Enhancing Space Communication Protocols for Future Missions

1. Taking the Politics out of Satellite and Space-Based Communications Protocols Will Ivancic wivancic@grc.nasa.gov 216-433-3494 roland.grc.nasa.gov/~ivancic

2. Space Exploration Program I’m so special! …….. Really? Why so much misinformation? Vocabulary Technology Evolution COTS, CCSDS and the Internet Gateways and Proxies Operational Environments Summary Presentation Outline

3. Space Communication ArchitectureSupporting Exploration and Science • Components • Earth • Moon • Mars • Deep Space • Key Technologies • Interplanetary laser communications • New standard protocols • Advanced low-power avionics Communication protocols must match the needs of the emerging Exploration Program as it matures

4. Projected Growth in DSN Downlink Requirements

5. Evolving the Lunar Architecture(One of many early concepts) An initial architecture recommendation is made based on an assumed human base at the South Pole2 relay satellitesOne inclined elliptical orbitAdvantage: long dwell times over the South Pole The 2 relays are moved to a circular orbit to support South and North Pole missions1 relay satellite is added to the constellation  3 totalOne circular polar orbitAdvantage: equal coverage of both poles, simple- minimized number of relays A second plane of relays is added to increase coverage at the South and North Poles, and provide global coverage3 relay satellites are added  6 totalTwo polar circular orbitsAdvantage: increased coverage at the poles, global coverage achieved The orbital planes are inclined to support global, far-side, and equatorial missionsFinal Configuration:6 relay satellitesTwo inclined circular orbitsAdvantage: global coverage, coverage is distributed more evenly than for polar orbits  better support to exploration at lower latitudes

6. Example Service and Data Rate Scenario for Lunar Communication (Work in progress)

7. My situation is unique! ….. Really? • Volume, mass and power are at a premium in space • mobile and ad-hoc communication • Intermittent connectivity is a common for planetary relays • Common for many military operations. • Delay and latency have to be considered for space-based protocols • Low-bandwidth, highly-processed, links may be in the order of seconds • Email and text messaging and are not terribly concerned about the delay so long as the message gets through eventually. • Reliability and redundancy are of major concern • Aeronautical, military and commercial networks • Space hardware must withstand radiation effects • Present in military and high-altitude applications.

8. Why so Much Misinformation? Much of this has been perpetuated by political turf battles and funding battles to the detriment of sound technical analysis $$$ POLITCS The Preverbial Rice Bowl

9. TCP over Noisy Links with Long Delays • TCP slow start takes a long time to reach equilibrium • log2 (bandwidth × delay) round-trip times (RTTs) • poor performance over long fat networks • particularly for short flows • on retransmission timeout, TCP enters slow start again • poor performance over lossy high capacity links • TCP infers congestion on all packet drops • even if the loss is due to packet corruption due to noise TCP congestion avoidance throttles source unnecessarily • TCP sends a burst of packets when window opens • this can cause congestion drops in intermediate routers

10. An Example of TCP Steady State Performance Does this infer that all Internet Protocols are not suitable for Interplanetary operations? Chart is from “Why not use the Standard Internet Suite for the Interplanetary Internet?” By Robert C. Durst, Patrick D. Feighery, Keith L. Scott

11. Theoretical Steady State Throughput TCP Performance equitation is from Mathis, M. et al, "The Macroscopic Behavior of the Congestion AvoidanceAlgorithm",Computer Communications Review, volume 27, number 3, July 1997. Delay Tolerant Increasing Delay Don’t Use TCP for long delays. However, one can still use IP and a rate-base protocol.

12. Vocabulary Circuit The complete path between two terminals over which one-way or two-way communications may be provided. Channel A single path provided by a transmission medium via either (a) physical separation, such as by multipair cable or (b) electrical separation, such as by frequency- or time-division multiplexing.. Link A conceptual circuit, i.e., logical circuit, between two users of a network that enables the users to communicate, even when different physical paths are used. At any level you are circuit-switched, you can always subvert that by being packetized at the next level up. Thus, you have virtual circuits running across packets running over circuits

13. Technology Evolution Yesterday Multiplexer Modulator

14. Technology Evolution Today

15. Ubiquitous Network Society Source: IPv6 Promotion Council of Japan Tomorrow • The society to be realized in 2010 • Anybody can / anytime / anywhere • without being aware of the network • benefits from the use of the terminals and networks RFID Space Communications technology Seamless Network Authentication RFID Tag • Mobile Network • 4G Systems • High-speed WLAN Robot Next Generation Core Network Digital Information Appliances Security Home Networks Quantum Communications technology Sensor Network Ad-hoc Network This document is based on the material of MIC

16. Lunar Access Surface Module • Initial operating capability 2015, but no later than 2020 • Technology freeze 6 years before first use for subsystems, 9 years before first use for systems of systems technologies • Communications Requirements • Provide the crew interface to monitor & command onboard systems and trajectory for TBD nominal and contingency operations. • Provide voice, video and data communications with Earth (Daily ops and planning, science, PMC, PFC, PAO events, vehicle systems status and navigational state telemetry, etc.)

