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Full-duplex data transmission means that data can be transmitted in both directions on a signal carrier at the same time. but my question is if we have an interface with 100Mb speed and full-duplex mode does it mean 100Mb to send and 100Mb to receive ??

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Full-duplex data transmission means that data can be transmitted in both directions on a signal carrier at the same time.

That is incorrect. It means devices can transmit and receive at the same time. They almost always use separate channels for each.

In the case of switched Ethernet, there are two channels formed by pairs of wires -- one pair for tx and one for rx -- or by two optical fibers.

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if we have an interface with 100Mb speed and full-duplex mode does it mean 100Mb to send and 100Mb to receive ?

Yes. The interface can send 100 Mbit/s and receive 100 Mbit/s at the exact same time. Of course, Ethernet also exists with 1000 Mbit/s or several other speed grades up to 400 Gbit/s (which exclusively use full duplex).

Forget the bit about the signal carrier as the normal baseband signalling in Ethernet doesn't use a carrier.

In strict telecommunications parlance, full duplex is a channel than can be used in both directions simultaneously. In network technology, this is the case for 1000BASE-T, 10GBASE-T and so on: these variants use all four pairs in a twisted-pair cable for receiving and transmitting simultaneously. 10BASE-T, 100BASE-T and the fiber variants use dual simplex where each direction has its own, independent channel: one twisted pair or one fiber strand in each direction.

In networking, full duplex is only used in contrast to half duplex: only once direction at a time is permitted to send and they need to take turns (as with 10BASE2 or Ethernet with repeaters).

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