Modems were initially only used for data transmission. However, with the continuous growth of user demand and fierce competition among manufacturers, more and more "2-in-1" and "3-in-1" modems have emerged in the market. In addition to data transmission, these modems also have fax and voice transmission functions.

1. Fax modem mode

Using a modem for fax transmission not only saves the cost of a dedicated fax machine, but also has many benefits: files from the computer can be directly faxed to the other party's computer or fax machine without the need to print out the files first; Can conveniently save or edit the received fax; It can overcome the problem of gradually fading handwriting caused by the use of thermal paper in ordinary fax machines; Due to the use of error correction technology in modems, fax quality is better than ordinary fax machines, especially for graphic faxes. Currently, most fax modems follow the V.29 and V.17 fax protocols. Among them, V.29 supports a fax rate of 9600bps, while V.17 can support a fax rate of 14400bps.

2. Voice Mode (Voice modem)

The voice mode mainly provides phone recording, message leaving, and full duplex hands-free calling functions, truly integrating the phone with the computer. Here, we mainly discuss a new voice transmission mode - DSVD (Digital Simultaneous Voice and Data). DSVD is a voice transmission standard proposed by companies such as Hayes, Rockwell, U.s. Robotics, Intel, etc. in 1995, which is an extension of the existing V.42 error correction protocol. DSVD uses Digi Talk's digital voice and data simultaneous interpreting technology to enable Modem to carry out data transmission and call at the same time on ordinary telephone lines.



DSVD modems reserve 8K of bandwidth (some modems reserve 8.5K of bandwidth) for voice transmission, while the remaining bandwidth is used for data transmission. Voice is compressed before transmission, and then combined with the data to be transmitted, and transmitted to the other user through telephone carrier. At the receiving end, Modem first separates voice from data, and then decompresses the voice signal and performs digital to analog conversion to achieve simultaneous interpreting of data/voice. DSVD modems have broad application prospects in remote teaching, collaborative work, online gaming, and other fields. However, at present, because the price of DSVD Modem is higher than that of ordinary Voice Modem, and to realize the data/voice simultaneous interpreting function, the other party needs to use DSVD Modem, which has hindered the popularity of DSVD Modem to a certain extent.