Configuring AudioCodes MP-112 VoIP Gateway for Fax with Asterisk

I am setting up an Asterisk/Elastix system to work with a Cox PRI circuit, and I needed a gateway for managing faxes.  I had previously used the AudioCodes MP-202, which was fairly easy to set up, but that one is no longer available.  Its replacement appears to be the MP-112.  However, the setup is far more complicated, largely because the MP-112 has a lot more capability, but also because the defaults for the MP-112 were not helpful for my application.

This is a very flexible computer and router, capable of mastering DHCP, acting as a firewall, etc.  However, it is set by default to intercept any faxes and route them via T.38.  T.38 only works if the receiving system is expecting T.38 (Asterisk is not capable of taking T.38 and turning it into a regular fax).  If you don’t disable the T.38, simple faxes might squeak through, but even full page faxes will get intercepted.  The symptom will be that only part of the fax page goes through.

Configuring the MP-112 requires first configuring it to register as a SIP extension, and then configuring it to send calls to the Asterisk server (as the “proxy”), and then disabling fax detection so that fax calls go through as regular voice calls.

You connect to the MP-112 via the web interface.  The default IP is .  The default username is Admin, and the default password is Admin .   Note that I (and others) have had trouble with Safari caching a cookie or something and having trouble authenticating.  I had better luck with Firefox or Chrome.  Note that, with Chrome, when I pressed the ‘t’ key, the whole page cleared!  If I needed a ‘t’, I was able to get it by pasting the text in.

For troubleshooting, you can view the MP-112’s log from the Status and Diagnostics tab, under the Status and Diagnostics folder within that tab, as “Message Log”.  Note that, as long as you are on that “Message Log” tag, the log is running.  I was able to select all and then copy the log to TextMate to review it.

Also under Status and Diagnostics/Gateway Statistics is “Registration Status”, which tell you whether your SIP “phones” have registered properly, as well as lots of other diagnostics.

Whenever you want to save the changes you have made on a page, click “Submit”.  You should do that for every page before leaving the page.  To save the changes permanently into flash (so they are not lost when the device is unplugged), press the “Burn” button.

There is lots of documentation on these very complex devices on the AudioCodes website.  This is just a “quick-start” for the common use case (for me) of using the AudioCodes to connect a fax machine or analog phone as a SIP extension on an Asterisk system.

Before you start, go to the Management tab, Software Update/Configuration File — from here you can download the configuration file from the MP-112 that describes the factory default.  If you ever want to go back, you can also upload a configuration file.  Once you get it working, after burning your configuration into the flash rom, save a configuration file so you can always go back.  With the hundreds of configuration settings for this device, the configuration file also gives you an easily-visualized view of the changes you have made.

AudioCodes nicely documents the configuration file format.  In the configuration file, there are sections indicated by [section name].  Those sections are only for human consumption, and do NOT have any effect on the function of the configuration file.  Thus, you can change the configuration file, and don’t have to worry about the sections.  The exception is the table configuration.  Tables are bounded by [ TABLENAME ] … [ TABLENAME ].  The tables have a very specific format, and for tables, the “section” names DO matter.  Also, if a configuration setting is not mentioned in the config file, generally a documented default is used.

When making changes to a page, be certain to hit the “submit” button on EACH page.  Don’t forget to hit “burn” when you are done.

First, you may want to go to the Configuration/Network Settings/IP Settings, and set the IP address,netmask, and default gateway.  Alternatively, the MP-112 will read its information from a DHCP server, if one is available, if DHCP is enabled on the device.  If you use DHCP, you will need to figure out the IP address assigned, so you can access the web interface.  If DHCP is available and enabled, it seems to override the setting under IP address.

The DHCP option is under Configuration/Network Settings/Application Settings/DHCP Settings/Enable DHCP, but it is hard to make it “stick” — Section 10.1.8 of the User Manual indicates that you have to do a reset with the reset button — however, that did not work for me.  I had to click “Submit”, and then “Burn”.  Then, unplugging and replugging the power cord worked to cause DHCP to be used.

Once you have IP configured, you have to get both ports to register with the SIP server (Asterisk) and route calls.

