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The big advantage of 10BASE-T wiring is not that the wiring is cheaper than coaxial cable as most folks like to say. The wire is cheaper per linear foot, but one needs so much more of it that the total cost of the wires themselves is likely to be about the same. In fact, the total cost is somewhat higher because the computers are not wired in a "bus" pattern, instead they are wired in a "star" pattern with a "hub" at the center of the star.
The big advantage of 10BASE-T is that the twisted pair wiring that it uses is the same kind of wiring used for telephone lines and the connectors on the end are RJ-45 modular jacks just like those used in multi-line phone plugs. It is also the same kind of wiring used for RS-232 serial data communications. Hence, many buildings are already pre-wired either with spare phone wires or existing serial lines. Also, there is a large pool of trained technicians on hand in most companies to work with this style of wiring and the fabrication of cables does not require a soldering iron.
In order to understand 10BASE-T Ethernet, we must understand what a hub really does. In terms of the terminology we have developed so far, we can think of a hub as being a multi-port repeater in the sense that it simply takes a bit in one port and pumps the same bit out each of the other ports. A hub does not work with frames, just with bits. More precisely, however, a hub contains the equivalent of an Ethernet "bus" topology inside it with the equivalent of a transceiver for each external port on the hub. Hence, the twisted pair wiring is really the equivalent of the transceiver cables used in 10BASE-5 systems.
Like a repeater, a hub adds a small amount of delay and should
be used with similar restraint on the number of hubs between interfaces.
Several adjectives are often used to describe the features of a hub. "Intelligent" hubs may be simply a hub that has logic circuits to detect a pattern in the bit stream coming over a port to shut down the port when the pattern indicates malformed frames are the rule rather than the exception. However, it may also be used as a synonym for a "managed" hub which has application-layer software installed so that it can be remote-controlled. Network management software is very popular in large organizations that have a dedicated network staff responsible for a network spread over many buildings. "Stackable" hubs provide a special cable to connect hubs that are in the same location without adding to the number of hubs bits must traverse between interfaces. Essentially, this cable connects the wires that are equivalent to the internal Ethernet bus in each hub so as to provide the equivalent of a larger number of transceivers on the same cable.
Twisted pair Ethernet is popular in part because it can reuse the wiring and the technical expertise of the telephone system in a commercial building. To appreciate how it is typically installed, we need to look at some wiring closet installations. First of all, most commercial buildings have at least one set of wiring closets with one closet on each floor directly above one another. The closets are connected with conduits so one can easily run cables from one closet to the next.
In the wiring closet, there are one or more punchdown blocks where cables coming from the wallplates in the offices on that floor are attached to one side. On the other side of the punchdown block is the connection for each cable to the service provider for that cable: telephone, serial line, or twisted-pair Ethernet.
Figure 1: Bundle of twisted pair lines in wiring closet attached to punchdown block (not shown)
Figure 2: Punchdown block (left) wired to two 12 port twisted pair Ethernet hubs (white box in center and black box on right). 12 standard RJ-45 modular jacks and 12 separate cables are used to connect each hub to the punchdown block.
Figure 3: Punchdown block (left) providing connections between office cables and hub cables. 10BASE-F fiber (thin orange cables) comes from a distance to provide service to a chassis-based hub (large white box on top) and two smaller hubs (near bottom) located on an upper floor of a Ball State building. High density cable bundles connect the hubs to the punchdown block, otherwise 60 separate thin cables would need to be used instead of just 3 thick ones.
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