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VoIP call manager IP phone questions

When a cisco phone boots, does it:

First get an IP address from dhcp server (if configured for DHCP)?

The mac shows up first in data vlan, then in voice. Why in the data vlan?

An IP phone shows a tftp server in the settings, is this provided by DHCP?

The TFTP server gives the phone it's configuration file. Where is the configuration file located (which server)and what is in it?

What exactly does the call manager do?

Does the phone only communicate with call manager and the call is directed from there?

2 REPLIES
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Re: VoIP call manager IP phone questions

Hi Richard,

The boot process is explained in this excellent document:

<http://www.netcraftsmen.net/rtrunk/Troubleshooting%20IP%20telephony%20Problems.pdf>

First get an IP address from dhcp server (if configured for DHCP)?

yes - indeed it does.

The mac shows up first in data vlan, then in voice. Why in the data vlan?

CDP neighborships must be established so the two network end point can agree on a number of parameters. Read the section headed 'Cisco' in the document highlighted above.

"When a Cisco phone is powered up, you will see the mute, headset and speakerphone indicators light up. Next,

the phone and switch exchange Cisco Discovery Protocol (CDP) data. CDP is a Cisco proprietary protocol that

lets interconnected Cisco devices learn about each other. The switch uses CDP to tell the phone which VLAN

will be used for voice traffic (Note: if you are not using separate VLANs for voice and data traffic, we need to

talk!). During this process the phone will display “Configuring VLAN.”

An IP phone shows a tftp server in the settings, is this provided by DHCP?

I have seen a default 10.2.114.0 (or something like this). But if the phone manages to get IP info from DHCP server, then a TFTP server address is provided here.

The TFTP server gives the phone it's configuration file. Where is the configuration file located (which server)and what is in it?

The file is located on the TFTP server. Each phone has a unique configuration file which is identified by the MAC address of the phone. The config file will contain information such as DN number and date/time for example.

What exactly does the call manager do?

In simple terms CCM is responsible for routing the call. Once a call is established - it's hands-off for Callmanger and both phones (or end points) communicate with one another. Two IP phones for example use RTP to do this.

Does the phone only communicate with call manager and the call is directed from there?

Yes. But other devices also talk to CCM. For instance gateways which use MGCP or H323 to talk to Callmanager

hth,

Ajaz

pls rate the post if it helped.

Re: VoIP call manager IP phone questions

1. First get an IP address from dhcp server (if configured for DHCP)?

Yes

The mac shows up first in data vlan, then in voice. Why in the data vlan?

No. This is true only for Avaya voip phone. cisco phones support CDP and extract the voice vlan info from it

An IP phone shows a tftp server in the settings, is this provided by DHCP?

yes

The TFTP server gives the phone it's configuration file. Where is the configuration file located (which server)and what is in it?

This could be a dedicated server or the Call manager itself. A configuration file contains a prioritized list of Cisco CallManagers for a device (telephones and gateways), the TCP port on which the device connects to those Cisco CallManagers, and an executable load identifier. Configuration files for Cisco IP Phone 7960 and 7940 models also contain URLs for the phone buttons: messages, directories, services, and information. Configuration files for gateways contain all their configuration information.

What exactly does the call manager do?

It is the heart of the Ip telephony system and can be compared to any PBX.

Does the phone only communicate with call manager and the call is directed from there?

The Phone registers with the call manager which helps in setting up the calls. Once the call is setup, the Audio stream flows directly between the two endpoints

http://www.cisco.com/en/US/products/sw/voicesw/ps556/

HTH

Narayan

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