Asymmetric CDC ROADMs for Efficient Support of Bi-directionally Asymmetric Traffic Demands

With the arrival of 5G era, Internet traffic is growing explosively. Meanwhile, the asymmetry of traffic in upstream and downstream directions is becoming more severe. Most current network architectures are designed based on the assumption of bi-directionally symmetric traffic demands. Network capacity in the direction that carries less traffic is largely wasted. To tackle this issue, we propose a new optical network architecture that can efficiently handle bi-directionally asymmetric traffic demands. Specifically, we design a novel asymmetric colorless, directionless, and contentionless (CDC) reconfigurable add/drop multiplexer (ROADM), which can adaptively configure numbers of ingress and egress 1N wavelength selective switches (WSSs) in each direction asymmetrically according to actual traffic demands, thereby avoiding wastage of 1N WSSs in the direction carrying less traffic. Also, we decouple each transponder into a pair of split transmitter (Tx) and receiver (Rx), and asymmetrically configure their numbers according to actual bi-directional traffic demands, significantly reducing the add/drop cost in a ROADM. To evaluate the benefit of the proposed asymmetric network architecture, we exploit the routing and spectrum assignment problem in an optical network. A novel analytical model to evaluate lightpath blocking performance with asymmetric numbers of opposite fibers on each link of an optical network is developed. Also, efficient heuristic algorithms to target asymmetric traffic are proposed. Simulation results show that the proposed asymmetric optical network architecture can greatly reduce the overall system cost compared to its counterpart symmetric architecture when carrying the same amount of traffic demand, and achieve significantly better lightpath blocking performance than the latter when their total system costs are close. Furthermore, the analytical model can accurately predict the blocking performance of an optical network based on the asymmetric architecture.