TCP-NCL: A serialized-timer approach for enhancing TCP over heterogeneous wired/wireless networks

Abstract In heterogeneous wired/wireless networks, TCP performs unsatisfactorily since packet reordering and non-congestive losses may be falsely interpreted as congestive losses. This causes TCP to trigger fast retransmission and fast recovery spuriously, leading to under-utilization of available network resources. In this paper, we have developed a smart TCP sender (STS) model to differentiate congestive issues from the non-congestive ones for constructing more reliable signals of packet loss and network congestion over general error-prone channels. Two serialized timers are employed so that their expirations offer two separate signals of a packet loss and network congestion. The first timer is started when a packet is first injected into the network, and it will be cancelled if the acknowledgement is received. Otherwise, the packet will be retransmitted and the second timer is started upon the expiration of the first timer. The STS model is constructed based on the concept of minimizing expected cost and optimal setting of expiration periods for timer is determined. We have devised a novel TCP variant, known as TCP for non-congestive loss (TCP-NCL), as a practical approximation of the STS model. TCP-NCL can thus serve as a unified solution for effective congestion control, sequencing control, and loss recovery over wireless networks. The deployment of TCP-NCL requires modifications to sender-side TCP only, thereby facilitating possible future wide deployment. Our simulation studies show that TCP-NCL is robust against packet reordering as well as non-congestive packet loss while maintaining good responsiveness against congestive loss.