In essence, a trunk serves as the gateway to a telephone system, enabling VitalPBX to connect with external resources like PSTN lines or other PBX systems for inter-system transfers. Trunks, whether physical (like PRI or PSTN lines) or virtual (via IP links), function as the PBX’s external phone lines, facilitating both outbound and inbound calls. Without a trunk, communication with the outside world becomes impossible – no outgoing calls can be made, and incoming calls cannot be received.
To create an new Trunk, you can go to NextGenSwitch> Call routing> Trunk, and the most important fields are:

• Name, this is the user-defined name for the profile.
• SIP User Info Such as given below :

• User name,
• Password,
• Host, this is the IP address or DNS hostname of the SIP provider. This is the destination server or network that PBX will send calls to when using this trunk.

• Port, this value sets the default port to be accessed on the remote endpoint device. Only required for SIP trunks.

• Transport, Choose your preferred mode of transportation, whether it’s UDP, TCP, or TLS.
  

Call Limit, set maximum number of simultaneous calls that can be received by this device.