Improving throughput of long-hop TCP connections in IP over OPS networks

Abstract

Optical Packet Switching (OPS) can provide the ever-increasing bandwidth required for Internet traffic and new applications for future networks. However, optical packet loss is the major problem for an OPS network. Moreover, by increasing the number of hops between a pair of ingress–egress switches in an OPS network, optical Packet Loss Rate (PLR) between this pair is increased. Therefore, due to a higher PLR for long-hop TCP connections, the throughput of these connections may be much lower than the short-hop TCP connections. To overcome this problem, it is proposed in this paper to use the retransmission idea in the optical domain not only to increase TCP throughput but also to improve the throughput of multi-hop TCP connections, and also to have a loss-free OPS network. Under retransmission in the optical domain, a copy of the transmitted traffic is kept in the electronic buffers of ingress switches and retransmitted in the optical domain whenever required. Note that the TCP layer has its own retransmission at the client packet level as well. By retransmission of lost packets in the optical domain, TCP would be unaware of the lost client packets, and therefore, TCP would not reduce its sending rate. In this paper, TCP throughput is studied in a bufferless slotted OPS network and the effectiveness of the proposed mechanism is evaluated.