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SIP Forum’s Fax over IP Task Group Achieves Milestone with the Publication of IETF RFC 6913

RFC 6913, “Indicating Fax over IP Capability in the Session Initiation Protocol (SIP),” enables intelligent FoIP routing for International faxing by introducing a new “sip.fax” media feature tag, and is a direct outcome of the SIP Forum’s global Interop testing effort with the i3 Forum

NORTH ANDOVER, MA (May 14, 2013) – The SIP Forum announced today its Fax over IP (FoIP) Task Group has achieved a significant milestone in its mission to improve international IP fax transport services with the publication of RFC 6913 – a new Internet Engineering Task Force (IETF) RFC that introduces a new “sip.fax” media feature tag that aims to enable the intelligent routing of International faxes and greatly improve the reliability of International faxing services.

RFC 6913, co-authored by David Hanes, Kevin Fleming and Gonzalo Salgueiro, defines and registers with IANA a new “fax” media feature tag for use with the Session Initiation Protocol (SIP). Currently, fax calls are indistinguishable from voice calls at call initiation. Consequently, fax calls can be routed to SIP user agents that are not fax capable. A “fax” media feature tag implemented in conjunction with caller preferences allows for early advertisement of fax capabilities and consequently, more intelligent fax call routing.

Carriers have long struggled with the quality and reliability of international IP faxing using the T.38 fax protocol in SIP networks — a critical challenge for global service providers transitioning from a TDM to an IP-based network infrastructure. With the new “sip.fax” media feature tag, service providers worldwide have a new tool available to them that will allow for standardized, well-defined and optimized intelligent routing policies whereby they can selectively direct FoIP calls over qualified FoIP routes. RFC 6913 is intended to enable a standards-based framework that eliminates implementation-dependent variability and to support successful end-to-end transmission of international fax calls between networks.

“Using RFC 6913, carriers can implement more intelligent and selective routing practices for IP fax calls. Based on the results of our extensive joint testing with i3 Forum carriers from around the globe, this ability to route fax calls down fax-optimized routes is especially critical in high delay environments like international tandem-carrier routes with one or more IP-to-TDM conversion points. Implementing these improvements to FoIP should help address the root causes of current transmission problems and move the FoIP Task Group a giant step closer towards achieving its goal of making global IP faxing reliable in 2013,” said Gonzalo Salgueiro, SIP Forum FoIP Task Group Chair.

SIP Forum FoIP Task Group

The SIP Forum’s FoIP Task Group is chartered with improving the quality and reliability of FoIP in SIP networks, particularly the inter-carrier use of FoIP. First launched in late 2008 to address the technical and interoperability challenges involving the transmission of fax documents over a SIP-enabled network, the group outlined some of the key issues in its 2009 FoIP Problem Statement, and the publication of the T.38 SIP-SDP Problem Statement.

FoIP Task Group leadership includes: Chair Gonzalo Salgueiro, Technical Leader at Cisco; Marc Robins, President and Managing Director of the SIP Forum; and Max Schroeder, Sr. VP. FaxCore, who serves as Task Group Whip.

In addition, Mike Coffee, CEO of Commetrex and former co-chair of the FoIP Task Group, was a key contributor in the formation, planning and execution of the groundbreaking joint testing program with the i3 Forum. His leadership and guidance were instrumental in making this multi-year coordinated effort with carriers from around the globe the most comprehensive attempt to identify and resolve the many challenges with international FoIP.

SIP Forum-i3 Forum Joint Testing Program

In 2011, the SIP Forum and i3 Forum joined forces to develop a new comprehensive testing program for carrier-based FoIP. The goal was to identify and qualify transmission impairments and interoperability challenges that arose in IP-based networks as the T.38 protocol became more widely deployed across carrier and enterprise networks.

“The joint testing initiative involved 12 carriers and marked the first time the global carrier community has come together with a holistic approach to solving this problem,” said Marc Robins, SIP Forum President and Managing Director.

To that end, i3 Forum carriers volunteered to participate in two testing phases. Task group members installed a fax server at each carrier’s location and conducted fax broadcast tests over a 14-week period.

Phase I of the testing identified consistent internetworking IP fax issues between SIP and SS7 networks. “FoIP calls transmitted internationally, using tandem-carrier connections between SIP networks and SS7 carrier networks, and utilizing least-cost routing methods, failed 50 percent of the time – a very high rate,” said Max Schroeder, FoIP TG Whip. “So we decided to look more closely at the routing issue and forensically examine the least-cost routing of fax messages.”

The Phase II testing was conducted over a five-month period beginning in the fall of 2011 and into early 2012. The purpose of this testing effort was to more closely examine the question of FoIP-qualified routing. Sixteen carriers participated and worked in pairs to trace FoIP calls end-to-end and identify the errors, exploring more closely the full routing information for each call.

“The findings conclusively showed that T.38 fax calls between IP and legacy SS7 carrier networks, using existing least-cost-routing methods, had a consistently high failure rate, unlike faxes that employed ‘intelligent routing’ policies,” Schroeder said.

The Phase I and Phase II testing results and analysis provided the basis for the FoIP Task Group’s technical and design recommendation to the IETF and the technical community at large.

About the SIP Forum

The SIP Forum is an IP communications industry association that engages in numerous activities that promote and advance SIP-based technology, such as the development of industry recommendations, the SIPit and SIPconnect-IT interoperability and testing events, special workshops, educational seminars, and general promotion of SIP in the industry. The SIP Forum is also the producer of the annual SIPNOC conferences (for SIP Network Operators Conference), focused on the technical requirements of the service provider community. One of the Forum’s notable technical activities is the development of the SIPconnect Technical Recommendation – a standards-based SIP trunking recommendation that provides detailed guidelines for direct IP peering and interoperability between IP PBXs and SIP-based service provider networks. Other important Forum initiatives include work in Fax-over-IP interoperability, User Agent Configuration, VRS interoperability, security, and SIP and IPv6. For more information, please visit:

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SIP Forum


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