13.5 Schemes for Optical Add/Drop Multiplexing
537
Fig. 13.20 Modular expandable passive OADM architecture
channels can be dropped. Such a configuration is useful if a large fraction of the N
wavelengths needs to be dropped and added. However, it is not cost-effective for
dropping and adding a small fraction of the incoming wavelengths.
Figure 13.20 shows a more modular OADM architecture. Here the N incoming
light channels are split into several bands of wavelengths. This function can be
achieved using either a set of thin-film filters or an AWG. The band to be dropped
can be sent through a second demultiplexer followed by processing of the individual
wavelengths. As an example, if N = 12 and three wavelengths need to be dropped,
the incoming wavelengths can be divided into four bands of three wavelengths each.
Added lightwave channels go through two stages of multiplexing to rejoin the passthrough bands. An advantage of this approach is that for future OADM upgrades
to drop another wavelength band at this node, network engineers can incorporate
another second-stage demultiplexer to handle the next desired wavelength band.
13.5.2 Reconfiguring OADM Equipment
The task of reconfiguring a fixed OADM manually may require several days of
planning and implementation of hardware changes. In contrast, the use of ROADMs
gives service providers the ability to reconfigure a network within minutes from
a remote network management console. The dynamic flexibility to drop and add
selected wavelengths quickly at a particular node upon customer demand for new
or expanded services is known popularly as service provisioning on the fly. This is
particularly important in metro networks where changes in service requests tend to be
significantly more dynamic than in long-haul networks and clients expect very rapid
responses to their requests. Such service requests can have fairly diverse origins such
as time-varying business applications, on-demand entertainment, and emergency or
disaster-response communications.
537
Fig. 13.20 Modular expandable passive OADM architecture
channels can be dropped. Such a configuration is useful if a large fraction of the N
wavelengths needs to be dropped and added. However, it is not cost-effective for
dropping and adding a small fraction of the incoming wavelengths.
Figure 13.20 shows a more modular OADM architecture. Here the N incoming
light channels are split into several bands of wavelengths. This function can be
achieved using either a set of thin-film filters or an AWG. The band to be dropped
can be sent through a second demultiplexer followed by processing of the individual
wavelengths. As an example, if N = 12 and three wavelengths need to be dropped,
the incoming wavelengths can be divided into four bands of three wavelengths each.
Added lightwave channels go through two stages of multiplexing to rejoin the passthrough bands. An advantage of this approach is that for future OADM upgrades
to drop another wavelength band at this node, network engineers can incorporate
another second-stage demultiplexer to handle the next desired wavelength band.
13.5.2 Reconfiguring OADM Equipment
The task of reconfiguring a fixed OADM manually may require several days of
planning and implementation of hardware changes. In contrast, the use of ROADMs
gives service providers the ability to reconfigure a network within minutes from
a remote network management console. The dynamic flexibility to drop and add
selected wavelengths quickly at a particular node upon customer demand for new
or expanded services is known popularly as service provisioning on the fly. This is
particularly important in metro networks where changes in service requests tend to be
significantly more dynamic than in long-haul networks and clients expect very rapid
responses to their requests. Such service requests can have fairly diverse origins such
as time-varying business applications, on-demand entertainment, and emergency or
disaster-response communications.