Transcript Towards Ubiquitous Multihop Wireless Networks: Addressing

Towards Ubiquitous Multihop
Wireless Networks:
Addressing Capacity and Security
Challenges
Ph.D. Defense
Kimaya Mittal
MOMENT Lab, Dept. of Computer Science
University of California, Santa Barbara
Introduction



Ubiquitous Internet access a pressing need
Wireless networks natural choice
Significant benefits



Users: Truly pervasive, untethered, mobile access
Network service providers: Easy, quick
deployment; reduced costs of wiring and
maintenance
New set of challenges
Kimaya Mittal, PhD Defense
Wireless Network Challenges

Different medium characteristics




Shared medium, limited bandwidth =>
limited capacity
Time-variant links, high error rates
Easy accessibility, vulnerability to attack
Different device and usage characteristics


Resource constraints
Mobility
Kimaya Mittal, PhD Defense
Single-hop & Multihop
Wireless Networks Intern et
Intern et
Single-hop
(Access-point-based)
Kimaya Mittal, PhD Defense
Multihop
(Mesh)
Multihop Wireless Networks

Significant benefits over single-hop





Minimize expensive wired infrastructure
Quick deployment
Adaptive and self-configuring
Easy to extend coverage
Tremendous potential to be technology of
choice for ubiquitous access
Kimaya Mittal, PhD Defense
Our Vision
Multihop wireless networks
are the technology of choice
for providing ubiquitous
Internet connectivity, and can
effectively support large user
populations and diverse
applications.
Kimaya Mittal, PhD Defense
Challenges


Multihop exacerbates wireless challenges
Two challenges most significantly obstructing
deployment and use of multihop

Capacity


Security


Inter-flow and intra-flow contention
Routing infrastructure exposed
Must be addressed to realize vision
Kimaya Mittal, PhD Defense
DISSERTATION
OVERVIEW
Ubiquitous
multihop wireless
networks
VISION
CHALLENGES
Capacity
Security
CONTRIBUTIONS
SPATIAL REUSE
COORDINATION AND
CONTROL OF MEDIUM
ACCESS
SECURE ROUTING
INFRASTRUCTURE
Network
Layer
Leveraging
User
Mobility
Intra-flow
Contention
Calculation
Authenticated
Routing
MAC
Layer
Mitigation of
Exposed
Terminals
Perceptive
Communication
Kimaya Mittal, PhD Defense
DISSERTATION
OVERVIEW
Ubiquitous
multihop wireless
networks
VISION
CHALLENGES
Capacity
Security
CONTRIBUTIONS
SPATIAL REUSE
COORDINATION AND
CONTROL OF MEDIUM
ACCESS
SECURE ROUTING
INFRASTRUCTURE
Network
Layer
Leveraging
User
Mobility
Intra-flow
Contention
Calculation
Authenticated
Routing
MAC
Layer
Mitigation of
Exposed
Terminals
Perceptive
Communication
Kimaya Mittal, PhD Defense
Focus of
this talk
Wireless Transmission
Characteristics
V
R
T
W
P
Q
U
S
Kimaya Mittal, PhD Defense
X
Wireless Transmission
Characteristics
Reception range of P
V
R
T
W
P
Q
U
S
Kimaya Mittal, PhD Defense
X
Wireless Transmission
Characteristics
Reception range of P
V
R
T
W
P
Q
U
S
Carrier-sense range of P
Kimaya Mittal, PhD Defense
X
Wireless Transmission
Characteristics
V
R
T
W
P
Q
U
S
X
Carrier-sense range of Q
Carrier-sense range of P
Kimaya Mittal, PhD Defense
DISSERTATION
OVERVIEW
Ubiquitous
multihop wireless
networks
VISION
CHALLENGES
Capacity
Security
CONTRIBUTIONS
SPATIAL REUSE
COORDINATION AND
CONTROL OF MEDIUM
ACCESS
SECURE ROUTING
INFRASTRUCTURE
Network
Layer
Leveraging
User
Mobility
Intra-flow
Contention
Calculation
Authenticated
Routing
MAC
Layer
Mitigation
of Exposed
Terminals
Perceptive
Communication
Kimaya Mittal, PhD Defense
Focus of
this talk
Mitigation of Exposed Terminals:
Introduction
CS range
X
Z





Y
Common artifact of CSMA
Wasted transmission opportunities
Reduced spatial reuse
Hidden Terminals


W
Exposed Terminals
Collisions, wasted capacity
P
CS range
Q
S
R
Complementary effects

