Internet-Draft DIS Modifications use cases June 2024
Papadopoulos Expires 15 December 2024 [Page]
Workgroup:
ROLL
Internet-Draft:
draft-papadopoulos-roll-dis-mods-use-cases-01
Published:
Intended Status:
Standards Track
Expires:
Author:
G. Papadopoulos
IMT Atlantique

Use cases for DIS Modifications

Abstract

This document presents use-cases which call for DIS flags and options modifications.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 15 December 2024.

Table of Contents

1. Introduction

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. Applications

This section details some use cases that require DIS modifications compared to the behaviour currently defined in [RFC6550]. The first use case is thatof a new leaf node joining an established DAG in an energy efficient manner. The second use case describes why node might want to use DIS to identify defunct DAGs for which it still maintains state. The third use case describes the need for adjacency probing and how DIS can used for that.

3.1. A Leaf Node Joining a DAG

This use case is typically of a smart meter being replaced in the field, while a RPL network is operating and stable. The new smart meter must join the network quickly, without draining the energy of the surrounding nodes, be they battery-operated RPL routers or leaf nodes. In this use case, the issues with the current RPL specification are

A proposed solution could be the following. A new leaf node that joins an established LLN runs an iterative algorithm in which it requests (using multicast DIS) DIOs from routers belonging to the desired DAG.

The DIS message has the "No Inconsistency" flag set to prevent resetting of Trickle timer in responding routers, thereby keeping the aggregated number of transmissions low. It also has the "DIO Type" flag set to make responding routers send unicast DIOs back, thereby not triggering full reception in nearby nodes that have state-of-the- art radio receivers with hardware-based address filtering.

The DIS message can include a Response Spreading option prescribing a suitable spreading interval based on the expected density of nearby routers and on the expected Layer 2 technology.

The DIS will likely include a Metric Container listing the routing constraints that the responding routers must satisfy in order to be allowed to respond [RFC6551].

At each iteration, the node multicasts such a DIS and waits for forthcoming DIOs. After a time equal to the spreading interval, the node considers the current iteration to be unsuccessful. The node consequently relaxes the routing constraints somewhat and proceeds to the next iteration.

The cycle repeats until the node receives one or more DIOs or until it has relaxed the constraints to the lowest acceptable values.

This algorithm has been proven in the field to be extremely energy-efficient, especially when routers have a wide communication range.

3.2. Identifying A Defunct DAG

A RPL node may remove a neighbor from its parent set for a DAG for a number of reasons:

Even if the conditions listed above exist, a RPL node may fail to remove a neighbor from its parent set because:

In such cases, a node would continue to consider itself attached to a DAG even if all its parents in the DAG are unreachable or have moved to different DAGs. Such a DAG can be characterized as being defunct from the node's perspective. If the node maintains state about a large number of defunct DAGs, such state may prevent a considerable portion of the total memory in the node from being available for more useful purposes.

To alleviate the problem described above, a RPL node may invoke the following procedure to identify a defunct DAG and delete the state it maintains for this DAG. Note that, given the proactive nature of RPL protocol, the lack of data traffic using a DAG can not be considered a reliable indication of the DAG's defunction. Further, the Trickle timer based control of DIO transmissions means the possibility of an indefinite delay in the receipt of a new DIO from a functional DAG parent. Hence, the mechanism described here is based on the use of a DIS message to solicit DIOs about a DAG suspected of defunction. Further, a multicast DIS is used so as to avoid the need to query each parent individually and also to discover other neighbor routers that may serve as the node's new parents in the DAG.

When a RPL node has not received a DIO from any of its parents in a DAG for more than a locally configured time duration:

3.3. Adjacencies probing with RPL

RPL avoids periodic hello messaging as compared to other distance vector protocols. It uses trickle timer based mechanism to update configuration parameters. This significantly reduces the RPL control overhead. One of the fallout of this design choice is that, in the absence of regular traffic, the adjacencies could not be tested and repaired if broken.

RPL provides a mechanism in the form of unicast DIS to query a particular node for its DIO. A node receiving a unicast DIS MUST respond with a unicast DIO with Configuration Option. This mechanism could as well be made use of for probing adjacencies and certain implementations such as Contiki uses this. The periodicity of the probing is implementation dependent, but the node is expected to invoke probing only when

3.3.1. Deliberations

  • Should the probing scheme be standardized? In some cases using multicast based probing may prove advantageous.

  • In some cases using multicast based probing may prove advantageous. Currently RPL does not have multicast based probing. Multicast DIS/DIO may not be suitable for probing because it could possibly lead to change of states.

4. Informative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC4861]
Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, , <https://www.rfc-editor.org/info/rfc4861>.
[RFC5184]
Teraoka, F., Gogo, K., Mitsuya, K., Shibui, R., and K. Mitani, "Unified Layer 2 (L2) Abstractions for Layer 3 (L3)-Driven Fast Handover", RFC 5184, DOI 10.17487/RFC5184, , <https://www.rfc-editor.org/info/rfc5184>.
[RFC5881]
Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, DOI 10.17487/RFC5881, , <https://www.rfc-editor.org/info/rfc5881>.
[RFC6550]
Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. Alexander, "RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks", RFC 6550, DOI 10.17487/RFC6550, , <https://www.rfc-editor.org/info/rfc6550>.
[RFC6551]
Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., and D. Barthel, "Routing Metrics Used for Path Calculation in Low-Power and Lossy Networks", RFC 6551, DOI 10.17487/RFC6551, , <https://www.rfc-editor.org/info/rfc6551>.

Author's Address

Georgios Papadopoulos
IMT Atlantique
2 rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
France