Re: [Teas] Mirja Kühlewind's Discuss on draft-ietf-teas-rsvp-te-scaling-rec-06: (with DISCUSS and COMMENT)

Vishnu Pavan Beeram <vishnupavan@gmail.com> Sun, 12 November 2017 21:57 UTC

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From: Vishnu Pavan Beeram <vishnupavan@gmail.com>
Date: Sun, 12 Nov 2017 16:57:51 -0500
Message-ID: <CA+YzgTsqAyWY=gepg=moJCmDr=JDTop_sy-+SHJ8u1qn8g2jsQ@mail.gmail.com>
To: "Mirja Kuehlewind (IETF)" <ietf@kuehlewind.net>
Cc: draft-ietf-teas-rsvp-te-scaling-rec@ietf.org, TEAS WG Chairs <teas-chairs@ietf.org>, The IESG <iesg@ietf.org>, "teas@ietf.org" <teas@ietf.org>, Lou Berger <lberger@labn.net>
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Subject: Re: [Teas] =?utf-8?q?Mirja_K=C3=BChlewind=27s_Discuss_on_draft-ietf-?= =?utf-8?q?teas-rsvp-te-scaling-rec-06=3A_=28with_DISCUSS_and_COMMENT=29?=
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Mirja, Hi!

Apologize for the delayed reply.
Please see inline for responses (prefixed VPB).

Regards,
-Pavan

On Mon, Oct 16, 2017 at 6:25 AM, Mirja Kuehlewind (IETF) <
ietf@kuehlewind.net>; wrote:

> Hi Vishnu,
>
> I don’t think what you proposed is a clarification at all. RF2961 clearly
> reads to me that you should not retry any more after the Rapid retry limit
> has been reached:
>

> "Rl is the maximum number of times a message will be
>            transmitted without being acknowledged.“
>

[VPB] Yes. As per RFC2961, the retry limit (Rl) is the maximum number of
times a message will be transmitted without being acknowledged. But this
just governs the number of times you retransmit the message during the
"rapid retransmission phase". RFC2961 is silent about what happens after
the "rapid retransmission phase" is complete and this is the clarification
that is being provided here in the <scaling-rec> draft. Note that the
associated RSVP Path/Resv state doesn't get cleaned up after the "rapid
retransmission" phase is complete. So at each subsequent refresh-interval,
the unacked Path/Resv message will be sent out again (note that if there is
no change in the state, the same MESSAGE_ID would get used). This behavior
has always existed in RSVP-TE implementations -- so it is incorrect to
deduce from the "RFC 2961" text above that the retransmission of the
unacked Path/Resv will never happen after the "Rl" is reached.


> Also RFC2961 suggests an initial Rf of 500ms with 7 retries and and delta
> of 2, that means you will see the following retries:
>
> 1. after 500ms
> 2. after 1000ms
> 3. after 2000ms
> 4. after 4000ms
> 5. after 8000ms
> 6. after 16000ms
> 7. after 32000ms
>
> and then give up. While you suggests to send all 300ms section afterwards
> forever. That is not acceptable and can lead to congestion.
>

No, that is not what is being suggested.
RFC2961 suggests an Rf of 500ms with 3 retries and a delta of 2. So the
rapid retransmissions would be:
1. after 500ms
2. after 1000ms
3. after 2000ms.

With the proposal in the <scaling-rec> draft, you would try 7 times and
then stop the "rapid retransmission phase". So, what that means is that the
rapid retransmission phase lasts 31.5 seconds (first retry is after 500ms
and the seventh retry is after 32000ms). After this "rapid retransmission
phase" is complete, you keep sending the message out every 30000ms
(30seconds is not 300ms) until an acknowledgement is received.

Hope this helps.



