Top

Basic Fax Concepts

T.38 Fax

The Mediatrix unit can send faxes in T.38 mode over UDP. T.38 is used for fax if both units are T.38 capable; otherwise, transmission in clear channel over G.711 as defined is used (if G.711 μ-law and/or G.711 A-law are enabled). If no clear channel codecs are enabled and the other endpoint is not T.38 capable, the fax transmission fails.



Note: The Mediatrix unit opens the T.38 channel only after receiving the “200 OK” message from the peer.
Note: Media5 recommends not to use a fax that does not send a CNG tone. If using such a fax to send a fax communication to the public network, this might result in a communication failure.

Top

Fax Parameters

The Mediatrix unit handles G3 fax transmissions at speeds up to 14.4 kbps. Automatic fax mode detection is standard on all endpoints. Real-Time Fax Over UDP with the T.38 protocol stack is also available.

A fax call works much like a regular voice call, with the following differences:
  • The fax codec may be re-negotiated by using a re-INVITE.
  • The goal of the re-INVITE is to allow both user agents to agree on a fax codec, which is either:
    • Clear channel (G.711 or G.726) without Echo Cancellation nor Silence Suppression (automatically disabled).
    • T.38.
  • Upon fax termination, if the call is not BYE, the previous voice codec is recovered with another re-INVITE.
  • For fax speeds higher than 14.4 kbps, the Clear channel codec is recommended.

Top

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

Top

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


Top

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


Top

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


Top
Top

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.

Top

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



Top

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



Top

Basic Fax Tasks

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



Top

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



Top

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



Top

Configuring the T.38 No Signal Timeout

Steps
  1. Go to Media/Codecs.
  2. Click located on the same row as T.38.
  3. 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.
  4. Click Apply.
Result



Top

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:


Top

Top

Basic Codec Concepts

Default vs Specific Endpoint Configuration

It is possible to configure all endpoints to the default value, or an endpoint to a specific value, or a mix of both.

When you do not change your configuration, the values keep the default configuration. In order to modify the codec settings for a specific endpoint, the endpoint must first be selected from the drop-down list. It is also possible to have a default configuration followed by one or more specific endpoint configurations.
  • Default configuration
  • Mix of default and specific endpoint configurations
  • All endpoints enabled with specific configurations

Top

Codec Configuration

This document describes the steps required to enable or disable the codecs of the Mediatrix unit, as well as access the codec-specific parameters.

The Codec section allows setting two types of configurations:
  • Default configurations that apply to all endpoints of the Mediatrix unit.
  • Specific configurations that override the default configurations. Specific configurations can be set for each endpoint in the Mediatrix unit.

Top

Codec Vs Bearer Capabilities

The Codec Vs. Bearer Capabilities Mapping section allows you to select the codec to prioritise or select in the outgoing INVITE when the incoming SETUP ITC (Information Transfer Capability) matches the configured one. It is also possible to select the ITC value to set in the outgoing SETUP bearer capabilities when the incoming INVITE codec matches the configured one.

Note: This section in only available for units with ISDN interfaces.

Top

Generic Voice Activity Detection (VAD)

VAD defines how the Mediatrix sends information pertaining to silence. This allows the unit to detect when the user talks, thus avoiding to send silent RTP packets.

The Generic Voice Activity Detection (VAD) section allows selecting two types of configurations:
  • Default configurations that apply to all endpoints of the Mediatrix unit.
  • Specific configurations that override the default configurations. Specific configurations can be set for each endpoint in the Mediatrix unit.

Top

Data Codec Selection Procedure Flow

The Mediatrix unit follows a procedure when selecting data codec. This procedure is the Mediatrix unit default behaviour. Some interop parameter may modify this procedure. Tones are detected on the analog ports only.




