Cisco 7940 Series IP Phone

This was the first IP Hardware Phone that I managed to get working with FreeSwitch, which has more to do with my lack of experience on IP telephony than any innate weakness in FreeSwitch. There were a number of steps required to get my Cisco 7940 configured to work with FreeSwitch and these are described here. This page gives an overview of the essential steps, for a detailed description of these activities, please refer to the Cisco Web Site.

Firmware

The Cisco IP Phone 7960 and 7940 platform has the ability to support three protocol application firmware versions. By default, Cisco IP phones are shipped loaded with Cisco's proprietary Skinny Call Control Protocol (SCCP) firmware, commonly called just skinny. This firmware is designed to work with Cisco's Call Manager product. More details on SCCP can be found in the Wikipedia page here.

Before you try to use the phone with FreeSwitch, unless the Cisco Session Initiation Protocol firmware has already  been loaded, you will need to replace the SCCP image with SIP. More details of the SIP protocol, can be found here or see the Wikipedia page here. Replacement SIP firmware is available without too much difficulty on the internet :-)

The third firmware option is Media Gateway Control Protocol (MGCP) which is used with third-party call agents (CAs) and is not relevant to this discussion.

Background

File Transfer Requirements

When loaded with SCCP firmware, 79xx series phones have a Web Browser Interface available where you can inspect the configuration of the phone by entering the IP address of the phone into a web browser. However, this functionality is lost when the SIP firmware is loaded and all configuration management needs to be done by file transfer. This requires that a Trivial File Transfer Protocol (TFTP) server is available on the network on the same subnet as the phone. A description of the TFTP can be found on the Wikipedia page here. TFTP is commonly used to transfer very small quantities of data when devices such as IP phones are booted from the network.

Although I have a Windows Server Domain running here, I do not have a Windows DHCP Server configured - I use the DHCP server in my ADSL Gateway/Router to provide IP addresses to the clients. I believe that the Windows Server DHCP allows you to provide the address of the TFTP server to the DHCP clients (DHCP Option 150). Since my router can't do that, and if you specify DCHP on the phone it expects to be told where the TFTP server is, I have configured my IP phones with fixed IP addresses and entered the IP address for the TFTP server manually.

Not having an existing TFTP server, the first step was to get one up and running. I looked around for one that was free and came across the Free TFTP Server from SolarWinds. It's one of a number of network utilities made available free by SolarWinds and can be downloaded once you register on their website.

To begin with, I configured the TFTP server on a spare machine on the network but as the quantity and frequency that the file transfers are required is small, I've since installed the TFTP server on the same machine as FreeSwitch which has not had any impact on the performance of FreeSwitch.

There were a couple of things that caught me out before I could get the TFTP server to serve files onto the network that you should be aware of - these issues are probably common to whatever TFTP server you choose to use.

1. Windows Firewall

TFTP uses UDP Port 69 as its transport protocol. I found that this port was blocked by the default Windows firewall configuration, at least it is in WindowsXP Service Pack 3. You'll need to open this port in the firewall of the TFTP server.

2. Security

You'll need to set appropriate security on the TFTP server's root directory and place all required files in this directory. The default directory used by the SolarWinds TFTP Server is C:\TFTPServer.

Infrastructure

Configure Network Settings

Before the phone can be provisoned by the TFTP server, the following network settings need to be configured to allow communication with the TFTP server

DHCP Enabled  - No

IP Address - e.g., 192.168.1.100

Subnet Mask - e.g., 255.255.255.0

Default Router - e.g., 192.168.1.1

Default Gateway - e.g., 192.168.1.1

Reset to Factory Defaults (If Required)

Note : before you can modify the network configuration, you need to be able to unlock the configuration  which is password protected. If you've picked up a second user phone, you may not know the password and may need to set the phone back to defaults.

To reset the phone to the "factory" default configuration, either power cycle the phone or hold the "*", "6" and "Settings" keys simultaneously - which will cause the phone to reset.

While the phone is booting, hold down the "#" key, the phone's display will display "Reset key sequence detected" and the Headset, Mute and Speaker leds will blink in cycle. While the Headset, Mute, and Speaker buttons begin to flash in sequence, release "#" button. The Headset, Mute, and Speaker buttons flash in sequence in order to indicate that the phone waits for you to enter the key sequence for the reset. Press "123456789*0#" within 60 seconds after the Headset, Mute, and Speaker buttons begin to flash.

If you enter this key sequence correctly, the phone displays this prompt: "Keep network cfg? 1 = yes 2 = no". In order to reset the network configuration settings when the phone resets, press "2". 

This will reset all settings, including the password to the default state, the default password is "cisco". You can then unlock the network configuration and enter the required network parameters listed above.

Phone Configuration

Required Boot Files

A good description of the boot process for the Cisco 7960 and 7940 platform is available from the Cisco web site here. I have included extracts from that reference here as it is necessary to understand which files are required to successfully provision the phone for SIP, the SCCP and MGCP firmware options are not discussed here.

The current boot mechanism for Cisco IP Phones uses the Universal Application Loader (UAL).

The UAL eliminates the need for a separate OS79XX.TXT file which used to be required for booting between protocols. The universal application loader operates in a manner very similar to the older SCCP, SIP, and MGCP systems. It relies on a TFTP server to supply information in text files known as "configuration files." The information in these files points to a new loads file, which contains the names of the desired application image and universal application loader. This system allows the universal application loader to know which image revision is desired in the phone. Once this information is known, the phone has the ability to upgrade itself and the application image as needed.

Although we're only concerned with SIP here, the UAL allows the system administrator to use SCCP, SIP, and MGCP, on the same network. To do this, a hunt algorithm is employed that searches for multiple configuration files. Depending on which configuration file is found first, the phone will automatically select that protocol. The hunt algorithm ensures that the administrator can assign a specific protocol to a specific phone. The hunt algorithm searches for files in the following order:

(where <-MAC-> is the MAC Address of the phone in question, format AABBCCDDEEFF)