Inter Planetary Network (IPN)

1. Inter Planetary Network (IPN) By Charles B Shah cbshah@cse.buffalo.edu

2. Contents • Introduction • Challenges • Architecture of IPN • Communication Suite • Transport Layer Issues • Protocol: TP Planet • Protocol: RCP Planet • Network Layer Issues • Appendix • References

3. Introduction Imagine ??? If I say a “Hi” to you and you hear it after 9 Hours !!!!!

4. Some Fast Facts • Time taken by light Earth – Jupiter : 32.7 min Earth – Saturn : 76.7 min Earth – Pluto : 5.5 hours Earth – Voyager1 : 13 hours Earth – Voyager2 : 10.4 hours.

5. Objectives • Time-Insensitive Scientific data delivery • Time-Sensitive scientific data delivery • Mission Status Telemetry • Command and Control

6. Challenges • Extremely long propagation delay • Asymmetrical forward and reverse Link capacities • High link error rates for radio-frequency (RF) communication channels • Intermittent link connectivity • Lack of fixed communication infrastructure • Effects of planetary distances on the signal strength and the protocol design • Power, mass, size, and cost constraints for communication hardware and protocol design • Backward compatibility requirement due to high cost involved in deployment and launching processes.

7. Architecture

8. Architecture (contd …) • InterPlanetary Backbone Network Communication among Earth, outer-space planets, moons, satellites, relay stations, etc. • InterPlanetary External Network Space crafts flying in groups in deep space between planets, clusters of sensor nodes, and groups of space stations.

9. Architecture (contd …) • Planetary Network • Planetary Satellite Network Satellites circling the planets provides relay services, communication & navigation services to surface elements. Includes links between orbiting satellites & links between satellite and surface elements. • Planetary Surface Network Links between high power surface elements (rovers, landers, etc). Surface elements that cannot directly talk to satellites, organized in an ad hoc manner.

10. Communication Protocol Suite • Current Space / Ground protocol used by CCSDS (Consultative Committee for Space Data Systems ). • Each component of the IPN may have to run different set of protocols to suite the environment. • CCSDS protocol consists of 8 Layers • Used for the Mars Exploration mission communications.

11. CCSDS Protocol

12. CCSDS Protocol • Protocol Layers • Space Wireless Frequency and Modulation • Space Channel Coding • Space Link • Space Networking • Space end-to-end Security • Space end-to-end Reliability • Space File transfer • Space Application

13. CCSDS Protocol Limitation Although the current protocol is viable, there is a need to make the protocol stack adaptable to different environmental changes allowing integration of highly optimized regional network protocols. This leads to the proposed Protocol by Delay Tolerant Networking Research Group (DTNRG).

14. DTNRG Protocol Stack • The protocol replies on a middleware layer called bundle layer that resides between the application and the lower layers. • The bundle layer resolves the intermittent connectivity, long or variable delay, asymmetric data rates, high error rates by using a store and forward mechanism similar to email. • It uses per-hop error control which increases the probability of data transmissions.

15. DTNRG Protocol

16. Transport Layer Issues • InterPlanetary Backbone poses the most challenging problems for reliable data and multimedia transport. • The transport layer functionalities are necessary for reliable transfer and timely delivery of multimedia information. • Most important challenges for the backbone • Very long propagation delay • High link error rates • Blackouts • Bandwidth Asymmetry

17. Why not use current protocols?? • Due to the window-based mechanism, there is a high performance degradation. • In slow start phase of TCP protocols, the congestion window size (W) is incremented by 1 for every ACK received until the slow start threshold (Wss). • For = 20 and RTT = 20 min, the slow start algo cannot utilize the link for 120 min in deep space. • TCP protocols are designed for wired links, assuming negligible bit error rates while space links have considerable bit error rates.

