Mediation overview

Diameter message mediation helps to solve interoperability issues. Mediation uses rules to manipulate header parts and Attribute-Value Pairs (AVPs) in incoming routable messages and peer to peer messages, when data in the message matches some specified conditions at a specified point of message processing. Tasks of the “if condition matches, then do some action” type can be solved in the most efficient way.

The Diameter Mediation feature can make the routable decisions of send reply, drop the message or set the destination-realm.

This feature extends the CAPM (Computer-Aided Policy Making) framework to allow for easy creation of Mediation rules for use in 3G, LTE and IMS networks. Mediation Rule Templates are created to define the Conditions that must be matched in a message and the Actions that are applied to modify the message on the routing decisions.

A Condition defines a part of the message that is used in the comparison, an operator for the type of comparison, and a type of data that must match the data in the message part. Two or more Conditions in the same Rule Template are collectively referred to as a Condition Set; the Condition Set are “ANDed", "ORed" or "Complex Expression" in the comparison process.
An Action can be adding, altering, or deleting AVPs; modifying the message header Version, Command-Code, or Application-ID Diameter components. Two or more Actions in a Rule Template are collectively referred to as an Action Set. The Message Copy Action is ignored if set at ATP10 (Diameter Answer message prior to be forwarded to connection).

After a Rule Template definition is complete, a Rule Set can be generated from the Rule Template. The data needed for the Conditions and the Actions is provisioned in the generated Rule Set.

A Mediation rule is an instance of the data needed for the execution of Mediation logic. The actual data needed for the Conditions and the Actions is provisioned in one or more rules in the generated Rule Set. All of the rules associated with one Mediation Rule Template are collectively referred to as the Rule Set for the Rule Template. See Rule Sets.

Rule Sets can be associated with pre-defined Request or Answer Trigger Points in the DSR message processing logic. When message processing reaches a Trigger point and the Conditions in an associated Rule Set are met, the Actions for that Rule Set are applied to the message. The changes to the message content can result in modifying the message processing behavior and the routing decision at that Trigger point in the processing logic. See Triggers.

The available Diameter Mediation Triggers are the:

Diameter Routing Function, which supports RTP1, RTP10, ATP1, ATP10 and RTP11 triggers.
Diameter Connection Function, which supports CER, CEA, DWR, DWA, DPR and DPA triggers.
Application Function, which supports RTP4, RTP6, ATP4, and ATP6 triggers.

Diameter Mediation provides a Rule Templates interface, a Rule Sets interface, and other GUI screens:

The Rule Templates interface is used primarily for the creation and modification of Rule Templates.
When the Mediation feature is activated in the system and Administrator privileges are activated for the feature, the Rule Templates folder appears under the Mediation folder in the Diameter left-hand GUI menu.

The Administrator privileges can be deactivated later, so that the Rule Templates folder does not appear under the Mediation folder. This prevents unauthorized modification of the created Rule Templates in the system.
A user, who could be designated as the Administrator, can use the Rule Templates GUI screens and other Mediation GUI screens to perform the following tasks:
- Add, edit, and delete Enumeration Types and Internal Variables that are used in creating Rule Templates (see Enumerations and Internal Variables).
- Create, modify, delete, copy, import, and export Rule Templates (see Rules Template).
- Add help text to a Rule Template; the help text will be available for the Rule Set that is generated from the Rule Template (see Rules Template).
- Associate Rule Sets with Triggers, and remove Rule Set associations with Triggers (see Triggers).
- Set the Action Error Handling property of a Rule Set (see State and Properties).
- Change the state of a Rule Template (see State and Properties)
  When a Rule Template is being created or modified, it is in the Development state.
  
  The Rule Template state can be changed from Development to Test to allow its Rule Set to be tested or to allow the Rule Template to be exported.
  
  The Rule Template state can be changed to Active to enable use of its generated Rule Set for live traffic.
  
  The Rule Template state can be changed from Test or Active back to Development to allow modification of the Rule Template (all existing rule provisioning for its associated Rule Sets will be deleted).
The Rule Sets interface is used primarily for the provisioning of rules and actual data in Rule Sets.
After a Rule Template is created and activated, the generation of the Rule Set from the Rule Template creates an entry in the Mediation Rule Sets GUI folder.
A user, who is designated as the Administrator can use the Rule Sets entries, Enumerations, Triggers, State & Properties and Internal Variables GUI screens, and other GUI screens to perform the following tasks, but cannot create, modify, copy, or export Rule Templates:
- Add a rule to a Rule Set, and provision the actual data that is used by the rule in the message matching process (see Rule Sets)
- Import/Export Rules that are provisioned in the rule templates in the "Test" or "Active" State (see Rule Sets).
- Edit and delete rules in Rule Sets (see Rule Sets)
- Delete Rule Sets (see Rule Sets)
- Change the state of a Rule Template (see State and Properties)
  The Rule Template state can be changed to Test for testing its Rule Sets or to Active for enabling its Rule Sets for use with live traffic.
  
  When Administrator privileges are deactivated, the state cannot be changed back to Development.
- Set the Action Error Handling property of a Rule Set (see State and Properties)
- Enable the Status of Rule Counters to display the Rule Counters (see State and Properties).
- Test a Rule Set
  A Diagnostics Tool is available to test Mediation rules before they are subjected to live traffic in the network. The DSR Diagnostics Tool logs the rules applied, Actions taken, and other diagnostics information when a test message is injected into the system. The tool generates traffic and sends Diameter Messages on a test connection. As a test message traverses the system, the DSR application logic generates diagnostics messages at Trigger points. The Diameter > Reports > Diagnostics Tool GUI is used to view the diagnostics log reports. See Reports in the DSR Diameter User’s Guide.
- Associate Rule Sets with Triggers, and remove Rule Set associations with Triggers (see Triggers)
- Import previously exported Rule Templates (see State and Properties)
  The state of an imported Rule Template is set to Test by default.
- View, create, edit and delete the Internal Variables that can be used in the rules (see Internal Variables)
- View, create, edit and delete the Enumeration types that can be used in the rules (see Enumerations)
- View, create, edit and delete the Vendors-specific AVPs that can be used in Rule Templates (see Vendors in the Diameter User's Guide)

Mediation-Triggered Diameter Message Copy

The Rule Template "Message Copy" Action can be defined to trigger Diameter Message Copy for messages that are processed by Diameter Mediation.

The Message Copy Action triggers Diameter Message Copy, and specifies the Message Copy Configuration Set (MCCS) that contains the Request/Answer content criteria to be used by the Message Copy function to copy the message to a DAS. The Message Copy Configuration Set specifies a Route List for the DAS. See Configuration in the DSR Diameter User’s Guide.

If Message Copy is triggered for the same message from multiple locations, the Message Copy Configuration Set for the latest Message Copy triggering prevails.

In the case of Request re-route due to invalid Result-Code, only the Message Copy Configuration Set that is associated with the Answer that completes the transaction at ATP1 is considered.

The Message Copy is performed after the completion of the original transaction. The copy of the message is not processed by the Mediation Triggering Points.