Configuring the Fax Service

NetEngine AR V300R019 CLI-based Configuration Guide - Voice

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This section describes the concept and configuration of the fax service.

Context

Depending on the transport protocol used, the fax service can be provided in transparent or T.38 mode.

In transparent mode, modulated fax data from a PSTN is forwarded over an end-to-end voice tunnel on an IP network. The gateway between the PSTN and the IP network directly forwards fax data to the peer gateway and fax machine as voice data, and does not perform fax modulation and demodulation. Fax transparent transmission is implemented using either of the following methods:

Preconfigured voice code is used to transmit fax data.
During fax processing, the gateway converts the fax code into G.711 lossless code through media negotiation or digitally re-encodes the fax signals using T.38. This helps reduce the impact on fax data caused by IP network jitter.

Figure 2-34 shows the process of fax transparent transmission.

Figure 2-34 Process of fax transparent transmission

In T.38 mode, the sender gateway demodulates the T.30 fax data from the PSTN. The demodulated fax data is encapsulated in datagrams and sent to the receiver across the IP network. The receiver gateway modulates the datagrams into T.30 fax data and sends the fax data to the receiver. Figure 2-35 shows the process of T.38 fax transmission.

Figure 2-35 Process of T.38 fax transmission

A fax machine can be directly connected to the FXS interface of the PBX or connected to the PBX through an integrated access device (IAD). Figure 2-36 shows a typical networking of the fax service.

Figure 2-36 Fax service networking

On this network:

The PBX connects to the IP PBX through a SIP trunk.
The IAD registers fax machine A with the PBX.
Fax machine B is a POTS user of the PBX.

Prerequisites

Before configuring the fax service, complete the following tasks:

Configure PBX users. For details about the configuration, see Configuring a PBX User.
Configure a call prefix for inter-office calls. For details about the configuration, see Configuring a Call Prefix.
Configure a SIP or H.323 trunk group. For details about the configuration, see Configuring Trunk Groups.

Procedure

The fax service can be transmitted in transparent or T.38 mode, and the codec negotiation mode can be negotiation or auto-switching. By default, transparent transmission and negotiation mode are used. The PBX must negotiate with the remote IP PBX about the transmission protocol or mode to improve fax transmission efficiency. To configure the transmission mode, perform the following steps.

