Dual-mode TCP: An Alternative Approach for Delay Tolerant Networks

Many real world networks are characterized by long delays, frequent path breaks, mobility, and lack of infrastructure. Class of networks which can cope up with such environments are called Delay Tolerant Networks (DTN). Architectures with a separate bundle layer, have been implemented in specific applications such as interplanetary networks (IPNs). However, the addition of bundle layer to existing network infrastructure still remains as a challenge. In this paper, we propose Dual-mode TCP which can work in both normal and DTN modes. It analyzes the network behavior and switches to DTN mode when the network exhibits DTN characteristics. For the estimation of network characteristics, Dual-mode TCP analyzes the RTT values and models the network based on RTTs normal distribution. If the network is found to be in DTN mode, the protocol uses a DTN congestion window to get adapted with the high delay environment. The advantage of Dual-mode TCP over traditional TCP is its ability to adapt with DTN environments while preserving the compatibility of TCP. We implemented Dual-mode TCP using light-weight IP and our results show that, in DTN environments, an average improvement of 11.64% in total transmission time can be achieved using Dual-mode TCP as compared to traditional TCP. With varying duration of link delays Dual-mode TCP achieves an average reduction of 36.19% in transmission time.