IP Phone Boot Up and Registration

Hi Reader and welcome to this blog on IP Phone Boot up process and Registration. I will explain to you all the things involved in registering an IP Phone and go through the entire process in detail. So here goes...

The very first thing that happens after we connect an IP Phone to a switch-port is that it receives power from the port.. Now, there are two ways in which an IP Phone can receive power and those are:
Inline Power:

• When the phone is connect to switch-port, the port sends FLPs (Fast Link Pulse) which are bursts of electric signal lasting 125 microseconds on the transmit pair.

• The switch-port expects to receive this back on the receive port.

• Devices that need power have a LPF (Low Pass Filter) between the transmit and receive pairs designed to pass only FLPs.

• On receiving the FLP, power is applied

• The port is taken out of discovery mode and put into ethernet auto-negotiate.

• "Wait for Link" timer of 5 seconds starts. If the phone link is detected, power is kept on else power is switched off and port goes back to discovery mode.

Power over Ethernet:

(Industry standard - IEEE 802.3af delivers upto 15.4 Watts of power per port, using 48 volts)

• When the phone is connected to switch-port, 2.7 V to 10 V is applied between the transmit and receive pairs.

• Devices that need power have a 25K ohms resistance between the transmit and receive pairs.

• If this is detected, then power is applied to the device if enough is available.

• If we disconnect the phone from the port, the power connection is terminated in less than 250ms.

Note: The switch-port doesn't have a power ON mode to protect the NICs (Network Interface cards) which do not expect to receive power from the network.The switch queries its NMP (Network Management Processor) to determine whether enough power is available to power a device. Power can be sent through the cable on spare pairs or data pairs (phantom power). CDP is used for power negotiation after the link is up and phone has booted on. If switch doesn't support CDP, there is no reduction in power.

Contact	Media Direct Interface Signal
1	Transmit +ve
2	Transmit -ve
3	Receive +ve
4	-ve
5	-ve
6	Receive -ve
7	+ve
8	+ve

Upon receiving power , the IP phone:

1) The phone obtains Voice VLAN information from the switch to which the IP phone is connected or uses statically defined Voice VLAN information [Admin VLAN ID]. Phone sends a maximum of 3 CDP messages requesting Voice VLAN ID. If it receives a response from switch with the VLAN, the packets are sent tagged, else the packets are untagged.

2) Requests DHCP information / uses statically configured settings. It provides the IP phone with the IP address of the TFTP server.

Settings > 3- Network Configuration > DHCP Enabled > YES -- AUTO

                                                                                         NO -- MANUAL

3)  Contacts TFTP server to download a configuration file - SEP<devicemac>.cnf.xml / SEPDefault.cnf.xml (if 1st one is not found)
These files contain :

• • List of three call managers plus an optional SRST router for IP phone to connect.
  • Load information specifying firmware version IP phone should be using.
  • URLs for directories, services, information and idle.

4) Phone reads load ID and version stamp and compares with current load.

If mismatched, loads new load from TFTP, IP phone resets and repeats entire boot process.

5) Phone attempts registration to its primary CUCM, If it is unavailable, IP phone tries the subsequent servers from the list provided via TFTP.

SKINNY CLIENT REGISTRATION :

- IP phone sets up a TCP connection with the CUCM

- IP phone sends a Alarm Message which contains Device name, load of the IP phone, Alarm status, Phone's IP address.

- IP phone sends a stationRegisterMessage containing Device name, Device type and IP.

- IP phone sends a StationIPPortMessage containing the TCP port on which it is listening.

- CUCM sends a StationRegisterAck to the IP phone to indicate successful registration.

- CUCM queries the IP phone about its capabilities to which the IP phone replies.

- IP phone requests for Softkey template, Button template, Softkey set, line status, speed-dial status and date and time.

- Apart from the above, CUCM sends the output prompt display message - Your Current Options.

I hope you understood the above and any doubts you can always comment here and I will help to solve them.

- Abhinay Mylavarapu.