utp pairs

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Question by Harvey Angulo posted 11 May 2000
icon utp pairs
I would like to know how many pairs are used in a cat5 cable to transmit at 100 mbps full duplex.
I believe 8 wires are used (4 pairs) if this is not the case then why 100BaseT networks aren't build with 4 wires cables then.

Another question, if your are using 10BaseT half duplex, could you use onle one pair ?


Answer by Roman Kitaev posted 12 May 2000
icon Hi, Harvey!

Fast Ethernet 100Base-TX and Ethernet 10Base-T use two pairs (2th and 3th) of Cat5 cabling. One pair is used for transmit, the second pair for receive. Full duplex means that receive and transmit happen at the *same* time, but, nevertheless, on *different* pairs.

100T4-T protocol uses 4 pairs of Cat3 cabling or higher. Gigabit Ethernet 1000Base-T uses 4 pairs of Cat5 or higher cabling.

You really can use 4-wire Cat5 cable for running Fast Ethernet, but it is not recommended because you will not be able to upgrade to another applications during the system's lifetime.

Theoretically, it is possible to run one 10Base-T link over one pair of pairs and the second link over the second pair of pairs of a Cat5 4-pair cable.

I would *strongly* not recommend it because it is not standards-complying (TIA/EIA-568A) and requires non-standard wiring schemes at patch panels and work area jacks making administration more difficult.

Best regards,
Roman Kitaev, RCDD

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