Patent Publication Number: US-9843985-B2

Title: Multi-media multi-modulation and multi-data rate mesh network

Description:
RELATED APPLICATIONS 
     This application is a continuation of, and claims priority to, U.S. application Ser. No. 13/648,095, filed on Oct. 9, 2012, which claims priority to European Application No. 12179445.7, filed on Aug. 6, 2012, both of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Communication networks, such as mesh networks, are used to connect a variety of different devices. For example, mesh networks have been employed in the utility industry to connect utility meters, cellular relays, transformers, and/or other nodes. The nodes in the mesh network are typically able to receive data from neighboring nodes and to relay or propagate messages to other neighbor nodes. 
     In traditional wired networks, routing metrics may be used which route messages based on a fewest number of hops between a source and a destination. In a mesh network, however, a data rate between nodes may vary substantially from one link to another. This variation in data rate may be due, at least in part, to the fact that mesh networks often contain multiple different generations of nodes having different characteristics and capabilities. For example, different generations of nodes may employ or be capable of employing different communication medias, different modulation techniques and operate at different or variable data rates. This may be particularly true for utility mesh networks in which nodes are placed into service gradually over time and are expected to remain in the field for relatively long life cycles (e.g., 20 years or more). Generally, newer generations of nodes are capable of additional modulations and higher data rates than older generations of nodes. Therefore, as newer generations or various models of nodes are deployed with the mesh network, there may be incompatibility issues that prevent some nodes from communicating with each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description is set forth with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical items. 
         FIG. 1  is a diagram showing a high-level view of a mesh network having nodes configured with multiple protocol receivers. 
         FIG. 2  is a schematic diagram showing additional detail of an example node from the mesh network of  FIG. 1 . 
         FIG. 3  is a diagram showing an example of packet structure usable with some multiple protocol receivers. 
         FIG. 4  is a flowchart illustrating an example method of determining a quality of links between nodes of the mesh network. 
         FIG. 5  is a flowchart illustrating an example method of routing transmissions in a mesh network according to a quality of links between nodes of the network. 
         FIG. 6  is a schematic diagram illustrating of an example frame structure of a request-to-send message that may be used to indicate that a node has data available to sent to another node. 
         FIG. 7  is a schematic diagram of an example frame structure of a clear-to-send message that may be used to indicate that a node is available to receive data. 
         FIG. 8  is a flowchart illustrating an example method of determining a degradation of a link during transmission of operational data. 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     Existing routing metrics are not well suited to routing communications in a heterogeneous mesh network, wherein nodes may utilize differing communication technologies, transmission medias, transmission data rates, modulations and/or protocols. As used herein, a “link” refers to a direct transmission path between two nodes of a network (i.e., a transmission that does not pass through another node). Such transmissions may be made by radio frequency (RF) signals and/or power line communication (PLC) signals. A data rate across a link between two nodes is at least partially dependent on the distance and propagation characteristics between the two nodes. Moreover, a maximum data rate across a path of links may be limited by the capabilities of the slowest node associated with the link. 
     This application describes techniques for intelligently routing communications between and/or among nodes of a heterogeneous mesh network that includes multiple different communication technologies (e.g., different transmission media, modulation techniques, data rates, protocols, etc.). Although this application describes various examples and embodiments in terms of a mesh network topology, other network topologies, such as star, fat tree, etc., may also utilize the technologies and embodiments described herein. In one example, this application describes using multiple protocol receivers that increase the connectivity of nodes, in part by determining a quality (e.g., figure of merit (FOM)) of links between nodes using different communication technologies, and routing communications based at least in part on the determined quality of the links. 
     Conventional routing metrics also typically do not account for the so-called “missing destination problem,” in which destination nodes may miss transmissions intended for them because they are busy communicating with another node. When employing a conventional routing metric, a node that does not receive a response from an intended destination node may think that a collision has occurred and increase the size of its contention window (i.e., the amount of time the node will wait before attempting to retransmit the message). This increased wait time may cause unnecessary delay and inefficiency in propagating the transmission to its intended destination. 
     This application also describes maintaining a busy device list for each node, which includes availability information for one or more neighbor nodes. Communications may be routed based in part on availability information of neighbor nodes maintained in the busy device list. 
     Thus, in various embodiments described in this application, transmissions may be routed in a mesh network, or in networks using topologies other than a mesh topology, such as a star topology, using various transmission media, various communication technologies and various data rates, based on one or more metrics associated with link quality (e.g., a FOM), availability of neighbor nodes (e.g., based on a busy device list), or both. Consequentially, connectivity between nodes in the mesh network is improved, thereby improving throughput. Additionally, routing techniques may become more inclusive, incorporating a greater number of nodes within a heterogeneous mesh network. 
     The routing techniques are described herein in the example context of a utility mesh network including a plurality of nodes having multiple protocol receivers. Nodes of the utility mesh network may include, for example, low-power digital radios, smart utility meters (e.g., electric, gas, and/or water meters), sensors (e.g., temperature sensors, weather stations, frequency sensors, etc.), control devices, transformers, routers, servers, relays (e.g., cellular relays), switches, valves, and other network devices. As such, these nodes may include nodes of low power and lossy networks (LLNs). While the routing techniques are described in the context of a utility mesh network, the routing techniques may additionally or alternatively be applicable to other networks, network topologies and/or other applications. As such, in other implementations, nodes may include any device coupled to a communication network and capable of sending and/or receiving data. 
     Example implementations and embodiments are described below. In a first section “Overview of a Multiple Protocol Receiver,” discusses an exemplary receiver of a node that may receive and process multiple types of communication technologies. A second section, “Overview of Routing Based on Link Quality,” discusses routing data between nodes. A further section, “Overview of Routing Based on Node Availability,” discusses an exemplary method of incorporating node availability with routing. A section entitled “Example Architecture” discusses an exemplary architecture of nodes in the mesh network. A section entitled “Example Node” discusses an exemplary architecture of a node usable to implement the link quality determination and routing techniques described herein. Several sections discuss example methods. A section entitled “Example Method of Determining Link Quality with Multiple Communication Technologies” discusses an exemplary use of a multiple protocol receiver to determine a quality of links. A section entitled “Example Method of Routing Based on Link Quality” discusses an exemplary use of link quality and routing. Following the discussion of the example routing processes, a section describing “Example Protocol Data Units (PDUs)” shows examples of link quality determination and routing methods. A section entitled “Example Method of Determining Degradation of an Operational Link” discusses an exemplary method of determining a degradation of a link during transmission of operational data. Finally, the application concludes with a brief “Conclusion.” This Overview and the following sections, including the section headings, are merely illustrative implementations and embodiments and should not be construed to limit the scope of the claims. 
     Overview of a Multiple Protocol Receiver 
     In one example implementation, nodes may utilize a multiple protocol receiver. The multiple protocol receiver may alternate between first and second states. In a first state, the multiple protocol receiver listens for a plurality of different communication technologies that may include different modulated signals (e.g., FSK, OFDM, OQPSK, CDMA, etc.), signals on different communications media (e.g., RF and PLC), signals associated with different protocols, signals associated with different or variable data rates, and the like. Such listening may be performed in a parallel manner, wherein a plurality of preamble detection processes operates in a multitasking environment, each listening for a different preamble across the various communication technologies. The listening may result in recognition and/or detection of a preamble of a packet by one of the preamble detection processes. Such detection may trigger transition of the multiple protocol receiver to the second state. The detected preamble may indicate a protocol used in transmission of the packet. A packet demodulator may be selected based on the protocol used. The received packet may then be demodulated according to a data rate, synchronization, error correction and/or other factors indicated by the protocol or other data in the packet. The demodulated packet and/or the detected preamble may also provide other information, such as a communication technology of the received signal, available data rates, or the like. The received packet may be utilized by the receiving node, retransmitted or routed to a neighbor node. The multiple protocol receiver may return to the first state to repeat and continue the procedure. 
     In another example, the multiple protocol receiver listens for a plurality of different communication technologies to determine or measure a strength of received signals on links from neighbor nodes in a mesh network. The multiple protocol receiver may then rank received signals based on their strength, or a measure of their relative strength, and maintain a list of top ranked received signals. As such, this ranked list may provide an initial measure of quality of links to neighbor nodes. 
     Overview of Routing Based on Link Quality 
     In one example, quality metrics of links between nodes may be determined. The links may utilize multiple different communication technologies, and communications (e.g., packets) may be routed based at least in part on the quality metrics. In this example, a node having a multiple protocol receiver may select an initial list of links to neighbor nodes ranked based on relative received signal strength (e.g., a received strength indicator (RSI)). The node may then exercise the initial list of links by communicating over the links using available data rates of the multiple different communication technologies of the links. Based at least in part on the communicating, the node may then determine refined quality metrics for the links associated with various communication technologies and various data rates. For each link exercised, the node may determine an optimum refined quality metric (e.g., optimum cross product, figure of merit (FOM), etc.) associated with a specific communication technology and a specific data rate. The node may then rank links based on their optimum refined quality metric. The node may then route communications by selecting links based in part on their associated optimum refined quality metric, and transmit the communications via a selected link using the associated specific communication technology at the specific data rate associated with the optimum refined quality metric. In an embodiment, a node may select multiple links, multiple communication technologies and/or multiple data rates, based on their associated optimum refined quality metrics, to communicate duplicate or redundant data deemed as “high priority” that must be delivered. 
     In one example, the node may qualify links having a refined quality metric above a predetermined threshold. The node may then route communications to neighbor nodes with which the node has a qualified link. In another example, the node may use a routing protocol to route communications to neighbor nodes based in part on the determined refined quality metric of links between the node and neighbor nodes associated with various communication technologies. 
     If a node has a relatively small number of neighbor nodes (e.g., less than 10), the node may determine quality of the links between it and all of its neighbor nodes. Alternatively, if the node has many neighbor nodes, the node may determine a link quality between itself and a subset of its neighbor nodes. The node may continue to determine quality of links with its neighbor nodes until it determines a predetermined number of links (e.g., 5, 10, 20, etc.) that meet a threshold number, thereby ensuring a sufficient number of good communication paths for the node. 
     In an example implementation, for at least one or more of the multiple different communication technologies, the node may exercise a link by sending a request-to-send (RTS) message to a neighbor node sharing the link. The request to send message may designate communication channels and/or one or more data rates to test. In response, the node may receive a clear-to-send (CTS) message from the neighbor node indicating that the neighbor node is available to receive transmissions. The node may then proceed to test communication channels and/or data rates between the node and the respective neighbor node by sending test data packets to the neighbor node. Upon receiving the test data packets, the neighbor node may send back test data packets according to the communication channels, specified data rates or other protocol elements designated for test. Each of the test data packets may include an indication of a cost in time of transmission through the link. In one example, the test data packets may include actual data packets. 
     Upon receiving back the test data packets from the neighbor node, the node may calculate one or more quality metrics between the node and the neighbor node. The node may also send a confirmation packet including a number of test data packets the node received from the neighbor node. The neighbor node may use the confirmation packet to evaluate the link quality between the node and the respective neighbor node. 
     In one implementation, the node may determine a communication technology and data rate that optimizes an FOM quality metric of a link. The node may then qualify the link and add the link, the FOM quality metric, the communication technology and the data rate to a list of FOM links data. For example, a link may be qualified for a data rate that is less than a maximum data rate of a corresponding communication technology if, for example, a higher data rate results in an unacceptable decrease in a communication success rate (e.g., increase in packet loss rate, increase in bit error rate, etc.). In some examples, the list of FOM links data may include a ranking of links to neighbor nodes according to the relative quality of links. 
     Various different metrics may be used to calculate link quality (e.g., FOM) for one or more data rates between nodes based on one or more different communication technologies available on a link. In one specific example, link quality may be calculated based on an expected transmission time (ETT) of communications across multiple communication technologies available on the link. ETT may be calculated according to the following equation: 
     
