U.S. patent application number 13/605528 was filed with the patent office on 2013-09-26 for dynamic division of routing domains in reactive routing networks.
This patent application is currently assigned to Cisco Technology, Inc.. The applicant listed for this patent is Jonathan W. Hui, Jean-Philippe Vasseur. Invention is credited to Jonathan W. Hui, Jean-Philippe Vasseur.
Application Number | 20130250811 13/605528 |
Document ID | / |
Family ID | 49211714 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130250811 |
Kind Code |
A1 |
Vasseur; Jean-Philippe ; et
al. |
September 26, 2013 |
DYNAMIC DIVISION OF ROUTING DOMAINS IN REACTIVE ROUTING
NETWORKS
Abstract
In one embodiment, a reactive routing network may be dynamically
divided into reactive routing network sub-domains that comprise a
plurality of nodes having bounded route request (RREQ) scopes
(e.g., search-domains) that are limited to a particular path
length. The transit node in a first reactive routing network
sub-domain may receive a RREQ from an originating node within the
first reactive routing network sub-domain for a target node
determined by the originating node to be beyond the bounded RREQ
scope of the originating node. The transit node may then discover a
route from the transit node to the target node, and return the
route to the originating node. In this manner, the transit node may
establish a complete route between the originating node and the
target node.
Inventors: |
Vasseur; Jean-Philippe;
(Saint Martin d'Uriage, FR) ; Hui; Jonathan W.;
(Belmont, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Vasseur; Jean-Philippe
Hui; Jonathan W. |
Saint Martin d'Uriage
Belmont |
CA |
FR
US |
|
|
Assignee: |
Cisco Technology, Inc.
San Jose
CA
|
Family ID: |
49211714 |
Appl. No.: |
13/605528 |
Filed: |
September 6, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61614703 |
Mar 23, 2012 |
|
|
|
Current U.S.
Class: |
370/255 ;
370/254 |
Current CPC
Class: |
H04L 45/32 20130101;
H04W 40/28 20130101; H04L 45/46 20130101; H04W 40/20 20130101; H04W
40/023 20130101 |
Class at
Publication: |
370/255 ;
370/254 |
International
Class: |
H04L 12/28 20060101
H04L012/28 |
Claims
1. A method, comprising: receiving, at a transit node, a route
request (RREQ) for a target node from an originating node within a
first reactive routing network sub-domain, wherein the first
reactive routing network sub-domain comprises a plurality of nodes
having a bounded RREQ scope limited to a particular path length,
and the target node is beyond the bounded RREQ scope of the
originating node; discovering a route from the transit node to the
target node; and returning the route to the originating node to
establish a complete route between the originating node and the
target node.
2. The method as in claim 1, wherein the bounded RREQ scope is set
by a segmentation message broadcast to the originating node.
3. The method as in claim 2, wherein the segmentation message
comprises a time-to-live indicator to be used in RREQs broadcast by
the plurality of nodes within the first reactive routing network
sub-domain.
4. The method as in claim 2, further comprising: triggering
broadcast of the segmentation message in response to control plane
overhead of the reactive routing network exceeding a predetermined
threshold value.
5. The method as in claim 2, wherein the segmentation message
comprises a time-to-live indicator which limits the plurality of
nodes contacted by the segmentation message and define a boundary
for the first reactive routing network sub-domain.
6. The method as in claim 1, wherein the RREQ for the target node
comprises the transit node as a first loose hop and the target node
as a final loose hop.
7. The method as in claim 4, wherein the segmentation message is
broadcast in response to an instruction from a management
device.
8. The method as in claim 1, wherein discovering further comprises:
multicasting the RREQ to one or more transit nodes in a reactive
routing network.
9. The method as in claim 1, wherein discovering further comprises:
broadcasting the RREQ to a reactive routing network.
10. The method as in claim 1, wherein discovering further
comprises: identifying a route to the target node based on a route
reply (RREP) received from a previous RREQ sent prior to the
receiving step.
11. The method as in claim 1, wherein the transit node is a border
router for the first reactive routing network sub-domain,
12. A method, comprising: receiving, at a node within a reactive
routing network, a segmentation message; establishing, in response
to the segmentation message, a bounded route request (RREQ) scope
for any RREQ originated by the node to cause each RREQ to be
limited to a particular path length; and forwarding at least one
RREQ to a transit node for any target node not identified by the
node as being within the bounded RREQ scope of the node.
13. The method as in claim 12, wherein the segmentation message
comprises a time-to-live indicator to be used in RREQs broadcast by
a plurality of nodes within a first reactive routing network
sub-domain.
14. The method as in claim 12, wherein the segmentation message is
received from the transit node.
15. The method as in claim 12, wherein the node, having determined
that the target node is not within the bounded RREQ scope, uses a
proactive directed acyclic graph (DAG) to provide a route to the
transit node, or broadcasts a RREQ to identify a route to the
transit node.
16. The method as in claim 12, wherein forwarding further
comprises: setting the RREQ to indicate the transit node as the
first loose hop and the target node as the final loose hop.
17. The method as in claim 12, further comprising: receiving a
route reply (RREP) from the transit node, the RREP indicating an
entire path from the originating node to the target node via the
transit node.
18. The method as in claim 12, further comprising: receiving
segmentation messages from two or more transit nodes; and picking
one particular transit node to receive forwarded RREQs.
19. An apparatus, comprising: one or more network interfaces to
communicate within a computer network; a processor coupled to the
network interfaces and adapted to execute one or more processes;
and a memory configured to store a process executable by the
processor, the process when executed operable to: receive, as a
transit node, a route request (RREQ) for a target node from an
originating node within a first reactive routing network
sub-domain, wherein the first reactive routing network sub-domain
comprises a plurality of nodes having a bounded RREQ scope limited
to a particular path length, and the target node is beyond the
bounded RREQ scope of the originating node; discover a route from
the transit node to the target node; and return the route to the
originating node to establish a complete route between the
originating node and the target node.
