Enhancing DTN capacity with Throwboxes (work-in-progress) Wenrui Zhao, Yang Chen, Mostafa Ammar, Mark Corner, Brian Levine, Ellen Zegura Georgia Institute of Technology University of Massachusetts Amherst

Delay Tolerant Networks (DTN) DTNs: non-Internet-like networks Intermittent connectivity Large delays High loss rates Examples of DTNs Tactical networks, disaster relief, peacekeeping Interplanetary networks, rural village networks Underwater acoustic networks DTN features Store-Carry-and-forward Message switching Represent some of the most critical cases of networking

Capacity Limitation in DTNs DTNs are intermittently connected Potentially low throughput, large delay Question: enough capacity for applications? What if not?

Enhancing DTN Capacity Use radios with longer range Deploy a mesh network as infrastructure Message ferrying This presentation: Throwboxes MF S M D

Our Work on MF/DTN MF with Mobile Nodes [MobiHoc 04] Ferry Route Design Problem [FTDCS 03] MF with Mobile Nodes [MobiHoc 04] Efficient use of Multiple Ferries [INFOCOM 05] The V3 Architecture: V2V Video Streaming [PerCom 05] Ferry Election/Replacement [WCNC 05] MF as a power-savings device [PerCom 05] Multipoint Communication in DTNs/MF [WDTN 05, WCNC 06] Power Management Schemes in DTNs/MF [SECON 05, PerCom 05] Road-side to Road-side relaying using moving vehicles [WCNC 06]

Throwboxes Basic idea: add new devices to enhance data transfer capacity between nodes Deploy throwboxes to relay data between mobile nodes Throwboxes are: small, inexpensive, possibly dispensable, battery-powered wireless devices Some processing and storage capability Easy to deploy and replenish No need to maintain a connected network

Throwboxes Processor Intel PXA255 400MHz Memory 64MB SDRAM 32MB Flash Power consumption < 500mA Size 3.5’’ x 2.5’’ Weight 47g

Example: DTN w/out Throwboxes

Example: DTN w/ Throwboxes

UMassDiesel DTN Example w/out TB w/ TB Total contact duration (sec) 631 11927 Effective capacity (Kbps) 3.5 66.3 Delay (sec) 63012 3120 Data transmission between bus 38 and bus 45 A single throwbox achieves an improvement factor of 19 for both capacity and delay

Main Question How to best deploy ‘s Where? How to route through them? When? -- Later work

Throwbox Deployment & Routing Framework Objective: throughput enhancement Important to deliver data May improve delay too Deployment issue Where to place throw-boxes? Routing issue How data are forwarded? Contact-oblivious Contact-based Traffic and Contact based Single path routing Multi-path routing Epidemic routing

Network Model DTN consists of mobile nodes Relative traffic demand between nodes bij Total throughput λ Given inherent capacity (w/out TBs) as a function of: Contacts – dictated by mobility patterns Data rate

Throwbox Assumptions Sufficient energy supplies No interaction between throwboxes Deployed to a given set of potential locations Center of Grid Cells Deployment Vector (0/1 vector)

Throwbox Deployment & Routing Framework Deployment approach Traffic & Contact based Contact based Contact oblivious Random or Regular Deployment Routing approach Multi-path routing Single path routing Epidemic routing

Throwbox Deployment & Routing Framework Deployment approach Traffic & Contact based Contact based Contact oblivious Random or Regular Deployment Routing approach Multi-path routing Single path routing Epidemic routing

Multi-Path Routing – Traffic and Contact-Aware Deployment Need to determine Deployment locations of throwboxes Routing paths and traffic load on each path Performance objective Given m throwboxes, maximize total throughput λ such that traffic load λbij is supported from node i to j

Multi-Path Routing – Traffic and Contact-Aware Deployment Formulated as an 0/1 linear programming problem Throwbox deployed at location  1 Solution also gives optimal flow vector describing use of multiple paths NP-hard to solve optimally

Greedy Heuristic Deploy throwboxes one by one Given throwbox locations, (2) is a concurrent flow problem Solved by network flow techniques or linear programming tools (1) for i=1 to m do (2) find location L that maximizes λ (3) deploy a throwbox at location L (4) end (5) compute routing

