Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-behaviour-08
Michael Menth <menth@informatik.uni-tuebingen.de> Mon, 02 January 2012 17:59 UTC
Return-Path: <menth@informatik.uni-tuebingen.de>
X-Original-To: gen-art@ietfa.amsl.com
Delivered-To: gen-art@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 082E311E80B1 for <gen-art@ietfa.amsl.com>; Mon, 2 Jan 2012 09:59:08 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -0.801
X-Spam-Level:
X-Spam-Status: No, score=-0.801 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, HELO_EQ_DE=0.35, HELO_MISMATCH_DE=1.448]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id HKg9a2332bDh for <gen-art@ietfa.amsl.com>; Mon, 2 Jan 2012 09:59:06 -0800 (PST)
Received: from mx5.informatik.uni-tuebingen.de (mx5.Informatik.Uni-Tuebingen.De [134.2.12.32]) by ietfa.amsl.com (Postfix) with SMTP id 00A6211E80B2 for <gen-art@ietf.org>; Mon, 2 Jan 2012 09:59:05 -0800 (PST)
Received: from localhost (localhost [127.0.0.1]) by mx5.informatik.uni-tuebingen.de (Postfix) with ESMTP id 9AFB45327; Mon, 2 Jan 2012 18:58:55 +0100 (MET)
X-Virus-Scanned: amavisd-new at informatik.uni-tuebingen.de
Received: from mx5.informatik.uni-tuebingen.de ([127.0.0.1]) by localhost (mx5.informatik.uni-tuebingen.de [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id fqvEYicMucOC; Mon, 2 Jan 2012 18:58:47 +0100 (MET)
Received: from zcs-bs.informatik.uni-tuebingen.de (zcs-bs.Informatik.Uni-Tuebingen.De [134.2.12.62]) by mx5.informatik.uni-tuebingen.de (Postfix) with ESMTP id 1CF6052A2; Mon, 2 Jan 2012 18:58:46 +0100 (MET)
Received: from [192.168.1.100] (HSI-KBW-078-043-207-214.hsi4.kabel-badenwuerttemberg.de [78.43.207.214]) by zcs-bs.informatik.uni-tuebingen.de (Postfix) with ESMTP id CCEFD3457F84; Mon, 2 Jan 2012 18:58:45 +0100 (CET)
Message-ID: <4F01F054.2050301@informatik.uni-tuebingen.de>
Date: Mon, 02 Jan 2012 18:58:44 +0100
From: Michael Menth <menth@informatik.uni-tuebingen.de>
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0) Gecko/20111105 Thunderbird/8.0
MIME-Version: 1.0
To: "Joel M. Halpern" <jmh@joelhalpern.com>
References: <CAHBDyN6PN-vp9wXo6fF8G4VfODXjkfbWBaJN8EPopeWfOg9PmQ@mail.gmail.com> <4EFF838D.5020704@joelhalpern.com> <BLU0-SMTP18EE1E01EAA97CC44A44FFD8900@phx.gbl> <4F00BAFD.2070201@joelhalpern.com> <4F00CAE1.60103@gmail.com> <4F00E181.7020605@joelhalpern.com> <4F01BD58.1080303@gmail.com> <4F01E15D.6080601@informatik.uni-tuebingen.de> <4F01E6F5.5080701@joelhalpern.com>
In-Reply-To: <4F01E6F5.5080701@joelhalpern.com>
Content-Type: text/plain; charset="ISO-8859-1"; format="flowed"
Content-Transfer-Encoding: 7bit
Cc: draft-ietf-pcn-sm-edge-behaviour@tools.ietf.org, Steven Blake <slblake@petri-meat.com>, gen-art@ietf.org, Bob Briscoe <bob.briscoe@bt.com>, Tom Taylor <tom.taylor.stds@gmail.com>, David Harrington <ietfdbh@comcast.net>
Subject: Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-behaviour-08
X-BeenThere: gen-art@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: "GEN-ART: General Area Review Team" <gen-art.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/gen-art>, <mailto:gen-art-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/gen-art>
List-Post: <mailto:gen-art@ietf.org>
List-Help: <mailto:gen-art-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/gen-art>, <mailto:gen-art-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 02 Jan 2012 17:59:08 -0000
Hi Joel, hi Tom, Am 02.01.2012 18:18, schrieb Joel M. Halpern: > Michael, I am not sure what to make of your recommended text abut ECMP. > ECMP is used by almost all operators. It is generally considered a > necessary tool in the tool-kit. > More significantly, at least for the egress understanding of the > ingress, it is not even the single operator's ECMP, but other > operators selections of paths that produce the issue. So even in the > unlikely event that this operator does not use ECMP, it still is not > sufficient. Then I better leave the ECMP issue for others to answer. The definition of U can be better corrected as follows (improved rewording of