20. The apparatus as in claim 19, wherein the process is configured
to broadcast a segmentation message indicating the bounded RREQ
scope.
21. The apparatus as in claim 20, the segmentation message
comprising a time-to-live indicator to be used in RREQs broadcast
by the plurality of nodes within the first reactive routing network
sub-domain.
22. The apparatus as in claim 20, the segmentation message
comprising a time-to-live indicator to limit the plurality of nodes
contacted by the segmentation message and define a boundary for the
first reactive routing network sub-domain.
23. The apparatus as in claim 19, wherein the process when executed
is further operable to: trigger broadcast of the segmentation
message in response to control plane overhead of the reactive
routing network exceeding a predetermined threshold value.
24. An apparatus, comprising: one or more network interfaces to
communicate within a computer network; a processor coupled to the
network interfaces and adapted to execute one or more processes;
and a memory configured to store a process executable by the
processor, the process when executed operable to: receive, as a
node within a reactive routing network, a segmentation message;
establish, in response to the segmentation message, a bounded route
request (RREQ) scope for any RREQ originated by the node which is
limited to a particular path length; and forward RREQs to a transit
node for any target node not identified by the node as being within
the bounded RREQ scope of the node.
25. The apparatus as in claim 24, wherein the segmentation message
comprises a time-to-live indicator to be used in RREQs broadcast by
a plurality of nodes within a first a reactive routing network
sub-domain
Description
RELATED APPLICATION
[0001] The present application claims priority to U.S. Provisional
Patent Application No. 61/614,703, filed Mar. 23, 2012, entitled
TECHNIQUES FOR USE IN REACTIVE ROUTING NETWORKS, by Vasseur, et
al., the contents of which are hereby incorporated by
reference.
TECHNICAL FIELD
[0002] The present disclosure relates generally to communication
networks, and, more particularly, to reactive routing in
communication networks.
BACKGROUND
[0003] Low power and Lossy Networks (LLNs), e.g., sensor networks,
have a myriad of applications, such as Smart Grid (smart metering),
home and building automation, smart cities, etc. Various challenges
are presented with LLNs, such as lossy links, low bandwidth,
battery operation, low memory and/or processing capability, etc.
Routing in LLNs is undoubtedly one of the most critical challenges
and a core component of the overall networking solution. Two
fundamentally and radically different approaches, each with certain
advantages and drawbacks, have been envisioned for routing in
LLN/ad-hoc networks known as:
[0004] 1) Proactive routing: routing topologies are pre-computed by
the control plane (e.g., IS-IS, OSPF, RIP, and RPL are proactive
routing protocols); and
[0005] 2) Reactive routing: routes are computed on-the-fly and
on-demand by a node that sends one or more discovery probes
throughout the network (e.g., AODV, DYMO, and LOAD are reactive
routing protocols).
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The embodiments herein may be better understood by referring
to the following description in conjunction with the accompanying
drawings in which like reference numerals indicate identically or
functionally similar elements, of which:
[0007] FIG. 1 illustrates an example communication network;
[0008] FIG. 2 illustrates an example network device/node;
[0009] FIGS. 3A-3J illustrate examples of dynamic division of a
reactive routing network into sub-domains as described herein;
[0010] FIG. 4 illustrates an example simplified procedure for
dynamic division of a reactive routing network into sub-domains,
particularly from the perspective of a transit node; and
[0011] FIG. 5 illustrates another example simplified procedure for
dynamic division of a reactive routing network into sub-domains,
particularly from the perspective of a requesting node.
DESCRIPTION OF EXAMPLE EMBODIMENTS
Overview
[0012] According to one or more embodiments of the disclosure, a
reactive routing network may be dynamically divided into reactive
routing network sub-domains that comprise a plurality of nodes
having bounded route request (RREQ) scopes (e.g., search-domains)
that are limited to a particular path length. A transit node may
receive a RREQ from an originating node within the first reactive
routing network sub-domain for a target node determined by the
originating node to be beyond the bounded RREQ scope of the
originating node. The transit node may then discover a route from
the transit node to the target node, and return the route to the
originating node. In this manner, the transit node may establish a
complete route between the originating node and the target
node.
[0013] According to one or more additional embodiments of the
disclosure, a node within a reactive routing network may receive a
segmentation message from a capable node (e.g., a transit node, a
LBR, etc.), and in response, establish a bounded route request
(RREQ) scope for any RREQ originated by the node which is limited
to a particular path length. As such, the node may forward RREQs to
a transit node for any target node not identified by the node as
being within the bounded RREQ scope of the node.
Description
[0014] A computer network is a geographically distributed
collection of nodes interconnected by communication links and
segments for transporting data between end nodes, such as personal
computers and workstations, or other devices, such as sensors, etc.
Many types of networks are available, ranging from local area
networks (LANs) to wide area networks (WANs). LANs typically
connect the nodes over dedicated private communications links
located in the same general physical location, such as a building
or campus. WANs, on the other hand, typically connect
geographically dispersed nodes over long-distance communications
links, such as common carrier telephone lines, optical lightpaths,
synchronous optical networks (SONET), synchronous digital hierarchy
(SDH) links, or Powerline Communications (PLC) such as IEEE 61334,
IEEE 21901.2, and others. In addition, a Mobile Ad-Hoc Network
(MANET) is a kind of wireless ad-hoc network, which is generally
considered a self-configuring network of mobile routes (and
associated hosts) connected by wireless links, the union of which
forms an arbitrary topology.
