1. Presence Information in Large Mesh Networks
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Presence Information in Large Mesh Networks
Date:
Authors:
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

2. Outline Presence protocol: Experiment: Protocol overview
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Outline
Presence protocol:
Protocol overview
Presence frame format
Presence table
Experiment:
Discovery and profile exchange time among 65 nodes
Convergence time (everyone knows about everyone else)
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

3. Presence Protocol Overview
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Presence Protocol Overview
A node receives presence beacons from its neighbors, eliminates duplicate information or information about itself, creates a new beacon that combines information the node already has with information it received and broadcasts a new beacon to its own neighbors.
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

4. Month Year
May 2008
doc.: IEEE yy/xxxxr0
Presence Protocol
Wait for a period T for presence beacons from neighboring nodes
For every beacon received:
For every entry in beacon:
if it is about the current node, or the current node is the witness, or the the serial number is not newer than the existing one, discard it!
if node/witness pair exists in presence table update number of arrivals and next arrival estimate both for node and witness
else add new entry in the table
Eliminate stale entries in presence table (ie. entries where the next arrival estimate has lapsed)
Create a new beacon using the minimum distances to each node in presence table
Broadcast beacon to neighbors
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

5. Presence Frame contents
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Presence Frame contents
ID of the node this entry is about
(MAC address, 6 bytes)
Unique ID for each entry published by
node <Node ID>
(2 byte)
ID of the node from which this entry was received
(MAC address, 6 bytes)
Distance from the current node to <Node ID>
(similar to ETX metric)
(1 byte)
Polychronis Ypodimatopoulos, MIT
P. Ypodimatopoulos
Presence Protocol for Large Mesh Networks
John Doe, Some Company

6. Distance calculation D = T/A Distance D: T: period of time
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Distance calculation
Distance D:
D = T/A
T: period of time
A: number of arrivals
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

7. Presence Table Presence information arriving at B: May 2008
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Presence Table
Presence information arriving at B:
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

8. Presence Table Presence information arriving at A: May 2008
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Presence Table
Presence information arriving at A:
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

9. Month Year
May 2008
doc.: IEEE yy/xxxxr0
Q: Why do we need multiple entries to a destination? A: To account for mobility
Presence information arriving at B:
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

10. Arrival estimates Count arrivals over time period T.
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Arrival estimates
Count arrivals over time period T.
Formulate a Poisson arrival rate (assuming arrivals are independent events)
Estimate time of next arrival with 90% accuracy
Example:
For T=1sec, accuracy 90%, next arrival must be in 2.3sec
For T=1sec, accuracy 100%, next arrival must be in infinity (!)
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

11. Features Constant protocol overhead:
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Features
Constant protocol overhead:
Overhead = N*B/T = 15*N^2/T = 15*N*f = O(N)
where B = 15*(N-1), T = N/f
N: number of nodes
B: size of presence beacon: ( )*(N-1) = O(N)
f: frequency at which we wish to receive presence beacons
T: period of time between consecutive presence beacons
Different beacon rates in different areas of the mesh network, according to node concentration
Routing protocol for communication with any other node in the network
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

12. Numbers Experiment: 65 nodes in full mesh (1-hop)
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Numbers
Experiment:
65 nodes in full mesh (1-hop)
Measured discovery and profile exchange time among all 65 nodes and convergence time (everyone knows about everyone else)
Each profile is 133 bytes and contains user information
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

13. Profile arrival times May 2008 doc.: IEEE 802.11-yy/xxxxr0 Month Year
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

14. CDF of Profile arrival times
Month Year
May 2008
doc.: IEEE yy/xxxxr0
CDF of Profile arrival times
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

15. Protocol overhead – Convergence time
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Protocol overhead – Convergence time
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

16. doc.: IEEE 802.11-yy/xxxxr0 Questions?
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Questions?
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

17. Numbers Experiment 2: Measured transfer time of a 2MB file to 27 nodes
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Numbers
Experiment 2:
Measured transfer time of a 2MB file to 27 nodes
27 nodes in full mesh (1-hop)
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

18. Test 2: File transfer: 2MB to 27 nodes
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Test 2: File transfer: 2MB to 27 nodes
Polychronis Ypodimatopoulos, MIT
John Doe, Some Company

19. Test 2: Transfer time vs. Number of nodes
Month Year
May 2008
doc.: IEEE yy/xxxxr0
Test 2: Transfer time vs. Number of nodes
Cerebro: 1Mbps (broadcast) simultaneous transfer.
TCP/IP: sequential, 10Mbps transfer is assumed to target nodes.
Polychronis Ypodimatopoulos, MIT
P. Ypodimatopoulos
Presence Protocol for Large Mesh Networks
John Doe, Some Company