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Unable to start cisco ip phone 7942


Hello Guys,

A friend of mine has given cisco ip phone 7942 to us (which was working good at his work desk)

We are trying to connect this phone at home but facing problem.

First thing we want to confirm is, does this phone require AC-DC power supply?

Reason for asking is we have connected all other things (cables) properly to get it working but we do not see anything on the display / phone screen.

Please check below picture for our connections ( Laptop - Phone - Modem and ADSL Phone Filter)

Friend has confirmed that they do not have any power connected to phone in office/work, so not sure if AC-DC power supply is really required?


Appreciate if you guys can help to resolve this.

Merry Christmas and Happy New Year!

- Mandy

4 Replies 4

Nadeem Ahmed
Cisco Employee
Cisco Employee

Hello Mandy

certainly you would required, in offices generally its connected to PORT (POE switches that has capable to provide Power over Ethernet).

Check table 2.


Please rate all useful post.

Br, Nadeem Please rate all useful post.


+5 for Nadeem for correct link.

Even if you get the proper power brick, what is your intent for the phone? the phone by itself is a dummy terminal and will not do anything unless it can register with a PBX/Proxy.  Will you be registering it with a specific SIP server or will you be installing a PBX such as Cisco Communications Manager, etc?




Hi Guys, thanks for your response.

I am thinking to get/buy this  Cisco CP-PWR-CUBE-3 VoIP Phone Power Supply

But I am confused with above response from Chris.

Will you be registering it with a specific SIP server or will you be installing a PBX such as Cisco Communications Manager, etc?

>>> I have no idea about this....I thought if I just simply get the power supply it should start working?

what is your intent for the phone?

>>> I just want to use this as my home phone. This phone was working at my friend's office desk.

Are you saying this phone is locked with something code etc? which won't allow me to use at home if I just get the power supply?

Please help me to understand this guys....

- Mandy

Hi Mandy,
Buying the power supply will only power up the phone.

Now you need a dial tone. The Cisco ip phone would need a call manager to boot up and get a dial tone and a number assigned to it. This is the scenario in normal office environment.

Outside your office since you don't have a call manager, you need a services provider and your IP service provider should be able to register it to their server using SIP protocol (generally) which is a bit more complicated and does not work out of the box. You have to check with them how they would register it (using a VPN ) / etc. in any case you would need a tftp server to get the SIP Firmware and pass the username and password etc.

In such scenarios, You would be better off using other phones like grand stream / polycom after checking with them for the recommended model if they don't support Cisco.

Regards / Durga Prasad

Sent from Cisco Technical Support iPad App

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