VoIP Voice and Fax Signal Processing

15.1 FAX OVER IP OVERVIEW

The classification of FoIP is given in Fig. 15.1. Store-and-forward fax is based on the T.37 recommendation [ITU-T-T.37 (1998)]. It is used for off-line fax transmission. Store-and-forward fax is similar to e-mails, but at both the end terminations, fax machines and computers are used to interface for fax pages. In the store-and-forward mode, the caller sends the fax messages stored on the simple mail transfer protocol (SMTP) server to another SMTP server, and finally reaches the destination VoIP fax interface. At the destination, a fax can be delivered as an e-mail message either with attachment or as a fax to a standard PSTN-based fax machine. The caller is notified on the fax delivery status. Store-and-forward fax is used with both computers and fax machines. Store-and-forward fax does not give users some fundamental advantages of fax technology. It lacks guaranteed delivery because store-and-forward fax services treat fax transmissions like e-mail without any guarantee of delivery. Psychological satisfaction will be missing, because of off-line operation. Store-and-forward fax allows retrieval of fax later similar to e-mails offering this as one of the service advantage. Store-and-forward fax details are not given in this book.

Figure 15.1. Fax over IP functional classification.

Real-time fax over IP works similar to a regular fax call. Fax machines ...