       
         
           
             
               
                 
                   
                     ETT 
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                       ETX 
                     
                   
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                           P 
                         
                       
                     
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                       P 
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                         1 
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                             ( 
                             
                               1 
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                               Pf 
                             
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                             ( 
                             
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                               Pr 
                             
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                   Equation 
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                     ( 
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     P is a loss rate on a link, 
     Pf is a probability that a data packet successfully arrives at the neighbor node, 
     Pr is a probability that a confirmation from the neighbor node is successfully received, 
     S is packet size of the data packet (e.g., in Bits, or other units), and 
     B is a bandwidth of the link between the two nodes (e.g., in Bits/second or other units). 
     For example, considering two nodes x and y, the Pf for node x will be the number of test data packets received by node y from node x divided by the number of test data packets sent by node x. The Pr for node x will be the number of test data packets received by node x from node y divided by the number of test data packets sent by node y. Pf and Pr for node y will be computed in the same way. Equation (1) is just one example routing metric that may be used to measure link quality, and, in other examples, various other metrics may be used to measure link quality. 
     If, after receiving the RTS, the neighbor node is not or will not be available to receive communications (e.g., the neighbor already has a previously scheduled communication), then the neighbor node may send back a not-clear-to-send (NCTS) message. If the neighbor node is busy communicating on another channel, then the neighbor node may not receive the RTS and, therefore, will not respond. If the node receives a NCTS or does not receive any response, then the node may wait a period of time and try again and/or may try a different neighbor node. 
     Overview of Routing Based on Node Availability 
     In another example implementation, a busy device list may be maintained for each node. The busy device list may include availability information for one or more neighbor nodes, and routing transmissions based on availability of the neighbor nodes. In this example, a node may receives some information (e.g., resource consumption data, a report, an alert, a status message, a software/firmware update, etc.) that is to be transmitted to a destination. The information may be received from a neighbor node or from a system or component (e.g., a local sensor or metrology module) of the node itself. Upon receipt of the information, the node may query a busy device list to determine an availability of one or more neighbor nodes. The node may then identify a neighbor node that, according to the busy device list, is available to receive transmissions and is capable of propagating the information to the destination. The node may then transmit the information to the identified neighbor node. 
     The busy device list is generally maintained in local memory of the node itself (e.g., at a medium access control (MAC) sub layer of the node). However, in some implementations, the busy device list may additionally or alternatively be maintained at another location on the network (e.g., a parent node, cellular router, relay, network storage device, or the like). 
     In one example, the busy device list may be generated, maintained, and updated based on reservation information contained in messages overheard on a control channel by the multiple protocol receiver of the node. The reservation information may identify nodes that are (or will be) busy and a duration during which they will be busy. This reservation information may be included in a variety of messages including, for example, request-to-send (RTS) messages addressed to other nodes of the mesh network, and/or clear-to-send (CTS) messages addressed to other nodes of the mesh network. 
     Example Architecture 
       FIG. 1  is a schematic diagram of an example architecture  100  of a multi-node mesh network using multiple protocol receivers in which transmissions can be routed according to link quality and/or availability of nodes. The architecture  100  includes a plurality of nodes  102 A,  102 B,  102 C . . .  102 N (collectively referred to as nodes  102 ) communicatively coupled to each other via direct communication paths or “links.” In this example, N represents a number of nodes in an autonomous routing area (ARA), such as a wide area network (WAN), metropolitan area network (MAN), local area network (LAN), neighborhood area network (NAN), field area network (FAN), personal area network (PAN), or the like. As an example, nodes  102  may be configured in an RF mesh, a PLC mesh, or both. In one example, nodes  102  may be part of a low power and lossy network (LLN). 
     The term “link” refers to a direct communication path between two nodes (e.g., a “one hop” transmission that does not pass through or become propagated by another node). Each link may represent a plurality of channels or one or more variable data rate channels over which a node is able to transmit or receive data. Each link may include multiple communication technologies, such as one or more RF communication technologies, one or more PLC communication technologies, or both. 
     Each of the channels may be defined by a frequency range which is the same or different for each of the channels. In some instances, one or more channels may comprise RF channels communicated using RF communications technologies. In other instances, one or more channels may use a power line communication (PLC) system communicated using a PLC communications technology. Thus, a link may include portions based on multiple communication medias, such as RF and PLC portions. Likewise, various links may use multiple different RF and/or PLC communications technologies (e.g., various modulation techniques, bandwidths, data rates, center frequencies, protocols, etc). 
     The channels on a link may include a control channel and multiple data channels. In some instances, the control channel is utilized for communicating one or more messages between nodes to specify one of the data channels to be utilized to transfer data. Generally, transmissions on the control channel are shorter relative to transmissions on the data channels. Once specified, the nodes may move to the data channel for communication. 
     Each of the nodes  102  may be implemented as, or associated with, any of a variety of conventional computing devices such as, for example, smart utility meters (e.g., electric, gas, and/or water meters), sensors (e.g., temperature sensors, weather stations, frequency sensors, etc.), control devices, transformers, routers, servers, relays (e.g., cellular relays), switches, valves, power line communication (PLC) transceivers, combinations of the foregoing, or any device couplable to a communication network and capable of sending and/or receiving data. 
     In this example, the nodes  102  are also configured to communicate with one or more central processing facilities  104  via an edge device (e.g., cellular relay, cellular router, edge router, destination oriented directed acyclic graph (DODAG) root, etc.) which serves as a connection point of the ARA to a backhaul network(s)  106 , such as the Internet or one or more public or private intranets. In the illustrated example, node  102 A may serve as an edge device and/or cellular relay to relay communications from the other nodes  102 B- 102 N of the ARA to and from the central office  104  via the network(s)  106 . 
     As an example, node  102 C may be representative of each of the nodes  102  and includes a radio with multiple protocol receiver  108 , a PLC transceiver  110  and a processing unit  112 . 
     The radio with multiple protocol receiver  108  comprises a radio frequency (RF) transceiver that may be configured to receive RF signals associated with multiple different RF communication technologies (e.g., FSK, OQPSK, OFDM, CDMA, etc.) at a variety of data rates, and transmit RF signals via one or more of a plurality of RF communication technologies. The radio with multiple protocol receiver  108  may be configured to listen for a plurality of different RF communication technologies in a parallel fashion across multiple links. Radio  108  may also be configured to determine, or facilitate determination of, a received signal strength, such as a “received signal indicator” (RSI) for one or more of the plurality of different RF communication technologies. 
     In some implementations, each of the nodes  102  includes a single radio with multiple protocol receiver  108  configured to send and receive data on multiple different channels, such as the control channel and multiple data channels of each communication link. The radio  108  may also be configured to implement a plurality of different data rates, protocols, signal strengths, and/or power levels. The architecture  100  may represent a heterogeneous network of nodes, in that the nodes  102  may include different types of nodes (e.g., smart meters, cellular relays, sensors, etc.), different generations or models of nodes, and/or nodes that otherwise are capable of transmitting on different channels and using different communication technologies, data rates, protocols, signal strengths, and/or power levels. 
     The power line communication (PLC) transceiver  110  is configured to transmit and/or receive one or more communication signals on electrical power wiring, including local power wiring and long distance high voltage transmission lines. PLC transceiver  110  may transmit and/or receive different types of power line communications that include one or more PLC communication technologies (e.g., narrowband PLC, broadband PLC, power line digital subscriber line (PDSL), power line telecom (PLT), power line networking (PLN), broadband over power lines (BPL), etc.) having one or more frequency bands, channels, data rates and/or types of modulation that may depend on the propagation characteristics of the power wiring used. 
     The processing unit  112  is coupled to radio  108  and PLC transceiver  110 , and may include one or more processor(s)  114  communicatively coupled to memory  116 . The memory  116  may be configured to store one or more software and/or firmware modules, which are executable on the processor(s)  114  to implement various functions. While the modules are described herein as being software and/or firmware executable on a processor, in other embodiments, any or all of the modules may be implemented in whole or in part by hardware (e.g., as an ASIC, a specialized processing unit, digital signal processor, etc.) to execute the described functions. 
     In the embodiment of  FIG. 1 , the memory  116  includes multiple protocol receiver module  118 , figure of merit (FOM) determination module  120 , busy device list module  122  and routing module  124 . 
     Multiple protocol receiver module  118  may be configured to receive, decode, demodulate, descramble, decrypt, measure and/or process signals and/or data received from both radio  108  and PLC transceiver  110 . Multiple protocol receiver module  118  may also be configured to control various features and functions of radio  108  and PLC transceiver  110 . In an implementation, multiple protocol receiver module  118  may determine or detect, or facilitate the determination or detection of, an RSI of signals received by radio  108  and PLC transceiver  110 . Multiple protocol receiver module  118  may also be configured to maintain a list of RSI values associated with communications technologies used on various links to neighbor nodes  102 . 
     The FOM determination module  120  may be configured to determine and maintain a measurement (e.g., figure of merit (FOM)) of a quality of RF and PLC links between the nodes  102 . As an example, FOM determination module  120  may be configured to send and receive data over specified links (e.g., links with a highest measured RSI) using available combinations of data rate, media (e.g., RF or PLC) and communication technology (e.g., modulation) for each specified link. FOM determination module  120  may be configured to determine an optimal combination of data rate, media and communication technology for each specified link based on a cross product of successfulness (e.g., communications success rate) and data rate for each of the available combinations. Additionally, as illustrated in  FIG. 1 , FOM determination module  120  may qualify links (i.e., a qualified link) having an FOM measurement that is above a pre-specified threshold and un-qualify links (i.e., an un-qualified link) having an FOM measurement that is below a pre-specified threshold. As such, nodes having qualified links may be determined to be neighbor nodes of node  102 C. 