Adjustment of CS range / transmit power
decreases one, increases other
Kimaya Mittal, PhD Defense
Prevalence of Hidden and
Exposed Terminals
Kimaya Mittal, PhD Defense

Grid Topology
25 nodes
(5 x 5)

8,688 link
pairs tested at
11 Mbps

37,476 link
pairs tested at
2 Mbps
Proposed Solution



Scope: Static mesh networks
Complementary to tuning of CS threshold
Two phases


Phase 1: Empirical detection of exposed terminals
Phase 2: Coordination of simultaneous
transmissions over exposed links
Kimaya Mittal, PhD Defense
Coordination of Simultaneous
Transmissions

New control messages



Request-To-Send-Simultaneously (RTSS)
Clear-To-Send-Simultaneously (CTSS)
CTSS synchronizes transmissions of mutually
exposed links
CS range
X
Z
W
Y
CTSS
Kimaya Mittal, PhD Defense
Coordination of Simultaneous
Transmissions

New control messages



Request-To-Send-Simultaneously (RTSS)
Clear-To-Send-Simultaneously (CTSS)
CTSS synchronizes transmissions of mutually
exposed links
CS range
X
Z
W
Y
Kimaya Mittal, PhD Defense
CTSS Implementation

CTSS frame before every data packet
generates high overhead


PLCP preamble and header sent at lowest rate
CTSS implemented as header on data packet
PLCP Hdr
CTSS
MAC Hdr
Kimaya Mittal, PhD Defense
Payload
X
CTSS Processing


Z
W
Y
CTSS
CTSS header processed independently as
soon as received
Interface switched to transmit mode
Node W
Transmitting
PLCP Hdr
CTSS Hdr MAC Hdr
(for node Y) (for node X)
Propagation delay
Node Y
CS range
PLCP Hdr
Rcving
CTSS Processed
Rcving
ACK
(from node X)
Payload
MAC Hdr
(for node Z)
Payload
Transmitting
Delay for switching from Rx to Tx mode
Kimaya Mittal, PhD Defense
ACK
(from node Z)
Rcving
The RTSS Message


Motivation: CTSS mechanism to be used only
when necessary
RTSS broadcast by node when required




Triggered by queue size
Lists backed-up links
Broadcast periodically as long as needed
CTSS sent only if RTSS received recently
Kimaya Mittal, PhD Defense
Lost/Unused CTSS

Causes:





Collisions
Transmission errors
Unavailability of data
Sensed interference
Low CTSS overhead critical
Kimaya Mittal, PhD Defense
Important Solution Parameters

CTSS Destination Selection Policy


Key factor impacting percentage of CTSS
successfully used
CTSS Data Rate

Can be different from rate used for data
transmission


PHY layer must know data rate
Tradeoff between range and overhead
Kimaya Mittal, PhD Defense
Evaluation: Grid Topology
A
B
C
D
E


F
G
H
I
J

K
L
M
N
O

P
Q
R
S
T
U
V
W
X
Y
Kimaya Mittal, PhD Defense
Inter-node spacing =
150m
4 gateways at
corners of grid
Pre-configured static
routes from each
node to a gateway
Routes minimize
hops and distribute
nodes evenly among
gateways
Gateway
Evaluation: Impact of CTSS
Destination Selection Policy

Throughput
improvement in
Scenario I



Throughput
improvement in
Scenario II


Kimaya Mittal, PhD Defense
RSS = 40%
Random = 27%
RSS = 16%
Random = 18%
Evaluation: Impact of CTSS
Data Rate
Kimaya Mittal, PhD Defense
Mitigation of Exposed Terminals:
Summary

RTSS/CTSS approach effective

Benefits





Very low overhead
Maintains distributed contention-based nature of
MAC protocol
No time synchronization
Complementary to solutions that tune CS range
Drawbacks


Increased complexity of PHY layer
Implementation with current hardware infeasible
Kimaya Mittal, PhD Defense
Mitigation of Exposed Terminals:
Summary (continued)

Throughput improvement depends on
topology and traffic patterns

Between 15% and 60% in simulated scenarios

Approach most beneficial in dense networks
with strong links

Future Work:



