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' <[email protected]>; [email protected] > 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 > > [email protected] > > https://www.ietf.org/mailman/listinfo/6tisch _______________________________________________ 6tisch mailing list [email protected] https://www.ietf.org/mailman/listinfo/6tisch
