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Fax Information Required for Troubleshooting

Information Type
Fax Transmission Protocol Clear Mode T.38
Fax Transmission Speed High speed Low speed
Fax mode Automatic Manual
Receiving fax Model Make
Sending fax Model Make
Fax mode ECM non- ECM
Firewall Yes No
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T.38 Fax Transmission

T.38 is an ITU recommendation for allowing transmission of fax over IP networks in real time.

PROs

  • Allows for redundancy, therefore increases the reliability of the transmissions.
  • Faxes in T.38 are not as sensitive to network imperfection like packet loss or jitter as faxes in Clear Channel.

CONs

  • The number of redundancy packets will increase the bandwidth used
  • The higher the speed, the more bandwidth is used.
  • May take more bandwidth than a fax in Clear channel.

Requirements

  • The Mediatrix must be able to detect a CNG , v21 preamble or T.38 packet to switch to T.38
  • Reasonable delay, 1 second round trip is acceptable however 2 seconds could cause timeout or collision

Configuration

Call Flow

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Enabling T.38 Fax Transmission

Steps
  1. Go to Media/Codecs.
  2. In the Codec section, click located on the same line as T.38.
  3. Set the Enable filed to Enable.
  4. Click Apply.
Result


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Setting the Redundancy Level

Steps
  1. Go to Media/Codecs.
  2. In the Codec section, click located on the same line as T.38.
  3. In the T.38 table, set the Redundancy Level .
    Note: Using redundancy increases transmission reliability, however the number of redundancy packets will also increase the bandwidth being used.
  4. Set the Frame Redundancy Level.
    Note: The repetition of the final frame will help prevent losing the end of a message, v.21 or end of page message. Losing the end of packet message can create a major problem in the transmission since the Redundancy is not use in this situation.
  5. Click Apply.
Result


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Allowing Unsecure T.38 with Secure RTP

Context

The T.38 protocol must be enabled under Media/Codec.

This procedure is required only if SRTP is used and is available provided the Select Endpoint selection list is set to Default.
Steps
  1. Go to Media/Security.
  2. In the Security table, under the RTP section, set the Mode selection list to Secure with fallback.
  3. Under the T.38 section, set the Allow Unsecure T.38 with Secure RTP selection list to Yes.
  4. Click Apply.
Result


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Configuring the Behavior of the T.38 INVITE Not Accepted

This task allows you to set the unit’s behaviour after receiving an error to a SIP INVITE for T.38 fax.

Steps
  1. Go to SIP/Interop.
  2. In the Behavior on T.38 INVITE Not Accepted table, from the Behavior selection list, set the required behavior for each SIP Error Code.
  3. Click Apply.
Result


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Fax Transmission through a Firewall

Using T.38 with a Firewall

Requirements

  • The communication channel must remain open for a fax to go through a firewall i.e. the unit sends "no signal" packets to fill the dead air intervals that could occur during a fax transmission and cause the closure of the firewall.

Configuration

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Configuring the T.38 No Signal

Steps
  1. Go to Media/Codecs.
  2. Click located on the same row as T.38.
  3. Set the No Signal selection list to Enable.
  4. Set the No Signal Timeout selection list to Enable.
    Note: In order to keep RTP ports opened for T.38 packets, the unit will send 'no signal' packets to fill the dead air intervals that could occur during a fax transmission and cause the closure of the firewall.
  5. Click Apply.
Result


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Clear Channel Fax Transmission

Modulated Fax information from the PSTN is passed in-band end-to-end over a voice speech path in a IP network.

There are 2 pass-through techniques.
  • The configured voice codec is used for fax transmission. This technique works only when the configured codec is G711 with no VAD and no echo cancellation (EC) or when the configured codec is a clear channel codec or G.726/32. Low bit-rate codecs cannot be used for fax transmission.
  • Gateway dynamically changes the codec from the codec configured for voice to G.711 with no VAD and no EC for the duration of the fax session. This method is referred to as "codec up speed" or "fax pass-through with up speed".

