Patent Publication Number: US-10320652-B2

Title: Dynamic installation of bypass path by intercepting node in storing mode tree-based network

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to dynamic installation of a bypass path by an intercepting node in a storing mode tree-based network. 
     BACKGROUND 
     This section describes approaches that could be employed, but are not necessarily approaches that have been previously conceived or employed. Hence, unless explicitly specified otherwise, any approaches described in this section are not prior art to the claims in this application, and any approaches described in this section are not admitted to be prior art by inclusion in this section. 
     A Low-power and Lossy Network (LLN) is a network that can include dozens or thousands of low-power router devices configured for routing data packets according to a routing protocol designed for such low power and lossy networks (RPL): such low-power router devices can be referred to as “RPL nodes”. Each RPL node in the LLN typically is constrained by processing power, memory, and energy (e.g., battery power); interconnecting links between the RPL nodes typically are constrained by high loss rates, low data rates, and instability with relatively low packet delivery rates. A network topology (a “RPL instance”) can be established based on creating routes toward a single “root” network device in the form of a directed acyclic graph (DAG) toward the root network device, also referred to as a “DAG root”, where all routes in the LLN terminate at the DAG root. 
     Downward routes (i.e., away from the DAG root) can be created based on Destination Advertisement Object (DAO) messages that are created by a RPL node and propagated toward the DAG root. The RPL instance implements downward routes in the DAG of the LLN in either a storing mode only (fully stateful), or a non-storing mode only (fully source routed by the DAG root). In storing mode, a RPL node unicasts its DAO message to its parent node, such that RPL nodes store downward routing table entries for their “sub-DAG” (the “child” nodes connected to the RPL node). In non-storing mode the RPL nodes do not store downward routing tables, hence a RPL node unicasts its DAO message to the DAG root, such that all data packets are sent to the DAG root and routed downward with source routes inserted by the DAG root. 
     Use of the DAG topology for routing wireless data packets between a source and a destination distinct from the DAG root, however, can result in one or more inefficient routing paths that needlessly burden the constrained resources of the RPL nodes along the inefficient routing paths. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent like elements throughout and wherein: 
         FIGS. 1A-1C  illustrate an example wireless data network having an apparatus for intercepting and causing installation of a bypass path for reaching destination device in a storing mode tree-based network, according to an example embodiment. 
         FIG. 2  illustrates an example implementation of any one of the network devices of  FIGS. 1A-1C . 
         FIGS. 3A-3B  illustrate an example method, by the apparatus of  FIG. 1 , of causing installation of a bypass path for reaching a destination device in a storing mode tree-based network, according to an example embodiment. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     In one embodiment, a method comprises promiscuously detecting, by a network device in a wireless data network having a tree-based topology for reaching a root device, a wireless data packet transmitted by a source network device and specifying a destination device in the wireless data network; determining, by the network device, that the destination device is within a first sub-topology provided by the network device to reach the root device, wherein the source network device is within a second distinct sub-topology provided by a parent device of the source network device to reach the root device; and causing installation of a bypass path, bypassing the root device, based on the network device generating and transmitting an instruction to the parent device to install a route entry causing a data packet destined for the destination device to be routed by the parent device directly to the network device. 
     In another embodiment, an apparatus comprises a device interface circuit and a processor circuit. The device interface circuit is configured for promiscuously detecting, in a wireless data network having a tree-based topology for reaching a root device, a wireless data packet transmitted by a source network device and specifying a destination device in the wireless data network. The processor circuit is configured for determining that the destination device is within a first sub-topology provided by the apparatus. The apparatus is implemented as a network device to reach the root device. The source network device is within a second distinct sub-topology provided by a parent device of the source network device to reach the root device. The processor circuit further is configured for causing installation of a bypass path, bypassing the root device, based on generating and transmitting, via the device interface circuit, an instruction to the parent device to install a route entry causing a data packet destined for the destination device to be routed by the parent device directly to the apparatus. 
     In another embodiment, one or more non-transitory tangible media are encoded with logic for execution by a machine and when executed by the machine operable for: promiscuously detecting, by the machine implemented as a network device in a wireless data network having a tree-based topology for reaching a root device, a wireless data packet transmitted by a source network device and specifying a destination device in the wireless data network; determining, by the network device, that the destination device is within a first sub-topology provided by the network device to reach the root device, wherein the source network device is within a second distinct sub-topology provided by a parent device of the source network device to reach the root device; and causing installation of a bypass path, bypassing the root device, based on the network device generating and transmitting an instruction to the parent device to install a route entry causing a data packet destined for the destination device to be routed by the parent device directly to the network device. 