     As an example, if a link has both a high data rate RF communication technology with a low communication success rate, and a low data rate PLC communication technology with a high communication success rate, FOM determination module  120  may determine that the PLC communication technology has a higher FOM than the high data rate RF communication technology. Thus, FOM determination module  120  may associate the FOM, data rate, and PLC communication technology having a highest combination of success rate and data rate with the link. Thus, FOM determination module  120  may rate links with a higher combination of success rate and data rate better (e.g., a higher FOM) than links with a lower combination of success rate and data rate (e.g., a lower FOM). Consequently, FOM determination module  120  may not rate links solely on their success rate or data rate alone, but rather on a combination (e.g., cross product) of their communication success rate and data rate. Additionally, FOM determination module  120  may be configured to evaluate these combinations for multiple available communication technologies (e.g., RF and PLC) of associated links to determine an optimal combination across the multiple available communication technologies of a link. 
     The busy device list module  122  may be configured to determine availability of nodes  102  and to maintain a listing of the nodes which are (or will be) busy and a duration that they will be busy. In the illustrated example of  FIG. 1 , the busy device list module  122  would indicate that node  102 B is busy transmitting data to node  102 A and is, therefore, unavailable to receive transmissions from node  102 C. 
     Routing module  124  is configured to implement and/or facilitate a routing protocol to route transmissions between and among nodes  102  of the ARA using available communication technologies (e.g., RF and PLC) based on a quality (e.g., FOM) of links between the nodes  102 , availability of the nodes  102  determined by the busy device list module  122 , and/or one or more other factors. As such, routing module  124  is configured to implement and/or facilitate a routing protocol that is agnostic regarding which communication technology is used when routing data among nodes  102 . In an embodiment, routing module  124  is configured to route transmissions, such as transmissions deemed “high priority”, in a duplicate or redundant fashion. As an example, routing module  124  may route “high priority” transmissions in a duplicate fashion, such that a “high priority” transmission may be simultaneously routed using multiple communication technologies (e.g., RF and PLC), multiple links, or the like. Additional details of how the routing module  124  may route communications based on these and other factors is provided below. 
     The memory  116  may comprise computer-readable media and may take the form of volatile memory, such as random access memory (RAM) and/or non-volatile memory, such as read only memory (ROM) or flash RAM. Computer-readable media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data for execution by one or more processors of a computing device. Examples of computer-readable media include, but are not limited to, phase change memory (PRAM), static random-access memory (SRAM), dynamic random-access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information for access by a computing device. As defined herein, computer-readable media does not include communication media, such as modulated data signals and carrier waves. 
     The network(s)  106  represents a backhaul network, which may itself comprise a wireless or a wired network, or a combination thereof. The network(s)  106  may be a collection of individual networks interconnected with each other and functioning as a single large network (e.g., the Internet and/or one or more intranets). Further, the individual networks may be wireless or wired networks, or a combination thereof. 
     The central office  104  may be implemented by one or more computing devices, such as servers, personal computers, laptop computers, etc. The one or more computing devices may be equipped with one or more processor(s) communicatively coupled to memory. In some examples, the central office  104  includes a centralized meter data management system which performs processing, analysis, storage, and/or management of data received from one or more of the nodes  102 . For instance, the central office  104  may process, analyze, store, and/or manage data obtained from a smart utility meter, sensor, control device, router, regulator, server, relay, switch, valve, and/or other nodes. Although the example of  FIG. 1  illustrates the central office  104  in a single location, in some examples the central office may be distributed amongst multiple locations and/or may be eliminated entirely (e.g., in the case of a highly decentralized distributed computing platform). 
     Example Node 
       FIG. 2  is a schematic diagram of example environment  200  showing additional details of example node  102 C of  FIG. 1 . Radio  108 , PLC transceiver  110 , processor(s)  114  and memory  116  are coupled together via a bus or other coupling mechanism  202 . Coupling mechanism  202  may comprise direct and/or indirect wired (e.g., cable, coax, fiber optic, etc.) or wireless connections, a wired or wireless network, one or more communication busses, or combinations thereof. Radio  108  may have antenna(s)  204  for receiving and/or transmitting RF signals, for example, between neighboring nodes  102 A,  102 B and  102 N. Antenna(s)  204  may include one or more directional or omni-directional antennas suitable to receive/transmit signals employing the various RF communication technologies used on links between nodes  102 . 
     The RF front end  206  may include high-frequency analog and/or hardware components that provide functionality, such as tuning and/or attenuating signals provided by antenna(s)  204  and obtained from one or more of the nodes  102 . As an example, RF front end  206  and antenna(s)  204  are configured to receive, in parallel, RF signals of RF communication technologies used by nodes  102 . The RF front end  206  may be configured to provide received signals to one or more signal processor(s)  208 . Likewise, signal processor(s)  208  may be configured to provide signals to RF front end  206  for transmission. 
     The signal processor(s)  208  may be configured to detect and/or process, in parallel or effectively in parallel, received signals of a plurality of RF communication technologies used by nodes  102  or other network devices. In one example, the signal processor(s)  208  may be configured to provide frequency, bandwidth, synchronization and/or channel selection functionality to radio  108 . For example, signal processor(s)  208  may include digital signal processors, mixers, filters, amplifiers, modulators, demodulators, detectors, etc., implemented in hardware and/or software executed by a processor or application specific integrated circuit (ASIC) or other embedded computing device(s). The signal processor(s)  208  may be configured to utilize processor(s)  114  and software defined or stored in memory  116 . Signal processor(s)  208  may be implemented at least in part using analog, digital or a combination of components. 
     As an example, signal processor(s)  208  may detect one or more signals of one or more RF communication technologies on links of node  102 C, and measure, or facilitate the measurement of, a received signal strength, such as a “received signal indicator” (RSI), of each received signal. In an implementation, signal processor(s)  208  may be configured to discriminate between received signals of the same, similar or different RF communication technologies based on their RSI. In an implementation, signal processor(s)  208  may be configured to select a signal of a RF communication technology based on, or indicated by, the RSI of the signal relative to one or more other received signals, or based on the RSI of the received signal itself. Signal processor(s)  208  may detect a signal of a corresponding RF communication technology and may configure itself to optimize the reception of the detected signal of the corresponding RF communication technology. To facilitate locking onto a received signal, signal processor(s)  208  may adjust a bandwidth, gain, attenuation, frequency and phase of an oscillator, frequency and phase of a clock, or the like. Signal processor(s)  208  may be configured to provide an intermediate frequency (IF) signal, baseband signal and/or digital signal associated with the received signal to software defined or stored in memory  116 . Likewise, signal processor(s)  208  may be configured to provide an intermediate frequency (IF) signal, baseband signal and/or digital signal to RF front end  206  for transmission to, for example, one or more of nodes  102 . 
     In an implementation, signal processor(s)  208  may be configured to determine and provide an RSI value for each of one or more received signals to software defined or stored in memory  116 . Additionally, signal processor(s)  208  may be configured to determine and provide an indication of the RF communication technology of each received signal to software defined or stored in memory  116 . As such, signal processor(s)  208  may be configured to provide software defined radio functionality. 
     PLC transceiver  110  may utilize PLC interface  210  to provide connection to a power line communication system. A power line communication system may allow node  102 C to communicate with, for example, other neighbor nodes that share connectivity with the power line communication system. PLC transceiver  110  may utilize processor(s)  114  and software defined or stored in memory  116  to facilitate communication over the power line communication system via PLC interface  210 . In an implementation, PLC transceiver  110  may be configured to provide the received signal, an intermediate frequency (IF) signal, baseband signal and/or digital signal associated with the signal received via the power line communication system to software defined or stored in memory  116 . Likewise, PLC transceiver  110  may be configured to provide a signal to PLC interface  210  for transmission via the power line communication system. 
     In one example, PLC transceiver  110  may be configured to determine, or facilitate a detection of, an RSI of a signal received via the power line communication system. PLC transceiver  110  may provide the RSI value, or an indicator of an RSI value, to software defined or stored in memory  116 . In an embodiment, PLC transceiver  110  may be configured to provide an indication of the PLC communication technology of the received signal to software defined or stored in memory  116 . 
     Multiple protocol receiver module  118  may reside all or in part in memory  116  and include software (SW) defined receiver  212 , preamble detection processes  214 , packet demodulator  216 , protocol management module  218 , state machine  220  and initial links determination module  222 . 
     In an embodiment, SW defined receiver  212  may be implemented by software stored in memory  116 . In an alternate embodiment, SW defined receiver  212  may be implemented by software stored in memory  116 , as well hardware (not shown) such as one or more digital signal processors, analog hardware, digital hardware, or combinations thereof. In an implementation, SW defined receiver  212  may include components, otherwise implemented using analog components (e.g. mixers, filters, amplifiers, modulators and/or demodulators, detectors, etc.), implemented in software executed by a processor or application specific integrated circuit (ASIC) or other embedded computing device(s). 
     SW defined receiver  212  may be configured to communicate with radio  108  and PLC transceiver  110 , for example, via interface  202 . The SW defined receiver  212  may utilize processor(s)  114  and software defined or stored in memory  116 . In an implementation, software-defined receiver  212  may work in conjunction with signal processor(s)  208 , as well as RF front end  206 , to facilitate measurement, detection, selection, identification, demodulation, synchronization, decoding, descrambling, decryption and/or processing of one or more signals received by radio  108 . Additionally, software-defined receiver  212  may facilitate or control the configuration of signal processor(s)  208 , as well as provide control for RF front end  206 . Software-defined receiver  212  may work in conjunction with radio  108  to determine an associated RF communication technology of signals received by radio  108 , as well as an RSI, effective RSI and/or normalized RSI of received signals. Software-defined receiver  212  may work in conjunction with radio  108  to facilitate selection of a signal when radio  108  receives more than one signal. 
     Software-defined receiver  212  may also be configured to work in conjunction with PLC transceiver  110  to facilitate detection, selection, identification, demodulation, synchronization, decoding, descrambling, decryption and/or processing of a signal received by PLC transceiver  110 . In one example, software-defined receiver  212  may process, determine or know a-priori a PLC communication technology of a signal received by PLC transceiver  110 . Additionally, the software-defined receiver  212  may be configured to determine an RSI, effective RSI and/or normalized RSI of a signal received by PLC transceiver  110  based on the received signal&#39;s strength and communication technology. 
     In one example, the software-defined receiver  212  may be configured to select, or facilitate selection of, one or more signals among one or more received RF signals and one or more received PLC signals based on signal strength or other signal quality criteria. 
     A plurality of preamble detection processes  214  may be configured for simultaneous, i.e., parallel, operation, such as in a multitasking environment. Each of the plurality of preamble detection processes  214  may be configured to detect and/or recognize a particular synchronization header and/or preamble of a particularly modulated signal and/or packet. Referring to the example of  FIG. 3 , which illustrates an example of a data packet received by the SW defined receiver  212 , each of the plurality of preamble detection processes  214  may be configured to detect or recognize the preamble  306  in the packet  300 . Similarly, each of the plurality of preamble detection processes  214  may be configured to detect the synchronization header  302 , such as by detection or recognition of the preamble  306  and/or the sync word  308 . Such detection or recognition may facilitate access to data  304  of packet  300 . 