[0015] Smart object networks, such as sensor networks, in
particular, are a specific type of network having spatially
distributed autonomous devices such as sensors, actuators, etc.,
that cooperatively monitor physical or environmental conditions at
different locations, such as, e.g., energy/power consumption,
resource consumption (e.g., water/gas/etc. for advanced metering
infrastructure or "AMI" applications) temperature, pressure,
vibration, sound, radiation, motion, pollutants, etc. Other types
of smart objects include actuators, which may be, e.g., responsible
for turning on/off an engine or perform any other actions. Sensor
networks, a type of smart object network, are typically
shared-media networks, such as wireless or PLC networks. That is,
in addition to one or more sensors, each sensor device (node) in a
sensor network may generally be equipped with a radio transceiver
or other communication port such as PLC, a microcontroller, and an
energy source, such as a battery. Often, smart object networks are
considered field area networks (FANs), neighborhood area networks
(NANs), etc. Generally, size and cost constraints on smart object
nodes (e.g., sensors) result in corresponding constraints on
resources such as energy, memory, computational speed and
bandwidth. Correspondingly, a reactive routing protocol may, though
need not, be used in place of a proactive routing protocol for
smart object networks.
[0016] FIG. 1 is a schematic block diagram of an example computer
network 100 illustratively comprising nodes/devices 200 (e.g.,
labeled as shown, "root," "11," "12," . . . "43," and described in
FIG. 2 below) interconnected by various methods of communication.
For instance, the links 105 may be wired links or shared media
(e.g., wireless links, PLC links, etc.) where certain nodes 200,
such as, e.g., routers, sensors, computers, etc., may be in
communication with other nodes 200, e.g., based on distance, signal
strength, current operational status, location, etc. Those skilled
in the art will understand that any number of nodes, devices,
links, etc. may be used in the computer network, and that the view
shown herein is for simplicity. Also, those skilled in the art will
further understand that while the network is shown in a certain
orientation, particularly with a "root" node, the network 100 is
merely an example illustration that is not meant to limit the
disclosure.
[0017] Data packets 140 (e.g., traffic and/or messages sent between
the devices/nodes) may be exchanged among the nodes/devices of the
computer network 100 using predefined network communication
protocols such as certain known wired protocols, wireless protocols
(e.g., IEEE Std. 802.15.4, WiFi, Bluetooth.RTM., etc.), PLC
protocols, or other shared-media protocols where appropriate. In
this context, a protocol consists of a set of rules defining how
the nodes interact with each other.
[0018] FIG. 2 is a schematic block diagram of an example
node/device 200 that may be used with one or more embodiments
described herein, e.g., as any of the nodes shown in FIG. 1 above.
The device may comprise one or more network interfaces 210 (e.g.,
wired, wireless, PLC, etc.), at least one processor 220, and a
memory 240 interconnected by a system bus 250, as well as a power
supply 260 (e.g., battery, plug-in, etc.).
[0019] The network interface(s) 210 contain the mechanical,
electrical, and signaling circuitry for communicating data over
links 105 coupled to the network 100. The network interfaces may be
configured to transmit and/or receive data using a variety of
different communication protocols. Note, further, that the nodes
may have two different types of network connections 210, e.g.,
wireless and wired/physical connections, and that the view herein
is merely for illustration. Also, while the network interface 210
is shown separately from power supply 260, for PLC the network
interface 210 may communicate through the power supply 260, or may
be an integral component of the power supply. In some specific
configurations the PLC signal may be coupled to the power line
feeding into the power supply.
[0020] The memory 240 comprises a plurality of storage locations
that are addressable by the processor 220 and the network
interfaces 210 for storing software programs and data structures
associated with the embodiments described herein. Note that certain
devices may have limited memory or no memory (e.g., no memory for
storage other than for programs/processes operating on the device
and associated caches). The processor 220 may comprise hardware
elements or hardware logic adapted to execute the software programs
and manipulate the data structures 245. An operating system 242,
portions of which are typically resident in memory 240 and executed
by the processor, functionally organizes the device by, inter alia,
invoking operations in support of software processes and/or
services executing on the device. These software processes and/or
services may comprise an illustrative routing process 244, as
described herein. Note that while the routing process 244 is shown
in centralized memory 240, alternative embodiments provide for the
process to be specifically operated within the network interfaces
210.
[0021] It will be apparent to those skilled in the art that other
processor and memory types, including various computer-readable
media, may be used to store and execute program instructions
pertaining to the techniques described herein. Also, while the
description illustrates various processes, it is expressly
contemplated that various processes may be embodied as modules
configured to operate in accordance with the techniques herein
(e.g., according to the functionality of a similar process).
Further, while the processes have been shown separately, those
skilled in the art will appreciate that processes may be routines
or modules within other processes.
[0022] Routing process (services) 244 contains computer executable
instructions executed by the processor 220 to perform functions
provided by one or more routing protocols, such as proactive or
reactive routing protocols as will be understood by those skilled
in the art. These functions may, on capable devices, be configured
to manage a routing/forwarding table (a data structure 245)
containing, e.g., data used to make routing/forwarding decisions.
In particular, in proactive routing, connectivity is discovered and
known prior to computing routes to any destination in the network,
e.g., link state routing such as Open Shortest Path First (OSPF),
or Intermediate-System-to-Intermediate-System (ISIS), or Optimized
Link State Routing (OLSR). Reactive routing, on the other hand,
discovers neighbors (i.e., does not have an a priori knowledge of
network topology), and in response to a needed route to a
destination, sends a route request into the network to determine
which neighboring node may be used to reach the desired
destination. Example reactive routing protocols may comprise Ad-hoc
On-demand Distance Vector (AODV), Dynamic Source Routing (DSR),
DYnamic MANET On-demand Routing (DYMO), LLN On-demand Ad hoc
Distance-vector (LOAD), etc. Notably, on devices not capable or
configured to store routing entries, routing process 244 may
consist solely of providing mechanisms necessary for source routing
techniques. That is, for source routing, other devices in the
network can tell the less capable devices exactly where to send the
packets, and the less capable devices simply forward the packets as
directed.
