Routing packets on a network using directed graphs

A method of routing a data packet between a first node and a second node on a communication network includes defining a first graph through the first node and the second node and zero or more intermediate nodes, associating several nodes which belong to the communication network with the first graph, associating a first unique graph identifier with the first graph and providing at least partial definitions of the first graph and the first unique identifier to at least some of the nodes associated with the first graph. The method then sends data packet with the graph identifier from the first node, and directs the data packet to the second node via the zero or more intermediate nodes using the graph identifier. This method may include forwarding the packet to a neighbor node of an intermediate node if the intermediate node and the neighbor node are nodes associated with the first graph and if the intermediate node and the neighbor node are connected by at least one direct communication connection.

FIELD OF TECHNOLOGY

This patent relates generally to communication protocols and, more particularly, to a method of routing packets between nodes of a mesh or a star mesh network.

BACKGROUND

Communication protocols rely on various routing techniques to transfer data between communication endpoints on a communication network. Communication or network protocols and the corresponding routing strategies are typically selected in view of such factors as knowledge of network topology, size of the network, type of medium used as a signal carrier, security and reliability requirements, tolerable transmission delays, and types of devices forming the network. Due to a large number of such factors, a typical routing technique meets some of the design objectives at the expense of the others. For example, a certain routing technique may provide a high level of reliability in data delivery but may also require a relatively high overhead. Thus, while there are many known approaches to routing and many protocols compatible with these routing methods, there remain communication networks with the specific requirements that are not fully satisfied by any of the available routing methods and protocols. Moreover, as new types of communication networks, with the increasing demands for efficiency, throughput, and reliability, emerge in various industrial and commercial applications, the architects and developers frequently encounter new problems which are not easily addressed by the existing protocols and the associated routing techniques.

Generally speaking, a communication network includes nodes which are the senders and recipients of data sent over communication paths (either hardwired or wireless communication paths) connecting the nodes. Additionally, communication networks typically include dedicated routers responsible for directing traffic between nodes, and, optionally, include dedicated devices responsible for configuring and managing the network. Some or all of the nodes may be also adapted to function as routers so as to direct traffic sent between other network devices. Network devices may be inter-connected in a wired or wireless manner, and network devices may have different routing and transfer capabilities than certain nodes within the network. For example, dedicated routers may be capable of high volume transmissions while some nodes may only be capable of sending and receiving relatively little traffic over the same period of time. Additionally, the connections between nodes on a network may have different throughput capabilities and different attenuation characteristics. A fiber-optic cable, for example, may be capable of providing a bandwidth several orders of magnitude higher than a wireless link because of the difference in the inherent physical limitations of the medium.

In order for a node to send data to another node on a typical network, either the complete path from the source to the destination or the immediately relevant part of the path must be known. For example, the World Wide Web (WWW) allows pairs of computer hosts to communicate over large distances without either host knowing the complete path prior to sending the information. Instead, hosts are configured with the information about their assigned gateways and dedicated routers. In particular, the Internet Protocol (IP) provides network layer connectivity to the WWW. The IP defines a sub-protocol known as Address Resolution Protocol (ARP) which provides a local table at each host specifying the routing rules. Thus, a typical host connected to the WWW or a similar Wide Area Network (WAN) may know to route all packets with the predefined addresses matching a pre-configured pattern to host A and route the rest of the packets to host B. Similarly, the intermediate hosts forwarding the packets, or “hops,” also execute partial routing decisions and typically direct data in the general direction of the destination.

In most network protocols, most or all network devices are assigned sufficiently unique addresses to enable hosts to exchange information in an unambiguous manner. At least in case of unicast (one-to-one) transmissions, the destination address must be specified at the source. For this reason, network protocols typically define a rigid addressing scheme. As one of ordinary skill in the art will recognize, modifying or expanding addressing schemes is a complicated and expensive process. For example, the transition from version 4 of the IP protocol (IPv4) to version 6 (IPv6) requires significant updates to much of the infrastructure supporting IPv4. On the other hand, defining addressing schemes with large capability for small networks creates an unnecessary overhead. Thus, a network protocol ideally suited for a particular application offers a sufficient number of possible addresses without an excessive overhead in data transmission.

In short, there is a number of factors influencing the implementation of particular protocols in particular industries. In the process control industry, it is known to use standardized communication protocols to enable devices made by different manufacturers to communicate with one another in an easy to use and implement manner. One such well known communication standard used in the process control industry is the Highway Addressable Remote Transmitter (HART) Communication Foundation protocol, referred to generally as the HART® protocol. Generally speaking, the HART protocol supports a combined digital and analog signal on a dedicated wire or set of wires, in which on-line process signals (such as control signals, sensor measurements, etc.) are provided as an analog current signal (e.g., ranging from 4 to 20 milliamps) and in which other signals, such as device data, requests for device data, configuration data, alarm and event data, etc., are provided as digital signals superimposed or multiplexed onto the same wire or set of wires as the analog signal. However, the HART protocol currently requires the use of dedicated, hardwired communication lines, resulting in significant wiring needs within a process plant.

There has been a move, in the past number of years, to incorporate wireless technology into various industries including, in some limited manners, the process control industry. However, there are significant hurdles in the process control industry that limit the full scale incorporation, acceptance and use of wireless technology. In particular, the process control industry requires a completely reliable process control network because loss of signals can result in the loss of control of a plant, leading to catastrophic consequences, including explosions, the release of deadly chemicals or gases, etc. For example, Tapperson et al., U.S. Pat. No. 6,236,334 discloses the use of a wireless communications in the process control industry as a secondary or backup communication path or for use in sending non-critical or redundant communication signals. Moreover, there have been many advances in the use of wireless communication systems in general that may be applicable to the process control industry, but which have not yet been applied to the process control industry in a manner that allows or provides a reliable, and in some instances completely wireless, communication network within a process plant. U.S. Patent Application Publication Numbers 2005/0213612, 2006/0029060 and 2006/0029061 for example disclose various aspects of wireless communication technology related to a general wireless communication system.

Similar to wired communications, wireless communication protocols are expected to provide efficient, reliable and secure methods of exchanging information. Of course, much of the methodology developed to address these concerns on wired networks does not apply to wireless communications because of the shared and open nature of the medium. Further, in addition to the typical objectives behind a wired communication protocol, wireless protocols face other requirements with respect to the issues of interference and co-existence of several networks that use the same part of the radio frequency spectrum. Moreover, some wireless networks operate in the part of the spectrum that is unlicensed, or open to the public. Therefore, protocols servicing such networks must be capable of detecting and resolving issues related to frequency (channel) contention, radio resource sharing and negotiation, etc.

In the process control industry, developers of wireless communication protocols face additional challenges, such as achieving backward compatibility with wired devices, supporting previous wired versions of a protocol, providing transition services to devices retrofitted with wireless communicators, and providing routing techniques which can ensure both reliability and efficiency. Meanwhile, there remains a wide number of process control applications in which there are few, if any, in-place measurements. Currently these applications rely on observed measurements (e.g. water level is rising) or inspection (e.g. period maintenance of air conditioning unit, pump, fan, etc) to discover abnormal situations. In order to take action, operators frequently require face-to-face discussions. Many of these applications could be greatly simplified if measurement and control devices were utilized; however, current measurement devices usually require power, communications infrastructure, configuration, and support infrastructure which simply is not available.

In yet another aspect, the process control industry requires that the communication protocol servicing a particular process control network be able to route data reliably and efficiently. On the other hand, the communication protocol should preferably allow sufficient flexibility with respect to transmitting different types of data. In particular, a process control network may transmit data related to device diagnostics, process variable measurements, alarms or alerts, device or loop configuration data, network management data, etc. These types of data may have different latency and reliability requirements, and may be associated with different amounts of information transmitted per unit of time.

SUMMARY

A hardware or software management entity residing in or outside a communications network including several network devices develops a routing scheme for the network by analyzing the topology of the network, defining a set of graphs for use in routing or transmitting data between various nodes of the network, each graph including one or more communication paths between pairs of network devices, and assigns a unique graph identifier to each graph. In some embodiments, the network is a wireless network and the graphs are directed graphs and, accordingly, the communication paths are unidirectional communication paths. In some embodiments, the network is a mesh network including network devices that originate and route data on behalf of other network devices. In a still further embodiment, the network conforms to a star mesh topology, in which some network devices can only receive data or originate data and some network devices can receive data, originate data, and relay data between other network devices.

