GIGABIT ETHERNET:
In order to provide higher order data rates it resulted in gigabit ethernet protocol. It standard is defined by IEEE as 802.3z. The main for designing gigabit ethernet is.
- It upgraded with the data rates upto 1 Gbps.
- It has same 48 bit address.
- Which has the same frame format compared with other standards.
In the full-duplex mode gigabit ethernet there is no collision; whereas the maximum length of the cable is determined by the signal attenuation in the cable.
Still there is use of half duplex in gigabit ethernet but it is rare. For this case the switch is replaced by hub.
While the physical layer is some complicated when compared with the traditional or standard methods. Let us discuss some features in the physical layer.
Gigabit is designed in such a way that we can connect two or more stations. If there is only one station it is connected in point-to-point. If their more than one station it is connected in a star topology with switch or hub at the center.
Gigabit ethernet can be categorized based on the wire implementation it may be two or four wire implementation. In two-wire implementation designer can use fiber-optic cable (100Base –SX, short wave, or 100 Base-LX, long range) or STP (shielded twisted pair)(1000 Base-CX)
. While in four-wire implementation designer can use category 5 twisted pair cable (1000 Base-T).
Gigabit ethernet using 8B/10B encoding scheme because Manchester encoding scheme involves high bandwidth. Where 8B/10B encoding scheme prevents long sequence of 0 or 1’s in the stream, but the resulting stream is 1.25 Gbps.
Where in four wire implementation it is not possible to use 2 wire for input and 2 wire for output, because each wire would need to carry 500 Mbps, which exceeds the category of 5 UTP to overcome the drawback designer used 4D-PAM5 encoding scheme to reduce the bandwidth.
Thus all, the four wire are involved in both input and output; while each wire carries 250Mbps, which is in the range of the category 5 UTP cable.