Taking Saratoga from space-based ground sensors to ground-based space sensors

Abstract

The Saratoga transfer protocol was developed by Surrey Satellite Technology Ltd (SSTL) for its Disaster Monitoring Constellation (DMC) satellites. In over seven years of operation, Saratoga has provided efficient delivery of remote-sensing Earth observation imagery, across private wireless links, from these seven low-orbit satellites to ground stations, using the Internet Protocol (IP). Saratoga is designed to cope with high bandwidth-delay products, constrained acknowledgement channels, and high loss while streaming or delivering extremely large files. An implementation of this protocol has now been developed at the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) for wider use and testing. This is intended to prototype delivery of data across dedicated astronomy radio telescope networks on the ground, where networked sensors in Very Long Baseline Interferometer (VLBI) instruments generate large amounts of data for processing and can send that data across private IP-and Ethernet-based links at very high rates. We describe this new Saratoga implementation, its features and focus on high throughput and link utilization, and lessons learned in developing this protocol for sensor-network applications. 12 TABLE OF CONTENTS 1. INTRODUCTION.

A sender-based TFRC for Saratoga: A rate control mechanism for a space-friendly transfer protocol

“…2: if (a request for a STATUS-feedback packet is due) then 3: Record the dummy sequence and the send-time of the packet to mark the end of a period. 4: end if 5: if (a request was sent with the previous packet) then 6: Record the dummy sequence and the send-time of the packet to mark the start of a period. 7: end if 8: Store the send-time of the packet in the history.…”

“…3: Using the recorded information specified in Algorithm 1, offsets of the lost packets reported by the receiver, and the information from Step 2, find dummy sequences of the packets lost in the cycle. 4: Update receive-times and delivery-fates (received or lost) of the packets sent during the cycle. 5: Estimate the receiver's throughput and compute the value of p. 6: Compute the sending rate.…”

“…This is an optional capability provided by Saratoga, and not in regular operational use. Saratoga is also currently being evaluated for use in private radio astronomy networks, where high-speed sensor data flows are a base requirement [4].…”

A Message Transfer Framework for Enhanced Reliability in Delay-Tolerant Networks

“…Saratoga is a UDP-based protocol, supporting a Selective Negative Acknowledgment (SNACK) with holes-to-fill strategy [41] for reliable retransmissions. Additionally, for reliable transfer, data packets are sent using UDP with checksums turned on.…”

“…− At the transport layer, we can assume a point-to-point reliability protocol such as Saratoga [41], [42]. Saratoga is a UDP-based protocol, supporting a Selective Negative Acknowledgment (SNACK) with holes-to-fill strategy [41] for reliable retransmissions.…”