Contention resolution

Whenever two or more data packets arrive at a network node at the same time and contend for the same output, external blocking occurs. All packets but one are perceived as superfluous, and have to be dealt with. Next to the obvious choice of dropping all excess packets, academic literature typically presents three solutions: buffering, deflection routing or wavelength conversion. Optical buffering uses fiber delay lines (FDLs) to delay the light, and is regarded as the most effective, but comes with the additional cost of the FDLs.

Implementation of optical buffers.As light cannot be frozen, an optical buffer is made of optical fibers, and is generally much larger than a RAM chip of comparable capacity. A single fiber can serve as a buffer. However, a set of more than one is usually used. A possibility, for example, is to choose a certain length D for the smallest fiber, and then let the second, third... have lengths . Another typical example is to use a single loop, in which the data circulates a variable number of times.

September 26, 2011

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