by Max Schroeder, SIP Forum FoIP TG Whip, and Marc Robins, SIP Forum Managing Director
The term “willing to go-the-extra-mile” is used for the extra effort employed to complete a project or resolve a problem. In the communications industry, “the last mile” is frequently used to emphasize that a communication must make it all the way from Point A to Point B. Stopping at mile-marker 1.5 is simply not an option. In the world of fax, this means that a sending fax device must connect to the receiving one and stay connected for the duration of the call. If this does not happen, the sending device will record the attempt as a failed fax.
Today’s global economy exists in great part because of the ability for people across great distances to communicate with each other in real-time. The PSTN has evolved significantly from its analog roots and is transitioning to an all-IP-based digital network. It consists of thousands of interconnected service providers of all sizes and varying capabilities. For providers that have deployed IP-based communications equipment on their networks, SIP is widely used to create and control these sessions.
The good news is that we have an increasingly interconnected global IP communications network that supports SIP. The bad news is the current state of interoperability, as each provider must be very careful to ensure their networks and technology deployments can work seamlessly with all of the others with which they interconnect. Although most of this focus regarding communications involves voice calls, achieving interoperability is particularly critical for fax communications.
Today’s fax technology is based on the T.30 protocol published by the International Telecommunication Union (ITU) in 1980 and the T.38 protocol published in 1998. Obviously T.30 was published prior to the rise of the Internet, and even T.38 was developed prior to widespread Internet implementation and use. Global service providers see voice communications as the communications elephant in the room, and so focused first on VoIP. Fax over IP (FoIP) was not a priority until after VoIP was running smoothly and, to be fair, virtually 100% of fax machines are not IP-capable anyway. The real value of FoIP is to integrate fax at the enterprise level using fax servers. This allows users to leverage VoIP PBXs, for example, and facilitates full-blown unified communications. This is the point where the problems began to surface. Simply put, today’s T.38 fax is simply not as reliable as legacy TDM fax.
This situation was recognized by the SIP Forum, which conducted a FoIP Interoperability Workshop in San Francisco on November 10, 2008, and a decision was made to study the issues in detail. The Fax-over-IP Task Group was established and Version 1.0 of their Problem Statement was published in August 2009.
This was not the only organization that recognized a problem existed. During the last quarter of 2009, Richard Shockey, current Chairman of the Board of the SIP Forum, initiated contact with the i3Forum (i3forum.org), which brings together more than 44 telecommunications operators representing a combined retail base in excess of one billion customers in over 80 countries. A conference call was conducted in December followed by discussions at i3 Forum meetings in January and June of 2010. Vendors and carriers both realized they could not do it separately and a joint effort was critical to make this project a success. As a result, the organizations jointly announced the launch of an international test program.
A fax server was installed on-site at each of the i3 Forum carriers that volunteered. The testing, which consisted of a fax broadcast from each participant to all others, was performed over a 14-week period in the first four months of 2011. Analysis and preliminary recommendations were completed over Q2-Q3 of 2011 and published in November. The primary conclusion was that international FoIP based on G.711 pass-through and T.38 was not currently practical.
Recent SIP FoIP TG work has focused on this routing issue. In simple terms, if a call can be identified during the SIP initiation process as a fax (FoIP or G.711), then carriers could route the call properly and eliminate the timing issues. There have been several alternatives suggested to be integrated into Phase II testing. The most promising is a new feature that is part of a recent Internet Engineering Task Force (IETF) RFC which proposes a new “media feature tag.” If this can be applied to contact headers (i.e. sip.fax), it may be a major part of the solution.
Currently the Task Group is working with the appropriate standards bodies and i3Forum to present findings and recommendations for additional discussion and comment.
More at sipforum.org