Step	Action	Command	Description
1	Enter the system view.	system-view	-
2	Enter the voice view.	voice	-
3	Enter the SIP server view.	sipserver	This configuration applies to communication between fax machines connected to the same PBX, for example, fax machine A and fax machine B. Both ends must use the same codec negotiation mode. NOTE: In the fax interaction process, if the fax recipient gives priority to the remote end, the fax recipient determines the fax transmission mode as follows: (Whether the remote end takes priority is controlled by control point 8. For details, see pbx number-parameter.) If the transmission mode of the fax sender is throughly or T38, check whether the local end supports this transmission mode. If the local end does not support the fax transmission mode, fax transmission fails. If the transmission mode of the fax sender is T38_throughly, check whether the local end supports the T.38 mode and transparent transmission mode in sequence, and use the transmission mode matched first to transmit data. If the transmission mode of the fax sender is throughly_T38, check whether the local end supports the transparent transmission mode and T.38 mode in sequence, and use the transmission mode matched first to transmit data. If the fax recipient gives priority to the local end, the fax recipient performs similar negotiation based on the transmission mode supported by the local end and the fax transmission mode specified in the fax message.
4	Configure the fax transmission mode for the SIP server.	fax-modem fax transmission-mode { T38 \| throughly \| T38_throughly \| throughly_T38 }
5	Configure the fax codec negotiation mode.	fax-modem common negotiation-mode { negotiate \| self-switch }
6	Return to the voice view.	quit	-
7	Enter the trunk group view.	trunk-group name	This configuration applies to communication between fax machines connected to different PBXs, for example, fax machine A/B and fax machine C. Both ends must use the same codec negotiation mode. NOTE: In the fax interaction process, if the fax recipient gives priority to the remote end, the fax recipient determines the fax transmission mode as follows: (Whether the remote end takes priority is controlled by control point 8. For details, see pbx number-parameter.) If the transmission mode of the fax sender is throughly or T38, check whether the local end supports this transmission mode. If the local end does not support the fax transmission mode, fax transmission fails. If the transmission mode of the fax sender is T38_throughly, check whether the local end supports the T.38 mode and transparent transmission mode in sequence, and use the transmission mode matched first to transmit data. If the transmission mode of the fax sender is throughly_T38, check whether the local end supports the transparent transmission mode and T.38 mode in sequence, and use the transmission mode matched first to transmit data. If the fax recipient gives priority to the local end, the fax recipient performs similar negotiation based on the transmission mode supported by the local end and the fax transmission mode specified in the fax message.
8	Configure the fax transmission mode for the trunk group.	fax-modem fax transmission-mode { T38 \| throughly \| T38_throughly \| throughly_T38 }
9	Configure the fax codec negotiation mode.	fax-modem common negotiation-mode { negotiate \| self-switch }
10	(Optional) Enable RFC 2833 fax and modem transmission.	nte-fax-modem enable	-
11	(Optional) Configure the packetization interval in transparent transmission mode.	fax-modem common rtp-interval { 5ms \| 10ms \| 20ms \| 30ms }	Both ends must have the same packetization interval configured.
12	(Optional) Configure the VBD attribute type.	fax-modem common vbd-attribute-type { chinatelecom \| extchinatelecom \| ietf \| v152 }	Both ends must have the same VBD attribute type configured.
13	(Optional) Configure the VBD codec mode.	fax-modem common vbd-codec { g711a \| g711u }	-
14	(Optional) Configure the mode to start the RFC 2198 redundancy transmission negotiation.	redundancy-negotiation-mode { negotiation \| fixed-start \| no-initiative-start }	-
15	(Optional) Configure the mode to start the RFC 2198 redundancy transmission.	redundancy-start-mode { ordinary2198 \| smart2198 }	-
16	(Optional) Enable RFC 2198 redundancy transmission of VBD.	redundancy-vbd enable	-
17	(Optional) Configure the mode to start the RFC 2833 transmission negotiation.	nte-negotiation-mode { negotiation \| fixed-start \| no-initiative-start }	-
18	(Optional) Return to the voice view.	quit	-
19	(Optional) Enter the DSP attribute view.	dsp-attribute	-
20	(Optional) Configure the T.4 redundancy parameters for T.38 fax transmission.	fax redundancy-t4 redundancy-t4-value	-
21	(Optional) Configure the T.30 redundancy parameters for T.38 fax transmission.	fax redundancy-t30 redundancy-t30–value	-
22	(Optional) Configure the fax training mode.	fax training-mode { e2e \| local }	-
23	(Optional) Configure the maximum fax training rate.	fax training-rate { v17 \| v29 \| v27 }	Set this parameter according to the maximum rate supported by the fax machines.
24	(Optional) Configure V8 negotiation parameters.	fax v8negotiate enable	-
25	(Optional) Enable the error correction mode (ECM) for T.38 fax transmission.	fax ecm enable	-

Example

To implement communication between fax machines connected to the same PBX, set the fax transmission mode to T.38 and set the codec negotiation mode to auto-switching.
To implement communication between fax machines connected to different PBXs, set the fax transmission mode to T.38 and set the codec negotiation mode to auto-switching.

<Huawei> system-view
[Huawei] voice
[Huawei-voice] sipserver
[huawei-voice-sipserver] fax-modem fax transmission-mode t38
[huawei-voice-sipserver] fax-modem common negotiation-mode self-switch
[huawei-voice-sipserver] quit
[huawei-voice-trunkgroup-1] fax-modem fax transmission-mode t38
[huawei-voice-trunkgroup-1] fax-modem common negotiation-mode self-switch
[huawei-voice-trunkgroup-1] nte-fax-modem enable
[huawei-voice-trunkgroup-1] quit

Verification

Action	Command	Expected Result
Verify the fax transmission parameter settings on the SIP server.	display voice sipserver fax-modem	The parameter values displayed in the command output are consistent with the settings.
Verify the fax transmission parameter settings in the trunk group.	display voice trunk-group[ name [ fax-modem ] ]

Action

Command

Expected Result

Verify the fax transmission parameter settings on the SIP server.

display voice sipserver fax-modem

The parameter values displayed in the command output are consistent with the settings.

Verify the fax transmission parameter settings in the trunk group.

display voice trunk-group[ name [ fax-modem ] ]

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Updated: 2021-11-30

Document ID: EDOC1100112359

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