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

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

4Master Thesis presentation

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.

5WoWMoM San Francisco 2012

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).

Coming next• Part A: Optimal Cost/Delay Tradeoff

Formulation• Part B: Cost/Delay Tradeoffs in

Geographic Routing• Part C: Simulation Environments and

Results

Part A: Optimal Cost/Delay Tradeoff Formulation.

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.

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.

WoWMoM San Francisco 2012 11

Punctual Cost/Delay Curve Example11

WoWMoM San Francisco 2012 12

PC/DC point

Delay, in epochs2 3 4

PC/DC point

Punctual vs. Optimal Cost/Delay Curve Example

1 2 3 4 5 6 7 8

PC/DC point

PC/DC OC/DC

Delay, in epochsMaster Thesis presentation

Part B: Cost/Delay Tradeoffs in Geographic Routing.

Geographic routing• In geographic routing a source sends a

message to the geographic location of the destination.

Destination

Geographic routing• Then, the packet route from source to

destination is calculated “on the fly”.

Source Destination Source Destination

Holder

DestinationHolder

DestinationPacket

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.

Protocol Family Example

Execute NERFind the bestCalculate

shortest-cost path

Forward the packet to the

next hop node

Packet

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.

Motion Vector (MoVe)(LeBrun et al.,2005)

• MoVe NER: Select as best the node with the current or future closest distance from the destination.

|AD||BD|

Minimizes |ZD|

AeroRP (Peters et al., 2011)

• AeroRP NER: Selects as best the node with the biggest relative velocity towards destination

|AD||BD|

vRBMaximizes vRB

Minimum Cost-per-Progress (MCpPR)

• MCpPR NER minimizes the ratio:

BDADCr BA

|AD||BD|

B22Master Thesis presentation

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

|AD||BD|

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 :

ABABAB rrC '','min

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.

Achievable Cost/Delay Tradeoff Example

1 t0 t0+2 t0+3 t0+4 t0+5 t0+6

Tunable parameters results

t0+7t0+1Delay, in epochs

Part C: Simulation Environments and Results.

Performance Evaluation Settings

• We evaluate our protocols in the 3 following settings:– empty space setting,– home region setting, and– urban setting.

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).

Empty Space Setting

50 100 150 200 250 3000

15x 10

Delay (in epochs)

MCpPRMoVeAeroRPBRRCROC/DC

Empty Space Setting – Fixed velocities and cost function

30 40 50 60 70 80 90 1000

2.5x 10

Delay (in epochs)

Home Region Setting

50 100 150 200 250 3000

15x 10

Delay (in epochs)

Urban Setting

50 100 150 200 250 300 3500

15x 10

Delay (in epochs)

Urban Setting-Fixed velocities

20 40 60 80 100 1200

15x 10

Delay (in epochs)

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.

Thank you

On the Cost/Delay Tradeoff of Wireless Delay Tolerant Geographic Routing

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