Routing in DelayTolerant Networks

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Routing in Delay-Tolerant Networks

• Presented by Hui Guo
• Dept of Sys. Computer Science
• Howard University

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DTN characteristics

• challenge mobile environments
• No end-to-end path existed all the time
• The reason
• Mobility
• radio range
• Obstructions
• Energy
• node density, etc.

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Category of DTN

• General category of DTN
• intermittently connected
• sparse
• disconnected
• highly partitioned
• opportunistic network.

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Applications

• Applications
• military networks,
• sensor networks for wildlife tracking,
• inter-planetary networks,
• remote rural communities accessing,
• pocket switched networks (social networks),
• vehicular ad hoc networks,
• underwater networks, etc.

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Mobility-assisted routing

• Is it possible that data can be delivered?
• path between a source and a destination maybe
  always wont exist
• Solution
• Traditional protocols Internet (RIP, OSPF) Ad
  hoc (DSR, AODV) would fail
• Formerly, mobility viewed as evil Now, its
  perfect
• Node mobility would be exploited to help deliver
  message (mobility-assisted or store-carry-and-forw
  ard)

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Overview of Routing schemes

• Two categories
• auxiliary nodes assisted (ANA) routing
• a set of special auxiliary nodes needed to assist
  data delivery
• independent mobile nodes (IMN) routing
• there is not any additional participants in the
  deployment area
• message delivery achieved by nodes inherent
  movement
• Proactive reactive

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ANA routing scheme

• Auxiliary Nodes Assisted routing
• there are a set of special auxiliary nodes around
  the deployment area and are responsible for
  carrying data between nodes
• Idea
• creating more contact opportunities actively
• Typical works
• Message Ferry Zhao et al. 2004, 2005
• ThrowBoxes Zhao et al. 2006
• Autonomous agents Burns 2005
• Courier nodes Koc 2005, etc.

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Message Ferrying

• Scheduled mobility use special mobile nodes
  (Ferry nodes) and designed trajectory

• Suitable for in the presence of network
  partitions
• Controlled mobility
• Predetermined node trajectory

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Message Ferrying

• Determine the ferry routes satisfy a required
  performance

The problem design optimal trajectories
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DTN without Throwboxes
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DTN with Throwboxes
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IMN routing scheme

• Independent mobile nodes routing
• exploits existing node mobility to help deliver
  data, i.e., message delivery solely relies on
  nodes inherent movement rather than any
  additional participants
• Idea
• a mobile node carries a packet for a period of
  time as part of realizing a path from source to
  the destination
• Two categories
• Flooding-based
• Knowledge-based

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Flooding-based Proposals

• Flooding everyone gets a copy (Epidemic Routing
  - Vahdat et al. 00)
• Note optimal delay only when traffic is very
  low!
• Reducing the overhead of flooding
• Randomized Flooding (Y. Tseng et al. 02)
  handover a copy with probability p lt 1
• Utility-based Flooding (A. Lindgren et al. 03)
  handover a copy to a node with a utility at least
  Uth higher than current
• Can use p and Uth to tradeoff transmissions for
  delay, BUT

Dilemma low p / high Uth? significant delay
increase high p / low Uth? degenerates to
flooding
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Epidemic Routing

• Give a message copy to every node encountered
• essentially flooding in a disconnected context

• Generate too much transmissions!

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Direct transmission

• Forward message only to its destination
• simplest strategy
• minimizes transmissions

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Randomized Flooding (Gossiping)

• Spread the message with a probability p 1 (Y.
  Tseng et al. 02)
• p 1) epidemic
• p 0) direct transmission

Outcome lt p) Give a copy
Outcome gt p) Dont give copy
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K-neighbor Epidemic

• Each node receiving a copy, can copy it again up
  to K times (spray and wait, Spyropoulos et al 05)

Already given 2 copies! Node E cannot fwd more
K 2
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Utility-based Routing
(A. Lindgren et al. 03)
D
Last encounter timers
Utility UX(Y) f(tX(Y)) Policy forward to B if
UB(D) gt UA(D) Uth
t(D) 26

• tX(Y) time since X last saw Y
• Indirect location information
• diffused with node mobility
• smaller timer ? closer distance
• For most mobility models

t(D) 0
tB(D) 100
A
B
tA(D) 138
t(D) 68
t(D) 218
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• Other knowledge-based routing
• MaxProp A variation of Dijkstras algorithm
• Link weight an estimate of delivery likelihood
  between two nodes
• MobySpace each node maintains a high-dimension
  Euclidean space
• Euclidean space to describe mobility pattern of
  each node
• Encounter occurred handover message only if the
  encountered node has more similar mobility
  pattern with the destination.

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Mobility Pattern

• Random walk
• In this mobility model, an MN moves from its
  current location to a new location by randomly
  choosing a direction and speed in which to travel
• The new speed and direction are both chosen
  from pre-defined ranges, speedmin speedmax and
  0 P respectively

p1/5
p1/5
p1/5
p1/5
p1/5
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Random walk
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Random Waypoint Mobility

• Random waypoint includes pause times between
  changes in direction and/or speed
• A mobile node stays in one location for a certain
  period of time (i.e., a pause time).
• Once this time expires, the node chooses a random
  destination Mn uniformly in area and a speed Vn
  that is uniformly distributed between vmin ,
  vmax
• Mobile moves towards Mn at constant speed Vn
• independent of past and present

Mn-1
Mn
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Random Waypoint Example
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Routing objective

• Performance metric
• Message delivery ratio
• The fraction of generated messages that are
  correctly delivered to the final destination
  within a given time period
• Transmission delay
• The time from a message is generated through it
  is received by destination
• Number of transmissions
• The number of message exchange occurred between
  two nodes

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Capacity of 2-hop relay

• Source gives a copy to any relay nodes
  encountered
• Relays can only give copy to destination

Relay C cannot FWD to B
Relay C can FWD to Dst
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Capacity of 2-hop relay

• Scalability of Ad hoc network
• Disappoint results (Gupta et al., 00)
• n number of nodes per unit area
• Tsd Throughput per source-to-destination pair
• Capacity of 2-hop relay
• Reasonable results (mobility exploited
  Grossglauser et al. 01)
• Each sender transmits packets to its nearest
  neighbor (relay nodes)
• Relay nodes transmit packets to destination
  directly

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2-hop relay (multiple copies)

• The performance of 2-hop scheme is close enough
  to multi-hop scheme (Burns et al, 05)
• Spray and wait scheme
• 2-hop relay scheme
• Spray a number of copies to the network, then
  wait until one of relay nodes meets the
  desination
• Limited number of copies to L
• Multi-path diversity to reduce delay
• Achieves O(1) per node capacity

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Binary Tree-based Spraying

• source starts with L copies
• whenever a node with L gt 1 copies finds a new
  node, it hands over half of the copies (L/2) that
  it carries Until L 1

L 1
L 1
L 1
L 1
L 4
L 2
L 2
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Estimated delay

• N number of nodes within deployment area
• Direct transmission (upper bound)
• Optimal transmission
• Spray and wait

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Summary

• Routing issue in DTN is challenge, attracting
  more attention
• Category of routing scheme
• Have good scalability of DTN by exploring node
  mobility
• Future direction develop more realistic
  networks from military to public application
• Vehicle-based networks
• Pocket-switched networks
• Social networks
• Wildlife tracking networks