     DETAILED DESCRIPTION 
     The Internet Engineering Task Force (IETF) has published a Request for Comments (RFC) 6550 entitled “IPv6 Routing Protocol for Low-Power and Lossy Networks”, also referred to as “RPL”, where a root network device can establish a directed acyclic graph (DAG) based network topology, and network devices (e.g., “RPL nodes”) operating in storing mode in the network topology can store downward routing tables for their “sub-DAG” (the “child” nodes connected to the RPL node) in response to received Destination Advertisement Object (DAO) messages from child nodes. 
     Particular embodiments can optimize communications within a tree-based topology, such as a DAG topology, based on an intercepting network device “I” causing a parent network device “P” of a transmitting network device “S” to install a bypass path for reaching a destination “D” via the intercepting network device “I” as opposed to any default path used by the parent network device “P” in the tree-based topology. The bypass path enables the parent network device “P”  12  to bypass any common parent between the parent network device “P” and the intercepting network device “I”, regardless of rank, for optimized routing to the destination “D” attached within a sub-DAG topology of the intercepting network device “I”. 
       FIG. 1A  is an example data network  10  comprising a plurality of network devices  12 , where any one network device  12  can install a bypass path for optimizing reachability to a destination device, according to an example embodiment. The data network  10  can comprise network devices (e.g., “N 1  through “N 14 ”)  12  attached to at least one of another network device  12  or a root network device “ROOT”  14  via wireless data links  16  that form a link layer mesh topology. Although only the network devices “N 1 ”, “N 2 ”, and “N 3 ” are labeled with the reference numeral “ 12 ” in  FIGS. 1A-1C  to avoid cluttering in the Figures, it should be apparent that all the network devices “N 1 ” through “N 14 ” are allocated the reference numeral “ 12 ” for purposes of the description herein. Further, it should be apparent that all the network devices “N 1 ” through “N 14 ”  12  can be configured for establishing wireless data links  16  (illustrated as curved lines radiating from each device  12  or  14 ), even though only the wireless data links for the network device “N 1 ”  12  and the root network device  14  are labeled with the reference numeral “ 16 ” to avoid cluttering in the Figures. Any one of the network devices  12  also can be connected to one or more root network devices  14 , for example where a plurality of root network devices can be connected via a wired data link to form a “backbone” network for the data network  10 . 
     Conventional approaches to generating a tree-based topology  20  overlying the link layer mesh topology, for example a destination-oriented directed acyclic graph (DODAG) topology  20 , assume that the root network device  14  outputs a routing advertisement message (e.g., a RPL DIO message according to RFC 6550, etc.) (not shown) that specifies the Objective Function (OF) to be used by network devices (e.g., RPL nodes implemented according to RFC 6550)  12  in evaluating whether to attach to the root network device  14  or other neighboring network devices  12 . The objective function specified in the routing advertisement message (e.g., an Objective Code Point (OCP) value according to RFC 6550) defines how network devices  12  select and optimize routes within the DODAG topology according to the objective function specified by the root network device  14 . Hence, the RPL nodes  12  can form the tree-based DODAG topology  20  of  FIG. 1A  based on the objective function specified by the root network device  14 . 
     A child network device  12  (e.g., “N 10 ”) also can unicast a DAO message to its parent network device (e.g., “N 9 ”), as described above, enabling the parent network device in storing mode to store a downward route entry indicating that the child network device is reachable via an identifiable interface of the parent network device; hence, the hop-by-hop propagation of DAO messages toward the root network device  14  enables each parent network device to install a downward route entry for reaching child network devices “below” the parent network device in its corresponding sub-DAG. As used herein “up” or “upstream” refers to a direction toward the root network device  14 , and “above” refers to an “upward” relative position that is toward the root network device  14 ; conversely, “down” or “downstream” refers to a direction away from the root network device  14  (i.e., toward one or more leaf nodes in the DODAG topology  20 ), and “below” refers to a “downward” relative position that is away from the root network device  14 . For example, network device “N 1 ”  12  is above network devices “N 2 ” through “N 14 ” and sends data packets downward to network devices “N 2 ”, “N 3 ”, or “N 4 ” (in the direction opposite the illustrated arrows), and leaf network device “N 10 ” is below network devices “N 8 ” and “N 9 ” and sends data packets upward (in the same direction as the illustrated arrows) to the network devices “N 8 ” and “N 9 ”. 
