Integrate Fax Services into IP Networks

Fax Printer Scanner

Fax usage decreases from year to year. More and more companies are uninstalling their fax infrastructure. Other companies replace pure fax machines by so-called multifunctional devices. The article describes integration variants of analog and digital fax machines as well as multifunctional devices into IP networks.

Analog Fax Machines

Analog fax machines for the transmission of scanned documents (facsimile, remote copying) have been in use for many years. Frequently in use are faxes according to the standard of the ITU-T group 3. This describes a transmission procedure over analog connections, usually the public telephone network.

How does it work?

A document is scanned during the transmission process and the obtained pixel information is converted into digital bit patterns (for black-and-white, gray values or colors). The bits now stored in local memory must be converted into acoustic tones to be transferred over analog transmission paths. For this purpose, a modem (artificial word from MOdulation and DEModulation) is installed in the fax machine. The rules for bit conversion to be sent during transmission are defined in ITU-T standards. Different standards are defined for different bit rates.

It is challenging to integrate these systems into pure IP networks. There are different approaches for this.


Analog Adapters for Analogue Fax Machines

Adapters that digitize analog modem signals of the fax machine and transmit via ISDN have been around for a very long time. The adapters differ in the way they digitize. If the analog modem signal is like a human speech signal, it can be digitized up to a limit frequency of 3400 Hz. This is still applicable for analog fax modems with maximum bit rates of 28800 bits per second. The demodulation of the analog signal is performed on the receiver side. The digital bit pattern is forwarded as pixel information to the printing system of the facsimile machine and printed out on paper.


ISDN Adapters for Analog Fax Machines

Fax modems that support higher bit rates (e.g., so-called “super-G3 devices”) generate complex signals that are not digitizable by scanning. Thus, a digital facsimile transmission with e.g. 33600 bits per second (after scanning) is not possible. In this case, the modem signal must be demodulated in the adapter on the transmitter side. The adapter transmits the pure useful (pixel) digital information via the ISDN over a B-channel with 64000 bits per second. On the receiver side, the correct adapter function must also be used, so that the signals can be reconverted using the correct methods. This requires at least a coordination of the communication partners.


IP Adapters for Analog Fax Machines

The same applies to IP solutions. The adapter receives the analog modem signal from the fax machine and scans it at regular intervals. The measured values are digitized in the adapter. For high bit rates (33600 bps), the adapter requires a demodulator which converts the analog modem signal into pixel information. The digital values are collected by the adapter in local memory and packaged into IP packets. A network transmits the transmitted IP packets to the receiver. Once there, the payload (in the data field of the IP packet) is unpacked. If these are the samples, they are converted back into an analog modem signal and forwarded to a fax modem of a fax machine. If this is already the pixel information of the scanner, this is directly forwarded to the printing system of the fax machine for printing.


ISDN Fax Devices

For direct transmission of faxes over the Integrated Services Digital Network (ISDN), the ITU-T specified fax group 4 features supporting full-speed and high-quality digital transmission (64000 bps). The modem function is not required.


Protocol Support

For the transport of the user information and for end-to-end control, the ITU-T specified the ITU-T T.30 protocol.

The ITU-T specified the standard T.38 to ensure the transmission of user information between analog adapters over IP networks. The standard describes the transport protocol for the transmission of fax messages (with the ITU-T T.30 protocol) over IP networks.


Multi-Functional Device (or Multi-Function Printer, MFP)

Multi-Functional devices (or „Multi-Function Printer“, MFP) support scanning, printing, copying and faxing. These are mainly used for printing, hence, hereinafter referred to as “multifunctional printer” (MFP).


Fax over MFP

The MFP has a full fax machine (usually the “Group 3” or “Super G3) installed. It supports an analog interface for analog fax transmission and direct access to a POTS (Plain Old Telephone System) interface of a provider or the private telephone system.


Integration of MFP via Analog Adapters

Is done in the same way as described in the chapters above.


Integration of MFP via Servers

Send fax via SMTP using email client software in the personal computer:

The MFP is equipped with an Ethernet port and is connected to a LAN switch port via a twisted pair cable. The PC user uses a program to scan a document in the MFP. The document is scanned and the information stored in a scan file (in various formats such as TIFF, PDF, Postscript and others) in a predefined directory of the PC or a network server. The user selects the sending of the scan file by email via the user menu.

