Robert Foxworth wrote:
>
> As you see, only pairs 2 and 3 conduct signal.
> Pairs 1 and 4 are electrically idle, but the spec
> says they are all connected. When making cables you
> need to connect them anyway to maintain proper
> wire position.
100baseTX uses one pair of wires for transmission (125Mbaud 4B/5B
encoding), and a second pair for collision detection and receive. Due to
the 20% overhead of 4B/5B encoding, 125Mbaud becomes 100Mbit.
100baseT4 uses 3 pairs for transmission (33Mhz per pair) and the fourth
pair for collision detection. The lower signalling rate makes it
possible to use Cat3 cabling.
1000baseT uses all 4 pairs for transmitting and receiving (125Mbaud
PAM-5 encoding). 4x250Mbit = 1Gbit.
With 10baseT and 100baseTX, both pairs are electrically active - the
balanced twisted pairs allow for detection and correction of errors
induced in both lines.
- Ian
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