Loss of the routing protocol messages due to network congestion can cause peering session failures in routers, leading to route flaps and routing instabilities. We study the effects of traffic overload on routing protocols by quantifying the stability and robustness properties of two common Internet routing protocols, OSPF and BGP, when the routing control traffic is not isolated from data traffic. We develop analytical models to quantify the effect of congestion on the robustness of OSPF and BGP as a function of the traffic overload factor, queueing delays, and packet sizes. We perform extensive measurements in an experimental network of routers to validate the analytical results. Subsequently we use the analytical framework to investigate the effect of factors that are difficult to incorporate into an experimental setup, such as a wide range of link propagation delays and packet dropping policies. Our results show that increased queueing and propagation delays adversely affect BGP's resilience to congestion, in spite of its use of a reliable transport protocol. Our findings demonstrate the importance of selective treatment of routing protocol messages from other traffic, by using scheduling and utilizing buffer management policies in the routers, to achieve stable and robust network operation.
We describe a new algorithm for rate allocation within the individual switches of an ATM network implementing a rate-based congestion control algorithm for Available Bit-Rate (ABR) traffic. The algorithm performs an allocation in 8(1) time, allowing it to be applied to ATM switches supporting a large number of virtual circuits. When the total available capacity or the requests of the individual connections change, the algorithm converges to the max-min allocation. Results from simulations using ATM sources show that the algorithm provides close to ideal throughput and converges to the max-min fair allocation rapidly when the available bandwidth or the individual requests change.
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