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Several Reasons Why Cisco Prefers T.38 FoIP


September 28, 2011

While voice over IP (VoIP) has revolutionized the world of telecommunications and is now a mainstream solution in most enterprise networks, fax over IP (FoIP) has been off to a slow start.

A major factor for remaining on the back burner is because fax communications has not been a dominant communications form of telephony for businesses. Now, as VoIP matures, organizations are pushing for comprehensive unified communications solutions, where IP is the backbone for all communications, including fax.

As FoIP evolves, T.38 protocol is gaining momentum for several reasons. In fact, according to David Hanes, technical leader for Cisco’s Customer Advanced Engineering, T.38 fax relay is the de facto standard for fax communications today. This was not the case when he first started working with FoIP about eight years ago. Earlier, Cisco customers preferred Cisco fax relay (Cisco's pre-standard fax relay implementation) or pass-through for transporting their fax communications over IP.

T.38 FoIP ptotocol was rarely implemented in those days, noted Hanes. According to Hanes, today’s rapid transition to T.38 is happening for several reasons. First, unlike proprietary Cisco fax relay only implemented on Cisco voice products, T.38 is a standards-based solution. Secondly, T.38 fax relay offers a robust redundancy mechanism. With packet loss being the most harmful impairment for fax communications in IP networks, T.38 fax relay offers multiple redundancy levels that can be separately configured for the low-speed T.30 signaling messages and the high-speed page transmissions. Cisco fax relay does not offer redundancy at all and while some pass-through implementations offer redundancy in the form of RFC 2198, T.38's redundancy is superior, stated Hanes.

Third, T.38 consumes the least amount of bandwidth. When dealing with fax communications over WAN links where bandwidth is usually contentious, T.38 fax relay is more efficient than Cisco fax relay and pass-throughs. Over the frame relay WAN protocol, Cisco fax relay uses 48 kbps per call and pass-through with its G.711 codec is over 80 kbps. While T.38 fax relay uses only 25 kbps per call.

Lastly, it offers interoperability. “This is the most important reason why T.38 has done so well,” asserted Hanes.


Ashok Bindra is a veteran writer and editor with more than 25 years of editorial experience covering RF/wireless technologies, semiconductors and power electronics. To read more of his articles, please visit his columnist page.

Edited by Tammy Wolf




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