my previous email): U represents the average ratio of PCN-supportable-rate to PCN-admissible-rate over all the links of the PCN-domain. -> U is a domain-wide constant which implicitly defines the PCN-supportable-rate by U*PCN-admissible-rate on all links of the PCN domain. Best wishes, Michael > > Yours, > Joel > > On 1/2/2012 11:54 AM, Michael Menth wrote: >> Hi Tom, hi Joel, >> >> I wish you a happy new year! >> >> Here are my comments to address Joel's concerns: >> >> ==================================================================== >> >> The issue with ECMP: I'd add a comment that CL and SM should not be in >> the presence of ECMP if routing information is used to determine >> ingress-egress-aggregates since this seems to be messy and error-prone. >> >> ==================================================================== >> >> The following text may clarify at the beginning of Section 3.3.2 the >> relation >> between admission control and flow termination to address one of Joel's >> comments (for both SM and CL): >> >> In the presence of light pre-congestion, i.e., in the presence of a >> small, >> positive ETM-rate (relative to the overall PCN traffic rate), new >> flows may >> already be blocked. However, in the presence of heavy pre-congestion, >> i.e., >> in the presence of a relatively large ETM-rate, termination of some >> admitted >> flows is required. Thus, flow blocking is logical prerequisite for flow >> termination. >> >> ==================================================================== >> >> The following sentence in 3.3.2 should be corrected (only SM-specific): >> >> U represents the average ratio of PCN-supportable-rate to >> PCN-admissible-rate >> over all the links of the PCN-domain. >> >> -> >> >> U represents the ratio of PCN-supportable-rate to PCN-admissible-rate >> for all >> the links of the PCN-domain. >> >> ==================================================================== >> >> I also recommend to change the following text as I think it may cause >> misinterpretations (applies both to SM and CL): >> >> If the difference calculated in the second step is positive, the >> Decision >> Point SHOULD select PCN-flows to terminate, until it determines that the >> PCN-traffic admission rate will no longer be greater than the estimated >> sustainable aggregate rate. If the Decision Point knows the bandwidth >> required by individual PCN-flows (e.g., from resource signalling used to >> establish the flows), it MAY choose to complete its selection of >> PCN-flows to >> terminate in a single round of decisions. >> >> Alternatively, the Decision Point MAY spread flow termination over >> multiple >> rounds to avoid over-termination. If this is done, it is RECOMMENDED >> that >> enough time elapse between successive rounds of termination to allow the >> effects of previous rounds to be reflected in the measurements upon >> which the >> termination decisions are based. (See [IEEE-Satoh] and sections 4.2 >> and 4.3 >> of [MeLe10].) >> >> -> >> >> If the difference calculated in the second step is positive (traffic >> rate to >> be terminated), the Decision Point SHOULD select PCN-flows to >> terminate. To >> that end, the Decision Point MAY use upper rate limits for individual >> PCN-flows (e.g., from resource signalling used to establish the >> flows) and >> select a set of flows whose sum of upper rate limits is up to the >> traffic >> rate to be terminated. Then, these flows are terminated. The use of >> upper >> limits on flow rates avoids over-termination. >> >> Termination may be continuously needed after consecutive measurement >> intervals for various >> reasons, e.g., if the used upper rate limits overestimate the actual >> flow rates. >> For such cases it is RECOMMENDED that enough time elapses between >> successive >> termination events to allow the effects of previous termination events >> to be >> reflected in the measurements upon which the termination decisions are >> based; >> otherwise, over-termination may occur. See [IEEE-Satoh] and