[0023] Notably, mesh networks have become increasingly popular and
practical in recent years. In particular, shared-media mesh
networks, such as wireless or PLC networks, etc., are often on what
is referred to as Low-Power and Lossy Networks (LLNs), which are a
class of networks in which both the routers and their interconnect
are constrained: LLN routers typically operate with constraints,
e.g., processing power, memory, and/or energy (battery), and their
interconnects are characterized by, illustratively, high loss
rates, low data rates, and/or instability. LLNs are comprised of
anything from a few dozen and up to thousands or even millions of
LLN routers, and support point-to-point traffic (between devices
inside the LLN), point-to-multipoint traffic (from a central
control point such at the root node to a subset of devices inside
the LLN) and multipoint-to-point traffic (from devices inside the
LLN towards a central control point).
[0024] An example implementation of LLNs is an "Internet of Things"
network. Loosely, the term "Internet of Things" or "IoT" may be
used by those in the art to refer to uniquely identifiable objects
(things) and their virtual representations in a network-based
architecture. In particular, the next frontier in the evolution of
the Internet is the ability to connect more than just computers and
communications devices, but rather the ability to connect "objects"
in general, such as lights, appliances, vehicles, HVAC (heating,
ventilating, and air-conditioning), windows and window shades and
blinds, doors, locks, etc. The "Internet of Things" thus generally
refers to the interconnection of objects (e.g., smart objects),
such as sensors and actuators, over a computer network (e.g., IP),
which may be the Public Internet or a private network. Such devices
have been used in the industry for decades, usually in the form of
non-IP or proprietary protocols that are connected to IP networks
by way of protocol translation gateways. With the emergence of a
myriad of applications, such as the smart grid, smart cities, and
building and industrial automation, and cars (e.g., that can
interconnect millions of objects for sensing things like power
quality, tire pressure, and temperature and that can actuate
engines and lights), it has been of the utmost importance to extend
the IP protocol suite for these networks.
[0025] As noted above, routing in LLNs is undoubtedly one of the
most critical challenges and a core component of the overall
networking solution. Two fundamentally and radically different
approaches have been envisioned for routing in LLN/ad-hoc networks
known as proactive routing (routing topologies are pre-computed by
the control plane) and reactive routing (routes are computed
on-the-fly and on-demand by a node that sends a discovery probes
throughout the network).
[0026] An example proactive routing protocol specified in an
Internet Engineering Task Force (IETF) Proposed Standard, Request
for Comment (RFC) 6550, entitled "RPL: IPv6 Routing Protocol for
Low Power and Lossy Networks" by Winter, et al. (March 2012),
provides a mechanism that supports multipoint-to-point (MP2P)
traffic from devices inside the LLN towards a central control point
(e.g., LLN Border Routers (LBRs) or "root nodes/devices"
generally), as well as point-to-multipoint (P2MP) traffic from the
central control point to the devices inside the LLN (and also
point-to-point, or "P2P" traffic). RPL may generally be described
as a distance vector routing protocol that builds a Directed
Acyclic Graph (DAG) or Destination Oriented Directed Acyclic Graphs
(DODAGs) for use in routing traffic/packets 140 from a root using
mechanisms that support both local and global repair, in addition
to defining a set of features to bound the control traffic, support
repair, etc. One or more RPL instances may be built using a
combination of metrics and constraints.
[0027] An example reactive routing protocol is specified in an IETF
Internet Draft, entitled "LLN On-demand Ad hoc Distance-vector
Routing Protocol-Next Generation (LOADng)"
<draft-clausen-lln-loadng-05> by Clausen, et al. (Jul. 14,
2012 version), which provides a reactive routing protocol for LLNs,
e.g., as derived from AODV. Other reactive routing protocol efforts
include the G3-PLC specification approved by the ITU, and also one
described in an informative annex of IEEE P1901.2.
[0028] One stated benefit of reactive routing protocols is that
their state and communication overhead scales with the number of
active sources and destinations in the network. Such protocols only
initiate control traffic and establish state when a route to a
destination is unknown. In contrast, proactive routing protocols
build and maintain routes to all destinations before data packets
arrive and incur state and communication overhead that scales with
the number of nodes, rather than the number of active sources and
destinations. Some believe that reactive routing protocols are
well-suited for certain Smart Grid Automated Meter Reading (AMR)
applications where a Collection Engine reads each meter one-by-one
in round-robin fashion. In such simplistic applications, only one
source-destination pair is required at any point in time.
[0029] Reactive routing protocols, however, have a number of
technical issues that are particularly exhibited in large-scale
LLNs, such as large utility networks. It is thus important to have
a robust solution for reactive routing. Therefore, various
techniques are hereinafter shown and described for use with
reactive routing networks to address such shortcomings.
[0030] Dynamic Division of Reactive Routing Networks into
Sub-Domains
[0031] Reactive routing protocols rely on flooding the whole
network with probes/messages (e.g., RREQs) to discover routes
between a source and a destination within the network.
Unfortunately, such network floods generate significant volumes of
network traffic. Several mitigation techniques have been developed
to reduce the negative effects of flooding by reducing/limiting the
number of broadcast packets generated by such floods.
Illustratively, these techniques may operate by attempting to limit
the flood scope, the number of duplicated messages (e.g., multicast
trickle), etc. Nevertheless, such network floods are still
generally required for any reactive routing protocol in order to
make sure that at least N probes/messages reach the
destination/target. It is important to note that while N may be
small in "classic" networks that have high delivery rates, N is
likely to be higher in LLNs in which the Packet Delivery Ratio
(PDR) is typically low. Unfortunately, these mitigation techniques
lead to a trade-off between storing network state and increasing
network load due to flooded messages (e.g., a RREQ broadcast). For
example, storing more network state information makes it possible
to reduce the number of times that the discovery process (e.g., a
network flood) must be triggered, and therefore decreases the
control plane overhead; however, storing more state information
requires more memory to store the routing entries for each
originator, especially in cases where the routes are not limited to
the best next hops, but rather include full end-to-end paths from
the source to the destination, which increases cost.
