Networking / Beginners

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Repeaters

A repeater is a gizmo that gives your network signals a boost so that the signals can travel farther. It's kind of like a Gatorade station in a marathon. As the signals travel past the repeater, they pick up a cup of Gatorade, take a sip, splash the rest of it on their heads, toss the cup, and hop in a cab when they're sure that no one is looking.

You need a repeater when the total length of a single span of network cable is larger than the maximum allowed for your cable type:

Cable	Maximum Length
10Base2 (Coaxial)	185 meters or 606 feet
10/100BaseT (Twisted Pair)	100 meters or 328 feet

For coaxial cable, the preceding cable lengths apply to cable segments - not individual lengths of cable. A segment is the entire run of cable from one terminator to another and may include more than one computer. In other words, if you have ten computers and you connect them all with 25-foot lengths of thin coaxial cable, the total length of the segment is 225 feet. (Made you look! Only nine cables are required to connect ten computers - that's why it's not 250 feet.)

For 10BaseT or 100BaseT cable, the 100-meter length limit applies to the cable that connects a computer to the hub or the cable that connects hubs to each other when hubs are daisy-chained with twisted-pair cable. In other words, you can connect each computer to the hub with no more than 100 meters of cable, and you can connect hubs to each other with no more than 100 meters of cable.

Figure below shows how you can use a repeater to connect two groups of computers that are too far apart to be strung on a single segment. When you use a repeater like this, the repeater divides the cable into two segments. The cable length limit still applies to the cable on each side of the repeater.

Here are some points to ponder when you lie awake tonight wondering about repeaters:

• Repeaters are used only with Ethernet networks wired with coaxial cable; 10/100BaseT networks don't use repeaters.
  Actually, that's not quite true: 10/100BaseT does use repeaters. It's just that the repeater isn't a separate device. In a 10/100BaseT network, the hub is actually a multiport repeater. That's why the cable used to attach each computer to the hub is considered a separate segment.
• Some 10/100BaseT hubs have a BNC connector on the back. This BNC connector is a thinnet repeater that enables you to attach a full 185-meter thinnet segment. The segment can attach other computers, 10BaseT hubs, or a combination of both.
• A basic rule of Ethernet life is that a signal can't pass through more than three repeaters on its way from one node to another. That doesn't mean you can't have more than three repeaters or hubs, but if you do, you have to carefully plan the network cabling so that the three-repeater rule isn't violated.
• Repeaters are legitimate components of a by-the-book Ethernet network. They don't extend the maximum length of a single segment; they just enable you to tie two segments together. Beware of the little black boxes that claim to extend the segment limit beyond the standard 185-meter limit for thinnet or the 100-meter limit for 10/100BaseT cable. These products usually work, but playing by the rules is better.