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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. Outline. Introduction Network Management Techniques Reliable graph routing - PowerPoint PPT Presentation
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Reliable and Real-time Communication in Industrial Wireless Mesh Networks
Song Han, Xiuming Zhu, Al MokUniversity of Texas at Austin
Deji Chen, Mark NixonEmerson Process Management
Outline• Introduction
• Network Management Techniques– Reliable graph routing– Schedule construction and channel management
• Performance Evaluation
• Implementation and Deployment
• Future Work
2
Introduction
• WirelessHART network– Secure and TDMA-based wireless mesh networking technology– Centralized network architecture– Stringent timing and reliability requirements
3
• 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)
Introduction (cont.)
• Goals– Achieve reliable graph routing in WirelessHART network– Achieve real-time communication by deterministic link and
channel assignment– Evaluate their performance in industrial environments
4
• Challenge– The complexity of network management is pushed to the
centralized manager but engineering decisions can have large performance impact.
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
5
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
6
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
7
To avoid infinite forwarding loop:1) Only one cycle of length 2 in Gv
2) Each DEV on the cycle has direct edges to v
Constructing GB
8
G
A A
12
4
5
3
• Drop the links with low Receive Signal Strength (RSS) in the original network topology G
S
Constructing GB
9
G
A A
12
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}
S
Constructing GB
10
G
A A
12
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}
S
Constructing GB
11
G
A A
12
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}
S
Constructing GB
12
G
A A
12
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}
S
Constructing GB
13
G
A A
12
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}
S
Constructing GB
14
G
A A
12
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}
Construct Gv
15
• 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
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
16
Low configuration cost
High Scalability
High Reliability
An example of SRDR
17
G
A1 A2
21 3
4 5
(a) Original network topology (b) Downlink graph: g2Sequential route for Dev 2: g2
G
A1 A2
21 3
4 5
(c) Downlink graph: g3Sequential route for Dev 3: g3
G
A1 A2
21 3
4 5
(d) Downlink graph: g1Sequential route for Dev 1: g2, g1
G
A1 A2
21 3
4 5
(e) Downlink graph: g4Sequential route for Dev 4: g2, g1, g4
G
A1 A2
21 3
4 5
(f) Downlink graph: g5Sequential route for Dev 5: g2, g5
G
A1 A2
21 3
4 5
(b)Avoid node failure at DEV2
Local graph
SRDR vs. Standard Downlink Graph
18
(b) Downlink graph: g5Sequential route for Dev 5: g2, g5
G
A1 A2
21 3
4 5
(c) Standard downlink graph for Dev 5
G
A1 A2
21 3
4 5
(a) Downlink graph for Dev 2
G
A1 A2
21 3
4 5
Configure cost is reduced by 3 links
More significant improvement in large scale networks
Sequential Reliable Downlink Routing (SRDR) Extensions
• Network layer header extension:
19
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.
20
Optimization on SRDR
21
• 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
An example of the SRDR-OPT
22
S 2 4
1 3
g2 g3 g4
S 2
1
g2
2 4
3
g4
2
1 3
g3
Communication Schedule and Channel Management
23
• 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
Schedule Construction (An Example)
24
G
A B
1 2 3
1 sec 2 sec 1 sec
Ch Offset
Slot
16
0
1
2
100 200 300
.
.
.
400
Dev 1
AP A
Dev 2
Global Channel-Time Slot Matrix
Device Schedule
Schedule Construction (An Example)
25
G
A B
1 2 3
1 sec 2 sec 1 sec
Ch Offset
Slot
16
0
1
2
100 200 300
.
.
.
400
Dev 2
AP A
AP B
Schedule Construction (An Example)
26
G
A B
1 2 3
1 sec 2 sec 1 sec
Ch Offset
Slot
16
0
1
2
100 200 300
.
.
.
400
Dev 3
AP B
Dev 2
Schedule Construction (An Example)
27
G
A B
1 2 3
1 sec 2 sec 1 sec
Ch Offset
Slot
16
0
1
2
100 200 300
.
.
.
400
Dev 2
AP A
AP B
Schedule Construction (An Example)
28
G
A B
1 2 3
1 sec 2 sec 1 sec
Dev 2
AP A
AP B
Ch Offset
Slot
16
0
1
2
100 200 300
.
.
.
400
Channel offset will be converted into practical channel number in the runtime
Performance Evaluation
29
Configuration overhead in broadcast graphs Reachability in broadcast graphs
Recovery overhead to regain reliability Reachability in downlink graph
Performance Evaluation
30
Configuration overhead in downlink graphs Average latency vs. Network size
Success ratio vs. Sample rate Network utilization vs. Sample rate
Reusable local graph makes the difference Shortcut makes the difference
WirelessHART Prototype System
31
Major Components in the prototype :
• Network Manager• Gateway• Host Application• Access Point• Device• Sniffer
PC Side
Embedded Side
Overall Design of the System
32
Overview of the Network Manager
33
Network Topology
Device Configuration
Routing Graphs
Global ScheduleDevice ScheduleDevice Bandwidth
Overview of the System
34
• 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
Deployment (Work-in-progress)
35
UT Pickle Research Center Petroleum Engineering Department
Network Manager, Gateway and Access Point
Future Work
36
• 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