Upon defining the set of graphs, the management entity communicates the relevant routing information to some or all network devices (nodes) so that a packet sent from one network device to another network device can be properly routed through the network according to the graph identifier included in the header or in the trailer of the data packet. In one aspect, the management entity improves the security of the network by not informing some or all of the network devices of a complete topology of the network. In another embodiment, the function of analyzing the network and obtaining the topology of the network is distributed among at least several network devices so that one or more network devices participate in defining unidirectional or bidirectional graphs. In a still further embodiment, the relevant routing information communicated to each network device includes a list of graph identifiers and, for each graph identifier, one or more of the neighboring devices which serves as possible next hops in the identified communication path (or “route”). In this embodiment, a network device may participate in “graph routing” by associating a graph identifier with a data packet, including the graph identifier in the header or trailer of the data packet, and sending the data packet to a destination device without specifying any additional routing information. An intermediate device, or a “hop” in the communication path, may properly route the data packet by processing only the graph identifier supplied with the data packet. In one embodiment, multiple non-identical graphs are defined between some or all of the pairs of devices for redundancy and increased reliability. In one embodiment, the management entity responsible, in part, for defining unidirectional graphs is a dedicated network manager and may be implemented as a software module run on a host residing in or outside of the network. In another embodiment, the network manager may be a dedicated physical device communicatively coupled to the network. In yet another embodiment, the network manager may be distributed among several devices residing in or outside of the network.

In an embodiment, a pair of communicating devices may include a gateway adapted to communicate with another network or a non-network host in addition to a network device. In accordance with this embodiment, directed graphs are defined in a downstream (from gateway to device) direction and in an upstream (from device to gateway) direction. In some embodiments, the graph including a downstream path from a gateway to a network device and the graph including an upstream path from the network device to the gateway are not symmetrical. In some embodiments, the network may include multiple network access points and redundant gateways. Additionally, the paths defined by the routes may be compatible with different transmission schedules and may be configured independently of allocating wireless resources to the transmitting and listening devices.

If desired, the wireless network may operate in a process control environment to support communications between wireless field devices, legacy field devices coupled to wireless adapters, portable monitoring devices, a gateway device providing access to one or more operator workstations, and other devices. Some or all of the devices participating in the wireless network report one, all, or any combination of process control measurements, diagnostic data, device management data, configuration data, network management data, etc. If desired, the wireless network applies the same routing techniques to each type of data, formats each type of data into data packets, and uses the same layer of a corresponding protocol stack to route the data packets of each type.

The wireless network may additionally implement source routing to allow a source network device to specify a complete deterministic communication path to a destination network device. In accordance with this feature, the management entity such as the network manager communicates a partial or a complete topology of the network to the network device so that the network device may specify each intermediate device in a communication path to a destination device. If desired, the network devices configured for both graph routing and source routing may select between graph routing and source routing according to a latency requirement of a packet. Additionally or alternatively, these network devices may select between graph routing and source routing according to a reliability requirement of the data packet. If desired, when the network is implemented in a process control environment, the network may select between graph routing and source routing based on whether a data packet is associated with process control or management data.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary communication network10in which the communication routing techniques described herein may be used. In particular, the network10may include a plant automation/control network12connected to a wireless communication network14. The plant automation network12may include one or more stationary workstations16and one or more portable workstations18connected over a communication backbone20which may be implemented using Ethernet, RS-485, Profibus DP, or any other suitable communication hardware and protocol. The workstations16,18and other equipment forming the plant automation network12may provide various control and supervisory functions to plant personnel, including providing access to devices in the wireless network14. The plant automation/control network12and the wireless network14may be connected via a gateway device22. More specifically, the gateway device22may be connected to the backbone20in a wired manner and may communicate with the plant automation/control network12using any suitable (e.g., known) communication protocol. The gateway device22, which may be implemented in any other desired manner (e.g., as a standalone device, a card insertable into an expansion slot of the host workstations16or18, as a part of the input/output (IO) subsystem of a PLC-based or DCS-based system, etc.), may provide applications that are running on the network12with access to various devices of the wireless network14. In addition to protocol and command conversion, the gateway device22may provide synchronized clocking used by time slots and superframes (sets of communication time slots spaced equally in time) of a scheduling scheme associated with a wireless protocol implemented in the wireless network14.

In some configurations, the network10may include more than one gateway device22to improve the efficiency and reliability of the network10. In particular, multiple gateway devices22may provide additional bandwidth for the communication between the wireless network14and the plant automation network12, as well as the outside world. On the other hand, the gateway device22may request bandwidth from the appropriate network service according to the gateway communication needs within the wireless network14. The gateway device22may further reassess the necessary bandwidth while the communication system is operational. For example, the gateway device22may receive a request from a host residing outside of the wireless network14to retrieve a large amount of data. The gateway device22may then request additional bandwidth from a dedicated service to accommodate this transaction. The gateway device22may also or at some later time request the release of the unnecessary bandwidth upon completion of the transaction.

To further increase bandwidth and improve reliability, the gateway device22may be functionally divided into a virtual gateway24and one or more network access points25, which may be separate physical devices in wired communication with the gateway device22. However, whileFIG. 1illustrates a wired connection26disposed between the physically separate gateway device22and the access points25, it will be understood that the elements22-26may also be provided as an integral device. Because the network access points25may be physically separated from the gateway device22, the access points25may be strategically placed in several different locations with respect to the wireless network14. In addition to increasing the bandwidth, the use of multiple access points25can increase the overall reliability of the wireless network14by compensating for a potentially poor signal quality at one access point25with the use of the other access point25. Having multiple access points25also provides redundancy in case of a failure at one or more of the access points25.

In addition to allocating bandwidth and otherwise bridging the networks12and14, the gateway device22may perform one or more managerial functions in the wireless network14. As illustrated inFIG. 1, a network manager software module27and a security manager software module28may be stored in and executed in the gateway device22. Alternatively, the network manager27and/or the security manager28may run on one of the hosts16or18in the plant automation network12. For example, the network manager27may run on the host16and the security manager28may run on the host18. The network manager27may be responsible for configuration of the wireless network14, scheduling communication between wireless devices, managing routing tables associated with the wireless devices, monitoring the overall health of the wireless network14, reporting the health of the wireless network14to the workstations16and18, as well as other administrative and supervisory functions. Although a single active network manager27may be sufficient in the wireless network14, redundant network managers27may be similarly supported to safeguard the wireless network14against unexpected equipment failures. Meanwhile, the security manager28may be responsible for protecting the wireless network14from malicious or accidental intrusions by unauthorized devices. To this end, the security manager28may manage authentication codes, verify authorization information supplied by devices attempting to join the wireless network14, update temporary security data such as expiring secret keys, and perform other security functions.

With continued reference toFIG. 1, the wireless network14may include one or more field devices30-36. In general, process control systems, like those used in chemical, petroleum or other process plants, include field devices such as valves, valve positioners, switches, sensors (e.g., temperature, pressure and flow rate sensors), pumps, fans, etc. Generally speaking, field devices perform physical control functions within the process such as opening or closing valves or take measurements of process parameters. In the wireless communication network14, field devices30-36are producers and consumers of wireless communication packets.

The devices30-36may communicate using a wireless communication protocol that provides the functionality of a similar wired network, with similar or improved operational performance. In particular, this protocol may enable the system to perform process data monitoring, critical data monitoring (with the more stringent performance requirements), calibration, device status and diagnostic monitoring, field device troubleshooting, commissioning, and supervisory process control. The applications performing these functions, however, typically require that the protocol supported by the wireless network14provide fast updates when necessary, move large amounts of data when required, and support network devices which join the wireless network14, even if only temporarily for commissioning and maintenance work.

In one embodiment, the wireless protocol supporting network devices30-36of the wireless network14is an extension of the known wired HART protocol, a widely accepted industry standard, that maintains the simple workflow and practices of the wired environment. In this sense, the network devices30-36may be considered and will be referred to herein as WirelessHART devices, and the wireless network14accordingly may be considered a WirelessHART network. The same tools used for wired HART devices may be easily adapted to wireless devices30-36with a simple addition of new device description files. In this manner, the wireless protocol may leverage the experience and knowledge gained using the wired HART protocol to minimize training and to simplify maintenance and support. Generally speaking, it may be convenient to adapt a protocol for wireless use so that most applications running on a device do not “notice” the transition from a wired network to a wireless network. Clearly, such transparency greatly reduces the cost of upgrading networks and, more generally, reduces the cost associated with developing and supporting devices that may be used with such networks. Some of the additional benefits of a wireless extension of the well-known HART protocol include access to measurements that were difficult or expensive to obtain with wired devices and the ability to configure and operate instruments from system software that can be installed on laptops, handhelds, workstations, etc. Another benefit is the ability to send diagnostic alerts from wireless devices back through the communication infrastructure to a centrally located diagnostic center. For example, every heat exchanger in a process plant could be fitted with a WirelessHART device and the end user and supplier could be alerted when a heat exchanger detects a problem.

