Dial-in is when attendees of a webinar or video conference connect to the event using a phone. Dial-in is used to overcome issues with audio and video. Traditional dial-in is possible with VolP technology. For webinars, SIP is used to facilitate the calls.
VolP, or voice over internet protocol, is any call made over the internet rather than via traditional phone lines. VolP is also called broadband phone service. Only voice can be exchanged with VolP. It is a low-cost communication method.
SIP stands for Session Initiation Protocol. It is an internet protocol that is used to send messages, video, voice, data, and other media in VolP applications for free.