Information Technology Reference
In-Depth Information
No separate transmit and receive pairs are present, so full-duplex operation is not possible.
8B6T coding.
100BaseFX
The 100BaseFX specifications for fiber are as follows:
Operates over two strands of multimode or single-mode fiber cabling
Can transmit over greater distances than copper media
Uses media interface connector (MIC), ST, or SC fiber connectors defined for FDDI and
10BaseFX networks
4B5B coding
1000 Mbps GE
Gigabit Ethernet is specified by two standards: IEEE 802.3z and 802.3ab. The 802.3z standard
specifies the operation of GE over fiber and coaxial cable and introduces the Gigabit MII
(GMII). The 802.3z standard was approved in July 1998. The 802.3ab standard specifies the
operation of GE over Category 5 UTP, as approved in June 1999. GE still retains the frame
formats and frame sizes of 10 Mbps Ethernet, along with the use of CSMA/CD in shared
segments. Similar to Ethernet and FE, full-duplex operation is possible. Differences can be
found in the encoding; GE uses 8B/10B coding with simple NRZ. Because of the 20 percent
overhead, pulses run at 1250 MHz to achieve 1000 Mbps. GE includes the following methods
to achieve 1 Gbps speed:
8B/10B Coding.
Bytes are encoded as 10-bit symbols.
Run-length limited (no long sequences of 1s or 0s).
Pulses on the wire run at 1250 MHz to achieve 1000 Mbps speed.
Table 4-5 shows how data is converted into 8B/10B code for transmission.
8B/10B Encoding
Table 4-5
Data
Binary (8B)
10B Code
00
00000000
0110001011
01
00000001
1000101011
02
00000010
0100101011
03
00000011
1100010100
04
00000100
0010101011
 
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