Communications & Data

1. Communications & Data Dave Finkleman

2. Overview • Introduction to Mobile ad-hoc Networking • OSI Layers • Routing • Disruptive Phenomena • Model Selection • Physical Layer • Link, Network, and Transport Layers • Missile Defense communication example • Conclusion

3. Mobile ad-hoc networking (MANET) • Self-organizing networks of • Dynamically mobile elements • With equal technical ability • Independent of fixed infrastructure or centralized control • General characteristics • Dynamic and often unpredictable network tolopogy • Variable capacity, often congested, bandwidth limited links • Energy and power constrained • Low physical security

4. Desirable capabilities • Scalable • From few widely distributed elements through multitudes of dense, randomly mobile elements • 802.11 is not scalable (10 nodes, 300 meters) • Bluetooth is neither scalable nor true MANET • Master-slave relationship • 100 meter range

5. Desirable capabilities • Mobile elements with static infrastructure (cellular, WAN, LAN) and fixed infrastructure networks (Internet) • Spectrum of route discovery and route maintenance schemes • Data link layer operation with a variety of embedded network and transport layer protocols

6. OSI framework: MANET • Open Systems Interconnect (OSI) • Physical layer (the environment) • Environment must be able to support communications • Channel loss (obstructions, atmospherics) • Interference • Mechanical and physical incompatibilities • Data link layer (the road map) • Must establish pathways within the communications medium • Make physical links consistent (MAC)

7. OSI framework: MANET • Network layer (the route) • Must accommodate changes in topology and discover routes (IP) • Transport layer (the traveler following the route) • Must match delay and dropout characteristics to sustain reliable communication • Application layer • Must be able to handle frequent and unanticipated disconnections (HLA)

8. Routing focus • Minimizing routing overhead • Control packets consume bandwidth • Minimizing delays • Links break and make randomly, interrupting ongoing communication • Optimizing paths • Many approaches sacrifice route optimization in order to diminish overhead and delays High altitude platforms can address all of these concerns

9. Routing focus • Preventing loops • Keeping route discovery from looping back on itself • Minimizing computational effort and storage • Route discovery and maintenance require complex logic and significant router memory • Scaling • Bandwidth and overhead can be totally consumed by internal route discovery and maintenance • Especially if every node maintains real time routing tables for every other node High altitude platforms can address all of these concerns

10. Routing issues • Location-dependent carrier sensing • Carrier sensing performed at transmitter - most influenced by phenomena near receiver • Hidden terminals: • Node out of range of sender but within range of receiver • Communication between the receiver & hidden node burdens channel • Exposed terminals: • Node within range of sender / out of range of receiver • Transmissions from exposed node deceive sender • Channel is occupied

11. Routing issues • Poor collision detection • Incoming signals weaker than transmissions • Acknowledgements (or lack of), latent • Potentially leading to unnecessary retransmission

12. Hidden terminal

13. Exposed terminal

14. Exposed terminal

15. Mitigating routing issues • Link layer protocol approaches • Proactive: regularly scheduled route discovery • Reactive: route discovery in response to link loss • Architectural approaches • Flat: all nodes equal • Hierarchical: some nodes elected or designated for special functionality • Hybrid approaches • Some proactive, some reactive • Some flat, some hierarchical

16. Fixed & ad-hoc routing • Fixed networks: exploit static routing tables • Distance vector: “shortest” path • Link state: avoid contention and broken links Bellman-Ford: In any graph there exists a spanning tree, a set of arcs that visits every node exactly once

17. Fixed & ad-hoc routing • ad-hoc network analogies • Distance vector • ad-hoc on demand distance vector (AODV) (reactive/flat) • Dynamic source routing (DSR) (reactive/flat) • Link state • Optimized link state routing (OLSR) (proactive/flat) Ad-hoc networks require a richer routing scheme

18. High altitude platform advantages • Ability to reach widely distributed inter-cluster nodes • No hidden or exposed nodes • Potentially all hybrid inter-cluster nodes visible • Ability to assist geographically aided intra-cluster routing • GPS enabling such as cell phones use, for example, potentially half duplex may be sufficient

19. High-altitude platform advantages • Availability of sufficient power and processing • Accommodates techniques whose overhead or energy requirements would swamp most mobile nodes MANET characteristics are not compromised, since The platform is not acting as a central controller

20. Measures of performance • Network size (number of nodes) • Network density • Network capacity • Connectivity structure (number of neighbors) • Mobility pattern (speed, range, …) • Link bandwidth • Traffic pattern (packet size, type of traffic, …) • Link characteristics (bidirectional, unidirectional) • Transmission medium (single vs multi-channel)

21. Modeling and simulation • OPNET-STK Example • Simulation configuration • Clusters • Land Vehicles with TBRPF and WRP (few, modest mobility) • Aircraft Cluster with AODV and DSR (few, high mobility • Inter-Cluster • Enabled by HAA • Realizations with ZRP and DREAM for comparison • Tradeoffs • Efficiency (hop count) and other measures of performance • Compare combinations of two element alternatives above

