In most offices, phones have four or five digit extension numbers. These are often the last four or five digits of the Direct-Inward-Dial (DID) phone number of the phone. By default, the extension number assigned to the phone is sent as the caller ID. For internal calls this makes perfect sense, but not for external calls. Imagine you get a call and the caller ID is 5734. I am not sure about you, but I might not even bother answering that call. In order to send out the Fully Qualified Number (FQN), an External Phone Number Mask can be assigned to a Cisco IP phone.

The configuration is actually done on the line level of the phone. Wildcards are used so that the extension number can be preserved and the rest of the number prepended to it. For example, if the extension number is 2002 and the FQN is 555-555-2002 the external phone number mask would be 555555XXXX. The X allows the original extension to pass through the mask. Figure 1 offers a graphical representation of how this works.

Figure 1

In some cases you may want to send out the company’s main number instead of the DID. This can be done be assigning the main number as the external phone number mask. For example, if the extension number is 2002 and the main number is 555-5555-5000 simply assign 5555555000 as the external phone number mask. Since no wildcards are in the mask, none of the extension number digits will pass through and 555-555-5000 will be sent out as the caller ID.

Photo Courtesy of Cisco Systems, Inc. Unauthorized use not permitted.

These phones boast a number of nice features. Here are peek at a few of them:

-640×480 Color Screen

The 9971 has a 5.6 inch screen while the 9951 sports a 5 inch screen

-Bluetooth 2.0

This is for Bluetooth headset support

-USB 2.0 Ports

Support USB headsets and the optional Cisco Unified Video Camera

-Gigabit Ethernet Port

Allows you to plug a PC into the back of the phone

These phones do look very nice but, like I said, I am not so sure I want all my calls to be video calls. I know that when I am in WebEx meetings and video streaming is enabled, no one ever seems to be sending video. The internet has seemed to lower people’s inhibitions, just go check out the status updates of your Facebook friends. I don’t know if people are ready for live video streaming of all their calls. I guess that might be why Cisco chose to design the phone so that the camera is an optional feature.

A large part of making sure something works reliably or fixing it when it doesn’t work, is to understand what happens when it is working properly. I started this post planning on discussing call flow but before you can even setup a call you need a working phone. So the focus of today’s post will be the registration of a Cisco IP phone. We will discuss call flow in another article.

For the purposes of this article, we will assume the phone that is going to register is a Skinny Client Control Protocol (SCCP) device. The first thing that phone will need is power. There are two ways the phone will receive its power. The first is wall power. A power supply is plugged into the wall and attached to the phone. The second and, more common, is referred to as inline power or Power over Ethernet (PoE). There are two types of PoE that Cisco Phones use: Cisco pre-standard and 802.3af. The details on how each work will be the topic of a future article but for now understand the the phone negotiates with the switch to determine power requirements. Once the switch determines that the attached device is a PoE device, power is provided.

The following are the steps that a phone goes through once it has power:

1. The phone boots using its firmware.

2. The VLAN is determined. If a voice VLAN has been configured, the phone will learn that VLAN otherwise it will use the access VLAN.

3. If the phone is using DHCP, a DCHP request is sent. When the phone recieves the DHCP information, it will also receive the IP address of the TFTP server.

4. Once the phone learns the TFTP server address, it requests a configuration file. Since every phone has a unique configuration, the MAC address is used as part of the configuration file name.

5. If the phone has previously been configured within Communications Manager, a configuration file will exist in the TFTP server and will be sent to the phone.

Note: If the phone has not been configured in the Communication Manager, the phone will attempt to begin the auto-registration process. This will only be successful if auto-registration has been configured.

6. Once the phone has loaded its configuration file, it will complete the registration with Communications Manager.

You know the phone has registered when the correct extension number appears on it and you can receive dial tone.

When troubleshooting phone failure, a few common issues you may run into are:

• Switch not configured to supply power.
• Incorrect DHCP configuration.
• Non-functioning  TFTP Server.
• Phone not configured in that Communications Manager.
• Improper setup of auto-registration.

Now that you know how the registration process should work, troubleshooting registration failures should be easier.