Re: [sip-overload] draft-ietf-soc-overload-design-05
Volker Hilt <volker.hilt@alcatel-lucent.com> Wed, 20 April 2011 01:09 UTC
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Date: Tue, 19 Apr 2011 21:09:48 -0400
From: Volker Hilt <volker.hilt@alcatel-lucent.com>
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Subject: Re: [sip-overload] draft-ietf-soc-overload-design-05
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Based on the discussion in this thread, I will keep the original text of the design draft (i.e., leave the message prioritization section unchanged). Thanks, Volker On 4/19/2011 10:30 AM, ken carlberg wrote: > > On Apr 19, 2011, at 9:43 AM, DRAGE, Keith (Keith) wrote: > >> With regard to your comment on 1), I believe nothing extra is >> required. Anyone setting up multiple namespaces has to define at each >> entity that is required to understand them how they are treated in >> relationship to each other. That is part of the implementation. That >> will define which namespaces exist, and which are used at the >> receiving entity to give any form of priority handling. There is no >> reason for SIP overload to alter that relationship in any way, shape, >> or form. > > this is somewhat scenario dependent. but I don't think we are gaining > any traction, so I'll stop here. > >> On 2), I do not believe your comment is correct. The fact that a >> namespace is a pre-emption namespace is not an invitation to pre-empt >> all other calls until you get your call through, even under situations >> of no overload. It merely states that calls can be pre-empted when >> this namespace is used. The same applies for priority. Usually the >> algorithm for handling these DOES NOT SAY – handle all calls with this >> namespace until there are none left, and then move onto others. It >> deals with things like percentage of traffic and so on. So what I am >> saying is that the RPH is not a guarantee to override all other >> traffic, whether overload exists or not. > > the preemption-capable systems I've worked on in the past *must* preempt > or tear down state when there are no available resources -- either > established calls (or flows) or call/session establishment. I guess > there are various scenarios and variations of implementations that one > can consider, but I think that continues down an endless series of > possibilities that never lead to a definitive answer. > > I think the subject has been beaten to a pulp. And to a large degree, we > have gone much further into topics than perhaps was necessary. The > purpose of the suggested new next was to broaden the picture and bring > up topics that are attributed to the RPH. The only position that was > taken in the text was to suggest in the form of a "should" the use of > the first RPH (which I meant to be the first "recognized/supported" > RPH). But I conceded that i was fine to remove that position. > > I'll stop here and leave it to the co-authors/co-chairs to decide how to > proceed. > > -ken > > > >> Regards >> Keith >> ------------------------------------------------------------------------ >> *From:*ken carlberg [mailto:carlberg@g11.org.uk] >> *Sent:*19 April 2011 14:23 >> *To:*DRAGE, Keith (Keith) >> *Cc:*Janet Gunn;sip-overload@ietf.org <mailto:sip-overload@ietf.org> >> *Subject:*Re: [sip-overload] draft-ietf-soc-overload-design-05 >> On Apr 19, 2011, at 9:03 AM, DRAGE, Keith (Keith) wrote: >> >> >> My confirmation was on what Janet wrote, rather than the original text. >> Two comments. >> 1) Any statement about some specific RPH being taken as a default are >> inappropriate. If you are using RPH you must handle them in the way >> you already know. If you do not know about an RPH value, then you have >> to ignore it (and possibly delete it in the outgoing INVITE depending >> on your policy). There are certainly use cases where multiple RPH >> values can exist, covering different aspects of priority on the same >> request. It may be the second one that is received that defines the >> priority in regard to the handling in the SIP server itself (as >> opposed to priority of giving a media stream or whatever). >> or it may be the first, or the last. I'll concede the difficulty in >> stating the first "recognized/supported" RPH is the one to be used. >> But I think one is deferring the problem that arises with no position >> taken at all. The primary point that I wanted to make was that the >> possibility of multiple RPHs may exist. I'm fine with removing the >> text of choosing a default RPH in that instance. >> >> >> 2) In a case of load shedding, I suspect that the discussion on >> whether either priority or pre-emption are relevant depend on whether >> you are using them to represent the request to the original target >> server that indicated overload, or to some other server. I believe >> that in the case of representing to the original targetted server it >> is inappropriate. It is making the assumption that some of the >> existing traffic directed from this server to that server is somehow >> responsible for the overload, and that is an entirely invalid assumption. >> again, the intent of the suggested added text was to point out to the >> reader that preemption and queuing are *examples* of what has been >> defined so far with respect to Namespaces. What you have stated above >> makes a case that another Namespace should be defined, otherwise, you >> one is overloading new characteristics from what has already been >> defined. >> -ken >> >> >> Regards >> Keith >> ------------------------------------------------------------------------ >> *From:*ken carlberg [mailto:carlberg@g11.org.uk] >> *Sent:*19 April 2011 13:39 >> *To:*DRAGE, Keith (Keith) >> *Cc:*Janet Gunn;sip-overload@ietf.org <mailto:sip-overload@ietf.org> >> *Subject:*Re: [sip-overload] draft-ietf-soc-overload-design-05 >> If your comment is about the original text, then we are in some >> measure of agreement. If you agree with a position that its incorrect >> to point out the characteristics for currently defined Namespaces as >> stated in rfc4412, then we are in disagreement. >> -ken >> On Apr 19, 2011, at 6:04 AM, DRAGE, Keith (Keith) wrote: >> >> >> >> Janet’s statements about RPH align with the way I understand RPH works. >> Keith >> ------------------------------------------------------------------------ >> *From:*sip-overload-bounces@ietf.org >> <mailto:sip-overload-bounces@ietf.org>[mailto:sip-overload-bounces@ietf.org]*On >> Behalf Of*Janet P Gunn >> *Sent:*18 April 2011 19:21 >> *To:*ken carlberg >> *Cc:*sip-overload-bounces@ietf.org >> <mailto:sip-overload-bounces@ietf.org>;sip-overload@ietf.org >> <mailto:sip-overload@ietf.org> >> *Subject:*Re: [sip-overload] draft-ietf-soc-overload-design-05 >> >> >> Ken, >> >> First of all, that text is included in quite a few of the soc >> documents, so if you change it in the design doc, it will need to be >> changed in the others too. >> >> More importantly, I STRONGLY disagree with the statement that "The >> action taken is determined by the characteristics defined for the set >> of priority values of a Namespace (e.g., preemption versus queuing)". >> >> Neither "preemption" nor "queuing" are appropriate responses to a >> request for load shedding. Either the request is shed, or it is not. >> AFAIK, there is no intention to "preempt" another request, nor to >> change in the order in which the messages respond to load shedding.. >> >> In particular, in systems already deployed, SIP messages using the >> ets/wps family of namespaces (which are defined as "queuing based" , >> and do queue for MEDIA resources) receive exemption from SIP server >> overload based shedding. They do NOT have any special queuing based >> behavior for SIP server resources. Not do they preempt other SIP requests. >> >> Furthermore, the behavior associated with a particular namespace is >> highly dependant on the particular network. dsn.flash-override is not >> going to elicit any priority behavior in a civilian or public network. >> It will certainly not preempt anything. Conversely, ets.0, wps.0 is >> not going to elicit any priority behavior in the DSN network >> >> The statement "An example local policy may even include exemptions >> from network management control." introduces a new term - " network >> management control" which would need to be defined. I presume that >> what you really mean in this context is "exemption from load >> shedding". This is already covered in i) of the existing text. >> >> I fail to see the reason for your proposed statement "However, for the >> sake of simplicity, a default position should be the use of the first >> RPH entry to determine the priority of the SIP request. " AFAIK, the >> order of the headers is not generally relevant to SIP, and I do not >> see any particular need to introduce it here. Furthermore, a given SIP >> agent only "understands" certain namespaces. It seems highly >> counterproductive to suggest that a SIP server, by default, should >> "use" a namespace it doesn't understand (just because it is "first") , >> and ignore the one(s) it does understand (just because not "first"). >> >> Even if you change the statement to read "the first RPH entry it >> understands", you would need a "default behavior" to go with the >> "default namespace." >> >> As far as I am concerned, if a particular SIP server does NOT have a >> local policy for RPH (both which namespaces are relevant/understood, >> and the appropriate behavior for each namespace or combination of >> namespaces), then it should simply ignore the RPH namespaces. This >> seems consistent with generic SIP behavior with regard to namespaces >> in general. >> >> I fail to see the significance of the statement about B2BUAs. ALL SIP >> servers, (not just B2BUAs) can and will insert, delete, or change the RPH. >> >> I also fail to see the need to refer explicitly to Namespaces not >> defined in RFC4412. There are already a large number of IETF >> registered RPH namespaces which do not appear in RFC4412 (see RFC 5478 >> for example) and others have been proposed (for instance >> draft-ietf-ecrit-local-emergency-rph-namespace). If you are suggesting >> that specific networks may be using purely "private" RPH namespaces >> that have never been subject to IETF review, that may well be true in >> practice, but I don't think it should be introduced into IETF >> documents- especially ones that are not primarily about RPH. >> >> Janet >> >> This is a PRIVATE message. If you are not the intended recipient, >> please delete without copying and kindly advise us by e-mail of the >> mistake in delivery. >> NOTE: Regardless of content, this e-mail shall not operate to bind CSC >> to any order or other contract unless pursuant to explicit written >> agreement or government initiative expressly permitting the use of >> e-mail for such purpose. >> >> >> >> From: >> >> ken carlberg <carlberg@g11.org.uk <mailto:carlberg@g11.org.uk>> >> To: >> >> sip-overload@ietf.org <mailto:sip-overload@ietf.org> >> Date: >> >> 04/17/2011 03:38 PM >> Subject: >> >> [sip-overload] draft-ietf-soc-overload-design-05 >> >> ------------------------------------------------------------------------ >> >> >> >> >> Hello, >> >> in following up on the discussion point I brought up at the >> Prague-IETF meeting concerning RPH related text, I've added some >> suggested text to section 12 ofdraft-ietf-soc-overload-design-05. The >> suggested text is bound by the following tags: >> <insert text> >> </insert text> >> >> The purpose of the new text is to present a more complete picture and >> point out aspects that others following this effort should be aware >> of. I've kept the rest of the original text for that section as is >> (ie, I did not remove any original text). I've also sent the suggested >> text to Martin and James for a sanity check before posting to the list. >> >> cheers, >> >> -ken >> >> >> 12. Message Prioritization >> >> Overload control can require a SIP server to prioritize requests and >> select requests to be rejected or redirected. The selection is >> largely a matter of local policy of the SIP server, the overall >> network, and the services it provides. As a general rule, SIP server >> should prioritize requests for ongoing dialogs over requests that set >> up a new dialog. Targeting requests for ongoing dialogs may prevent >> users from modifying or terminating an ongoing dialog. >> >> While there are many factors which can affect the prioritization of >> SIP requests, the Resource-Priority header field [RFC4412] is a prime >> candidate for marking the prioritization of SIP requests. Depending >> on the particular network and the services it offers, a particular >> namespace and priority value in the RPH it could indicate i) a high >> priority request, which should be preserved if possible during >> overload, ii) a low priority request, which should be dropped during >> overload, or iii) a label, which has no impact on message >> prioritization in this network.<insert text>The action taken is >> determined by the characteristics defined for the set of priority values >> of a Namespace (e.g., preemption versus queuing) as well as the >> local policies defined for the various Namespaces supported by the >> server. An example local policy may even include exemptions from >> network management control. >> >> We note that [RFC4412] allows the presence of multiple RPH entries >> per SIP request. Local policy would determine which Namespace and >> Priority tuple are used to prioritize requests. However, for the sake of >> simplicity, a default position should be the use of the first RPH entry to >> determine the priority of the SIP request. >> >> Another scenario that should be considered is the presence of Back >> to Back User Agents (B2BUA) that may strip out the RPH from the >> upstream SIP request. Operators or Administrators may choose to >> insert their own RPH to support downstream prioritization of the SIP >> request. This RPH inserted by the B2BUA may conform to a >> Namespace set defined in [RPH4412], or it may reflect a new >> Namespace set. >> </insert text> >> >> For a number of reasons, responses should not be targeted in order to >> reduce SIP server load. Responses cannot be rejected and would have >> to be dropped. This triggers the retransmission of the request plus >> the response, leading to even more load. In addition, the request >> associated with a response has already been processed and dropping >> the response will waste the efforts that have been spent on the >> request. Most importantly, rejecting a request effectively also >> removes the request and the response. If no requests are passed >> along there will be no responses coming back in return. >> >> Overload control does not change the retransmission behavior of SIP. >> Retransmissions are triggered using procedures defined in RFC 3261 >> [RFC3261] and not subject to throttling. >> _______________________________________________ >> sip-overload mailing list >> sip-overload@ietf.org <mailto:sip-overload@ietf.org> >> https://www.ietf.org/mailman/listinfo/sip-overload >> >> >> >
- [sip-overload] draft-ietf-soc-overload-design-05 ken carlberg
- Re: [sip-overload] draft-ietf-soc-overload-design… Volker Hilt
- Re: [sip-overload] draft-ietf-soc-overload-design… ken carlberg
- Re: [sip-overload] draft-ietf-soc-overload-design… Janet P Gunn
- Re: [sip-overload] draft-ietf-soc-overload-design… ken carlberg
- Re: [sip-overload] draft-ietf-soc-overload-design… Volker Hilt
- Re: [sip-overload] draft-ietf-soc-overload-design… DRAGE, Keith (Keith)
- Re: [sip-overload] draft-ietf-soc-overload-design… Janet P Gunn
- Re: [sip-overload] draft-ietf-soc-overload-design… ken carlberg
- Re: [sip-overload] draft-ietf-soc-overload-design… ken carlberg
- Re: [sip-overload] draft-ietf-soc-overload-design… ken carlberg
- Re: [sip-overload] draft-ietf-soc-overload-design… DRAGE, Keith (Keith)
- Re: [sip-overload] draft-ietf-soc-overload-design… ken carlberg
- Re: [sip-overload] draft-ietf-soc-overload-design… Janet P Gunn
- Re: [sip-overload] draft-ietf-soc-overload-design… DRAGE, Keith (Keith)
- Re: [sip-overload] draft-ietf-soc-overload-design… ken carlberg
- Re: [sip-overload] draft-ietf-soc-overload-design… Vijay K. Gurbani
- Re: [sip-overload] draft-ietf-soc-overload-design… Janet P Gunn
- Re: [sip-overload] draft-ietf-soc-overload-design… James M. Polk
- Re: [sip-overload] draft-ietf-soc-overload-design… Janet P Gunn
- Re: [sip-overload] draft-ietf-soc-overload-design… ken carlberg
- Re: [sip-overload] draft-ietf-soc-overload-design… James M. Polk
- Re: [sip-overload] draft-ietf-soc-overload-design… Volker Hilt
- Re: [sip-overload] draft-ietf-soc-overload-design… DRAGE, Keith (Keith)