Then assume, further, that this customer??™s data traffic patterns are
highly variable, with high-volume unicast and multicast streams originating and being
consumed at different sites at different moments in time, as the customer sees fit.
Question: Does the provider actually want to carry that customer??™s traffic along the
most direct path from site to site?
Figure 13.11 shows such a network, simplified to only four customer connections
C1??“C4. Assuming that the most direct paths between the various customer sites are as
shown by the dotted arrows in Figure 13.11, you can see that this one customer??™s data
is scattered all over the network. In fact, there are only three links, T-V, T-W, and V-Y,
that never carry data for this customer. And even those links would be used if some
sort of equal-cost multipathing were used in the network. While such diffusion is often
desirable in an enterprise network, in order to spread the load as much as possible in
a carrier network, such advantages can easily be outweighed by the added difficulty of
ensuring quality of service guarantees, determining how much bandwidth is required
on any given link, and debugging data-dependent customer problems.
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