Remote BUSY Congestion

Note:

Remote BUSY Congestion is not supported for RADIUS.

The Remote BUSY Congestion feature can be used per Connection to reduce the amount of message traffic sent to a Diameter Connection when an adjacent Diameter Peer Node is unable to process messages as fast as they are sent to it on the Connection.

Note:

The User Configured Message Priority feature is a prerequisite for the Remote BUSY Congestion feature.

A Connection is considered congested or BUSY if the following conditions exist:

An Answer message containing Diameter_TOO_BUSY Result Code is received on the Connection
The Answer message was originated by the Peer Node (the Origin-Host of the Answer message is the same as the Connections Peer FQDN.

The status is set to BUSY only for the Connection of a Peer on which DIAMETER TOO BUSY is received. The other Connections between the diameter signaling router and the Peer might or might not be BUSY.

Remote BUSY Congestion applies only to adjacent nodes. If the node which initiated the DIAMETER_TOO_BUSY, as determined by the Origin-Host AVP value, is not a Peer Node, then the DIAMETER_TOO_BUSY is ignored.

Message traffic reduction is managed through the use of four Remote BUSY Congestion Levels: CL-0. CL-1, CL-2, and CL-3, where CL-0 indicates no congestion and CL-3 is the highest level of congestion.

A Remote BUSY Congestion Level for a Connection is determined from the Priority of the egress transactions rejected by a DIAMETER_TOO_BUSY response. When a transaction of Priority X is rejected by a DIAMETER_TOO_BUSY on a Connection whose Remote BUSY Congestion Level is X or smaller, then the Remote BUSY Congestion of the Connection is set to a value that prevents the Diameter Routing Function from sending subsequent transactions of the same or lower Priority than the rejected transaction (in this case, the Remote BUSY Congestion Level is set to X+1). For example, if a DIAMETER_TOO_BUSY response is received for a Priority 1 transaction, then the Remote BUSY Congestion Level is set to CL-2 to prevent subsequent transactions of Priority 1 and lower from being forwarded on the Connection.

Whenever the Remote BUSY Congestion Level is increased, Remote BUSY Congestion abatement is re-started, using the configured Remote Busy Abatement Timeout value. When the Remote Busy Abatement Timeout expires, the Congestion Level is decremented by 1, allowing transactions with the next lower Priority to be forwarded on the Connection; the Remote Busy Abatement Timeout is restarted. This process continues until the Congestion Level of the Connection drops back to CL-0.

Whenever the Remote BUSY Congestion Level is increased, Remote BUSY Congestion abatement is re-started by starting the Remote BUSY Congestion Abatement Timer. When the Remote Busy Abatement Timeout expires, the Congestion Level is decremented by 1, thus allowing transactions with the next lower Priority to be forwarded on the Connection; and the Remote Busy Abatement Timeout is restarted. This process continues until the transactions of the Connection drop back to CL-0.

Because Remote BUSY Congestion is detected by inspecting the Result-Code AVP embedded in an Answer response, detection is performed by the Diameter Routing Function.

Except for Remote BUSY Congestion detection, the Diameter Transport Function is responsible for handling all of the tasks associated with Remote BUSY Congestion, such as:

Managing the Remote BUSY Congestion Level
Managing Remote BUSY abatement
Updating the Connection Priority Level (CPL) for the Connection
Keeping OAM informed of the Remote BUSY Congestion status

When the Diameter Routing Function determines that the Remote BUSY Congestion Level needs to be increased, it notifies the Diameter Transport Function instance that is currently controlling the Diameter Connection.

Because multiple Diameter Routing Function instances can be simultaneously forwarding transactions to the same Diameter Connection and detecting Remote BUSY Congestion, an internal procedure minimizes the number of simultaneous the Diameter Routing Function-to-Diameter Transport Function detection notifications that are associated with any single Diameter Connection.

The Connection Congestion Levels CL-0, CL-1, CL-2, CL-3 and CL-98 are mapped to Connection Priority Level (CPL) values 0, 1, 2, 3, 98 respectively.

Diameter Configuration for Remote BUSY Congestion

The Remote BUSY Congestion feature is configured using the following elements on the Diameter > Configuration > Connections page:

Remote Busy Usage: Enabled, Disabled
Remote Busy Abatement Timeout - time period (in seconds) that a Connection is considered BUSY from the last time a DIAMETER_TOO_BUSY response was rec

The configuration elements cannot be modified when the Connection is in service (Connection Admin State=Enabled).

The Remote BUSY Congestion feature can be enabled and disabled for each configured Diameter Connection.