[0032] The techniques herein provide dynamic division of a reactive
routing network into sub-domains by allowing a routing sub-domain
to be dynamically divided into search-domains based on the observed
message flood rate within the network, thus significantly reducing
the message flood rate in the network, as well as the associated
control plane cost.
[0033] Specifically, according to one or more embodiments of the
disclosure as described in detail below, a reactive routing network
may be dynamically divided into reactive routing network
sub-domains that each include nodes with bounded route request
(RREQ) scopes (e.g., search-domains) that are limited to a
particular path length. In other words, a reactive routing network
sub-domain includes a plurality of nodes, each of which has a
search-domain with a limited number of surrounding nodes that may
receive a RREQ from that particular node. A transit node may
receive a RREQ from an originating node within a first reactive
routing network sub-domain for a target node determined by the
originating node to be beyond the bounded RREQ scope (i.e.,
search-domain) of the originating node. The transit node may then
discover a route from the transit node to the target node, and
return the route to the originating node. The discovered route may
include at least one node in a second reactive routing network
sub-domain, which is outside of the first reactive routing network
sub-domain. In this manner, the transit node may establish a
complete route between the originating node and the target node. In
addition, according to one or more additional embodiments of the
disclosure, a node within a reactive routing network may receive a
segmentation message from a capable node (e.g., a transit node, a
LBR, etc.), and in response, establish a bounded RREQ scope (e.g.,
a search-domain) for any RREQ originated by the node that is
limited to a particular path length. As such, the node may forward
RREQs to one or more transit nodes for any target node not
identified by the node as being within the search-domain of the
node.
[0034] Illustratively, the techniques described herein may be
performed by hardware, software, and/or firmware, such as in
accordance with the routing process 244, which may contain computer
executable instructions executed by the processor 220 (or
independent processor of interfaces 210) to perform functions
relating to the novel techniques described herein. For example, the
techniques herein may be treated as extensions to conventional
routing protocols, such as the various reactive routing protocols,
and as such, may be processed by similar components understood in
the art that execute those protocols, accordingly.
[0035] The techniques herein may dynamically divide a reactive
routing network into reactive routing sub-domains based on observed
message flood patterns within the network and/or based on network
conditions (e.g., link/node congestion state). Advantageously, the
reactive routing sub-domains of the disclosure may restrict
flooding scope within the network as a whole by, for example,
establishing a search-domain for each node within the reactive
routing sub-domain that comprises a limited number of surrounding
nodes that may receive a RREQ from that particular node. In the
event that a node within a reactive routing sub-domain (e.g., an
originating node) initiates a RREQ within its search-domain and is
unable to identify a path to a desired target node, the originating
node may then attempt to identify the target node with the aide of
a transit node. For example, unicast or loose source routing may be
used to reach out (or out-of-search-domain) target destinations via
dynamically discovered points of transit (e.g., transit nodes),
with a resulting decrease in control plane cost overhead.
Additionally, capable nodes within the reactive routing network may
serve to establish search-domain boundaries within the network,
which may be based on control plane cost overhead due to flooded
messages (e.g., network state) within the reactive routing network
prior to reactive routing network division into reactive routing
sub-domains.
[0036] According to the techniques herein, route discovery in a
reactive routing network may be facilitated by the use of transit
nodes. For example, FIG. 3A depicts a reactive routing network
comprising eleven nodes, including a Root/LBR. Consider the
situation in which node 13 needs to find a route in the network to
node 43. In a typical reactive routing network, node 13 will
broadcast a probe/message (e.g., a RREQ) in order to discover a
route to node 43. Given this scenario, there are multiple
approaches that may be taken for such route discovery: [0037] 1)
Node 43 may return all of the received messages/probes to node 13
with the recorded path (e.g., a route reply or "RREP"), and path
selection may be performed by node 13 on the basis of the path
cost, as indicated by the received messages/probes; [0038] 2) Node
43 may arm a timer upon receiving the first message/probe from node
13, and once the timer has expired, node 43 may select the received
message/probe with the "best" path according to the path cost;
and/or [0039] 3) Node 43 may immediately return the first received
message/probe to node 13 in order to avoid wasting time before
sending the data packet, and may store the path cost for that
particular message/probe and only return further messages/probes if
their path cost is better then the path cost for the original
message/probe by a particular value "X" (e.g., by X %).
[0040] Illustratively, once a route is discovered between node 13
(e.g., source/requestor) and node 43 (e.g., destination), for
example 13-12-22-32-43 as shown in FIG. 3B, the source may arm a
timer T1, which establishes the period of time the route may be
maintained. In another embodiment, the timer T1 may also be aimed
by intermediate nodes when a hop-by-hop routing protocol is used.
After the expiration of timer TI, the route may be flushed and the
route discovery process may occur again the next time a new path to
node 43 is needed. It will be appreciated by the skilled artisan
that increasing the value of T1 may minimize the undesirable effect
of flooding messages/probes at the risk of increasing the amount of
states in the nodes (e.g., number of stored routed), but more
importantly may increase the probability of using a stale
route.
[0041] Operationally, the techniques herein may provide a software
module referred to as a Distributed Intelligent Agent-Broadcast
(DIA B), which may be hosted by a capable node/device (e.g., the
LBR) within the reactive routing network or on a separate device,
such as a network management server (NMS) or other management
device. For example, the DIA-B may be encompassed by routing
process 244 (see, e.g., FIG. 2). As shown in FIG. 3C (depicting a
simplified view of an expanded network), the DIA-B may monitor the
amount of control-plane traffic occurring in the network. In
particular, the DIA-B may monitor the amount/volume of discovery
messages/probes that are being flooded in the network. It is
important to note that in the situation where the scope of
particular messages/probes broadcast within the network is limited,
such messages/probes may not reach the DIA-B. Consequently, the
level of control plane traffic observed by the DIA-B may establish
a lower bound for a particular network region when the discovery
messages/probes are limited in scope. However, discovery
messages/probes that are not limited in scope incur much more cost,
and the DIA-B may monitor these messages/probes. Furthermore, the
DIA-B may monitor the current state of the network by collecting
information about a variety of network parameters such as, for
example, traffic load, congestion, and the like, from various nodes
within the network to either the LBR or a NMS. It is contemplated
within the scope of the disclosure that link usage/congestion areas
may be locally available at the LBR/DIA-B or may be obtained from
the NMS/CIC (e.g., a central intelligence controller).
