100BASE-T

w^rl0rd

If I understand correctly, 100BASE-T4 has a transfer rate of up to 100MBps using CAT-3 cabling which has a maximum throughput of 16MBps. How is this possible?

Webmaster

100baseT4 supports transmission over Cat 3, Cat 4 or 5 cabling, it uses 4 pairs of wires (in contrary to 100BaseTX, which uses only 2 pairs), 3 are used for data transmission, the fourth pair is used for colission detection,
the use of all wires makes it possible to reach the high bandwidth, this also the reason why it doesn't support full-duplex, there are no separate pairs for sending and receiving.

(note: you don't need to know this kind of detail for the A+ exam)

Johan

w^rl0rd

What about full and half duplex? I should probably know that. Is Ethernet full-duplex?

Webmaster

You need to know what it is, here's a piece about it from a TechNote I've written for the CCNA exam:

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Half duplex
Half-duplex means that only one host can communicate at a given time, two hosts communicating with each other will take turns transmitting. This is the default on non-switched LANs.

Full-duplex
In full-duplex communication both hosts can transmit at the same time, theoretical allowing twice as much data to be transmitted over the same connection.
In order for full-duplex to work, some requirements must be met:
- The NICs, hubs etc. must support it,
- Collision Detection and Loopback functions must be disabled.
In reality the connections able to run at full-duplex are cross-cable connections and connection to a port on a switch, where collisions cannot occur because each end has it's own wire pair (segment).
****

Is Ethernet full-duplex?

Depends on which Ethernet specification(here's a list) , for example 100BaseT4 isn't As you read above there are other requirements that have to be met before full-duplex can operate. Again, more detailed than you need to know for the A+ network but here's something about Ethernet www.techexams.net/technotes/networkplus/mediatopo.shtml

I hope this helps,

Johan

w^rl0rd

Thanks alot. I think I'm overstudying for this exam. Meyers' book gives me the basics like bandwidth, segment length, # of devices, cabling, connectors, and respective topology. I guess I should stick to that. I'm just afraid that with only 30 questions my margin for error is small.

RussS

Hey Shinobi

Shoot, it is good to have a little extra knowledge in some areas as by having that knowledge you KNOW that you know your stuff when it comes time for your exam. And THAT makes you a little more relaxed, which makes you think better, which makes a good score

bellboy

Shinobi wrote:

Thanks alot. I think I'm overstudying for this exam. Meyers' book gives me the basics like bandwidth, segment length, # of devices, cabling, connectors, and respective topology. I guess I should stick to that. I'm just afraid that with only 30 questions my margin for error is small.

that sounds pretty much like all the a+ will quiz you on. go to the comptia website and download the objectives. they will help keep you on track nothing wrong with learning more than you need, as the extra knowledge could help you with further exams.

i actually stopped buying computer magazines when i studied for a+ as the exam only went up to piii cpu and i started getting confused with the newer technologies being released that were being reviewed/previewed in the mags and what i actually had to know for the exam.