Diameter Message Copy overview

For a message that was routed through the DSR, the Diameter Message Copy feature provides the ability to forward a copy of the Diameter Request message, and optionally the Answer message, to a Diameter Application Server (a DAS Peer). Diameter Message Copy can be triggered by a configuration or can be dictated by a DSR Application.

Diameter Message Copy copies both Diameter Request and Answer messages as directed by one or more Trigger Points within the DSR node. The Trigger Points can be any processing functions acting on the messages, including Diameter Mediation, DSR Applications, and Peer Routing Rules. Message Copy Configuration Sets define the contents and conditions on which the copy needs to be performed.

Message Copy Configuration Sets provide a mechanism for determining the messages to be copied (Request or Answer), the Result-Code/Experimental Result-Code on which the Message Copy is initiated, and number of retries to be made if the Message Copy attempt to DAS fails. The Message Copy Trigger Point must specify a Message Copy Configuration Set when the message is marked for copying.

Trigger Points mark the message ready for copy, based on the circumstances and requirements specific to the Trigger Points. The Diameter Message Copy feature determines the condition at which the copy needs to made and ensures that the copied message is delivered to DAS. A triggering condition or rule can be configured. The Trigger Points also supply a Message Copy Configuration Set to specify the conditions on which the copy needs to be initiated and the contents to be included in the Copied Message.

A copy of certain Diameter Request messages that transit a DSR network can be used for such functions as bookkeeping and verification or for offering additional services. The criteria or triggering condition to copy a Request to a DAS Peer can be simple or complex, and might be based on the presence of certain AVPs and their values in the Request message and certain Result Codes in the Answer received in response to the Request.

When a Diameter Request meeting the triggering condition is received by the DSR, the message is marked as 'ready to copy' by the entity that processes the message.

When the response to the Request (the Answer) is received, if the Answer contains the matching Result Code as specified by a Message Copy Configuration Set, the resultant action is executed - in the case of Diameter Message Copy, the action would be to copy the Request and optionally the Answer and send the Copied Message to a DAS Peer.

The Message Copy feature copies only the Diameter portion of the Request, and optionally the Answer, matching a triggering condition; the transport and IP layers are not copied. Diameter Message Copy is not a 'port mirror' that replicates everything received on the wire on a specific port to an egress port. Figure 1 depicts this message flow overview:

Diameter Message Copy Message Flow

Possible use cases for Diameter Message Copy include the following cases:

Use Case 1: A copy of all Requests that match certain basic criteria are sent to a DAS. For example, an incoming ULR over the S6a interface. In this case, the operator may wish to send a welcome SMS based on the success of the ULR. (It is assumed that the DAS has additional intelligence to distinguish an initial registration from a re-registration)
Use Case 2: A copy of all Requests that match some advanced criteria (like the presence of an application level AVP or if its value equals a pre-configured value) are sent to a DAS. For example, a Lawful Intercept server maybe in interested in the registration of a specific IMSI.
Use Case 3: A DSR Application determines the Requests to be copied to a DAS. For example, the Charging Proxy Application (CPA) marks all messages in a session that has the Called-Station-Id AVP set to a specific value in the ACR-Start message.

Message Copy Trigger Points

The Diameter Message Copy feature can be separated into a trigger action and the actual copy operation. The actual copy operation is performed by the Diameter Routing Function. The trigger action is executed either within the Diameter Routing Function or from a local DSR Application. When a Request message received by the DSR, the different tasks that could process a message can determine whether the messages should be tagged for copy.

The Diameter message to be copied can be the Request Message as it arrived at the DSR Node (Ingress Request Message) or the final processed Request message routed out of the DSR Node (Egress Request Message). The Trigger Point can determine whether the response Answer message received by the DSR (Ingress Answer Message) to the Request message also needs to be copied along with the Request message. The Trigger Point tags the message for copy and uses a Message Copy Configuration Set to convey the details and conditions for copying the message.

Each Trigger Point must specify a Message Copy Configuration Set. If there are multiple Trigger Points acting on the same message (from Mediation or PRT triggering, or both), the Message Copy Configuration Set specified by the last Trigger Point will be used (with its specified Route List).

Note: CPA still provides a Route List in place of a Message Copy Configuration Set. See Charging Proxy Application (CPA) Message Copy. Diameter Message Copy implementation ensures that CPA functioning is not affected by the introduction of the Message Copy Configuration Sets.

The copy rules and trigger actions could be implemented as described in the following examples:

The Charging Proxy Application (CPA) allows configuration of rules based on the value of the Diameter Called-Station-Id AVP in the Diameter Accounting Request (ACR) message. If CPA receives an ACR message with a value in the Called-Station-Id AVP that matches the configured rule, the Message Copy action is triggered.
A Message Copy trigger can be initiated from the Diameter Peer Routing Rules. Peer Routing Rules determine the Route List based on the characteristics of the egress Request message. The criteria configured in the Peer Routing Rules can also be used for triggering a message copy, by specifying a Message Copy Configuration Set in a Peer Routing Rule.
The Diameter Mediation feature can trigger a Message Copy, by specifying a Message Copy Configuration Set in a Rule Template Action. See Diameter Mediation User s Guide for information about rule templates.