     Although the DODAG topology  20  provides optimized connections for network devices  12  to reach the root network device  14  according to the objective function chosen by the root network device  14 , the DODAG topology may be sub-optimal for network traffic between different network devices  12  in the DODAG topology  20 , for example between a source network device “S” (e.g., “N 10 ”)  12  and a destination network device “D” (e.g. “N 14 ”). As illustrated in  FIG. 1A , the best available default route in the DODAG topology  20  for a data packet transmitted from the source network device “S”  12  to the destination network device “D”, starting with the parent network device “P” (e.g., “N 9 ”)  12  of the source network device “S”  12  and passing via the common parent network device “N 1 ”, is the nine (9)-hop sequence of “P” (“N 9 ”)-“N 7 ”-“N 3 ”-“N 1 ”-“N 2 ”-“N 11 ”-“N 12 ”-“N 13 ”-“D” (“N 14 ”). Hence, the DODAG topology  20  can result in poor performance for ad-hoc data flows between a source network device and a destination network device in the wireless data network  10 . 
     According to example embodiments, a network device referred to herein as an intercepting device “I” (e.g., “N 12 ” of  FIGS. 1A-1C )  12  can be configured for promiscuously detecting an upwardly-propagating wireless data packet  18  that is transmitted (e.g., unicast) by a source network device “S” (e.g., “N 10 ”)  12  to its parent network device “P” (e.g., “N 9 ”)  12 , where the wireless data packet  18  specifies a destination device “D” (e.g., “N 14 ”) in the wireless data network  10 . In response to the intercepting device “I”  12  promiscuously detecting the wireless data packet  18  (indicated by the dashed line  22  in  FIG. 1A ) destined for a destination device “D”  12  within its sub-topology (e.g., within the sub-DAG of the intercepting device “I”  12 ), the intercepting device “I” can generate and output a data packet ( 24  of  FIG. 1B ) that includes an instruction that causes the parent network device “P”  12  to install a route entry for a bypass path ( 26  of  FIG. 1C ) that bypasses the default parent (e.g., “N 7 ”) (and the root network device  14 ) of the parent network device “P”  12 . The data packet  24  generated by the intercepting network device “I”  12  and carrying the instruction for the parent network device “P”  12  can be implemented, for example, as a cut-through limited (CTL) destination advertisement object (DAO) message (“CTL-DAO”) as an extension to existing DAO messages as specified in RFC 6550; the CTL-DAO message  24  sent to the parent network device “P”  12  can specify that the destination device “D” (e.g., “N 14 ”) is reachable via the intercepting network device “I” (e.g., “N 12 ”)  12 . 
     Hence, the parent network device “P”  12  operating in storing mode can respond to the CTL-DAO message  24  by creating an internal route entry (also referred to herein as a bypass route entry) specifying that the destination “D” (e.g., “N 14 ”) is reachable via the intercepting network device “I” (e.g., “N 12 ”)  12 , enabling the parent network device “P”  12  to reroute a received data packet ( 30  of  FIG. 1C ) along the bypass path  26  for next-hop forwarding to the intercepting network device “I”  12 . Hence the intercepting network device “I”  12  can forward the rerouted data packet  30  within its sub-DAG based on its stored downward route entry for reaching the destination device “D”  12  via its child network device “N 13 ”  12  for delivery of the rerouted data packet  30  by the child network device “N 13 ” to its child network device “N 14 ”  12  as the intended destination of the rerouted data packet  30  along optimized source-destination route  28  established based on the bypass path  26 . As apparent from the foregoing, the network device “N 13 ”  12  can generate a stored downward route entry for reaching the destination device “N 14 ”  12  based on a previously-received DAO message from the destination device “N 14 ”, and the intercepting network device “I”  12  can create a stored downward route entry for reaching the destination device “N 14 ” based on a previously-received DAO message from the network device “N 13 ”  12  specifying the destination device “N 14 ”  12  is reachable via the network device “N 13 ”  12 . 
