In this work we point out the issue of the IETF RPL routing protocol’s two different downward routing schemes not being able to interoperate with each other. This problem is less of an issue when low-power and lossy networks (LLNs) are deployed homogeneously but with the industrial kickoff and large scale deployments, the interoperability of heterogeneous standards-compliant implementations will become a significant issue. To accomplish this, we suggest some changes to the current RFC 6550. We show, with two different LLN IPv6 implementations in TinyOS and NanoQplus, that our suggestions help different implementations to successfully exchange point-to-point messages that require downwards routing.

1. Towards Full RPL Interoperability:
Addressing the Case with Downward Routing
JeongGil Ko1, Jongsoo Jeong2, Jongjun Park1, Jong Arm Jun1 and Naesoo Kim1
1IoT Architecture Research Team, Electronics and Telecommunications Research Institute, Korea
2Real-time SW Research Team, Electronics and Telecommunications Research Institute, Korea
{jeonggil.ko, jsjeong, juny, jajun, nskim}@etri.re.kr
Introduction
In this work we point out the issue of the IETF RPL routing protocol’s two different downward routing
schemes not being able to interoperate with each other. This problem is less of an issue when low-power
and lossy networks (LLNs) are deployed homogeneously but with the industrial kickoff and large scale
deployments, the interoperability of heterogeneous standards-compliant implementations will become a
significant issue. To accomplish this, we suggest some changes to the current RFC 6550. We show, with
two different LLN IPv6 implementations in TinyOS and NanoQplus, that our suggestions help different
implementations to successfully exchange point-to-point messages that require downwards routing.
Root Root
Storing Storing
mode mode
node node
Common
Parent
Non-storing Root
mode node (Storing mode)
Non-
Non-storing storing
Destination Source Destination Source mode node mode
node
Storing mode Non-storing mode Mixture of storing and non-storing
DAO Hop-by-hop End-to-end nodes can partition a single network.
(to the DAO parents) (to the DODAG root
directly)
In RFC 6550, when a RPL node joins a network
Downward
RPL with a different MOP, it may only join the
Packet IPv6 Data IPv6 SRH Data
Format
Opt.
network as a leaf node, which is not allowed to
Routing Each node (distributed) Only root (centralized)
forward others’ packets. While this is a safe
Table decision, it limits the benefits and applications
Two types of RPL downwards routing modes that interoperating RPL systems can introduce
Making Different RPL
Evaluation
Modes Interoperate Root: purple
TinyOS: green
NanoQplus: yellow
1. New MOP: Hybrid Mode with Storing or Non-
storing Features
2. Storing mode nodes should be capable of
adding and understanding SRHs when needed.
3. All DAO messages should be forwarded on a
hop-by-hop basis rather than end-to-end to
the DODAG root.
4. Parent Address field should be specified in the Topology for interoperability testing and PRR
transit information option of the DAOs. with and without our proposed changes.
5. Optionally, nodes should indicate whether they
Simulation setup
are a route storing node or not in the DAO
• Simulator: Cooja Contiki Simulator
base message.
• RPL Objective Function: OF0
• RPL DAO period: 1 packet / 30 seconds
Storing Storing • The root (TinyOS) sends packets periodically
mode
node
mode
node
each second while changing destination of the
packet sequentially.
Results
Non-storing Root
mode node (Hybrid mode) • No Interoperability Support: ~25 % PRR
Non-
• Interoperability Support: ≈ 100% PRR
Non-storing storing • Memory footprints increase only minimally
mode node mode
node compared to non-interoperable MOPs.
Minimal changes to RFC 6550 allow
Operation Mode ROM RAM
efficient interoperation of different modes.
NanoQplus MOP 1 to 4
• Hop-by-hop DAO transmission allows +0.18 KB +0 KB
(Non-Storing)
intermediate storing mode nodes maintain sub-
DODAG routes. TinyOS MOP 2 to 4
+1.66 KB +0.10 KB
• Storing mode nodes can forward packets to (Storing)
non-storing mode nodes. Also, they can attach Memory footprint increases for TinyOS and
SRH before forwarding if needed. NanoQplus nodes