ScopTEL Asterisk T.38 Fax Gateway

Full T.38 Capabilities

Initial support for handling of T.38 sessions was merged into the Asterisk 1.4 codebase. Inside of Asterisk 1.4, it is possible to perform what is referred to as T.38 passthrough. T.38 Passthrough allows Asterisk to carry T.38 UDPTL from one T.38-speaking endpoint to another T.38-speaking endpoint. Asterisk does not modify the media. Asterisk 1.6, in addition to its T.38 passthrough capabilities, introduced T.38 termination support, such that T.38 fax sessions could be initiated from locally stored TIFF files (SendFax) or that T.38 fax sessions could be terminated into locally stored TIFF files (ReceiveFax). The basic faxing capabilities of Asterisk 1.8 remained the same as 1.6.

The limitation of these versions of Asterisk is that while 1.6 - 1.8 are fully capable of passing through or terminating T.38 sessions, there is no capability for T.38 gateway. Older versions of Asterisk cannot directly pass a fax from the PSTN or a non-T.38 endpoint to a T.38 endpoint. Instead, older versions of Asterisk require that two separate calls be established - e.g. one to receive the Fax into a TIFF file (ReceiveFax), and an entirely separate call to send the Fax from a TIFF file to a fax machine (SendFax), or vice versa.

ScopTEL Asterisk 11+ overcomes this limitation and provides full T.38 Fax Gateway support. T.38 Gateway provides a number of advantages over the older, two-step store-and-forward method (generally referred to as T.37). Advantages include: end-to-end confirmation of receipt (with two separate calls the callee doesn't necessarily know the caller was trying to send them a fax), reduced time to fax (not receiving and then sending separately cuts the time in half), and increased reliability (no concerns about the reliability of local file storage or the TIFF interpreters).

ScopTEL Background and Pre-requisites

You must already be using a currently supported version of Asterisk

You must be using minimum scopserv-server version 2.4.1

You must be using minimum scopserv-telephony25-6.9.13.2.20200622-2

You must be using minimum scopserv-core version 3.5.27

Package hylafax must be installed

Package avantfax must be installed

Package iaxmodem must be installed

Package sendmail or postfix must be installed

Valid VoIP Account

Use the Packages Manager>Versions Information tab to install any missing or non-compliant packages • Do NOT enable T.38 options if your SIP carrier does not support T.38

Packages Manager Review

Server>Packages Manager>Versions Information

Navigate to Telephony>Configuration>Telephony Modules and click Edit

Check the option for SIP Channels: Yes

Check the option for Virtual Fax: Yes

Disable T.38 Fax (UDPTL) Passthrough

Save

Navigate to Telephony>Configuration>Channels>IAX Channel

Enable Jitter Buffer ? : No

Save

Navigate to:

Telephony>Interfaces

Edit an existing or new SIP VoIP Account

Click on the Options tab

Check the option for Enable Fax T.38 Gateway: [x]

Save

NOTE

This will enable T.38 Gateway support on all incoming calls to this interface. You will still need to set a destination(s) for incoming faxes. And you will need to configure DNIS routing for each DID so the Virtual Fax Routing can set the proper destination.

Navigate to:

Telephony>Interfaces

Edit an existing or new SIP VoIP Account

Click on the Network tab

Check the option for Can Reinvite >[x]

Navigate to Telephony>Virtual Fax Virtual Fax: Modems>General

Click Add a new Modem • Mode: Virtual Modem from drop down list

Name: must be unique

Port ID: must be numerical and unique

Click on Options tab when finished

Virtual Fax: Modems>Options Virtual Fax: Modems>Identification

Choose the desire d Class of Services (Outgoing):  • Enter custom values in each text field object from the drop down list • This example shows default values and subsequent • Click on the Identification tab when done prefixes

Click Add when done

Virtual Fax: Fax Routing

Click on the Fax Routing tab

Click Add a new Route

Virtual Fax: Fax Routing

This is where the Incoming Lines info does a lookup for the destination email address

Match/Route: Choose DNIS

Enter a valid DNIS Pattern which must match an Incoming Line Pattern

Select the Format/Type: of the attachment from the list

Enter the Destination (Email): address

Click Add when done

Virtual Fax: Authentication

Click on Add a new Authentication

Virtual Fax: Authentication

Enter a Username

Enter a secure Password

Click on the Contact tab

Virtual Fax: Authentication Virtual Fax: Options

Enter custom info into the required fields • Use the mouse to highlight each Virtual Modem

