BASET Ethernet

10BASE-T solved several problems with the early Ethernet specifications. 10BASE-T allowed the use of telephone cabling that was already installed, or simply allowed the use of cheaper, easier-to-install cabling when new cabling was required. 10BASE-T networks make use of devices called hubs, as shown in Figure 3-5.

Figure 3-5

Small Ethernet 10BASE-T Network

10BASE-T, Using Shared Hub - Acts Like Single Bus

10BASE-T, Using Shared Hub - Acts Like Single Bus

Archie

Solid Lines Represent Twisted Pair Cabling

Archie

Solid Lines Represent Twisted Pair Cabling

The physical 10BASE-T Ethernet uses Ethernet cards in the computers, cabling, and a hub. The hubs used to create a 10BASE-T Ethernet are essentially multiport repeaters. That means that the hub simply regenerates the electrical signal that comes in one port and sends the same signal out every other port. By doing so, 10BASE-T creates an electrical bus, just like 10BASE2 and 10BASE5. Therefore, collisions can still occur, so CSMA/CD access rules continue to be used.

The use of 10BASE-T hubs gives Ethernet much higher availability compared with 10BASE2 and 10BASE5 because a single cable problem could, and probably did, take down those types of LANs. With 10BASE-T, a cable is run from each device to a hub, so a single cable problem affects only one device.

The concept of cabling each device to a central hub, with that hub creating the same electrical bus as in the older types of Ethernet, was a core fact of 10BASE-T Ethernet. Because hubs continued the concept and physical reality of a single electrical path that is shared by all devices, today we call this shared Ethernet: All devices are sharing a single 10-Mbps bus.

A variety of terms can be used to describe the topology of networks. The term star refers to a network with a center, with branches extended outward—much like how a child might draw a picture of a star. 10BASE-T network cabling uses a star topology, as seen in Figure 35. However, because the hub repeats the electrical signal out every port, the effect is that the network acts like a bus topology. So, 10BASE-T networks are a physical star network design, but also a logical bus network design. (Chapter 11 covers the types of topologies and their meaning in more depth.)

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