Lecture 13: Multiaccess Networks

Twisted Pair (10BaseT) Ethernet

For various reasons, this is now the preferred Ethernet technology. In this system, stations are "star-wired" to a central hub, using a high-performance 4-pair twisted pair cable, thus:

The hub acts as a repeater, so whilst this superficially looks like a group of point-to-point links, all stations still "see" each other's transmissions, just the same as the coax-cable bus topology. In other words, it's still a "shared medium" network, and the attached computers still occupy a single collision domain.

The cable is usually "Category-5" (always abbreviated to "Cat5") unshielded twisted pair (UTP) although some installations (eg, your lecturer's office!) are still cabled with the older, lower performance Cat-3 cable. In practice, there are various hardware technologies involved in a typical installation: in-wall fixed wiring, patch cables, patch panels, etc. There are also strong limits on "cable-run" lengths.

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