Page 68 - Handout Computer Network.

Figure 3-14 shown an Ethernet Technologies and the OSI Model

Figure 3-15 shown a MAC Address Format

Without MAC addresses, the LAN would be a group of computers without identifiers,
and it would be impossible to deliver an Ethernet frame. Therefore, at the data link layer, a
header and a trailer are added to upper-layer data. The header and trailer contain control
information intended for the data link layer entity in the destination system. Data from upper-
layer entities is encapsulated in the data link layer header and trailer. Ethernet and 802.3 LANs
are broadcast networks. All stations see all frames. Each station must examine every frame to
determine whether that station is the desired destination. On an Ethernet network, when one
device wants to send data to another device, it can open a communication pathway to the
other device by using its MAC address. When a source device sends data out on a network,
the data carries the MAC address of its intended destination. As this data propagates along
the network medium, the NIC in each device on the network checks to see if its MAC address

68