velength channel data rate and arrives at 150kHz for transmission at 10 Gbit/s. The header associated with this signaling technique can be accessed with a receiver similar to that used for pilot tones SO that information can be retrieved at each site of the network. Moreover, the transmission is quite robust versus dispersion and other transmis- sion impairments due to its low speed. 10.3.3.3 Optical Code Division Multiplexing This technique relies on the use of orthogonal codes for the transmission of the useful channel and the header in the same bandwidth. Let us consider an alphabet A{a} with the structure of a finite field, composed by l elements. Using the alphabet letters, let us build a code that is a collection C{(a1,i, an,i), c}, of C code words composed by n elements each. The code C is called normalized orthogonal if, whatever couple of code words is selected, its product is null and the norm is one, that is, (10.15) where Sj,k is the Kronecker symbol that is one for j = k and zero otherwise. A great amount of studies has been done on orthogonal codes due to their utility in code division multiple access (CDMA) communications [42]. This technique to convey the OCh header is constructed like a wideband CDMA, where the wideband signal (i.e., the data transported on the wavelength) is superimposed on the same frequency bandwidth by a short bandwidth signal (i.e., the header) via the use of an orthogonal code. In particular, let us select a binary orthogonal code having M different words, where M is greater or equal to the number of channels to be identified in the network. It is not dif- ficult if the length of the code is sufficient, since once given the code length N, and the code Next Generation Networking: Enabling Technologies, Architectures, and Performances words weight W (number of ones, assumed the same for each code word), the number of different orthogonal words Cw with the given length N and weight W is (10.16) that is, for example, that a 32 bit code with weight 10 has about 44,000 orthogonal