|
Gigabit Ethernet merges aspects of 802.3
Ethernet and fiber channel, a gigabit technology intended for
high-speed interconnections between file servers as a LAN
replacement. The fiber-channel standard details a layered network
model capable of scaling to bandwidths of 4 gigabits per second (Gbps)
and to extend to distances of 10 km. Gigabit Ethernet borrows the
bottom two layers of the standard: FC-1 for encoding/decoding and
FC-0, the interface and media layer. FC-0 and FC-1 replace the
physical layer of the legacy 802.3 model. The 802.3 MAC and LLC
layers contribute to the higher levels of Gigabit Ethernet. The
Figure illustrates the merger of the standards to form Gigabit
Ethernet.
The fiber-channel standard
incorporated by Gigabit Ethernet transmits at 1.062 MHz over fiber
optics and supports 800-Mbps data throughput. Gigabit Ethernet
increases the signaling rate to 1.25 gigahertz (GHz). Further,
Gigabit Ethernet uses 8B/10B encoding, meaning that 1 Gbps is
available for data. The 8B/10B encoding is similar to 4B/5B
discussed for 100BASE-TX, except that for every 8 bits of data, 2
bits are added, creating a 10-bit symbol. This encoding technique
simplifies fiber-optic designs at this high data rate. The optical
connector used by fiber channel, and therefore by Gigabit Ethernet,
is the switching controller (SC) style connector. This is the
push-in/pull-out, or snap-and-click connector used by manufacturers
to overcome deficiencies with the snap-and-twist (ST) style
connector. The ST style connector previously preferred was a
bayonet-type connector that required finger space on the front panel
to twist the connector into place. The finger-space requirement
reduced the number of ports that could be built into a module.
|