Hi Pascal, pascal> Maybe we could amend/ERRATA the RFC to recommend different settings.
It'd be nice to have some amendment or an errata entry for the following sentence. rfc8180> (5.3. Trickle Timer, RFC 8180) 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]). At least, "MUST" in this sentence should be replaced with something, in my opinion. Best, Yatch > On Aug 27, 2018, at 17:45, Pascal Thubert (pthubert) <pthub...@cisco.com> > wrote: > > Starting a discussion on your last point, Yatch: > > RFC 6206 says: > > " > Finally, a protocol SHOULD set k and Imin such that Imin is at least > two to three times as long as it takes to transmit k packets. > " > By default k n RPL is set to very conservative > DEFAULT_DIO_REDUNDANCY_CONSTANT of 10, so there is not suppression unless > there is a high density. > So with the 1.01s slotframe, RFC 6206 recommends that Imin should be 20 to 30 > seconds... > > Maybe we could amend/ERRATA the RFC to recommend different settings. > > What do others think? > > Pascal > >> -----Original Message----- >> From: Pascal Thubert (pthubert) >> Sent: lundi 27 août 2018 17:29 >> To: 'Yasuyuki Tanaka' <yasuyuki.tan...@inria.fr>; 6tisch@ietf.org >> Subject: RE: [6tisch] Questions on RPL Settings in RFC 8180 >> >> 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 >>> rfc8180> 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 >>> rfc8180> ETX 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 >>> rfc8180> the 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
