Design of an Internet fax and voice gateway

There has been a growing interest in recent years in developing real-time v oice and fax communication software for use over the Internet. This paper d iscusses the design of an Internet Telephony Gateway (ITG) that is used to support the delivery of fax and/or voice services through the Internet to c onventional telephones and fax machines on the Public Switched Telephone Ne twork (PSTN). The interface board can offer multiple ports of voice and fax services in a single slot using the EISA bus. The hardware system comprise s two microprocessors and one digital signal processor (DSP). One of the mi croprocessors is used for telephone trunk line interface management and sys tem control while the other one is used solely for fax modem control. The D SP is used to compress and decompress the voice signal for real-time voice communication. Two algorithms to compress the digitized voice signal, i.e., Global System for Mobile Communication (GSM) and Code Excited Linear Predi ction (CELP), are used in the design. GSM is used to compress primary voice data packets while CELP is used to compress redundancy voice data packets to cater for potential lost data packets during network transmission. The s oftware on the server gateway provides the functionality between two commun icating gateways and manages the exchange of fax and voice between senders and recipients by using the Internet as the transport medium. (C) 1999 Else vier Science B.V. All rights reserved.