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Q.1 Write down the features of Fast Ethernet and Gigabit Ethernet.


Answer:
Fast Ethernet :
The basic idea behind fast Ethernet was simple: keep all the old frame formats, interfaces, and procedural rules, but just reduce the bit time from 100 nsec to 10 nsec.


  • 100Base-T4 uses a signaling speed of 25 MHz, only 25 percent faster than standard Ethernet's 20 MHz. However, to achieve the necessary bandwidth, 100Base-T4 requires four twisted pairs.
  • 100Base-TX is simpler because the wires can handle clock rates of 125 MHz. Only two twisted pairs per station are used, one to the hub and one from it. Straight binary coding is not used; instead a scheme called used4B/5Bis It is taken from FDDI and compatible with it. The 100Base-TX system is full duplex; stations can transmit at 100 Mbps and receive at 100 Mbps at the same time.
  • 100Base-TX and 100Base-T4 are collectively referred to as 100Base-T.
  • 100Base-FX, uses two strands of multimode fiber, one for each direction, so it, too, is full duplex with 100 Mbps in each direction. The distance between a station and the hub can be up to 2 km.

Gigabit Ethernet
Goals of Gigabit Ethernet goals:
  • Make Ethernet go 10 times faster yet remain backward compatible with all existing Ethernet standards.
  • Gigabit Ethernet supports two different modes of operation: full-duplex mode and half-duplex mode.
  • Gigabit Ethernet had to offer unacknowledged datagram service with both unicast and multicast, use the same 48-bit addressing scheme already in use, and maintain the same frame format, including the minimum and maximum frame sizes.

Gigabit Ethernet supports both copper and fiber cabling, as listed in Fig.
Gigabit Ethernet uses new encoding rules on the fibers. Manchester encoding at 1 Gbps would require a 2 Gbaud signal, which was too difficult and also too wasteful of bandwidth. Instead a new scheme, called 8B/10B, was chosen, based on fiber channel. Each 8-bit byte is encoded on the fiber as 10 bits; hence the name 8B/10B.Gigabit Ethernets using 1000Base-T use a different encoding scheme since clocking data onto copper wire in 1 nsec is too difficult.


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