Dear all People are complaining that the MUST 2*ETX is too strong. I agree with that. Minimal 10 has
According to this specification, Sp SHOULD be set to 2*ETX to favour shorter routes. The SHOULD opens the way to 1*ETX and that would be wrong, because implementations that do 1* and 2* ETX would not coexist well. What MUST be ensured is that the normalization function in OF0 is followed properly to enable implementations that do not compute a step of rank in a same fashion to coexist meaningfully. This is discussed in OF0 as follows: The Rank of a node is obtained by adding a strictly positive, indirectly normalized scalar, rank_increase (Section 6.1<https://tools.ietf.org/html/rfc6552#section-6.1>), to the Rank of a selected preferred parent. The rank_increase is based on a step_of_rank (Section 6.1<https://tools.ietf.org/html/rfc6552#section-6.1>) normalized scalar that can vary with a ratio from 1 (excellent) to 9 (worst acceptable) to represent the link properties. The step_of_rank can be multiplied by a configurable factor called rank_factor (Section 6.2<https://tools.ietf.org/html/rfc6552#section-6.2>) that amplifies the rank_increase to reflect the relative preferences between different link types that would be used in the same RPL Instance. RPL OF0 defines in section 6.3 of RFC 6552: DEFAULT_STEP_OF_RANK: 3 MINIMUM_STEP_OF_RANK: 1 MAXIMUM_STEP_OF_RANK: 9 RPL OF0 says in section 4.1 An implementation MUST maintain the stretched step_of_rank between the fixed constants MINIMUM_STEP_OF_RANK and MAXIMUM_STEP_OF_RANK (Section 6.3<https://tools.ietf.org/html/rfc6552#section-6.3>). This range allows the reflection of a large variation of link quality. I'd suggest that we replace: According to this specification, Sp SHOULD be set to 2*ETX to favour shorter routes. By: An implementation MUST follow OF0's normalization guidance as discussed in section 1 and 4.1 of [RFC 6552], maintaining Sp between MINIMUM_STEP_OF_RANK of 1 to indicate a great quality and MAXIMUM_STEP_OF_RANK of 9 to indicate a really poor quality, with DEFAULT_STEP_OF_RANK indicating a normal, average quality. One RECOMMENDED way to achieve this in an interoperable fashion is to set Sp to 2*ETX. What do others think? Pascal
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