     Hence, the generation and transmission of the CTL-DAO message  24  (requesting installation of a bypass route entry for the bypass path  26  for the destination device “D”  12 ) by the intercepting network device “I”  12  in response to the promiscuous detection  22  of the wireless data packet  18  enables the parent network device “P”  12  to install the bypass path  26  for direct transmission of the rerouted data packet  30  to the intercepting network device “I”  12  along the optimized source-destination route  28 , enabling bypassing of the default parent “N 7 ”  12  of the parent network device “P”  12 , as well as bypassing any other comment parent network devices such as the network device “N 1 ”  12 , one or more root network devices  14 , etc. Hence, the rerouted data packet  30  can reach the destination network device “D”  12  without burdening the constrained resources of the network devices along the default path in the storing mode topology, namely the devices “N 7 ”, “N 3 ”, “N 1 ” “N 2 ”, “N 11 ”, or the root network device  14 , resulting in the conserved energy in the bypassed network devices. 
     Hence, the example embodiments enable the intercepting network device “I”  12  to create an optimized source-destination route  28  in a storing-mode wireless data network, on an ad hoc basis for at least a temporary time interval, without the necessity of inserting a source-route header into the data packet. The parent network device “P”  12  can install the bypass route entry for the bypass path  26  on a temporary basis, for example based on a temporary time interval specified by the intercepting network device “I”  12  in the CTL-DAO message  24 , a determined lack of data flows between the source network device “S” and the destination network device “D” for a prescribed interval (e.g., a timeout interval) specified in the CTL-DAO message  24  and/or set in the parent, etc. The intercepting network device “I”  12  also can send an updated instruction to the parent network device “P”  12  to delete the bypass route entry in response to the intercepting network device “I”  12  detecting an identifiable level of inactivity in the data flow between the source network device “S” and the destination network device “D”. Hence, the example embodiments enable localized optimization for at least a temporary time interval based on an ad hoc initiation of a data flow between the source network device “S” and the destination network device “D”. 
       FIG. 2  illustrates an example implementation of any one of the network devices  12  and/or  14  of  FIG. 1 , according to an example embodiment. Each apparatus  12  and/or  14  is a physical machine (i.e., a hardware device) configured for implementing network communications with other physical machines  12  and/or  14  via the network  10 . The term “configured for” or “configured to” as used herein with respect to a specified operation refers to a device and/or machine that is physically constructed and arranged to perform the specified operation. Hence, the apparatus  12  and/or  14  is a network-enabled machine implementing network communications with other machines  12  and/or  14  via the network  10 . 
     Each apparatus  12  and/or  14  can include a device interface circuit  40 , a processor circuit  42 , and a memory circuit  44 . The device interface circuit  40  can include one or more distinct physical layer transceivers for communication with any one of the other devices  12  and/or  14 ; the device interface circuit  40  also can include an IEEE based Ethernet transceiver for communications with the devices of  FIG. 1  via any type of data link (e.g., a wired data link, a wireless data link  16 , an optical link, etc.). The processor circuit  42  can be configured for executing any of the operations described herein, and the memory circuit  44  can be configured for storing any data structure or data packets as described herein, including a routing table  46  configured for storing route entries, for example downward route entries, bypass route entries, a default router list identifying one or more available parent network devices, etc. 
     Any of the disclosed circuits of the devices  12  and/or  14  (including the device interface circuit  40 , the processor circuit  42 , the memory circuit  44 , and their associated components) can be implemented in multiple forms. Example implementations of the disclosed circuits include hardware logic that is implemented in a logic array such as a programmable logic array (PLA), a field programmable gate array (FPGA), or by mask programming of integrated circuits such as an application-specific integrated circuit (ASIC). Any of these circuits also can be implemented using a software-based executable resource that is executed by a corresponding internal processor circuit such as a microprocessor circuit (not shown) and implemented using one or more integrated circuits, where execution of executable code stored in an internal memory circuit (e.g., within the memory circuit  44 ) causes the integrated circuit(s) implementing the processor circuit to store application state variables in processor memory, creating an executable application resource (e.g., an application instance) that performs the operations of the circuit as described herein. Hence, use of the term “circuit” in this specification refers to both a hardware-based circuit implemented using one or more integrated circuits and that includes logic for performing the described operations, or a software-based circuit that includes a processor circuit (implemented using one or more integrated circuits), the processor circuit including a reserved portion of processor memory for storage of application state data and application variables that are modified by execution of the executable code by a processor circuit. The memory circuit  44  can be implemented, for example, using a non-volatile memory such as a programmable read only memory (PROM) or an EPROM, and/or a volatile memory such as a DRAM, etc. 
