SIP School

FoIP Interop Workshop

The W San Francisco Hotel – (across the street from the Moscone Convention Center and the VoiceCon show)
Workroom #2, 3rd Floor.
181 Third Street, San Francisco CA 94103
Date & Time: Monday, November 10, 2008 – 11:00am – 3:00pm
Cost: FREE
Organizer: SIP Forum
Lead Sponsor: Dialogic


The demand for fax and fax services remains high. Fax Over IP (FoIP) is gaining momentum in the industry, but a number of issues remain that seriously impact interoperability and reliability.

Issue: G.711 Fax Reliability

The ITU-T T.38 FoIP protocol standard overcame many of the issues experienced when transmitting a fax over G.711. However, many Service Providers use VoIP Gateways that do not support T.38. These Carriers pass fax traffic through their network using G.711. Fax traffic is highly sensitive to packet loss. The loss of fax packets (from latency or jitter for example) results in faxes to fail and be re-transmitted which uses more bandwidth and lowers the end user’s satisfaction. Many carriers desire a FoIP solution that allows them to utilize their non-T.38 infrastructure to reliably carry fax traffic.

Issue: T.38 Fax Interoperability

Many enterprises use T.38 for fax transmission. However, variations in the interpretation of the T.38 specification have lead to various interoperability challenges between vendors. There is speculation that improvements or profiles during session setup can alleviate many of these problems.

Workshop Overview

The SIP Forum FoIP Interoperability Workshop brought together researchers, engineers, and service providers to exchange ideas, share experiences, and propose approaches to address FoIP problems.  Particular focus was on the use and applicability of SIP to address systemic or architectural problems. We did not examine implementation errors.

Topics of interest included but were not limited to:

  • Interoperability failures seen in the field or lab
  • Reliability or quality issues seen in the field or lab
  • Deployment experiences
  • Development experiences
  • Architectural principals
  • Proposals for achieving a higher degree of FoIP interoperability and/or FoIP reliability
  • Proposals for soliciting additional real-world feedback from implementers and service providers

Discussion Materials

The purpose of having position papers for this workshop was to help focus discussion and allow participants to get a feel for what other participants are thinking about. This was not a scholarly conference. PowerPoint presentations were acceptable. The goal of the workshop was not to publish high-quality research papers. The goal of the workshop was to publish a report discussing the technical issues that are of the utmost importance to the industry, as well as a roadmap for how to address them.

We encouraged individuals to submit position papers relevant to FoIP. Acceptable formats were IETF Internet Draft style (in HTML or plain text), IEEE Computer Society Proceedings Manuscripts style (in PDF), ACM Transactions style (in PDF), or presentation style (in PDF).

View submitted papers and presentations in the Workshop document repository.

Workshop Format

This was a highly interactive workshop. In order to frame the conversation, the workshop chair opened the discussion. At the discretion of the workshop chair and dependent upon the quality and number of position papers received, the workshop chair requested formal presentations. Note that all position papers were published on the SIP Forum web site, unless the author(s) requested withholding publication.

Workshop Feeds

The workshop, including lunch, was free of charge to active participants.

Workshop Chair

Richard Shockey

Program Whip

Max Schroeder

Program Committee

Eric Burger

Workshop Minutes and Materials

View archived information relating to the Workshop, including the submissions from the Workshop.