Typical LAN Features for OSI Layer

OSI Layer 2, the data link layer, defines the standards and protocols used to control the transmission of data across a physical network. If you think of Layer 1 as "sending bits," you can think of Layer 2 as meaning "knowing when to send the bits, noticing when errors occurred when sending bits, and identifying the computer that needs to get the bits."

Similar to the section about the physical layer, this short section describes the basic data link layer functions. Later, you will read about the specific standards and protocols for Ethernet.

Data link protocols perform many functions, with a variety of implementation details. Because each data link protocol "controls" a particular type of physical layer network, the details of how a data link protocol works must include some consideration of the physical network. However, regardless of the type of physical network, most data link protocols perform the following functions:

■ Arbitration—Determines when it is appropriate to use the physical medium

■ Addressing—Ensures that the correct recipient(s) receives and processes the data that is sent

■ Error detection—Determines whether the data made the trip across the physical medium successfully

■ Identification of the encapsulated data—Determines the type of header that follows the data link header

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