     Accordingly, each of the plurality of preamble detection processes  214  may be configured to recognize a particular preamble associated with a particular packet. Thus, detection and/or recognition by one of the plurality of preamble detection processes  214  of a particular preamble results in a determination or recognition of a particular protocol that was used to modulate a packet associated with the detected preamble. This association, between a recognized preamble and a protocol used to modulate the packet having the recognized preamble, may be made in any of a number of manners. In one example, preambles may be linked to protocols in a data structure. In a second example, each preamble detection processes  214  may point to an appropriate packet demodulator  216  from among a plurality of packet demodulators, wherein each packet demodulator is associated with one of a plurality of protocols. Accordingly, detection of a preamble by one of the plurality of preamble detection processes results in knowledge of a protocol and of an appropriate packet demodulator  216  associated with the protocol for use in demodulating the packet of a received signal. Such detection may be performed across RF and PLC communication technologies utilized by nodes  102 . 
     A plurality of packet demodulators or packet demodulating processes  216  may be configured for serial or parallel operation. In one example, each of the plurality of packet demodulators  216  is associated with one of the plurality of preamble detection processes  214 . In operation, successful detection of a preamble by a preamble detection process results in execution of a packet demodulator associated with that preamble detection process. Thus, once a protocol is recognized, a packet demodulator  216  associated with the recognized protocol is selected and executed. Execution of the packet demodulator  216  demodulates the packet and/or the data  304  according to the protocol associated with the demodulator. Thus, the packet demodulator  216  demodulates data (e.g., data  304 ) within the packet associated with the detected preamble using a bit rate, synchronization, error correcting redundancy, etc., associated with the protocol. Additionally, the packet demodulator  216  may configure and/or direct operation of software-defined receiver  212 . 
     A protocol management module  218  may configured to manage operation of the preamble detection processes  214 , the packet demodulators  216 , the software defined receiver  212  and other structures, software objects and devices, as indicated by a particular application or design. In one example, the protocol management module  218  may utilize a state machine  220  or other logical construct to assist in the management of preamble detection, protocol recognition, packet demodulator selection and packet demodulation. Alternatively, a different logical control may be utilized to obtain similar results. 
     The state machine  220  may be defined to assist in the management of the operation of the multiple protocol receiver module  118 . The state machine  220  is representative of any of a number of logical devices, constructs or techniques used to manage control and operation of a process, and to thereby call one or more processes or modules in a desired sequence and according to a desired timing. As an initial example, state machine  220  may utilize two or more states and allow movement between the states. 
     Example states include: (1) simultaneously listening for signals received by radio  108  and/or PLC transceiver  110  that indicate a packet, (2) detecting a preamble associated with the packet, (3) determining a protocol indicated by the preamble, and (4) demodulating the received packet according to the protocol. Each iteration of the above four states could be performed sequentially, and completion of the four states or failure at any state could result in return to the first state. 
     The initial links determination module  222  may periodically, or a-periodically, gather and maintain information pertaining to current received signal strength (e.g., RSI) across links of a node  102 , such as exemplary node  102 C. As such, initial links determination module  222  may be configured to facilitate discovery of nodes  102 , such as neighbor nodes of node  102 C. As an example, initial links determination module  222  may obtain, determine, process and/or maintain RSI information for links associated with node  102 C in a list. Initial links determination module  222  may obtain RSI information associated with the links of node  102 C during a real time operation of node  102 C, while node  102 C is in a listening mode, in response to one or more requests from node  102 C, in response to one or more external requests for neighbor nodes of node  102 C to transmit over their associated links, or combinations thereof. 
     Initial links determination module  222  may be configured to associate and maintain one or more RSI values of a link with the link&#39;s corresponding communications technology(s), media(s) and/or protocol(s). In addition to maintaining an RSI value that indicates a detected received energy or received power level of a received signal, initial links determination module  222  may be configured to determine an RSI value of a received signal as an effective or normalized RSI value as a function of a media and/or communication technology of the received signal on a link. As an example, initial links determination module  222  may determine effective or normalized RSI values that allow for comparing a received signal strength of a signal having FSK (i.e., frequency shift keying) modulation to a received signal modulated using, for example, QAM (quadrature amplitude modulation) and having OFDM (orthogonal frequency-division multiplexing) encoding. Initial links determination module  222  may access information (e.g., conversion tables, formula tables, etc.) from initial links data  224  storage required for determining effective or normalized RSI values. 
     Initial links determination module  222  may be configured to rank links to neighbor nodes of node  102 C based on their associated RSI values, effective RSI values and/or normalized RSI values. Initial links determination module  222  may be configured to select a number of links associated with neighbor nodes having a highest ranked RSI value. The number of links selected may be predetermined, may be a percentage of total detected links, may be based on the RSI values themselves (e.g., RSI values above a predetermined threshold, relative strength of RSI values, etc.), or combinations thereof. As an example, initial links determination module  222  may select the top 10-20 neighbor nodes (e.g., short list of neighbor nodes) having links with the top ranked RSI values. Initial links determination module  222  may store information associated with top ranked links—such as link designators, RSI values corresponding to link designators, media and communication technologies associated with RSI values corresponding to link designators, etc.—in initial links data  224  storage. 
     In one example, the SW defined transmitter  226  may be configured to facilitate transmission of a packet, other data or signal via radio  108  or PLC transceiver  110 . SW defined transmitter  226  may transmit the packet, data or signal using a configurable or pre-specified communication technology. SW defined transmitter  226  may be configured to control various aspects of radio  108  and PLC transceiver  110  to facilitate transmission of data using various different RF and PLC communication technologies. As an example, SW defined transmitter  226  may be configured to facilitate transmission of a packet, other data or signal in a duplicate or redundant fashion in a simultaneous, or near simultaneous manner via both radio  108  and PLC transceiver  110 . SW defined transmitter  226  may be configured to facilitate transmission of a packet, other data or signal in a duplicate or redundant fashion in a simultaneous, or near simultaneous manner using different communication technologies over the same or different links. 
     The FOM determination module  120  may be configured to determine and maintain a measurement (e.g., figure of merit (FOM)) of a quality of RF and PLC links between nodes  102 , such as links to nodes neighboring node  102 C. As an example, FOM determination module  120  may exercise links indicated by initial links determination module  222  as having a top ranked RSI value. By focusing on these specified links, FOM determination module  120  may save time and resources relative to exercising a greater number of links, including links having lower RSI values. 
     In one example, the FOM determination module  120  may exercise specified links by sending data over the specified links and measuring data returned in response. Since the specified links may be ranked or associated with top ranked RSI values, the RSI value associated with each link may be thought of as an initial quality measurement. Thus, by exercising the specified links, FOM determination module  120  may refine a quality metric associated with each specified link to obtain a better or refined (e.g., more accurate, more confident, reduced variance, etc.) measurement of the quality of the specified links. 
     In a further example, the FOM determination module  120  may exercise specified links by sending and receiving data using combinations of available data rate(s), available channels, available media (e.g., RF and PLC) and available communication technologies (e.g., modulation schemes) for each specified link. As an example, FOM determination module  120  may ascertain (e.g., a-priori, via query, via data extracted from a communication, via table lookup, etc.) that a node on a specified link supports two RF communication technologies (e.g., two different modulation schemes, two modulation schemes operating in different bandwidths, etc.) and a PLC communication technology. FOM determination module  120  may then exercise both RF communication technologies and the PLC communication technology at available data rates to determine an optimal combination of data rate and communication technology for the link. FOM determination module  120  may then associate an FOM value or metric with the optimum combination, and store the optimal FOM value or metric, data rate and communication technology in FOM links data  228 . 
     In an alternate embodiment, FOM determination module  120  may limit exercising a link to the communication technology indicated by initial links determination module  222  as having the top ranked RSI value. As an example, a node on the other end of a specified link may support an RF communications technology and a PLC communications technology. Initial links determination module  222  may have previously determined that the RF communications technology of the node has a top ranked RSI value, while the PLC communications technology of the node has a low ranked RSI value. Thus, to further conserve time and resources, FOM determination module  120  may focus solely on exercising the RF communications technology of the node having the top ranked RSI value to find the optimal FOM and optimal data rate using the RF communications technology. FOM determination module  120  may then store the optimal FOM value, data rate and communication technology associated with the link in FOM links data  228 . 
     The example embodiments of FOM determination module  120  presented above are not intended to limit how FOM determination module  120  may exercise links. As another example, a link may support two RF communication technologies and a PLC communication technology. In this example, FOM determination module  120  may exercise a first of the two RF communication technologies indicated as having a top ranked RSI value, as well as the PLC communication technology, and store the optimal determined FOM value, data rate and communication technology associated with the link in FOM links data  228 . FOM determination module  120  may also store an FOM value and optimal data rate for both the first RF communications technology and the PLC communications technology in FOM links data  228 . Other example embodiments are within the scope teachings herein. 
     In various implementations, FOM determination module  120  may determine and maintain a refined quality (e.g., an FOM) of a link based on a cross product of successfulness (e.g., a communications success rate) and a data rate for available data rate combinations. As an example, for a given link, the FOM determination module  120  may find an optimal combination of media, communications technology and data rate that minimizes (or maximizes an optimization of) the ETT value of Equation 1. In a different implementation, the FOM determination module  120  may use other suitable quality optimization metrics for finding an optimal FOM associated with a highest data rate and minimum packet loss or minimum bit error rate combination for the available communication technologies of a link. 
     The FOM determination module  120  may store FOM data for associated links in FOM links data  228  store. FOM links data  228  store may also contain the combination of media, communication technology and data rate associated with the FOM data for each specified link. In an alternate embodiment, FOM determination module  120  may maintain FOM values and their associated combination of media, communication technology and data rate for a subset of the specified links or additional links in FOM links data  228  store. As an example, upon exercising the specified links, FOM determination module  120  may determine that one or more of the specified links having a top ranked RSI value exhibited a link quality below a relative, pre-specified or pre-determined threshold. Thus, FOM determination module  120  may not store information pertaining to these links in FOM links data  228  store. In an embodiment, FOM determination module  120  may also store one or more protocols supported by nodes on links that are exercised. 
