Wireless Up Layers

1. Wireless Up Layers

2. Outline • MANETs • Overview • Network Routing Protocols • Transport Layer Protocols • Content Sharing Applications

3. MANET Overview • Set of wireless mobile devices dynamically set up temporary network • No central infrastructure • Flexible and cost-effective Adapted from Fig. 16.1 in [1]. Line thickness indicates link strength.

4. MANET Overview (2) • Various applications: • Disaster recovery • Military operations • Vehicular networking • Content sharing (our focus) • Central challenges: • Time-varying wireless channel: interference, noise • Network topology control • Robust routing with single-hop failures • Power conservation

5. Network Layering in MANETs (1) • Physical layer: transmit bits over wireless link • Modulation, coding, diversity, etc. [1] • Not our focus • MAC layer: controls how users access shared wireless channel • Mechanisms: ALOHA, CSMA, scheduling • Power control • Error recovery Adapted from Figure 16.2 in [1].

6. Routing in MANETs • Aim: determine “optimal” way of finding “optimal” nodes • Dynamic links • Broken links must be updated when a node moves out of communication range with another node • New links must be formed when a node moves into communication range with another node • Based on this new information, routes must be modified • Frequency of route changes: a function of node mobility

7. Proactive vs. Reactive Routing • Proactive routing: nodes continuously evaluate & update routes • Periodic updates • Triggered updates—when a link changes • Efficient if routes used often • Large amount of overhead • Similar to conventional routing protocols • Reactive routing: nodes evaluate and update routes only when they are needed • When a node has a packet to send, it checks to see if it has a valid route • If no valid route known, node must send out a route-request message to obtain a valid route (controlled flooding of network) • Data sent using valid route • Efficient if routes not used often

8. Proactive Routing Protocols • Each node maintains consistent, up-to-date routing information in the form of a table with the next hop to reach each node in the network • Changes in link state transmitted throughout the network to update each node’s routing table • Proactive routing protocols • Destination sequenced distance vector (DSDV) • Cluster head gateway switch routing (CGSR)

9. Reactive Routing Protocols • Routes created only when needed • Requires “route discovery” and “route maintenance” • Also called “source-initiated on-demand routing” • Goal: minimize amount of overhead compared with proactive routing at the expense of latency in finding a route when it is needed • Reactive routing protocols • Ad hoc on-demand distance vector (AODV) • Dynamic source routing (DSR)

10. Problems of Current TCP • TCP cannot distinguish wireless errors from congestion. • Frequent errors ⇒ Frequent window reductions ⇒ Low throughput

11. TCP Over Wireless • Link Layer Mechanisms • TCP Aware Link Layer Protocols • Explicit Notification Schemes • TCP-BuS • Ad Hoc TCP (ATCP) • Partial ACK Mechanisms • Split TCP Solutions • Other Transport Schemes

12. Snoop Protocol • Split connection and link level retransmission • Base monitors returning ACKs. Retransmits on duplicate ACKs and drops the duplicate ACK • Advantages: Only soft state at BS. Only BS modified. No changes to FH or MH. • If wireless link delay is less than 4 packets, 3 duplicate ACKs will not happen and a simple link-level retransmission without dropping duplicate ACK will also work. • Disadvantages: Does not work with encrypted packets • Does not work on asymmetric paths

13. WTCP • Similar to Snoop • Snoop can cause increased RTT • WTCP corrects RTT by modifying the timestamp in returning ACKs • Disadvantages: • Useful only if retransmission times are large (> 1 tick) • Does not work on shared LANs, where overload ⇒ increased delay

14. Content Sharing in MANETs • Existing mobile handset solutions • Others’ research work • Our own work: Enclave

15. Existing Mobile Handset Solutions • LoKast [13] • Creates “Spaces” in physical proximity where users share content • LoKast builds on AllJoyn [14] middleware bridging WiFi (Direct), cellular networks, and the Internet • Frostwire [15]: BitTorrent client; upload/download files over WiFi networks • Can also set up ad hoc/master mode WiFi, share via media server LoKast FrostWire