Enhancing CTSS destination selection policy
Dynamic online detection of exposed links
Determining applicability to given network
deployment
Kimaya Mittal, PhD Defense
DISSERTATION
OVERVIEW
Ubiquitous
multihop wireless
networks
VISION
CHALLENGES
Capacity
Security
CONTRIBUTIONS
SPATIAL REUSE
COORDINATION AND
CONTROL OF MEDIUM
ACCESS
SECURE ROUTING
INFRASTRUCTURE
Network
Layer
Leveraging
User
Mobility
Intra-flow
Contention
Calculation
Authenticated
Routing
MAC
Layer
Mitigation of
Exposed
Terminals
Perceptive
Communication
Kimaya Mittal, PhD Defense
Focus of
this talk
Perceptive Communication:
Introduction

Limited capacity makes coordination and control of
medium access critical

With CSMA-based MAC, medium shared with CSN

Medium-related operations depend on/affect
medium state at CSN
Need for communication among CSN

V
R
T
Transmission range
Carrier-sense range
P
Q
W
U
S
Kimaya Mittal, PhD Defense
X
Examples of Need for
Communication Among CSN

Prioritized Medium Access


Admission Control


Need to know bandwidth availability and traffic
priorities at CSN
Topology Control


Need to know priorities of packets at CSN
Need to know number of CSN resulting from
different transmission power settings
Channel Assignment

Need to know CSN at each channel
Kimaya Mittal, PhD Defense
Potential Approaches to
Communicate Among CSN




Direct communication
 Impossible (CS range > Tx range)
High-power transmission [Yang 03]
 More energy, less spatial reuse
Multihop forwarding [Yang 03]
 Requires relay node
Lower rate transmission code
 May not be supported, may not reach all CSN
Kimaya Mittal, PhD Defense
Perceptive Communication


During transmission, change in carrier signal
perceived by CSN
Certain characteristics can be detected



Duration of transmission
Silence between transmissions
Information encoded in perceivable
characteristics

Can be inferred by CSN by monitoring carrier
signal, packet need not be decoded
Kimaya Mittal, PhD Defense
Detection of Perceptive
Characteristics



Node records received signal strength
(RSS) continuously (i.e. in every time
slot)
Tracks signal strength over time
Identifies transmissions and silences
from this information
Kimaya Mittal, PhD Defense
Detection of Transmission
Duration




Idealized graph of
signal strength vs.
time
Packet Y sensed, not
decoded
Duration of packet Y
(Ty) perceived
Information encoded
in and inferred from
Ty
RSS
RxThresh
CSThresh
Kimaya Mittal, PhD Defense
X
Y
Ty
time
Detection of Silence Duration




Every transmission
RSS
preceded by preframe
Inter-frame space
perceived, duration
RxThresh
(Ts) detected
Ts < Tdifs (inter-packet CSThresh
space)
Information encoded
in and inferred from
Ts
Kimaya Mittal, PhD Defense
Pre-frame
Inter-frame space
Packet
Inter-packet space
Y
Ts
Tdifs
Time
Application of Perceptive
Communication

Application-specific codebook


Maps transmission durations or inter-frame
space durations to meanings
Examples

Communication of identity through size of
Hello messages


Size modified by appending ‘tail’
Communication of packet priority through
duration of inter-frame space
Kimaya Mittal, PhD Defense
Testbed Evaluation

Motivation



Do actual graphs of signal strength vs. time
resemble ideal graphs?
How accurately can perceptive characteristics be
measured on wireless hardware?
Implementation

Prototype implementation on Mica2 mote


Only platform with API for per-slot RSS
Challenging platform due to resource constraints
Kimaya Mittal, PhD Defense
Evaluation: Plot of RSSI vs.
Time
Kimaya Mittal, PhD Defense
Evaluation: Effect of Received Signal
Strength
Kimaya Mittal, PhD Defense
Perceptive Communication:
Summary

Perceptive communication among CSN
feasible and effective on wireless hardware




80% detection accuracy when clearly out of
reception range
Detection accuracy can be improved with more
sophisticated detection algorithm
Powerful mechanism
Creates new possibilities for managing
wireless medium

Several potential applications
Kimaya Mittal, PhD Defense
DISSERTATION
OVERVIEW
Ubiquitous
multihop wireless
networks
VISION
CHALLENGES
Capacity
Security
CONTRIBUTIONS
SPATIAL REUSE
COORDINATION AND
CONTROL OF MEDIUM
ACCESS
SECURE ROUTING
INFRASTRUCTURE
Network
Layer
Leveraging
User
Mobility
Intra-flow
Contention
Calculation
Authenticated
Routing
MAC
Layer
Mitigation of
Exposed
Terminals
Perceptive
Communication
Kimaya Mittal, PhD Defense
Focus of
this talk
Basic idea: Users get more bandwidth by
moving to less-loaded network location
 Even traffic distribution, better spatial reuse
 Network intelligently directs users
 Users are selfish, motivated by self-gain only
 Game-theoretic analysis of stability
CONTRIBUTIONS

