Re: [6tisch] Questions on RPL Settings in RFC 8180
"Pascal Thubert (pthubert)" <pthubert@cisco.com> Wed, 05 September 2018 07:04 UTC
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From: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
To: Yasuyuki Tanaka <yasuyuki.tanaka@inria.fr>
CC: "6tisch@ietf.org" <6tisch@ietf.org>
Thread-Topic: [6tisch] Questions on RPL Settings in RFC 8180
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Date: Wed, 05 Sep 2018 07:04:28 +0000
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Subject: Re: [6tisch] Questions on RPL Settings in RFC 8180
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Agreed, Yatch. Can the authors have a look and propose a resolution? Then we'll see how to publish the fix. Many thanks Pascal > -----Original Message----- > From: Yasuyuki Tanaka <yasuyuki.tanaka@inria.fr> > Sent: mardi 28 août 2018 10:56 > To: Pascal Thubert (pthubert) <pthubert@cisco.com> > Cc: Yasuyuki Tanaka <yasuyuki.tanaka@inria.fr>; 6tisch@ietf.org > Subject: Re: [6tisch] Questions on RPL Settings in RFC 8180 > > 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) <pthubert@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.tanaka@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 > >>> rfc8180> (DEFAULT_STEP_OF_RANK) indicates an average quality link. > >>> rfc8180> Candidate parents with 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] Questions on RPL Settings in RFC 8180 Yasuyuki Tanaka
- Re: [6tisch] Questions on RPL Settings in RFC 8180 Pascal Thubert (pthubert)
- Re: [6tisch] Questions on RPL Settings in RFC 8180 Pascal Thubert (pthubert)
- Re: [6tisch] Questions on RPL Settings in RFC 8180 Yasuyuki Tanaka
- Re: [6tisch] Questions on RPL Settings in RFC 8180 Pascal Thubert (pthubert)
- Re: [6tisch] Questions on RPL Settings in RFC 8180 Yasuyuki Tanaka
- Re: [6tisch] Questions on RPL Settings in RFC 8180 Pascal Thubert (pthubert)