There are some limitations to the number of simultaneous inbound and outbound calls that can be placed and received using Twilio's Programmable Voice, Client, and Elastic SIP Trunking products. This guide explains the restrictions for these products.
Outbound SIP and API request calls
By default, each Twilio project can make 1 outgoing call per-second (CPS). This rate limit applies to both Outbound API-requested Programmable Voice calls, and Elastic SIP Trunking calls. You can have as many concurrent calls as your servers will allow, but calls can only be placed at the rate of one per second.
Notice: API requests for calls that exceed the CPS rate limit will be queued, and executed as capacity is available.
Exceeding the CPS rate on an Elastic SIP Trunk will result in a failed call with a
SIP 503 Trunk CPS limit exceeded response.
If your project requires additional outbound call throughput, you can increase your CPS limit from Twilio Console:
- Programmable Voice and Client: Set CPS in the "Calls per Second" section on the Voice Setting page.
- Elastic SIP Trunking: Set CPS per region in the "Calls per Second" section of your trunk's Termination settings page.
Outbound <Dial> calls
There is no rate limit for outgoing <Dial> calls for forwarding, conferencing, or Client. That said, there are limitations at the destination for these calls:
- Twilio <Dial> forwarding to another phone number limitations depend on the destination phone number. Calls exceeding the limit may not connect or be marked busy.
- Twilio <Conference> has a maximum limitation of 250 participants, but rooms can be configured to have a lower maximum.
- Twilio <Client> calls forwarded to a user who is already connected will fail with a
SIP 486 Busy hereresponse.
Twilio places no limitations on the rate at which projects can receive inbound calls. Every incoming call received at your Twilio phone number corresponds to an HTTP request we submit to your webhook / request URL or SIP Trunk Origination URI. We recommend users make sure your server is capable of handling the load if you are expecting a large amount of concurrent inbound traffic.