Yet another benefit is the ability to monitor conditions that present serious health and safety problems. For example, a WirelessHART device could be placed in flood zones on roads and be used to alert authorities and drivers about water levels. Other benefits include access to a wide range of diagnostics alerts and the ability to store trended as well as calculated values at the WirelessHART devices so that, when communications to the device are established, the values can be transferred to a host. In this manner, the WirelessHART protocol can provide a platform that enables host applications to have wireless access to existing HART-enabled field devices and the WirelessHART protocol can support the deployment of battery operated, wireless only HART-enabled field devices. The WirelessHART protocol may be used to establish a wireless communication standard for process applications and may further extend the application of HART communications and the benefits that this protocol provides to the process control industry by enhancing the basic HART technology to support wireless process automation applications.

Referring again toFIG. 1, the field devices30-36may be WirelessHART field devices, each provided as an integral unit and supporting all layers of the WirelessHART protocol stack. For example, in the wireless network14, the field device30may be a WirelessHART flow meter, the field devices32may be WirelessHART pressure sensors, the field device34may be a WirelessHART valve positioner, and the field device36may a WirelessHART pressure sensor. Importantly, the wireless devices30-36may support all of the HART features that users have come to expect from the wired HART protocol. As one of ordinary skill in the art will appreciate, one of the core strengths of the HART protocol is its rigorous interoperability requirements. In some embodiments, all WirelessHART equipment includes core mandatory capabilities designed to allow equivalent device types (made by different manufacturers, for example) to be interchanged without compromising system operation. Furthermore, the WirelessHART protocol is backward compatible to HART core technology such as the device description language (DDL). In the preferred embodiment, all of the WirelessHART devices should support the DDL, which ensures that end users immediately have the tools to begin utilizing the WirelessHART protocol.

If desired, the wireless network14may include non-wireless devices. For example, a field device38ofFIG. 1may be a legacy 4-20 mA device and a field device40may be a traditional wired HART device. To communicate within the wireless network14, the field devices38and40may be connected to the WirelessHART network14via a WirelessHART adapter (WHA)50or50A. Additionally, the WHA50may support other communication protocols such as Foundation® Fieldbus, PROFIBUS, DeviceNet, etc. In these embodiments, the WHA50supports protocol translation on a lower layer of the protocol stack. Additionally, it is contemplated that a single WHA50may also function as a multiplexer and may support multiple HART or non-HART devices.

Plant personnel may additionally use handheld devices for installation, control, monitoring, and maintenance of network devices. Generally speaking, handheld devices are portable equipment that can connect directly to the wireless network14or through the gateway devices22as a host on the plant automation network12. As illustrated inFIG. 1, a WirelessHART-connected handheld device55may communicate directly with the wireless network14. When operating with a formed wireless network14, the handheld device55may join the wireless network14as just another WirelessHART field device. When operating with a target network device that is not connected to a WirelessHART network, the handheld device55may operate as a combination of the gateway device22and the network manager27by forming its own wireless network with the target network device.

A plant automation network-connected handheld device (not shown) may be used to connect to the plant automation network12through known networking technology, such as Wi-Fi. This device communicates with the network devices30-40through the gateway device22in the same fashion as external plant automation servers (not shown) or in the same fashion that the workstations16and18communicate with the devices30-40.

Additionally, the wireless network14may include a router device60. The router device60is a network device that forwards packets from one network device to another network device. A network device that is acting as a router device uses internal routing tables to conduct routing, i.e., to decide to which network device a particular packet should be sent. Stand alone routers such as the router60may not be required in those embodiments where all of the devices on the wireless network14support routing. However, it may be beneficial (e.g. to extend the network, or to save the power of a field device in the network) to add one or more dedicated routers60to the network14.

All of the devices directly connected to the wireless network14may be referred to as network devices. In particular, the wireless field devices30-36, the adapters50, the routers60, the gateway devices22, the access points25, and the wireless handheld device55are, for the purposes of routing and scheduling, network devices, each of which forms a node of the wireless network14. In order to provide a very robust and an easily expandable wireless network, all of the devices in a network may support routing and each network device may be globally identified by a substantially unique address, such as a HART protocol address, for example. Some or all of the network devices in the wireless network14may include a processor and a memory to store data, programmable instructions, and other information. The processing and storage capabilities of the network may vary significantly. It will be appreciated that the network devices may be made by different manufacturers or may represent different versions or generations of a particular device.

The network manager27may contain a complete list of network devices and may assign each device a short, network unique nickname. Additionally, each network device may store information related to update rates, connection sessions, and device resources. In short, each network device may maintain up-to-date information related to routing and scheduling within the wireless network14. The network manager27may communicate this information to network devices whenever new devices join the network or whenever the network manager27detects or originates a change in topology or scheduling of the wireless network14.

Further, each network device may store and maintain a list of neighbor devices that the network device has identified during listening operations. Generally speaking, a neighbor of a network device is another network device of any type potentially capable of establishing a communication connection with the network device in accordance with the standards imposed by a corresponding network. In case of the WirelessHART network14, the connection is a direct wireless connection. However, it will be appreciated that a neighboring device may also be a network device connected to the particular device in a wired manner. As will be discussed later, network devices promote their discovery by other network devices through advertisement, or special messages sent out during designated periods of time. Network devices operatively connected to the wireless network14have one or more neighbors which they may choose according to the strength of the advertising signal or to some other principle.

In the example illustrated inFIG. 1, each of a pair of network devices connected by a direct wireless connection65recognizes the other as a neighbor. Thus, network devices of the wireless network14may form a large number of inter-device connections65. The possibility and desirability of establishing a direct wireless connection65between two network devices is determined by several factors, such as the physical distance between the nodes, obstacles between the nodes (devices), signal strength at each of the two nodes, etc. Thus, each wireless connection65may be characterized by a large set of parameters related to the frequency of transmission, the method of access to a radio resource, etc. One of ordinary skill in the art will recognize that, in general, wireless communication protocols may operate on designated frequencies, such as the ones assigned by the Federal Communications Commission (FCC) in the United States, or in the unlicensed part of the radio spectrum (e.g., 2.4 GHz). While the system and method discussed herein may be applied to a wireless network operating on any designated frequency or range of frequencies, the example embodiment discussed below relates to the wireless network14operating in the unlicensed, or shared part of the radio spectrum. In accordance with this embodiment, the wireless network14may be easily activated and adjusted to operate in a particular unlicensed frequency range as needed.

With continued reference toFIG. 1, two or more direct wireless connections65may form a communication path between nodes that cannot form a direct wireless connection65. For example, the direct wireless connection65A between the WirelessHART hand-held device55and WirelessHART device36, along with the direct wireless connection65B between the WirelessHART device36and the router60, may form a communication path between the devices55and60. As discussed in greater detail below, at least some of the communication paths may be directed communication paths (i.e., permitting data transfer in only one direction between a pair of devices). Meanwhile, the WirelessHART device36may directly connect to each of the network devices55,60,32, and to the network access points25A and25B. In general, network devices operating in the wireless network14may originate data packets, relay data packets sent by other devices, or perform both types of operations. As used herein, the term “end device” refers to a network device that does not relay data packets sent by other devices and term “routing device” refers to a network device that relays data packets traveling between other network devices. Of course, a routing device may also originate its own data. One or several end devices and routing devices, along with several direct connections65, may thus form a part of a mesh network.

