Experimental characterization of space optical communications with disruption-tolerant network protocols

Abstract

Abstract-Disruption-tolerant networks (DTNs) are groups of network assets connected with a suite of communication protocol technologies designed to mitigate the effects of link delay and disruption. Application of DTN protocols to diverse groups of network resources in multiple sub-networks results in an overlay network-of-networks with autonomous data routing capability. In space environments where delay or disruption is expected, performance of this type of architecture (such as an interplanetary internet) can increase with the inclusion of new communications mediums and techniques. Space-based optical communication links are therefore an excellent building block of space DTN architectures. When compared to traditional radio frequency (RF) communications, optical systems can provide extremely power-efficient and high bandwidth links bridging sub-networks. Because optical links are more susceptible to link disruption and experience the same light-speed delays as RF, optical-enabled DTN architectures can lessen potential drawbacks and maintain the benefits of autonomous optical communications over deep space distances. These environmentdriven expectations -link delay and interruption, along with asymmetric data rates -are the purpose of the proof-of-concept experiment outlined herein. In recognizing the potential of these two technologies, we report an initial experiment and characterization of the performance of a DTN-enabled space optical link. The experiment design employs a point-to-point freespace optical link configured to have asymmetric bandwidth. This link connects two networked systems running a DTN protocol implementation designed and written at JPL for use on spacecraft, and further configured for higher bandwidth performance. Comparing baseline data transmission metrics with and without periodic optical link interruptions, the experiment confirmed the DTN protocols' ability to handle real-world unexpected link outages while maintaining capability of reliably delivering data at relatively high rates. Finally, performance characterizations from this data suggest performance optimizations to configuration and protocols for future opticalspecific DTN space link scenarios.

A Delay Tolerant Networking-Based Approach to a High Data Rate Architecture for Spacecraft

“…HiDRA is working towards the successful migration of DTN from a protocol to an operational implementation hinges on the ability to transmit data in the 10-200Gbps regime to meet the needs of current and future high speed space networks, such as those realized by laser communications. An early and successful experiment of the ION implementation of DTN running over a free-space laser communications link was conducted at the Jet Propulsion Laboratory (JPL) [25]. The many papers inspered from this experiment, as well as IONAC-Lite [16] have lead to not only the problem statement, but towards a solution.…”

Demonstration of Disruption Tolerant Networking across Lunar Optical Communications Links

“…10 For optical links, passing clouds may cause extended data outages longer than can typically be accommodated with underlying coding or interleaving and therefore, stand to benefit more from the LTP performance. 11 For events when a primary ground station's link conditions are degrading, larger data buffers and LTP can allow for a handoff to an alternate ground station without the loss of data.…”

High Data Rate Architecture (HiDRA)

“…Adoption of DTN into future high speed space networks, and especially those realized by laser communications, hinges on the ability to successfully transmit data in at least the Gb/s order of magnitude range. A successful test was performed at JPL with the ION implementation running over a Free-Space Optical (FSO) network [12]. Forcing the central processing unit (CPU) to move data from non-volatile storage to RAM to the communications system interface at these rates would cause undue burden and bottlenecking.…”