Top

Basic Codec Tasks

Enabling Default Codecs

Steps
  1. Go to Media/Codecs.
  2. From the Select Codec Bank, choose if you want the G.722 , the G.723.1, G.726 or G.729 codec.
    Note: All Codec Banks include the T.38, the Clear Mode, the Clear Channel, and the X-CCD codecs.
  3. In the Codec table, select the desired codecs and Enable / Disable them.
    Note: Codecs that appear in Red are not part of the selected codec Bank, thus they can be disabled without a problem.
  4. Click for Advanced codec settings.
    Note: When enabling two codecs or more, the priority order can be modified by selecting the advanced options.
  5. Click Apply.
Result



Top

Enabling Codecs For Specific Endpoints

Steps
  1. Go to Media/Codecs.
  2. From the Select Codec Bank, choose if you want the G.722 , the G.723.1, G.726 or G.729 codec.
    Note: All Codec Banks include the T.38, the Clear Mode, the Clear Channel, and the X-CCD codecs.
  3. From the Select Endpoint drop-down list select the port you want to configure.
  4. In the Codec table, from the Endpoint Specific drop-down list, select Yes for the desired codecs and Enable/Disable them.
    Note: When enabling two codecs or more, the priority order can be modified by selecting the advanced options.
  5. Click for Advanced codec options.
  6. Click Apply.
Result



Top

Configuring Codec Vs. Bearer Capabilities Mapping

Steps
  1. Go to Media/Codecs.
  2. In the Codecs vs. Bearer Capabilities Mapping table, select Enable from the Enable drop-down list.
  3. For each enabled codec, complete the fields are required.
  4. Click Apply.
Result



Top

Configuring Generic Voice Activity Detection (VAD)

Steps
  1. Go to Media/Codecs.
  2. From the Select Codec Bank, choose if you want the G.722 , the G.723.1, G.726 or G.729 codec.
    Note: All Codec Banks include the T.38, the Clear Mode, the Clear Channel, and the X-CCD codecs.
  3. In the Generic Voice Activity Detection (VAD) table,
  4. set Enable (G.711, G.722 and G.726) to the proper setting from the drop-down list.
  5. Click Apply.
Result



Top

Configuring Generic Voice Activity Detection (VAD) For Specific Endpoint

Steps
  1. Go to Media/Codecs.
  2. From the Select Endpoint drop-down list select the port to configure.
  3. In the Generic Voice Activity Detection (VAD) table, from the Endpoint Specific drop-down list, select Yes.
  4. Enable the G.711 and G.726 Voice Activity Detection (VAD) by selecting the proper setting in the drop-down list.
  5. Click Apply.
Result



Top

Advanced Parameters

Configuring Codec Advanced Parameters

Steps
  1. Go to Media/Codecs.
  2. From the Select Codec Bank, choose if you want the G.722, the G.723.1, G.726 or G.729 codec.
    Note: All Codec Banks include the T.38, the Clear Mode, the Clear Channel, and the X-CCD codecs.
  3. In the Codec table, click next to the codec you wish to configure.
  4. From the Select Endpoint drop-down list, select Default to apply changes to all endpoints or select the specific Endpoint to apply changes to the selected endpoint.
  5. Complete the fields as required.
  6. Click Apply.
Result
This is an example for the G.729 Codec.


Top

Mipt Default vs Specific Endpoint Configuration Examples

Global>Mipt.EpSpecificCodec
 _____________________________________________________________
| EpId     | EnableConfig  | GenericVoiceActivityDetection    |
|__________|_______________|__________________________________|
| FXO1     | Disable       | Conservative                     |
| FXO2     | Disable       | Conservative                     |
| FXO3     | Disable       | Conservative                     |
| FXO4     | Disable       | Conservative                     |
| FXS1     | Disable       | Conservative                     |
| FXS2     | Disable       | Conservative                     |
| FXS3     | Disable       | Conservative                     |
| FXS4     | Disable       | Conservative                     |
|__________|_______________|__________________________________|
Global>Mipt.epSpecificCodecG711Mulaw
 ___________________________________________________________________
| EpId   | EnableConfig  | VoiceEnable | VoicePriority | DataEnable | 
|________|_______________|_____________|_______________|____________|
| FXO1   | Disable       | Enable      | 0             | Enable     |  
| FXO2   | Disable       | Enable      | 0             | Enable     |
| FXO3   | Disable       | Enable      | 0             | Enable     |
| FXO4   | Disable       | Enable      | 0             | Enable     |
| FXS1   | Disable       | Enable      | 0             | Enable     |
| FXS2   | Disable       | Enable      | 0             | Enable     |
| FXS3   | Disable       | Enable      | 0             | Enable     |
| FXS4   | Disable       | Enable      | 0             | Enable     |
|________|_______________|_____________|_______________|____________|
 _______________________________________________
| EpId   | DataPriority | MinPtime | MaxPtime   |
|________|______________|__________|____________|
| FXO1   | 0            | 30       | 30         |  
| FXO2   | 0            | 30       | 30         |
| FXO3   | 0            | 30       | 30         |
| FXO4   | 0            | 30       | 30         |
| FXS1   | 0            | 30       | 30         |
| FXS2   | 0            | 30       | 30         |
| FXS3   | 0            | 30       | 30         |
| FXS4   | 0            | 30       | 30         |
|________|______________|__________|____________|