18. Why not use current protocols?? • Even protocols for satellite links could not be applied for IPN, as the satellite links have RTT of the order of 500ms and also the packet loss due to the blackout conditions may also mislead the congestion control mechanisms. • TCP is expected to respond to Network State. The higher RTT is experienced, the older information about link conditions is received at the source. This might not lead to correct action. • TCP uses retransmission which calls for higher buffer size (1.2GB for RTT = 20min, for 1MB/s

19. TP Planet • Developed for the end-points are backbone nodes such as the relay satellites orbiting around the planets or the ground stations which are capable of direct deep space communications. • It runs on top of Internet Protocol (IP) layer and does not require any specific modification to the lower layers in the current TCP/IP protocol suite. • The structure of the protocol consists of two Algorithms: Initial State and Steady State

20. TP Planet

21. Initial State (TP Planet) • Composed of 2 parts – Immediate Startup and Follow-Up. • Immediate start up ( 0 ≤ t ≤ RTT ) • Divides actual RTT into equal intervals of size T • During Immediate Start, it emulates slow start and congestion avoidance algorithms of current TCP protocols by treating intervals of T as RTTs of the emulated connection. • Along with data packets, it transmits low priority NIL segments to probe the link resources when t ≤ RTT • The number of data packets sent during each interval T is maxed to ssthreshe

22. Immediate Startup

23. Immediate Startup • cwnd is increased till ssthreshe and after that remains constant at cwnd as there is still no feedback on the link condition. • During Emulated Slow Start, cwnd + cwndn≤ ssthreshe • During Emulated Congestion Avoidance cwnd = ssthreshe and cwndnis increased till ssthreshe

24. Follow Up • Follow Up Phase ( RTT ≤ t ≤ 2.RTT ) • The packets are received at the other end • To save scarce resources one ACK is send for several packets by a delayed SACK ( Selective ACK) • Each NIL segment received indicates that the link is not utilized completely, so it counts the total no of NIL received in one period T and sends this information as NIL ACK. • The sender has cwnd = ssthreshe for RTT ≤ t ≤ RTT + T and later it changes the cwnd based on the information in NIL ACKs. • Source also transmits NIX packets for congestion monitoring

25. Steady State ( t ≥ 2.RTT ) • Congestion Control • Low and high priority NIX segments of 40 bytes • Sent at same rate as Data packets, so they experience same packet loss rate due to space link errors. • Low priority NIX get discarded first. • Sink counts number of received low (Nlow) and high priority (Nhigh) NIX segments in a window of Tw • Received NIX are not acknowledged, instead reception statistics within a window Twis carried by NIX ACKs.

26. Steady State

27. Steady State • Congestion Control (contd…) • Let Φ = Nlow /Nhigh • Source infers that a congestion exists if Φ < 1. • Let Φd , Φi be preset rate decrease and increase thresholds • If Φ < Φd : Congestion is experienced along the path. Source goes to Decrease Rate state where transmission S is decreased multiplicatively. • If Φd ≤ Φ ≤ Φi : the rate S is kept unchanged until further feedback is recieved. • If Φ > Φi : No congestion is experienced. Consequently, it increases data transmission rate S additively.

28. Steady State • Blackout • Link outages due to loss of line-of-sight by orbital obscuration lead to burst packet losses & decrease in the throughput. • If the source does not receive any type of ACK ( data or NIX ) for a certain period Tw, it infers Blackout. • During Blackout, source keeps sending low and high priority NIX segments without changing the transmission rate. • Similar action is taken by the sink and it sends NIX ACKs with (Nlow, Nhigh) as (0,0) called ZERO NIX ACKs. • Since RTT is very high, the effect of blackout on performance changes with it relative location of blackout wrt sink.

29. Blackout • Let blackout occur at t = t0and let L be the duration of the blackout. Let the blackout occur at x seconds from sink. • For rtt = RTT/2 , there are 2 cases: L < 2x and L≥ 2x. • Case when L < 2x : • After rtt – x from t0i.e. at t1 = t0+ rtt – x, the source detects the period without ACKs. If this duration is > Tw, the source enters Blackout state. • Now, source does not send any new data packets, but keeps sending low and high priority NIX segments with same rate. • At t2 = t1+ L, source receives normal ACKs for a duration of 2x – L. Source infers that Blackout is over and enters either hold, increase or decrease based on info received in ACKs • At t3 = t2 + 2x – L, the source receives ZERO ACKs transmitted by sink, now source remains in Hold state.