16. Research in Content Sharing • P2P content distribution in Bluetooth MANETs [16] • BitTorrent over Bluetooth [17] • Network coding seems to help content sharing protocols adapt to dynamic MANET topology [18] • Haggle [19]: content sharing middleware for mobiles • Publish/subscribe systems for content sharing [20]

17. Our Research Work: Enclave Context: Ubiquitous Electronic World

18. Sources of Electronic Information Fixed Locations Mobile Objects People with smartphones Vehicles transmitting signals • Building history • Store advertisements Art Deco style John Buckeye Student, OSU 20% off Traffic accident Hybrids: e.g., people relaying store coupons or traffic accidents

19. A Key Problem • Promote unobtrusive, secure communications with the electronic world • Significance: • Smartphone users want easy interactions with real-world electronic information sources, e.g.: • Discover nearby buildings, attractions in an area • Social networking in physical proximity • Quickly relay emergency bulletins to nearby people • Currently, wireless communications hinder such interactions in the electronic world • Need manual connection establishment, network configuration

20. State of the Art • Our current research work solved this problem • Paper accepted at WASA 2012 • Design and implement Enclave, system for unobtrusive and secure communication with electronic world

21. Challenge (1): Electronic Barrier • Wireless communications technology forms “electronic barrier” • Information in electronic signals coded, modulated for reliable communication • Entails tedious connections, configurations • Hinders unobtrusive communication with electronic world

22. Challenge (2): Security Concerns • Wireless users not filtering information at risk of attack • Exposure to obscenity • Malicious codes, battery-drain attacks, … • “Hardens” electronic barriers

23. Our Solution: Enclave • We propose Enclave, a system that promotes unobtrusive and secure communication with the electronic world

24. Enclave (1) • Separate delegate wireless device ( ) between owner’s smartphone ( ) and electronic world

25. Enclave (2) • Delegate device is enclave device ( ); smartphone is master device ( ) • Enclave device can be remotely reset

26. Rationale for Separation • Can implement Enclave on single smartphone • Too heavyweight for single device • Risky: • Sensitive data on smartphones • Malicious code detection not fully studied • Enclave device: rented, old mobile device • Enclave differs from sandbox and proxy • Aim: promote secure, unobtrusive communication with electronic world

27. Enclave Architecture • Enclave device filters data from electronic world • Security filter screens for malicious code • User policy determines what master receives

28. Supporting Technologies • Unobtrusive communication: NameCast • Publish short messages via wireless names (no connection) • Lowers the electronic barrier • Facilitates mass P2P information dissemination • Secure communication: PicComm • Transmit textual images from Enclave to master, which parses text using optical character recognition (OCR) • Proximate visual channel encumbers snooping • Feedback via NameCast or sound

29. NameCast • Goal: unobtrusive communication between mobiles, electronic world • Problem: Discovery processes too slow • Leverage strengths of Bluetooth/WiFi so they can help each other • Use WiFi to control Bluetooth • Piggyback message dissemination atop discovery Bluetooth/WiFi Discovery Times Bluetooth/WiFi Characteristics

30. NameCast Forwarding Example Note: +means discovered

31. Reliable NameCast Forwarding • Leverage fountain codes for large-scale forwarding • Concepts: • Bluetooth frame: message with all nearby devices’ Bluetooth names • Encoded chunk: piece of (encoded) Bluetooth frame (chunks equal sized) • Devices keep generating Bluetooth frames; publishing/receiving chunks via Bluetooth; scanning for control frames via WiFi + means discovered - means not discovered # chunks to decode frame Bluetooth frame ID Fountain coding in use

