Re: [Roll] Telechat update notice: <draft-ietf-roll-trickle-mcast-11.txt>
"Adrian Farrel" <adrian@olddog.co.uk> Sun, 01 February 2015 16:55 UTC
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From: Adrian Farrel <adrian@olddog.co.uk>
To: 'Badis Djamaa' <badis.djamaa@gmail.com>
References: <20150118201333.15474.51860.idtracker@ietfa.amsl.com> <32747.1421682839@sandelman.ca> <CAPm4LDQUBUDfGcPeuj1FXy3D7ZtfEHnM7RjnU5ett7A8Moaacw@mail.gmail.com>
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Date: Sun, 01 Feb 2015 16:55:34 -0000
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Cc: 'Routing Over Low power and Lossy networks' <roll@ietf.org>
Subject: Re: [Roll] Telechat update notice: <draft-ietf-roll-trickle-mcast-11.txt>
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Hi Badis, I'm finally processing your comments on this draft before it goes in front of the IESG on Thursday. Comments in line. > Draft 11, Section 5.4. MPL Parameters states: > > MPL-TEXT: DATA MESSAGE_IMAX The maximum Trickle timer interval, as defined in > [RFC6206], for MPL Data Message transmissions. DATA_MESSAGE_IMAX > has a default value equal to DATA_MESSAGE_IMIN. > Starting from the above statement (dubbed MPL-TEXT), I have two main comments > 1) terminology related: [RFC6206] (4.1. Parameters and Variables) defines "The > maximum Trickle timer interval" as: > RFC6206-TEXT1: The maximum interval size, Imax, is described as a number of > doublings of the minimum interval size (the base-2 log(max/min)). > For example, a protocol might define Imax as 16. If the minimum > interval is 100 ms, then the amount of time specified by Imax is > 100 ms * 65,536, i.e., 6,553.6 seconds or approximately > 109 minutes. > > MPL-TEXT refers to RFC6206 for the definition of "The maximum Trickle timer > interval". However, I think "The maximum Trickle timer interval" usage in > MPL-TEXT is different than its definition in RFC6206-TEXT1. Thus, I think it > would be better to explicitly specify what is meant by "The maximum Trickle > timer interval" to avoid any ambiguity. I agree this is somewhat confusing. However, it states that Imax "is described as a number of doublings" not that Imax is a count of doublings. Sigh - we should have made this clearer in 6206. Of course, an implementation can do this however it likes, but Imax specifies an amount of time, and I think 6206 is clear about this in the text you quoted. That means that the text in this draft is also unambiguous that Imax specifies a time. > Note that the same comment is also valid for this MPL text (Draft 11, Section 5.4. > MPL Parameters ) CONTROL_MESSAGE_IMAX The maximum Trickle timer interval, > as defined in [RFC6206], for MPL Control Message transmissions. > CONTROL_MESSAGE_IMAX has a default value of 5 minutes. Same answer :-) > 2) Now arriving to the main concern, suppose that DATA_MESSAGE_IMAX > literally means the maximum trickle interval (the time specified by Imax using > RFC6206 terminology), then: "DATA_MESSAGE_IMAX has a default value equal > to DATA_MESSAGE_IMIN." in MPL-TEXT could result in a "non-wanted" behavior. > This is because RFC6206's section 4.2. Algorithm Description, rule 6 states: > RFC6206-TEXT2: 6. ...If I is equal to Imin when Trickle hears an > "inconsistent" transmission, Trickle does nothing... > Recommending "DATA_MESSAGE_IMAX has a default value equal to > DATA_MESSAGE_IMIN." makes the trickle timer always fall under RFC6206-TEXT2 > and hence the timer will never get reset when hearing "inconsistencies" > However, if this default recommendation is deliberately designed considering the > above point, then choosing a non-default value of DATA_MESSAGE_IMAX will > result in a different behavior (nodes will reset their timers when receiving > inconsistencies). This might even propagate faster than the default recommendation. > > To avoid the aforementioned ambiguities, I can think of recommending either a > default DATA_MESSAGE_IMAX equals 2*DATA_MESSAGE_IMIN or propose a > change to RFC6206-TEXT2 in the MPL draf, if the current default recommendation > is not deliberately designed to work as shown above. Otherwise, explicitly state > in the MPL text that choosing a non-default value of DATA_MESSAGE_IMAX may > result in different behavior. Well, we can come back and work on 6206, but we only have *this* document in front of us at the moment. I tripped over the IMAX==IMIN piece until reading (later in the section) the explanation... | Setting DATA_MESSAGE_IMAX to the same as DATA_MESSAGE_IMIN | in this case is acceptable since subsequent MPL Data Message | retransmissions are triggered by MPL Control Messages, where | CONTROL_MESSAGE_IMAX is greater than CONTROL_MESSAGE_IMIN. > 3) By the way, RFC6206 also contains a typo, which might confuse the reader, > in the following text (RFC6206 4.2. Algorithm Description, rule 1): > Current: > 1. When the algorithm starts execution, it sets I to a value in the > range of [Imin, Imax] -- that is, greater than or equal to Imin > and less than or equal to Imax. The algorithm then begins the > first interval. > Following the definition of the maximum interval size (RFC6206-TEXT1, > above) this rule should be rewritten > Proposed: > 1. When the algorithm starts execution, it sets I to a value in the > range of [Imin, Imin x POW(2, Imax)] -- that is, greater than or equal to Imin > and less than or equal to the time specified by Imax. The algorithm then begins > the first interval. This could be approached with an Errata Report for RFC 6206, but I think you have fixated on how Imax is expressed, rather than the fact that Imax is a time. Thanks, Adrian
- Re: [Roll] Telechat update notice: <draft-ietf-ro… Michael Richardson
- Re: [Roll] Telechat update notice: <draft-ietf-ro… Badis Djamaa
- Re: [Roll] Telechat update notice: <draft-ietf-ro… Adrian Farrel
- Re: [Roll] Telechat update notice: <draft-ietf-ro… Adrian Farrel
- Re: [Roll] Telechat update notice: <draft-ietf-ro… Badis Djamaa