Regarding the call routing, the MP-112 can use a SIP proxy, a routing table, or both.  Unfortunately, the defaults do not favor either option.

Under Configuration/Protocol Configuration/Proxies-IPGroups-Registration/Proxy & Registration/Use Default Proxy, set this to Yes.  This is “IsProxyUsed” in the config file.  In the Proxy Sets Table (the button is on the same page), put the IP address of your Asterisk server under Proxy Address, and UDP under transport type.  You only need the one proxy, so just fill in the first line.

You need to set the authentication to Per Endpoint, so that each port can register. Set Configuration/Protocol Configuration/Proxies-IPGroups-Registration/Proxy & Registration/Authentication Mode to “Per Endpoint” Then, you need to set Configuration/Protocol Configuration/Proxies-IpGroups-Registration/Proxy & Registration/Enable Registration to Enable.

Open the Authentication page:Configuration/Protocol Configuration/Endpoint Settings/Authentication and enter the SIP username and password for each endpoint.  Each endpoint is configured as a separate extension.  In Elastix/FreePBX, the username is typically the extension number, although that’s not the most secure way to configure your PBX.

On Configuration/Protocol Configuration/Endpoint Number/EndPoint Phone Number, you can set the extension number for each of your ports.  If you put 1-2 under “Channels”, the “Phone Number” is the phone number for the first FXS port, and the phone number for the second is the phone number for the first, plus one.  If you put “1” under channel in the first line, and “2” under channel in the second line, you can assign independent extension numbers for each port.  Press “Register” to register with the Asterisk server.  You can check whether registration worked under Status & Diagnostics/Gateway Statistics/Registration Status, and/or from the CLI interface on Asterisk using SIP SHOW PEERS.

Make sure that the MP-112 shows “Registered” for your ports before you move on.

Next, you need to set Max Digits in Phone Num (Configuration/Protocol Configuration/Protocol Definition/DTMF and Dialing/Max Digits in Phone Num) to something like 30 (or at least a number no less than the greatest number of digits you want to be able to dial).  If you don’t, the default is 3, and every time you enter three digits, the MP-112 will try to connect the call using only those three digits.

Now, if SIP registration is working, you should be able to make phone calls into and out of your MP-112.  Test that before working on the fax setup.  You can use the Status & Diagnostics/Status & Diagnostics/Message Log to see the SIP messages and additional debugging info, but be certain NOT to leave that as the active tab in your browser.

Now, for the fax handling:

On the configuration/Protocol Configuration/Coders and Profile Definitions/Coders page, I left only G.711A-law and G.711U-law as the codecs being used.  If you want to use different codecs, enter them here, but some compression schemes may not work well transporting faxes.

To avoid the T.38 fax interception described above, you will need to use “Fax / Modem Transparent Mode”, as described in section (page 252) of the MP-112 users manual.  This page shows the parameters you want:

First, set IsFaxUsed = 0 ; This is at Configuration/Protocol Configuration/Protocol Definition/SIP General Parameters/Fax Signaling Method: 0 = No Fax

Then, set FaxTransportMode = 0 ; This is at Configuration/Media Settings/Fax-Modem-CID Settings/Fax Transport Mode: 0 = Disable = transparent mode

Then, set the transport types:

V21ModemTransportType = 0 ; at Configuration/Media Settings/Fax-Modem-CID Settings/V.21 Modem Transport Type: 0 = Disable = transparent mode

Do the same for V22ModemTransportType = 0 (disable) , V23ModemTransportType = 0 (disable) , V32ModemTransportType = 0 (disable), V34ModemTransportType = 0 (disable)

The docs also say to set BellModemTransportType = 0 , but that is apparently NOT in the web interface.  However, 0 = disable is the default for BellModemTransportType.

Note that those parameters are as shown in the configuration file.  They are described in the table in section 10.9, “General SIP Parameters”. IsFaxUsed is mentioned on page 385. It is ISFAXUSED in the configuration file, and it is under Configuration/Protocol Configuration/Protocol Definition/SIP General Parameters/Fax Signaling Method in the web interface.

At this point, I was able to send and receive faxes with no problem.  If you have trouble, be sure to check out the troubleshooting tips above.

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