DAG—Directed Acyclic Graph. A directed graph having the property that
all edges are oriented in such a way that no cycles exist. All edges are
contained in paths oriented toward and terminating at one or more root nodes.
DAG root—A DAG root is a node within the DAG that has no outgoing
edges. Because the graph is acyclic, by definition all DAGs must have at least
one DAG root and all paths terminate at a DAG root.
DODAG—Destination Oriented DAG. A DAG rooted at a single destination,
i.e. at a single DAG root (the DODAG root) with no outgoing edges.
DODAGID—The identifier of a DODAG root. The DODAGID must be unique
within the scope of a RPL Instance in the LLN.
DODAG Iteration—A specific version number iteration (version) of a
DODAG with a given DODAGID.
DODAG parent—A parent of a node within a DODAG is one of the immediate
successors of the node on a path towards the DODAG root. The DODAG parent of a
node will have a lower rank than the node itself.
DODAG root—A DODAG root is the DAG root of a DODAG.
DODAG sibling—A sibling of a node within a DODAG is defined in this
specification to be any neighboring node which is located at the same rank
within a DODAG. The siblings defined in this manner do not necessarily share a
common DODAG parent.
DODAGVersionNumber—A sequential counter that is incremented by the root
to form a new Version of a DODAG. A DODAG Version is identified uniquely by the
(RPLInstanceID, DODAGID, DODAGVersionNumber) tuple.
Down—The direction from DODAG roots towards leaf nodes, going against
the orientation of the edges within the DODAG.
Goal—A host or set of hosts that satisfy a particular application
objective / OF. Whether or not a DODAG can provide connectivity to a goal is a
property of the DODAG. For example, a goal might be a host serving as a data
collection point, or a gateway providing connectivity to an external
Grounded—A DODAG is said to be grounded, when the root can reach the
Goal of the objective function.
Floating—A DODAG is floating if it is not Grounded. A floating DODAG is
not expected to reach the Goal defined for the OF. As they form networks, LLN
devices often mix the roles of 'host' and 'router' when compared to traditional
IP networks. The host refers to an LLN device that can generate but does not
forward RPL traffic, router refers to an LLN device that can forward as well as
generate RPL traffic, and node refers to any RPL device, either a host or a
LBR—Low power and lossy network Border Router. A device that connects
the Low power and Lossy Network to another routing domain such as a Local Area
Network (LAN), Wide Area Network (WAN) or the Internet where a possibly
different routing protocol is in operation. In some cases, in addition to
acting as a routing device, the LBR may also be a host performing functions
such as data collector or aggregator.
LLN—Low power and Lossy Networks. These networks are typically composed
of many embedded devices with limited power, memory, and processing resources
interconnected by a variety of links, such as IEEE 802.15.4 or Low Power WiFi.
There is a wide scope of application areas for LLNs, including industrial
monitoring, building automation (HVAC, lighting, access control, fire),
connected home, healthcare, environmental monitoring, urban sensor networks,
energy management, assets tracking and refrigeration.
OCP—Objective Code Point. An identifier, used to indicate which
Objective Function is in use for forming a DODAG. The Objective Code Point is
further described in METRIC.
OF—Objective Function. Defines which routing metrics, optimization
objectives, and related functions are in use in a DODAG. The Objective Function
is further described in METRIC.
Rank—The rank of a node in a DAG identifies the nodes position with
respect to a DODAG root. The farther away a node is from a DODAG root, the
higher is the rank of that node. The rank of a node may be a simple topological
distance, or may more commonly be calculated as a function of other properties
as described later.
RPL Instance—A set of possibly multiple DODAGs. A network may have more
than one RPL Instance, and a RPL node can participate in multiple RPL
Instances. Each RPL Instance operates independently of other RPL Instances.
This document describes operation within a single RPL Instance. In RPL, a node
can belong to at most one DODAG per RPL Instance. The tuple (RPLInstanceID,
DODAGID) uniquely identifies a DODAG.
RPLInstanceID—Unique identifier of a RPL Instance.
Sub-DODAG—The set of other nodes in the DODAG that might use a path
towards the DODAG root that contains that node. Nodes in the sub-DODAG of a
node have a greater rank than that node itself (although not all nodes of
greater rank are necessarily in the sub-DODAG of that node).
Up—The direction from leaf nodes towards DODAG roots, following the
orientation of the edges within the DODAG.