Gigabit Ethernet Design Rules

The most recent development in the Ethernet arena is Gigabit Ethernet. Gigabit Ethernet is specified by two standards: IEEE 802.3z and 802.3ab. The 802.3z standard specifies the operation of Gigabit Ethernet over fiber and coaxial cable and introduces the GigabitcMonetdiniau es Independent Interface (GMII). The 802.3z standard was approved in June 1998.

The 802.3ab standard specifies the operation of Gigabit Ethernet over Category 5 UTP. Gigabit Ethernet still retains the frame formats and frame sizes and it still uses CSMA/CD. As with Ethernet and Fast Ethernet, full duplex operation is possible. Differences can be found in the encoding; Gigabit Ethernet uses 8B/10B coding with simple nonreturn to zero (NRZ). Because of the 20 percent overhead, pulses run at 1250 MHz to achieve a 1000 Mbps. Table 4-8 covers Gigabit Ethernet scalability constraints.

Table 4-8 Gigabit Ethernet Scalability Constraints

Type

Speed

Maximum segment length

Encoding

Media

1000BaseT

1000 Mbps

100m

5-level

Cat 5 UTP

1000BaseLX (long wave)

1000 Mbps

550m

8B/10B

Single/multiple mode fiber

1000BaseSX (short wave)

50 micrometers: 500m

8B/10B

Multimode fiber

1000BaseCX

1000 Mbps

25m

8B/10B

Shielded balanced copper

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