An Egress Throttle Group is a collection of Diameter Connections or Peers, or both, that are logically grouped together to monitor Egress Message Rate and Pending Transactions for multiple Peers and Connections across multiple DA-MPs on a DSR Network Element. If a Peer is assigned to the Egress Throttle Group, then all Diameter Connections to that Peer are implicitly part of the Egress Throttle Group.
ETG Rate Limiting and Pending Transaction Limiting throttling are done for Request Messages only.
Egress Message Rate controls are used to throttle traffic levels to a set of Diameter Nodes so that the cumulative rate of traffic is controlled. EMR controls are across a set of configured connections and/or peers.
Egress Pending Transactions controls are used to control the maximum number of Pending Requests that can be sent to a set of Diameter Nodes. This can be used for load-balancing when a network element is not responding at expected rates, and limits the total number of Requests that can be pending to a set of Diameter Nodes. EPT controls are across a set of connections and/or peers, and are cumulative across all DA-MPs.
Egress Throttle Groups are implemented as part of the Diameter Routing Function.
An Egress Throttle Group is independent of a Route Group (Connection Route Group or Peer Route Group). The members of an Egress Throttle Group may or may not be same as defined in a Route Group; there is no defined relationship between Egress Throttle Groups and Route Groups.
The Egress Message Rate throttling is controlled by the configured maximum Egress Message Rate (EMR) on an aggregated basis and the "Egress Throttle Group - Rate Limiting Congestion Level (ETG-R CL-) (range: CL-0- CL-3) for the ETG.
The Egress Pending Transaction Limiting throttling is controlled by the configured maximum Egress Pending Transactions (EPT) on an aggregated basis and the "Egress Throttle Group - Pending Transaction Limiting Congestion Level (ETG-PCL) (range: CL-0- CL-3) for the ETG.
DSR supports a maximum of 5 congestion levels (CL-0 to CL-4) that indicate the Congestion Level of a resource. CL0 indicates that the resource has no congestion, and CL-4 indicates that the resource is completely blocked. CL-1, CL-2, and CL-3 indicate increasing levels of congestion.
Egress Throttle Groups (ETG) can be configured in Diameter Configuration; each Egress Throttle Group will have its own Congestion Level states based on its configuration.
As the Egress Throttle Group 's Congestion Level increases, Message Priority becomes a factor in determining if a message can be routed to a member of the Egress Throttle Group, or will be throttled. Requests with Message Priority less than Congestion Level will not be routed to any member of the Egress Throttle Group.
Diameter Request messages are assigned a Message Priority 0, 1, or 2; Answers always have Priority 3. The Priority of the Request message controls when an ETG performs throttling is shown in Table 1
| Request Message Priority | When Permitted to route to Member of ETG |
|---|---|
| 0 | Congestion Level 0 |
| 1 | Congestion Level 0, 1 |
| 2 | Congestion Level 0, 1, 2 |
When the EMR for an Egress Throttle Group reaches the Egress Throttle Group 's Maximum Egress Request Rate or the Egress Throttle Group 's Pending Transactions reaches the Egress Throttle Group 's Maximum Egress Pending Requests, no Requests will be routed to any members of the Egress Throttle Group.
The ETG Message Rate Controls are optional, but if defined and enabled, then ETG Message Rate Congestion level will be updated as indicated in Table 2.
