Page 126 - Optical Switching And Networking Handbook

06_200023_CH05/Batesx 1/17/01 8:19 AM Page 111

Wave-Division and Dense-Wave-Division Multiplexing 111

ATM switches and Internet Protocol (IP) routers. ATM networks are
expected to use SONET/SDH physical layer interfaces with OC-12
add-drop multiplexers. ATM can carry voice, video, and data com-
munications in the same transport and switching equipment.
WDM systems require nonzero-dispersion fiber. This type of fiber
introduces a small amount of dispersion that decreases nonlinear
component effects. Originally, SONET equipment makers expected
to be forced to make reliable OC-192 (10-Gbps) systems or face stiff
competition from DWDM manufacturers.
Thus a new era was born in the use of WDM. By adding a tightly
separated wavelength of light on the same cable, more capacity could
be obtained. In normal fiber transmission, the use of two standard
wavelengths was originally deployed, as shown in Figure 5-4. First,
a red band of light was used to transmit the signal from the origi-
nating end. A blue band was used at the opposite end. Therefore, the
same cable can carry both send and receive traffic using different
color bands. The original OC-48 transmission (operating at 2.5
Gbps) was exciting, using a single wavelength of light and driving
the signal over 20 to 30 miles of fiber. However, the carriers soon rec-
ognized that the skyrocketing demand for bandwidth would outpace
the throughput of this single-wavelength transmission.

Fiber MUX Fiber MUX
Figure 5-4
The colors of light Red
separate the bands Xmit OC-48
Rec. Red Band
carried on the
cable.

Blue
OC-48
Recv. Xmit Blue Band

20 - 30 miles