Because a process plant may have hundreds or even thousands of field devices, the wireless network14operating in the plant may include a large number of nodes and, in many cases, an even larger number of direct connections65between pairs of nodes. As a result, the wireless network14may have a complex mesh topology, and some pairs of devices that do not share a direct connection65may have to communicate through many intermediate hops to perform communications between these devices. Thus, a data packet may sometimes need to travel along many direct connections65after leaving a source device but before reaching a destination device, and each direct connection65may add a delay to the overall delivery time of the data packet. Moreover, some of these intermediate devices may be located at an intersection of many communication paths of a mesh network. As such, these devices may be responsible for relaying a large number of packets originated by many different devices, possibly in addition to originating its own data. Consequently, a relatively busy intermediate device may not forward a transient data packet immediately, and instead may queue the packet for a relatively significant amount of time prior to sending the packet to a next node in the corresponding communication path. When the data packet eventually reaches the destination device, the destination device may reply with an acknowledgement packet which may also encounter similar delays. During the time the packet travels to the destination device and the corresponding acknowledgment packet travels back to the originating device from the destination device, the originating node may not know whether the data packet has successfully reached the destination device. Moreover, devices may leave the wireless network14due to scheduled maintenance and upgrades or due to unexpected failures, thus changing the topology of the mesh network and destroying some of the communication paths. Similarly, the devices may join the wireless network14, adding additional direct connections65. These and other changes to the topology of the wireless network14may significantly impact data transmissions between pairs of nodes if not processed in an efficient and timely manner.

Importantly, however, the efficiency of delivering data packets may largely determine the reliability, security, and the overall quality of plant operations. For example, a data packet including measurements indicative of an excessive temperature of a reactor should quickly and reliably reach another node, such as the hand-held device55, so that the operator or a controller may immediately take the appropriate action and address a dangerous condition if necessary. To efficiently utilize the available direct wireless connections65and properly adjust to the frequently changing network topology, the network manager27may maintain a complete network map67, may define a routing scheme that connects at least some pairs of network devices30-50, and may communicate the relevant parts of the routing scheme to each network device that participates in the routing scheme.

In particular, the network manage27may define a set of directed graphs including one or more unidirectional communication paths, assign a graph identifier to each defined directed graph, and may communicate a relevant part of each graph definition to each corresponding network device, which may then update the device-specific, locally stored connection table69. As explained in more detail below, the network devices30-50may then route data packets based on the graph identifier included in the headers or the trailers of the data packets. If desired, each connection table69may only store routing information directly related to the corresponding network device, so that the network device does not know the complete definition of a directed graph which includes the network device. In other words, the network device may not “see” the network beyond its immediate neighbors and, in this sense, the network device may be unaware of the complete topology of the wireless network14. For example, the router device60illustrated inFIG. 1may store a connection table69A, which may only specify the routing information related to the neighboring network devices32,36,50, and34. Meanwhile, the WHA50A may store a connection table69B, which accordingly may specify the routing information related to the neighbors of the WHA50A.

In some cases, the network manager27may define duplicate communication paths between pairs of network devices to ensure that a data packet may still reach the destination device along the secondary communication path if one of the direct connections65of the primary communication path becomes unavailable. However, some of the direct connections65may be shared between the primary and the secondary path of a particular pair of network devices. Moreover, the network manager27may, in some cases, communicate the entire communication path to be used to a certain network device, which may then originate a data packet and include the complete path information in the header or the trailer of the data packet. Preferably, network devices use this method of routing for data which does not have stringent latency requirements. As discussed in detail below, this method (referred to herein as “source routing”) may not provide the same degree of reliability and flexibility and, in general, may be characterized by longer delivery delays.

The network manager27may also manage the available radio resources. In particular, the network manager27may partition the radio bandwidth allocated to the wireless network14into individual communication channels, and further measure transmission and reception opportunities on each channel in such units as Time Division Multiple Access (TDMA) communication timeslots, for example. In particular, the wireless network14may operate within a certain frequency band which, in most cases, may be safely associated with several distinct carrier frequencies, so that communications at one frequency may occur at the same time as communications at another frequency within the band. One of ordinary skill in the art will appreciate that carrier frequencies in a typical application (e.g., public radio) are sufficiently spaced apart to prevent interference between the adjacent carrier frequencies. For example, in the 2.4 GHz band, IEEE assigns frequency 2.455 to channel number21and frequency 2.460 to channel number22, thus allowing the spacing of 5 KHz between two adjacent segments of the 2.4 GHz band. The complete network map67may thus associate each communication channel with a distinct carrier frequency, which may be the center frequency in a particular segment of the band.

Meanwhile, as typically used in the industries utilizing TDMA technology, the term “timeslot” refers to a segment of a specific duration into which a larger period of time is divided to provide a controlled method of bandwidth sharing. For example, a second may be divided into 10 equal 100 millisecond timeslots. Although the complete network map67preferably allocates resources as timeslots of a single fixed duration, it is also possible to vary the duration of the timeslots, provided that each relevant node of the wireless network14is properly notified of the change. To continue with the example definition of ten 100-millisecond timeslots, two devices may exchange data every second, with one device transmitting during the first 100 ms period of each second (i.e., the first timeslot), the other device transmitting during the fourth 100 ms period of each second (i.e., the fourth timeslot), and with the remaining timeslots being unoccupied. Thus, a node on the wireless network14may identify the scheduled transmission or reception opportunity by the frequency of transmission and the timeslot during which the corresponding device may transmit or receive data.

The communication protocol supporting the wireless network14generally described above is referred to herein as the WirelessHART protocol70, and the operation of this protocol is discussed in more detail with respect toFIG. 2. However, it will be noted that the WirelessHART protocol70is presented herein by way of example only, and that a suitable protocol may be also defined without sharing one or more layers with the existing HART technology. In accordance with the example protocol stack described below, each of the direct wireless connections65may transfer data according to the physical and logical requirements of the WirelessHART protocol70. Meanwhile, the WirelessHART protocol70may efficiently support communications within timeslots and along communication paths of the directed graphs defined by the network manager27.

FIG. 2schematically illustrates the layers of one example embodiment of the WirelessHART protocol70, approximately aligned with the layers of the well-known ISO/OSI 7-layer model for communications protocols. By way of comparison,FIG. 2additionally illustrates the layers of the existing “wired” HART protocol72. It will be appreciated that the WirelessHART protocol70need not necessarily have a wired counterpart. However, as will be discussed in detail below, the WirelessHART protocol70can significantly improve the convenience of its implementation by sharing one or more upper layers of the protocol stack with an existing protocol. As indicated above, the WirelessHART protocol70may provide the same or greater degree of reliability and security as the wired protocol72servicing a similar network. At the same time, by eliminating the need to install wires, the WirelessHART protocol70may offer several important advantages, such as the reduction of cost associated with installing network devices, for example. It will be also appreciated that althoughFIG. 2presents the WirelessHART protocol70as a wireless counterpart of the HART protocol72, this particular correspondence is provided herein by way of example only. In other possible embodiments, one or more layers of the WirelessHART protocol70may correspond to other protocols or, as mentioned above, the WirelessHART protocol70may not share even the uppermost application layer with any of the existing protocols.

As illustrated inFIG. 2, the wireless expansion of HART technology may add at least one new physical layer (e.g., the IEEE 802.15.4 radio standard) and two data-link layers (e.g., wired and wireless mesh) to the known HART implementation. In general, the WirelessHART protocol70may be a secure, wireless mesh networking technology operating in the 2.4 GHz ISM radio band (block74). If desired, the WirelessHART protocol70may utilize IEEE 802.15.4b compatible direct sequence spread spectrum (DSSS) radios with channel hopping on a transaction by transaction basis. This WirelessHART communication may be arbitrated using TDMA to schedule link activity (block76). As such, all communications are preferably performed within a designated time slot. One or more source and one or more destination devices may be scheduled to communicate in a given slot, and each slot may be dedicated to communication from a single source device, or the source devices may be scheduled to communicate using a CSMA/CA-like shared communication access mode. Source devices may send messages to one or more specific target devices or may broadcast messages to all of the destination devices assigned to a slot.

Because the WirelessHART protocol described herein allows deployment of mesh topologies, a significant network layer78may be specified as well. In particular, the network layer78may enable establishing direct wireless connections65between individual devices and routing data between a particular node of the wireless network14(e.g., the device34) and the gateway22via one or more intermediate hops. In some embodiments, pairs of network devices30-50may establish communication paths including one or several hops while in other embodiments, all data may travel either upstream to the gateway device22or downstream from the gateway device22to a particular node.

