VoIP Tutorial


Voice over IP (VoIP) defines a way to carry voice calls over an IP network including the digitization and packetization of the voice streams. IP Telephony utilizes the VoIP standards to create a telephony system where higher level features such as advanced call routing, voice mail, contact centers, unlimited calling, long distance calling etc., can be utilized.

VoIP and IP telephony are ever more admired by large corporate organizations and consumers. Many people are in impression that Internet Protocol (IP) is limited only as a way to transport data, but that is not actually a true statement. IP is also a protocol tool that simplifies and streamlines a wide range of business applications.

VoIP—or voice over IP—is the basis for the foundation of more advanced unified communications applications—these include:

  • Web and video conferencing. These features help businesses to completely transform the way they do business for their benefit.
  • VoIP technology. This is the technique that carries phone calls over an IP network. It doesn’t matter whether you are on internet or your own internal network. VoIP helps your business to reduce expenses as voice calls travel over the data network rather than the phone company’s network.


Voice over Internet Protocol (VoIP) technology usually works on broadband internet connections VoIP communicates and makes phone calls over established internet connections, similar  with analog telephone lines.  A basic VoIP system makes calls over to another person who is also receiving calls on internet connection.

Interconnected VoIP services also allow you to make and receive calls to and from traditional landline numbers, usually for a service fee. Some VoIP services require a computer or a dedicated VoIP phone, while others allow you to use your landline phone to place VoIP calls through a special adapter.

VoIP is today a very attractive and cheap communication option available in telecom industries.

Today VoIP services gain much popularity and day by day it is increasing drastically offering high voice quality and cheap call rates over basic broadband connections.

As the VoIP penetration to consumers increases, so the potential threats to the users. Apart from the cheap and attractive services by VoIP, it is also vulnerable to many threats, scams, and attacks because VoIP calls now traverse the internet.


In a basic VoIP network setup we have the following important components.


Router’s basic function is routing the data traffic. However, routers allow you also to use your traditional phone to place VoIP calls if you have a special adapter installed on the router device.

They are connected with cable/DSL modem (or any high speed internet connection) and allow you to connect a telephone on them. They need to be configured with an appropriate VoIP provider and service plan, with no special software requirements to interact with the computer. You just have to pick up your phone and dial a number at the dial tone.


Switches act as the channel that forward the incoming data from multiple input sources to the specific output port towards the intended destination. These are used to connect a number of IP phones or analog phones and computer systems for the users as per the numbers required. These switches then forward the data to single destination (to the router usually) which then routes the traffic to the configured destination path and move forward the VoIP call.

 Adapters (USB)

Adapters are used to use traditional phones to place VoIP calls. They usually are in the form of USB adapter connectors that is larger than a typical thumb drive. You can attach an ordinary phone line to the standard jack modular phone provided in that. Once you finish with the connection, you phone will behave like a standard phone service. But actually a Voip software is running at the backend of the system which helps to make a call.

Software-controlled VoIP applications: “softphones”

There are many softphone applications available in the market that help you to place a VoIP call directly from your normal PC with any headset, microphone etc. These applications and services can be provided by telecom providers. With these applications users are allowed to talk to other people using many services (such as voice and video) almost at no cost. A VoIP application based on software instead of hardware is installed on your computer. This is the Softphone. These are quite attractive and cheap as well for the consumer.

Dedicated VoIP phones

There are also dedicated phones available today in the market with several advanced features. VoIP phones are like simple and ordinary phones available for home with cord or without cord/cordless phones. A VoIP phone which has a dedicated connection consists of phone and base station which further connects to the internet or can also operate on local wireless network. Same like VoIP adapters, dedicated Phones can also be offered from voip provider with service plans to work.

Requirements for VoIP and Availability

VoIP services don’t have all the features, functionality and other options equally as with traditional landline services; there are some basic requirements, availability and some possible service limitations of VoIP service compared to traditional landline telephony. Before you opt in to VoIP as a primary means of communication or an enhancement to your current services you need to know the requirements and limitations.


The main and basic requirement for a VoIP system to work is to have basic internet connection through an ISP that allows a VoIP service to actually make the calls or a VoIP service to extend the reach to traditional landlines. But Plain Old Telephone Service doesn’t need any of these services to make the call. It is important to note that Digital Subscriber Line (DSL) internet service uses traditional phone lines for your internet connection; so that your internet with DSL already have telephone service to begin with.

Availability of Power Supply

Power outage is the major threat with the VoIP service as they become unavailable under typical power outage. VoIP devices like computers, routers, adapters etc all rely on power supply to run. So power supply is the most critical resource for VoIP to function properly. If you really don’t want this to happen in case of emergency you can use an uninterruptable power supply (UPS) with a VoIP installation if you are in urgent need of connectivity during power outage or in any emergency.

