Chapter 5 Introducing SDN Control in MPLS Networks - High ...

196 CHAPTER 5. INTRODUCING SDN CONTROL IN MPLS NETWORKS(a)(b)Fig. 5.10 (a) DiffServ with regular MPLS-TE (b) DS-TEDS-TE tries to solve this problem by trying to steer away traffic for such a trafficclass(Fig. 5.10b). It does so by allowing tunnels to reserve bandwidth only for a certainclass-of-traffic; out of a sub-pool of link-bandwidth that matches the queue-bandwidthfor that class. For example, if the queue for the highest-priority traffic supports 100Mbps, then tunnels for that class can only reserve link-bandwidth from the sub-pool of100 Mbps, even if the max-reservable bandwidth may be 1 Gbps. This way if one tunnelfor this class reserves 100 Mbps from the sub-pool, then other tunnels are not admitted onthis link and thus forced to steer away from it.SDN-based DS-TE: Diffserv-aware TE uses the same mechanisms as regular MPLS-TE; the subset of link-bandwidth advertized per-class, as well as per-class tunnelreservation and admission-control are all still purely control plane concepts. And so withSDN we can perform all of these tasks in the Controller. But the SDN basedimplementation has two distinct advantages:• The process of forwarding class-specific traffic down a DS-TE tunnel is not trivialand hard to automate in networks that use DS-TE today. Auto-Route cannot help asthe mechanism does not distinguish between traffic-classes. The only choice is theuse of Policy Based Routing (PBR) [92], which requires configuration via manualinterventionand is not very programmatic. This is essentially the same issue aspointed out in the section on Auto-Route. With SDN and the use of OpenFlow,