A performance comparison of DTN protocols for high delay optical channels

Designed for long propagation delay and frequent channel disruptions, delay tolerant networking (DTN) protocols are supporting the latest proposed optical space internetworking communication missions. While previous DTN-based testbeds experimented with bandwidth capacity in megabits, this paper presents a channel emulation testbed that supports multiple gigabit-bandwidth Ethernet clients and servers simultaneously. In addition to capacity, this testbed modeled optical link properties with channel emulation, and provided high flexibility by utilizing virtual LANs and link aggregation connected through a gigabit switch. The testbed emulated propagation delay, asynchronous channel rates, and bit errors, including free-space optical bit errors that varied as a function of time. We emulated an optical flight terminal relaying data between ground stations, and measured the maximum goodput of various DTN configurations while increasing the relay´s round trip times. Results showed that for a 200 ms to one second round trip time, BP/TCPCL/TCP transmitted higher goodput than BP/LTP/UDP, and TCP/IP. For round trip times longer than one second, BP/LTP/UDP transmitted higher goodput than BP/TCPCL/TCP, and TCP/IP.