Connectivity Bandwidth Availability

High-speed internet connection is another important requirement for reliable functionality of VoIP communication. In fact, speed of the internet connectivity may affect your voice quality and many other interruptions you may face while calling. Slow bandwidth may degrade your quality of service. For example if you are trying to make a call and some other person are using a lot of bandwidth like some downloading on the same internet connection, the sound quality of your call will be affected badly.

911 services

911 service is available for many interconnected VoIP and traditional landline services but this is not a service with basic voip (VoIP to VoIP setup). Even if you have interconnected VoIP services, 911 services are not assumed to be present and working. You need to see the terms of service agreement to make sure you have 911 services. There are some tips and some challenges for VoIP services described under the FCC agreement for subscribers.


In this VoIP network architecture setup there are two sites Site A and Site B which are connected by a point to point serial connection.  The two sites are connected by two Cisco 2811 ISR routers. For the LAN connectivity we have used two Cisco 3560 POE switches to connect all local LAN devices such as phones, computers etc.

What should be the output of the architecture?

  • Setup Working PPP WAN between two sites
  • Setup NAT at each site if you need internet access
  • Configure Routers telephony services
  • Setup Configuration of Phones
  • Setup a Site-to-Site Calling


Equipment Used in Architecture

  • 2 – Cisco 2811 Routers w/WIC-1T
  • 2 – Cisco 3560 24port POE
  • 4 – Cisco 7960 IP Phones
  • 4 – Computers


Site Configuration

Site 1


  • LAN IP (data):
  • LAN IP (voice):
  • WAN IP:
  • VLANS: Data-40, Voice-50
  • Phone Ext. – 54001, 54002

Step 1: Configure interface FastEthernet 0/0 and DHCP server  on RouterA (2811 router)

!Configure the FA 0/0 interface


RouterA#configure terminal

RouterA(config)#interface FastEthernet0/0

RouterA(config-if)#ip address

RouterA(config-if)#no shutdown

The DHCP server is needed to provide an IP address and the TFTP server location for each IP phone connected to the network.

! Create DHCP pool named VOICE

RouterA(config)#ip dhcp pool VOICE

! DHCP network 192.168.10 with /24 mask


! #The default router IP address#


! #Mandatory for voip configuration. Option 150 is the server for the phones to boot up

RouterA(dhcp-config)#option 150 ip

After the configuration, wait a moment  and check that ‘IP Phone 1’ has received an IP address.

Step 2: Configure the Call Manager Express telephony service on RouterA

You must now configure the Call Manager Express telephony service on RouterA to enable VoIP on your network.

! #Configuring the router for telephony services#


! #Define the maximum number of directory numbers#


RouterA(config-telephony)#max-dn 5

! #Define the maximum number of phones#

RouterA(config-telephony)#max-ephones 5

! #IP Address source used for the telephony service

RouterA(config-telephony)#ip source-address port 2000

! ! #Automatically assigning ext numbers to buttons#

RouterA(config-telephony)#auto assign 4 to 6

RouterA(config-telephony)#auto assign 1 to 5


Step 3: Configure a voice vlan on SwitchA

Apply the following configuration on SwitchA interfaces.

This configuration will separate voice and data traffic in different vlans on SwitchA.

Data packets will be carried on the access vlan.

! #Configure interface range#

SwitchA(config)#interface range fa0/1 – 5

SwitchA(config-if-range)#switchport mode access

! #Define the VLAN on which voice packets will be handled#

SwitchA(config-if-range)#switchport voice vlan 50

Step 4: Configure the phone directory for IP Phone 1

Although ‘IP Phone 1’ is already connected to SwitchA, it needs additional configuration before being able to communicate. You need to configure RouterA CME to assign a phone number to this IP phone.

! #Defining the first directory entry#

RouterA(config)#ephone-dn 1

! #Assign the phone number to this entry#

RouterA(config-ephone-dn)#number 54001

Step 5: Verify the Configuration

Ensure that the IP Phone receives an IP Address and the phone number 54001 from RouterA  (this can take a short while).

Step6: Configure the phone directory for IP Phone 2

Connect IP Phone 2 to SwitchA and power the phone ON using the power adapter.

!#Defining the second directory entry#

RouterA(config)#ephone-dn 2

! #Assign a phone number to this entry#

RouterA(config-ephone-dn)#number 54002

Task 7: Verify the configuration

Ensure that the IP Phone 2 receives an IP Address and the phone number 54002 from RouterA  (this can take a short while). Same procedure as task n°5.

Dial 54001 and check if IP phone 1 correctly receives the call.


Site 2

  • LAN IP (data):
  • LAN IP (voice):
  • WAN IP:
  • VLANS – Data-40, Voice-50
  • Phone Ext. 2000


Similar configuration as Site 1


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