Page 66 - Handout Computer Network.

https://www.youtube.com/watch?v=a5SMTyhn0U8 .

3.7 Ethernet Fundamentals

Ethernet, in its various forms, is the most widely used local-area network (LAN)
technology. Ethernet was designed to fill the middle ground between long-distance, low-speed
networks and specialized, computer-room networks carrying data at high speeds for very
limited distance. Ethernet is well suited to applications in which a local communication
medium must carry sporadic, occasionally heavy traffic at high-pack data rates. It was designed
to enable sharing resources on a local workgroup level. Design goals include simplicity, low
cost, compatibility, fairness, low delay, and high speed. In this chapter, you learn about the
history of Ethernet and IEEE Ethernet standards. This Section discusses the operation of
Ethernet, Ethernet framing, and error handling, as well as the different types of the collisions
on Ethernet networks. In addition, this section introduces collision domains and broadcast
domains. Finally, this section describes function of STP protocol.

3.7.1 IEEE 802.3/Ethernet and the OSI Model

LAN standards define the physical media and the connectors used to connect devices
to media at the physical layer of the OSI reference model. LAN standards also define the way
devices communicate at the data link layer. In addition, LAN standards define how to
encapsulate protocol-specific traffic in such as way that traffic going to different upper-layer
protocols can use the same channel that passes though that layers of the OSI model. To
provide these functions, the IEEE Ethernet data link layer has two sublayers:

• Media Access Control (MAC) (802.3)—As the name implies, the MAC sublayer
defines how to transmit frames on the physical wire. It handles physical addressing
associated with each device, network topology definition, and line discipline.
• Logical Link Control (LLC) (802.2)—As the name implies, the LLC sublayer is
responsible for logically identifying different protocol types and then encapsulating
them. A type code or a service access point (SAP) identifier performs the logical
identification. The type of LLC frame used by an end station depends on what
identifier the upper-layer protocol (such as IP) expects.
Although IEEE 802.2 represents one standard type of frame encapsulation, there are
others, such as Ethernet II (used primarily with TCP/IP–based Ethernet LANS.

As shown in Figure 3-13, the IEEE 802.3 standard defines the physical layer (Layer 1)
and the MAC portion of the data link layer (Layer 2).

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