Ad Hoc Networks A New Communication Paradigm

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Ad Hoc Networks - A New Communication Paradigm?
Prof. Zygmunt J. Haas Wireless Networks
Laboratory School of Electrical Engineering
Cornell University, Ithaca, NY
14853 haas_at_ee.cornell.edu http//www.ee.cornell.ed
u/haas/wnl.html
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Introduction to Ad-Hoc Networks ?

• Ad-hoc networks are network architecture
• that can be rapidly deployed
• that do not rely on pre-existing infrastructure
• whose set of nodes is continuously changing
• which self-adapts to the connectivity and
  propagation patterns, and
• which adapts to the traffic and
• mobility patterns
• Establishment of the IEFT MANET Working Group to
  study IP-based routing in ad-hoc networks

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Use of the Ad-Hoc Technology for Military
Communications
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Ubiquitous networking
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Applications of Ad-Hoc Networks

• Application of the ad-hoc network technology is
  appropriate when a network needs to be rapidly
  deployed without prior planning and to provide
  reliable communication in harsh propagation
  conditions.
• Example of applications
• Military for tactical communications
• National security in times of natural disaster
  or global war
• Rescue missions in lieu of adequate wireless
  coverage
• Law enforcement similar to tactical
  communications
• Commercial use for setting up sales
  presentations
• Education wall-free (virtual) classrooms
• Local Area Networks (LANs) for limited-coverage
  communication
• Sensor Networks
• Extension of the cellular technology

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Challenges in Ad-Hoc NetworksZ.J. Haas and S.
Tabrizi, On Some Challenges and Design Choices
in Ad-Hoc Communications, IEEE MILCOM98

• The challenges in the design of Ad-Hoc networks
  stem from the following facts
• the lack of centralized entity ? self-organizing
  and distributed protocols
• the possibility of rapid platforms movement
  (highly versatile topology) ? efficient and
  robust protocols
• all communication is carried over the wireless
  medium ? power and spectrum efficient
  communications
• Compare this with the fixed (cellular) networks

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Characteristics of Ad-Hoc Networks

• The distinctive differences between ad-hoc
  networks and cellular networks are
• no fixed infrastructure is present
• multi-hop routing (network diameter gtgt node
  transmission range)
• peer-to-peer operation
• frequent changes of associations

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Challenges of Ad-Hoc Networks?

• Application/Market penetration
• is multihop technology commercializable?
• Design/Implementation
• reliable, manageable, survivable, and secure
• Operational/Business-related
• how to manage the network? how to bill for
  services?

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Some Ad-Hoc Architectural Design Choices

• Routing/Mobility Management
• Proactive vs. Reactive Routing Protocol
• Medium Access Control
• To Sense or Not to Sense, this is a question!
• Multimedia Traffic
• How to handle QoS for real-time traffic? Is it
  possible at all?
• Security
• Authentication, Authorization, Privacy, in the ad
  hoc networking environment.

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An Introduction to Ad-Hoc Networks

• Selected examples of ad-hoc architectural
  choices
• flat vs. hierarchical (multi-tiered) network
• proactive vs. reactive routing protocols
• degree of globalization in topological changes
• frequency of communication of topological changes
• criteria for route selection / max route
  determination
• sizing of nodal transmission radius
• synchronized vs. unsynchronized operation
• CSMA vs. dialog-based MAC

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The Ad-Hoc Networks Design Choices

• The Flat Network Architecture

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The Ad-Hoc Networks Design Choices

• Hierarchical Ad-Hoc Network Architecture

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Proactive Vs. Reactive Routing

• Proactive Protocols
• continuously update the reachability
• information at all the network nodes
• when a route is requested, it is immediately
  available
• examples of proactive protocols are
  Distance-Vector (DV), Shortest Path First (SPF),
  Open Shortest Path First (OSPF)
• Proactive protocols are inappropriate for the
  ad-hoc networking environment as they waste too
  much wireless resources, especially for large,
  highly mobile network.

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Proactive Vs. Reactive Routing

• Reactive Protocols
• discover routes only upon demand
• involve some sort of global search
• there may be a significant delay
• associated with the route discovery
• examples of reactive protocols are the family of
  flooding protocols
• Reactive protocols are inappropriate for the
  ad-hoc networking environment as they are too
  slow and consume too much network resources,
  especially for large, highly mobile network.

