RPL Protocol

 The ROLL working group mainly designed the RPL to operate in the LLN. The LLN

exhibited certain unique features that the routing protocol had to consider for successful

operation. The main features of the LLN depicted in RFC 6550 are as follows:

1. The LLN consists of thousands of nodes that are resource constrained in terms

of memory, limited processing capability, and power as most of the nodes are

battery operated.

2. The constrained nodes are operating in the lossy networks that normally consist of lossy links that support low data rates.

3. The LLN supports different traffic flows, Multipoint-to-Point (M2P), Point-to-

Multipoint (P2M), and Point-to-Point (P2P).

The ROLL workgroup also published several key requirements by taking several

example applications. Some of the crucial industrial requirements for routing in LLN are presented as follows:


 Traffic Support: The routing protocol for LLN must have the potential to support

periodic data, event data, and to transfer the bulk of data in multiple packets.

 Reliability: It must be able to deliver packets within a bounded latency, while

ensuring correct data, and also guaranteeing maximum disruption time mandating

upper bound for route maintenance.

 Device-Aware: Since most of the nodes are battery operated, they have to take

into account long-term and short-term energy consideration, and hence, the protocol

must ensure minimum energy consumption.

 Protocol Performance: It must be able to converge and establish connectivity to

the newly added node within a time frame. It must also ensure route computation

before selecting a path to the destination.

 Mobility Support: It must support the network dynamics that arise due to node

changing its position and ensure mobile node connectivity to the network within

a few seconds.

 Security: Routing protocol must be secured so that it is not manipulated by unauthenticated

nodes and ensure that the attackers do not affect the routing performance.

Overview of IPv6 Routing Protocol for Low power and Lossy Networks

To meet the requirements of the LLN, the IETF has standardized the RPL protocol. The

RPL is designed specially to route packets over a network that has the characteristics

of a lossy nature and consists of resource constraint devices. It is a distance-based

gradient routing protocol, which constructs a Destination-Oriented Directed Acyclic Graph (DODAG) tree on top of the physical network. The nodes in the DODAG tree

are directed towards the DODAG root node that is connected to an external network.

Figure shows an example of the DODAG tree, which consists of three types of nodes

that perform differently in the routing mechanism


 DODAG root: It is responsible for creating a DODAG tree and collecting information

from all the nodes in the tree topology. It is also responsible for connecting

the LLN to the Internet.

 Router node: The router node associated with the DODAG tree in the RPL protocol

is responsible for generating traffic and also for forwarding data packets to

other nodes. It acts as an intermediate node between the DODAG root and the

leaf node.

 Leaf node: The leaf node is the end node of the DODAG tree. It is only responsible

for generating data traffic in the RPL protocol.


More about RPL in the next Article

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