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Module7- Data Link Layer 1 Overview 2 Overview Upon completion of this chapter, you will be able to: • Explain the role of Data Link layer protocols in data transmission. • Describe how the Data Link layer prepares data for transmission on network media. • Describe the different types of media access control methods. • Identify several common logical network topologies and describe how the logical topology determines the media access control method for that network. • Explain the purpose of encapsulating packets into frames to facilitate media access. • Describe the Layer 2 frame structure and identify generic fields. • Explain the role of key frame header and trailer fields, including addressing, QoS, type of protocol, and Frame Check Sequence. 3 Data Link Layer – Accessing the Media 4 Supporting & Connecting to Upper Layer Services The Data Link layer provides a means for exchanging data over a common local media. • The Data Link layer performs 2 basic services: 1. Allows the upper layers to access the media using techniques such as framing. 2. Controls how data is placed onto the media and is received from the media using techniques such as media access control and error detection. 5 Terms 7.1.1.1 6 Media • • Media is the physical copper cable, optical fiber, or atmosphere through which the signals travel. In this chapter media does not refer to content programming such as audio, animation, television, and video as used when referring to digital content and multimedia. 7 Logical Networks • Logical networks are defined at the Network layer by the arrangement of the hierarchical addressing scheme. 8 Physical Networks • Physical networks represent the interconnection of devices on a common media. Sometimes, a physical network is also referred to as a network segment. 9 Supporting & Connecting to Upper Layer Services 7.1.1.2 • • The Data Link layer effectively insulates the communication processes at the higher layers from the media transitions that may occur end-to-end. A packet is received from and directed to an upper layer protocol, in this case IPv4 or IPv6, that does not need to be aware of which media the communication will use. 10