Dynamic Issues in MPLS Service Restoration

The rapid growth of real-time and high-priority traffic over IP networks makes network survivability more critical. Several MPLS-based recovery mechanisms have been proposed to ensure continuity of service following network impairments. These approaches, however, suffer from the transient effects that negatively impact the traffic that is being rerouted onto the protection paths. Packet loss and reordering are the most significant negative effects resulting from protection switching. In conventional MPLS networks, the detection and retransmission of out-of-order or lost packets is left to the higher layers, which in effect, degrades the overall performance. This paper proposes a signaling mechanism to minimize the impact of protection switching on packet loss and reordering. The proposed signaling protocol is general and independent of the particular MPLS protection mechanism. The signaling protocol uses the existing queues on the nodes to buffer incoming traffic and hence reduce loss of data and packet reordering during recovery operations. Easy to implement calculations are used by the nodes to estimate the required queue sizes and to control the signaling procedure. The protocol has been implemented and studied in the three MPLS protection mechanisms under consideration. The results of our simulation study show that, with the implementation of the proposed signaling scheme in the basic protection mechanism, the number of packets reordered is significantly reduced while maintaining or improving packet loss without imposing much overhead on the nodes in the network.