07-06-2012, 01:10 PM
Optical Networks
Optical Networks .ppt (Size: 93 KB / Downloads: 21)
Medium Characteristics
Attenuation:
Wavelength dependent
0.85, 1.3, 1.55 micron windows
Attenuation caused by impurities as well as scattering
Dispersion
Inter-modal
Chromatic
Wavelength Division Multiplexing (WDM)
All the bandwidth could not be used due to the electronic bottleneck
Two breakthroughs
WDM
Erbium-doped fiber amplifier (EDFA)
WDM vs. FDM
WDM is passive and hence reliable
WDM carrier frequency orders of magnitude higher
DWDM Evolution
Faster (higher speed per wave),
40 Gb/s on the horizon
Thicker (more waves),
160 waves possible today
Longer (link lengths before regeneration)
A few thousand km possible today
160 waves at 10 Gb/s = 1.6 Tb/s
25 million simultaneous phone calls
5 million books per minute
How Did We Get Here?
SONET over WDM
Conventional WDM deployment is using SONET as standard interface to higher layers
IP over ATM
IP packets need to be mapped into ATM cells before transporting over WDM using SONET frame
OEO conversions at every node is easier to build than all optical switch
Wavelength Routed
An OXC is placed at each node
End users communicate with one another through lightpaths, which may contain several fiber links and wavelengths
Two lightpaths are not allowed to have the same wavelength on the same link.
