Opportunistic Routing Algorithms in Delay T olerant Networks Eyuphan Bulut Rensselaer Polytechnic Institute Department of Computer Science and Network Science and Technology (NeST) Center PhD Thesis Defense Feb 4 th , 2011
Outline • Introduction to DTNs – Challenges of routing • Proposed Algorithms 1) M ulti-period Spray and Wait routing 2) M ulti-period erasure coding based Simulation Results routing Based on Real and S ynthetic Traces 3) Efficient single-copy routing utilizing correlation between node meetings 4) Social relation based routing • Summary of Contributions 2/ 4/ 2011 Bulut: PhD Defense (RPI) 2
Outline • Introduction to DTNs – Challenges of routing • Proposed Algorithms 1) M ulti-period Spray and Wait routing 2) M ulti-period erasure coding based routing 3) Efficient single-copy routing utilizing correlation between node meetings 4) Social relation based routing • Summary of Contributions 2/ 4/ 2011 Bulut: PhD Defense (RPI) 3
Delay Tolerant Networks • Intermittently connected mobile networks – Sparse mobile networks • M ain difference from M ANETs – Lack of continuous end-to-end connectivity – Utilizes “store-carry-and-forward” paradigm in routing 2/ 4/ 2011 Bulut: PhD Defense (RPI) 4
Applications of DTNs • Space networks Jupiter • Satellites and planets • M ilitary Networks Mars • Soldiers, aircrafts Earth • Social Networks • People, base stations • Vehicular Networks • Underwater networks 2/ 4/ 2011 Bulut: PhD Defense (RPI) 5
Routing in DTNs • Challenges: – Dynamic and sparse topology – Low probability of end-to-end connectivity – How to locate destination with local knowledge? – Opportunistic message exchanges • When nodes come to the range of each other • How to decide whom to forward/copy a message? B C A B E C D 2/ 4/ 2011 Bulut: PhD Defense (RPI) 6
Routing in DTNs Knowledge Number of carriers Full knowledge History based Single Multiple • Future meetings Opportunistic • Position information (Whenever they are in the range of each other) Replication-based Erasure coding- based Random Selective i.e. first node met (Prediction-based Flooding Quota based or Probabilistic) Use information extracted from encounter history to predict future meetings 2/ 4/ 2011 Bulut: PhD Defense (RPI) 7
Our Research Path M ulti-copy Random M obility M odels Reliability based (Random walk, waypoint, direction) Erasure coding based Analysis of Real DTN Traces (E ffects of pair-wise relations in routing) Correlated node mobility Social Behavior (Repetitive behavior, (Human carried wireless devices) Importance of past) Single-copy based Single-copy based 2/ 4/ 2011 Bulut: PhD Defense (RPI) 8
Outline • Introduction to DTNs – Challenges of routing • Proposed Algorithms 1) M ulti-period Spray and Wait routing 2) M ulti-period erasure coding based routing 3) Efficient single-copy routing utilizing correlation between node meetings 4) Social relation based routing • Summary of Contributions 2/ 4/ 2011 Bulut: PhD Defense (RPI) 9
Spray and Wait * • Random mobility model – Exp. dist. intermeeting times L 3 Cdf of delivery probability L 2 L 1 L 1 < L 2 < L 3 time M essage Destination delivered Node with message copy M essage M essage Node without message copy copied copied * Spyropoulos et. al. Transactions on Networking, 08 2/ 4/ 2011 Bulut: PhD Defense (RPI) 10
Two Period Spray & Wait • Spray L 1 copies at the beginning • Spray additional L 2 - L 1 copies at time x d (start of second period) GOALS: 1) M aintain the same delivery rate by deadline (td) L 2 L 2) Lower the average cost L 1 (P)+ L 2 (1-P) < L L 1 Delivery probability in first period 2/ 4/ 2011 Bulut: PhD Defense (RPI) 11
Three Period Spray & Wait L 3 L L 2 L 1 3 rd 2 nd 1 st Period Period Period 2/ 4/ 2011 Bulut: PhD Defense (RPI) 12
M ultiple Period Spray & Wait • If we currently have k spray and wait periods, to obtain k+1 periods: – Partition each period into two sub-periods optimally – Take the one which makes the overall cost minimum 2 periods: L 1 and L 2 L 2 L 6 L L 5 L 1 3 periods: L 4 Select either a) L 1 , L 5 and L 6 L 3 b) L 3 , L 4 and L 2 2/ 4/ 2011 Bulut: PhD Defense (RPI) 13
Acknowledgment of delivery • Two types: – Type I: Acknowledgment by flooding • Pros: Acks are small, lower cost • Cons: Takes time to reach all nodes, thus extra copying may occur – Type II: Single broadcast with powerful radio • Pros: Immediate acknowledgment • Cons: Cost of powerful radio 2/ 4/ 2011 Bulut: PhD Defense (RPI) 14
Optimum L i ’s from Analysis Cost=4.64 Cost=5.87 Cost=4.28 X d =285s 2/ 4/ 2011 Bulut: PhD Defense (RPI) 15
