Special Report: Next Generation Internet Applications
2.3 Optical Network Classes Examination of various optical network classes provides insight into the evolution of various optical switching architectures. Widely implemented are optical link networks and broadcast and select optical networks. Research is underway into wavelength routed networks and photonic packet-switched networks. Progress in optical network design is rapid and will soon yield transparent, infinitely scalable, and robust network architectures which could proliferate throughout industry. The following sections describe these network classes in greater detail.
2.3.1 Optical Link Networks Optical link networks provide connectivity in a point-to-point fashion across an optical network. Switching for optical link networks is done entirely in the electrical domain. The optical components are all static in nature, and thus, no network reconfiguration is possible without physical intervention.[18] Optical link networks are prevalent throughout industry. Their broad use is a good indication of industry's interest in alloptical networks. There are two distinct types of optical link networks. First, point-to-point links consist of DWDMs interconnecting electronic switches. Figure 13 depicts a common point-to-point optical link network. The second type of optical link network is the shared-medium broadcast network. This class of network utilizes the functionality of a DWDM Passive Star Coupler, which distributes a DWDM optical signal to additional network segments. Figure 14 depicts a shared-medium broadcast optical link network. 2.3.2 Broadcast and Select Optical Networks Broadcast and select optical networks, as shown in Figure 15, leverage the benefits of tunable optical transmitters and receivers. These networks incorporate wavelength-agile receivers that tune to the appropriate signaling wavelength. Broadcast and select optical networks can be strictly optical or a hybrid with OEO conversion networks between the receivers and the DWDM or DWDM passive star coupler.[18] Tunable receivers add the benefits of scalability to optical link networks. Tunable Optical Signal A Optical Signal B Optical Signal C Optical Signal D 2.3.3 Wavelength Routed Optical Networks Wavelength routed optical networks employ the light path switching functions of OADMs and OXCs. They may optionally use tunable transmitters and receivers to provide routing within a larger-scale network. Wavelength routed optical networks, as depicted in Figure 7, provide the ability to optically add and remove wavelengths from the network with multiplexing/demultiplexing. The implementation of optical cross connects further expands the network's ability to optically pass information between networks. Wavelength routed optical networks can be either circuit switched or packet switched, depending upon the configuration of the OADMs, OXCs, and whether the optical transceivers are wavelength-agile or not.
2.3.4 Photonic Packet-Switched Optical Networks Photonic packet-switched optical networks are the final step towards completely transparent all-optical networks. Optical packet switches are fully in the optical domain with OEO conversions only performed at the edge of the optical networks. All optical components are implemented to provide necessary functionality for all-optical processes throughout the network. Optical switches provide scalable, high-speed, reliable network performance while minimizing infrastructure costs in the long term. Figure 16 depicts an all-optical photonic packet-switched optical network. 2.4 Optical Switching Architectures Photonic switching architectures have resulted from the marriage of optical networking infrastructures, processing techniques, and creative network interconnection classes. The previous three sections have presented a background understanding of the enabling technologies implemented within photonic switching architectures. Several forms of photonic switching architectures surface from this advanced research. Optical packet switching forms a basis for high-speed all-optical data communications. Optical burst switching is viewed as a modification to the photonic packet switching design. Multiprotocol lambda switching (MP'S) blends multiprotocol label switching (MPLS) with optical communications in an effort to produce a more efficient means of provisioning resources within the optical cross connects (OXCs). MP'S will be analyzed in the context of its implementation within switching architectures.
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