On the Cost/Delay Tradeoff of Wireless Delay Tolerant Geographic Routing
Argyrios Tasiopoulos MSc, student, AUEB
Master Thesis presentation
Introduction• Many networks are characterized by:
– Intermittent Connectivity.– Long or variable delays.
• In both cases traditional TCP/IP protocols fail.
• Delay Tolerant Networking addresses these issues. 4 to 20 minutes
Master Thesis presentation
Delay Tolerant Networks (DTNs)
• In Delay-Tolerant Networks each node can hold packets indefinitely in a persistent buffer.
• The previous problems are addressed by store-and-forward message switching.
Mobile Delay Tolerant Networks• In mobile DTNs, nodes can carry a packet
physically in their buffer.• Therefore, we actually have store-carry-
and-forward packet switching.
Source Destination
Buffer
Packet
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DTNs Protocol Design• In DTNs we have an extra degree of freedom
regarding the delay in data delivery.• We can trade off delay in order to improve
other metrics.• Our case of study concerning the improvement
of aggregate transmission cost.– We care about the behavior of aggregate
transmission cost of a packets given a delivery delay.
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Aggregate Transmission Cost• What we mean in this work when we talk
about aggregate transmission cost?– The cost of interference (typically proportional
to transmission area), and/or– the energy consumption of a transmission
(typically fixed).
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Coming next• Part A: Optimal Cost/Delay Tradeoff
Formulation• Part B: Cost/Delay Tradeoffs in
Geographic Routing• Part C: Simulation Environments and
Results
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Part A: Optimal Cost/Delay Tradeoff Formulation.
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Optimal Cost/Delay Tradeoff• We take the typical approach of evolving
graphs (Ferreira 2004).• We divide the time into discrete time
intervals, called epochs.• We make the assumptions that during each
epoch:– the network topology remains fixed, hence
creates a network replica for the specific epoch, and
– all packet transmissions can take place.9Master Thesis presentation
Cost/Delay Evolving Graph
• We define as Cost/Delay Evolving Graph (C/DEG) the graph comprised by:– consecutive replicas,– link arcs, which
connect nodes along the same replica, and
– storage arcs, which connect the same nodes along consecutive replicas.
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Punctual vs. Optimal Cost/Delay Curve
• Given a packet source we can execute any one-to-many shortest path algorithm.
• We define the Punctual Cost/Delay Curve (PC/DC), as the minimum-cost journey of exactly t epochs, between two nodes.
• We define the Optimal Cost/Delay Curve (OC/DC), as the minimum-cost journey of all journeys with the maximum duration of t epochs.
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Punctual Cost/Delay Curve Example11
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PC/DC point
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PC/DC point
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PC/DC point
PC/DC
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Punctual vs. Optimal Cost/Delay Curve Example
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PC/DC point
PC/DC OC/DC
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Delay, in epochsMaster Thesis presentation
Part B: Cost/Delay Tradeoffs in Geographic Routing.
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Geographic routing• In geographic routing a source sends a
message to the geographic location of the destination.
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Destination
R
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Geographic routing• Then, the packet route from source to
destination is calculated “on the fly”.
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Source Destination Source Destination
Holder
DestinationHolder
DestinationPacket
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Complete network topology
Protocol family• Each node which executes a protocol of
this family:– Applies a Neighbor Evaluation Rule (NER)
to its immediate neighbor nodes, which returns the best of them.
– Calculates the minimum-cost path to the best neighbor.
– Forwards the packet to the next hop node along the minimum-cost path.
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Protocol Family Example
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Execute NERFind the bestCalculate
shortest-cost path
Forward the packet to the
next hop node
Packet
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Protocol Family Variations• Next we define 5 member of this protocol
family.• All rules differ on NER.• For the rest of this presentation:
– node A is the packet holder which performs the NER,
– node B is a candidate neighbor of A, and– node D the packet destination.
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Motion Vector (MoVe)(LeBrun et al.,2005)
• MoVe NER: Select as best the node with the current or future closest distance from the destination.
A
D
Z
B vB
|AD||BD|
|ZD|
Minimizes |ZD|
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AeroRP (Peters et al., 2011)
• AeroRP NER: Selects as best the node with the biggest relative velocity towards destination
A
D
Z
vB
|AD||BD|
|ZD|
B
vRBMaximizes vRB
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Minimum Cost-per-Progress (MCpPR)
• MCpPR NER minimizes the ratio:
BDADCr BA
AB '
D
Z
vB
|AD||BD|
|ZD|
A
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Balance Ratio Rule (BRR)• Our first novel protocol minimizes the ratio:
• We define α as the conversion coefficient.– Which strikes a balanced between cost and
delay by trying to keep them both low.
ZDADdCr ZBBA
AB
''
A
D
Z
B vB
|AD||BD|
|ZD|
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Composite Rule (CR)• MCpPR rule tries to maximize the
immediate transmission gains.• BRR tries to maximize the benefits of the
physical transportation of store-carry-and-forward packet switching.
• Hence, we define Composite Rule (CR) as the best of two worlds which minimizes simultaneously the ratios of MCpPR and BRR :
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ABABAB rrC '','min
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Achievable Cost/Delay Curve (AC/DC)
• We define the AC/DC as the curve that give for each epoch, the minimum aggregate transmission cost that a protocol can achieve for a pair of nodes.
• If the protocol has tunable parameters concerning the tradeoff, an achievable cost/delay curve (AC/DC) is calculated in a similar way to OC/DC, over the complete range of results of these parameters.
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Achievable Cost/Delay Tradeoff Example
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1 t0 t0+2 t0+3 t0+4 t0+5 t0+6
Tunable parameters results
AC/DC
t0+7t0+1Delay, in epochs
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Part C: Simulation Environments and Results.
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Performance Evaluation Settings
• We evaluate our protocols in the 3 following settings:– empty space setting,– home region setting, and– urban setting.
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Simulation parameters• The common tunable parameter for all these
protocols is the restricted radius R’ which determines the maximum transmission hop length.
• CR and BRR have the extra tunable parameter α.
• Standard case: The nodes move with random velocities and we have a quadratic aggregate transmission cost function (equal to d2 where d the transmission distance).
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Empty Space Setting
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15x 10
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Delay (in epochs)
Cos
t (in
m2 )
MCpPRMoVeAeroRPBRRCROC/DC
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Empty Space Setting – Fixed velocities and cost function
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30 40 50 60 70 80 90 1000
0.5
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Delay (in epochs)
Cos
t (in
m2 )
MCpPRMoVeAeroRPBRRCROC/DC
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Home Region Setting
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50 100 150 200 250 3000
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15x 10
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Delay (in epochs)
Cos
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m2 )
MCpPRMoVeAeroRPBRRCROC/DC
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Urban Setting
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15x 10
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Delay (in epochs)
Cos
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MCpPRMoVeAeroRPBRRCROC/DC
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Urban Setting-Fixed velocities
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Delay (in epochs)
Cos
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MCpPRMoVeAeroRPBRRCROC/DC
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Conclusions• Our immediate contributions:
– The formulation of optimal tradeoff between the packet delivery delay and the aggregate transmission cost existing in all DTNs.
– The study of this tradeoff in the context of geographic routing
– Our two novel rules with results close to the optimal.• Our most important contribution:
– We set the agenda for a systematic evaluation of cost/delay tradeoffs in a variety of DTNs settings.
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Thank you