R2511-HP MSR Router Series Voice Configuration Guide(V5)

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Configuring fax over IP

Traditional fax machines transmit and receive faxes over PSTN. Fax has gained wide acceptance due to

its many advantages, such as high transmission speed and simple operations. By far, G3 fax machines

dominant fax communications. A G3 fax machine adopts the signal digitizing technology. Image

signals are digitized and compressed internally, then converted into analog signals through a modem,

and finally transmitted into the PSTN switch through common subscriber lines.

FoIP means sending and receiving faxes over the Internet. Routers can provide the FoIP function after the

FoIP feature is added, on the basis of the VoIP function. Because the FoIP is the Internet-based fax service,

sending national and international faxes costs less.

The network diagram for FoIP is similar to that for VoIP. You just replace the IP phone with a fax machine

to implement the fax function. As long as you can use IP phones, you can use the fax function. This makes

the fax function very simple.

The following figure illustrates an FoIP system structure.

Figure 88 FoIP system structure

FoIP protocols and standards

IP real-time fax complies with the ITU-T T.30 and T.4 protocols on the PSTN side and the H.323 and T.38

protocols on the IP network side.

• T.30 protocol pertains to file and fax transmission over PSTN. It describes and regulates the

communication traffic of G3 fax machines over common telephone networks, signal format, control

signaling, and error correction to the full extent.

• T.4 protocol is a standard protocol involving the G3 fax terminals for file transmission. It provides a

standard regulation for the G3 fax terminals on image encoding/decoding scheme, signal

modulation and speed, transmission duration, error correction, and file transmission mode.

• T.38 protocol pertains to the real-time G3 fax over IP networks. It describes and regulates the

communication mode, packet format, error correction and some communication flows of real-time

G3 fax over IP networks.

Fax flow

In FoIP, the call setup, handshake, rate training, packet transfer, and call release are always real-time.

From the perspective of users, FoIP is no different than faxing over PSTN.

PSTN

Internet

Fax Fax