Information Technology Reference
In-Depth Information
Again, for switched networks, the maximum distance between the switch and the host
is 100 m.
Gigabit Ethernet Design Rules
Gigabit Ethernet was first specified by two standards: IEEE 802.3z-1998 and 802.3ab-1999.
The IEEE 802.3z standard specifies the operation of Gigabit Ethernet over fiber and coaxial
cable and introduces the Gigabit Media-Independent Interface (GMII). These standards are
superseded by the latest revision of all the 802.3 standards included in IEEE 802.3-2002.
The IEEE 802.3ab standard specified the operation of Gigabit Ethernet over CAT 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. Differ-
ences appear in the encoding; Gigabit Ethernet uses 8B10B coding with simple nonreturn
to zero (NRZ). Because of the 20 percent overhead, pulses run at 1250 MHz to achieve a
1000 Mbps throughput.
Ta ble 3 - 4 gives an overview of Gigabit Ethernet scalability constraints.
Ta b l e 3 - 4
Gigabit Ethernet Scalability Constraints
Type
Speed
Maximum Segment
Length
Encoding
Media
1000BASE-T
1000
Mbps
100 m
Five-level
CAT 5 UTP
1000BASE-LX
(long wavelength)
1000
Mbps
550 m
8B10B
Single-mode/multi-
mode fiber
1000BASE-SX
(short wavelength)
1000
Mbps
62.5 micrometers: 220 m
50 micrometers: 500 m
8B10B
Multimode fiber
1000BASE-CX
1000
Mbps
25 m
8B10B
Shielded balanced
copper
The following are the physical specifications for Gigabit Ethernet, each of which is de-
scribed in the following sections:
1000BASE-LX
1000BASE-SX
1000BASE-CX
1000BASE-T
1000BASE-LX Long-Wavelength Gigabit Ethernet
IEEE 1000BASE-LX uses long-wavelength optics over a pair of fiber strands. The specifi-
cations are as follows:
Uses long wave (1300 nanometers [nm]).
Use on multimode or single-mode fiber.
 
 
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