|  | 3.1 | Basic LAN Devices
| 3.1.5 | Repeaters

As mentioned on the network media page, there are many types of media, and each one has advantages and disadvantages. One of the disadvantages of the type of cable that we primarily use (CAT5 UTP) is cable length. The maximum length for UTP cable in a network is 100 meters (approximately 333 feet). If we need to extend our network beyond that limit, we must add a device to our network. This device is called a repeater.

The term repeater comes from the early days of visual communication, when a man situated on a hill would repeat the signal he had just received from the person on the hill to his left, in order to communicate the signal to the person on the hill to his right. It also comes from telegraph, telephone, microwave, and optical communications, all of which use repeaters to strengthen their signals over long distances, or else the signals will eventually fade or die out.

The purpose of a repeater is regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media. Watch out for the Four Repeater Rule for 10Mbps Ethernet, also know as the 5-4-3 Rule, when extending LAN segments. This rule states that you can connect five network segments end-to-end using four repeaters but only three segments can have hosts (computers) on them.

The term repeater traditionally meant a single port "in" and a single port "out" device. But in common terminology today the term multiport repeater is often used as well. Repeaters are classified as Layer 1 devices in the OSI model, because they act only on the bit level and look at no other information. The symbol for repeaters is not standardized, therefore, you will use the symbol shown in the Figure throughout the CCNA curriculum.
For more information about commercially available repeaters, visit:

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