     The busy device list module  122  is configured to determine availability of nodes  102  and to maintain a listing of the nodes which are (or will be) busy and a duration that they will be busy. Busy device list module  122  may store availability information associated with nodes in busy device list  230  store. In the illustrated example of  FIG. 1 , the busy device list module  122  may indicate that node  102 A is busy receiving data from node  102 B and is, therefore, unavailable to receive transmissions from node  102 C. In this example, a multiple protocol receiver of node  102 A may be in a receive state. Thus, the multiple protocol receiver of node  102 A is not currently in a listen state, where it can detect a communication request, such as a request to send (RTS) packet from node  102 C. Therefore, for each neighbor node  102 , busy device list module  122  may maintain a neighbor node availability and a duration that the neighbor node will be busy in busy device list  230 . Additionally, for each neighbor node  102 , busy device list module  122  may maintain, in busy device list  230 , neighbor node state information indicating a current state of neighbor nodes (e.g., listening for signals, processing a signal, etc.). 
     While the initial links data  224 , the FOM links data  228  and the busy device list  214  are shown as being lists of data stored in local memory of the node  102 C, in other embodiments, the link quality and node availability information may be stored in a single list or in a non-list form. Furthermore, in some embodiments, the link quality and node availability information and other information stored in initial links data  224 , the FOM links data  228  and the busy device list  214  may additionally or alternatively be maintained at one or more other locations on the network (e.g., a parent node, cellular router, relay, network storage device, or the like). 
     In some implementations (e.g., when the node is a utility meter), the memory  116  may also include a metrology module  232  configured to collect consumption data of one or more resources (e.g., electricity, water, natural gas, etc.), which may then be transmitted to one or more other nodes  102  for eventual propagation to the central office  104  or other destination. In various implementations, metrology module  232  may periodically or a-periodically provide data for transmission, may be queried and provide data in response to a query, may provide data for transmission once a predetermined amount of data has been collected, or the like. 
     Routing module  124  facilitates the implementation of a routing protocol (e.g., Routing Protocol for Low power and Lossy Networks (RPL), LOAD, DODAG based routing, distance vector routing, routing based on a current or predicted load of one or more nodes, etc.) based on FOM values of links associated with node  102 C, availability of the nodes  102 , and/or one or more other factors. As an example, for routing a packet at node  102 C destined for node  102 A, routing module  124  may facilitate a routing protocol to choose the direct link between node  102 C and  102 A (as shown in  FIG. 1 ), based on the FOM value of that link relative to other links as indicated in FOM links data  228  and the current availability of node  102 A as indicated in busy device list  230 . As such, routing module  124  may access FOM links data  228  to determine an optimal combination of media, communications technology and data rate associated with the FOM value of the selected link between node  102 C and  102 A. Assuming node  102 A is currently available, routing module  124  may facilitate the routing protocol to route the packet to node  102 A via the link. As an alternative, if node  102 A is currently specified as busy, routing module  124  may facilitate choosing to wait for node  102 A to become available based on a duration that node  102 A will be busy as specified in busy device list  230 . As another alternative, the routing protocol may choose a different link associated with node  102 C based on the different link&#39;s FOM value and associated node availability. Thus, routing module  124  may choose an optimal combination of media, communications technology and data rate associated with the FOM value of the different link. In a further example, the routing module  124  may configure and/or direct SW defined transmitter  226  to transmit the packet over a determined link, using the specified media, communications technology and data rate for that link. 
     Example Method of Determining Link Quality with Multiple Communication Technologies 
       FIG. 4  illustrates an example method  400  of determining quality of links having multiple communication technologies between nodes of a mesh network. The method  400  is described with reference to the example architecture  100  of  FIG. 1  for convenience. However, the method  400  is not limited to use with the example architecture  100  of  FIG. 1  and may be implemented using other architectures and devices. 
     At operation  402 , a node determines a strength of received signals on communication links from neighbor nodes in a mesh network. In one example, the received signals include multiple different communication technologies. In the context of the examples of  FIGS. 1 and 2 , the determination of received signal strength may be performed by node  102 C using radio  108 , PLC transceiver  110 , multiple protocol receiver module  118 , SW defined receiver  212 , initial links determination module  222 , or combinations thereof. As an example, if node  102 C is in a listening state, node  102 C may listen, in parallel, to links to nodes  102 A,  102 B and  102 N, and measure an RSI of multiple different communication technologies on each of the links to determine an associated RSI, effective or normalized RSI for communication technologies utilized on the links. The communication technologies may include RF and PLC communication technologies used on each of the links. As another example, node  102 C may measure an RSI of multiple different communication technologies on links as part of operational communications with associated neighbor nodes. 
     Node  102 C, as well as its corresponding neighbor nodes may include nodes of a low power and lossy network (LLN). The multiple different communication technologies may include multiple different radio frequency (RF) communication technologies having different RF modulation schemes as well as one or more power line communication (PLC) technologies. 
     At operation  404 , in the context of the examples of  FIGS. 1 and 2 , initial links determination module  222  of node  102 C selects a subset of the communication links based in part on the strength of the received signals. At operation  406 , a subset of communications links is exercised by sending data and receiving response data via each of the subset of the communication links. As an example, FOM determination module  120  may perform the sending of data and the receiving of response data at available data rates of a communication technology used over each of the subset of the communication links. As another example, FOM determination module  120  may perform the sending of data and the receiving of response data using more than one communication technology used over one or more of the subset of the communication links. The data sent and received as part of the exercising may include test data, operational data, or a mix of test and operational data. Test data may include any repetitive or non-repetitive data that facilitates the exercising. Operational data may include actual data, such as payload data, metric data obtained by the node, metering data, or the like. Operational data may also include frame data as illustrated in  FIGS. 6 and 7  herein. 
     At operation  408 , in the context of the examples of  FIGS. 1 and 2 , FOM determination module  120  analyzes the response data. Based in part on analyzing the response data, at operation  410 , FOM determination module  120  evaluates a link quality as a function of an available data rate of each of the subset of the communication links. As an example, FOM determination module  120  may compute an ETT of Equation 1 as part of evaluating the link quality. FOM determination module  120  may evaluate the link quality as a function of an available data rate that includes determining a figure of merit (FOM) represented by a cross product of a communication success rate and an available data rate, wherein an optimum FOM is indicated by a highest available data rate that optimizes the cross product (e.g., minimizes ETT). In an alternate implementation, FOM determination module  120  may determine a figure of merit (FOM) associated with a maximum combination of the link quality and the available data rate for communication technologies of each of the subset of the communication links. 
     In one example, busy device list module  122  of node  102 C maintains information including an availability, unavailability and duration of unavailability of at least a subset of neighbor nodes in busy device list  230 , while FOM determination module  120  maintains information identifying a communication technology and an available data rate associated with the FOM for each of the subset of the communication links in FOM links data  228 . Then, in the context of the examples of  FIGS. 1 and 2 , routing module  124  may employ a routing protocol to select a communication link of the subset of the communication links for routing of a data packet to a neighbor node based in part on the FOM associated with the selected communication link and the availability of the neighbor node, and direct SW defined transmitter  212  to transmit the data packet to the neighbor node using the optimum communication technology and the optimum available data rate of the selected communication link (e.g., via radio  108  or PLC transceiver  110 ). As another example, routing module  124  may select multiple links, multiple communication technologies and/or multiple available data rates based in part on their associated FOM to transmit a “high priority” data packet in a redundant or duplicate fashion to assure delivery of the “high priority” data packet. Associated data may be stored in initial links data  224 , FOM links data  228  and busy device list  230  prior to node  102 C requiring to route the data packet, such that associated RSI and FOM data is not required to be determined as part of a “handshaking” procedure between nodes performed based on the requirement to route the data packet. 
     Method  400  may be performed when a new node is added to the network and periodically or a-periodically for existing nodes of the network. All or parts of method  400  may be performed in response to a determination that a link quality has degraded below a determined or pre-specified threshold, such as during a communication of operational data or by any determination of suspected or actual link quality degradation. 
     Example Method of Routing Based on Link Quality 
       FIG. 5  illustrates an example method  500  by which a quality of links may be determined. The links may utilize multiple communication technologies, thereby connecting nodes of a mesh network and routing communications based at least in part on the link quality. The method  500  is described with reference to the example architecture  100  of  FIG. 1  for convenience. However, the method  500  is not limited to use with the example architecture  100  of  FIG. 1  and may be implemented using other architectures and devices. 
     At operation  502 , a node determines, via a multi-protocol receiver of the node, a strength of received signals on communication links from neighbor nodes in a mesh network, the received signals including signals having multiple different radio frequency (RF) communication technologies and one or more power line communication (PLC) communication technologies. In the context of the examples of  FIGS. 1 and 2 , the determination of received signal strength may be performed by node  102 C using radio  108 , PLC transceiver  110 , multiple protocol receiver module  118 , SW defined receiver  212 , initial links determination module  222 , or combinations thereof. 
     At operation  504 , a subset of the communication links based in part on the strength of the received signals is selected. For example, initial links determination module  222  of node  102 C selects the subset of the communication links based in part on the strength of the received signals. 
     At operation  506 , in the context of the examples of  FIGS. 1 and 2 , FOM determination module  120  exercises the subset of the communication links by communicating data at available data rates of each of the subset of the communication links. FOM determination module  120  may perform the exercising by using more than one communication technology of one or more of the subset of the communication links, such as an RF and a PLC communication technology or a first RF communication technology and a second RF communication technology that differs from the first RF communication technology. The data utilized for the exercising may include test data, operational data, or a mix of test and operational data. Test data may include any repetitive or non-repetitive data that facilitates the exercising. Operational data may include actual data, such as payload data, metric data obtained by the node, metering data, or the like. Operational data may also include frame data as illustrated in  FIGS. 6 and 7  herein. 
     At operation  508 , in the context of the examples of  FIGS. 1 and 2 , FOM determination module  120  evaluates a link quality as a function of the available data rates for each of the subset of the communication links based in part on the communicating data. As an example, if a communication technology of a link has N (i.e., N being an integer greater than zero) available data rates, FOM determination module  120  may exercise all N data rates, or a subset of the N data rates, to evaluate link quality as a function of the available data rates. 
