S4: Small State and Small Stretch Routing for Large Wireless Sensor Networks

1
S4 Small State and Small Stretch Routing for
Large Wireless Sensor Networks

• Yun Mao2, Feng Wang1, Lili Qiu1,
• Simon S. Lam1, Jonathan M. Smith2
• Univ. of Texas at Austin1, Univ. of Pennsylvania2

2
Background

• Smart wireless sensor networks call for
  inter-node communication
• In network processing
• In network storage
• Challenges for a point-to-point routing protocol
  in wireless sensornets
• Limited resources Scalability
• RF phenomena Efficiency, Resilience

3
The core theme a tradeoff

• State the routing table size describing the
  network topology
• Stretch

4
Design space
state
Shortest-path routing
O(n)
hierarchical routing
Virtual-coordinate routing
O( )
geographic routing
O(1)
avg/worst-case stretch
5
Goals

• Small stretch
• Efficient usage of the wireless resources.
• Constant bound for worst-case stretch and
  near-optimal for average cases
• Small state
• Memory size is increasing, but still limited
• 0.5KB (WeC) ? 1KB(Dot) ? 4KB (Mica, Mica2) ? 10KB
  (telos) ? 64KB (iMote)
• O( ) bound
• Reasonable control traffic to maintain the state
• Practical
• Dont assume perfect radios
• No GPS or preconfigured physical locations

6
S4 routing algorithm in a nutshell

• Theoretical foundation on compact routing
  SPAA01
• Worst-case routing stretch is 3
• O( ) state per node
• Node classification
• beacon nodes
• nodes
• regular nodes
• Know how to route to the beacons
• Node clusters
• Each regular node d has a cluster, in which each
  node knows how to route to d.
• Radius is the distance to the closest beacon.
• Different from hierarchical routing.

7
Example
Beacon 1
Source
Beacon 3
Dest

• Rules
• Inside cluster route on the shortest path
• Outside cluster
• route towards the beacon closest to the dest

Beacon 2
8
Protocol Design Challenges

• How to maintain routing state inside a cluster?
• Flooding is expensive
• How to maintain routing state for beacon nodes?
• Unreliable broadcast may affect routing stretch
• Routes to beacons may not be optimal.
• Unnecessarily long radius
• How to provide resilience against node/link
  failure?
• Transient failure
• During routing state convergence

9
Key components of S4

• Disseminate routing states inside the clusters
  Scoped Distance Vector (SDV)
• ltd, nexthop(d), seq(d), hop(d), radius(d)gt
• Incremental update
• Inter-cluster routing Resilient Beacon Distance
  Vector (RBDV)
• Passively listen to further broadcasts of
  neighbors
• Re-broadcast if overhearing too few broadcasts
  within a certain time.
• Failure handling
• Distance Guided Local Failure Recovery (DLF)

10
Distance-guided local failure recovery
Dest
6
4
5
1 asks for help from neighbors.
1
source
2
The nodes closer to dest reply earlier. Priorities
are estimated from SDV RBDV.
3
3 suppresses unnecessary packets.
1 chooses the best neighbor to forward.
11
Other design issues

• Location Directory
• Beacon node maintenance
• Link quality estimation, neighbor selection
• Please refer to the paper for details

12
Evaluation

• Methodology
• High-level simulation with ideal radio model
• No loss, no contention, circle communication
  range
• TOSSIM packet level simulation
• Lossless and lossy link with contention
• Mica2 test bed evaluation
• Real environment, unpredictable obstacles
• Use Beacon Vector Routing (BVR) NSDI 2005 as
  benchmark
• Virtual coordinate approach
• A similar goal practical
• Code available

13
Questions to answer

• Does S4 achieve small stretch?
• routing stretch and transmission stretch
• Average case vs worst case
• Does S4 achieve small state?
• How does S4 perform under failure?
• How well does S4 work in a real testbed?
• Many others in the paper..

14
Routing/transmission stretch in TOSSIM
of beacons lossless link with
contention and collision
n
S4 has smaller avg. stretch and variation.
15
routing state per node
BVR
S4

• Routing state of S4 increases at the scale of O(
  )
• The amount of state is evenly distributed between
  beacon and non-beacon nodes.

16
Stretch under irregular topologies
BVR
S4
The stretch of S4 is not affected by the
irregular topology, even for those worst cases.
17
Distance-guided local failure recovery
DLF greatly increases the success rate of S4
under node failures.
18
Testbed Deployment

• 42 mica2 motes
• 915MHz radios
• 11 of them (called gateway motes) are connected
  to MIB600 Ethernet board, powered by the adapters
• 31 of them are powered by batteries
• Reduce power level to create multi-hop topology
• A link between two nodes exists if the packet
  delivery rates of both directions are above 30
• The network diameter is around 4 to 6 hops.

19
ACES Building 5th Floor NW _at_ UT Austin
20
Routing success rate
6 random beacon nodes Sources are randomly chosen
from all nodes. Destinations are randomly chosen
from 11 gateway nodes.
21
Routing under node failures
22
Summary

• Key properties
• avg stretch 1 worst-case stretch lt3
• State O( )
• Key components
• Scoped distance vector (SDV)
• Resilient beacon distance vector (RBDV)
• Distance guided local failure recovery (DLF)
• Extensive simulation and experimental results
• Limitations and Future work
• ETX aware
• Rapid mobility
• http//www.cs.utexas.edu/lili/projects/s4.htm

23
Backup slides
24
3-stretch guarantee
B
S
D

• distlt BDSB (shortcut)
• lt BD (BDSD) (triangle
  inequality)
• SD 2BD
• ltSD 2SD (cluster definition)
• lt3SD

25
Control traffic overhead
26
Link quality over time
Real world is tough unstable, asymmetric links
do exist
27
stretch comparison
High-level simulation 3200 nodes, high density
For average cases, S4 has routing and
transmission stretches close to optimal,
consistently smaller than BVR.
28
Transmission Stretch in TOSSIM simulation
BVR
S4
BVR stretch increases when the simulation is
more realistic S4 no change
29
Topology
A link between two nodes exists if the packet
delivery rates of both directions are above 30