Information Technology Reference
In-Depth Information
Media Access Control (MAC)
Gigabit Media Independent Interface (GMII)
1000BASE-X 8B/10B
Encoder/Decoder
1000BASE-T
Encoder/Decoder
1000BASE-SX
Transceiver
1000BASE-LX
Transceiver
1000BASE-CX
Transceiver
1000BASE-T
Transceiver
802
.
3z
802.3ab
Figure 26.23
Gigabit Ethernet functional elements
26.13.1 Ethernet transceiver
The IEEE 802.3z task force spent much of their time defining the gigabit Ethernet standard
for the transceiver (physical layer), which is responsible for the mechanical, electrical and
procedural characteristics for establishing, maintaining and deactivating the physical link
between network devices. The physical layers are:
•
1000BASE-SX
(low cost, multimode fibre cables). These can be used for short inter-
connections and short backbone networks. The IEEE 802.3z task force have tried to in-
tegrate the new standard with existing cabling, whether it be twisted-pair cable, coaxial
cable or fibre optic cable. These tests involved firing lasers in long lengths of multimode
fibre cables. Through these tests it was found that a jitter component results which is
caused by a phenomenon known as differential mode delay (DMD). The 1000BASE-SX
standard has resolved this by defining the launch of the laser signal, and enhanced con-
formance tests. Typical maximum lengths are: 62.5
µ
m, multimode fibre (up to 220 m)
m, multi-mode fibre (550 m).
•
1000BASE-LX
(multimode/singlemode fibre cables). These can be used for longer runs,
such as on backbones and campus networks. Single-mode fibres are covered by the long-
wavelength standard, and provide for greater distances. External patch cords are used to
reduce DMD. Typical lengths are: 62.5
and 50
µ
µ
m, multimode fibre (up to 550 m); 50
µ
m, mul-
m, single-mode fibre (up to 5 km).
•
1000BASE-CX
(shielded balanced copper). This standard supports interconnection of
equipment using a copper-based cable, typically up to 25 m. As with the 1000BASE-
LX/SX standards, it uses the Fibre channel-based 8B/10B coding to give a serial line rate
of 1.25 Gbps. The 1000BASE-T is likely to supersede this standard, but it has been rela-
tively easy to define, and to implement.
•
1000BASE-T
(UTP). This is a useful standard for connecting directly to workstations.
timode fibre (up to 550 m) and 50
µ
