1Module 7

Data Link Layer

2Objectives

Data Link Layer Accessing the Media Media Access Control Techniques Media Access Control Addressing and Framing Data

3Data Link Layer Accessing the Media

4Data Link Layer Supporting and Connecting to Upper Layer Service

The Data Link layer performs two basic services: Allows the upper layers to access the media using techniques such as framing Controls how data is placed onto the media and is received from the media using

techniques such as media access control and error detection

5Upper Layer Access to Media

6Data Link Layer Controlling Transfer across Local Media

The Data Link layerprepares network datafor the physical network

7Data Link Layer Creating a Frame

Frame Header and Trailer information may tell: Which nodes are in communication with each other When communication between individual nodes begins and when it ends Which errors occurred while the nodes communicated

8Data Link Layer Creating a Frame

Formatting Data for Data Transmission

9Data Link Layer Connecting Upper Layer Services to the Media

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Data Link Layer Connecting Upper Layer Services to the Media

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Data Link Layer Standard

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Media Access Control Techniques

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Media Access Control for Shared Media

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Media Access Control for Shared Media

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Media Access Control for Shared Media

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Media Access Control for Non-Shared Media

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Media Access Control for Non-Shared Media

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Media Access Control for Non-Shared Media

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Logical Topology vs Physical Topology

Logical and physical topologies typically used in networks

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Point-to-Point Topology

In point-to-point networks, if data can only flow in one direction at a time, it is operating as a half-duplex link. If data can successfully flow across the link from each node simultaneously, it is a full-duplex link.

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Logical Point-to-Point Networks

In some cases, the logical connection between nodes forms what is called a virtual circuit.

The two nodes on either end of the virtual circuit exchange the frames with each other. This occurs even if the frames are directed through intermediary devices.

Virtual circuits are important logical communication constructs used by some Layer 2 technologies

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Multi-Access Topology

Logical Multi-Access Topology

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Ring Topology

In a logical ring topology, each node in turn receives a frame. If the frame is not addressed to the node, the node passes the frame to the next node. This allows a ring to use a controlled media access control technique called token passing

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Media Access Control Addressingand Framing Data

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Data Link Layer Protocols The Frame

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Framing Role of the Header

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Addressing Where the Frame Goes

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Frame Roles of the Trailer

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Data Link Layer Protocols The Frame

Examples of Layer 2 Protocols

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Good luck with this module!