Voice over IP is an exciting technology being implemented by businesses today, It allows a company tp attach a special IP Phone to an RJ-45 data outlet just like to PC connects to a network. The phone uses the same network connectivity as traditional network devices such as PCs, servers and network printers.
VoIP can be implemented using specital Cisco software installed on specific models of routers or software installed on ta traditional network server, servers use Cisco CallManager, and router use CallManager express(CME).
CME is typically used in small business installations(fewer than 240 phones). CME is supported on specific router models such as the 1700.2600XM,2691,2800,3700 and 3800 series. CallManager typically is used in larger corporate installions with more than 240 phones, CEM is use to show the basics of IP telephony .
Basic Requirements for VoIP Implementation
Implementing VoIP means buying special IP Phones and using the CallManager software on the router or on the server to control the phones. when planning for a VoIP installtion, you must consider serveral things, all of which are discuccssed throught this chapter. Two important considerations are the VoIP Phone's power and data outlets. Power can be applied to the phone in one if three ways.
(1) External 48 VDC power brick
(2) Power over ethernet(PoE) connectivoty from a PoE switch
(3) Connectivity to a PoE patch panel
Most companies use one of the PoE solutions.
VLAN Review
Virtual LANs allow you to create different networks on a layer 2 switch, VLAN breakup broadcast domains because they allow different networks to be created, A broadcast is sent only over the same network, the VLAN assigned to every port on a switch by default is VLAN1
VLAN 1 gets confusing because it has many names--default VLAN, management VLAN , native VLAN . Each of these names is correct for a switch that has not had its coniguration changed to anything else, The following list clarifies these terms and a related term for the purposes of this chapter.
(1)Default VLAN---> The VLAN that is assigned to a switch port without changes being made , All switch ports belong to VLAN1 , so , calling VLAN1 the default VLAN is a good name .
(2) Management VLAN-->The VLAN that is used to connect to the switch from a remote location,All switches by default have a mangement VLAN of 1, changing the management VLAN to another VLAn besides VLAN 1 is a ggod idea, This way , broadcasts that are sent over the management VLAN cannnot be captured easily by a workstation that is on VLAN1.
(3) Tagging the frame-->when frames are sent across a trunk. they have a special section to designate the VLAN to which the frame belongs, This is called tagging the frame,A frame coming from a host on VLAN 2 that crosses a trunk would have its frame tagged with the VLAN identifier of 2.
(4) Native VLAN-->Traffic from the native VLAN is not tagged as it crossed the trunk, If the trunk fails, but connectivity still exists , traffic from the native VLAN is still allowed across the link.
IP Phone Connectivity Options
One common connectivity option used by commanies is connecting the existing networked office PC to an RJ-45 jack on the IP Phone and using the existing PC-to -Wll outlet cable to connect to the IP Phone.
Office PC-----IP Phone-----Wall Outlet----Switch--IP Tele Router
run from the patch panel to the office and allowes for the use of existing wiring , the existing wiring can also provide power to the phone if a PoE power panel or switch is being used.
The PC and the Cisco IP Phone need to be on different networks even though they both use a single connection to the swith, This is done using VLANs, The connection from the phone to the switch is a trunk that carries both the data VLAN(the information from the PC) and the voice VLAN(the data from the IP Phone).
Office PC---------IP Phone--------------Switch------------Router
10.1.4.88/24 10.1.2.5/24 Trunk between Trunk between
VLAN 4 VLAN 2 Phone and Switch Switch and R
how the PC and the phone are on two different networks and have IP addresses assigned accordingly ,the trunk between the IP Phone and the switch carries the two VLANs, Configuring the trunk is an important concept and configuration step.
Special Commands for the Labs
Whether the switch ports are on a specialized module in a router or a separate network device, the "switch port trunk native vlan X "command is used on the port that has an IP Phone attached(with a PC attached to the phone).
The "native" keyword defines this VLAN as the one that is not tagged with VLAN information when a frame(from the native VLAN) crossed the trunk between the IP Phone and the switch, In a IP telephony configuation , this native VLAN is the data VLAN--the VLAn to which the PC attaches.This allows the PC that connects to the IP Phone to be on a different subnet than the IP Phone and still receive an IP addresse from a DHCP server.The command also allows data traffic to still traverse the link between the phone and the switch even if the trunk fails. the show interface trunks or show interfaces interface-id switchport commands canbe used to verify trunk operations.
For the port that connect to the IP Phone, you must configure the switch so that 802.1Q knows which VLAN contains voice traffic, you can accomplish this configuratuion with the "switchport voice vlan "command.
On switches such as the 3560, the "switchport trunk" command is not required, Only the voice VLAN(switchport voice vlan X) and the data VLAN(switchport access vlan XX) commands are required to define which VLAN is used for voice and which VLAN is used for data. The "switchport trunk" command is still required on the switch modules installed in routers and older switches.
When you configure the router, It is important to program the correct interface, this can get quite confusing , For example ,sone routers have the first FastEthernet interface shwo as Fa0, whereas other routers show the same first interface as Fa0/0, This is not an issue with the switch module that inserts into a router, The specific slot/port-adapter/port parameter used with the interface command depends on the physical router slot that contains the swith module, A sample command is interface fastethernet0/10/ use the show diag and show ip interface brief commands to verify the naming of the installed interfaces.
