Blocking in Multiwavelength TDM Networks

only wavelength translation is higher than that when TSI is introduced, either alone or in addition to the wavelength translation. However, for one-and two-hop paths, the observed blocking probability with wavelength translation alone is below that obtained with TSI, and above the blocking probability for the corresponding paths in networks without either wavelength translation or TSI. Similarly, when only TSI is introduced the blocking probability for longer paths is above that for paths with both wavelength translation and TSI. However, for one-hop paths this relationship is reversed. Figure 8 also shows that, again, in a network with a small number of wavelengths and a relatively large number of time slots per wavelength, the introduction of wavelength translation alone results in a moderate decrease in the dependence of blocking probability on path length. However, the introduction of TSI alone results in performance which is again almost identical to that achieved using both wavelength translation and TSI. 5. CONCLUSION In this paper, we have examined the blocking performance of so-called shared-wavelength TDM systems 5]. Shared-wavelength TDM systems are multiwavelength systems in which connections are assigned on demand to a wavelength, and to a time slot on that wavelength. We have examined the relative importance of wavelength translation and time-slot interchange in reducing blocking, or increasing utilisation, in these systems. We have developed an analytical description of blocking on multiple-hop paths in shared-wavelength TDM systems , and we have performed simulations of a mesh-torus shared-wavelength TDM network. Our results have shown that, in a shared-wavelength TDM system with a small number of wavelengths and a relatively large number of time slots per wavelength, time-slot interchang-ers alone, without wavelength translators, provide almost all of the performance improvement introduced by both time-slot interchangers and wavelength translators. However, moderate improvements are also achieved using only wavelength translators, without time-slot inter-changers. Similarly, in a network with a large number of wavelengths and a relatively small number of time slots per wavelength, we have shown that wavelength translators alone can provide almost all of the performance improvements introduced by both time-slot interchang-ers and wavelength translators. However, moderate improvement may also be obtained using only time-slot interchangers, without wavelength translators. 6. ACKNOWLEGMENTS The authors wish to thank Alan Kennington from DSTO and Steve Madden from TRL for helpful discussions. Jennifer Yates also thanks TRL for nancial support. Figure 7: Blocking in an 11 11 mesh-torus network with 2 wavelengths …