Optical Networks - _Chapter 12 Photonic Packet Switching_132

Optical Networks - _Chapter 12 Photonic Packet...

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12 chapter Photonic Packet Switching I n this chapter, we study optical networks that are capable of providing packet- switched service at the optical layer. We call these networks photonic packet- switched (PPS) networks. Packet-switched services are provided today using elec- tronic switches by many networks, such as IP and Ethernet networks. Here, we are interested in networks where the packet-switching functions are performed op- tically. The goal of PPS networks is to provide the same services that electronic packet-switched networks provide, but at much higher speeds. The optical networks that we have studied so far provide circuit-switched ser- vices. These networks provide lightpaths, which can be established and taken down as needed. In these networks, the optical nodes do not switch signals on a packet- by-packet basis, but rather only switch at the time a circuit is established or taken down. Packet switching is done in the electronic domain by other equipment such as IP routers or Ethernet switches. These routers and switches make use of lightpaths provided by the optical layer to establish links between themselves as needed. In addition to switching packets, routers and switches make use of sophisticated soft- ware and hardware to perform the control functions needed in a packet-switched network. In this chapter, we will see that all the building blocks needed for optical packet switching are in a fairly rudimentary state today and exist only in research labora- tories. They are either difficult to realize, very bulky, or very expensive, even after a decade of research in this area. Moreover, it is likely that we will need electronics to perform the intelligent control functions for the foreseeable future. Optics can be used to switch the data through, but it does not yet have the computing capabilities 653
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654 Photonic Packet Switching to perform many of the control functions required, such as processing the packet header, determining the route for the packet, prioritizing packets based on class of service, maintaining topology information, and so on. However, there are a few motivations for researching optical packet switching. One is that optical packet switches hold the potential for realizing higher capacities than electronic routers (although this potential is yet to be demonstrated!). For instance, the capacity of the best routers today is less than 100 Tb/s, with the highest- speed interfaces being at 40 Gb/s. In contrast, optical switches are, for the most part, bit rate independent, so they can be used to switch tens to hundreds of Tb/s of traffic. Another motivation for studying optical packet switching is that it can improve
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This note was uploaded on 01/15/2011 for the course ECE 6543 taught by Professor Boussert during the Spring '09 term at Georgia Institute of Technology.

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Optical Networks - _Chapter 12 Photonic Packet...

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