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With the widespread deployment of VoIP, customers have seen the benefits of increased competition and lower costs for voice communications. However, many casual telephone line applications remain committed to using legacy carrier switched voice circuits. Applications for utility meter reading, cable/satellite box configuration, security systems and, yes, even the guest in the home who wants to use a dial-up modem can not be satisfied with most VoIP devices today. Fax over IP (ala T.38) is finally being supported and may even function between multiple vendors. However, Modem over IP (as implemented by the V.150 series) seems to be far less prevalent.
Even with the adoption of Fax over IP or Modem over IP, the remote endpoint or remote service provider must provide gateway equipment to accept analog signals used to remodulate the local modem signals as seen by the home's VoIP device. This is an unnecessary and redundant deployment of rather sophisticated signal processing devices. And it will inevitably consume more power overall than if better home VoIP device services are employed.
The voice signal processing functions performed by the home's VoIP devices, usually in the form of an analog telephone adapter (ATA), are usually comparable in complexity to the signal processing functions required by a modem. VOCAL's Remote Access Server over IP™ (RASoIP™) solution is based on distributing the existing concept of Remote Access Servers into the local ATA devices. Each ATA has a full set of ITU standard data modem protocols to fully replace a dial-up remote server gateway. SIP and SDP are used to negotiate the operation of the RASoIP features. Data can be delivered in a variety of forms including Telnet and RFC 5194 Framework for Real-Time Text over IP Using the Session Initiation Protocol (SIP).
Fax services (transmit and receive) may also be directly handled by a Distributed Remote Gateway over IP™ (RGoIP™), or Distributed Gateway over IP™ (DGoIP™), which provides both data and fax modem services directly in the home's ATA VoIP device. In this model, the distant equipment controls the home's distributed modem using ordinary AT commands. Standard fax applications may be used by a fax server to send and receive faxes. Special buffering, command anticipation and keep alive methods are employed within the ATA to ensure high reliability of operation.