Click on the Options tab • Use the mouse to highlight each DNIS/DID (Routing)

Click Add

Example 1

Incoming Line Dedicated to Virtual Fax Modem

Lines Manager

Incoming Lines>General 

Example: 9055551234

Type = Extension (DNIS)

Extension (DNIS) = 9055551234

Trunk = 9055551234

Example 1, cont’d

Incoming Line Dedicated to Virtual Fax Modem

Lines Manager

Incoming Lines>Options

Fax Extension (Routing): can be left blank.  The default is to use the General tab’s DNIS value to Virtual Fax Route

A custom DNIS value can be used to override the default incoming DNIS Examples: 

Telco sends DNIS 2234 and you want to send the fax to virtual fax route 9055551234

POTS lines do not support DNIS but you still want to send them to a virtual fax route

You want to send many Incoming Lines to the same virtual fax route 9055551234

In any of these examples you could set the Fax Extension (Routing) : <DNIS> to a custom numerical value

Example 1, cont’d

Incoming Line Dedicated to Virtual Fax Modem

Lines Manager

Incoming Lines>Destination

Destination: use the drop down list selector to chose Virtual Fax

After choosing the Virtual Fax Destination use the drop down list selector to select your Virtual Modem Port

Add or Save your configuration

Example 2

Incoming Line Shared between Voice and Fax

Lines Manager

Incoming Lines>General

Example: 9055551234

Type = Extension (DNIS)

Extension (DNIS) = 9055551234

Trunk = 9055551234

Example 2, cont’d

Incoming Line Shared between Voice and Fax

Lines Manager

Incoming Lines>Destination

Example 2, cont’d

Incoming Line Shared between Voice and Fax

Lines Manager

Incoming Lines>Options

Fax Extension (Routing): can be left blank.  The default is to use the General DNIS value to Virtual Fax Route

A custom DNIS value can be used to override the default incoming DNIS • Examples: 

Telco sends DNIS 2234 and you want to send the fax to virtual fax route 9055551234

POTS lines do not support DNIS but you still want to send them to a virtual fax route

You want to send Incoming Lines to the same virtual fax route 

9055551234

In any of these examples you could set the Fax Extension (Routing) : <DNIS> to a custom numerical value

Example 2, cont’d

Incoming Line Shared between Voice and Fax

Lines Manager

Incoming Lines>Options

You must check Enable Fax Detection ? [x] to share between voice and fax routing

You should check Indicate Ringing during Fax Detection ? [x] to supply ring back to voice callers

Add or Save your configuration

Outgoing Lines

You must enable Fax T.38 Gateway :[x] to allow Asterisk to enable T.38 Gateway processing for outgoing faxes.

• Lines>Outgoing Lines>Dial Options>Advanced 

Options>Enable Fax T.38 Gateway :[x]

Virtual Fax>Email-to-Fax

How it works:

The user sends a fax attachment using any email client or webmail service.

Supported fax attachment types are PDF, TIFF

The POP3 mail server account can be a shared account as in faxes@domain.com

The user enters the external fax number in the subject line including any PBX prefix or long distance prefix

The user must also enter any fax token in the subject line if the administrator has configured this feature to implement additional security.

Examples of subject line:

5551212

95551212

915555551212

With token = faxpassword

5551212 faxpassword

95551212 faxpassword

915555551212 faxpassword

The ScopTEL server will attempt to login to the POP3 server and use the POP3 credentials specified in the POP3 Settings tab to download attachments. Once an attachment is downloaded the ScopTEL server will use the subject line to select an outgoing Fax Modem port to dial and send the fax.

Virtual Fax>Email-to-Fax

General Tab • Options

Give your Email-to-Fax account a name • The server will use the Options settings to 

Virtual Fax>Email-to-Fax

Telephony General Services

Check HylaFAX (Virtual Fax): [x] • Commit

Check IAXmodem (Virtual Modem): [x] • Start IAXmodem (Virtual Modem)

Click Apply Change • Restart HylaFAX (Virtual Fax)