Sections 4.2 >> and >> 4.3 of [MeLe10]. >> >> ==================================================================== >> >> [IEEE-Satoh] is not a good key for Daisuke's work as the prefix "IEEE" >> makes it look like a reference to a standards document. >> You better use [SaUe10] or [Satoh10]. Applies both to CL and SM. >> >> >> >> Best wishes, >> >> Michael >> >> >> Am 02.01.2012 15:21, schrieb Tom Taylor: >>> It shall be as you say, subject to comment from my co-authors when >>> they get back from holiday. >>> >>> On 01/01/2012 5:43 PM, Joel M. Halpern wrote: >>>> In-line... >>>> >>>> On 1/1/2012 4:06 PM, Tom Taylor wrote: >>>>> >>>>> >>>>> On 01/01/2012 2:58 PM, Joel M. Halpern wrote: >>>>>> Thank you for responding promptly Tom. Let me try to elaborate on >>>>>> the >>>>>> two issues where I was unclear. >>>>>> >>>>>> On the ingress-egress-aggregate issue and ECMP, the concern I >>>>>> have is >>>>>> relative to the third operational alternative where routing is >>>>>> used to >>>>>> determine where the ingress and egress of a flow is. To be blunt, >>>>>> as far >>>>>> as I can tell this does not work. >>>>>> 1) It does not work on the ingress side because traffic from a given >>>>>> source prefix can come in at multiple places. Some of these >>>>>> places may >>>>>> claim reachability to the source prefix. Some may not. While a given >>>>>> flow will use only one of these paths, there is no way to determine >>>>>> from >>>>>> routing information, at the egress, which ingress that flow used. >>>>>> 2) A site may use multiple exits for a given destination prefix. >>>>>> Again, >>>>>> while the site will only use one of these egresses for a given flow, >>>>>> there is no way for the ingress to know which egress it will be >>>>>> on the >>>>>> basis of routing information. >>>>>> Thus, the text seems to allow for a behavior that simply does not >>>>>> work. >>>>> >>>>> [PTT] I think the disconnect here is that you read the text to say >>>>> that >>>>> an individual node uses routing information to determine the IEA. >>>>> That >>>>> wasn't the intention. Instead, administrators use routing >>>>> information to >>>>> derive filters that are installed at the ingress and egress nodes. >>>> >>>> As far as I can tell, your response describes a situation even less >>>> effective than what I assumed. >>>> Firstly, it does not matter whether it is the edge node, the decision >>>> node, or the human administrator. Routing information is not enough to >>>> determine what the ingress-egress pairing is. The problems I describe >>>> above apply no matter who is making the decision. >>>> Secondly, having a human make the decision means that as soon as >>>> routing >>>> changes, the configured filters are wrong. >>>> >>>> I would suggest that the text in question be removed, and replaced >>>> with >>>> a warning against attempting what is currently described. >>>> >> My view is also that CL ans SM do not work in the presence of ECMP. This >> should be indicated as a warning. >> >>>>>> >>>>>> I am still confused about the relationship of section 3.3.2 to the >>>>>> behavior you describe. 3.3.2 says that as long as any excess >>>>>> traffic is >>>>>> being reported, teh decision point shall direct the blocking of >>>>>> additional flows. That does not match 3.3.1, and does not match your >>>>>> description. >>>>> >>>>> [PTT] I can't see the text in section 3.3.2 that says you continue to >>>>> block as long as any excess traffic is being reported. What I >>>>> think it >>>>> says is that as long as excess traffic is reported, the decision >>>>> point >>>>> checks to see whether the traffic being admitted to the aggregate >>>>> exceeds the supportable level. Excess traffic may be non-zero, yet no >>>>> termination may be required (i.e., traffic is below the second >>>>> threshold). >>>> >>>> I think I see what you are saying. If I am reading this correctly, the >>>> decision process must re-calculate to determine if there is >>>> termination >>>> every time it receives a report with non-zero excess