Optical Networks - _Chapter 10 WDM Network Design_116

Optical Networks - _Chapter 10 WDM Network Design_116 - 10...

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10 chapter WDM Network Design I n previous chapters, we learned that the optical layer provides high-speed circuit-switched connections, or lightpaths, between pairs of higher-layer equip- ment such as SONET/SDH muxes, IP routers, and Ethernet switches. The optical layer realizes these lightpaths over the physical fiber using elements such as optical line terminals (OLTs), optical add/drop multiplexers (OADMs), and optical cross- connects (OXCs). We called a network using such lightpaths a wavelength-routing network. In this chapter, our goal is to study how to design a wavelength-routing network. This involves studying not only how to design the optical layer but also how the higher-layer SONET or IP network is to be designed because the design of the two layers is closely coupled. We illustrate with an example. Example 10.1 In Figure 10.1(a), there are three nodes labeled A, B, and C, connected by WDM fiber links. For simplicity, assume the traffic generated is in the form of IP packets from routers located at these nodes. Similar examples hold if the higher layer consists of SONET/SDH muxes. For concreteness, also assume that all router interfaces operate at 10 Gb/s, which is also the transmission ca- pacity on each wavelength on the WDM links. Now suppose, based on estimates of the IP packet traffic, 50 Gb/s of capacity is required between all three pairs of routers: A–B, B–C, and A–C. The network can be designed to handle this traffic in two ways. 1. No optical add/drop: In the first method, we set up 10 wavelengths on each of the links A–B and B–C connecting the routers at the ends of these links. We observe that the traffic flowing on link A–B is 50 Gb/s (traffic from A–B) 573
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574 WDM Network Design A BC Router Router (a) (b) (c) Figure 10.1 (a) A three-node network. (b) Nodes A–B and B–C are interconnected by WDM links. All wavelengths are dropped and added at node B. (c) Half the wavelengths pass through optically at node B, reducing the number of router ports at node B. + 50 Gb/s (traffic from A–C that must use link A–B) = 100 Gb/s. Similarly, the traffic flowing on link B–C is also 100 Gb/s. Thus the 10 wavelengths on each of the links A–B and B–C are sufficient to carry this traffic. In this case,
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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 10 WDM Network Design_116 - 10...

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