| Onset and Abatement Thresholds | ETG Rate Congestion Level (ETG-RCL) Impact |
|---|---|
| Onset Threshold-3 (OT-3) | When ETG rate exceeds Threshold, set ETG-RCL = CL-3 |
| Abatement Threshold-3 (AT-3) | When ETG rate falls below Threshold, set ETG-RCL = CL-2 |
| Onset Threshold-2 (OT-2) | When ETG rate exceeds Threshold, set ETG-RCL = CL-2 |
| Abatement Threshold-2 (AT-2) | When ETG rate falls below Threshold, set ETG-RCL = CL-1 |
| Onset Threshold-1 (OT-1) | When ETG rate exceeds Threshold, set ETG-RCL = CL-1 |
| Abatement Threshold-1 (AT-1) | When ETG rate falls below Threshold, set ETG-RCL = CL-0 |
In an Egress Throttling Group, if Maximum Egress Request Rate is configured, then OT-1 and AT-1 thresholds must be configured. OT-2, AT-2, OT-3 and AT-3 are optional but must be configured in pairs; for example, if OT-2 is configured, AT-2 must also be configured. Finally, AT-3 must be configured if OT-3 is expected to be configured.
The EMR is calculated every 100ms by subtracting the oldest traffic count from the newest traffic count, and averaging the difference over the elapsed time between them.
EMR onset requires only one EMR sample to exceed an onset threshold to advance the ETG-RCL. Multi-step throttling is supported. For example, the EMR Congestion Level can be increased from CL-0 to CL-1, CL-2, or CL-3 after one EMR sample period. This allows for a rapid response to traffic load increases while taking a more conservative approach to traffic load decreases.
Only single step abatement is supported. For example CL-3-> CL-2 abatement is supported but not CL-3-> CL-1.
| Onset and Abatement Thresholds | ETG Pending Transaction Congestion Level (ETG-PCL) Impact |
|---|---|
| Onset Threshold-3 (OT-3) | When ETG Pending Transactions exceeds Threshold, set ETG-PCL = CL-3 |
| Abatement Threshold-3 (AT-3) | When ETG Pending Transactions falls below Threshold, set ETG-PCL = CL-2 |
| Onset Threshold-2 (OT-2) | When ETG Pending Transactions exceeds Threshold, set ETG-PCL = CL-2 |
| Abatement Threshold-2 (AT-2) | When ETG Pending Transactions falls below Threshold, set ETG-PCL = CL-1 |
| Onset Threshold-1 (OT-1) | When ETG Pending Transactions exceeds Threshold, set ETG-PCL = CL-1 |
| Abatement Threshold-1 (AT-1) | When ETG Pending Transactions falls below Threshold, set ETG-PCL = CL-0 |
In an Egress Throttling Group, if Maximum Egress Pending Transactions is configured, then OT-1 and AT-1 thresholds must be configured. OT-2, AT-2, OT-3 and AT-3 are optional but must be configured in pairs; for example, if OT-2 is configured, AT-2 must also be configured. Finally, AT-3 must be configured if OT-3 is expected to be configured.
The local sample of number of pending Transactions to an ETG is periodically collected and sent to the DA-MP Leader for aggregation. The aggregated value is then sent back to each DA-MP for threshold and abatement calculation. No adjustment is applied to EPT, and aggregated values are sent back to each DA-MP.
The EPT Abatement Time is the amount of time that egress Pending Transactions must remain below an abatement level before allowing it to abate to a lower Congestion Level. No adjustment is applied to EPT abatement.
Pending Transaction Limiting must be enabled Maintenance GUI before Egress Pending Transaction Limiting can be started for Egress Throttle Groups. If Egress Pending Transaction Limiting is enabled, then any pending Request sent to a Peer or Connection on any DA-MP on that NE contained in the Egress Throttle Group will be used for Pending Transaction Limiting calculation.
Egress Throttle Groups are used to perform 2 functions: Rate limiting and Pending Transaction Limiting. Each of the functions are independent of each other and can be optionally configured and controlled separately.
The Diameter > Configuration > Egress Throttle Groups GUI pages provide fields for configuring each function. Each function, if configured in the system, must have its Admin State changed to Enabled on the Diameter > Maintenance > Egress Throttle Groups GUI page.
Egress Throttle Groups configuration procedures are provided in Egress Throttle Groups configuration.
Egress Throttle Groups maintenance information and procedures are provided in Egress Throttle Groups.