|  | 7.2 |
| Gigabit and 10-Gigabit Ethernet
|  | 7.2.1 |
| 1000-Mbps Ethernet
The 1000-Mbps Ethernet or Gigabit Ethernet standards represent transmission using both fiber and copper media. The 1000BASE-X standard, IEEE 802.3z, specifies 1 Gbps full duplex over optical fiber. The 1000BASE-X standard, IEEE 802.3z, specifies 1 Gbps full duplex over optical fiber. 1000BASE-TX, 1000BASE-SX, and 1000BASE-LX use the same timing parameters, as shown in Figure . They use a 1 nanosecond (0.000000001 seconds) or 1 billionth of a second bit time. The Gigabit Ethernet frame has the same format as is used for 10 and 100-Mbps Ethernet. Depending on the implementation, Gigabit Ethernet may use different processes to convert frames to bits on the cable. Figure shows the Ethernet frame formats. The differences between standard Ethernet, Fast Ethernet and Gigabit Ethernet occur at the physical layer. Due to the increased speeds of these newer standards, the shorter duration bit times require special considerations. Since the bits are introduced on the medium for a shorter duration and more often, timing is critical. This high-speed transmission requires frequencies closer to copper medium bandwidth limitations. This causes the bits to be more susceptible to noise on copper media. These issues require Gigabit Ethernet to use two separate encoding steps. Data transmission is made more efficient by using codes to represent the binary bit stream. The encoded data provides synchronization, efficient usage of bandwidth, and improved Signal-to-Noise Ratio characteristics. At the physical layer, the bit patterns from the MAC layer are converted into symbols. The symbols may also be control information such as start frame, end frame, medium idle conditions. The frame is coded into control symbols and data symbols to increase in network throughput. Fiber-based Gigabit Ethernet (1000BASE-X) uses 8B/10B encoding which is similar to the 4B/5B concept. This is followed by the simple Non-Return to Zero (NRZ) line encoding of light on optical fiber. This simpler encoding process is possible because the fiber medium can carry higher bandwidth signals.
Web Links
1000-Mbps Ethernet http://grouper.ieee.org/groups/802/3/ tutorial/march98/mick_170398.pdf