To enhance reliability, the WirelessHART protocol70may combine TDMA with a method of associating multiple radio frequencies with a single communication resource, e.g., channel hopping. Channel hopping provides frequency diversity which minimizes interference and reduces multi-path fading effects. In particular, the data link76may provide a mechanism for a network device to cycle through multiple carrier frequencies during the same or different transmission sessions. For example, the network device38may transmit a certain type of data to the network access point25A once every second in a 10-millisecond timeslot. During a certain 1-second interval, the network device38may transmit this data at frequency F1; during the subsequent 1-second interval, the network device38may transmit similar data at a frequency F2; etc. In view of various sources of interference which the wireless network14may encounter during operation, channel hopping may provide a higher level of reliability by effectively “hedging” the risk of transmitting at a poor-quality channel.

In one embodiment, the network manager27is additionally responsible for allocating, assigning, and adjusting time slot resources associated with the data link layer76. If a single instance of the network manager27supports multiple WirelessHART networks14, the network manager27may create an overall schedule for each instance of the WirelessHART network14.

The WirelessHART protocol70may further define links or link objects in order to logically unite scheduling and routing. In particular, a link may be associated with a specific network device, a specific superframe, a relative slot number, one or more link options (transmit, receive, shared), and a link type (normal, discovery, broadcast, join). As illustrated inFIG. 2, the data link layer76may be frequency-agile. More specifically, a channel offset may be used to calculate the specific radio frequency used to perform communications. The network manager27may define a set of links in view of the communication requirements at each network device. Each network device may then be configured with the defined set of links. The defined set of links may determine when the network device needs to wake up, and whether the network device should transmit, receive, or both transmit/receive upon waking up.

Referring still toFIG. 2, the transport layer80of the WirelessHART protocol70allows efficient, best-effort communication and reliable, end-to-end acknowledged communications. As one skilled in the art will recognize, best-effort communications allow devices to send data packets without an end-to-end acknowledgement and no guarantee of data ordering at the destination device. User Datagram Protocol (UDP) is one well-known example of this communication strategy. In the process control industry, this method may be useful for publishing process data. In particular, because devices propagate process data periodically, end-to-end acknowledgements and retries have limited utility, especially considering that new data is generated on a regular basis. In contrast, reliable communications allow devices to send acknowledgement packets. In addition to guaranteeing data delivery, the transport layer80may order packets sent between network devices. This approach may be preferable for request/response traffic or when transmitting event notifications. When the reliable mode of the transport layer80is used, the communication may become synchronous.

Reliable transactions may be modeled as a master issuing a request packet and one or more slaves replying with a response packet. For example, the master may generate a certain request and can broadcast the request to the entire network. In some embodiments, the network manager27may use a reliable broadcast to tell each network device in the WirelessHART network14to activate a new superframe. Alternatively, a field device such as the sensor30may generate a packet and propagate the request to another field device such as to the portable HART communicator55. As another example, an alarm or event generated by the34field device may be transmitted as a request directed to the gateway device22. In response to successfully receiving this request, the gateway device22may generate a response packet and may send the response packet to the device34, acknowledging receipt of the alarm or event notification.

Referring again toFIG. 2, the session layer82may provide session-based communications between network devices. End-to-end communications may be managed on the network layer by sessions. A network device may have more than one session defined for a given peer network device. If desired, all or almost all network devices may have at least two sessions established with the network manager27: one for pairwise communication and one for network broadcast communication from the network manager27. Further, all network devices may have a gateway session key. The sessions may be distinguished by the network device addresses assigned to them. Each network device may keep track of security information (encryption keys, nonce counters) and transport information (reliable transport sequence numbers, retry counters, etc.) for each session in which the device participates.

Finally, both the WirelessHART protocol70and the wired HART protocol72may support a common HART application layer84. The application layer of the WirelessHART protocol70may additionally include a sub-layer86supporting auto-segmented transfer of large data sets. By sharing the application layer84, the protocols70and72allow for a common encapsulation of HART commands and data and eliminate the need for protocol translation in the uppermost layer of the protocol stack.

In addition to optimizing routing by analyzing the network topology, the network manager27may define graphs and allocate resources during scheduling in view of the type of data a particular network device may transmit and, for each type of data, the expected frequency of transmission at each particular device. More specifically, the WirelessHART protocol70may support several types of network communication traffic. Both the existing HART protocol72and the WirelessHART protocol70support exchanging request/response data, publishing of process data, sending broadcast messages, and block data transfer of large data files. The WirelessHART protocol70may also support transmission of management data, such as network configuration data, and device communications, such periodic measurements reported by field devices, using the same protocol and the same pool of resources, thus allowing for greater efficiency in scheduling.

Thus, by using the WirelessHART protocol70or a similar protocol, the wireless network14may provide reliable and efficient transmission of data packets in a variety of industrial applications.FIG. 3provides a specific example of forming a wireless mesh network in a tank farm130to illustrate one of the possible applications of the routing techniques described herein. In this particular example, the tank farm130may utilize several WirelessHART devices for level monitoring. More specifically, the tank farm130contains several tanks132as part of an existing installation. One of ordinary skill in the art will appreciate that in order to add gauging or monitoring capability to the tank farm130and to make every tank132visible to a DCS134, the currently known solutions require running cables to each tank to connect newly installed meters or sensors. Without sufficient spare capacity within the existing cable runs, this operation may be an expensive and time-consuming option. On the other hand, the wireless solution described herein could utilize self-powered instruments to report the new process measurements. These measurements could come, for example, from wireless contact temperature monitoring devices136which are simple to fit. Moreover, because the engineers and technicians servicing the tank farm130would not need to run cables or purchase and install controller input modules, the resulting cost saving could make it economically viable to add several process measurement points to improve process visibility. Thus, as illustrated inFIG. 3, pressure sensors36may be additionally added to each tank. The pressure sensors36, the wireless contact temperature monitoring devices136, a gateway device137, and additional wireless devices not shown inFIG. 3may form a wireless network140.

As generally discussed above in reference toFIG. 1, it is important to consider the location of the wireless devices on each tank132so that the wireless network140can establish itself in an efficient and reliable form. In some cases, it may be necessary to add routers60in those locations where plant equipment could block or seriously affect a wireless connection. Thus, in this and in similar situations, it is desirable that the wireless network140be “self-healing,” i.e., capable of automatically addressing at least some of the delivery failures. To meet this and other design requirements, the wireless network140may define redundant paths and schedules so that in response to detecting a failure of one or more direct wireless connections65, the network14may route data via an alternate route. Moreover, the paths may be added and deleted without shutting down or restarting the wireless network140. Because some of the obstructions or interference sources in many industrial environments may be temporary or mobile, the wireless network140may be capable of automatically reorganizing itself. More specifically, in response to one or more predetermined conditions, pairs of field devices may recognize each other as neighbors and thus create a direct wireless connection65or, conversely, dissolve previously direct wireless connections65. The network manager142(illustrated inFIG. 3as residing in the gateway device137) may additionally create, delete, or temporarily suspend paths between non-neighboring devices.

Irrespective of whether a particular network configuration is permanent or temporary, the wireless network140requires a fast and reliable method of routing data between nodes. In one possible embodiment, the network manager142may analyze the information regarding the layout of the network, the transmission capability and update rate of each network device36,136, and137, as well as other relevant information. The network manager142may then define routes and schedules in view of these factors. When defining routes and schedules, the network manager142may recognize the wireless network140as conforming to one of several network topologies compatible with the routing and techniques of the present disclosure.

FIGS. 4-6schematically illustrate some of these network topologies. For the sake of clarity, each ofFIGS. 4-6illustrates bidirectional connections between pairs of devices. However, it will be appreciated that each of the topologies illustrated inFIGS. 4-6is also compatible with unidirectional connections or mixed bidirectional and unidirectional connections (i.e., including both bidirectional and unidirectional connections). Moreover, each connection illustrated inFIGS. 4-6may support several unidirectional connections in one or both directions, with each unidirectional connection associated with a particular time of transmission, for example. Referring specifically toFIG. 4, a network150may have a star network topology. The star network150includes a routing device152and one or more end devices154. The routing device152may be a network device arranged to route data while the end device154may be a network device arranged to send data only on its own behalf and to only receive (or decode) data addressed to the end device154. Of course, the routing device152may also be a recipient and originator of data and may perform routing functions in addition to other tasks. As illustrated inFIG. 4, end devices154may have a direct connection165to the routing device152but end devices154cannot be connected directly in a star topology. The direct connection165may be a direct wireless connection65or a wired connection.

