Re: [Dime] DOIC: Self-Contained OLRs

["Wiehe, Ulrich (NSN - DE/Munich)" <[e-mail]>]

Hi Susan,

let me come back to your S6a example.

The MME (C) sends a request without Destination-Host towards the HPLMN (realm). There must be an agent (A) in the HPLMN (realm) that selects the HSS (S). 
We would have two distinct DOIC associations: one between C and A, another between A and S (see figure 5 in clause 5.1). The two DOIC associations may have different supported/negotiated features. An OLR sent from S to A based on supported/negotiated features valid for the DOIC association between A and S is at least problematic (out-of context) when sent from A to C.

When the MME (C) sends a subsequent request with Destination-Host towards the HSS (S), there is no agent that selects the HSS (as the HSS is already selected). For this session there is only one DOIC association between C and S (see figure 3 in clause 5.1) and OLRs sent from S to C are not problematic.

Best regards
Ulrich


-----Original Message-----
From: ext Shishufeng (Susan) [mailto:[e-mail]] 
Sent: Monday, December 09, 2013 11:30 AM
To: Wiehe, Ulrich (NSN - DE/Munich); ext [e-mail]; ext Jouni Korhonen; Ben Campbell
Cc: [e-mail] list
Subject: RE: [Dime] DOIC: Self-Contained OLRs

Hi Ulrich,

I have different views. In any case, I think the host-type OLR should not be ignored by the clients. On the contrary, the realm-type OLR can be thought as optimization, which may not even be needed at all for all cases, especially in 3GPP. Here is an example of S6a, in the case the first attach request comes from the UE to the MME, the MME can only derive the realm information, and sends a request without Destination-Host towards the HPLMN. Since the subscriber corresponding to the UE belongs to a specific HSS, and the HSS may provide its overload report to the MME, and the MME is able to know how to react regarding the requests towards the HSS, which would be the normal case. Whether Realm report will be provided by the HSS or the agent serving the HSS is kind of optimization which may help the MME to know how to react on the requests towards the realm, not specific to the HSS.

Best Regards,
Susan

-----Original Message-----
From: Wiehe, Ulrich (NSN - DE/Munich) [mailto:[e-mail]] 
Sent: Thursday, November 28, 2013 6:30 PM
To: ext [e-mail]; ext Jouni Korhonen; Ben Campbell
Cc: [e-mail] list
Subject: Re: [Dime] DOIC: Self-Contained OLRs

Lionel,

my understanding was that _the_ reporting end point provides _the_ OLR.

If we go for two OLRs in the answer we should indicate which OLR is the actual OLR created by the reporting end point and which OLR is an additional OLR created by another node.

We have two cases:
a) The request sent by the client (reacting end point) contains no Destination Host. The agent (reporting node) (after forwarding the request to the selected server and receiving the answer) returns a realm-type OLR as the actual reporting-node-created OLR and optionally in addition a host-type OLR as learned from the selected server.  The client may ignore the additional OLR.
b) The request sent by the client (reacting endpoint) contains the Destination Host. The Server (reporting node) returns a host-type OLR as the actual reporting-node-created OLR in the answer. The agent may optionally insert a realm-type OLR as additional OLR to the answer. The client may ignore the additional OLR.

Ulrich



-----Original Message-----
From: ext [e-mail] [mailto:[e-mail]]
Sent: Thursday, November 28, 2013 10:31 AM
To: Wiehe, Ulrich (NSN - DE/Munich); ext Jouni Korhonen; Ben Campbell
Cc: [e-mail] 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:[e-mail]] De la part de Wiehe, Ulrich (NSN - DE/Munich) Envoyé : jeudi 28 novembre 2013 10:26 À : ext Jouni Korhonen; Ben Campbell Cc : [e-mail] 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:[e-mail]] On Behalf Of ext Jouni Korhonen
Sent: Wednesday, November 27, 2013 11:44 PM
To: Ben Campbell
Cc: [e-mail] list
Subject: Re: [Dime] DOIC: Self-Contained OLRs


On Nov 28, 2013, at 12:27 AM, Ben Campbell <[e-mail]> 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.
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