In this section:
The following diagram displays the message path, and the congestion and flow control function blocks. The bracketed letters (x) within the diagram indicate where the configuration changes take effect on the messages.
The following list defines each letter used in the diagram:
- I – The message importance can be modified at this point.
- M – The message importance can be used at this point to evaluate the survivability of the message.
- R – Rate Limiters may be assigned to the message at this point.
- D – The messages may be discarded or rejected at this point.
- H – The congestion handling specified by a capacity parameter set can be applied at this point.
- F – The message flow control behavior can be controlled by a capacity parameter at this point.
The Ingress and Egress Topology Mapping tables do not affect congestion or flow controls and have only been included in the diagram for reference.
Received Message
This block represents messages received from any Diameter ADN.
Ingress Queue
This function block is the main queue that supplies messages to the DSC routing engine.
The collective of all of the Ingress Queues is used to determine the Local Overload status of the DSC application. Message handling in response to Local Overload conditions is also performed here. This is also where the limit on the Diameter memory will take affect.
Incoming Answer Preprocess Table
This function block can assign ingress message importance to answers and can also direct answer messages into Ingress Rate Limiters. Ingress Rate Limiter congestion status is compared to the message importance and congestion handling can be applied.
The order the modification commands assign message importance and assign Rate Limiters will affect the message.
This table is only accessible if a set-answer-rt <routingTableName> command is applied to request messages using the Outgoing Request Routing Table, where the routing table name is applied to the answer. For more information, see Configuring Modification Commands.
Answer Ingress Rate Limiters
This function block limits the input rate of answer messages (previously determined by the Incoming Answer Preprocess Table) into the DSC routing engine, using additional capacity parameters.
Initial Routing Table
This configurable function block directs the main DSC routing engine. In addition to the main purpose of specifying routing rules, this function block may be used to reassign importance and direct messages into General Rate Limiters. These changes apply before the messages are routed to any specific ADN.
The associated configuration attribute is on the DSC Node, see Configuring DSC Nodes.
General Rate Limiters
This function block is the set of Rate Limiters that are independent of any specific ADN or ADN Connection. They are assigned to relevant message through the routing tables by the Initial Routing Table entry point.
Egress ADN Selection and Load Balancing
This function block selects an egress path using the candidate routes established by the routing engine. It evaluates the availability and congestion status of each possible route, then forwards the message to the first available route. If no available route is found, the message is either rejected or discarded.
Outgoing Request and Answer Routing Tables
These function blocks can reassign importance and direct messages into Egress Rate Limiters. These are configured per ADN and can make changes to specific ADNs.
The Rate Limiters assigned by these table entry points are applied to each instance of message transmission, including re-transmissions.
Egress Rate Limiters
This function block is the ADN-specific Egress Rate Limiters assigned by the Outgoing Request and Answer Routing Tables. These Rate Limiters impose additional capacity parameters to relevant egress messages.
Egress Queue
This block is the main queue to buffer egress messages.
Transmit Message
This block represents the encoding and transmission of Diameter messages.