32. PicComm • Uses visual channel for “picture communication” among enclave, master devices • Impetus: wireless communication shows MAC address, attacks possible • Enclave device displays textual images; master device takes picture, performs OCR • Problems: • OCR not always accurate • Screen size fixed (limit font size) Enclave device Textual image… Textual image… Master device

33. Dynamic Resolution Adjustment (1) • Resolution: font size and letter spacing • CRC code at bottom of enclave device screen • Rest of screen partitioned into blocks • For each block: • Master device sends ACK to enclave device if OCR successful, NAK otherwise (NameCast, sound) • If NAK, increase resolution

34. Dynamic Resolution Adjustment (2) • Design “locality-sensitive” OCRHash to pinpoint OCR errors (per block) • Probability of recognizing char C as Ei [2]: • Group chars by OCRHash grouping approach

35. References (1) • A. Goldsmith, Wireless Communications, Cambridge University Press, 2005. (chap. 16) • C.-K. Toh, Ad Hoc Mobile Wireless Networks: Protocols and Systems, Prentice Hall, 2001. (chap. 11) • P. Zheng and L. M. Ni, Smart Phone & Next Generation Computing, Morgan Kaufmann, 2006. • http://w3.antd.nist.gov/wahn_home.shtml • X. Lin, N. B. Shroff, and R. Srikant, “A Tutorial on Cross-Layer Optimization in Wireless Networks,” IEEE Journal on Selected Areas in Communications, 24(8), Aug. 2006 • S. Boyd and L. Vandenberghe, Convex Optimization, Cambridge University Press, 2004 • W. Heinzelman, ECE 586: Advanced Topics in Wireless Networking, University of Rochester, 2005, http://www.ece.rochester.edu/courses/ECE586/lectures/ • C. S. R. Murthy and B. S. Manoj, Ad Hoc Wireless Networks: Architectures and Protocols, Prentice Hall, 2004.

36. References (2) • E. Royer, S.-J. Lee and C. Perkins, “The Effects of MAC Protocols on Ad hoc Network Communication,” Proc. IEEE Wireless Communications and Networking Conf. (WCNC), 2000. • E. M. Royer and C.-K. Toh, “A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks,” IEEE Personal Communications, Apr. 1999, pp. 46–55. • J. Broch, D. Maltz, D. Johnson, Y.-C. Hu, and J. Jetcheva, "A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols," Proc. ACM MobiCom, Oct. 1998. • R. Jain, “TCP Over Wireless Networks,” 2006, http://www.cse.wustl.edu/~jain/cse574-06/ • LoKast, http://www.lokast.com • AllJoyn, https://www.alljoyn.org/ • FrostWire, http://frostwire.com • U. Lee,S. Jung, D.-K. Cho, A. Chang, J. Choi, and M. Gerla, “P2P Content Distribution to Mobile Bluetooth Users,” IEEE Trans. on Vehicular Technology, 59(1), 2010, pp. 356–367.

37. References (3) • S. Jung and U. Lee and A. Chang and Cho, D.-K. and M. Gerla, “Bluetorrent: Cooperative Content Sharing for Bluetooth Users,”Pervasive and Mobile Computing, 3(6), 2007, pp. 609–634 • U. Lee, J.-S. Park, S.-H. Lee, W. W. Ro, G. Pau and M. Gerla, “Efficient Peer-to-peer File Sharing using Network Coding in MANET,”Proc. ACM MobiShare, 2006. • J. Su, J. Scott,P. Huim, J. Crowcroft, E. de Lara, C. Diot, A. Goel, M. H. Lim, and E. Upton, “Haggle: Seamless Networking for Mobile Applications,” Proc. Int’l. Conf. on Ubiquitous Computing, 2007 • O. R. Helgason, E. A. Yavuz, S. T. Kouyoumdjieva, L. Pajevic, and G. Karlsson, “A Mobile Peer-to-Peer System for Opportunistic Content-Centric Networking”, Proc. ACM MobiHeld, 2010.