PROs

  • Less intrusive, does not modify the packets
  • Does not allows for redundancy
  • Takes less bandwidth than a T.38 fax transmission
  • The bandwidth usage is practically constant.
  • Bandwidth only affected by the P-Time.

CONs

  • Sensitive to network imperfection like packet loss or jitter

Configuration

Configuring the Clear Channel Fax Transmission
Call Flow

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Configuring the Clear Channel Fax Transmission

Steps
  1. Go to Media/Codecs.
  2. In the Codec section, click located on the same line as the Codec you wish to use for Fax Transmission.
  3. In the selected Codec table, set the fields as required.
  4. Make sure to enable the Data Transmission.
  5. Click Apply.
Result
For example:

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FAX Detection Flow

IF AND THEN
If T.38 is enabled
  • A CNG tone is detected, or
  • A V.21 preamble is detected, or
  • T.38 packets are received on the IP side
 Then the Mediatrix switches to T.38
  • If a CED tone is detected (Answer Tone or ANS) and no other conditions indicates that a fax is present, or
  • If a fax is detected but T.38 is deactivated
Then the Mediatrix unit switches to Clear mode.
If a CED
Note: Note that the CED tone can be detected on both the IP side (egress side) or on the analog side (ingress side). is detected before a CNG
 The Mediatrix unit will first switch to Clear Channel and if T.38 is enabled, it will then switch to T.38.
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Configuring Machine Detection

Context
Note: This procedure is only required if your fax machine is directly connected to a specific FXS port and if this port is not used for modem transmission.
Steps
  1. Go to Media/Misc.
  2. Set the CNG Tone Detection selection list to Enable.
  3. Set the CED Tone Detection selection list to Enable.
  4. Set the V.21 Modulation Detection selection list to Enable.
  5. Set the Behavior On CED Tone Detection selection list to Fax Mode.
  6. Click Apply.
Result


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Parameters

Although the services can be configured in great part in the web browser, some aspects of the configuration can only be completed with the MIB parameters by:
  • using a MIB browser, such as the Mediatrix Unit Manager Network (UMN);
  • using the CLI;
  • creating a configuration script containing the configuration parameters.
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Online Help

If you are not familiar with the meaning of the fields and buttons, click Show Help, located at the upper right corner of the Web page. When activated, the fields and buttons that offer online help will change to green and if you hover over them, the description will bedisplayed.

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DGW Documentation

Mediatrix devices are supplied with an exhaustive set of documentation.

Mediatrix user documentation is available on the Media5 Documentation Portal.

Several types of documents were created to clearly present the information you are looking for. Our documentation includes:
  • Release notes: Generated at each GA release, this document includes the known and solved issues of the software. It also outlines the changes and the new features the release includes.
  • Configuration notes: These documents are created to facilitate the configuration of a specific use case. They address a configuration aspect we consider that most users will need to perform. However, in some cases, a configuration note is created after receiving a question from a customer. They provide standard step-by-step procedures detailing the values of the parameters to use. They provide a means of validation and present some conceptual information. The configuration notes are specifically created to guide the user through an aspect of the configuration.
  • Technical bulletins: These documents are created to facilitate the configuration of a specific technical action, such as performing a firmware upgrade.
  • Hardware installation guide: They provide the detailed procedure on how to safely and adequately install the unit. It provides information on card installation, cable connections, and how to access for the first time the Management interface.
  • User guide: The user guide explains how to customise to your needs the configuration of the unit. Although this document is task oriented, it provides conceptual information to help the user understand the purpose and impact of each task. The User Guide will provide information such as where and how TR-069 can be configured in the Management Interface, how to set firewalls, or how to use the CLI to configure parameters that are not available in the Management Interface.
  • Reference guide: This exhaustive document has been created for advanced users. It includes a description of all the parameters used by all the services of the Mediatrix units. You will find, for example, scripts to configure a specific parameter, notification messages sent by a service, or an action description used to create Rulesets. This document includes reference information such as a dictionary, and it does not include any step-by-step procedures.
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Copyright Notice

Copyright © 2023 Media5 Corporation.

This document contains information that is proprietary to Media5 Corporation.

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