The end device154may be the same type of physical device as the routing device152and may be physically capable of routing data. The routing capability of the end device154may be disabled during the installation of the end device154or in operation of a corresponding network (such as the WirelessHART network14). Moreover, the routing capability of the end device154may be disabled by the end device154itself or by a dedicated service such as the network manager27. In some sense, the star network150corresponds to the simplest of possible topologies. It may be appropriate for small applications that require low power consumption and low latency. Additionally, it will be noted that the star network150is deterministic because there is only one possible route between the routing device152and a particular end device154.

Now referring toFIG. 5, a network170is arranged in a mesh network topology. Each network device of the mesh network170is a routing device152. Mesh networks provide a robust network with multiple paths between various devices. In wireless applications, mesh networks are better able to adapt to changing radio environments. For example, the device174of the network170may send data to the device176via an intermediate hop178or an intermediate hop180, provided that the corresponding paths182-188allow transmission in this direction. As illustrated inFIG. 5, both a path182and a path184enable the routing device174to send data to the routing device176, providing redundancy and thus improved reliability to the network170.

Another type of network topology is illustrated inFIG. 6. The network190incorporates elements of both star and mesh topologies. In particular, the star mesh network190includes several routing devices152(labeled “R”) and end devices154(labeled “E”). The routing devices152may be connected in a mesh format and may support redundant paths. The selection of a particular topology may be performed automatically by a network component, such as the network manager27, or by a user configuring the network. In particular, the user may choose to override the topology selected by the network manager27or the default topology associated with the WirelessHART protocol70. It is contemplated that in most applications, mesh topology may be the default topology because of the inherent reliability, efficiency, and redundancy of this topology. Clearly, because WirelessHART devices may act as router devices, several different configurations may be compatible with the same physical disposition of field devices and routers.

Both source routing and graph routing may be applied to the topologies discussed in reference toFIGS. 4-6. Although both types of routing may be equally useful in different situations, graph routing will be discussed first. Generally, in mathematical theories and applications, a graph is a set of vertices (nodes such as152or154) and edges (direct connections65or165). The WirelessHART protocol70or another protocol servicing the wireless network14or140may use graphs to configure paths connecting communication endpoints such as the device30to the gateway22illustrated inFIG. 1, for example. In some embodiments, graphs and the associated paths are configured by the network manager27. The network manager27may also configure individual network devices such as field devices30-40, routers60, etc. with partial graph and path information, which may be stored in the connection tables69. The wireless network14may contain multiple graphs, some of which may overlap. Further, a certain network device may have paths of multiple graphs going through the device, and some of the paths may direct data to the same neighbor of the device. Preferably, every graph in a network is associated with a unique graph identifier.

The protocol servicing the wireless network14or140(such as the WirelessHART protocol70) may be configured to operate with a number of different topologies to support various application requirements. As a result, the wireless network14or140may concurrently support several methods of routing, such as unidirectional graph routing and source routing, for example. Although the forthcoming examples of a wireless network support these two approaches, it will be appreciated that the wireless network14or140may additionally support bidirectional graph routing, or may route data using only one of these techniques. However, irrespective of a type and number of concurrent routing techniques, each device on the wireless network14or140may be assigned a unique network address. Once every potential receiver of data acquires some form of unambiguous identification with respect to other network elements, decisions related to routing may be made by individual devices such as field devices30-40, by a centralized dedicated service such as the network manager27, or by individual devices acting in cooperation with the centralized service. As indicated above, at least one possible implementation of the wireless network14may rely on the network manager27to carry out most or all of the routing decisions and to communicate the relevant data to the network devices30-50to be stored in the connection tables69. Further, routing decisions can be made at the originating point (i.e. at the source of a data packet) or at a centralized location. Moreover, routing decisions can be adjusted at each intermediate stop, or “hop,” in the path of the packet from the source to a destination.

In the examples discussed below, a wireless network provides at least two approaches to routing that may be selected according to the specific requirements and conditions of a given system, such as the physical layout of the network elements that make up the system, the number of elements, the expected amount of data to be transmitted to and from each element, etc. Moreover, the two approaches may be used by the wireless network at the same time and each may be selectively applied to a particular type of data or to a particular host or a set of hosts in view of certain aspects of performance of each of the two approaches. For example, a measurement of a process variable or a command to open a valve may tolerate a relatively small delay in delivery and the wireless network14may accordingly apply the faster and the more reliable of the two methods. Meanwhile, a device configuration command or a response may tolerate a longer delay and may be suitable for the other approach.

As briefly indicated above, it is common for a certain distributed control networks and, in particular, to networks connecting devices in the process control industry, to direct data to a certain device for management, diagnostic, log collection, and other purposes.FIGS. 7-9illustrate several perspectives of a wireless network200which implements data transfer in two general directions: toward a gateway202(referred to herein as the “upstream” direction) and away from the gateway202(referred to herein as the “downstream” direction). For security reasons, the network200does not allow direct data transfer between peer field devices although the technique described herein could be used in such a situation if so desired.

FIG. 7illustrates upstream routing in the network200. In particular, the network manager202A (or the stand-by network manager202B) may define several directed graphs, each graph including either the network access point205A or a second network access point205B as the terminal node. A virtual gateway (not shown) may run, for example, on a host connected to the communication backbone20and may share the physical host with the network manager202A or202B. In at least some of the embodiments, each graph terminating at either the network access point205A or a second network access point205B may be logically associated with the virtual gateway of the network200. In other words, although the paths of each graph in the exemplary network200lead to and terminate at one of the two network access points205A or205B, these graphs also define communication paths to the virtual gateway. Specifically, a graph210(shown in solid bold arrows) may include network devices212,214,216,218, and the network access point205A wherein the paths associated with the graph210may include direct wireless connections220,222,224,226, and228. A graph240(shown in dotted bold arrows) may include network devices212,216,218,242, and the network access point205A, with a path that includes direct wireless connections244,246,248,250, and252. In the directed graph210, the network device212may be called the head of the directed graph210and the network access point205A may be called the tail of the directed graph210. Similarly, the network device212is the head of the directed graph240and the network access point205B is the tail of the directed graph240. The network manager202A or, under certain operating conditions, a backup network manager202B may define the graphs210and240and may communicate complete or partial definitions of these graphs210and240to the network devices212-218and242. As discussed above in reference toFIG. 1, the network devices212-218and242may maintain up-to-date versions of the connection tables69storing these partial path definitions. In some embodiments, the network access points205A-B may not require the information regarding the graphs210and240if the corresponding communication path terminates at one the network access point205A-B. However, it will be appreciated that the virtual gateway may also originate data and may store information regarding one or more graphs with paths originating from the network access point205A-B. It will be further noted that in general, a path of a certain graph may traverse the network access point205A or205B as an intermediate node; however, the exemplary network200defines paths that always either originate or terminate at one of the network access points205A or205B.

By using multiple network access points25A-B or205A-B in conjunction with a virtual gateway, the wireless network14or200may achieve higher reliability. Equally importantly, the multiple network access points25A-B or205A-B may serve to define multiple communication paths to the virtual gateway, and each path may be associated with different wireless (e.g., radio) resources such as channels, timeslots, carrier frequencies, etc.

To send a data packet along a certain graph, a source network device may include an identifier of the graph in the header or trailer of the data packet. The data packet may travel via the paths corresponding to the graph identifier until it either reaches its destination or is discarded. To be able to route packets in the graph210, for example, a connection table69of each network device that belongs to the graph210may contain entries that include the graph identifier and address of a neighbor network device which (1) belongs to the same graph, and (2) is one hop closer to the destination. For example, the network device216may store the following connection table:

GRAPH IDENTIFIERNODEGRAPH_210218GRAPH_240218GRAPH_240242
while the network device242may store the following information in the connection table:

GRAPH IDENTIFIERNODEGRAPH_240205B
While the exemplary connection tables above simply list the devices associated with a particular entry, it will be noted that the NODE column of the connection table may store the address of the neighboring device as defined in the addressing scheme of the network200or WirelessHART network14.

In another embodiment, the NODE column may store the nickname of the neighboring device, an index into an array storing full or short addresses of the neighbors, or any other means of unambiguously identifying a network device. Alternatively, the connection table may store graph identifier/wireless connection tuples as illustrated below:

GRAPH IDENTIFIERCONNECTIONGRAPH_210226GRAPH_240246GRAPH_240248
In other words, the connection table may list one or more direct wireless connections65corresponding to a particular graph. The network device216may, for example, consult the connection table and transmit a packet carrying the graph identifier240via the direct wireless connection246or248.

