[Dime] [dime] #70 (draft-ietf-dime-ovli): Appendix B - Example

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#70: Appendix B - Example

 In the example included in Appendix B, it is considered that the Agent
 reports Host overload directly back to the Client, when the Client request
 was for the Realm, withouth Destination Host (or direct connection).
 I do not agree about this behaviour.
 Agent will provide Host overload to the Client only when the request was
 sent to one specific host.

 Example shall be modified.

 Proposed modification:


         Client     Agent      S1        S2        S3
            |         |         |         |         |
            |(1) Request (DR:realm)       |         |
            |-------->|         |         |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |Agent selects S1   |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |(2) Request (DR:realm)       |
            |         |-------->|         |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |         |S1 overloaded, returns OLR
            |         |         |         |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |(3) Answer (OH:S1,OLR:RT=DH)
            |         |<--------|         |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |sees OLR,routes next DR traffic to S2&S3
            |         |         |         |         |
            |(5) Request (DR:realm)       |         |
            |-------->|         |         |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |Agent selects S2   |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |(6) Request (DR:realm)       |
            |         |------------------>|         |
            |         |         |         |         |
            |         |         |         |         |
            |         |         |         |S2 is overloaded...
            |         |         |         |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |(7) Answer (OH:S2, OLR:RT=DH)|
            |         |<------------------|         |
            |         |         |         |         |
            |         |         |         |         |
            |         |Agent sees OLR, realm now overloaded
            |         |         |         |         |
            |         |         |         |         |
            |         |         |         |         |
            |(8) Answer (OLR: RT=R)
            |<--------|         |         |         |
            |         |         |         |         |
            |         |         |         |         |
            |Client throttles DR:realm
            |         |         |         |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |         |         |         |
            |         |         |         |         |



       Figure 8: Mix of Destination-Host and Destination-Realm Routed
                                  Requests

    1.  The client sends a request with no Destination-Host AVP (that is,
        a Destination-Realm routed request.)

    2.  The agent follows local policy to select a server from its peer
        table.  In this case, the agent selects S2 and forwards the
        request.

    3.  S1 is overloaded.  It sends an answer indicating success, but also
        includes an overload report.  Since the overload report only
        applies to S1, the ReportType is "Destination-Host".

    4.  The agent sees the overload report, and records that S1 is
        overloaded by the value in the Reduction-Percentage AVP.  It
        begins diverting the indicated percentage of realm-routed traffic
        from S1 to S2 and S3.

    5.  The client sends another Destination-Realm routed request.

    6.  The agent selects S2, and forwards the request.

    7.  It turns out that S2 is also overloaded, perhaps due to all that
        traffic it took over for S1.  S2 returns an successful answer
        containing an overload report.  Since this report only applies to
        S2, the ReportType is "Destination-Host".

    8.  The agent sees that S2 is also overloaded by the value in
        Reduction-Percentage.  This value is probably different than the
        value from S1's report.  The agent diverts the remaining traffic
        to S3 as best as it can, but it calculates that the remaining
        capacity across all three servers is no longer sufficient to
        handle all of the realm-routed traffic.  This means the realm
        itself is overloaded.  The realm's overload percentage is most
        likely different than that for either S1 or S2.
        The agent generates a new report for the realm of
        "realm", and inserts that report into the answer.  The client
        throttles requests with no
        Destination-Host AVP at requested rate.

-- 
-------------------------------------+-------------------------------------
 Reporter:                           |      Owner:  draft-ietf-dime-
  [e-mail]  |  [e-mail]
     Type:  defect                   |     Status:  new
 Priority:  minor                    |  Milestone:
Component:  draft-ietf-dime-ovli     |    Version:
 Severity:  Active WG Document       |   Keywords:
-------------------------------------+-------------------------------------

Ticket URL: <http://trac.tools.ietf.org/wg/dime/trac/ticket/70>
dime <http://tools.ietf.org/wg/dime/>