Modern IT Technologies offer a new revolutionary approach to communication by means of a global world wide network. Internet technologies have substituted faxing in many areas of business and social life. But from another hand they created a new opportunities for fax sending in form of so cold Internet Fax.

This technique are based on fax transmission over the IP-based packet network, rather than over the traditional public switched telephone network (PSTN). The main principals of this technology are formulated in ITU-T Recommendation F.185 “Internet facsimile: Guidelines for the support of the communication of facsimile documents” This document defines two main types of the Internet facsimile:

  • Real-time session oriented Internet facsimile (“real-time”)
  • Store-and-forward facsimile

Real-time session oriented Internet facsimile involves the transmission/reception of a facsimile in a single session such that confirmation of receipt is provided to the transmitting terminal prior to disconnection. Real-time session oriented communication over the Internet between two facsimile terminals conforming to the relevant ITU-T Recommendations is accomplished when:

 1) the contents and sequence of standard messages exchanged between the sending and receiving terminals are preserved, as far as practicable;

2) the call duration using the Internet is comparable to that of a facsimile session using the GSTN/ISDN between the two terminals.

Store-and-forward facsimile involves the transmission/reception of a facsimile other than in real-time. Such transmission/reception takes place via the store-and-forward mode on the Internet using Internet Email.

“Simple” mode store-and-forward facsimile communication over the Internet is accomplished when only the coded image is transmitted.

“Full” mode store-and-forward facsimile communication over the Internet between two facsimile terminals conforming to the relevant ITU-T Recommendations is accomplished when:

1) the capabilities of the terminals are exchanged;

2) an acknowledgement of receipt is exchanged between gateways and may be transferred from the receiving terminal to the sending terminal;

3) the contents of standard messages used by the transmitting terminal are preserved.

Models for Internet access

The diagrams below show different methods of Internet access for PC Email clients, Internet Aware Facsimile terminals and standard facsimile terminals connected via a gateway. Such connections may be used for store-and-forward facsimile or real-time facsimile.

Figure 1 shows the methods for store-and-forward Internet facsimile and Figure 2 shows the methods for real-time Internet facsimile.

Figure 1. Store-and-forward operation

Figure 2. Real-time operation

The definition of the objects shown on the diagrams in accordance with ITU-T  F.185  :

Standard facsimile terminal – A standard facsimile terminal is a system currently capable of sending and receiving facsimile documents in accordance with the relevant ITU-T Recommendations. Such a terminal has no capabilities to enable it to send or receive store-and forward facsimile. A standard facsimile terminal may be connected to a gateway to provide the functionality of an Internet Aware Facsimile.

Gateway – A gateway provides access to the Internet for standard facsimile terminals. A gateway service is capable of accepting facsimile documents from, and capable of sending facsimile documents to, standard facsimile terminals.

Email client – An Email client is a UA capable of sending and receiving Internet Email and capable of store-and-forward facsimile. Such a client may be an Email package conforming to the relevant Internet standards and the connection to the Internet may be via a local network or via a dial-up call over the GSTN or ISDN.

Internet Aware Facsimile terminal (IAF) – For store-and-forward facsimile, an Internet Aware Facsimile terminal combines the capabilities of a standard facsimile terminal and an Email client. For real-time facsimile, an Internet Aware Facsimile terminal has the capabilities of a standard facsimile terminal as well as having an IP address or domain name together with its GSTN address. In either mode, it is capable of sending and receiving facsimile documents via the appropriate network.

As it follows from the diagrams shown on Figure 1 and Figure 2, there are 2 protocols for transmitting Internet Fax:

  • 37 for Store-and-forward operation
  • 38 for Real-time operation

The bough are regulated by correspondent ITU-T standards:

ITU-T T.37 “Procedures for the transfer of facsimile data via store-and-forward on the Internet”

ITU-T T.38 “Procedures for real-time Group 3 facsimile communication over IP networks”

The main difference between mentioned protocols is that only T.38 allows Real time transmission, which makes it much more similar to traditional faxing.

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