Re: [Dime] DOIC: Self-Contained OLRs

Maria Cruz Bartolome <maria.cruz.bartolome@ericsson.com> Mon, 02 December 2013 15:57 UTC

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From: Maria Cruz Bartolome <maria.cruz.bartolome@ericsson.com>
To: "dime@ietf.org" <dime@ietf.org>
Thread-Topic: [Dime] DOIC: Self-Contained OLRs
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Date: Mon, 2 Dec 2013 15:57:36 +0000
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Subject: Re: [Dime] DOIC: Self-Contained OLRs
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Dear all,

About self-contained OLRs, I agree with Nirav, Lionel and JJ.
Duplication of information should be avoided, once we have considered piggybacking as the overload info conveyance mechanism.

Best regards
/MCruz


-----Original Message-----
From: DiME [mailto:dime-bounces@ietf.org] On Behalf Of TROTTIN, JEAN-JACQUES (JEAN-JACQUES)
Sent: viernes, 29 de noviembre de 2013 16:05
To: dime@ietf.org
Subject: Re: [Dime] DOIC: Self-Contained OLRs

Dear all

In the baseline mechanism as currently defined in the draft, the OLR content is simple, and is related to the message conveying it in particular application  origin host/realm and destination to which the OLR is sent back. As Lionel indicated, it is not so important to know which node inserts the OLR or to have other information.
 
There is a performance aspect to consider: the OLRs defined in the baseline  may be frequently sent  (in particular to compensate possible message losses and to manage the loopback to the reporting node ensuring the quick convergence towards the optimal throughput). So we have to minimize the processing of these OLRs. As OLRs are piggybacked  in the relevant messages,  they may be simply forwarded in the same message by the DAs on the path except if there are particular reasons a DA to act on them.  

I am cautious about duplication of information, it always means additional checks to ensure consistency. If  the OLR has  an application id and origin host  different from the message conveying it, what to do with this OLR, is it an error case? or should it be put in another message in the path? Our current piggybacking mechanism allows the OLR to remain in the same message from the reporting node to the reacting node. 

An important  point is extensibility, as we may have to introduce other type of OLRs, additional AVPs, more sophisticated processing, but these extensions  should not impact the baseline mechanism by making the baseline more complex. the current draft allows extensions without impacting the baseline.

Currently I do not see drawbacks on the OLRs defined for the baseline mechanism. So my comments join the Nirav and Lionel's ones.

Best regards 

JJacques 


-----Message d'origine-----
De : DiME [mailto:dime-bounces@ietf.org] De la part de lionel.morand@orange.com Envoyé : vendredi 29 novembre 2013 15:32 À : Nirav Salot (nsalot); Jouni Korhonen; Wiehe, Ulrich (NSN - DE/Munich); dime@ietf.org list Cc : Ben Campbell Objet : Re: [Dime] DOIC: Self-Contained OLRs

I totally agree with Nirav. No need to revert at this stage the working assumption on piggybacking of OLR in application answer messages, especially when the aim is to define a basic mechanism called "reduction".

Anyone would be able to further add extra info for optimization if needed but there is no need at all for the basic mechanism.

Regards,

Lionel

-----Message d'origine-----
De : DiME [mailto:dime-bounces@ietf.org] De la part de Nirav Salot (nsalot) Envoyé : vendredi 29 novembre 2013 12:24 À : Jouni Korhonen; Wiehe, Ulrich (NSN - DE/Munich); dime@ietf.org list Cc : Ben Campbell Objet : Re: [Dime] DOIC: Self-Contained OLRs

Jouni, Ben,

I am totally against the idea of self-contained OC-OLR specifically since we have adopted the principles of piggybacking the OC-OLR over existing application message.
Self-contained OC-OLR - which means adding all the information which defines the scope of the OC-OLR into the OC-OLR - does not make sense in the piggybacking approach. In fact, it is adding lot of information, which is anyway available within the message containing the OC-OLR, into the OC-OLR. So it is adding lot of redundant information in a message which increases the processing requirement for the sender as well as the receiver. (And this is un-optimization, in my view).

