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Voice Feature Guide 01

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
What Is FoIP

What Is FoIP

Definition

Fax over Internet Protocol (FoIP) is a fax service provided on an IP network or between an IP network and a traditional PSTN. Figure 1-115 shows the network application of FoIP.
Figure 1-115 FoIP network application

Basic Process

The basic process of fax can be described as follows:
  1. The fax transmitting machine scans a page to obtain image information.
  2. The fax transmitting machine digitalizes and compresses the image signals.
  3. The fax transmitting machine modulates the image signals into analog signals, and transmits the signals to the fax receiving machine through common subscriber lines (as defined in the T.30 protocol).

Commonly Used Protocols for Fax

The following protocols are commonly used for fax:
  • T.30: It is a fax protocol based on the PSTN network. T.30 defines in detail the process for transmitting fax signals on a PSTN network. It also defines the modulation mode (V.17/V.21/V.27/V.29/V.34) and transmission format (HDLC) of data, and the physical standard for fax signals. The T.30 fax messages and data can be transmitted transparently between AGs. This is called the T.30 transparent transmission mode. The quality of fax in this mode may not be high due to packet loss, delay, and packet disorder on the IP network.
  • T.38: It is a protocol that defines the process for carrying fax services over a packet IP network. Serving as a supplementary protocol to T.30, T.38 implements packet encapsulation based on T.30 in order to adapt to IP applications. In T.38 fax service, the T.38 redundancy mechanism is used to ensure service quality.

Typical Fax Process Defined in T.30

T.30 defines 5 phases for a typical fax process, as shown in Figure 1-116.
  • Phase A: A call for fax is established. This phase is similar to a telephone call establishment phase.
  • Phase B: The earlier phase of the packet transmission process. In this phase, the devices at both ends perform capability negotiation and training.
  • Phase C: This is the packet transmission phase and also the packet transmission control phase.
  • Phase D: The later phase of the packet transmission process. In this phase, packets are verified, errors are corrected, and multiple pages are continuously transmitted.
  • Phase E: The call for fax is released.
Figure 1-116 Typical fax process defined in T.30
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Updated: 2019-02-22

Document ID: EDOC1100067358

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