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.
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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

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Proactive vs. Reactive Routing

• Proactive routing nodes continuously evaluate
  update routes
• Periodic updates
• Triggered updateswhen 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

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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 nodes routing table
• Proactive routing protocols
• Destination sequenced distance vector (DSDV)
• Cluster head gateway switch routing (CGSR)

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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 (gt
  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

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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

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Our Research Work Enclave
Context Ubiquitous Electronic World
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Sources of Electronic Information

• Fixed Locations

• Mobile Objects

• Building history
• Store advertisements

• People with smartphones
• Vehicles transmitting signals

Art Deco style
John Buckeye Student, OSU
20 off
Traffic accident
Hybrids e.g., people relaying store coupons or
traffic accidents
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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

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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

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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

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Challenge (2) Security Concerns

• Wireless users not filtering information at risk
  of attack
• Exposure to obscenity
• Malicious codes, battery-drain attacks,
• Hardens electronic barriers

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Our Solution Enclave

• We propose Enclave, a system that promotes
  unobtrusive and secure communication with the
  electronic world

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Enclave (1)

• Separate delegate wireless device ( ) between
  owners smartphone ( ) and electronic world

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Enclave (2)

• Delegate device is enclave device ( )
  smartphone is master device ( )
• Enclave device can be remotely reset

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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

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Enclave Architecture

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

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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

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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

Protocol Windows Mobile 6.1 Android 2.3
Bluetooth 1822 s 1020 s
WiFi 1.01.1 s 1.11.2 s
Bluetooth/WiFi Discovery Times
Protocol Length (bytes) Discovery time (s)
Bluetooth 248 10.24 s (inquiry) 12 s (paging)
WiFi 32 12 s
Bluetooth/WiFi Characteristics
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NameCast Forwarding Example
Note means discovered
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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
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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

OCR Performance Font Size Letter spacing
Good Large Large
Fair Medium Medium
Poor Small Small
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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
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References (1)

1. A. Goldsmith, Wireless Communications, Cambridge
   University Press, 2005. (chap. 16)
2. C.-K. Toh, Ad Hoc Mobile Wireless Networks
   Protocols and Systems, Prentice Hall, 2001.
   (chap. 11)
3. P. Zheng and L. M. Ni, Smart Phone Next
   Generation Computing, Morgan Kaufmann, 2006.
4. http//w3.antd.nist.gov/wahn_home.shtml
5. 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
6. S. Boyd and L. Vandenberghe, Convex Optimization,
   Cambridge University Press, 2004
7. W. Heinzelman, ECE 586 Advanced Topics in
   Wireless Networking, University of Rochester,
   2005, http//www.ece.rochester.edu/courses/ECE586/
   lectures/
8. C. S. R. Murthy and B. S. Manoj, Ad Hoc Wireless
   Networks Architectures and Protocols, Prentice
   Hall, 2004.

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References (2)

1. 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.
   
2. 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. 4655.
3. 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.
4. R. Jain, TCP Over Wireless Networks, 2006,
   http//www.cse.wustl.edu/jain/cse574-06/
5. LoKast, http//www.lokast.com
6. AllJoyn, https//www.alljoyn.org/
7. FrostWire, http//frostwire.com
8. 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. 356367.

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References (3)

1. 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. 609634
2. 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.
3. J. Su, J. Scott,P. Huim, J. Crowcroft, E. de
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