DTN Outdoor Mobile Environment UMass: Mark Corner DTN Outdoor Mobile Environment UMass: Mark Corner Brian Neil Levine GaTech: Mostafa Ammar Ellen Zegura

Overview / Phase II Goals Prototyping DTN/Mesh Synergy Traces Throwbox power management DTNRG .net implementation Deliverables

Prototyping: DieselNet 40 equipped buses, routes spanning 150 sq. mi. Town center (4 sq.mi.) is hub of network. Each bus: 577Mhz, 256MB ram, 802.11b radio 802.11b AP, GPS, 40GB drive, XTend radio, GPRS. Custom software

Transfer Opportunities Red dots: bus-to-bus transfers during 1-month. Each transfer we record duration, data, location, speed and direction. Amherst downtown and UMass: 4 sq mi

Creating the DOME Cisco 1500 mesh APs Existing 40 buses Diversity: Mobility (scheduled / unscheduled) Nodes (mobile / stationary) Power (grid / diesel / solar) Radios (802.11 / XTend / GRPS) Storage (40GB down to 32MB) Cisco 1500 mesh APs Existing 40 buses PC104 boxes in vehicles Throwboxes

Prototyping: Throwbox Multi-platform Device: TelosB Mote (sensor) 900 MHz XTend radio 8 Mhz microcontroller Stargate 802.11b CF card 400Mhz PXA255 Xscale 64 MB ram, 32MB store Java 1.3 all DieselNet code AA rechargeable batteries / solar power

Prototyping: Throwbox

Trace collection Traces of DieselNet are on the web: Bytes transferred Inter-transfer opportunity time Traces of DieselNet are on the web: http://prisms.cs.umass.edu/diesel Used in [Burgess-Infocom06], [Jun-Chants06] To be added: throwbox data, mesh synergy

Throwbox Design low-power radio will remain idle unnecessarily. High power consumption leads to short lifetimes. Intermittent power is more efficient, but may not improve performance. An idle, low-power hailing radio that wakes a data radio will save energy. Tx Rx Idle Sleep WaveLan PC card 1.33 0.96 0.84 0.0664 Chipcon CC1000 0.08 0.02 0.00003 Usual assumption: dense networks DTNs: contacts are infrequent low-power radio will remain idle unnecessarily.

Throwbox Design Solution: use model of node mobility to avoid wasted idle periods. low-power radios are very efficient at duty-cycling. We can optimize wakeup periods to discover enough contacts to send given traffic load. After optimizing for both radios, we see a gain in energy efficiency over a single radio. Hyewon Jun, Mostafa Ammar, Mark Corner, Ellen Zegura. Hierarchical Power Management in Disruption Tolerant Networks with Traffic-Aware Optimization. In Proc. ACM SIGCOMM Wkshp on Challenged Networks (ACM CHANTS). September, 2006.

New Approach Short-range radios waste energy when only a brief contact is available. By definition, contact opportunities are short-shrifted. New tiered platform: tier-0: Mote (8Hmz, 10k,20mW) and XTend radio (~1.5km) tier-1: Stargate (400MHz, 64MB,2.5W) and 802.11b (~150m) Tier-0 searches for peers and predicts mobility. Tier-1 manages data transfers (and routing). Range Rx Tx Sleep XTend 1000m 0.36 W 1.0 W 10 mW 802.11 150m 1.2 W 50 mW

Approach

Mobility Prediction Buses transmit: pos, dir, speed. Box predicts: Will bus reach data-range before tier-1 can be woken: D1/v > T? Length of time in range: (P)(D2/v) P is prob node enters data-range given cells to traverse. Statistics kept on each cell. Markovian assumption allows simple calculation.

Scheduling is NP-Hard Each contact incurs a fixed cost to wake tier-1. Most efficient strategy: wake for largest opportunities. Scheduling corresponds to the knapsack problem: choose items to carry s.t. (∑weight ≤ capacity) and ∑value is maximized. {c1...cn } events. each event ci has total energy cost ei (weight) bytes transferred di (value) Energy constraint P∙t (capacity) Solution is subset of events that maximizes bytes transferred ∑di such that (∑ei ≤ P∙t)

Ignored or skipped events Token Bucket Approach Tokens arrive as per average power constraint. Q: take this event, next event, or both? Algorithm: 1. Estimate the size & energy cost of event. Ignore if insufficient tokens. 2. Compute expected tokens generated in time for next event. 3. If sufficient tokens for both events, current event is taken. Otherwise take event if larger than mean. new tokens Events Battery capacity ? Taken events Ignored or skipped events

Preliminary results Fully functional prototype. Solar cell produced 65mW over 24 hours (expected 85mW). Solar cell slightly larger than the box will run perpetually.

Routing performance Three boxes deployed in UMass DieselNet allowed trace-driven evaluations.

.Net DTNRG Implementation Goals: 100% compliant with bundle spec As compatible as possible with reference implementation (but spec takes precedence) Cross-platform, to include handhelds Status: 90% complete C# implementation in .NET Windows on laptops Compact Framework on handhelds Mono on linux Missing data store and automatic discovery Can demo (but not here) laptop1-PDA-laptop2 Release date target: October 2006 for version 0.9 Personnel: Jon Olson, Kevin Webb (GT)

Deliverables (Part 2) New throwbox power-management power management algorithms. A throwbox platform prototype built from COTS components. Data from a long-running DTN testbed. Implementation of DTN specification in .Net Mechanisms for synergistic networks consisting of DTN and mesh regions. Implementation of applications that leverage the routing-related services.