Global>Mipt.epSpecificCodecG711Mulaw[EpId=FXS1].DataPriority=10
Global>mipt.Restart
Global>Mipt.epSpecificCodecG711Mulaw
____________________________________________________________________
| EpId   | EnableConfig  | VoiceEnable | VoicePriority | DataEnable | 
|________|_______________|_____________|_______________|____________|
| FXO1   | Disable       | Enable      | 0             | Enable     |  
| FXO2   | Disable       | Enable      | 0             | Enable     |
| FXO3   | Disable       | Enable      | 0             | Enable     |
| FXO4   | Disable       | Enable      | 0             | Enable     |
| FXS1   | Disable       | Enable      | 0             | Enable     |
| FXS2   | Disable       | Enable      | 0             | Enable     |
| FXS3   | Disable       | Enable      | 0             | Enable     |
| FXS4   | Disable       | Enable      | 0             | Enable     |
|________|_______________|_____________|_______________|____________|

________________________________________________
| EpId   | DataPriority  | MinPtime  | MaxPtime |
|________|_______________|___________|__________|
| FXO1   | 0             | 30        | 30       |  
| FXO2   | 0             | 30        | 30       |
| FXO3   | 0             | 30        | 30       |
| FXO4   | 0             | 30        | 30       |
| FXS1   | 10            | 30        | 30       |
| FXS2   | 0             | 30        | 30       |
| FXS3   | 0             | 30        | 30       |
| FXS4   | 0             | 30        | 30       |
|________|_______________|___________|__________|

Global>Mipt.EpSpecificCodec[EpId=FXS1].EnableConfig=Enable
Global>Mipt.EpSpecificCodec[EpId=FXS1].GenericVoiceActivityDetection=Transparent
Global>Mipt.EpSpecificCodec
 ____________________________________________________________
| EpId   | EnableConfig   | GenericVoiceActivityDetection    |
|________|________________|__________________________________|
| FXO1   | Disable        | Conservative                     |
| FXO2   | Disable        | Conservative                     |
| FXO3   | Disable        | Conservative                     |
| FXO4   | Disable        | Conservative                     |
| FXS1   | Enable         | Transparent                      |
| FXS2   | Disable        | Conservative                     |
| FXS3   | Disable        | Conservative                     |
| FXS4   | Disable        | Conservative                     |
|________|________________|__________________________________|

Top

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 be displayed.


Top

DGW Documentation

Mediatrix units are supplied with an exhaustive set of documentation.

Mediatrix user documentation is available on the Media5 Documentation Portal at http://documentation.media5corp.com

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.

Top

Copyright Notice

Copyright © 2020 Media5 Corporation.

This document contains information that is proprietary to Media5 Corporation.

Media5 Corporation reserves all rights to this document as well as to the Intellectual Property of the document and the technology and know-how that it includes and represents.

This publication cannot be reproduced, neither in whole nor in part, in any form whatsoever, without written prior approval by Media5 Corporation.

Media5 Corporation reserves the right to revise this publication and make changes at any time and without the obligation to notify any person and/or entity of such revisions and/or changes.