As illustrated inFIG. 7and in the tables above, redundant paths may be set up by having more than one neighbor associated with the same graph identifier. Thus, a data packet arriving at the network device216and containing the graph identifier240in the header or trailer may be routed to either the network device218or to the network device242. While executing a routing operation, the network device216may perform a lookup in the connection table by the graph identifier240, and send the packet to either (or both) of the network devices218or242. Moreover, the routing selection between two or more possible hops may be random or may be carried out according to a predefined algorithm. For example, the selection may be made in consideration of a load balancing objective or in view of the delivery statistics. Thus, the network device216may learn, through a peer network device or from the network manager27, that selecting the network device218as the next hop while routing packets along the graph240has a lower probability of delivering the packet successfully or has a longer expected or average delay in delivery. The network device216may then attempt to route more or possibly all of the packets associated with the graph240to the network device242.

In one embodiment, a neighbor device acknowledges the receipt of a data packet by sending a confirmation packet. In the example above, once the neighboring network device218or242acknowledges receipt of the packet, the network device216may immediately release it. If, on the other hand, the acknowledgement is not received within a predefined time period, the network device216may attempt to route the packet via the alternate hop or path. Additionally, the network device216may collect statistics of both successful delivery attempts and of failed delivery attempts. The subsequent routing decisions, such as selecting between the hops218and242, may include or be based on the adjusted statistical data. Of course, the network device216may apply the statistics related to network devices218and242to other relevant graphs and may also communicate the statistics to other network devices, either directly or via the network manager27.

As discussed above, in the graph routing approach, a network device sends packets with a graph identifier in a network header along a set of paths to the destination. Importantly, a graph identifier alone is sufficient for routing packets and, while other routing information may be also included in the header, each packet can be properly delivered based solely on the graph identifier. All network devices on the way (i.e., on the path) to the destination may be pre-configured with graph information that specifies the neighbors to which the packets may be forwarded. Because graph routing requires pre-configuration of intermediate network devices for each potential destination, graph routing may be better suited for communications from a network device to a gateway and from a gateway to a network device.

Now referring toFIG. 8, the network manager202A or202B may also support routing downstream with respect to one or both of the gateways205A-B. In particular, a graph280(shown in solid bold arrows) may include the nodes215,214, and212, and the direct wireless connections282-286. The network access point205A is the head of the graph280and wireless device212is the tail of the graph280. Meanwhile, a graph290(shown in dotted bold arrows) may similarly connect the network access point205A to the wireless device212, with the network access point205A as the head of the graph290. However, the graph290may include the nodes205A,218,242,216, and212, and the direct connections292-298. Thus, to send a data packet to the wireless device212, the network access point205A may include a graph identifier in the header or the trailer of the data packet which corresponds to either the graph280or290. It will be appreciated that each of the graphs280or290may also include duplicate connection paths to ensure reliability and that, in general, the network manager202A or202B may use techniques similar to those discussed above in reference toFIG. 7. Also, it will be noted that the connection table69of each of the wireless devices212-218and242may include graph route information related to both downstream and upstream graphs used for routing purposes.

As illustrated inFIG. 9, the wireless network200may additionally use source routing. In source routing, pre-configuration of the relaying devices is not necessary. To send a packet to its destination using source routing, the source network device may include, in the header of a data packet, for example, an ordered list of devices through which the data packet must travel. The ordered list of devices may effectively define a communication path for the data packet. As the packet traverses the specified path, each routing device may extract the next node address from the packet to determine where the data packet should travel next, i.e., where the next data packet should be sent in the next hop. Consequently, source routing requires advance knowledge of the topology of the wireless network14. If, however, a certain network device does not find itself on the routing list, the network device may send the packet back to the first device specified in the source routing list. Source routing allows packets to go to an arbitrary destination without an explicit or preconfigured setup of intermediate devices.

For example, the network device212may send a packet to the network access point205A by specifying the complete path in the packet header or the packet trailer. As illustrated inFIG. 9, the network device212may generate a routing list310containing the addresses of network devices214,215, and205A and send the list310along with the packet to the first hop or device on the list, i.e., the network device214. The network device214may then traverse the list310, locate the identity of the network device214, extract this field from the list310, identify the network device215as the next hop for the received packet, and finally send the data packet to the network device215. The source routing list may reside in the optional area of the network header, and may be of variable size depending on number of hops to the destination. Similarly, the network device215may traverse the list310, locate its own address or identity, and send the data packet to the next hop or device in the list310(in this case, the network access point205A).

In general, only those network devices that have obtained full network information from the network manager27,142, or202A-B use source routing because only the network manager27,142, or202A-B knows the complete topology of the network. An additional limitation of source routing is that it provides no redundancy at intermediate network devices because each packet is originated with a header or a trailer that explicitly specifies each intermediate hop and does not provide any routing alternatives. Thus, if one of the intermediate network devices fails to relay the packet as specified by the packet header or trailer, the delivery of the packet along the specified source route fails. The intermediate node which has detected the source route failure may nevertheless attempt to deliver the data packet by deferring to graph routing. Thus, each data packet specifying source routing in the header or trailer preferably includes a graph identifier as a routing backup. When a failure in source routing occurs, the intermediate (or, in some case, the source) node notifies the network manager27,142, or202A-B with a path failure message. It is then the responsibility of the network manager27,142, or202A-B to reprogram or reconfigure the source with an alternate route. To facilitate the detection of such error cases, the wireless network14,140, or200requires network devices to send routing failure notifications to the network manager27,142, or202A-B. Accordingly, a protocol such as the WirelessHART protocol70may provide a message type or an information element in the protocol definition for reporting this and other types of delivery failures. In another embodiment, the routing list310(referring toFIG. 9) may specify alternate routes in addition to the route selected by the sender. In yet another embodiment, primary and one or more alternate routes may be partially merged to avoid duplication of common parts of the path in the packet header or trailer.

Preferably but not necessarily, the routing list310includes a complete path definition defining a complete route from the source to the destination. Alternatively, a data packet may be sent without a complete list310and may only specify the communication path up to a certain intermediate device. As discussed above, the intermediate device may then route the data packet to the final destination using the graph routing technique.

Referring generally toFIGS. 1,3, and7-9, the network manager27,142, or202A-B may maintain a list of all devices in the network. The network manager27,142, or202A-B may also contain the overall network topology including a complete graph of the network and the up-to-date portions of the graph that have been communicated to each device. The network manager27may generate the route and connection information using the information that the network manager27receives from the network devices30-40,50,60,55, etc. The network manager27,142, or202A-B may then build the graph of the network from the list of network devices and the neighbors reported by each network device. Referring back toFIG. 1, for example, the network device50B may report “seeing” the neighbor devices60and34. The network manager27,142, or202A-B may be also responsible for generating and maintaining all of the route information for the corresponding network. In one embodiment, there is always one complete network route and several special purpose routes which are used to send setpoint and other settings from the network manager202A or202B to the recipients of control commands (FIGS. 7-9). Further, broadcast routes (which flow through most or all of the devices in the network) may be used to send broadcast messages from the network manager27,114, or202A-B to all of the devices of the network14or200. Still further, the network manager27,114, or202A-B may also carry out the scheduling of network resources once the routing information and burst mode update rates are known.

When devices are initially added to the network14,140, or200, the corresponding network manager may store all neighbor entries as reported from each network device. The network manager27,114, or202A-B may use this information to build an initial complete network graph and to revise the graphs during operation. The network graph is put together optimizing several properties including hop count, reporting rates, power usage, and overall traffic flow as reflected by the statistics gathering discussed above. One key aspect of the topology is the list of connections that connect devices together. Because the presence and health of individual connections may change over time, the network manager27,114, or202A-B may be additionally programmed or configured to update the overall topology, which may include adding and deleting information in each network device. In some embodiments, only the network manager27,114, or202A-B and the gateway22or202A-B may know enough information to use source routing. More specifically, it may be desirable to prevent peer-to-peer communication between any two arbitrary devices for security purposes.

In short, graph routing may direct traffic both upstream and downstream with respect to the network manager27or gateway22and both graph and source routes can be optimized to satisfy applications with low latency requirements, which includes measurement information that is transferred from network devices to the gateway and control information that is transferred from gateway devices to final control commands such as regulating valves, on-off valves, pumps, fans, dampers, as well as motors used in many other ways.