Simulation Results • Percentage of Saving – While achieving the same delivery ratio by deadline 2/ 4/ 2011 Bulut: PhD Defense (RPI) 16
Extensive Simulations • Theoretical results are matching with simulation results • Effect of different number of nodes, different desired delivery ratios etc. • Results on Real Traces – Demonstrates benefit, but still needs careful analysis due to heterogeneous meeting behavior of different nodes [IEEE/ACM Transactions on Networking’10], [Globecom’08], [ACIT A’08] 2/ 4/ 2011 Bulut: PhD Defense (RPI) 17
Outline • Introduction to DTNs – Challenges of routing • Proposed Algorithms 1) M ulti-period Spray and Wait routing 2) M ulti-period erasure coding based routing 3) Efficient single-copy routing utilizing correlation between node meetings 4) Social relation based routing • Summary of Contributions 2/ 4/ 2011 Bulut: PhD Defense (RPI) 18
Replication vs. Erasure Coding • Replication Source In total L relay nodes Destination A message Wait for 1 of them to (M bytes) reach destination L copies If L=R, then the cost M*L bytes of data is transmitted to the (transmitted bytes over the network radio) becomes equal. • Erasure Coding (EC) Destination Source In total R*k relay nodes Encoded into Wait for k of them to reach A message R*k blocks destination (M bytes) Divided into k ~M*R bytes of data is transmitted to the small parts (M/k R: Replication network ( independent from k) bytes of each) factor 2/ 4/ 2011 Bulut: PhD Defense (RPI) 19
Replication vs. Erasure Coding • Which one is better? 1. Spraying L messages and waiting for 1 (to reach destination)? – Spraying duration takes less time than the second one 2. Spraying Φ =R* k messages and waiting for k? Costs are the same when R=L “EC” also provides more reliable routing: In a failure of one packet, the performance of “ replication” routing is affected more than the performance of “erasure coding” based routing. 2/ 4/ 2011 Bulut: PhD Defense (RPI) 20
Replication vs. Erasure Coding • If desired delivery rate is higher, we can achieve more cost saving with erasure coding based routing compared to replication routing. • Optimum Single-period erasure coding based routing: – Try to minimize Replication factor (R) since cost is proportional to R. – M aintain delivery rate by deadline (R 1 ,k) R 1 > R 2 (R 2 ,k) 2/ 4/ 2011 Bulut: PhD Defense (RPI) 21
M ulti-period Erasure Coding-based Routing In 1 st period: • – Create Φ 2 =kR* coded blocks, where R * >R opt (optimum R in single period) • Linear time complexity of creating these packets (Tornado codes) – Spray Φ 1 = α kR* of them and try delivery with them If delivery doesn’t happen in 1 st period (by x d ) • Start of second period – Spray remaining Φ 2 - Φ 1 of them in 2 nd period • Same goals: – M aintain delivery rate by deadline – Achieve lower cost on average 2/ 4/ 2011 Bulut: PhD Defense (RPI) 22
Simulations • M essage size 100Kb • Costs at the delivery (Type II) and after all nodes are acknowledged (Type I): 1 period 2 periods 2 period 2 period 1 period 1 period Replication Replication Replication Replication Based Based Based Based Cost=478 Cost=464 Cost=587 Cost=578 [ICC’10] Lower cost than Replication based Routing Lower cost than Replication based Routing 2/ 4/ 2011 Bulut: PhD Defense (RPI) 23
Outline • Introduction to DTNs – Challenges of routing • Proposed Algorithms 1) M ulti-period Spray and Wait routing 2) M ulti-period erasure coding based routing 3) Efficient single-copy routing utilizing correlation between node meetings 4) Social relation based routing • Summary of Contributions 2/ 4/ 2011 Bulut: PhD Defense (RPI) 24
Analysis of Real DTN Traces • Haggle Project (people, conference, Imote) • M IT Reality Project (campus, phone) • UM ass Diesel-Net Project (bus meetings) • RollerNet Traces (roller skate tour, Imote) • Others: – Zebra, taxi etc. M eeting (contact) duration Inter-meeting • Extracted information: – Pair-wise and aggregate inter-meeting and contact duration 2/ 4/ 2011 Bulut: PhD Defense (RPI) 25
Single-copy DTN Routing • Shortest-path based routing A B E – DTN Graph M odel: D C • Vertices are nodes, edges are links between nodes • Weights of edges are average inter-meeting times G F – Ex: M ED, M EED etc. H I • M etric-based (utility) routing – When two nodes meet, one forwards its message to other if the other’s metric suggests more delivery chance with destination – Ex: Prophet, Fresh, SimBet etc. 2/ 4/ 2011 Bulut: PhD Defense (RPI) 26
Recommend
More recommend