Besides, I am not convinced with the other reasons provided here:
- One software module within a node can provide OC-OLR to another software module in the same node without passing other related info
   Within a node, based on the design, lots of information may need to be passed between two software modules and we cannot optimize those aspects by replicating unnecessary information in a protocol message.
   In summary, it is node's internal software design issue and we need not optimize that at protocol level.

- Once the reporting node realizes that it is overloaded, it has to wait for right answer to send OC-OLR
  What is the point of sending OC-OLR for a context for which there is no messaging? Why should the reacting node care if it never sends a message for a context for which the reporting node is overloaded?
  So this waiting is justified since it ensures that the overload is reported only when necessary and only to the applicable reacting node. Not to all the nodes in the network.

- The agent needs to wait for the answer generated by the server and the right context
   The same argument as applicable for the server applies here. The agent need not send out-of-context overload info to a node.
   Why should reacting node receive/process/store the overload info for the scope for which it is not sending any messages.

- For sending OC-OLR in dedicated Diameter application???
  Piggybacking was the first basic principle we agreed before putting other principles in place. So we may want to go back the drawing board if we decide to change this principle.

Regards,
Nirav.

-----Original Message-----
From: DiME [mailto:dime-bounces@ietf.org] On Behalf Of Jouni Korhonen
Sent: Friday, November 29, 2013 2:50 PM
To: Wiehe, Ulrich (NSN - DE/Munich); dime@ietf.org list
Cc: Ben Campbell
Subject: Re: [Dime] DOIC: Self-Contained OLRs



So, are we reaching any level of consensus here?

- JOuni

(as a note.. that we are converging back to where we started with OLRs ;)



On Nov 28, 2013, at 12:40 PM, "Wiehe, Ulrich (NSN - DE/Munich)" <ulrich.wiehe@nsn.com>; wrote:

