Section 14.7. Summary

14.7. Summary

This chapter focused on optical communication networks, beginning with basic definitions and a review of such optical devices as optical filters , wavelength-division multiplexers , optical switches , and optical buffers and optical delay lines .

Optical switches can be classified as non-electro-optical switches using non-electro-optical devices such as mechanical optical switches or thermo- optic switches , and electro-optic switches using directional couplers . The cost of large-scale optical switches constructed by a one-segment optical switch is high. Therefore, several topologies of large-scale switching networks use simple switch elements, such as crossbar and Spanke-Bene network architectures.

Optical networks constructed with optical devices provide routing, grooming, and restoration of data at the wavelength level. Two popular models for managing the network (IP) layer and the optical layer are the overlay model and the peer model . In the overlay model, the optical layer and IP layer each have their own independent control planes.

Wavelength reuse and allocation in optical networks is a key topic. Because of the maximum capacity on the number of wavelengths that can be carried on a link, a network may not be able to handle all lightpath requests; consequently, some requests may be blocked. To keep lightpaths separated on a same link, they should be allocated different wavelengths. Wavelength allocation can be analyzed in two ways. One way is to assume that the probability of a wavelength being used on a link is independent of the use of the same wavelength on all other links of the lightpath. The other method does not make any assumption of independence.

An all-optical switching network called spherical switching network (SSN) was presented as a case study. Routing in that network is fairly simple and self-routing. Any switch element is given an index number. Depending on whether the flowing traffic is directed toward decreasing index or toward increasing index, the self-routing is performed by decremental or incremental addressing respectively.

The next chapter discusses multicast protocols and algorithms. In addition, switching techniques at the node level are used to show how copies of packets are made in switch fabrics .