1. Song Han, Xiuming Zhu, Al Mok University of Texas at Austin
Reliable and Real-time Communication in Industrial Wireless Mesh Networks
Song Han, Xiuming Zhu, Al Mok
University of Texas at Austin
Deji Chen, Mark Nixon
Emerson Process Management

2. Outline Introduction Network Management Techniques
Reliable graph routing
Schedule construction and channel management
Performance Evaluation
Implementation and Deployment
Future Work

3. Introduction WirelessHART network Previous work
Secure and TDMA-based wireless mesh networking technology
Centralized network architecture
Stringent timing and reliability requirements
Previous work
Full-blown WirelessHART stack (RTAS’08)
Compliance test suite (RTAS’09)
Data quality maintenance techniques in wireless network (RTSS’05, TC’08, RTSS’09)

4. Introduction (cont.) Challenge Goals
The complexity of network management is pushed to the centralized manager but engineering decisions can have large performance impact.
Goals
Achieve reliable graph routing in WirelessHART network
Achieve real-time communication by deterministic link and channel assignment
Evaluate their performance in industrial environments

5. Reliable Graph Routing
Reliable Broadcast Graph (GB)
GB is a graph connecting Gateway (GW) downward to all DEVs
Broadcasts common configuration and control messages
Each DEV has at least two parents in GB
Give some bullets to explain the definitions

6. Reliable Graph Routing (Cont.)
Reliable Uplink Graph (GU)
GU is a graph connecting all DEVs upward to the Gateway
DEVs propagate periodic process data
Each DEV has at least two children in GU
Both GB and GU have no fewer than 2 Access Points
Give some bullets to explain the definitions

7. Reliable Graph Routing (Cont.)
Reliable Downlink Graph (Gv)
The graph from the Gateway to DEV v
Transmit unicast messages from the GW and NM to v
Each intermediate DEV has at least two children in Gv
There exists at least one directed cycle in Gv
To avoid infinite forwarding loop:
Only one cycle of length 2 in Gv
Each DEV on the cycle has direct edges to v

8. Constructing GB
Drop the links with low Receive Signal Strength (RSS) in the original network topology G G A A 1 2
An animation to show the construction 3 4 5

9. Constructing GB
Drop the links with low RSS in the original network topology G
Maintain a set of explored node S, initially S = {G, APs} S G A A 1 2
An animation to show the construction 3 4 5

10. Constructing GB S S = {G, Aps, 1}
Drop the links with low RSS in the original network topology G
Maintain a set of explored node S, initially S = {G, APs}
Grow S according to
S = {G, Aps, 1} S G A A 1 2
An animation to show the construction 3 4 5

11. Constructing GB S S = {G, Aps, 1, 2}
Drop the links with low RSS in the original network topology G
Maintain a set of explored node S, initially S = {G, APs}
Grow S according to
S = {G, Aps, 1, 2} S G A A 1 2
An animation to show the construction 3 4 5

12. Constructing GB S S = {G, Aps, 1, 2, 4}
Drop the links with low RSS in the original network topology G
Maintain a set of explored node S, initially S = {G, APs}
Grow S according to
S = {G, Aps, 1, 2, 4} G S A A 1 2
An animation to show the construction 3 4 5

13. Constructing GB S S = {G, Aps, 1, 2, 4, 5}
Drop the links with low RSS in the original network topology G
Maintain a set of explored node S, initially S = {G, APs}
Grow S according to
S = {G, Aps, 1, 2, 4, 5} S G A A 1 2
An animation to show the construction 3 4 5

14. Constructing GB S S = {G, Aps, 1, 2, 4, 5, 3}
Drop the links with low RSS in the original network topology G
Maintain a set of explored node S, initially S = {G, APs}
Grow S according to
S = {G, Aps, 1, 2, 4, 5, 3} S G A A 1 2
An animation to show the construction 3 4 5

15. Construct Gv More complicated than GB and GU:
Only involves part of the nodes in G
The existence of cycle
Restrictions: One cycle (length 2) between the parents of destination node v
Standard Reliable Downlink Graph
Construct a completely new graph from GW to DEV v
Configuration in intermediate nodes cannot be reused
High configuration cost and poor scalability
An animation to show the construction

