The Data Link layer packages raw bits from the Physical layer into frames. This layer is responsible for transferring frames from one computer to another, without errors. A network data frame includes checksum, source and destination address, and data. The largest packet that can be sent through a data link layer defines the Maximum Transmission Unit (MTU).
The Data Link layer's functionality includes flow control, error detection and control, defining topologies such as star, bus, ring and media access control (MAC).
Ethernet addresses a host using a unique, 48-bit address called its Ethernet address or Media Access Control (MAC) address. MAC is closely associated with the physical layer and defines the means by which the physical medium may be accessed. MAC addresses are usually represented as six colon-separated pairs of hex digits, e.g., 8:0:20:11:ac:85. This number is unique and is associated with a particular Ethernet device; the first 3 bytes 8:0:20 specify the vendor/manufacturer of the NIC; the other 3 bytes 11:ac:85 define the host. The data link layer's protocolspecific header specifies the MAC address of the packet's source and destination. When a packet is sent to all hosts (broadcast), a special MAC address (ff:ff:ff:ff:ff:ff) is used.
The DataLink Layer Devices include switch, bridge.
DataLink Layer example include: 802.3, ATM, Frame Relay, PPP, Token Ring, ARP, SLIP
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