- Early Bus Networks (10BASE-5 and 10BASE-2)
- Development of 10BASE-T Wiring
- Enter the Switch
- Token Passing Topologies
- Exam Prep Questions
- Need to Know More?
This chapter is from the book
This chapter is from the book
This chapter is from the book
Development of 10BASE-T Wiring
Even though 10BASE-2 made coaxial networks a little easier to work with, the installations were still prone to catastrophic failures when the cable was nicked, expensive to install and maintain, and difficult to work with. However, what was the alternative? Well, a lot of people were asking why networking could not be more like telephones and utilize a simple pair of wires. Actually, there were some good reasons why networks could not use paired wires. Networks operated at frequencies that were well into the radio spectrum. At those frequencies a pair of wires would act like a giant antenna and radiate all over the place. The pair of wires would also receive the signals of other radio frequency devices such as fluorescent lights, monitors, and CPU units. All in all not a good thing, and the very reason coaxial cable was used in the first place.
It would be nice to use paired wire in networks, but it just wasn't going to happen. And it did not happen until a couple of engineering types figured out that if the wires were twisted the radiation would be cancelled out, and that sending two signals down the wires 180 degrees out of phase and then measuring the difference would make other sources of radio frequency noise irrelevant.
The world of networking changed overnight. The twisted-pair cable required by the new network was later standardized as Category 5 cable, and the whole configuration was standardized as 10BASE-T (10 megahertz, base band, twisted pair). Ethernet would remain a bus topology, but the coaxial cable that formed the bus was shrunk to about a foot long. The taps, which included repeaters, were attached to the bus at the factory, and each tap/repeater was terminated in a modular receptacle much like the RJ-45 jack used by the telephone company. The whole assembly was encased in a box with the receptacles mounted on the outside. Today we call that box a hub (see Figure 3.6) and its use created a topology called a star wired bus.
The new topology was called a star wired bus because the bus remained within the cabinetry of the hub. Of course, the coaxial cable was replaced by traces on a printed circuit board, but the functionality of the bus was still there. 10BASE-T cables radiated out from the hub to each station on the network, which is why it is called "star wired."
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Figure
3.6 A typical star wired bus topology.
The advent of the hub and 10BASE-T wiring eliminated most of the problems inherent in a coaxial cable based bus network. The hub cabinetry protected the physical bus, taps, and repeaters, eliminating damage from nicks, cuts, and leaky tap connections. The difficult job of tapping into the bus was performed and tested at the factory, which allowed field connections to be as simple as snapping a Category 5 connector into the jack on the hub. That plagued coaxial cable-based networks. Because each station had a dedicated cable connecting it to a repeater in the hub, individual cable runs could be up to 100 meters with cable faults like cuts isolated to a single station. The dedicated hub connection also isolated damage caused by cable faults to a single station. Lastly, when compared to coaxial cable, 10BASE-T cable was extremely easy and inexpensive to install.