     Further, any reference to “outputting a message” or “outputting a packet” (or the like) can be implemented based on creating the message/packet in the form of a data structure and storing that data structure in a non-transitory tangible memory medium in the disclosed apparatus (e.g., in a transmit buffer). Any reference to “outputting a message” or “outputting a packet” (or the like) also can include electrically transmitting (e.g., via wired electric current or wireless electric field, as appropriate) the message/packet stored in the non-transitory tangible memory medium to another network node via a communications medium (e.g., a wired or wireless link, as appropriate) (optical transmission also can be used, as appropriate). Similarly, any reference to “receiving a message” or “receiving a packet” (or the like) can be implemented based on the disclosed apparatus detecting the electrical (or optical) transmission of the message/packet on the communications medium, and storing the detected transmission as a data structure in a non-transitory tangible memory medium in the disclosed apparatus (e.g., in a receive buffer). Also note that the memory circuit  44  can be implemented dynamically by the processor circuit  42 , for example based on memory address assignment and partitioning executed by the processor circuit  42 . 
       FIGS. 3A-3B  illustrate an example method, by the apparatus of  FIG. 1 , of causing installation of a bypass path for reaching a destination device in a storing mode tree-based network, according to an example embodiment. The operations described with respect to any of the Figures can be implemented as executable code stored on a computer or machine readable non-transitory tangible storage medium (i.e., one or more physical storage media such as a floppy disk, hard disk, ROM, EEPROM, nonvolatile RAM, CD-ROM, etc.) that are completed based on execution of the code by a processor circuit implemented using one or more integrated circuits; the operations described herein also can be implemented as executable logic that is encoded in one or more non-transitory tangible media for execution (e.g., programmable logic arrays or devices, field programmable gate arrays, programmable array logic, application specific integrated circuits, etc.). Hence, one or more non-transitory tangible media can be encoded with logic for execution by a machine, and when executed by the machine operable for the operations described herein. 
     In addition, the operations described with respect to any of the Figures can be performed in any suitable order, or at least some of the operations in parallel. Execution of the operations as described herein is by way of illustration only; as such, the operations do not necessarily need to be executed by the machine-based hardware components as described herein; to the contrary, other machine-based hardware components can be used to execute the disclosed operations in any appropriate order, or at least some of the operations in parallel. 
     Referring to  FIG. 3A , the processor circuit  42  of the root network device  14  is configured for establishing in operation  50  the tree-based DODAG topology  20  in storing mode, for example based on outputting DIO messages according to RFC 6550 to generate a DODAG according to RPL. Each network device  12 , in response to attaching to a parent network device  12  and/or  14  in the tree-based DODAG topology  20 , can generate and unicast output a DAO message according to RFC 6550, enabling each parent network device to create in its corresponding routing table  46  a downward route entry for reaching the network device based on the received DAO. Hence, the downstream transmission of DIO messages initiated by the root network device  14  in operation  50 , and the DAO messages transmitted upstream by the attached network devices  12 , establish the non-storing mode of the tree-based DODAG topology  20  illustrated in  FIG. 1A . 
     The source network device “S” (e.g., “N 10 ”) of  FIG. 1A  in operation  52  can transmit a wireless data packet  18  that identifies its default next-hop parent network device “P” (e.g., “N 9 ”) as the target of the wireless data packet  18 , and that identifies the destination network device “D” (e.g., “N 14 ”) as the final destination of the wireless data packet  18 . In response to receiving the wireless data packet  18 , the processor circuit  42  of the parent network device “P” (e.g., “N 9 ”) can determine from its routing table  46  that the wireless data packet  18  should be forwarded upward along the default route toward the root network device  14  via its parent network device “N 7 ”; as apparent from the foregoing, the wireless data packet  18  is forwarded upstream until reaching the common parent “N 1 ”  12  that stores within its routing table  46  a downward route entry for reaching the destination network device “D” (e.g., “N 14 ”) via an attached child network device (e.g., “N 2 ”). 