     At operation  510 , in the context of the examples of  FIGS. 1 and 2 , FOM determination module  120  determines a figure of merit (FOM) based in part on a cross product that indicates a maximum combination of the link quality and the available data rates evaluated for each of the subset of the communication links. As an example, FOM determination module  120  may compute an ETT of equation 1 as part of determining the FOM. FOM determination module  120  may determine a figure of merit (FOM) represented by a cross product of a communication success rate and an available data rate evaluated, wherein an optimum FOM is indicated by a highest available data rate evaluated that optimizes the cross product (e.g., minimizes ETT). The optimum FOM may indicate a tradeoff of an optimization where connectivity is maximized while capacity (e.g., throughput) is maintained as high as possible. In an alternate implementation, FOM determination module  120  may determine a figure of merit (FOM) associated with a maximum combination of the link quality and the available data rates evaluated for each link of the subset of the communication links. 
     At operation  512 , in the context of the examples of  FIGS. 1 and 2 , FOM determination module  120  maintains one or more records of the determined FOM, available data rate evaluated and communication technology associated with the determined FOM for each of the subset of the communication links in a data store, such as FOM links data  228 . 
     At operation  514 , in the context of the examples of  FIGS. 1 and 2 , routing module  124  routes a data packet to a neighbor node based in part on the FOM associated with each of the subset of the communication links. As an example, routing module  124  accesses FOM links data  228  to obtain FOM data records for links to neighbor nodes of node  102 C. Routing module  124  may then use the FOM data to facilitate a routing protocol to select one of the subset of the communication links for the routing of the data packet. In an alternate implementation, routing module  124  may also access busy device list  230  to obtain availability information regarding neighbor nodes. Routing module  124  may then use the FOM data and the availability data to facilitate a routing protocol to select one of the subset of the communication links for the routing of the data packet. As such, the FOM may be exploited by a variety of routing protocols. Thus, if the technology enables parallel detection of incoming messages on a total collection of media, modulation type and data rates, then maximum connectivity may be achieved in the mesh network without sacrificing capacity, which is typical with many time and/or frequency division techniques. 
     At operation  516 , based on the link selected by the routing protocol, in the context of the examples of  FIGS. 1 and 2 , routing module  124  accesses FOM links data  228  to identify the data rate and communications technology associated with the selected link. Routing module  124  then directs SW defined transmitter  212  to transmit the data packet to the neighbor node via the selected link using the data rate and communication technology (e.g., RF or PLC) specified in FOM links data  228 . In an alternate embodiment, routing module  124  may access FOM links data  228  to identify multiple data rates and/or communications technologies associated with one or more links to determine how to route “high priority” data in a duplicate or redundant fashion. 
     Method  500  may be performed when a new node is added to the network and periodically or a-periodically for existing nodes of the network. All or parts of method  500  may be performed in response to a determination that a link quality has degraded below a determined or pre-specified threshold, such as during a communication of operational data or by any determination of suspected or actual link quality degradation. 
     Example Protocol Data Units (PDUs) 
       FIGS. 6 and 7  illustrate several example protocol data units (PDUs) which may be transferred via a control channel and/or data channel. The term PDU is used herein to refer generally to any communication, message, or transmission within a communication network, such as that shown in  FIG. 1 . The term PDU is based, at least in concept, on the Open Systems Interconnection (OSI) Model, an IP (Internet Protocol) Model, or the like, and may comprise, for example, a bit, a frame, a packet, a segment, etc. In some instances, one or more layers of the OSI/IP model may be effectively utilized to transfer one or more PDUs between nodes. For example, the data link layer of the OSI/IP model may be utilized to transfer PDUs between two or more of the nodes  102  in the architecture  100 . In particular implementations, the media access control (MAC) sub-layer of the data link layer may be utilized to transfer PDUs between two or more of the nodes  102 . Further, in some implementations, an access method may be utilized to transfer PDUs, such as the carrier sense multiple access with collision avoidance (CSMA/CA) method. 
       FIG. 6  illustrates an example request-to-send (RTS) frame  600  that may be used to indicate that a node wishes to send data to another node, while  FIG. 7  illustrates an example clear-to-send (CTS) frame  700  that may be used to indicate that a node is available to receive data.  FIGS. 6 and 7  show example field orderings in the corresponding frames, however, other orderings may be used. In some examples, upon receiving a RTS message, a node may respond (if available) by sending a CTS message. In this example, the RTS and CTS frame structures are defined in part by the IEEE 802.15.4(e) standard. However, in other examples other PDU structures may be used for the RTS messages, CTS messages, or other communications conveying reservation information associated with the multi-channel communication network (e.g., IEEE 802.11, IEEE 802.15, IEEE 802.16, IEEE P1901, IEEE P1675, IEEE P1775, etc.). 
     As discussed above, the RTS frame  600  and the CTS frame  700  (collectively referred to as data frames  600  and  700 ) contain information that is usable to qualify and facilitate evaluation of links between nodes of a mesh network and to route communications between and among nodes of the mesh network. The frames  600  and  700  are described with reference to the example network of architecture  100  of  FIG. 1  and the example methods  400  and  500  for convenience. However, the example frames  600  and  700  are not limited to use with the example architecture  100  or the methods  400  and  500 , and may be implemented using other architectures and devices and/or to perform other methods. 
     Referring to  FIG. 6 , the example RTS frame may be used for one or more communication technologies to inform neighboring nodes that a node wishes to send data and will not be available for another transmission, and to negotiate a particular data channel and one or more physical (PHY) parameters (e.g., data rate and/or modulation technique) with an intended recipient node. As shown in  FIG. 6 , the RTS frame includes the following fields: frame control (FC), sequence number, destination personal area network (PAN) identifier, destination address, source PAN identifier, source address, auxiliary security header, payload, and frame check sequence (FCS). Details of the foregoing fields of the RTS frame other than the payload are well known to those skilled in the art and are not described in detail herein. The payload of the RTS frame, however, is customized to implement the routing techniques described above, as well as other functionalities. The payload may be variable in size and may include, for example, one or more of the following fields:
         Type: This field indicates a type of the frame, e.g., RTS, CTS, not-clear-to-send (NCTS), etc. In the example of  FIG. 6 , this field indicates that the frame is an RTS frame.   HW: This field indicates a type of hardware of a node sending the RTS frame. The type may include, for example, a version or generation of device, and/or any other information usable to determine capabilities of the node (e.g., battery powered, modulation techniques, PLC capabilities and/or available data rates that are supported by the node).   Rank: This field indicates a Routing Protocol for Low power and Lossy networks (RPL) rank (if known) of the node which is sending the RTS frame. The rank represents the cost of the path from the neighbor to the cell router and may be computed using, for example, the metric of Equation (1) to compute the ETT. The higher the rank is, the farther the node is from the cell router. This field may be utilized by a receiving node for routing consistency detection at the MAC sub-layer.   DODAG_ID: This field is a Destination Oriented Directed Acyclic Graph (DODAG) identifier (ID), which identifies a DODAG root (e.g., a network border router, cellular router, relay, etc.), through which the node sending the RTS is connected to a backhaul network, such as an intranet or the Internet, for communication with central office or other network computing device. In the context of the architecture  100  of  FIG. 1 , Node A is an example of a DODAG root of the architecture  100  which is in communication with network  106 , which is an example of a backhaul network. The DODAG_ID allows a node which receives the RTS frame to accept or reject the RTS frame by verifying routing consistency conditions at the MAC sub-layer.   Duration: This field indicates a total expected time for exchanging data frame(s) specified in the RTS. The duration may include time to transmit the specified data frames, waiting times such inter-frame spacing (IFS) (e.g., SIFS, GIFS, etc.) between frames, and acknowledgment (ACK) or non-acknowledgement (NACK) responses. The duration field may be used to determine a duration that a node will be busy communicating with another node and therefore unavailable to receive. The duration field may be used to populate the “Duration” column of a busy device list, such as busy device list  230  shown in  FIG. 2 .   Ch. On: This field includes a flag indicating whether the RTS includes a channels list.   Channels List: This field includes a channels list including a list of channels that are available to a node sending the RTS frame. A node receiving the RTS frame may select one or more channels from the available channels and specify the chosen channels inside a CTS frame. In some examples, the channel list may include less than all channels that are available to a node. For example, if a Direct-Sequence Spread Spectrum (DSSS) modulation is employed, the channel list may be limited to 13 channels in the 915 MHz ISM band. The channel list may comprise, for example, a list of qualified channels between the node that sent the RTS and the node that received the RTS. The list of qualified channels may be maintained in memory of the node that sent the RTS and/or the node that received the RTS, such as in the FOM links data  228  maintained in memory  116  of node  102 C described with reference to  FIG. 2 .   Data Rate (DR) parameters: This field indicates a maximum data rate and/or available data rates supported and/or proposed by a node sending the RTS frame. A node receiving the RTS frame may utilize this field to determine data rates of which both the sending and receiving nodes are capable, such as for exercising a node. The determined data rates may be sent to the sending node using a CTS frame. The determined data rates may be set to at most the maximum data rate of a slower of the two nodes. Thus, if the RTS proposes a data rate higher than the receiving node is capable of, the receiving node will set a lower data rate (at most the maximum data rate of the receiving node) when sending the CTS frame.   Data_ID: This field includes an ID of a data packet. This ID may be present inside the RTS frame. This field may be utilized if, for example, the data packet was received by a particular node but an acknowledgement was not received at a node which sent the data packet. In this case, the node which sent the data packet with Data_ID may assume that the data packet was not received and may resend an RTS frame for the same Data_ID. In some cases, when the particular node keeps track of a number of last Data_IDs received, the particular node may respond with an ACK frame instead of a CTS frame, thus avoiding a retransmission of the data frame.   F_ID: This field includes a MAC frame ID of the RTS frame. The intended destination of the RTS frame will copy this F_ID in the CTS frame answering to this RTS frame. When the node sending RTS frame receives a CTS frame, it may use the F_ID in CTS frame to determine if the CTS frame is the expected one (i.e., it was sent in answer to the RTS frame the node has sent previously).   NP: This field indicates a number of packets to be exchanged with a node receiving the RTS frame. This field tells the receiving node how many packets to listen for on a specified data channel before switching back to listen on the control channel. This field may also be useful in determining availability of particular channels.   Pre_Ch: This field indicates one or more channels that a node prefers to utilize for exchanging data frames, such as the test data frames. Nodes which are not involved in this exchange, but which overhear the RTS, may update their busy device lists (e.g., as described with reference to  FIG. 2 ) based on this field. By default, the recipient of the RTS frame may select this channel for data exchange, if possible. However, if this channel is busy or is not a qualified channel of the link, the recipient node may designate a different channel in the CTS.   DIR: This field indicates whether traffic is from a root or is to be sent to the root. Traffic sent from a root toward a leaf is said to be “downstream,” while all communications sent toward the root are said to be “upstream.” The field may be set to 1 for upstream traffic and 0 for downstream traffic, for example.       