The email client software runs on the PC (e.g., MS Outlook). An empty email is automatically opened by the client program (with email sender address of the user). The program automatically appends the scan file as an attachment to the email. The user defines the email destination address, the text of the “Subject:” line, and edits the message text. Then he sends out the message.


Send via SMTP using e-mail client software in the MFP:

The MFP is connected to the LAN. The document is scanned and the information is written into a scan file (in different formats such as TIFF, PDF, and others) and stored in the MFP or a predefined directory of a network server. The email client software runs on the MFP. Depending on the product, several email accounts (mailboxes) can be set up. Each individual mailbox is assigned its own name, which is sent to the communication partner as sender identification.

The email server used for email transmission is defined by configuration. The scan file will be attached to the email.

The user enters the telephone number of the recipient fax machine on the MFP. The MFP adds this number to the “Subject” line of the email to be sent.

The destination email address is a specially configured account of an email server with gateway function.

The e-mail is sent to the pre-configured email server (with gateway function) for forwarding via SMTP (with email sender address of the MFP). This converts the email into a fax message and sends it via the PSTN to a fax machine.

On the email server with gateway function, a username must be configured for each MFP.

If necessary, title pages or notes (e.g., as text in the email) can be inserted.


Receiving faxes in e-mail client of the personal computer:

An e-mail client software runs on the personal computer. It receives the incoming emails in which the fax messages are embedded, like any other e-mail. The attachments (scan files) in the different formats can be opened with locally installed programs. No other equipment is required.


Receiving fax messages from the MFP email client:

Depending on the solution, the email client function is included in the MFP. This allows you to directly forward emails to the MFP, which can print attachments directly.

The simultaneous transmission of fax messages to email users and MFPs is possible as well.

MFPs can be configured to forward incoming faxes to other users via email (“fax forwarding”). In the configuration of the MFP, enter the email address of the recipient who should receive a copy of the fax by email.



Faxes, transmitted as emails, are not readable as paper prints for anyone who passes a fax machine. Authentication methods and encryption techniques are available for higher requirements. New cloud services support advanced security features (such as encrypted web access to e-mail or fax accounts).



Depending on the manufacturer, different connectors for MFPs are available for integration into existing solutions.


Fax Server Solution

Multifunction devices can be integrated very well with fax servers. After configuring the MFP, the device is able to automatically send scan documents to a fax server on the network for forwarding. The transmission can take place very differently depending on the configured solution. Suitable protocols are FTP, SFTP, SMB (Microsoft Networking), HTTP / HTTPS (supported by, for example, Microsoft Internet Information Services (IIS) or Apache), SMTP, and others. Depending on the use of the previously mentioned protocols, different parameters must be configured.



Internet Fax Solution

Internet Fax allows you to scan documents via the control panel of the MFP and transfer them via email. Receiving and printing email attachments are also supported. A telephone line is not required.

The Simple Mail Transfer Protocol (SMTP) must be configured to send, and the Post Office Protocol (POP) to receive emails.

Email parameters such as “Subject” line, email body text, usernames or email addresses, device identifiers, and other details that should appear in the message body have to be configured.

You may use a directory service or a local, device-specific phone book to retrieve or store contact information from your communications partners.


Cloud Service Solutions

Cloud services are very popular. They allow the rapid provision of cost-effective and very powerful services. Communication services such as email, chat, but also video conferencing services have been in use for many years.

Although fax infrastructure disappears, fax transmissions are still required. The reasons are manifold. In order to provide all employees of a company with fax services, however, companies are increasingly using fax services from the cloud.

These differ essentially in the scope of functions and the tariffs.


Examples of Cloud Service Providers:


Advantages of today’s fax solutions, as described above:

⇒ No printout required

⇒ Any MFP product can be integrated

⇒ The solution is usable from any location

⇒ Every communication process is logged (important for compliance requirements)

⇒ Cost savings because no analog ports are required for faxes, separate faxes are no longer required, fax messages are treated like emails

⇒ Can be integrated into business processes like any email communication (reply, forward, archive, etc.).



Multifunction devices are available from manufacturers such as:









Additional information

Courseware and text books:

Voice over IP Technology

Corporate Telephony Strategies for Enterprise Customers and Organizations


About the author

Ronald Schlager is an independent trainer, consultant, book author and blogger with an emphasis on communications technologies and their application.

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Image source:, artist: KlausAires