Route Selection
The route selection process and its usage in retries are as follows:
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There is no requirement for the service to send Destination-Host and Destination-Realm AVPs in CCR.
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When there are no Destination fields in a message from the SMF service, the diameter endpoint evaluates the Destination-Host and Destination-Realm from the host selection profile. It associates with the passed client profile in the request.
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Host selection profile has a mandatory primary and an optional secondary host-realm pair. While realm is an optional CLI, it sets to a default value.
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The host and realm serve as an input to the route search algorithm to find possible multiple matching routes. The order depends on the flag and weight.
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Select the peer of the highest ordered active route to send a message. While on delivery failure and on retries configuration, the next route in the sequence is chosen to deliver the message.
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When the found routes run through due to failures and higher retry count, it fetches the secondary host to find the next set of ordered routes.
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When there are no or failed routes, it drops the request and the service responds accordingly.
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In the absence of host selection profile configuration, the peer management module selects and sorts all the active routes in the route table.
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For a subsequent CCR-U and CCR-T requests, the service populates a message with Destination-Host and Destination-Realm. It captures the details from the Origin-Host and Origin-Realm respectively from the CCA-I response.
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In CCR-U and CCR-T requests, for service with the existing Destination-Host and Destination-Realm, it skips the host selection logic.