and the port is >>>> already blocked. But it does not have to actually block anything. >>>> This however seems to depend upon the correct relative >>>> configuration of >>>> the limit that flips it into blocked state, the value of U, and maybe >>>> some other values. >>>> Put differently, I understand that the two are not contradictory. >>>> However, since the two things use different calculations, it is not at >>>> all clear that they are consistent. This may well be acceptable. >>>> But the >>>> difference in methods is likely to lead to confusion. So, as a minor >>>> (rather than major) comment, I would suggest that you provide >>>> clarifying >>>> text explaining why it is okay to use one condition to decide if there >>>> is blocking, but a different condition (which could produce a lower >>>> threshold) to decide how much to get rid of. >>>> >>>> Yours, >>>> Joel >>>> >>>>>> >>>>>> Yours, >>>>>> Joel >>>>>> >>>>>> On 1/1/2012 2:48 PM, Tom Taylor wrote: >>>>>>> Thanks for the review, Joel. Comments below, marked with [PTT]. >>>>>>> >>>>>>> On 31/12/2011 4:50 PM, Joel M. Halpern wrote: >>>>>>>> I am the assigned Gen-ART reviewer for this draft. For >>>>>>>> background on >>>>>>>> Gen-ART, please see the FAQ at >>>>>>>> <http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>. >>>>>>>> >>>>>>>> Please resolve these comments along with any other Last Call >>>>>>>> comments >>>>>>>> you may receive. >>>>>>>> >>>>>>>> Document: draft-ietf-pcn-sm-edge-behaviour-08 >>>>>>>> PCN Boundary Node Behaviour for the Single Marking (SM) Mode of >>>>>>>> Operation >>>>>>>> Reviewer: Joel M. Halpern >>>>>>>> Review Date: 31-Dec-2011 >>>>>>>> IETF LC End Date: 13-Jan-2012 >>>>>>>> IESG Telechat date: N/A >>>>>>>> >>>>>>>> Summary: This documents is almost ready for publication as an >>>>>>>> Informational RFC. >>>>>>>> >>>>>>>> Question: Given that the document defines a complex set of >>>>>>>> behaviors, >>>>>>>> which are mandatory for compliant systems, it seems that this >>>>>>>> ought to >>>>>>>> be Experimental rather than Informational. It describes something >>>>>>>> that >>>>>>>> could, in theory, later become standards track. >>>>>>> >>>>>>> [PTT] OK, we've wobbled on this one, but we can follow your >>>>>>> suggestion. >>>>>>>> >>>>>>>> Major issues: >>>>>>>> Section 2 on Assumed Core Network Behavior for SM, in the third >>>>>>>> bullet, >>>>>>>> states that the PCN-domain satisfies the conditions specified >>>>>>>> in RFC >>>>>>>> 5696. Unfortunately, look at RFC 5696 I can not tell what >>>>>>>> conditions >>>>>>>> these are. Is this supposed to be a reference to RFC 5559 >>>>>>>> instead? No >>>>>>>> matter which document it is referencing, please be more specific >>>>>>>> about >>>>>>>> which section / conditions are meant. >>>>>>> >>>>>>> [PTT] You are right that RFC 5696 isn't relevant. It's such a long >>>>>>> time >>>>>>> since that text was written that I can't recall what the intention >>>>>>> was. >>>>>>> My inclination at the moment is simply to delete the bullet. >>>>>>>> >>>>>>>> It would have been helpful if the early part of the document >>>>>>>> indicated >>>>>>>> that the edge node information about how to determine >>>>>>>> ingress-egress-aggregates was described in section 5. >>>>>>>> In conjunction with that, section 5.1.2, third paragraph, seems to >>>>>>>> describe an option which does not seem to quite work. After >>>>>>>> describing >>>>>>>> how to use tunneling, and how to work with signaling, the text >>>>>>>> refers to >>>>>>>> inferring the ingress-egress-aggregate from the routing >>>>>>>> information. In >>>>>>>> the presence of multiple equal-cost domain exits (which does >>>>>>>> occur in >>>>>>>> reality), the routing table is not sufficient information to make >>>>>>>> this >>>>>>>> determination. Unless I am very confused (which does happen) this >>>>>>>> seems >>>>>>>> to be a serious hole in the specification. >>>>>>> >>>>>>> [PTT] I'm not sure what the issue is here. As I understand it, >>>>>>> operators >>>>>>> don't assign packets