MGCP Configuration with cisco 2921 Gateway

Working to replace a cisco CM (v9.4) system to FreePBX (v14.0.1.36 / Asterisk 15.1.5).

Have several issues:

  • Current trunks are MGCP that are part of a cisco 2921 gateway. Looking for Asterisk module “” to load and show as part of “Trunks” (Create new trunk). We are also looking to change the MGCP T1 trunk to SIP (future, vendor dependent).

  • Access to older intercom system that runs off an “analog” card in the cisco 2921 gateway. Found a route pattern “5.#00” that routes to “AALN/S0/SU2/[email protected]_Voice_GW.cghs.crusaders”.

  • Tech note: on cisco IP Phones (Model 79XX), the “Display Name” when creating extensions is only 11 characters. The extension number is what cisco CM puts here, and a “SpeedDial” button is “labeled” for the actual user display name. Also, the “Secret” 32-charachter sequence is limited to 31-charachters.

Any help here is worth while to move this project along.

Geoff Zieman
Senior Network Engineer
Digitz Computers - Raleigh, NC
…on site at Cardinal Gibbons High School

OK - first things first.

  • MGCP isn’t “supported” in FreePBX, per se. It’s an Asterisk thing and FreePBX can work around it. The availability of the MGCP channel driver module will depend on the FreePBX Asterisk version you want to use. The sooner you can get away from the MGCP trunk and switch to a SIP trunk (or even a PRI/T1) the sooner your pain will decrease.

  • The older Intercom System is “analog”, but that’s an entire class of solutions from simple click-to-talk Boden style to a phone interfaced via a POTS style line. The identifying information on the PA system will tell us more about how you need to make it work. At this point, there’s no way we can really help you.

  • Like MGCP, the phones are not SIP. They use a protocol called SCCP, which is “dumb terminal” protocol for the phones. You can flash these phones to SIP, but there are so many problems with that, that I almost always recommend against it. Instead, I would either use the “native” Skinny channel driver, or load the Chan-SCCP-B interface. Note that the latter is my preferred solution. It leaves the phones in Skinny mode and allows you to manage the phone. (Insert long explanation about problems with button configs, memory, and CPU in phone not being optimal for moving processing to phone using SIP).

So, to move your project forward, I would recommend the following:

  1. Head over the Chan-SCCP-B Github site and use the “FreePBX Instructions” I wrote to get the channel driver installed. Set up the phones so that they can connect to the FreePBX server (basically, build the config file by hand and install it). There was a SCCP management program for FreePBX a long time ago, but it’s no longer supported or recommended for use (security issues).

  2. Get the model information on the PA system. Someone should be able to steer you in a direction on that.

  3. See if the district will consider using a SIP connection for their inbound and outbound dialing (instead of using the centralized service provider they are using now).

February 14, 2018 09:13 ET


Glad to hear from you. Thanks for the insight into my project.

Using phones that are no longer supported (product End-of-Life) by cisco is not helping my cause. Fortunately, cisco has released just one more release of software (Feb 14, 2017) for these old “cisco Unified IP Phones” (v9.4(2)SR3 in both SCCP and SIP). These “antiques” do support SIP with some exceptions: The phones do not support “intercom”. The hardware is just not there (based on the cisco product support guides). FreePBX EndPoint Manager does offer direct support of the cisco phones using SIP. Title bar on phones (what FreePBX is calling “Display Name”) only supports up to 11 characters. In cisco Call Manager, the “Display Name” is used for numbers only (extension number or like). And the “secret” to register the phone only supports 31-characters, not 32. IP Phones that I have working: 7941G, 7945G, 7962G and 7975G, all with SIP.

I am in total agreement that MGCP is a “dying” protocol. I am working to get to SIP. At this point it is a matter of vendor support for our old T1 line (which runs a total length of 6 inches before turning back into an IP stream) and the reconfiguration of the cisco 2921 gateway.

The “old” intercom system (more antique) I am still trying to trace lines. The core system is an outdated (with “wire wrap” terminals) that requires a device with RS-232 communications (requires a RS-232 null-modem cable, running WinXP, virtualized RS-232 via USB is NOT supported (Win versions Win7 or newer)). The system is a Rauland-Borg Telecenter System 21 which also doubles for the “Bell System” (start-end of class “bells”). Of course POTS might be the issue. I will look further into that. The system is accessed via cisco Call Manager (v9.4) thru a cisco router 2921 serial port (internal route/end point: AALN/S0/SU2/[email protected]_Voice_GW.cghs.crusaders).

Again, thanks for the insight. Any help is welcome.

More research on my part is still needed.


Geoff Zieman
Senior Network Engineer
Digitz Computers – Raleigh, NC
…on site at Cardinal Gibbons High School

These (and more) are the reasons I suggested NOT using the SIP image and either using the “already integrated” ‘skinny’ drive, or installing the Chan-SCCP-B channel driver (to support the phones in ‘sccp’ mode). The phones then can do things like Intercom (under-chin paging is covered in the Wiki article I wrote) and don’t have to have passwords any more (authentication is done through the MAC address of the phone). Of course, if EPM is an important consideration for you, then you are stuck with the SIP downgrade.

There are T1 cards for your FreePBX system that can accept a T1/PRI/DS1 line for telephone termination. That might get you further along more quickly than trying to get MGCP working. Note that doesn’t solve the “bell/intercom” enunciator, but we will burn that bridge in a minute.

I found this:

Telecenter System 21 User Manual

out there in the Interwebs. I can’t download it, but the same website appears to have a schematic for connecting the system to your various pieces and parts. I’ll bet you could connect it to the FreePBX system directly and write a simple script that would make this old technology stand up and bark like a big dog.

Important note - my day job is programming an IBM Series-1 Communications Processor, so I have plenty of experience with old hardware. :slight_smile:

I have been looking for a valid “chan_sccp_b” channel driver for FreePBX/Asterisk now for a couple of days. It appears that the versions that I have found are referring to a online path that does not exist:

It is the …/7/… path that is invalid. There is a …/5/… and …/6/… at the site only.

So at this point I am at a loss on where to find a version of “chan-sccp-b” that is compatible with FreePBX.

Did you read the Wiki page I wrote, where I tell you exactly how to do this?

[solved] EndPoint Manager not finding Cisco phone

Has a good discussion, as well as a link to the Chan-SCCP-B Wiki.

The WiKi pages that you are referring to are not accessible ( The page displays as “Forbidden” (HTML Error 403).

Please check your permissions to the link.

The page got moved to GitHub.