When modelling synchronous digital hierarchy (SDH) networks it is usual to consider the algorithms responsible for the planning of these networks. These algorithms are well defined and consider a wide range of inputs describing the network scenario, including the demands of the network, the configuration of nodes, available physical layer capacity as well as restrictions placed on the design by various technological issues. During planning it is also common to incorporate deliberate structures such as rings to achieve additional attributes such as resilience as we have already seen in Chapter 2. Hierarchies are also used in the network to make the management of capacity easier.
It would seem that the real-world result could therefore be easily deduced from knowledge of the demands and the planning algorithm used. In this chapter we will show that even with strict planning, emergent and unplanned topological traits appear in the real-world SDH network considered here. The existence of such traits within large-scale networks is not without precedence, however. It has been previously shown [1] that the Internet demonstrates similar traits at a number of levels, from router connectivity to the connectivity of sub-domains. In stark contrast, however, the Internet is not globally planned like an SDH network, does not have enforced structure and often uses dynamic routing techniques to adapt to network conditions. It may not therefore be surprising to find such emergent topological traits there.
This chapter begins by examining the overall...
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