The IESG has approved the following document: - 'The Minimum Rank with Hysteresis Objective Function' (draft-ietf-roll-minrank-hysteresis-of-11.txt) as Proposed Standard This document is the product of the Routing Over Low power and Lossy networks Working Group. The IESG contact persons are Adrian Farrel and Stewart Bryant. A URL of this Internet Draft is: http://datatracker.ietf.org/doc/draft-ietf-roll-minrank-hysteresis-of/ Technical Summary An objective function specifies how RPL [RFC6550] selects paths. Objective functions can choose paths based on routing metrics or constraints. For example, if an RPL instance uses an objective function that minimizes hop-count, RPL will select paths with minimum hop count. The nodes running RPL might use a number of metrics to describe a link or a node [RFC6551] and make it available for route selection. These metrics are advertised in RPL Destination Information Object (DIO) messages using a Metric Container suboption. An objective function can use these metrics to choose routes. The only exception is the ETX metric, which is used without the metric container as described in Section 3.5. To decouple the details of an individual metric or objective function from forwarding and routing, RPL describes routes through a value called Rank. Rank, roughly speaking, corresponds to the distance associated with a route. An objective function is responsible for computing a node's advertised Rank value based on the Rank of its potential parents, metrics, and other network properties. This specification describes MRHOF, an objective function for RPL. MRHOF uses hysteresis while selecting the path with the smallest metric value. The metric that MRHOF uses is determined by the metrics in the DIO Metric Container. For example, the use of MRHOF with the latency metric allows RPL to find stable minimum-latency paths from the nodes to a root in the DAG instance. The use of MRHOF with the ETX metric allows RPL to find the stable minimum-ETX paths from the nodes to a root in the DAG instance. MRHOF can only be used with an additive metric that must be minimized on the paths selected for routing. Working Group Summary A relatively quiet WG process with no discontent. There were several late- breaking review comments that caused the document to be recycled after WG last call, but this was not contentious. Document Quality There are several known implementations of this specification. Personnel JP Vasseur (jpv@cisco.com) is the Document Shepherd. Adrian Farrel (adrian@olddog.co.uk) is the Responsible AD