In some embodiments, path redundancy may be a matter of policy of the network manager27,114, or202A-B rather than a coincidental overlap of graphs. In other words, the network manager27,114, or202A-B may attempt to define at least two neighbors for each device. Thus, the network manager27,114, or202A-B may be configured to actively pursue a mesh or a star mesh topology. The supporting protocol, such as the WirelessHART protocol70, may thus provide a very high end-to-end data reliability. From the physical perspective, each field device or other network device should be within communication range of at least two other devices that can receive messages from the field device and forward them.

The network manager27,114, or202A-B may additionally verify each graph definition in order to ensure that no loops have been formed. In those embodiments where the network manager27,114, or202A-B actively pursues path redundancy and defines many graphs of various size, a communication path may be sometimes erroneously defined to direct data packets from a source back to the same source. In accordance with such faulty graph definition, a packet may be routed back to the source directly from the source or may visit one or more intermediate hops prior to arriving back at the source. Loop verification may be performed each time the topology of the associated network changes, such as due to an addition or removal of a device, or whenever the network manager27adjusts the routing graphs and schedules for any reason. Alternatively, the network manager27may perform loop checking periodically as a background task.

As indicated above, devices involved in routing refer to the graph route, the source route, or to the address of the destination in order to deliver and properly relay data packets. The address of each network device must be globally unique in order for the WirelessHART network14to properly co-operate with a larger network which may include wired HART devices. For this reason, the WirelessHART protocol70may additionally provide an unambiguous addressing scheme and additionally provide an efficient mapping of addresses to a larger network context.

FIGS. 10 and 11illustrate example procedures related to routing which the network devices in the wireless networks14,140, or200may execute when originating and relaying data packets, respectively. In particular, a network device may store a procedure350as a set of computer instructions in the memory of the network device, or may implement the procedure250as a dedicated electronic circuit (ASIC).

In a block352, the procedure350retrieves a data packet for transmission to a destination, or “target” network device. In particular, the procedure may receive a payload which includes process control data (e.g., a command to open a valve, a pressure measurement, etc.), a network configuration data (e.g., a request to allocate more bandwidth, an indication that a new neighbor had been discovered, etc.), or other type of data. The procedure may prepare the data packet for transmission by populating the header, the trailer, or other relevant part(s) of the data packet with sufficient routing information to allow the data packet to reach a destination device. In the example embodiment illustrated inFIG. 10, the procedure350may check, in a block354, whether the data packet requires a low latency. If the data packet does not have a low latency requirement, the procedure350may choose to send the data packet by means of source routing, rather than graph routing, in order to better allow higher priority data to use time-critical resources. As discussed above, the procedure350may identify process control data as low-latency data and network management data as non-low-latency data, for example. Of course, the procedure350may also perform other types of checking in the block354, such as checking whether the data packet is related to a high-priority alarm, for example.

If the data packet received in the block352does not have a low latency requirement, the procedure350may check whether the network device has sufficient information about the topology of the network to specify a complete path to the destination (block355). Referring back toFIG. 1, for example, in order for the network device34to specify a complete path to the gateway device22, the network device34would need to know about the direct connections65between the pairs of network devices34and32,32and50A,50A and25A, provided that these connections support connections in the required direction. Thus, the procedure350may determine in the block355that a complete path to the target device cannot be fully identified, and may send the data packet by means of graph routing.

If, on the other hand, the procedure350determines in the block354that the data packet has a low latency requirement (or if the procedure350determines in the block355that complete path to the target device is unknown), the procedure350may identify an appropriate graph in the block356. Referring back toFIG. 7, for example, the wireless device216may identify the graph240as a possible path to the network access point205B. As discussed above, the wireless device216may store the information sufficient to make this determination in the connection table69. Next, in a block358, the procedure350may attach the graph identifier of the graph240to the header or trailer of the data packet. It will be appreciated that, in general, the protocol servicing the wireless network (such as the WirelessHART protocol70, for example) may provide various efficient means of associated routing information with a data packet. Thus, one of ordinary skill in the art will appreciate that the specific example of inserting the graph identifier into the header or trailer of a data packet is provided by way of example only, and that other alternatives are also contemplated.

The procedure350may then identify the next hop in the communication path associated with the graph selected in the block358(block360). Referring again toFIG. 7, the device-specific connection table69of the wireless device216may store the following entry:

GRAPH IDENTIFIERNODEGRAPH_240218GRAPH_240242
In this particular case, the network device252may select between two options, both suitable for routing the data packet along the graph240. As discussed above, the procedure350may use a number of methods to select between the available options in the block360. Finally, the procedure350may send the packet to the next hop in a block362. To continue with the example discussed above in reference to the network device216ofFIG. 7, the procedure350may send the packet to the node218.

If, in the block354, the procedure350determines that enough information for specifying a complete path for the data packet is available, the procedure350may proceed to a block364and obtain the path information. For example, when the wireless device214(FIG. 7) is sending a data packet to the network access point205A, the device214may retrieve the list including the addresses or other type of identifiers of the network devices218and205A. Next, similar to a step358discussed above, the procedure350may attach the complete path information to the data packet as an ordered list specifying the network devices218and205A, to continue with the same example. The procedure may then look up the next hop in the generated list (block368), as illustrated in detail inFIG. 9with respect to the list310, for example. The procedure350may then proceed to the block362, in which the network device transmits the data packet to the neighbor identified either in the block360or in the block368.

Upon receiving the data packet, the neighbor may in turn execute a routing procedure400(FIG. 11) to either receive and process the data packet sent to the neighbor or forward the data packet to the next hop in the communication path. The procedure400may receive the data packet including the header, the trailer, or other priority-related and routing-related information in a block402and may check the type of routing in a block404. To indicate the type of routing (graph routing, source routing, etc), the wireless protocol may use a flag in the header, for example, or any other known or desired means of signaling the type of information that is to follow in the packet. If the procedure400determines that graph routing is used, the procedure400may then check whether the graph identified in the header or trailer of the data packet terminates in the device (block406). Referring back toFIG. 8, the wireless device242may, for example, receive a data packet including a graph identifier associated with the graph290. In the block406of the procedure400, the wireless device242may check the device-specific routing table69to see whether the wireless device242is listed as a tail of the graph290. In other words, the wireless device242may determine whether the data packets carrying the identification of the graph290are sent to the wireless device242or merely via the wireless device242to another network device. If the procedure400determines that the network device executing the procedure400is not the tail of the graph identified in the block404, the wireless device242may determine the next hop in the list by checking the device-specific connection table69, as discussed above in reference toFIG. 6or10(block408). Otherwise, the procedure400may proceed to processing, or “consuming” the data packet in the block410.

Alternatively, the procedure400may proceed to a block412upon identifying the type of routing as source routing in the block404. In this case, the procedure400may traverse the list to locate the identity of the device executing the procedure400. As discussed earlier in reference toFIG. 9, the list310may sequentially list every intermediate and possibly terminating network device in the corresponding communication path. Upon locating its own identity, the device executing the procedure400may then check whether this identity information is the last identity in the list310(block414). It will be appreciated that the other methods of identifying the target or destination network device may also be used. For example, each data packet may include the destination information in addition to the list310or the graph identifier. However, the example procedure400may derive the target information from the position of the device identity relative to the end of the list310. The procedure400may process or consume the data packet if the device identity is not followed by any information identifying further hops in the list310(block410). Otherwise, the procedure400may attempt to extract the address of the next hop (block416) and, if the procedure400finds the address and identifies a neighbor device corresponding to the address (block417), the procedure400may send the data packet to the identified network node (block418). If, on the other hand, the procedure400cannot successfully extract the next hop information in the block417, the procedure400may attempt to use an appropriate graph route instead. In at least some of the embodiments, a data packet including source routing information such as the list310may additionally include a graph identifier. In this sense, the data packet may specify source routing as a primary routing method and graph routing as a secondary routing method.

In some embodiments, the procedure400may perform additional manipulation of the list310at each intermediate hop. For example, the procedure400may delete the identity of the current hop from the list310to reduce the size of the header. Thus, the list310may shrink every time the corresponding data packet traverses a link if source routing is used.

It will be appreciated that some of the methods discussed above need not be restricted to data packets and may be applied to other communication techniques. For example, a network may use a circuit-switched approach and instead of traveling in packets of a finite size, the data may be transmitted as a stream over a dedicated channel between communication endpoints. In this case, the routing information such as graph identity or complete path information may be supplied separately from the circuit over a dedicated channel, for example.