We usually know fax as the transmission of text or image over telephone lines, a specific number is associated with the fax machine. Fax machine scans the original text or image and convert it to a bitmap. After converting, these text and images are sent through electrical signals using telephone lines. On the other hand, the receiver of this electrical signal is a fax machine which again reconverts it into text and images.

Advancement in technology has also affected faxing methodology. FoIP (Fax over Internet Protocol) has changed the way of transmission of fax over telephone lines to the internet. FoIP is a method of sending and receiving fax over a VoIP network. Working of FoIP is the same as voice over internet protocol (VoIP). If you know how VoIP is initiated then you know FoIP as well. The difference between these two is just that FoIP uses data protocol whereas VoIP uses voice codec. In this method, fax is transmitted via IP packets rather than analog telephone lines which send signals. FoIP is an economical method of fax broadcasting or transmission as compare to old telephone lines. FoIP provides low long-distance costs and eliminates the cost of PBX maintenance. By using hardware visualization the cost of hardware dependency is reduced.

T.38 is a real-time faxing over Internet Protocol. T.38 is designed in such a way that it works like traditional faxing. T.38 fax gateway is used for reliable and quality fax transmission over the IP network and also for PSTN fax transmission. VoIP connections are not strongly used for a fax modem. Most of them use low bit codec which cannot accurately transmit the modem signal. In the case of a high bit rate codec mostly VoIP connection disconnect and arise time adjustment issues which are not bearable for modem. When we talk about the LAN, the disconnection ratio is low but time adjustment makes modem unreliable which happens in VoIP. In T.38 basic problems exist like packet loss, delay rate high, time adjustment and jitter, and poor networking performance.