Re: [RTG-DIR] [Detnet] Rtgdir last call review of draft-ietf-detnet-mpls-04

[Lou Berger <[e-mail]>]

okay, will leave it - but we generally don't provide the motivation for 
every tradeoff / design decision in IETF standards.

Lou

On 1/27/2020 10:08 AM, Carlos Pignataro (cpignata) wrote:
> Hi, Lou,
>
>> 2020/01/27 午前9:41、Lou Berger <[e-mail]>のメール:
>>
>> Hi,
>>
>> Balázs thank you for the clarification -- see below for one comment.
>>
>> On 1/10/2020 8:56 AM, Balázs Varga A wrote:
>>> Yes, but why not the Preferred CW?
>>>
>>> <Balazs>/<Stewart> Sum of mailing + proposed fixing:
>>> The PCW only supports a 16bit sequence number and it has the skip zero auto-signaling of active S/N feature.
>>> This was a problem for DetNet because:
>>> - We were worried about S/N rollover frequency in some applications and so we wanted the option of a larger S/N.
>>> - We wanted to have the option to propagate the S/N from the payload to the transport to simplify the implementation
>>> in some cases. These applications have a non-skip zero S/N. Skip zero is an irritation to implement and we should probably
>>> have signaled in in PWs.
>>> As you note in is only a preferred design for PWs, DetNet is not constrained by that and there were good reasons to adopt
>>> this alternate approach.
>>> We assume to fix this with adding above information to the text.
>>> NEW text to be added in section 4.2.1:
>>>      "This format of the d-CW was created in order (1) to allow larger S/N space to
>>>      avoid S/N rollover frequency in some applications and (2) to allow non-skip
>>>      zero S/N what simplifies implementation."
>> While I completely agree with the rational and validity of the good question, I don't think such motivation belongs in the document.  We generally don't document every design decision in a specification.  I don't feel strongly about this so if others do, I'll defer to their opinion...
>>
>> Balázs, Carlos, Do you think it should stay?
>>
> I have no strong feelings either way, but I believe if this is a departure from a “preferred” format from a BCP, then a one-liner explanation would not hurt. I’d leave this one in.
>
> Thanks,
>
> Carlos.
>
>> Thanks,
>>
>> Lou (as contributor)
>>