Calls per Second (CPS)

Calls per Second (CPS) refers to the limit on the number of calls your account can send or receive within one second. These limits are categorized into outbound and inbound calling, each with its own threshold. By default, upon signing up, we assign an outbound CPS limit of 2 and an inbound CPS limit of 10. To view your current inbound and outbound CPS allocations, visit the Voice Overview page in the Plivo console and check the Account section.

Outbound CPS

For outbound calling, CPS represents the maximum rate at which calls can be initiated using APIs for your specific account. It's important to note that outbound CPS limits apply solely to calls made via APIs and do not affect calls made using the Dial XML element.

When you exceed your allocated outbound CPS, your additional calls won't be dropped. Instead, they will be queued and dispatched once the CPS rate drops below your set limit. While you can maintain as many concurrent calls as your servers allow, the initiation rate of these calls is governed by your account's CPS allocation.

Examples:

  • Scenario 1: If your outbound CPS limit is set to 10 and you initiate 10 API calls within one second, all 10 calls will be executed simultaneously without any delay.

  • Scenario 2: If your outbound CPS limit is 10 and you attempt to place 12 API calls in one second, the first 10 calls will be executed immediately. The remaining 2 calls will be queued and executed in the next available CPS interval.

Inbound CPS

For inbound calling, CPS represents a limit on the rate of inbound calls to Plivo numbers, and also to the rate of outbound calls originating from SIP and browser clients. (The term "inbound CPS" is used because outgoing call requests from SIP and browser clients are essentially inbound requests to Plivo.) Calls that surpass the specified inbound CPS limit based on the above criteria are rejected with SIP code 486.

How does CPS differ from Concurrent Calls?

Understanding the distinction between CPS and concurrent calls is essential for effective call management.

CPS refers to the rate at which calls are initiated or received per second. It controls how many new calls can start each second, focusing on the speed of call initiation or reception. For example, if your outbound CPS limit is 10, you can initiate up to 10 new calls every second.

On the other hand, concurrent calls refer to the total number of active calls happening simultaneously at any given moment. This number depends on your server capacity and system resources rather than being directly controlled by CPS limits. For instance, if each call lasts five minutes, having a high number of concurrent calls means your system is handling many ongoing calls at the same time, regardless of the CPS rate at which they were initiated.

Example to Illustrate the Difference:

Imagine you have an outbound CPS limit of 10 and you initiate 10 API calls in one second:

  • From a CPS perspective, all 10 calls are initiated simultaneously within that second.
  • From a concurrent calls perspective, if each call lasts five minutes, you now have 10 active concurrent calls ongoing.

If you initiate another 10 API calls in the next second:

  • The CPS allows these new 10 calls to be initiated immediately, adhering to the CPS limit.
  • The total number of concurrent calls increases to 20, assuming none of the previous calls have ended.

Can I increase my allocated CPS?

If you have a use case that requires a higher CPS limit, contact the Plivo support team.

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