By Opting For The Exam 70-680: Server Administrator Certificate

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The Data-Link layer provides for the flow of data over a single physical link from one device to another. It accepts packets from the Network layer and packages the information into data units called frames ; these frames are presented to the Physical layer for transmission. The Data- Link layer adds control information, such as the frame type, to the data being sent. This layer also provides for the error-free transfer of frames from one mcsa certification
computer to another. A cyclic redundancy check (CRC) added to the data frame can detect damaged frames, and the Data-Link layer in the receiving computer can request that the CRC information be present so that it can check incoming frames for errors. The Data-Link layer can also detect when frames are lost and request that those frames be sent again.

In broadcast networks such as Ethernet, all devices on the LAN receive the data that any device transmits. (Whether a network is broadcast or point-to-point is determined by the net- work protocols used to transmit data over it.) The Data-Link layer on a particular device ...
... is responsible for recognizing frames addressed to that device and throwing the rest away, much as you might sort through your daily mail to separate good stuff from junk. Figure 1.3 shows how the Data-Link layer establishes an error-free connection between two devices.

The Institute of Electrical and Electronics Engineers (IEEE) developed a protocol specification known as IEEE 802.X. (802.2 is the standard that divides this layer into two sublayers. The Media Access Control layer, more commonly called the MAC layer, varies depending on the net- work type and is described further in standards 802.3 through 802.5.) As part of that specification (which today we know as Ethernet), the Data-Link layer is split into comptia security certification
two sublayers: The Logical Link Control (LLC) layer establishes and maintains the logical communication links between the communicating devices.

The Media Access Control (MAC) layer acts like an airport control tower—it controls the way multiple devices share the same media channel in the same way that a control tower regulates the flow of air traffic into and out of an airport.

The LLC sublayer provides service access points (SAPs) that other computers can refer to and use to transfer information from the LLC sublayer to the upper OSI layers. This is defined in the 802.2 standard.

The MAC sublayer, the lower of the two sublayers, provides for shared access to the network adapter and communicates directly with network interface cards. A unique 48-bit address, commonly represented as a 12-digit hexadecimal MAC address (frequently called the hardware Ethernet address ), is assigned to network interface cards before they leave the factory where they are made. The LLC sublayer uses MAC addresses to establish logical links between devices on the same LAN. Ethernet is an example of a protocol that exists at the Data-Link layer.