[0042] In addition, the techniques herein provide that all DIA-B
processes, or other capable nodes/devices, may announce themselves
as potential transit nodes. For example, DIA-B processes may
self-identify as potential transit nodes via an IPv6 broadcast
message(s), or via a routing protocol that may advertise their node
capability such as, for example, a routing metric specified in IETF
Internet Draft, entitled "Routing Metrics used for Path Calculation
in Low Power and Lossy Networks"
<draft-ietf-roll-routing-metrics-19> by Vasseur, et al. (Mar.
1, 2011 version) for the RPL protocol, or IS-IS node capability
extensions in the event that ISIS may be used by the LBR on the
core network backbone.
[0043] Operationally, the techniques herein provide a control plane
overhead threshold value that may determine when routing region
division should occur within the reactive routing network. For
example, if the DIA-B process determines that the control plane
overhead due to flooded messages/probes (e.g., RREQs) does not
exceed the pre-defined threshold value, or that there are no
congested areas in the network that would benefit from a reduction
of the number of flooded messages/probes, then the DIA-B process
may determine that no action is required with respect to routing
region division. However, if the DIA-B process determines that the
control plane overhead due to flooded messages/probes does exceed
the pre-defined threshold value, then the DIA-B process may trigger
dynamic division of the reactive routing network into one or more
routing sub-domains via the following exemplary set of actions.
[0044] A capable node/device (e.g., an LBR, a NMS, a transit node,
etc.) may perform a scoped flood of a new message, referred to
herein as the Segmentation Message (e.g., an IPv6 message), for all
destinations within a specific distance such that all nodes
receiving the Segmentation Message comprise a reactive routing
sub-domain. The Segmentation Message may cause nodes receiving the
message to bound the scope of any subsequent route discovery
messages (e.g., RREQs) flooded by such receiving nodes, e.g., by
setting the TTL value of the flooded route discovery messages to
specified path length "PL(i)", as described below, which may create
search-domains for each node within the reactive routing
sub-domain. In this manner, the Segmentation Message may create a
threshold at which the receiving node (e.g., a source node) may
transition from a flooding protocol to a transit node transmission
protocol when discovering routes within the network. For example,
the Segmentation Message may establish a threshold level at which a
source node may transition from a protocol of flooding a RREQ
within the bounded scope of surrounding nodes/devices set by the
Segmentation Message (i.e., a search-domain), to a protocol of
transmitting messages directly to a transit node (e.g., the transit
node that originated the Segmentation Message, or another transit
node), which may then continue the search to complete the route
request (if the transit node is not already aware of the intended
target node of the route request).
[0045] Illustratively, direct transmission from the source node to
the transit node may occur by unicasting or by "loose-hop" routing
with the transit node set as the first next loose hop. In other
words, a capable node may transmit a Segmentation Message to a
subset of nodes/devices within a reactive routing network via a
scoped flood (e.g., a sub-domain), and the Segmentation Message may
then direct the subset of nodes/devices (i.e., the routing
sub-domain) to use flooding to identify any target node .ltoreq."X"
hops away (e.g., PL(i)), which creates a search-domain, and if no
RREP is received within "N" attempts, to then transmit that
corresponding RREQ directly to a transit node via unicast or loose
hop routing so that the transit node may continue the search for
the target node.
[0046] Note that in one embodiment, the Segmentation Message may be
unicast to any capable node (e.g., a LBR, a transit node, a NMS,
etc.), which may then flood the Segmentation Message with a
time-to-live (TTL) indicator (i.e., a scoped flood of the
Segmentation Message). Advantageously, this approach may allow the
capable node (e.g., the LBR/root or transit node) to divide the
network into one or more routing sub-domains by delivering the
Segmentation Message to a localized region of the network. In
another embodiment, the Segmentation Message may be broadcast to
all nodes in the network (e.g., from a central network management
device), and may affect how all nodes in the network operate. In
still another embodiment, the Segmentation Message may be unicast
to individual nodes within the reactive routing network. It is
contemplated within the scope of the disclosure that a routing
sub-domain may, or may not, contain a transit node.
[0047] Illustratively, FIG. 3C depicts an expanded network in which
the DIA-B may monitor the message/probe broadcast rate within the
expanded network. If the DIA-B process determines that the level of
flooding within the expanded network is too high, or that
particular links within the expanded network (e.g., 13-LBR2 or
23-24) are congested, the DIA-B process may dynamically signal one
or more nodes (e.g., the Root/LBR) to advertise itself/themselves
as a "transit node(s)." For example, as shown in FIG. 3D, LBR1 may
self-identify as a transit node and begin broadcasting segmentation
message (SM) 300, which may cause dynamic division of the routing
region of the expanded network into two or more routing
sub-domains, as shown in FIG. 3E.
[0048] Upon receiving the SM 300, each node within the network may
begin bounding the scope of any flooded message/probe (RREQ) by
setting the TTL value of the packet to PL(i), effectively creating
search-domains within the routing sub-domain. For example, if PL=3,
then node 21 in the expanded network would not be able to find a
direct route to node 25 using RREQ messages because it exceeds the
hop threshold. Instead, a route from node 21 to note 25 may be
established using the mechanism described below.
