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3-2. Media Access Control (MAC)
MAC Addressing
Because LAN is composed of many nodes, for the data exchanged among these nodes, each
node must have its own unique address to identify who should send the data or who should receive the
data. In OSI model, each layer provides its own meaning to identify the unique address in some form, for
example, IP address in network layer.
The MAC is belonged to Data Link Layer (Layer 2), the address is defined to be a 48-bit long and
locally unique address. Since this type of address is applied only to the Ethernet LAN media access
control (MAC), they are referred to as MAC addresses.
The first three bytes are Organizational Unique Identifier (OUI) code assigned by IEEE. The last
three bytes are the serial number assigned by the vendor of the network device. All six bytes are stored in
a non-volatile memory in the device. Their format is displayed in the following table and normally written
in the form as aa-bb-cc-dd-ee-ff, 12
hexadecimal digits separated by hyphens, in which the aa-bb-cc is
the OUI code and the dd-ee-ff is the serial number assigned by manufacturer.
Fig. 3-2 SAP Format