> Hi,
> 
> another question:
> 
> If we go for explicit self contained OLRs, why would we then need the ReportType?
> 
> The realm-type OLR would explicitly contain application-Id, Realm, but no Host whereas the host-type OLR would explicitly contain application-Id, Host, but probably (I'm not sure) no Realm.
> 
> Ulrich
> 
> 
> 
> -----Original Message-----
> From: ext lionel.morand@orange.com [mailto:lionel.morand@orange.com]
> Sent: Thursday, November 28, 2013 10:31 AM
> To: Wiehe, Ulrich (NSN - DE/Munich); ext Jouni Korhonen; Ben Campbell
> Cc: dime@ietf.org list
> Subject: RE: [Dime] DOIC: Self-Contained OLRs
> 
> Hi,
> 
> There is no assumption on which entity is providing the realm overload status. It could be provided an agent inserting this info in answers received from a server behind but also from a server that would know this info by some internal magic.
> But in any case, if we assume that the client will received a successful answer from the server for an initial request with only Dest-Realm AVP, it should be possible to have both report types in the answer: one for the server itself, one for the realm for new request sent to the realm with only Dest-Realm AVP.
> 
> Lionel
> 
> -----Message d'origine-----
> De : DiME [mailto:dime-bounces@ietf.org] De la part de Wiehe, Ulrich 
> (NSN - DE/Munich) Envoyé : jeudi 28 novembre 2013 10:26 À : ext Jouni 
> Korhonen; Ben Campbell Cc : dime@ietf.org list Objet : Re: [Dime]
> DOIC: Self-Contained OLRs
> 
> Hi,
> 
> I don't see how the possibility to send more than one OLR in an answer is aligned with the "endpoint principle". If the ReportType is "realm" this indicates to the reacting end point that the reporting end point is an agent (e.g. SFE) rather than a server. If the ReportType is "host" this indicates to the reacting end point that the reporting end point is a server. How can the reporting end point be both agent and server?
> 
> Ulrich
> 
> -----Original Message-----
> From: DiME [mailto:dime-bounces@ietf.org] On Behalf Of ext Jouni 
> Korhonen
> Sent: Wednesday, November 27, 2013 11:44 PM
> To: Ben Campbell
> Cc: dime@ietf.org list
> Subject: Re: [Dime] DOIC: Self-Contained OLRs
> 
> 
> On Nov 28, 2013, at 12:27 AM, Ben Campbell <ben@nostrum.com>; wrote:
> 
>> Hi,
>> 
>> I mentioned in another thread that I prefer putting an explicit 
>> ReportType AVP in an OLR, rather than
> 
> The more I spent time thinking/writing the actual procedures on the 
> endpoints, the more it makes sense to me to keep the ReportType in the 
> OC-OLR. Even if the baseline does not have agent overload etc, the 
> ReportType fits well to the "endpoint principle" we have in the draft.
> It indeed gives more tools to make a host vs. realm base decision on the reacting node and is plain more clear.
> 
> I skip the rest of the mail.. too much text ;-)
> 
> 
> - Jouni
> 
> 
> 
> 
> 
>> making a responding node infer the type or meaning of the OLR from a Diameter request that corresponds to the answer containing the OLR. My reasons for that go beyond just ReportType, so I'm starting a separate thread.
>> 
>> As currently described, a consumer of an OLR must infer several things from other context. In most cases, that context is in the Diameter answer that carries the OLR. For example, the OLR implicitly refers to the application identified by the Application-Id field of the enclosing answer, the realm identified by Origin-Realm, and so on. This means that the "meaning" of an OLR cannot be determined from the OLR contents alone; OLRs only have meaning in the context of the enclosing answer. If you moved an OLR from one answer to another, it's meaning may change completely.
>> 
>> I think this approach is a mistake. I would greatly prefer that we explicitly include such values in the OLR itself, for multiple reasons:
>> 
>> 1) It's more complex to interpret implicit, contextual values than explicit values. The consumer cannot simply look at the OLR; it must look in various other AVPs to find all the information it needs. For example, I think a common software design for overload control processing to be separated from application processing. The consumer cannot simply hand the OLR to that module and expect things to work. The OC module must not only parse the OLR, but parse any other AVPs that are relevant. As OLR contents get extended (assumedly following the same strategy as the base spec), the number of "context" avps that must be interpreted can grow large. This approach is error prone, and will likely encourage brittle, hard-to-maintain code. Self-contained OLRs would keep all the information related to overload in one place. making for simpler implementations.
>> 
>> 2) It's more complex for the reporting node to send implicit values than explicit values. The sender cannot simply set the context to match the OLR--all those other AVPs have application or protocol layer meanings. Once a reporting node realizes that it is overloade, it has to wait for the right answer that contains the right context before it can send the OLR. This is particularly troublesome for agents, since they will typically have to insert OLRs into answers created by other nodes. 
>> 
>> If the reporting node screws this up, the meaning of the OLR may change significantly. So again, implicit meaning gives us error prone implementations. Self-contained OLRs are simpler to create and send.
>> 
>> 3) Implicit values don't work at all for certain problems. For 
>> example, if an agent needs to originate an OLR, it typically needs to 
>> insert that OLR into an existing Diameter answer created by a server.
>> It can't create its own answer without affecting the application 
>> state. If the responding node assumes the OLR comes from or refers to 
>> the node identified by the Origin-Host AVP in the enclosing answer, 
>> things break. (For examples of when an agent needs to send OLRs that 
>> are distinct from those sent by a server, see Steve's agent overload 
>> draft, or my dh/dr example.)
>> 
>> OTOH, explicit values will work for all cases where we need to associate some arbitrary value with an OLR.
>> 
>> 4) Implicit values seriously constrain the future evolution of Diameter OC standards. For example, lets say we find a good reason to allow OLRs to be sent out of band, or be sent in a dedicated Diameter application. If overload reports were self-contained, one could just reuse the report format we specify here. But if the meaning of an OLR depends on the way it's transported, this won't work. We would have to create a new or significantly modified OLR format if we found a need to transport OLRs in different ways. Self-contained OLRs would allow much greater flexibility.
>> 
>> So, in summary, I think that self-contained OLRs would lead to simpler implementations, less brittle deployments, and more flexibility for future evolution of standards.
>> 
>> Thanks!
>> 
>> Ben.
>> _______________________________________________
>> DiME mailing list
>> DiME@ietf.org
>> https://www.ietf.org/mailman/listinfo/dime
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