 words. Let us assign to each channel a specific code word. Calling s;(t) the signal corresponding to the jth channel in the network, T = 1/R the data bit duration, and TH >> T the header duration, the following signal is built at the transmit- ter of the jth channel (10.17) where h(i) are the bits of the header bi are the bits of the data rect(t) is the Heaviside rectangular function Every header bit occupies a time interval much longer with respect to a signal bit, while a code bit occupies exactly a signal bit interval, SO that there are several repetitions of the code word associated with the channel within the header duration. As an example, the signal and the code can run at 10 Gbit/s while the header is simply 100 Mbit/s, SO that a header bit contains 100 signal bit intervals. If the header is composed of 40 bits, and a 16 bit code is used, the code word associated with the channel is repeated 250 times in the header duration interval. When the header is to be decoded, part of the signal is split via an unbalanced directional coupler, and after conditioning via optical filtering and other electronics functions up to sampling, it is divided in M replicas and convolved with M signals given by (10.18) The result of the convolution on the kth branch of this processing is a series of samples x(t;) given by (10.19) The first term of Equation 10.18 can be evaluated using the orthogonal property of the code. It presents a sharp peak in correspondence to m = j, allowing the individuation of the channel ID (j in this case) and the reading of the other contents of the OCh header. After the convolution, this term has a bandwidth equal to RH = 1/T. Telecommunication Networks The other signals, with m # j, and the second term involving the information bearing message result in a sort of pseudo-noise term with a bandwidth of R + RH and a power composed by two terms: the random correlation of the signal containing bm with the code word and a term due to non ideal orthogonal nature of the physical signals representing the 