IP Phone troubleshooting story

A tool to fix a 'broken' phone in the field

If you ever tried to convert a Cisco IP phone from Skinny to SIP or vice versa, you probably experienced that uncertainty when the phone was rebooting and pulling something from the TFTP but then it stopped.

Usually it's making a progress and after a few minutes and additional load files the phone converts, the same happens when upgrading firmware due to call manager version upgrade or service packs. Sometimes it's not happening at all like you would expect and you are finding yourself starring at a device that keeps rebooting and rebooting and nothing seems to be progressing.

At this point you can either give up and RMA the phone (if you have it under warranty) or start trying different versions until one works. This is basically the situation I was involved with not long ago and due to the availability of a great tool, it was resolved without an RMA.

When a phone upgrade/conversion fails, there are numerous things that can be causing this:

1. Mis configured DHCP server.

2. Faulty TFTP server that can not support big files

3. Missing files on the TFTP server.

4. Corrupted files on the TFTP server.

5. Certification mismatch between the phone and the new version.

6. Faulty/mis configured network.

7. Hardware defect in the phone.

And there are many more ...

You can either try to go through this list one item after the other and eliminating one item at a time, knowing that some might require multiple steps, or you can go look right into the heart of the problem and pin point the root cause.

How can you do that? when the screen does not load and if it does by the time you click settings the phone resets, you need a console cable!

On phone models that support this option, this tool is a life saver. It's not that important for configuration purposes but it is priceless for seeing what is it that the phone is doing while constantly rebooting. Try it and you will not go back, I'm going to keep this console cable with me from now on side by side with the IOS console cable.

How can you get it? not sure if it's for sale but all you need is an RJ-11 to an RJ-45 cable which has the follwing pinout:

RJ-11 - RJ-45

2 - 6

3 - 4

4 - 3

The RJ-45 end goes to the standard RJ-45 to DB9 connector and the RJ-11 goes into the phone, set your terminal application to 9600,N,8,1 and power the phone.

This specific pinout works for 7970, I'm still researching about all the other supported models and will post again with the details.

later ...

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