Closed parasitic flow loops and dominated loops in networks

The paper raises awareness of the presence of closed parasitic flow loops in the solutions of published algorithm for maximising the throughput flow in networks. If the rooted commodity is interchangeable commodity, a closed parasitic loop can effectively be present even if the routed commodity does not physically travel along a closed loop. The closed parasitic flow loops are highly undesirable loops of flow, which effectively never leave the network. Parasitic flow loops increase the cost of transportation of the flow unnecessarily, consume residual capacity from the edges of the network, increase the likelihood of deterioration of perishable products, increase congestion and energy wastage. Accordingly, the paper presents a theoretical framework related to parasitic flow loops in networks. By using the presented framework, it is demonstrated that the probability of existence of closed and dominated flow loops in networks is surprisingly high. The paper also demonstrates that the successive shortest path strategy for minimising the total length of transportation routes from multiple interchangeable origins to multiple destinations fails to minimise the total length of the routes. It is demonstrated that even in a network with multiple origins and a single destination, the successive shortest path strategy could still fail to minimise the total length of the routes. By using the developed theoretical framework, it is shown that a minimum total length of the transportation routes in a network with multiple interchangeable origins, is attained if and only if no closed parasitic flow loops and dominated flow loops exist in the network. Accordingly, an algorithm for minimising the total length of the transportation routes by eliminating all dominated parasitic flow loops is proposed

On the Design of Next-Generation Routers and IP Networks

This thesis investigates distributed router architectures and IP networks with centralized control. While the current trend in IP-router architectures is towards decentralized design, there have also been research proposals for centralizing the control functions in IP networks. With continuous evolution of routers and IP networks, we believe that eventually IP networks in an autonomous system (AS) and a distributed router might converge into one network system. This system, which can be considered both as a distributed router and a centrally-controlled IP network, is divided into a control plane and a forwarding plane. The control plane is responsible for routing, management and signalling protocols, while the forwarding plane is responsible for forwarding packets. The work in this thesis covers both the forwarding and control planes. In the forwarding plane, we study network processor systems that function as forwarding elements in a distributed router. We introduce a system model and a simulation tool based on the model. Using the simulation tool, we investigate network processor system design by studying throughput, utilization, queueing behavior and packet delays. In addition to network processor systems, we study IP-address lookup, which is one of the key packet processing functions in Internet routers. Our work in IP-address lookup contains an efficient lookup algorithm, a scheme to divide the lookup procedure into two-stages in a distributed router, and an approach to perform efficient lookup on a router supporting multiple virtual routers. In the control plane, we study three emerging research issues with centralized control. We provide a thorough study of the routing convergence process in networks with centralized control, and compare it with decentralized link-state routing protocols. We propose an efficient approach to perform traffic engineering and routing in networks with centralized control, and compare it with an approach using optimized link weights. Finally, we present an approach to perform loop-free updates of forwarding tables when the forwarding paths change. This loop-free update approach is particularly useful in networks with centralized control. The results presented in this thesis are useful for building next-generation routers and IP networks with centralized control that might eventually converge into one network system.QC 2010072