Despite being considered outdated by some, 17 billion faxes are still sent annually due to their safety and accessibility. With the shift towards SIP trunk technology, sending a fax with a SIP trunk is becoming more common. T.38 protocol enables faxing over data networks, converting fax signals into images for transmission. CSID identifies the recipient's fax machine. Each number must be designated for receiving either voice calls or faxes but not both.