A QoS oriented analytical model for BGP multihomed networks

An analytical model for multihomed BGP networks is developed which calculates the probabilities of all network states assuming independent link failures. Contrary to previous models, the focus is not only on network reliability in terms of maintaining connectivity, but rather on the network's Quality of Service (QoS) and its ability to meet a certain Service Level Agreement (SLA). Therefore, reliability analysis becomes a special case of this general model. Various parameters are used to realistically represent the properties of end-to-end routes. These properties include the number and composition of multipaths, the degree of multihoming as well as the number of hops in each serial path. The joint Probability Mass Function (PMF) for the number of available multipaths and the number of multihomed routes is derived and then averaged to obtain the marginal PMF for multihomed routes only. Simple numerical examples use Erlang C traffic formulas to illustrate the effects of link failures - occurring in various sections of the routes - on the network's ability to meet a certain SLA. The model can be used by Application Service Providers (ASPs) to properly dimension their multihomed sections or to quantify their resilience against link failure conditions.