SSLFax®

Despite the rumors otherwise, fax is alive and well -- and getting faster. Advances in fax technology have allowed zPaper to refine existing modes of communication behind the scenes. One of those improvements is SSLFax, which provides fast, reliable document communications and keeps fax technology relevant in the age of the internet.

Using HylaFAX technology, SSLFax can help healthcare companies reduce bottlenecks in fax intake systems. ​ Tremendous amounts of faxed data can be transmitted in seconds instead of the 2 minutes per page standard of a typical fax by establishing an SSLFax on both ends of the transmission.

What is SSLFax?

After a typical fax call is initiated, during the fax handshaking procedure, two fax devices with support for SSLFax can pass additional handshaking signals. A secure internet connection between the two servers is initiated, and fax communication can then be conducted over the established secure internet connection.

How does SSLFax work?

TU T.30 assigns two bits in the DIS and DCS signals which indicate internet fax support. Use of these bits enables support for CSA and TSA frames in the fax protocol. CSA and TSA frames allow fax devices to communicate internet fax support information.

When an SSLFax device sees a CSA or TSA frame indicating an SSLFax URL as described, it will make an SSL client connection to the given hostname at the given port. After SSL handshaking completes, the given passcode is communicated from the client to the server as a security and identification measure.

After the proper SSLFax connection is made, the balance of the fax communication is made over the SSL connection rather than the connection on the telephone line.

The use case for gateways

Voice gateways are already in the habit of recognizing fax CNG and CED tones, obscuring NSF signals, and manipulating DIS signals in order to establish an IP connection (usually T.38). Here is an example:

The typical trouble with this process is that the IP connection often traverses an abysmal SIP UDP/IP connection, and jitter can still interfere with fax signal communication even with the repeated packets that T.38 allows.

Voice gateways can utilize SSLFax as a superior alternative to T.38 by adding the internet fax components to DIS and DCS signals when appropriate, add or remove CSA and TSA signals where appropriate, and otherwise facilitate SSLFax operation. In the example below, neither of the two fax endpoints support SSLFax. So, the two gateways establish an SSLFax session between each other.

SSLFax Examples

In this example, FAX1 supports SSLFax, but FAX2 does not, and so GATEWAY2 added the internet fax bits to the DIS signal from FAX2, removed the internet fax bits from the signal from FAX1, and handled and removed the TSA signal from FAX1. GATEWAY1 stays out of the way while GATEWAY2 performs SSLFax with FAX1 and translates that to FAX2.

In the next example FAX1 does not support SSLFax, but FAX2 does. So, GATEWAY1 added the internet fax bits to the DCS signal from FAX1 and handled and removed the CSA signal from FAX2. GATEWAY2 stays out of the way while GATEWAY1 performs SSLFax with FAX2 and translates that to FAX1.

In the above scenarios, the fax communication speed is bottlenecked at the 33,600-to-2,400 bps rate that traditional fax operates at, but reliability will be improved as jitter will be eliminated. Above all, it is important that voice gateways not obfuscate the internet fax bits in DIS and DCS, and do not otherwise interfere with SSLFax when both endpoints support it.