Throwbox Deployment & Routing Framework Deployment approach Traffic & Contact based Contact based Contact oblivious Random or Regular Deployment Routing approach Multi-path routing Single path routing Epidemic routing

Multi-Path Routing – Contact-Based Deployment Throwbox deployment is based on contact information, but not traffic information Benefits varying traffic patterns May not be optimal for specific traffic Maximize Absolute contact enhancement Maximize absolute enhancement of contact between nodes Relative contact enhancement Maximize relative enhancement of contact between nodes As shown in UMass example

Throwbox Deployment & Routing Framework Deployment approach Traffic & Contact based Contact based Contact oblivious Random or Regular Deployment Routing approach Multi-path routing Single path routing Epidemic routing

Single Path Routing Single path routing Data for a S-D pair follow a single path Adapt greedy algorithm for multi-path routing by enforcing the “single path” requirement

Throwbox Deployment & Routing Framework Deployment approach Traffic & Contact based Contact based Contact oblivious Random or Regular Deployment Routing approach Multi-path routing Single path routing Epidemic routing

Epidemic Routing Epidemic routing (ER) Difficult to characterize traffic load among nodes because of flooding ER exploits all paths to propagate data Multi-path heuristic Proportional allocation heuristic

Performance Evaluation ns simulation deployment/routing computation traffic demand node mobility throwbox locations routing path/load Objectives Utility of throwboxes in performance enhancement Performance impact of various routing and deployment approaches

Simulation Settings Node mobility models Simulation Parameters Predictable/constrained: UMass model based on measured bus trace Random/unconstrained: Random waypoint model Random/constrained: Manhattan model Simulation Parameters 9 nodes in a 25Km x 25 Km area 802.11 MAC, radio range: 250m, bandwidth: 1Mbps 20 source-destination pairs, message size is 1500 bytes, Poisson message arrival with same data rate FIFO buffer, buffer size is 50000 messages

Delivery Ratio vs. Number of Throwboxes 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 1 2 3 4 5 6 7 8 Message delivery ratio Number of throw-boxes T &C Aware AbsoluteContact RelativeContact Random Grid Multi-path routing

Delivery Ratio vs. Number of Throwboxes 0.45 0.4 0.35 0.3 Single path routing 0.25 Message delivery ratio 0.2 0.15 T & C Aware 0.1 AbsoluteContact RelativeContact 0.05 Random Grid 1 2 3 4 5 6 7 8 Number of throw-boxes

Delivery Ratio vs. Number of Throwboxes 0.05 0.1 0.15 0.2 0.25 0.3 0.35 1 2 3 4 5 6 7 8 Message delivery ratio Number of throw-boxes MultiPath Proportional AbsoluteContact RelativeContact Random Grid Epidemic routing

Delay vs. Number of Throwboxes (High Traffic Load) 2000 4000 6000 8000 10000 12000 14000 1 2 3 4 5 6 7 8 Message delay (second) Number of throw-boxes T & C AbsoluteContact RelativeContact Random Grid Multi-path routing

Delay vs. Number of Throwboxes (Low Traffic Load) 6000 5000 4000 Multi-path routing Message delay (second) 3000 2000 T & C AbsoluteContact 1000 RelativeContact Random Grid 1 2 3 4 5 6 7 8 Number of throw-boxes

Summary of Simulation Results RWP mobility Manhattan UMass Multi-path routing Single path Epidemic Delay improvement (high traffic load) Throughput improvement (low traffic load)

Summary of Simulation Results (2) Contact based T & C Multi-path routing Single path Epidemic Contact oblivious T & C/ T & C / High Low Throughput improvement Routing approach

Summary Study the use of throwboxes for capacity enhancement in mobile DTNs Develop algorithms for throwbox deployment and routing Routing: multi-path, single path, epidemic Deployment: traffic and contact, contact-based, contact-oblivious Evaluate the utility of throwboxes and various routing/deployment approaches Throwboxes are effective in improving throughput and delay, especially for multi-path routing and predictable node mobility

Questions?

Message Ferrying MF S S M MF D D M