Information Technology Reference
In-Depth Information
The OC-3 rate is in many ways considered the base rate of the synchronous
optical network (SONET), STM-1, and subsequent higher rates are at multiples of
four from that base. So, the next speed chosen was 4
622 Mbps, or a mul-
tiple of 12 from OC-1, thus OC-12. A multiple of 24 would technically yield a rate
of 1244 Mbps, or a little above Gigabit Ethernet, but it is rarely employed. Instead,
the next higher rate that is commonly used is again 4 times greater: 2.488 Gbps for
OC- 48. OC-192 then is about 10 Gbps, and OC-768 (the highest rate currently in
vogue) is about 40 Gbps. See Table 12.4.
155
TABLE 12.4
Sonet Optical Carrier Rates
Synchronous
transport level
Optical carrier
Carrier rate
Data rate
(electrical)
level (optical)
(actual, in Mbps)
classification
STS-1
OC-1
51.84
52 Mbps
STS-3
OC-3
155.52
155 Mbps
OC-12
622.08
622 Mbps
OC-24
1,244.16
1244 Mbps
OC-48
2,488.32
2.4 Gbps
OC-192
9,953.28
10 Gbps
OC-768
39,813.12
40 Gbps
It is fortunate that so much modern cabling infrastructure has been installed in the
past few years. Had we not been aggressively installing Category 5 copper links and
multimode cable to the work area, it is likely that technologies to support gigabit
speeds would have diverged. As it turned out, the vast high-speed cable plants have
acted as both enabling and guiding forces to focus the introduction of Gigabit
Ethernet and other gigabit-speed networking technologies.
The most widely deployed cabling standard is TIA-568-C. This standard has
provided a structured approach to cabling the workplace, and has been a very sig-
nificant factor in “normalizing” the wiring infrastructure in commercial buildings.
The standard continues to evolve to incorporate new developments. Over the past
few years, many enhancements have been made to the science and art of high-speed
data wiring. The TIA's TR-42 User Premises Telecommunications Infrastructure
Standards Group has been quick to recognize advances in the field and has imple-
mented study groups to define standards and practices for new technological devel-
opments, including gigabit networking.