[0049] If a destination node cannot be reached within the source
node's search-domain (e.g., no RREP packet has been received after
"N" trials, where N.gtoreq.1), then the source node may begin to
use loose routing, with LBR1 set as the first next loose hop,
essentially, to let the transit node complete the unknown path to
the destination/target node. If the route to the LBR1 is known,
then the source node may source route the packet with the last two
entries listed as loose hops. For example, if the packet received
by node 42 seeks a path to node 25, the packet may carry the
following source route: 42-32-22-12-LBR1(L)-25(L) (where "(L)"
indicates the ends of a loose hop). If the source node does not
know the source route to the closest transit node, it may either
send a message/probe to discover a path to the node or, if
available, it may use a simple proactive DAG to provide hop-by-hop
upward routing to the LBR of interest. Upon receiving such a loose
route message/probe, LBR1 may then add the next hop entry (e.g.,
LBR2) in any of a variety of ways. For example, LBR1 may multicast
the RREQ to other transit nodes within the reactive routing network
to determine whether any may be able to complete the route to the
target node. If none of the queried transit nodes are able to
complete the route (e.g., if the target node is not located within
a transit node associated network sub-domain), LBR1 may then flood
the RREQ to the entire network to identify a route to the target
node.
[0050] In the event that the target node is located within the LBR2
network sub-domain, and LBR2 knows the path to the target node,
then LBR2 may return the completed route to LBR1. However, if LBR2
does not know the route to the target node, it may then initiate a
local message/probe broadcast with the destination target node
desired by the source node with, for example, a TTL value of PL(2)
(i.e., the value of the Path Length in its own search-domain). Upon
receiving the reply (e.g., a RREP) from the destination node, the
discovered path may be added to the RREP messages and sent back to
the requesting LBR, which may, in turn, return the RREP to the
source node with the fully discovered path 310, for example,
42-32-22-12-LBR1-LBR2-14-25, as shown in FIG. 3F.
[0051] In addition, the LBRs may keep track of the number of
identified loose routes so as to dynamically adjust the values of
PL(i). Larger values of PL(i) may lead to wider search-domains and
more optimal paths at the cost of increased broadcast domains.
[0052] Notably, the value of PL(i) may have a number of
consequences, and may be chosen by the initiating LBR according to
the presence of other LBRs to make sure that PL(i) (i being the
search-domain) may be chosen so as to guarantee existence of a path
between each pair of nodes in the network. For example, as
described above, if LBR2 sets the TTL value as PL(1)=4, then node
42 would not be able to establish a route to node 14. In order to
compensate for this scenario, LBR2 may set the value of PL(2) high
enough to guarantee that a path will be found.
[0053] In view of the foregoing, one of skill in the art will
appreciate that FIGS. 3C-3F represent simplified views of an
exemplary extended network. For example, FIG. 3G depicts dynamic
division of a reactive routing network into routing sub-domains in
a more complex reactive routing network. As described above, a node
within the reactive routing network may self-identify as a transit
node (e.g., TN1)--upon its own determination or upon instruction
from a management device--and broadcast an SM 300 with a PL(1)
value of, for example, PL(1)=2. The broadcast of SM 300 with a TTL
of 2 may establish TN1 routing sub-domain 315, as shown in FIG. 3G,
in which each node may have a bounded RREQ scope of PL(1)=2.
Accordingly, each node within TN1 routing sub-domain 315 may have
its own bounded RREQ scope search-domain 320, as shown in FIG. 3G
(for illustrative purposes, only one such search-domain is depicted
for a specific node--shown as source node 309). Said differently,
each node within a range of the SM 300 (e.g., two hops away from
the transit node) may each have their own search boundary that is
PL(1) away (e.g., two hops away from the particular node). As
described above, if source node 309 initiates a local-scoped flood
of a RREQ for target node 311 within bounded scope search-domain
320, and no RREP is received within "N" attempts, then source node
309 may unicast the RREQ directly to TN1 (or it may switch to loose
routing with TN1 set as the first next loose hop).
[0054] It is contemplated within the scope of the disclosure that
reactive routing network sub-domains may, or may not, overlap. As
shown in FIG. 3H, TN2 may identify as a transit node and broadcast
a SM 300 with PL(2)(not shown) to generate TN2 routing sub-domain
325, which may be (though need not be) approximately the same size
as, and overlap with, TNT routing sub-domain 315. Such overlapping
sub-domains do not create an issue for the techniques herein
because of the overlapping nature of the bounded RREQ scope
search-domains for each node within TN1 routing sub-domain 315
and/or TN2 routing sub-domain 320. In other words, due to their
bounded RREQ scope search-domains and geo-spatial location within
the reactive routing network, some nodes within TN1 routing
sub-domain 315 may be able to directly query some nodes in TN2
routing sub-domain 320, but not others. For the latter nodes, the
RREQ may transit via TN1 to reach the desired target node in TN2
routing sub-domain 320 by any of the methods described above. Note
that should a node receive two segmentation messages, that node may
simply select one of the corresponding transit nodes, or may
load-balance between the two.
[0055] In addition, as described above, the techniques herein
provide that a source node within a particular routing sub-domain
may route a RREQ to one or more different transit node(s). For
example, FIG. 31 depicts a reactive routing network in which TN1
has initiated a scoped broadcast of a Segmentation Message that
establishes TN1 routing sub-domain 330. However, the Segmentation
Message may establish bounded search scope search-domains for nodes
within TN1 routing sub-domain 330 that may be completely different
from the scope of its own initial broadcast (i.e., the routing
sub-domain). In this context, a source node within TN1 routing
sub-domain 330 may be positioned within the network such that a
different transit node (e.g., TN2) is closer to the source node
than TN1. In this case, if source node 309 initiates a local-scoped
flood of a RREQ for target node 311 within bounded scope
search-domain 335, and no RREP is received within "N" attempts,
then source node 309 may unicast the RREQ directly to TN2 instead
of TN1. In one embodiment, the source node 309 may keep track of
the "closest" transit node by any of a variety of distance metrics
(e.g., hop count, reliability, latency, etc.). In one embodiment,
this distance metric may be obtained from the Segmentation Message.
