Providing QoS support in OSPF based best effort network

In an open shortest path first (OSPF) based best effort network, when a packet experiences congestion, the routing subsystem cannot send it through an alternate path. Thus, it fails to provide desired quality of service (QoS) during congestion. A load sensitive routing algorithm (LSR) has been reported which finds alternate path based on OSPF property. The operating parameter (or coefficient) of LSR was chosen such that total number of alternate paths in the network is maximized. In this paper, we argue that a better operating parameter would be one that maximizes total number of alternate paths subject to the constraint that maximum number of nodes have at least one alternate path. Using simulation, we show that this new algorithm, called efficient LSR (E-LSR) performs better than OSPF and LSR in terms of delay and packet loss. Besides, this paper presents more efficient algorithm for determining the optimal operational E-LSR coefficient by pruning the search space and using a simple objective function. In E-LSR algorithm, the number of alternate paths depend on the topology and costs assigned to the links. Hence, this paper provides a topology guideline that may be followed by the implementers to make E-LSR more effective