Subject: [tsvwg] WGLC on Tunnel Congestion Feedback draft - David Black's comments

From: "Black, David" <[email-masked]>
Date: Sun, 13 Nov 2016 04:50:37 +0000

Reviewing as document shepherd - the draft's generally clear.  I found a few
things that need attention beyond what's already been discussed about the
relationship to RFC 6040.

-- Technical --

Paragraph spanning pp.5-6:

   If the routers support Explicit Congestion Notification (ECN), after
   router's queue length is over a predefined threshold, the routers
   will marks the ECN-capable packets as Congestion Experienced (CE) or
   drop not-ECT packets with the probability proportional to queue
   length; if the queue overflows all packets will be dropped. If the
   routers do not support ECN, after router's queue length is over a
   predefined threshold, the routers will drop both the ECN-capable
   packets and the not-ECT packets with the probability proportional to
   the queue length. It's assumed all routers in the tunnel support ECN.

"will marks" ->  "mark" 
"proportional" -> 'based on" (twice)
	(don't want to imply strict linear proportionality)

Last sentence should no longer be correct for this draft.  Remove it
or change "assumed" to "preferred".

Second paragraph on p.6 is where the changes need to be made to
align with RFC 6040, as already discussed on the list.

p.8: I don't understand this sentence:

   SCTP allows partially reliable
   delivery [RFC3758], which ensures the feedback message will not be
   blocked in case of packet loss due to network congestion.

Is this draft recommending use of  SCTP partial reliability for tunnel
congestion feedback?  If so, that needs to be stated.

Section 5: How does IPFIX report packet losses within the tunnel, and/or
how does the controller or ingress calculate that?  This is an important
input to congestion measurement and management in addition to
the ECN marking counts.

-- Editorial --

p.3 -  "inner" is not the best word, as it typically refers to the inner IP header.
I suggest rephrasing:

OLD
   In order to perform congestion management at ingress, the ingress
   must first obtain the inner tunnel congestion level information.
NEW
   In order to perform congestion management at ingress, the ingress
   must first obtain information about the level of congestion within
   the tunnel.

In the next paragraph, just remove the word "inner" from:

   This document provides a mechanism of feeding back inner tunnel
   congestion level to the ingress.

Last sentence in 3.1:

   The ingress here will act as both the decision point that
   decides how to do congestion management and the action point that
   implements congestion management decision.

Add "(AP)" after "the action point" to expand the acronym in the diagram.

Last sentence in Section 4:

   The counting
   can also be at the granularity of individual customer's traffic or a
   specific set of flows to learn about their congestion contribution.

Please say that the means of configuring packet counting to count only
specific flows is not discussed in this document.

p.8: I don't understand this sentence:

   SCTP allows partially reliable
   delivery [RFC3758], which ensures the feedback message will not be
   blocked in case of packet loss due to network congestion.

Is this draft recommending use of  SCTP partial reliability for tunnel
congestion feedback?  If so, that needs to be stated.

Section 5: How does IPFIX report packet losses within the tunnel, and/or
how does the controller or ingress calculate that?  This is an important
input to congestion measurement and management in addition to
the ECN marking counts.

Thanks, --David
--------------------------------------------------------
David L. Black, Distinguished Engineer
Dell EMC, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953     Cell: +1 (978) 394-7754
[email-masked]  <=== NEW ===
--------------------------------------------------------

---

From: "Weixinpeng (Jackie)" <[email-masked]>
Date: Sun, 13 Nov 2016 11:16:29 +0000

Hi David,
    Thanks for your comments and suggestions, I will take the comments and suggestions into considerations in the next version.

Regards,
-Xinpeng (Jackie) 
________________________________________
发件人: tsvwg [[email-masked]] 代表 Black, David [[email-masked]]
发送时间: 2016年11月13日 12:50
收件人: [email-masked]
主题: [tsvwg] WGLC on Tunnel Congestion Feedback draft - David Black's    comments

-- Technical --

"will marks" ->  "mark"

-- Editorial --

OLD

Last sentence in 3.1:

   The counting

Thanks, --David