Deploying Cisco® Voice over IP Solutions

Summary 353

Summary

This chapter discussed traditional fax over circuit-switched networks and described how

store and forward fax gateways can take calls from G3 fax machines, convert them into

e-mail messages, and transport them over the Internet as e-mail attachments. At the

terminating end of the call, another store and forward fax gateway receives the e-mail

message, converts it back into a fax message, and delivers it to a G3 fax machine. We

explained how the ITU developed the T.30 protocol and adopted the SMTP for fax called

MIME as part of the T.37 standard for store and forward fax.

We also described the ITU T.38 recommendation for fax relay and real-time fax with

spoofing. Using this standard, real-time fax gateway can deliver faxes to remote fax

machines while the sending fax machines are still processing fax pages. With fax relay, the

gateway receives an analog fax signal and demodulates it into its digital form using a fax

modem. The digital, demodulated fax is then packetized and transmitted over the IP

network. At the receiving end, the fax gateway remodulates the digital fax packets into T.30

analog fax signals to be transmitted to the destination fax machine through a gateway

modem.

We described in detail how Cisco implements T.37 store and forward fax, and we gave

configuration guidelines and examples for both on-ramp and off-ramp fax gateways.

Finally, we described how Cisco implements T.38 real-time fax and fax rollover, or never-

busy fax, and we gave configuration guidelines for those applications.