Local and congestion-driven fairness algorithm in arbitrary topology networks

摘要

Typically, bandwidth reservation is not made for data applications. Therefore, the only way to provide minimum bandwidth guarantees to such an application is by using a fairness mechanism to regulate the access to the network and by controlling the packet loss (i.e., congestion) inside the network. There are numerous works treating fairness in ring networks, however, there are almost no such works on fairness in arbitrary topology networks. The context of this work is fairness in an arbitrary topology network, the MetaNet, which employs convergence routing, a loss-free routing technique which is a variant on deflection routing. We note that minimum bandwidth guarantee combined with loss-free routing are the desired quality-of-service (QoS) attributes for most data applications. While developing the mechanisms, we also present performance measures to assess the new access- and flow-control algorithm: i) locality and congestion-driven-only the subnetwork containing conflicting traffic streams becomes involved in the fairness regulation. Furthermore, the fairness regulation is activated only when congestion occurs. This implies that when there is no congestion, nodes can access the network immediately and freely, which is a key requirement for distributed computing. ii) Scalability-the data-structure sizes used in the algorithm are a function of the switching node degree, and use constant space control signals of two bits only (the ATM standard, for example, dedicates four bits in the header of each cell to generic flow-control). iii) Linear access time in the congested subnetwork-measured by "the maximal clique in what we call the conflict graph to which a node belongs," and a frequency which is inverse linear in this parameter (when the traffic pattern stabilizes).