Minimizing the differential delay for virtually concatenated Ethernet over SONET systems

We consider the problem of minimizing the differential delay in a virtually concatenated Ethernet over SONET (EoS) system by suitable path selection. The link capacity adjustment scheme (LCAS) enables network service providers to dynamically add STS-n channels to or drop them from a virtually concatenated group (VCG). A new STS-n channel can be added to the VCG provided that the differential delay between the new STS-n channel and the existing STS-n channels in the VCG is within a certain bound that reflects the available memory buffer supported by the EoS system. We model the problem of finding such a STS-n channel as a constrained path selection problem where the cost of the required (feasible) path is constrained not only by an upper bound but also by a lower bound. We propose two algorithms to find such a path. Algorithm I uses the well-known k-shortest-path algorithm. Algorithm II is based on a modified link metric that linearly combines the original link weight (the link delay) and the inverse of that weight. The theoretical properties of such a metric are studied and used to develop a highly efficient heuristic for path selection. Simulations are conducted to evaluate the performance of both algorithms in terms of the miss rate and the execution time (average computational complexity).