This layer specifies the physical interface on a device connected to a LAN and also
the associated cabling. Typically, the physical connectivity manifests in a transceiver,
the Network Interface Card (NIC), that physically plugs into a device??™s (could be a
computer or for that matter any device requiring Ethernet connectivity) motherboard.
A NIC is identified by a three-part nomenclature based on the attributes of the physical
connection: transmission rate, transmission method, and media type or signaling. For
example, 10Base-T indicates a 10 Mbps baseband6 over two twisted-pair cables, while
a 1000Base-LX refers to 1000 Mbps, based band, long wavelength over fiber.
Each of the NICs has a unique static address (assigned by the manufacturer from a
block of addresses purchased from the IEEE); this address is referred to as its MAC or
Ethernet address, and it is based on a flat-addressing space7 and uses 6 bytes written
in a hexadecimal format.
Data-Link layer (DLL) layer The Data-Link layer provides the functionality to
transfer data bits between entities in a network (basically between the numerous computers
that are inter-connected) and detects and corrects, if necessary, any errors that
occur at the Physical layer.
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