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Routing Protocols for Ad-Hoc Networks

• The following are few examples of routing
  protocols
• for ad-hoc networks
• ? OLSRP Optimized Links State Routing
  Protocol
• draft-ietf-manet-olsrp-04.txt
• ? DSR Dynamic Source Routing
• draft-ietf-manet-dsr-05.txt
• ? AODV Ad-hoc On-Demand Distance Vector
• draft-ietf-manet-aodv-08.txt
• ? TORA Temporary-Ordered Routing Algorithm
• draft-ietf-manet-tora-spec-03.txt
• ? ZRP Zone Routing Protocol
• draft-ietf-manet-zone-ierp-01.txt
  draft-ietf-manet-zone-iarp-01.txt draft-i
  etf-manet-zone-brp-01.txt

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Optimized Link State Routing Protocol (OLSRP)

• The OLSRP is a proactive protocol.
• It is an optimization based on the pure link
  state routing algorithm.
• It uses the Multi-Point Relays (MPRs) to
  determine the route to a destination in the
  network. (MPRs are selected nodes that forward
  messages as part of the flooding process.)
• An OLSRP route consists of the identity of the
  MPRs.
• OLSRP is particularly suitable for large and
  dense networks.

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Common Features of Reactive Routing Protocols
(i.e. AODV, DSR, TORA)

• Route discovery process is initiated only when a
  route is needed.
• Route discovery is based on the exchange of
  queries and replies.
• Route queries are broadcast.
• Route discovery process may produce multiple
  routes.
• Protocol design ensures loop freedom of routes.
• A route maintenance mechanism is provided to
  inform nodes of invalid routes.

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Zone Routing Protocol (ZRP) Z.J. Haas and M.R.
Pearlman, "The Performance of Query Control
Schemes for the Zone Routing Protocol," ACM/IEEE
Transactions on Networking, August 2001

• The Zone Routing Protocol (ZRP) is a hybrid
  between the proactive and reactive protocol
  schemes. A salient feature of the protocol is
  that it can adjust to the network, traffic, and
  mobility conditions based on sizing a single
  parameter - the Zone Radius.

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The Notion of a Routing Zone

• A routing zone is defined for each node and
  includes the nodes whose minimum distance in hops
  from the node in question is at most some
  predefined number, which is referred to here as
  the zone radius.

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Definition of a
Zone Radius
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The Notion of Peripheral Nodes

• Nodes, whose minimum distance from the node in
  question is exactly equal to the zone radius are
  referred to as peripheral nodes.

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Definition of a
Zone Radius
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The Bordercasting Operation

• Bordercasting is an operation of sending a
  location query by a node to all or some of its
  peripheral nodes.

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Definition of a
Zone Radius
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The Operation of the ZRP
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An example of IERP operation
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The ZRP Constituents

• ZRP consists of two subprotocols
• IntrA-zone Routing Protocol (IARP) and
• IntEr-zone Routing Protocol (IERP)
• Using IARP, a node learns the topology of its
  zone only. Since the zone is much smaller than
  the network, the amount of the control traffic is
  significantly reduced.
• Using IERP, a destination beyond the sources
  zone is efficiently searched. Since the search
  progresses in quantum of zone radius, it is
  fast and consumes much less resources.

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How to terminate the search?
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Desired
Desired
search
search
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direction
direction
Desired
search
. . .
direction
source
. . .
. . .
Desired
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search
Desired
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direction
search
direction
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Guiding the search in desirable directions
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Flood termination techniques

• Loopback Search Prevention 1 A bordercasted-to
  node that receives a query checks whether any
  nodes in the Accumulated Route are within its
  routing zone.

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Some Representative ZRP Performance Results
ZRP traffic relative to flood search vs routing
zone radius
ZRP route query response time vs routing zone
radius
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Typical ZRP Characteristic Curves
control traffic volume
proactive
reactive
zone radius
optimal zone radius
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CSMA vs. RTS/CTS-based access ...

• Collisions occur at the receiver, not at the
  transmitter
• The above observation results in two access
  problems
• the hidden terminal problem, and
• the exposed terminal problem

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The hidden-terminal problem
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The exposed-terminal problem
?
B
C
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D
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The RTS/CTS - dialogue

• An alternative to Carrier Sensing was proposed in
  which the coordination among the stations is
  performed by two basic control messages
  Request-To-Send and Clear-To-Send.
• These messages reserve spatially and
  temporarily the channel for the
  about-to-communicate nodes.

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The RTS/CTS - dialogue
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B
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RTS
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CTS
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DATA
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MAC Protocols for Ad-hoc Networks

• The following are examples of MAC protocols,
  as they might apply to the ad-hoc communication
  environment.
• ? MACA
• ? MACAW
• ? FAMA
• ? DBTMA

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Dual Busy Tone Multiple Access(Z.J. Haas and J.
Deng, Dual Busy Tone Multiple Access (DBTMA) A
New Medium Access Control for Packet Radio
Networks, IEEE Transactions on Communications)

• DBTMA solves the hidden and the exposed terminal
  problems by separating the two communication
  directions through the use of two Busy Tones - a
  receive busy tone (BTr) and a transmit busy tone
  (BTt).
• In DBTMA, data packets are never destroyed and
  the exposed terminal problem is addressed.

