Link capacity dimensioning is the periodic task where ISPs have to make provisions for sudden traffic bursts and network failures to assure uninterrupted operations. This provision comes in the form of link working capacities with noticeable amounts of headroom, i.e., spare capacities that are used in case of congestions or network failures. Distributed routing protocols like OSPF provide convergence after network failures and have proven their reliable operation over decades, but require overprovisioning and headroom of over 50 . However, SDN has recently been proposed to either replace or work together with OSPF in routing Internet traffic. This paper addresses the question of how to robustly dimension the link capacities in emerging hybrid SDN OSPF networks. We analyze the networks with various implementations of hybrid SDN OSPF control planes, and show that our idea of SDN Partitioning requires less amounts of spare capacity compared to legacy or other hybrid SDN OSPF schemes, outperformed only by a full SDN deployment.
Background OSPF is a distributed routing protocol that requires its local implementation in every router. This provides that all routers in the network can exchange topology information, which in turn allows each router to locally determine for each destination the most suitable port to forward packets by processing a shortest path algorithm. OSPF's information updates are referred to as Link State Advertisements (LSAs) and a router participating in OSPF distributes all its topological information by flooding LSAs throughout the entire network. In case of a network failure, the routers adjacent to that failure start flooding the according topology updates. Each router that receives such an update instantly recomputes its routing and reconfigures its packet forwarding accordingly. This process is referred to as OSPF convergence and may take tens of seconds @cite_9 in large IP networks.
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Open Shortest Path First (OSPF), a link state routing protocol, is a popular interior gateway protocol (IGP) in the Internet. Wide spread deployment and years of experience running the protocol have motivated continuous improvements in its operation as the nature and demands of the routing infrastructures have changed. Modern routing domains need to maintain a very high level of service availability. Hence, OSPF needs to achieve fast convergence to topology changes. Also, the ever-growing size of routing domains, and possible presence of wireless mobile adhoc network (MANET) components, requires highly scalable operation on part of OSPF to avoid routing instability. Recent years have seen significant efforts aimed at improving OSPF's convergence speed as well as scalability and extending OSPF to achieve seamless integration of mobile adhoc networks with conventional wired networks. In this paper, we present a comprehensive survey of these efforts.