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1Inter Planetary Network (IPN)By Charles B [email protected] Introduction Challenges  Architecture of IPN  Communication Suite Transport Layer Issues Protocol: TP Planet Protocol: RCP Planet Network Layer Issues Appendix ReferencesIntroductionImagine ???If I say a “Hi” to you and you hear it after9 Hours !!!!!Some Fast Facts  Time taken by light Earth – Jupiter : 32.7 minEarth – Saturn : 76.7 minEarth – Pluto : 5.5 hoursEarth – Voyager1 : 13 hoursEarth – Voyager2 : 10.4 hours.2Objectives Time-Insensitive Scientific data delivery Time-Sensitive scientific data delivery Mission Status Telemetry Command and ControlChallenges 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.Architecture Architecture (contd …) InterPlanetary Backbone NetworkCommunication among Earth, outer-space planets, moons, satellites, relay stations, etc. InterPlanetary External NetworkSpace crafts flying in groups in deep space between planets, clusters of sensor nodes, and groups of space stations.3Architecture (contd …) Planetary Network Planetary Satellite NetworkSatellites 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 NetworkLinks between high power surface elements (rovers, landers, etc). Surface elements that cannot directly talk to satellites, organized in an ad hoc manner.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.CCSDS Protocol CCSDS Protocol Protocol Layers1. Space Wireless Frequency and Modulation2. Space Channel Coding3. Space Link4. Space Networking5. Space end-to-end Security6. Space end-to-end Reliability7. Space File transfer8. Space Application4CCSDS Protocol LimitationAlthough 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).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.DTNRG Protocol 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 Asymmetry5Why 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 algocannot 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.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/sTP 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 StateTP Planet6Initial 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 ssthresheImmediate StartupImmediate Startupcwndis increased till ssthresheand after that remains constant at cwndas there is still no feedback on the link condition.  During Emulated Slow Start, cwnd+ cwndn≤ssthreshe During Emulated Congestion Avoidance cwnd= ssthresheand cwndnis increased till ssthresheFollow 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= ssthreshefor RTT ≤ t ≤ RTT + T and


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UB CSE 620 - Inter Planetary Network

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