randomly to a given path in the presence of >>>>>>> alternatives -- they choose one based on values in the packet >>>>>>> header. >>>>>>> The basic intent is that packets of a given microflow all follow >>>>>>> the >>>>>>> same path, to prevent unnecessary reordering and minimize >>>>>>> jitter. The >>>>>>> implication is that filters can be defined at the ingress nodes to >>>>>>> identify the packets in a given ingress-egress-aggregate (i.e. >>>>>>> flowing >>>>>>> from a specific ingress node to a specific egress node) based on >>>>>>> their >>>>>>> header contents. The filters to do the same job at egress nodes >>>>>>> are a >>>>>>> different problem, but they are not affected by ECMP. >>>>>>>> >>>>>>>> Minor issues: >>>>>>>> Section 3.3.1 states that the "block" decision occurs when the CLE >>>>>>>> (excess over total) rate exceeds the configured limit. However, >>>>>>>> section >>>>>>>> 3.3.2 states that the decision node must take further stapes if >>>>>>>> the >>>>>>>> excess rate is non-zero in further reports. Is this inconsistency >>>>>>>> deliberate? If so, please explain. If not, please fix. (If it is >>>>>>>> important to drive the excess rate to 0, then why is action only >>>>>>>> initiated when the ratio is above a configured value, rather than >>>>>>>> any >>>>>>>> non-zero value? I can conceive of various reasons. But none are >>>>>>>> stated.) >>>>>>> >>>>>>> [PTT] We aren't driving the excess rate to zero, but to a value >>>>>>> equal to >>>>>>> something less than (U - 1)/U. (The "something less" is because of >>>>>>> packet dropping at interior nodes.) The assumption is that (U - >>>>>>> 1)/U is >>>>>>> greater than CLE-limit. Conceptually, PCN uses two thresholds. >>>>>>> When the >>>>>>> CLE is below the first threshold, new flows are admitted. Above >>>>>>> that >>>>>>> threshold, they are blocked. When the CLE is above the second >>>>>>> threshold, >>>>>>> flows are terminated to bring them down to that threshold. In >>>>>>> the SM >>>>>>> mode of operation, the first threshold is specified directly on a >>>>>>> per-link basis by the value CLE-limit. The second threshold is >>>>>>> specified >>>>>>> by the same value (U - 1)/U for all links. With the CL mode of >>>>>>> operation >>>>>>> the second threshold is also specified directly for each link. >>>>>>>> >>>>>>>> >>>>>>>> Nits/editorial comments: >>>>>>>> >>>>>>>> >>>>>>> >>>>>> >>>>>> >>>>> >>>> >> -- Prof. Dr. habil. Michael Menth University of Tuebingen Faculty of Science Department of Computer Science Chair of Communication Networks Sand 13, 72076 Tuebingen, Germany phone: (+49)-7071/29-70505 fax: (+49)-7071/29-5220 mailto:menth@uni-tuebingen.de http://kn.inf.uni-tuebingen.de
- [Gen-art] Review: draft-ietf-pcn-sm-edge-behaviou… Joel M. Halpern
- [Gen-art] A *new* batch of IETF LC reviews - 2011… Mary Barnes
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Tom Taylor
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Joel M. Halpern
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Tom Taylor
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Joel M. Halpern
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Tom Taylor
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Michael Menth
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Joel M. Halpern
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Michael Menth
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Joel M. Halpern
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… David Harrington
- [Gen-art] Review: draft-ietf-pcn-sm-edge-behaviou… Joel M. Halpern
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Russ Housley
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Joel M. Halpern
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Tom Taylor
- Re: [Gen-art] Review: draft-ietf-pcn-sm-edge-beha… Tom Taylor
- [Gen-art] Gen-Art review of draft-ietf-sipcore-rf… Alexey Melnikov
- Re: [Gen-art] Gen-Art review of draft-ietf-sipcor… Adam Roach
- Re: [Gen-art] Gen-Art review of draft-ietf-sipcor… Alexey Melnikov