> Mirja
>
>
>
>
> > Am 05.10.2017 um 22:27 schrieb Vishnu Pavan Beeram <
> vishnupavan@gmail.com>;:
> >
> > Mirja, Hi!
> >
> > This was discussed in my response to Elwyn. I apologize for not
> responding directly.
> >
> > RFC2961 doesn't discuss what to do with the retransmissions after the
> retry limit is reached. It doesn't discuss how retransmissions need to be
> paced after the rapid retries are stopped. Section 2.3 (ver 7) of the
> current draft clarifies this and proposes the use of a "not so rapid
> (30secs)" retransmission interval.
> >
> > There were a couple of questions from this section that you wanted to
> get discussed:
> > ----
> > (1) Why is there no termination criteria specified?
> > There is nothing new about Path and Resv messages getting transmitted
> indefinitely (this is normal soft-state signaling behavior). All that is
> being discussed in this section is how these transmissions get paced after
> the rapid retry limit is reached. The slower timer transmission will go on
> until either an ack is received (at which point the regular "refresh
> interval" comes into play) or the corresponding LSP instance state is torn
> down.
> >
> > ----
> > (2) Why couldn't the regular refresh interval be used for these un-acked
> retransmissions?
> > The primary goal of the retransmission is to eke out an acknowledgement
> from the neighbor as quickly as you can. You can use the same value as the
> the regular refresh interval provided it is small enough (like in the case
> of the conventional refresh interval of 30 secs) . However, we are
> recommending the use of a "large refresh interval" (20 mins) in the RI-RSVP
> technique -- we can't wait that long for retrying the transmission of an
> unacked message.
> >
> > Consider a rudimentary state machine with the following states (assuming
> the defaults suggested in the Appendix of the draft):
> > - first retransmit (exponential back off)
> > - second retransmit (exponential back off)
> > ...
> > - seventh retransmit (exponential back off)
> > - 30s retransmission
> > - 20m refresh (regular refresh timer)
> >
> > At any point when the Ack is received, you transition to the 20m refresh
> state.
> >
> > ---
> >
> > Do these two responses adequately answer your questions?
> >
> > Regards,
> > -Pavan
> >
> > On Thu, Oct 5, 2017 at 7:57 AM, Mirja Kuehlewind (IETF) <
> ietf@kuehlewind.net>; wrote:
> > Hi Pavan,
> >
> > I don’t see any changes in the new version that addresses may actual
> discuss on section 2.1.3 (now section 2.3). Can you please clarify?
> >
> > Thanks,
> > Mirja
> >
> >
> > > Am 28.09.2017 um 05:45 schrieb Vishnu Pavan Beeram <
> vishnupavan@gmail.com>;:
> > >
> > > Mirja, Hi!
> > >
> > > Thanks for the review. We just posted a new revision (-07) to address
> the Gen-Art review comments. Please go through the new diffs (
> https://www.ietf.org/rfcdiff?url2=draft-ietf-teas-rsvp-te-scaling-rec-07)
> and let us know if additional changes are required.
> > >
> > > Also, please go through the responses provided to the other review
> comments and let us know if there are still any unanswered questions.
> > >
> > > Regards,
> > > -Pavan
> > >
> > >
> > >
> > > On Tue, Sep 26, 2017 at 2:01 PM, Mirja Kühlewind <ietf@kuehlewind.net>;
> wrote:
> > > Mirja Kühlewind has entered the following ballot position for
> > > draft-ietf-teas-rsvp-te-scaling-rec-06: Discuss
> > >
> > > When responding, please keep the subject line intact and reply to all
> > > email addresses included in the To and CC lines. (Feel free to cut this
> > > introductory paragraph, however.)
> > >
> > >
> > > Please refer to https://www.ietf.org/iesg/stat
> ement/discuss-criteria.html
> > > for more information about IESG DISCUSS and COMMENT positions.
> > >
> > >
> > > The document, along with other ballot positions, can be found here:
> > > https://datatracker.ietf.org/doc/draft-ietf-teas-rsvp-te-scaling-rec/
> > >
> > >
> > >
> > > ----------------------------------------------------------------------
> > > DISCUSS:
> > > ----------------------------------------------------------------------
> > >
> > > I'm uncertain what section 2.1.3. actually recommends. My
> understanding is that
> > > it is recommend to still send retransmit some message even if the Rl
> was
> > > reached and to that every 30s basically forever. First of all I think
> this
> > > still needs a termination criteria when to stop to try to retransmit
> finally.
> > > And the I don't understand why this is needed, instead of e.g. just
> using a
> > > larger Rl value? Can you please clarify!
> > >
> > >
> > > ----------------------------------------------------------------------
> > > COMMENT:
> > > ----------------------------------------------------------------------
> > >
> > > I fully agree with the gan-art review (Thanks Elwyn!) and Alvaro, that
> this
> > > reads from time to time like a BCP but is actually a extension
> specification. I
> > > would strongly recommend to apply the changes proposed by the gen-art
> review,
> > > and there is also a very detailed list of nits/edits that should
> probably be
> > > applied. Please have a look at that!
> > >
> > >
> > > _______________________________________________
> > > Teas mailing list
> > > Teas@ietf.org
> > > https://www.ietf.org/mailman/listinfo/teas
> > >
> >
> >
>
>