Nifty idea, mostly pushed by Cisco. The idea is that instead of wiring your buildings with Ethernet and phone, you just wire them with Ethernet and you use VoiceOverIP. So you have very nifty phones that plug into Ethernet and use DHCP, H.323 etc. Very nifty.

Cisco IP Phone 7912 Series

Sorry for messing up this page - busy :)

First Looks:


  • Looks cool!
  • Appears to be able to access a basic HTML webpage for phone directory lists/etc that is served on the local LAN
  • Appears to support PoE.
  • Has extra Ethernet port on the back - this means you plug your Ethernet cable into the phone, then plug the 2m Ethernet cable supplied with the phone into the phone, then into your computer. This means only one UTP (Ethernet) cable is required.


  • The Ethernet cord(s) attached at the back interfere with the phone sitting down on the desk, e.g. the phone has a bracket that sits the phone at a 45 degree angle to desk - Ethernet plugs into the back between the desk and bottom of this bracket - would be better to have no rubber-boot/plug-doo-dad-wotsit on the UTP plug... on second thoughts, I think Cisco' book mentioned that you should use no jackets on the UTP plugs...
  • Does not come with SIP image pre-loaded (only Cisco' Skinny? image)... you need to get a Cisco SMARTNet support contract, then when you have that, create an account on their website, then upgrade your Cisco account with the SMARTNet details, which let you access the SIP images for the phone!
  • Requires a 48V DC @ 200mA power supply - somewhat hard to come by... cheaply.
  • Once the SIP image was loaded, and (very) basic setup sorted, phone had a 60ms ping time to it when not even being used...

Network Config Deployment Notes:

Configuration I used - Centralised, via DHCP, and config files/images via (separate-to-DHCP-server) TFTP-Server. (I.e. separate DHCP server, and TFTP-server/SIP-server on the same machine...)

Note for configuring a TFTP Server - the file/RPM to get (FC2) is 'tftp-server', NOT simply 'tftp'. That is a client...

If the TFTP server is NOT running on the DHCP server:

On the DHCP server, in dhcpd.conf (/etc/dhcpd.conf (FC2)), add
'option tftp-server-name "<your-tftp-server-name";'.

The phone will grab this address, and hopefully get all of its SIPDefault.cnf/SIP-images/etc from here.

For specifying the hardware address, use:

' host { hostname <your-phones-hostname> { hardware-ethernet <phones-MAC-address-here> } } '

To be completed...

More dhcpd.conf tomfoolery...

Apparently you need to use 'custom' dhcp options to let the phone get the tftp-servers location from dhcp server...

'option 66 .....???????....... '

Used for when you want to specify individual tftp-servers to individual-phones...???

'option 150 ..........?????????...........'

Used for when you want to specify groups (arrays?) of tftp-servers to all phones...???

More mess:

I first managed to get the new SIP image loaded into the phone using something like (in dhcpd.conf);

'group {

  1. VoIP Phones Group

next-server <tftp-server-ip-addy-here> hostname <your-phones-hostname> { hardware-ethernet <phones-MAC-address-here> }



So far:

To get SIP image loaded into your phone, use the 'group' bit above in yer dhcpd.conf. It now appears as though you need to tell the phone more options - 'scuse the pun - (possibly the 'option 66/150' mentioned previously?) to be able to get further than loading just the phone images...

Basics steps from 'Skinny' phone to working 'SIP' Phone:

Sort out a DHCP server and get it working. Phone by default should get an IP address by itself. Then it needs to know where it should download its config files from (SIPDefault.cnf/etc). Somehow this is done via DHCP, most likely the 'option 66/150' bit. I haven't got this working yet. Then hopefully when it has its config files, it gets the info out of them of the address of the SIP server...

OK. Got as far as the phone requesting it's config files from the tftp server (on the tftp server, do 'tcpdump -vv host <ip-address-of-phone>'. This shows incoming packets of data from the phone to tftp server.

Config (that seems to work) is as follows:


' option tftp-server-name "<ip-of-tftp-server>";

.... .... ....

group {

  1. VoIP Phones Group - Cisco 7912

host <phones-hostname> { hardware ethernet <phones-MAC-address>; } } '

Don't miss out the ' " ' -- and the ' { ' and ' } ' -- NOT ' ( ' or ' ) ' that. Also the ' ; ' is important too :-)

Once the phone has contact with the TFTP server, it seems to try to load the file called 'gk<your-phones-MAC-address-here>.cnf' if it can find it; otherwise it tries to load 'gkdefault.cfg'. NOTE: My 'gkdefault.cfg contained the name of the SIP image to be loaded into the phone from the TFTP server...

Apparently you can configure the SIP server address from either of these files - I just don't know how... yet.

This looks like a work of genius:

And it is.

Will document later.

VoIP VoiceOverIP Asterisk