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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

An example of SRDR Avoid node failure at DEV2 Local graph

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

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

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.

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

An example of the SRDR-OPT

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

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

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

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

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

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

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

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

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

Overall Design of the System

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

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

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

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