     According to an example embodiment, the device interface circuit  40  of the intercepting network device “I”  12  is configured for promiscuously detecting in operation  22  of  FIGS. 1A and 3A  the wireless data packet  18  transmitted by the source network device “S”  12 , the wireless data packet  18  identifying the source network device “S” (e.g., “N 10 ”)  12 , the next-hop parent network device “P” (e.g., “N 9 ”), and the destination network device “D” (e.g., “N 14 ”)  12 . As illustrated in  FIGS. 1A-1C , the intercepting network device “I”  12  provides a sub-topology (e.g., sub-DAG) containing the destination network device “D” (e.g., “N 14 ”)  12  and that is distinct from the sub-topology (e.g., sub-DAG) provided by the parent network device “P”  12  and containing the source network device “S”  12 ; in other words, the intercepting network device “I”  12  does not share any data link with the parent network device “P” (e.g., “N 9 ”) or with its corresponding parent network device “N 7 ” that would enable the intercepting network device “I”  12  to receive the wireless data packet  18  along its default upward path of “S”-“N 9 ”-“N 7 ”-“N 3 ”-“N 1 ”. Hence, the destination network device “D” (e.g., “N 14 ”) is within a first sub-topology (comprising network device “N 13 ”) provided by the intercepting network device “I”  12  to reach the root network device  14  (via its parent “N 11 ”, etc.), and the source network device “S”  12  is within a second distinct (i.e., non-overlapping) sub-topology provided by the parent network device “P”  12  to reach the root network device  14  (via its parent “N 7 ”, etc.). 
     Although the example embodiments illustrate the source network device “S” as a leaf node (e.g., “N 10 ”) having originated the data packet, the source network device “S” also could be a forwarding node that is the first wireless network device within transmission range of the intercepting network device “I”  12 . 
     In response to the device interface circuit  40  of the intercepting network device “I”  12  promiscuously detecting in operation  22  the wireless data packet  18  transmitted by the source network device “S”  12  and identifying the next-hop parent network device “P”  12  and the destination device “D” (e.g., “N 14 ”)  12 , the processor circuit  42  of the intercepting network device “I”  12  can determine in operation  54  whether the wireless data packet (e.g., “P 1 ”)  18  is traveling upward toward the root network device  14 , for example based determining whether a downward flag is reset to zero in the wireless data packet  18  (e.g., according to Section 11.2 of RFC 6550). If the processor circuit  42  of the intercepting network device “I”  12  determining the downward flag is not reset to zero, indicating the wireless data packet  18  is traveling downward, the processor circuit  42  of the intercepting network device “I”  12  drops the promiscuously-detected data packet that is already traveling downward. 
     In response to the processor circuit  42  of the intercepting network device “I”  12  determining in operation  54  that the wireless data packet  18  is traveling upward, the processor circuit  42  of the intercepting network device “I”  12  in operation  56  can determine from its routing table  46  that the destination device “D” (e.g., “N 14 ”) is within its sub-topology via its child network device “N 13 ”  12 . As described previously, the routing table  46  of the intercepting network device “I”  12  can identify all children (e.g., “N 13 ”, “N 14 ”) within its sub-DAG based on the received DAO messages from its attached children. The processor circuit  42  of the intercepting network device “I”  12  also can determine from its routing table  46  in operation  56  that the parent network device “P” (e.g., “N 9 ”) and the source network device “S” (e.g., “N 10 ”) are not within its sub-topology based on a determined absence of any route entry in its processor circuit  42  for either the parent network device “P” (e.g., “N 9 ”) or the source network device “S” (e.g., “N 10 ”). Consequently, the processor circuit  42  of the intercepting network device “I”  12  in operation  56  can determine that the parent network device “P” (e.g., “N 9 ”) and the source network device “S” (e.g., “N 10 ”) are in a distinct (i.e., non-overlapping) sub-topology. 
     The processor circuit  42  of the intercepting network device “I”  12  in operation  58  can cause installation of a bypass path  26  that bypasses the default parent “N 7 ” and the root network device  14  (and the common parent “N 1 ”) based on the processor circuit  42  of the intercepting network device “I”  12  generating and transmitting to the parent network device “P”  12  a CTL-DAO message  24  specifying an instruction to install into its corresponding routing table  46  a bypass route entry that causes any data packet (e.g.,  30  of  FIG. 1C ) destined for the destination network device “D” (e.g., “N 14 ”) to be routed by the parent network device “P” directly to the intercepting network device “I”  12  via the bypass path  26 , instead of the default route used by the parent network device “P”  12 . As described previously, the device interface circuit  40  of the intercepting network device “I”  12  executes a unicast transmission of the CTL-DAO message  24  only to the parent network device “P”  12 , such that the CTL-DAO message  24  is executed only by the parent network device “P”  12  and no other network device  12 ; in other words, the CTL-DAO message  24  is not forwarded to any other network device  12 , but is executed only by the intended target, namely the parent network device “P”  12 . 
