Standard irons wrinkles out of IP fax

More than 40% of telephone charges in large corporations are the result of fax transmissions. Using IP networks to route fax calls can save a significant amount of money.

IP fax is a store-and-forward method. The fax server receives the entire image from the originating desktop, formats it and sends it like an e-mail over the IP network. The remote fax server receives the file and delivers it to the remote fax machine over the local telephone network, bypassing longdistance phone charges.

It's no surprise that corporations and service providers would want to take advantage of this cost-saving method. However, sending fax traffic over IP networks is not as easy as it looks in terms of interoperability.

In order for IP fax to work efficiently, both the originating fax server and the remote fax server have to be from the same vendor and within the same network. Service providers and fax server vendors have implemented propriety methods for routing fax files, thereby preventing interoperability and ultimately resulting in higher phone bills for users.

To remedy this problem, the International Telecommunications Union (ITU) created the T.37 full mode standard for store-and-forward fax communication. This work was based on the Internet Engineering Task Force (IETF) specifications RFC 2305, which set IP fax protocol specifications, and RFC 2301, defining standard file formats. The result is that both the IETF and ITU have endorsed a common definition for extended/full-mode Internet faxing.

T.37 uses Simple Mail Transfer Protocol addressing to send fax messages. T.37 provides a standardized means of integration into e-mail software packages and allows the comingling of corporate and fax service provider equipment and networks to provide local fax server coverage anywhere.

When first released, the T.37 "simple mode" offered no negotiation between fax servers, so only the lowest common denominator of image compression and page size formats were supported. In this mode, T.37 IP fax offered no confirmation of delivery.

The T.37 "full-mode" standard released in September provides for capability negotiations with the recipient, positive delivery confirmation and support for six additional Tag Image File formats. These new file formats allow delivery of compressed fax files and color faxes.

One of the reasons that faxing continues to proliferate despite e-mail is that it is rightfully perceived to have higher reliability and document integrity for critical business communications. To be successful, Internet faxing must provide reliability and performance equal to or better than traditional public switched telephone network faxing. By enabling positive delivery confirmation, the T.37 standard adds a level of reliability that fax users have come to expect.

The last critical link to successful end-to-end IP fax delivery is the transmission of the document, which relies on the entire network chain being robust. The Enterprise Computer Telephony Forum's T.30 fax standard provides the protocol for controlling the transmission of the fax document image.

It's estimated that more than 100 million installed fax machines from dozens of manufacturers are in service - some more than a decade old. With this huge installed base, there is wide-ranging quality of T.30 implementation, an inconsistency that sometimes prevents the transmission of faxes. To successfully connect and transmit a fax to every machine in this installed base requires a robust T.30 implementation within the fax server hardware. Fax servers that are based on traditional Class 1 and Class 2 data/fax modems (similar to the ones found in PCs) don't have this capability. For the best IP fax implementation, fax servers require intelligent fax boards that can fully support the T.30 and T.37 standards.

Using IP networks for cost-reduced fax delivery is not new. However, as intelligent fax board implementations based on T.30 and T.37 come to market, we can expect more multivendor interoperability and better reliability. The result will be even more cost-effective fax capabilities in the marketplace.

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