       FIG. 7 , meanwhile, illustrates an example CTS message  700  for one or more communication technologies in the form of a frame that may be communicated to indicate that a node is available to receive data. The CTS frame  700  may include, for example, PHY parameters and one or more data channels selected by the first node. In some instances, the CTS frame is utilized to inform neighboring nodes that the node sending the RTS and the node sending the CTS will be unavailable and that the selected data channel will be busy during a specified time period. In the example of  FIG. 7 , the CTS frame includes the following fields: FC, sequence number, destination PAN identifier, destination address, source PAN identifier, source address, auxiliary security header, payload, and FCS. Details of the foregoing fields of the CTS frame other than the payload are well known to those skilled in the art and are not described in detail herein. The payload of the CTS frame, however, is customized to implement the routing techniques described above, as well as other functionalities. The payload of the CTS frame may be variable in size and may include, for example, one or more of the following fields:
         Type: This field may indicate information similar to that described above in reference to  FIG. 6 . In the example of  FIG. 7 , this field indicates that the frame is a CTS frame.   HW: This field includes hardware parameters (e.g., type of device, version or generation of device, etc.) of a node that received the RTS frame (i.e., the node that will send the CTS frame).   Rank: This field is analogous to the corresponding field of the RTS frame, but as applied to the CTS frame. This field may be used in ranking links according to their relative quality in, for example, FOM links data  228 , shown in  FIG. 2 .   DODAG_ID: This field is analogous to the corresponding field of the RTS frame, but as applied to the CTS frame. Specifically, this field is a DODAG identifier providing a choice for a node which receives the CTS frame to accept or reject by verifying routing consistency conditions at a MAC sub-layer.   Duration: This field is analogous to the corresponding field of the RTS frame, but as applied to the CTS frame, and may be used in determining availability and duration of availability, such as for maintaining the busy device list  230  of  FIG. 2 .   Channel: This field indicates a data channel selected by the node that received the RTS frame.   DR: This field indicates a data rate selected by the node that received the RTS frame. The data rate may be the same (if the receiving node is capable of the data rate) or different than the data rate specified in the RTS (if the receiving node is not capable of the data rate specified in the RTS). This data rate may be implemented to transfer data on a data channel, such as test data packets.   F_ID: This field includes a MAC frame ID of the CTS frame, which may be identical to the F_ID value of the RTS frame.       