16. Sequential Reliable Downlink Routing (SRDR)
Key Principles
Each node only keep a small local graph
Local graphs are reusable building blocks for constructing reliable downlink graph for multiple destinations
Low configuration cost
High Scalability
High Reliability

17. An example of SRDR
Avoid node failure at DEV2
Local graph

18. SRDR vs. Standard Downlink Graph
Configure cost is reduced by 3 links
More significant improvement in large scale networks

19. Sequential Reliable Downlink Routing (SRDR) Extensions
Network layer header extension:

20. SRDR Extensions Routing module extension:
retrieve the earliest graph ID in the graph list and route the packet on this graph
If current node is the sink of the graph, remove this graph ID and route the packet on the next earliest graph.
If routing is failed, remove this graph ID and try the next earliest graph ID if it has the corresponding edges.

21. Optimization on SRDR
In SRDR, routing is performed strictly according to the sequence in the ordered graph list.
SRDR-OPT
Observation: each node can keep graph info to multiple destination.
Have chance to take the “shortcut”
Principle: Search the ordered graph list backward and route the packet on the first graph ID that is stored in its table

22. An example of the SRDR-OPT

23. Communication Schedule and Channel Management
Key Principles:
Spread out the channel usage in the network
Apply Fastest Sample Rate First policy (FSRF)
Allocate the links iteratively from Src to Dest
Split traffic (bandwidth) among all successors
An animation to show the construction

24. Schedule Construction (An Example)
Ch Offset
Slot 16
Global Channel-Time Slot Matrix . 2 1
100
200
300
400
Device Schedule G
An animation to show the construction
Dev 1
AP A
Dev 2 A B 1 2 3
1 sec
2 sec
1 sec

25. Schedule Construction (An Example)
Ch Offset
Slot 16 . 2 1
100
200
300
400 G
An animation to show the construction
Dev 2
AP A
AP B A B 1 2 3
1 sec
2 sec
1 sec

26. Schedule Construction (An Example)
Ch Offset
Slot 16 . 2 1
100
200
300
400 G
An animation to show the construction
Dev 3
AP B
Dev 2 A B 1 2 3
1 sec
2 sec
1 sec

27. Schedule Construction (An Example)
Ch Offset
Slot 16 . 2 1
100
200
300
400 G
An animation to show the construction
Dev 2
AP A
AP B A B 1 2 3
1 sec
2 sec
1 sec

28. Schedule Construction (An Example)
Ch Offset
Slot 16
Channel offset will be converted into practical channel number in the runtime . 2 1
100
200
300
400 G
An animation to show the construction
Dev 2
AP A
AP B A B 1 2 3
1 sec
2 sec
1 sec

29. Performance Evaluation
Configuration overhead in broadcast graphs
Reachability in broadcast graphs
An animation to show the construction
Recovery overhead to regain reliability
Reachability in downlink graph

30. Performance Evaluation
Configuration overhead in downlink graphs
Average latency vs. Network size
Reusable local graph makes the difference
Shortcut makes the difference
Focus on the local graph, give an animation here
Success ratio vs. Sample rate
Network utilization vs. Sample rate

31. WirelessHART Prototype System
Major Components in the prototype :
Network Manager
Gateway
Host Application
Access Point
Device
Sniffer
PC Side
Embedded Side

32. Overall Design of the System

33. Overview of the Network Manager
Network Topology
Routing Graphs
Device Configuration
Add some comments here about the GUI
Global Schedule
Device Bandwidth
Device Schedule

34. Overview of the System 10 devices and 1 AP in the system
Devices publish data to GW with different sampling rates (1sec – 8sec)
Retry happens but no packet loss is detected

35. Deployment (Work-in-progress)
Network Manager, Gateway and Access Point
Remove the UT ACES
UT Pickle Research Center
Petroleum Engineering Department

36. Future Work A general and adjustable framework
Applications have different requirements on timing, security, …
Building an adjustable MAC state machine
Collaborative wireless system
Wifi, WirelessHART, ZigBee,…
Competition -> Collaboration