22. M&S selection criteria • Represent at least four lower OSI layers (1-4) • Represent discrete events • Represent highly non-linear complex systems • Capable of broad statistical analysis and Monte Carlo • Represent wireless interface from emission through propagation to reception • Encompasses antenna placement & characteristics, refraction, diffraction, absorption, & scattering

23. M&S selection criteria • Represent mission environment including mobility characteristics of potential nodes & other matters affecting data exchange • Represent diversity of land, sea, air, near-space, space nodes & platforms • Generate or accept data traffic from missile defense mission & other subscribers

24. M&S selection criteria • Flexibility and Scalability • Expansion to arbitrary numbers of distributed, nodes • open and modular software design • Ease of use for the purpose intended • Cost-modeling & simulation must fit the resources allocated to project

25. Major modeling candidates • Network Simulation/Parallel-Distributed Network Sim: Discrete event simulator targeted at networking research (public domain) • Dynamic Network Emulation Backplane Project: Brings multiple network simulators together in single experiment • GloMoSim/Parsec: Scaleable, discrete event, network simulation. Library for the Parallel Simulation Environment for Complex Systems (PARSEC) parallel, discrete event, simulation language (public domain)

26. Major modeling candidates • QualNet: Derived from GloMoSim. Well-supported & maintained COTS product • SSF (Scalable Simulation Framework): Includes SSF Network Models (SSFNet), with "open-source Java models of protocols, network elements, & assorted support classes for realistic multi-protocol, multi-domain Internet modeling & simulation • Dartmouth SSF (DaSSF): Process-oriented, conservatively synchronized parallel simulator

27. Major modeling candidates • OMNet++: Component-based, simulation package suitable for traffic modeling, protocol analysis & evaluating complex software systems. • OPNET: Leading commercial network simulator, including "library of detailed protocol and application models. Widely used to diagnose performance of real-world networks & adjust or reconfigure them. • MLDesigner (MLD): Integrated platform for modeling & analyzing architecture, function & performance of high- level system designs

28. Physical layer modeling • Real world events require more than descriptions of interconnects • Models & simulations of physics & dynamics of executing missions evolve actions that enable “event driven” network models & simulations • Only two enterprises support the needs of this effort well: • FreeFlyer, produced by AI Solutions, • COTS suite that supports the entire specific mission operations lifecycles • Satellite ToolKit (STK), produced by Analytical Graphics, Inc • STK can evaluate complex in-view relationships among dynamic space, air, land and sea objects instantiated in great physical detail

29. STK,STK-COMM STK-V0, STAMP (MFT) STK-OPNET Object exchange OPNET, OPNET Modeler STK-OPNET Co-simulation New or advanced routing, network discovery, protocols & latency- tolerant techniques Co-simulation, hardware in the loop, advanced waveforms Analysis approach Dynamic Comm Paths, Latency, LOS, Doppler Histories Aggregated latencies & network performance Dynamic Comm Paths, Latency, LOS, Doppler Histories Application of Existing Mobile Ad-Hoc Networking Techniques

30. ICO CommSat High Altitude Airship Full Duplex Comms with Interceptors in Flight Representative mission geometry, sensors & links

31. Initial Defensive Operations (IDO)

32. Active links with interceptor

33. Raw accesses to interceptor

34. Doppler histories & free space losses • Approx. 30 db less path loss than to lowest accessible commsat • More favorable physical geometry than to geo comsats • More manageable two-way doppler variations

35. OPNET analysis • Modulation scheme driven by Doppler dynamics • Network discovery & routing driven by node mobility & nomadicity • Protocols driven by required latency, reliability & security • Implementation driven by device envelope, power generation & thermal management, mechanics or electronics of beam formation & steering

36. OPNET: Interceptor communications • “Wired” links • Protocol tailoring • Node processing & buffering • Error correction schemes • Network performance capability vs. realized

37. OPNET: Interceptor communications

38. Missile defense comms

39. Conclusion • STK facilitates analysis of modern mobile ad-hoc networking • “Mobile Networking with Strong Physical Layer Interactions” • Physical phenomena occur on time scales comparable to, or less than, network transactions • Hypervelocity vehicles (including satellites) • Interplanetary missions • STK matched with “wired” network simulations • Event-driven • Physical-world “frozen” during network transactions (OPNET) • Efficiently and uniquely suited for wireless, mobile, ad-hoc networks • We have demonstrated significance of intimate interactions among lower-four OSI layers

40. Summary • Introduction to mobile, ad-hoc, networking • OSI layers • Routing • Disruptive phenomena • Model selection • Physical layer • Link, network & transport layers • Missile defense communication example • Conclusion

41. BACKUPS

42. Flat routing comparisons N : # of nodes in the network e : # of communication pairs in the network

43. Hierarchical routing comparison N : # of nodes in the network M : average # of nodes in a cluster e : # of communication pairs in the network H : # of logical levels L : average # of nodes in a logical group G : # of logical groups in the network

44. Location-assistedrouting comparisons • N = # of nodes in the network • e = # of communication pairs in the network • M = Average # of nodes in a cluster