1-1 CMPE 259 Sensor Networks Katia Obraczka Winter 2005 Topology Control

1-2 Announcements

1-3 What’s topology control?

1-4 What’s topology control? r When nodes are deployed, how do they organize into a network? r Neighbor-discovery protocol. r If neighborhood is sparse, use all neighbors. r What if neighborhood is dense? m Use a subset of neighbors. m How?

1-5 Approaches to topology control r Adjust transmit power. r Turn nodes on/off.

1-6 ASCENT

1-7 ASCENT: scenario r Ad hoc deployment. r Energy limitations. r Arbitrarily large scale. r Unattended operation. r Assume CSMA.

1-8 ASCENT: goals r Self-organization of nodes into topology that allows sensing coverage and communication under tight energy constraints.

1-9 ASCENT: approach r Nodes turn themselves on/off depending on assessment of operating conditions. m Neighborhood density. m Data loss.

1-10 State diagram Test Active Passive Sleep After Tt Nbors > NT or Loss > Nbors<NT And Loss>LT or Help After Tp After Ts

1-11 In “test” state: r Signaling (e.g., neighbor announcements). r After Tt, goes to “active”. r Or, if before Tt, number of neighbors>NT or average data loss (Tt) > average data loss (T 0 ), go to “passive”.

1-12 In “passive” state: r After Tp, go to “sleep”. r If neighborhood is sparse loss > LT or “help” from “active” neighbor, go to “test”.

1-13 In “sleep”: r Turn off radio. r After Ts, go to “passive”.

1-14 In “active”: r Node does routing and forwarding. r Sends “help” if data loss > LT. r Stays on until runs out of battery!

1-15 Considerations r Why passive and test states? r Why once in active, a node runs until battery dies? r How to set parameters? m NT, LT. m Tt, Tp, Ts.

1-16 Neighborhood and loss r Node is neighbor if directly connected and link packet loss < NLS. r NLS is adjusted according to node’s number of neighbors. r Average loss date uses data packets only. r Packet is lost if not received from any neighbors.

1-17 Performance evaluation r Modeling, simulation, experimentation. r Metrics: m Packet loss. m Delivery ratio. m Energy efficiency. m Lifetime. Time till 90% of transit nodes die.

1-18 Results r From the paper…

1-19 PEAS

1-20 PEAS r Probing Environment, Adaptive Sleeping. r “Extra” nodes are turned off. r Nodes keep minimum state. m No need for neighborhood-related state. r PEAS consiers very high node density and failures are likely to happen.

1-21 Bi-modal operation r Probing environment. r Adaptive sleeping.

1-22 PEAS state diagram Working Sleeping Probing No reply for probe Wakes up Hears probe reply.

1-23 Probing r When node wakes up, enters probing mode. r Is there working node in range? m Broadcasts PROBE to range Rp. m Working nodes send REPLY (randomly scheduled). m Upon receiving REPLY, node goes back to sleep. Adjusts sleeping interval accordingly. m Else, switches to working state.

1-24 Considerations r Probing range is application-specific. m Robustness (sensing and communication) versus energy-efficiency. r Location-based probing as a way to achieve balance between redundancy and energy efficiency. r Randomized sleeping time. m Better resilience to failure. m Less contention. m Adaptive based on “desired probing rate”.

1-25 More considerations… r Multiple PROBEs (and multiple REPLIES) to compensate for losses. m Multiple PROBEs randomly spread over time. r Multiple working nodes in the neighborhood. m Favor “oldest” one. r Nodes with fixed transmit power. r Deployment density.

1-26 Evaluation r Simulations. r Simulated failures: failure rate and failure percentage. r Metrics: m Coverage lifetime. m Delivery lifetime.

1-27 Results r With and without failures. r From the paper…