PDF of this tutorialAs technology improvements allow greater bundles of fiber to terminate in an office and DWDM builds a foundation of hundreds of wavelengths per fibers, carriers are challenged with finding the space and power for the necessary communications equipment. In the current mode of operation, most optical signals are converted to lower-level electrical signals. The signals are generally groomed and cross-connected before being converted back into an optical signal for transport. These functions require hundreds of electronic chips, and these chips require space and power. Each process, grooming and cross-connects, requires a minimum set of functionalities. In the past these separate elements were designed to optimize each function. Grooming involved demuxing signals into lower bit rates and then repackaging the signals to more efficiently transport them to their next destination. Cross-connects were used to more efficiently manage signals between transport equipment. With the amount of optical signals that can now terminate in an office, carriers would either require very tall high rises or need city blocks just to hold all the transport and cross-connect equipment.
If a carrier overcomes the real-estate challenge, it is faced with the daunting task of supplying power for all of this equipment.
Figure 9. Space and Power Savings
All-optical O-O-O switches hold the promise of significantly reducing both the footprint and power consumption required in a communications office. All-optical switches supporting 1000 x 1000 ports will be available in a space of two to four bays of equipment.
Each bay will require one kilowatt (kW) or less of power for a total of two to four kW. This compares to SONET–based digital cross-connects ranging in size from 25 to 32 bays of equipment. Each electronic cross-connect bay requires four to five kW for a total of 100 to 128 kW of power. The all-optical switch can therefore provide a 92 percent reduction in floor space requirements and a 96 percent reduction in power requirements.
The power savings result in cost savings at multiple levels. First of all, each rack will save about three kW each of power. This translates into a footprint and cost savings for power-generating and distribution equipment such as batteries, rectifiers, and diesel generators. Each of those units must be maintained, requiring monthly test routines and periodic burn-off of diesel fuel. Thus, there is also an operations and maintenance savings. Lastly, the carrier must purchase and maintain air-conditioning units capable of cooling their offices. The lower the heat dissipation, the lower the monthly cooling charges. These are operational costs that are not only tangible, but also significant.
