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Calls per Second (CPS) — Trunking Termination


Trunking Termination Calls per Second (CPS) refers to how many new SIP Trunking call setups are allowed in a second for Trunking Termination (outgoing traffic from your communications infrastructure to the PSTN). Twilio, by default, provides the ability for you to place 1 CPS per Trunk per Region (see limits). Optionally, you may increase your CPS settings per Region for a monthly fee (see pricing).

In order to receive increased CPS, your traffic profile shall comply with the following guidelines:

  • Average call duration must be greater than 30 seconds
  • No more than 10% of your calls should have a call duration of less than or equal to 12 seconds
  • ASR (Answer-Seizure rate) must be greater than 70%

CPS options for Trunking Termination

There are two options for increasing Termination CPS for SIP Trunking:

Trunk Level CPS

It is possible to make changes to your Calls Per Second (CPS), settings on each individual trunk. Your CPS value can be changed via the Console. Click on the trunk you wish to edit, then go to Termination settings and set the per trunk CPS to a number between 1 and 15.

It is recommended that you provision a trunk for each region with the specific CPS required.

Increasing CPS values may occur anytime during the month, and you’ll be shown prorated charges. Changes will happen immediately upon acknowledgement.

Decreasing CPS values can only be made for the 1st day of the month. The decrease occurs automatically on the 1st day of the month, and therefore, should be scheduled in advance to avoid any delay in the decrease (i.e. if you wait until the 1st of the month, it's possible the change will not take effect until the 1st day of the following month).

If you would like to change your CPS value greater than 15, please reach out to our sales team.

Master account CPS

Provision your Master Account with the CPS you require for each Region. Pay per Master Account, per Region. The Master CPS settings are a pooled resource used by any Trunk in the given account or corresponding sub-accounts. We give you the ability to also enforce Trunk level CPS settings in Console, when Master Account CPS is enabled and allow you to over provision CPS at the Trunk level, and you'll only be billed for the Master Account CPS settings.

Master CPS is best fit for your needs if you have several trunks across multiple sub-accounts that need increased CPS, but you aren’t sure what level you’ll need on each of those trunks.

There are two “checkpoints” used to determine when calls will be allowed or rejected.

(1) Actual Calls on each Trunk vs. Trunk CPS Limits: Do actual calls on a specific Trunk exceed the CPS settings set on that Trunk for a given Region?

  • Yes - Calls start to be rejected based on the Trunk CPS settings
  • No - Go to next rule

(2) Total Actual Calls across all Trunks vs. Master account CPS Limits: Do total actual calls across all Trunks exceed the Master CPS settings in a given Region?

  • Yes - Calls start to be rejected based on the Master account CPS settings
  • No - All calls will go through

Master account CPS example

Here’s an example of how this works:

Master Account CPS setting:

*North America - Oregon (US2): 25 CPS

Trunk 1 Trunk 2 Trunk 3 Totals
Provisioned 20 CPS 25 CPS 30 CPS 75 provisioned across all Trunks (over-provisioned)
Actual Calls 30 CPS 24 CPS 30 CPS 84 actual Terminating Calls attempted across all Trunks
Rule 1 - Trunk Limits Calls capped at 20 CPS All 24 CPS allowed All 30 CPS allowed 74 actual CPS allowed based on Trunk CPS settings
Rule 2 - Master account Limits Cap calls at 25 CPS (calls from any trunk may be rejected)

Regional CPS

Twilio has introduced 'Twilio Regions' for isolating the data storage and processing in data centers located in specific geographic locations. For customers who have created a trunkin a Region other than Ashburn, VA (formerly referenced as us1), you will be required to use Master account CPS to increase the CPS settings on your trunk. If you have self-served an increased CPS value or spoken with Sales for CPS values greater than 15, you may need to switch from your existing Trunk Level CPS setting to the Master CPS model in order to service your trunks hosted in Twilio regions outside of Ashburn. Please talk to Salesif you are considering purchasing increased CPS for your Regional Twilio Elastic SIP Trunks.

Debugger Alerts

Twilio will log a Debugger Alert record when you're CPS limits are reached, our Debugger Alert will tell you which limit was hit; either the Trunk level or Master account CPS level.

These debugger alerts are:

These may be very useful to determine if you need to increase your CPS settings. You can configure Alert Triggers to fire based on your preferences on any Alert error code; optionally, you can also send a corresponding webhook or an email notification.

If you would like to modify your Master Account or increase more than 15 CPS for Trunk Level or decrease Trunk Level CPS, please contact sales here.

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