T.38 Fax Relay

T.38 Fax Relay

The T.38 approach to fax relay is similar to the Cisco approach, but represents the industry standard. Because T.38 is an open standard from the ITU, it is compatible between different vendors. A Cisco voice-enabled router can be configured as a T.38 gateway, and the transmission methodology is similar to the Cisco fax relay method. However, with T.38 it is possible to deliver documents to virtual fax machines, such as PCs and servers that are configured with software that is compatible with T.38 fax.

As illustrated in Figure 2-45, a T.38 gateway is required at both ends. The T.38 method uses DSP chips to intercept the fax signal at each end and convert the signal to its original digital format, for example, 9600 bps Group 3 fax. The resulting bit stream is then packetized into the T.38 packet format and sent across the IP network.

Figure 2-45. T.38 Fax Relay

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