How to convert a Cisco 7940 from SCCP to SIP

Note: This guide has been tested with firmware version pos3.08.12.00. Be aware that different firmware revisions may have different functionality.

This document will describe how to get a Cisco 7940 with SCCP (Skinny) protocol, convert it to SIP and get it to work with 3CX Phone System. For a full guide on how to configure the phone including it’s configuration file read Configure Cisco 7940 / 7960 IP Phones for 3CX Phone System.

Step 1: Obtain the Firmware files

Download the Supported 3CX Cisco 79XX SIP Firmware files. These are the latest tested Cisco 79XX files firmware version P003-8-12-00. Extract the .zip package to a folder on your computer.

Step 2: Prepare a TFTP Server to deploy the firmware files to the phone

Download any TFTP* server software. The one that was used in this specific SIP upgrade is called Pumpkin, but you can use any TFTP software.

Install the TFTP server. Specify the location where where you have extracted the .zip package. Configure the TFTP server so that Read Request Behaviour is set to “Give all Files” without “Prompt before giving file”. This way you make sure that the read request of the phone happens without any complications.

* The Trivial File Transfer Protocol (TFTP) is normally used only for booting diskless workstations. The TFTP server package provides the server for TFTP, which allows users to transfer files to and from a remote machine.


Step 3: Configure your DHCP Server to tell the phone where to get the Firmware files

  1. Configure your DHCP server and create a DHCP reservation for your Cisco Phone.
  2. When done, edit the reservation and click on Configure options.
  3. Find Option 66 and enter the IP Address where the TFTP is installed. It is recommended to install the TFTP server on the same machine where 3CX Phone System is installed.


Step 4: Complete the upgrade

Put all the files along with the extracted SIP image files in the TFTP server root directory the one you defined on the TFTP server options and restart the device. The device will be assigned an IP Address from the DHCP server and will be told to search for booting files and media from the IP Address specificed in the option 66 section.

For details on how to build the configuration file of the CISCO 7940G phone take a look at this guide.

NOTE: Please be aware that most CISCO phones do not have a web interface. The only way to configure of give configuration updates is via Configuration files using TFTP.