30. Blackout ( contd … ) • Case when L ≥ 2x. • Source detects no ACKs and goes to Blackout state at t1= t0 + rtt – x. • At t2 = t1 + L, source receives ZERO NIX ACKs for a duration of 2x and leaves Blackout state. • At t3 = t2 + 2x, ZERO NIX ACK period is over and transits to a state depending on the info in the ACKs Consequently, the Blackout State reduces the throughput degradation due to blackout conditions and improves the link utilization for duration of L or 2x in the cases L < 2x and L ≥2x, respectively.

31. Delayed SACK • If the data packets are 1KB, SACK packets are of 40B, i.e. the ratio of the traffic in the forward and reverse links is 25:1 • However, the ratio in case of space links is of the of 1000:1, and hence even a single SACK can cause congestion in the reverse link. • Therefore, TP Planet sink maintains a delayed-SACK factor, d, and sends one packet every d packets received.

32. RCP Planet • Transport Layer protocol for multimedia traffic • Multimedia does not require 100% reliability but has strict req on bounded jitter, minimum b/w • Challenges to multimedia traffic in IPN: • Bounded Jitter • Minimum Bandwidth • Smooth Traffic ( maintain steady rate ) • Error Control • Non Suitable methods for IPN • Store and forward • Use multiple paths

33. RCP Planet • RCP planet is a rate control scheme • Two States: Initial State and Steady State • Uses Tornado codes to recover from packet losses • Uses rate probing mechanism ( probing sequence ) • Uses new rate control mechanism • Handles Blackout state as in TP Planet

34. RCP Planet

35. Network Layer Issues • Naming and Addressing • Factors influencing Naming and Addressing • What objects are named • Whether a name can be used directly by a data router • The method by which the name/object binding are managed. • DNS not suitable for the foll reasons: • If an object on remote planet wants to resolve earth based name it could query the DNS server on earth, but long RTT would hamper the performance • It could maintain a secondary server locally, however updates will dominate the communication channel • It could have static name resolution, but that would not allow scalability.

36. Network Layer Issues • Compatible with IPv4 and IPv6 • Proposed Network Layer Protocol is ( SCPS-NP ), Space Communication Protocol Standards – Network Protocol. • Open Issues: • Distribution of topology information. • Path Calculation • Interaction with transport layer protocols. • Efforts: • Epidemic Routing • Sensor Web Project

37. Appendix An Example of using bundling for deep space communication.

38. Appendix • DSN ( Deep Space Networks) http://deepspace.jpl.nasa.gov/dsn/ • The DSN currently consists of three deep-space communications facilities placed approximately 120 degrees apart around the world: at Goldstone, in California's Mojave Desert; near Madrid, Spain; and near Canberra, Australia. • One 34-meter (111-foot) diameter High Efficiency antenna. • One 34-meter Beam Waveguide antenna. • One 26-meter (85-foot) antenna. • One 70-meter (230-foot) antenna.

39. Appendix • Doppler Effect/ Shift used to Trace/Probe the satellite in transit. • The apparent change in wavelength of sound or light caused by the motion of the source, observer or both. • If you have ever had a motorcycle speed up from behind you, only to fly past you on the freeway, you probably noticed how the engine sound seemed to get higher in pitch as it approached you, only to drop down lower once it had passed. This change in pitch is an example of a Doppler shift.

40. Appendix • Some more facts: • The Cassini spacecraft is carrying two Motorola Tracking, Telemetry, and Control (TT&C) deep space transponders which provide the only communications link between the spacecraft and the numerous terrestrial tracking stations that comprise NASA's Deep Space Network. • Mars Mission Cost = $400 Million • ESA Mars mission cost = 150 million Euros • Cassini mission cost = $3 billion

41. References • O.B. Akan, J. Fang, I.F. Akyildiz, TP-Planet: a reliable transport protocol for InterPlaNetary Internet, IEEE Journal on Selected Areas in Communications. • I. F. Akyildiz, O. B. Akan, C. Chen, J. Fang, andW. Su, “InterPlaNetary Internet: State-of-the-art and research challenges ” • R.C. Durst, P.D. Feighery, K.L. Scott, “Why not use the standard internet suite for the interplanetary internet” • O.B. Akan, J. Fang, “Performance of Multimedia Rate Control Protocols • in InterPlaNetary Internet” • http://www.planetary.org/html/news/articlearchive/headlines/2001/casshuygfix.html • http://deepspace.jpl.nasa.gov/dsn/ • http://www.gdds.com/press1997/1008cassini.html