     As discussed above, the RTS and CTS frames  600  and  700  are merely examples of some PDUs that may be used to implement the routing techniques described herein. In other embodiments various other PDUs may be employed to implement the described routing techniques. 
     Example Method of Determining Degradation of an Operational Link 
       FIG. 8  illustrates an example method  800  of determining a degradation of a link during communication of operational data. The method  800  is described with reference to the example architecture  100  of  FIG. 1  for convenience. However, the method  800  is not limited to use with the example architecture  100  of  FIG. 1  and may be implemented using other architectures and devices. 
     At operation  802 , a node is communicating operational data with another node using a previously specified data rate and communication technology. At operation  804 , a node obtains quality information regarding the link. The quality information may pertain to operational characteristics of the link as they pertain to the previously specified data rate and communication technology. In an embodiment, a node may use the operational data to measure a FOM of the link, such that the link quality information includes the measured FOM. Alternatively, a node may obtain signal strength information, bit error rate information, packet loss information, FOM information, or the like, as link quality information regarding the quality of the link. 
     At operation  806 , a node may determine that the quality of the link has significantly degraded. For example, a node may compare the link quality information to a predetermined threshold to determine whether the quality of the link has significantly degraded. At operation  806 , if it is determined that link quality has not significantly degraded, control will pass to operation  802 . However, if it is determined that link quality has significantly degraded, control will pass to operation  808 . At operation  808 , a node may exercise the link to determine an FOM, as described herein, for various data rates and communication technologies available for the link. At operation  810 , a node may select a data rate and communication technology using the determined FOM values. Control then passes to operation  802 , where the nodes communicate using the newly selected data rate and communication technology. 
     CONCLUSION 
     Although the application describes embodiments having specific structural features and/or methodological acts, it is to be understood that the claims are not necessarily limited to the specific features or acts described. Rather, the specific features and acts are merely illustrative some embodiments that fall within the scope of the claims of the application.