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Dual Busy Tone Multiple Access(DBTMA) (cont)

• Use two busy tones
• BTr set up by receiver, protecting data packets
• BTt set up by transmitter, notifying neighbor
  nodes
• Nodes sensing these tones need to defer

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DBTMA performance

• Nodes in N independent groups competing to send
  to a common receiver
• Each group contains large number of nodes
• Comparison of the performance of DBTMA with
  different busy tone sensing delay and other
  schemes

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Supporting QoS in Ad Hoc Networks

• Due to the frequent reconfiguration rate of ad
  hoc networks, the lifetime of links (and
  correspondingly of paths) tend to be limited. As
  such, a natural question arise whether it is
  possible to support QoS communication in such a
  dynamic network topology.
• A more general question is what are the ranges of
  the network parameters (e.g., network size,
  number of nodes, nodal mobility, etc) for which
  some definition of QoS communication can be
  supported.

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What is Multipath Routing? A. Tsirigos and Z.J.
Haas Using Multipath Routing In a Mobile Ad Hoc
Network EnvironmentNetworks, MILCOM01

• Instead of using a single path (route) between
  source and destination, many - preferably
  disjoint - paths are utilized in order to send
  data.
• The goal is to provide load balancing, reduced
  end-to-end delay and improved packet delivery
  ratio (reduced probability that the message needs
  to be dropped).

path 3
Source
Destination
path 1
path 2
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The routing scenario

• Assume that n paths are available from source to
  destination, with max number of paths nmax
• The i-th path has a probability of failure pi (
  equivalently the success probability of each path
  is qi 1-pi )
• Each packet at the source is fragmented into
  multiple blocks and a certain number of overhead
  blocks is computed (Diversity Coding)

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Performance Improvement

• The maximum gain is defined as

Maximum gain for r lt 2
0.35
n
10
max
n
20
0.3
max
n
30
max
0.25
0.2
- maximum gain
0.15
max
G
0.1
0.05
0
0.4
0.5
0.6
0.7
0.8
0.9
1
q - path success probability
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QoS in Ad Hoc Networks through the use of
Multipath Routing

• The use of multiple paths along with diversity
  coding increases the packet delivery ratio.
• The evaluation of the packet delivery ratio can
  be achieved even when only general information
  about the path quality (average and standard
  deviation) is available.
• Improvement in the packet delivery ratio can also
  be achieved when the paths are not independent,
  but experience some correlation.

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Securing Ad-Hoc Networks L. Zhou and Z.J. Haas,
Securing Ad Hoc Networks,IEEE Network Magazine,
vol. 13, no.6, November/December 1999

• Secure lower layers (e.g., MAC)
• Secure routing
• Secure high-level communication
• Availability
• Authentication
• Integrity Public Key
  Infrastructure
• Confidentiality
• Nonrepudiation

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Securing Ad-Hoc Networks (cont)

• Security is important for many ad hoc networks
  application e.g., military communications, but
  its also a tough problem
• The main problems in securing ad hoc
  communications are
• lack of a central element e.g., no CA
• frequent changes of topology trust relations are
  change frequently as well
• vulnerable wireless transmission medium e.g.,
  easy eavesdropping, denial of service,
  impersonation, replay, etc, attacks
• scalability to large networks is required

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Securing Ad-Hoc Networks (cont)

• Our approach is to rely on two principles
• (1) high degree of redundancy in the network
  topology
• (2) distribution of trust among many network
  nodes, rather than relying on a single or small
  set of nodes
• (2) assumes that if the probability of having t
  nodes being compromised at any point in time is
  small, distributing the trust among t1 nodes
  suffices to ensure sufficient level of security

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Some final thoughts ...

• Although the ad hoc networking technology is an
  exciting new direction do not tear down your
  cellular infrastructure yet ?
• The most promising direction (in my opinion) for
  wide commercial technology transfer is the
  extension of the cellular infrastructure (4G
  systems (?)) and extensions of current wireless
  LAN technologies.

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Some final thoughts (cont)

• The hot topics in studying the ad hoc networking
  technology are (still)
• scalable routing/mobility management
• multicasting
• integration with other wireless/wired
  technologies
• support for real-time multimedia traffic (QoS)
• security and access control
• service discovery and node configuration

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• Thank you for listening!

Happy Summer Vacation!