In another embodiment, the node may flood a RREQ to discover one or
more transit nodes. Although such a transit node discovery method
would initiate a network flood, the flood only occurs to the extent
necessary to find suitable transit nodes, to which unicast RREQs
may then be sent to discover routes to other target devices.
[0056] In addition, the techniques herein also provide that TN1 may
directly query specific "linked" transit nodes within the
dynamically divided reactive routing network in order to complete
route discovery. For example, as shown in FIG. 3J, TN1 may maintain
proactive DAGs to specific "linked" transit nodes within the
network such as, for example, TN2, TN3, and TN4. In order to query
"non-linked" transit nodes such as, for example, TN5, or nodes that
are not resident within a transit node-associated network
sub-domain (e.g., slant hashed nodes in FIG. 33), TN1 may flood the
RREQ of the originating node to the entire network.
[0057] The techniques herein provide a significant increase in
efficiency and decrease in control plane overhead because the
bounded RREQ scope search-domains and the ability of transit nodes
to efficiently complete route discover may significantly decrease
overall network traffic. In addition, even if it is necessary for a
particular transit node (e.g., LBR1/TN1) to initiate a network
flood to identify a route to a target node, the techniques herein
may allow that discovered route to remain available for other nodes
within the LBR1 sub-domain looking to reach the same target node,
which may prevent additional network floods.
[0058] FIG. 4 illustrates an example simplified procedure 400 for
dynamic division of a reactive routing network into reactive
routing sub-domains in accordance with one or more embodiments
described herein, particularly from the perspective of a transit
node. The procedure 400 may start at step 405, and continue to step
410 where, as described above, a transit node in a first reactive
routing network sub-domain may receive a RREQ from an originating
node within the first reactive routing network sub-domain for a
target node determined by the originating node to be beyond the
bounded RREQ scope search-domain of the originating node. As shown
in step 415, the transit node may then discover a route from the
transit node to the target node. As shown in step 420, the transit
node may then return the route to the originating node. In this
manner, the transit node may establish a complete route between the
originating node and the target node, and then the procedure 400
may illustratively end at step 425. In other words, the transit
node may act as an intermediary between the first reactive routing
network sub-domain and target nodes within other reactive routing
network sub-domains, which dramatically decreases the control
overhead required to discover and establish complete paths between
an originating node and a target node within a reactive routing
network.
[0059] Similarly, FIG. 5 illustrates an example simplified
procedure 500 for dynamic division of a reactive routing network
into reactive routing sub-domains in accordance with one or more
embodiments described herein, particularly from the perspective of
a requesting node. The procedure 500 may start at step 505, and
continue to step 510 where, as described above, a node within a
reactive routing network may receive a segmentation message from an
originating capable node (e.g., a transit node, a LBR, etc.). As
shown in step 515, the segmentation message may function to
establish a bounded RREQ scope for any RREQ originated by the node
that is limited to a particular path length, effectively
establishing a search-domain centered around the node. As shown in
step 520, when the node originates a RREQ within the predetermined
bounded scope of the search-domain and fails to identify the
desired target node, the node may then forward the RREQ to a
receiving transit node, and then the procedure 500 may
illustratively end at step 525. In this manner, the originating
node initiates an efficient bounded scope search for the target
within the search-domain, and if this search is unsuccessful the
originating node forwards the RREQ to a receiving transit node,
which may or may not be within the first reactive routing network
sub-domain, to act as an intermediary to complete the route
request. Accordingly, the techniques herein may dramatically
decreases the control overhead required to discover and establish
complete paths between and originating node and a target node.
[0060] It should be noted that while certain steps within
procedures 400 and 500 may be optional as described above, the
steps shown in FIGS. 4 and 5 are merely examples for illustration,
and certain other steps may be included or excluded as desired.
Further, while a particular order of the steps is shown, this
ordering is merely illustrative, and any suitable arrangement of
the steps may be utilized without departing from the scope of the
embodiments herein. Moreover, while procedures 400-500 are
described separately, certain steps from each procedure may be
incorporated into each other procedure, and the procedures are not
meant to be mutually exclusive.
[0061] The techniques described herein, therefore, provide for
dynamic division of reactive routing networks into reactive routing
sub-domains in order to control/minimize flooding, which provides
increased scalability for reactive routing networks. By using the
transit nodes as a bridge to help reach the final destination node,
the techniques herein may reduce congestion in reactive routing
networks. In particular, the techniques herein increase scalability
both for an increase in the number of nodes in a network, and for
small networks as the number of active P2P flows in the network
increases.
[0062] While there have been shown and described illustrative
embodiments of techniques for use with reactive routing in
communication networks, it is to be understood that various other
adaptations and modifications may be made within the spirit and
scope of the embodiments herein. For example, the embodiments have
been shown and described herein with relation to LLNs. However, the
embodiments in their broader sense are not as limited, and may, in
fact, be used with other types of networks, regardless of whether
they are considered constrained. In addition, while certain
protocols are shown, other suitable protocols may be used,
accordingly.
[0063] The foregoing description has been directed to specific
embodiments. It will be apparent, however, that other variations
and modifications may be made to the described embodiments, with
the attainment of some or all of their advantages. For instance, it
is expressly contemplated that the components and/or elements
described herein can be implemented as software being stored on a
tangible (non-transitory) computer-readable medium (e.g.,
disks/CDs/RAM/EEPROM/etc.) having program instructions executing on
a computer, hardware, firmware, or a combination thereof
Accordingly this description is to be taken only by way of example
and not to otherwise limit the scope of the embodiments herein.
Therefore, it is the object of the appended claims to cover all
such variations and modifications as come within the true spirit
and scope of the embodiments herein.
* * * * *