12.3 Header Processing 673 duration of the clock signal. This clock can then be used to either read parts of the packet or to demultiplex the data stream. 12.3 Header Processing For a header of ﬁxed size, the time taken for demultiplexing and processing the header is ﬁxed, and the remainder of the packet is buffered optically using a de-lay line of appropriate length. The processing of the header bits may be done electronically or optically, depending on the kind of control input required by the switch. Electrically controlled switches employing the electro-optic effect and fabricated in lithium niobate (see Section 3.7) are most commonly used in switch-based network experiments today. In this case, the header processing can be car-ried out electronically (after the header bits have been demultiplexed into a par-allel stream). The packet destination information from the header is used to de-termine the outgoing link from the switch for this packet, using a look-up table. For each input packet, the look-up table determines the correct switch setting,
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