Q & A on Ethernet Transceivers and "10BaseT",

Q: I had a few questions regarding ethernet ..

Unlike thicknet, thinnet and twisted pair do not have a explicit transceiver - dont they require one or it is in the NIC(for thinnet) or hub for twisted pair

A: You are correct, thinnet and twisted pair do not have an external transceiver. The necessary transmission hardware is part of the network interface card (NIC) for thinnet. In twisted pair Ethernet, the hub contains active electronics that can amplify and retransmit signals. Thus, the NIC in a given computer only needs to propagate the signal as far as the hub.

Q: Why is 10Base-T called so

A: The "10" stands for the transfer rate of 10 megabits per second. The "T" stands for twisted pair. Thicknet, which has a maximum cable segment length of 500 meters, is named 10Base-5, and thinnet, which has a maximum cable length of 200 meters is named 10Base-2. (Note: the names can be written without the dash).

Q: In Twisted pair - we refer to the logical topology as a BUS but the physical topology is Star - have I got it right.

A: Yes. The original Ethernet was, of course, both a physical and logical bus -- a single cable comprised the medium over which signals were transmitted. From the point of view of an attached computer, twisted pair Ethernet appears logically to be exactly the same as a single cable (i.e., twisted pair Ethernet uses CSMA/CD for media access just like the original Ethernet). Physically, however, twisted pair Ethernet consists of a hub to which each computer connects, making it a physical star. One often hears the terms "star-shaped bus" or "bus-in-a-box" used to describe the configuration.

Q: Why is that the hosts on the ethernet need to be seperated by a minimum distance (3m?). I understand the need for maximum distance.

A: This answer from Tim Korb:

It's in 7.6.2 of the spec. The placement is to reduce signal reflections and, in particular, to make sure that placement does not "add in phase to a significant degree". The spec is not to insure a minimum distance, but to insure regular placement. The placement distance, incidentally, is 2.5 meters.