the devices can either transmit or receive on the media at one time • Full-duplex communication means that the devices can both transmit and receive on the media simultaneously

  13. LAN TopologiesPhysical LAN Topologies

  14. LAN TopologiesShared Media Access • To prevent total chaos, a Carrier Sense Multiple Access (CSMA) process is used to detect if the media is carrying a signal • it is possible that the CSMA process will fail when two devices transmit at the same time – data collision • CSMA is usually implemented in conjunction with either of the two methods for resolving media contention • CSMA/Collision Detection (CSMA/CD) • CSMA/Collision Avoidance (CSMA/CA)

  15. LAN TopologiesContention-Based Access

  16. LAN TopologiesMulti-Access Topology • Enables a number of nodes to communicate using a shared media • Data from only one node can be placed on the medium at any one time • Only the node to which the frame is addressed processes the content of the frame • MAC methods are usually CSMA/CD or CSMA/CA

  17. LAN TopologiesControlled Access

  18. LAN TopologiesRing Topology • Each node in turn receives a frame • the node removes the frame from the ring and examines the address • the node passes the frame to the next node if it is not addressed to it • Only one frame at a time is usually carried by the media • MAC technique used is Token Passing • a node can only place a data frame on the media when it has the token

  19. Data Link FrameLAN and WAN Frames • The actual Layer 2 protocol used depends on the logical topology of the network and the implementation of the Physical layer • The Layer 2 protocol used for a particular network topology is determined by the technology

  20. Data Link FrameWAN Link Connection Options

  21. Data Link FrameEthernet Frame

  22. Data Link FramePoint-to-Point Protocol Frame

  23. Data Link Frame802.11 Wireless Frame

  24. Animation • 4313/4445 Different frames • 4314 Transfer of frames • 4434 Logical multi-access topology • 4436 Logical ring topology Activity • 4323/4449 Frame fields

  25. Introduction to Networks Chapter 4: Network Access Further Exploration …

  26. Data Link LayerLayer 2 Standards

  27. Layer 2 StandardsData Link Layer Standards

  28. Data Link FrameThe Frame

  29. Data Link FrameThe Header

  30. Data Link FrameLayer 2 Address

  31. Data Link FrameThe Trailer

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