We can define more DNs than devices, and on a real system we can use dual-line or even octo-line DNs to use such things as call waiting or conference calls. These will hold the extension (or line) numbers of the ephones.
This number will vary model by model, the software supports maximum of 42 (perhaps because this is the “ Answer to The Ultimate Question of Life, the Universe, and Everything” ? Ephone can be a physical device or software (a softphone).
At this stage the phones will get their addresses, and if we look at their GUI, the “Configuring CM list” message appears. At the same time we can see that DHCP has a lot of other options besides the basic ones.
In this case the TFTP server will be the router itself.
One important piece of information here: the last line tells the clients where to find a TFTP server from which they can download their configuration. Of course, before this we need some basic configuration: In a small office we can use static addresses as well, but PT doesn’t support static settings on the phones. On the router we need to configure the DHCP service, as we want to assign the IP addresses of the phones dynamically. To define the voice VLAN on all the used ports issue the following commands: Voice VLAN is a VLAN designed for the special requirements of carrying voice data over the network, and it’s always a good practice to use this – but now we use the default VLAN for this purpose. Although we don’t use separate VLANs for data and voice in this first example, PT needs to define the voice VLAN. Don’t forget to connect the power adapter to the phones on the Physical tab.
The phones have a PC and a Switch slot, now we need to connect them with the Switch. Place the components to the workplace and connect them. Last but not least we need two IP phones. In the second version we’ll change this to a 3560 type switch, which provides Power over Ethernet (PoE) – this will eliminate the need of many cables. The simplest solution is to use a Catalyst 2960 switch, but in this case we need to use separate power adapters to every phone. Another important device is a switch to connect the end devices to. The heart of the VoIP system is a router with an IOS containing the Call Manager Express (CME), which will control the calls, as the name implies. Let’s begin with the necessary devices which are available in Packet Tracer (PT). Click here to download Packet Tracer files for this lab