Ifax update tool software#

The termination gateway then uncompresses and decodes the sample and plays it out to the termination fax machine. With inband faxing, the initial modulated signal is encoded and compressed by the codec on the source router and passed across the VoX network, just as if it was a voice sample. A technique known as upspeeding allows the gateway to initially load the configured voice compression codec into the DSP for voice calls and change it to a low compression codec if fax tones are detected. This method of fax transmission through the voice codec is usually referred to as inband faxing or fax passthrough. For more information about compression codecs, see Voice over IP - Per Call Bandwidth Consumption.įaxes can be transmitted successfully when codecs with lower compression ratios or no compression at all (such as G.726 and G.711 with no echo cancellation or Voice Activity Detection) are used. In fact, the modulated signals of fax transmissions usually do not correctly pass through when these codecs are used, and fax calls fail as a result. High compression codecs, such as G729 and G723, are optimized for voice and compress the voice to a low bandwidth (8 kbps, which excludes overhead for G.729) yet maintain good quality, but G.729 and other high compression codecs are not optimized for fax. The voice compression codecs are usually high compression codecs so that less bandwidth is used for each voice call. For more information about DSPs, see Voice Hardware: C542 and C549 Digital Signal Processors (DSPs). Both types of calls cause the gateway to load the configured voice compression codec in the digital signal processor (DSP). Gateways in a VoX network initially treat voice and fax calls the same. This modulated signal can usually be heard as different audio tones.

Both analog modems and fax machines are digital devices that must use a modulated analog signal to pass the digital information over the PSTN. Since the PSTN was designed for human speech, Group 3 uses analog encoding or modulated signals as would an analog modem. Group 3 fax devices were designed to be used over the public switched telephone network (PSTN). T.4 pertains to how the fax image is encoded by a fax device, and T.30 details the facsimile negotiations and communication protocol. Fax Group 3 is a standards-based technology that is made up primarily of the T.4 and T.30 ITU recommendations. Most modern fax devices are Group 3 compliant. Conventionsįor more information on document conventions, see the Cisco Technical Tips Conventions. If you work in a live network, ensure that you understand the potential impact of any command before you use it. All of the devices used in this document started with a cleared (default) configuration. The information presented in this document was created from devices in a specific lab environment. This point is noted in the Debugging section of this document.

Ifax update tool software#

Some debug information was taken from a Cisco IOS gateway that ran Cisco IOS Software Release 12.2(7). The information in this document is based primarily on Cisco IOS Software Release 12.2(5), although most of the information will also be useful for other Cisco IOS Software releases. T.38 Fax Relay and the other VoX technologies are also discussed. The primary focus of this document is Cisco proprietary fax relay on Cisco IOS gateways, which operates across VoIP networks. In addition, three main Packet Telephony technologies are in use today, collectively referred to as Voice over 'X' (VoX): Readers of this document should be aware that several techniques are used to pass fax calls across a Packet Telephony network on Cisco IOS ® gateways: An overview of fax and Cisco fax relay is also provided.

The technical intricacies of faxes and fax relay are not covered in detail, but you should be able to troubleshoot for a majority of common fax relay issues. The purpose of this document is to provide a basic guide to troubleshoot and resolve Cisco fax relay issues.