SPATIAL REUSE
IMPROVING
COORDINATION AND
CONTROL OF MEDIUM
ACCESS
SECURING
ROUTING
INFRASTRUCTURE
Network
Layer
Leveraging
User
Mobility
Intra-flow
Contention
Calculation
Authenticated
Routing
MAC
Layer
Mitigation of
Exposed
Terminals
Perceptive
Communication
Kimaya Mittal, PhD Defense





Essential component of network admission control
Two protocols proposed: PRP and RRT
Use perceptive communication
Upto 60% less latency and 50% less overhead
Some loss of accuracy
CONTRIBUTIONS
SPATIAL REUSE
COORDINATION AND
CONTROL OF MEDIUM
ACCESS
SECURE ROUTING
INFRASTRUCTURE
Network
Layer
Leveraging
User
Mobility
Intra-flow
Contention
Calculation
Authenticated
Routing
MAC
Layer
Mitigation of
Exposed
Terminals
Perceptive
Communication
Kimaya Mittal, PhD Defense




One of the first security analyses of
popular wireless routing protocols
Describes and classifies several attacks
Defines different security environments
Presents secure routing protocol ARAN
CONTRIBUTIONS
SPATIAL REUSE
COORDINATION AND
CONTROL OF MEDIUM
ACCESS
SECURE ROUTING
INFRASTRUCTURE
Network
Layer
Leveraging
User
Mobility
Intra-flow
Contention
Calculation
Authenticated
Routing
MAC
Layer
Mitigation of
Exposed
Terminals
Perceptive
Communication
Kimaya Mittal, PhD Defense
Summary


Limited capacity and security two of the
biggest challenges obstructing widespread
deployment and use of multihop wireless
networks
Our contributions address challenges by:



Increasing spatial usage of medium
Enabling better coordination and control of
medium access
Securing routing infrastructure
Kimaya Mittal, PhD Defense
Publications








K. Mittal and E. Belding. “RTSS/CTSS: Mitigation of Exposed Terminals in Static
802.11-Based Mesh Networks”. WiMesh 2006.
A. Jardosh, K. Mittal, K. Ramachandran, E. Belding, and K. Almeroth. “IQU: Practical
Queue-based User Association Management for WLANs”. MobiCom 2006.
K. Sanzgiri, I. Chakeres, and E. Belding-Royer. “The Utility of Perceptive
Communication between Distant Wireless Nodes”. TridentCom 2006.
K. Sanzgiri, I. Chakeres, and E. Belding-Royer. “Pre-Reply Probe and Route Request
Tail: Approaches for Calculation of Intra-Flow Contention in Multihop Wireless
Networks”. MONET Journal 2006.
K. Sanzgiri, B. Dahill, D. LaFlamme, B. Levine, C. Shields, and E. Belding-Royer. “An
Authenticated Routing Protocol for Secure Ad Hoc Networks”. JSAC 2005.
K. Sanzgiri, I. Chakeres, and E. Belding-Royer. “Determining Intra-Flow Contention
Along Multihop Paths in Wireless Networks”. BroadNets 2004.
K. Sanzgiri and E. Belding-Royer. “Leveraging Mobility to Improve Quality of Service in
Mobile Networks”. MobiQuitous 2004.
K. Sanzgiri, B. Dahill, B. Levine, C. Shields, and E. Belding-Royer. “A Secure Routing
Protocol for Ad Hoc Networks”. ICNP 2002.
Kimaya Mittal, PhD Defense
Impact

Solutions for better spatial reuse



Perceptive communication



Explore previously untapped approaches
Spawn new avenues for further research
Powerful technique
Creates new possibilities for medium management
Secure routing


Pioneering work
Referenced/extended by several researchers
Kimaya Mittal, PhD Defense
What’s Next?


Capacity problem far from solved
What more is needed?


PHY layer advancements
New MAC protocol for multihop



Better spatial, temporal, spectral reuse
PHY/MAC evaluation on real deployments
Tools for practical application of research
Kimaya Mittal, PhD Defense
Conclusion



Contributions significantly advance
state-of-the-art in wireless networking
Open various avenues for further
research
Bring vision of ubiquitous multihop
wireless network closer
Kimaya Mittal, PhD Defense
Thank you!
Questions/Comments?