Re: [Roll] Retrying DCO/DAO, retry parameters

Mirja Kuehlewind <ietf@kuehlewind.net> Fri, 05 July 2019 13:32 UTC

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From: Mirja Kuehlewind <ietf@kuehlewind.net>
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Date: Fri, 05 Jul 2019 15:32:36 +0200
Cc: Rahul Arvind Jadhav <rahul.jadhav@huawei.com>, Routing Over Low power and Lossy networks <roll@ietf.org>, Alvaro Retana <aretana.ietf@gmail.com>
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To: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
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Subject: Re: [Roll] Retrying DCO/DAO, retry parameters
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Hi all,

RFC8085 recommend a maximum sending of one packet per 3 sec (if the RTT is unknown). This seems to be also a plausible mininum retry interval for your scenarios described below. Can we just add that as a requirement (as original proposed in my discuss)?

Also would be okay to define the maximum of 6 retries as a requirement?

Mirja


> On 5. Jul 2019, at 14:48, Pascal Thubert (pthubert) <pthubert@cisco.com> wrote:
> 
> Looks good to me, Rahul
> 
> All the best,
> 
> Pascal
> 
>> -----Original Message-----
>> From: Rahul Arvind Jadhav <rahul.jadhav@huawei.com>
>> Sent: vendredi 5 juillet 2019 14:30
>> To: Pascal Thubert (pthubert) <pthubert@cisco.com>
>> Cc: Routing Over Low power and Lossy networks <roll@ietf.org>; Mirja
>> Kühlewind <ietf@kuehlewind.net>; Alvaro Retana <aretana.ietf@gmail.com>
>> Subject: RE: [Roll] Retrying DCO/DAO, retry parameters
>> 
>> Can we add something like;
>> 
>> The DCO retry time should be dependent on the maximum depth of the
>> network and average per hop latency. Thus this could range from 2 sec to 120
>> seconds depending on the deployment. The number of retries could be set
>> between 2 to 6 depending upon how critical the route invalidation could be
>> for the deployment and the link layer retry configuration. For networks
>> supporting only MP2P and P2MP flows, such as in AMI and telemetry
>> applications, the 6LRs may not be very keen to invalidate routes, unless they
>> are highly memory-constrained. For home and building automation networks,
>> with P2P traffic, the 6LRs might be keen to invalidate efficiently because it
>> may additionally impact the forwarding efficiency.
>> Note that the DCO might in turn be retried at link layer if link layer supports
>> Ack for unicast packets. In such cases where link layer employs retry-
>> mechanism for unicast packets, retrying more than 3 times may not be
>> necessary, depending on link layer retry configuration.
>> 
>> Any thoughts?
>> 
>> Regards,
>> Rahul
>> 
>> 
>> -----Original Message-----
>> From: Roll [mailto:roll-bounces@ietf.org] On Behalf Of Mirja Kuehlewind
>> Sent: 04 July 2019 19:28
>> To: Pascal Thubert (pthubert) <pthubert@cisco.com>
>> Cc: Routing Over Low power and Lossy networks <roll@ietf.org>
>> Subject: Re: [Roll] Retrying DCO/DAO, retry parameters
>> 
>> I think that is also a good additional to have. I would recommend to discus
>> the boundaries in both directions: what the maximum rate I should ever to
>> for in order to not permanently overload the network and what are the usual
>> considerations to set these parameters correctly for my use case.
>> 
>> Mirja
>> 
>> 
>>> On 4. Jul 2019, at 13:22, Pascal Thubert (pthubert) <pthubert@cisco.com>
>> wrote:
>>> 
>>> You have a point there, Mirja.
>>> 
>>> UDP over LLNs may have to live with durations that are 1 to 2 orders of
>> magnitude longer than usual in more classical links these days. It can take a
>> minute and more to get a message through.
>>> 
>>> So yes, a bit of text that says that the typical latencies and turn-around-trip
>> delays observed on the Internet and the default settings that derive from that
>> may not apply in LLNs and need to be revisited depending on the link type
>> and the number of hops in case of a mesh network.
>>> 
>>> Is that what you are indicating to us?
>>> 
>>> Pascal
>>> 
>>>> -----Original Message-----
>>>> From: Mirja Kuehlewind <ietf@kuehlewind.net>
>>>> Sent: jeudi 4 juillet 2019 13:05
>>>> To: Alvaro Retana <aretana.ietf@gmail.com>; Pascal Thubert (pthubert)
>>>> <pthubert@cisco.com>
>>>> Cc: Routing Over Low power and Lossy networks <roll@ietf.org>
>>>> Subject: Re: [Roll] Retrying DCO/DAO, retry parameters
>>>> 
>>>> Hi,
>>>> 
>>>> My request wasn’t to specify this in detail for every scenario, it
>>>> was to set boundaries about what's safe to do. The 3 seconds I
>>>> mentions are the recommendation given in RFC8085, however, if you
>>>> have a good reason to use different values that possible but it would
>>>> be good to provide more reasoning then about when it is still safe to
>>>> use the values and when it should be avoided.
>>>> 
>>>> Mirja
>>>> 
>>>> 
>>>>> On 4. Jul 2019, at 12:44, Alvaro Retana <aretana.ietf@gmail.com> wrote:
>>>>> 
>>>>> On June 27, 2019 at 1:54:11 AM, Pascal Thubert (pthubert)
>>>> (pthubert@cisco.com) wrote:
>>>>> 
>>>>> Hi!
>>>>> 
>>>>>> RPL is designed to operate in very different environment, and some
>>>>>> LLNs
>>>> can be very slow, very lossy or even both. This is why RFC 6550
>>>> refrains from being too specific.
>>>>>> Maybe it is good enough to add text indicating that the values used
>>>>>> for DCO
>>>> are expected to be similar/consistent with those used in DAO?
>>>>> I agree with Pascal.  In fact, the diversity of environments not
>>>>> only makes it
>>>> very hard to be too specific, but it is one of the reasons the WG has
>>>> produced Applicability Statements for them: not all deployments are the
>> same.
>>>>> 
>>>>> Thanks!
>>>>> 
>>>>> Alvaro.
>>>>> 
>>>>> 
>>> 
>> 
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