Hello Yatch > > (1) Rank Computation > > RFC 8180 says: > > rfc8180> 5.1.1. Rank Computation > rfc8180> (...) > rfc8180> Sp SHOULD be calculated as (3*ETX)-2. The minimum value of Sp > rfc8180> (MINIMUM_STEP_OF_RANK) indicates a good quality link. The > rfc8180> maximum value of Sp (MAXIMUM_STEP_OF_RANK) indicates a poor > rfc8180> quality link. The default value of Sp (DEFAULT_STEP_OF_RANK) > rfc8180> indicates an average quality link. Candidate parents with ETX > rfc8180> greater than 3 SHOULD NOT be selected. > > https://tools.ietf.org/html/rfc8180#section-5.1.1 > > MAXIMUM_STEP_OF_RANK is defined to 9. Why? > [PT>] This is defined in OF0. 9 denotes a worst possible quality that is still acceptable and makes it equivalent to 9 hops at the best quality for that technology. The number enables 7 hops at the worst rank factor (4) and with the worst quality.
> Sp is calculated as (3 * ETX) - 2 and the worst acceptable ETX is 3. It looks > like 7 is > the possible largest value of Sp... > [PT>] True, so we never reach 9 and stay compatible with OF0. I guess the max ETX of 3 is arbitrary, we could have gone up to 11/3... > (2) Trickle Timer > > RFC 8180 says: > > rfc8180> 5.3. Trickle Timer > rfc8180> (...) > rfc8180> For this specification, the Trickle timer MUST be used with the > rfc8180> RPL-defined default values (see Section 8.3.1 of [RFC6550]). > > https://tools.ietf.org/html/rfc8180#section-5.3 > > So, Imin for DIO Trickle timer starts with 8 ms, which looks too short for the > minimal TSCH schedule where one shared cell in a slotframe of 1.01s. This > setting could cause congestion by DIO traffic... > > Why is this default value (DEFAULT_DIO_INTERVAL_MIN) reasonable for the > 6TiSCH minimal configuration...? [PT>] [PT>] I agree that this needs discussion. Note that the minimal schedule of 1.01s is just an example. The initial value of I (see RFC 6206) is between Imin and Imax. With the default, that is between 8ms and 2.3 hours. Hopefully I is not always 8ms! The DIO will not fire before I/2. I agree we should use a somewhat higher Imin, but then that pushes Imax to the say and I may be set to that. IOW I'd have liked to restraint the initial setting of I to something in between, like between a few seconds and a few minutes while keeping Imax to 2^20 times Imin. Take care, Pascal > _______________________________________________ > 6tisch mailing list > 6tisch@ietf.org > https://www.ietf.org/mailman/listinfo/6tisch _______________________________________________ 6tisch mailing list 6tisch@ietf.org https://www.ietf.org/mailman/listinfo/6tisch
