TCP / IP For Dummies
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The first two layers of the Open Systems Interconnection (OSI) model deal with the physical structure of the network and the means by which network devices can send information from one device on a network to another. By far, the most popular set of protocols for the Physical and Data Link layers is Ethernet.

Ethernet has been around in various forms since the early 1970s. The current incarnation of Ethernet is defined by the IEEE standard known as 802.3.

Various flavors of Ethernet operate at different speeds and use different types of media. However, all the versions of Ethernet are compatible with each other, so you can mix and match them on the same network by using devices such as bridges, hubs, and switches to link network segments that use different types of media.

The actual transmission speed of Ethernet is measured in millions of bits per second, or Mbps. Ethernet comes in three different speed versions: 10 Mbps, known as Standard Ethernet; 100 Mbps, known as Fast Ethernet; and 1,000 Mbps, known as Gigabit Ethernet. Network transmission speed refers to the maximum speed that can be achieved over the network under ideal conditions. Actual throughput of an Ethernet network rarely reaches this maximum speed.

Ethernet operates at the first two layers of the OSI model — the Physical and the Data Link layers. However, Ethernet divides the Data Link layer into two separate layers known as the Logical Link Control (LLC) layer and the Medium Access Control (MAC) layer.


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