"services" and ports for Asterisk
 

Hello. I am in the process of configuring Asterisk on my VPS server using Linux and ISPmanager. I am having issues with outgoing voice transmission/playback and the suggestion has been made that it may be related to firewall settings. I need to open some specific "UDP" ports and when i look in the firewall section they are not listed as "opened". There is no "add" option in this section and it looks to me like i need to "add" a "service" before i can specify which port to open. Am I understanding this correctly? If so, what type of service would an Asterisk PBX be considered? Thank-you!