     Also note that the CTL-DAO message  24  is sent by the intercepting network device “I”  12  to the parent network device “P”  12  independent of any relative rank values between the intercepting network device “I”  12  and the parent network device “P”  12 , e.g., regardless of the respective ranks (e.g., number of hops or depth) relative to the root network device  14 . Nevertheless, the CTL-DAO message  24  can specify a rank value of the intercepting network device “I”  12  in the event the parent network device “P”  12  receives another CTL-DAO message from another network device (e.g., from network device “N 11 ”), enabling the parent network device “P”  12  to select between the intercepting network device “I”  12  and any other network device (e.g., “N 11 ”) having promiscuously detected the wireless data packet, based on the corresponding rank. 
     In response to the device interface circuit  40  of the parent network device “P”  12  receiving in operation  60  the CTL-DAO message  24  from the intercepting network device “I”  12  (and for example from the network device “N 11 ”), the processor circuit  42  of the parent network device “P”  12  in operation  60  can install in its routing table  46  the highest-ranking bypass route entry (i.e., closest to the destination network device “N 14 ”  12 ) specifying the bypass route “D via I” (or “N 14  via N 12 ”, and/or its IPv6 address equivalent, etc.) for implementing the bypass path  26 . Hence, in response to the parent network device “P” receiving in operation  62  of  FIG. 3B  another data packet “P 2 ” ( 30  of  FIG. 1C ) destined for the destination device “D” (e.g., “N 14 ”), the processor circuit  42  of the parent network device “P”  12  can reroute the rerouted data packet  30  directly to the intercepting network device “I”  12  via the bypass path  26 , enabling the processor circuit  42  of the intercepting network device “I”  12  in operation  64  to forward the rerouted data packet  30  to the destination network device “D”  12  via its child network device “N 13 ” based on its downward route entry specifying the destination network device “N 14 ”  12  is reachable via the child network device “N 13 ”. 
     Hence, the rerouting of the rerouted data packet  30  along the optimized source-destination route  28  via the bypass path  26  enables the parent network device “P”  12  to bypass the default route via its parent network device “N 7 ”, bypass the common parent device “N 1 ”  12  of the parent network device “P” and the intercepting network device “I”  12 , and bypass the root network device  14 . 
     As described previously, the bypass route entry could be added on a temporary basis based on, for example, the presence of data flows between the source network device “S” and the destination network device “D”, etc. Hence, the processor circuit  42  of the intercepting network device “I”  12  in operation  66  can send a second instruction (e.g., a CTL-DAO-CANCEL message), to the parent network device “P”  12 , for removal of the bypass route entry based on the processor circuit  42  of the intercepting network device “I” detecting a determined level of inactivity between the source network device “S”  12  and the destination network device “D”  12 , or if the bypass route entry needs to be deleted to conserve constrained resources for a higher-priority data flow, etc. 
     The parent network device “P”  12  in response can remove the bypass route entry from its routing table  46  in response to the second instruction (e.g., based on a determined absence of activity in the data flow between the source network device “S” and the destination network device “D”, higher-priority data flows, constrained resources, etc.). Hence, the bypass route entry enables localized optimization, at least on a temporary basis, for optimized transmission between the source network device “S” and the destination network device “D”. 
     According to example embodiments, unnecessary transmissions of a wireless data packet can be minimized based on an intercepting network device initiating at least temporary installation of a bypass route entry in a parent network device located in a distinct sub-topology, enabling rerouting of a wireless data packet along an optimized route that enables one or more “upstream” network device transmissions to be bypassed. The example embodiments improve efficiency by minimizing power consumption in an LLN network, based on minimizing unnecessary power consumption. 
     While the example embodiments in the present disclosure have been described in connection with what is presently considered to be the best mode for carrying out the subject matter specified in the appended claims, it is to be understood that the example embodiments are only illustrative, and are not to restrict the subject matter specified in the appended claims.