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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 should receive the data. In OSI model, each layer provides its own
mean 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 these six bytes are stored in a non-volatile
memory in the device. Their format is as the following table and normally written in
the form as aa-bb-cc-dd-ee-ff, a 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