17. COTS, CCSDS and the Internet

18. COTS Satellite Modem Operation RF Framing (Media Access) COTS Router Radio Commercial Satellite Modem UP/Down Converter RF IF Baseband Framing

19. Common CCSDS Operation CCSDS Framing Radio Bit Synchronizer UP/Down Converter Modem RF IF Front End Processor Baseband

20. CCSDS relationship with the OSI Layers

21. IP 4/6 NIC NIC Modem

22. CCSDS and HDLC Ground Support Comparison NP or IP NP or IP Packet Insert VCDU Framing FEC Encode Packet Extract VCDU Framing FEC Decode Commercial Router/ Frame Relay Switch Very similar except the HDLC commercial world separates FEC and framing at a bitstream level interface CCSDS Net PDU IP IP HDLC Framing HDLC Framing Frame FEC Encode FEC Decode 101010 (bits) Randomize Derandomize Randomize Derandomize Conv. Encode Conv. Decode Conv. Encode Conv. Decode Bit sync Bit sync Modulator Demod Modulator Demod Transmitter Receiver Transmitter Receiver Upconvert Downconvert Upconvert Downconvert Antenna Using standard internet protocols and applications in space - Hogie

23. Gateways • Provide a translation interface between two different protocols at the same layer of the protocol stack. • Require maintenance when protocols change – and they do change! • Unintentionally break some protocols as you move data between one protocol with one set of assumptions and semantics and another, different, protocol with different assumptions and semantics. • An inconvenience on the ground compared with getting two different systems to interoperate • In space-based systems, gateway maintenance is much more difficult. • Custom gateways are relatively expensive, as they must completely implement and support more than one protocol at a layer. • Gateways are a tool that is best avoided if possible. However, sometimes a gateway is a necessary evil. • e.g. Interplanetary Internet

24. Network Cloud COTS Interface NIC Gateway or Encapsulation Space Ground

25. Performances Enhancing Proxies PEPs Internet Internet • Used to optimize for control loops • Generally need to see into protocols • Network layer encryption renders most gateways useless Control Loop 2 Control Loop 1 Control Loop 3 End-to-End Control Loop

26. Performances Enhancing Proxies • IETF RFC2488, "Enhancing TCP Over Satellite Channels using Standard Mechanisms" • IETF RFC2760, "Ongoing TCP Research Related to Satellites” • IETF RFC 3819, “Advice for Internet Subnetwork Designers” • IETF RFC 3150, “End-to-end Performance Implications of Slow Links” • IETF RFC 3155, “End-to-end Performance Implications of Links with Errors” • IETF RFC 3366, “Advice to link designers on link Automatic Repeat reQuest (ARQ)” • IETF RFC 3449, “TCP Performance Implications of Network Path Asymmetry” – give URLs. Non-IETF people won’t know where to find these.

27. Operational Environments • Surface • Low Delay, Symmetric, 1/R2 where radius is small (power vs bandwidth) • Closely matches characteristics of today’s Internet • Near Planetary • Moderate Delay, Asymmetric, 1/R2 where radius is becoming a factor (power vs bandwidth) • Intermittent connectivity • Interplanetary • Extremely large delay, Highly asymmetric, 1/R2 where radius extremely large (power vs bandwidth) • Intermittent connectivity • Feedback is an issue • Ongoing research in IRTF Delay Tolerant Networks and previously in IRTF Interplanetary Internet working groups

28. Top Level Solar SystemSpace Communication Architecture If the Moon is a test bed for Mars, should we be developing and testing protocols for the Moon or Mars? ~6.5 - 40 Minutes ~4 Minutes Hours

29. Spiral 2 – Lunar Surface Exploration Network Rover (1) Human on EVA Science Instrument (4-6) (Multiple) Lunar SBN Relay Earth Human on EVA Surface Terminal Repeater (4-6) Lander Teleoperated Robot (1) Autonomous Robot Legend Very high rate backbone network to Earth High rate orbiter access network Low power, medium rate surface-to-surface network Low rate, long range links

30. Interplanetary Communications Key Issues • New Protocols • Bundled/Messaging Store and Forward Protocols • Interplanetary time synchronization • Scheduling Assets • When to turn on and off

31. Summary • Vocabulary is very important when speaking of networking. Be precise. • Packet-based switching is generally simpler to configure, more flexible and often provides better bandwidth utilization than circuit-base switching. • The operating environment heavily dictates what protocols can be used – particularly delay, bandwidth, and intermittent connectivity. • Many protocols in the TCP/IP protocol suite operate well in space. Others, such as TCP or routing protocols are applicable only to surface and some near-planetary applications. • CCSDS protocols have evolved over time as technology and processing power has improved. Originally designed to optimize power and processing on point-to-point links, CCSDS has begun incorporating networking capabilities with the advent of SCPS. • Neither IPv4 nor IPv6 interoperate with SCPS-NP. A gateway is necessary.

32. Current CCSDS data-link protocols are incompatible with COTS data-link protocols, requiring a data-link gateway for interoperability. Many CCSDS protocols – particularly legacy systems – merge layers and thus require application level gateways to operate with COTS protocols such as general Internet protocols. Such merging of layers results in one-off implementation and makes interoperation difficult. Great care should be taken when deploying PEPs. Understand their limitations. Gateways, including PEPs, must be maintained as protocols change. This can be an expensive proposition. Security is difficult anywhere. Sophisticated key management systems are not practical for space-based networks. Thus space-based security architectures should be as simple as policy will allow. Summary

33. Conclusion Some should not be used. Some work OK Some are designed for the job at hand Protocols are tools for communication One size does not fit all.