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4.1 | |
Introduction to Ethernet/802.3 LANs | |
| 4.1.9 | |
Full-duplex transmitting |
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Full-duplex Ethernet allows the transmission
of a packet and the reception of a different packet at the same time.
This simultaneous transmission and reception requires the use of two
pairs of wires in the cable and a switched connection between each node.
This connection is considered point-to-point and is collision free.
Because both nodes can transmit and receive at the same time, there are
no negotiations for bandwidth. Full-duplex Ethernet can use an existing
cable infrastructure as long as the medium meets the minimum Ethernet
standards. To transmit and receive simultaneously, a dedicated switch port is required for each node. Full-duplex connections can use 10BASE-T, 100BASE-TX, or 100BASE-FX media to create point-to-point connections. The NICs on all connected devices must have full-duplex capabilities. The full-duplex Ethernet switch takes advantage of the two pairs of wires in the cable by creating a direct connection between the transmit (TX) at one end of the circuit and the receive (RX) at the other end. With the two stations connected in this manner a collision free environment is created as the transmission and receipt of data occurs on separate non-competitive circuits.
Ethernet usually can only use 50%-60% of the available 10 Mbps of
bandwidth because of collisions and latency. Full-duplex Ethernet offers
100% of the bandwidth in both directions. This produces a potential 20
Mbps throughput, which results from 10 Mbps TX and 10 Mbps RX.
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