Get started Bring yourself up to speed with our introductory content.

LearnIT: VoIP basics

This guide provides an overview of voice over IP, the standards, regulations, preparing your network and more.




ATM (asynchronous transfer mode)


Differentiated Services


Internet Protocol (IP)


IP telephony






Internet Engineering Task Force (IETF)












public switched telephone network (PSTN)




OSI model


SIP (Session Initiation Protocol)












Take a QUIZ

Learn IT in ten easy steps

Directions: Read steps 1-8 and their related links. Use the glossary to look up any terms you do not know. When you're done, go to step 10 and take a quiz to see how much you've learned!

1. First things first… VoIP defined 

VoIP (voice over IP - that is, voice delivered using the Internet Protocol) is a term used in IP telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol (IP). In general, this means sending voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public switched telephone network (PSTN).


2. Let's look at the difference between VoIP and voice and data convergence

VoIP specifically refers to sending voice traffic over an IP (Internet Protocol) network. Voice and data convergence refers to sending both voice and data (such as LAN traffic) over any data network (typically an IP network, frame relay network or ATM network).


And, while we're at it, let's quickly explain the difference between VoIP and IP telephony.  IP telephony refers to any "telephone" type service carried over IP - this could include faxing VoIP is voice over IP only.  Sometimes telephony also includes text messaging.


Related Links:

Site expert, Carrie Higbie can help with your VoIP questions.



3. Let's take a look at the standards… 

H.323 is a standard approved by the International Telecommunication Union (ITU) in 1996 to promote compatibility in videoconference transmissions over IP networks. H.323 was originally promoted as a way to provide consistency in audio, video and data packet transmissions in the event that a local area network (LAN) did not provide guaranteed service quality (QoS). Although it was doubtful at first whether manufacturers would adopt H.323, it is now considered to be the standard for interoperability in audio, video and data transmissions as well as Internet phone and voice-over-IP (VoIP) because it addresses call control and management for both point-to-point and multipoint conferences as well as gateway administration of media traffic, bandwidth and user participation.


SIP (Session Initiation Protocol) is an Internet Engineering Task Force (IETF) standard protocol for initiating an interactive user session that involves multimedia elements such as video, voice, chat, gaming, and virtual reality. 


Like HTTP or SMTP, SIP works in the Application layer of the Open Systems Interconnection (OSI) communications model. The Application layer is the level responsible for ensuring that communication is possible. SIP can establish multimedia sessions or Internet telephony calls, and modify, or terminate them. 


H.323 and SIP are often compared and do compete with each other for VoIP services. H.323 has been the early leader in this market so it is very popular. There are standards groups who view the Session Initiation Protocol (SIP) as the way to go in the future but sometimes the early leader ends up winning anyway. H.323 is still very important to product development and time will tell which one survives or whether both survive or remain important.


Related Links:

H.323 versus SIP: A Comparison (Excellent resource guide.)


4. Getting to know VoIP regulations

Unfortunately, the biggest challenge to the total adoption of VoIP isn't the complex technology, or the lack of experienced implementers, or even compelling business cases. It's regulatory hoopla. VoIP is simply illegal in an astonishing number of countries, while the rest are mired in enough red tape to often negate the cost savings.


In recent weeks, we've seen intense interest in a court case where a Minnesota judge ruled that a certain vendor's Internet phone service is an "information service" rather than a "telecommunications service" and is beyond the reach of traditional telephone regulations. It's an early win for VoIP vendors in what is expected to be a drawn-out legal battle against state regulators and local carriers concerned about competition and lost revenue.  We're keeping track of developments and will update this report as we learn more.


Related Links:

This link provides more information on regulations, and this article, "Next Stop After VoIP Decision: The FCC" (Oct 21, 2003) discusses recent rulings.


5. Does your network have what it takes? 

One of the biggest challenges in implementing a VoIP solution is making sure you have all the necessary components. This can be especially daunting if you're new to VoIP.


Among the things you can do before you even pick a vendor are:


*Identify the types of traffic on your network and prioritize them (voice may not be the most important).


*Determine existing call-traffic statistics and predict future statistics, including cost, average simultaneous calls, average duration, and source/destination pairs.


*Examine your infrastructure both physical and your electronics to be sure that enough bandwidth is available and reliable enough to add additional applications.  (Note from Carrie Higbie:  This is the single key that causes most implementations to fail.)


*If you will be supplying power to your IP phones via Power over Ethernet you will want to be sure that the switches supply power to the pairs on which the phones expect to receive it.  There are two different applications allowed for in the standard.


*Check your vendors references for accounts of similar size and implementation.


Related Links:

 Here's a list of things you'll need.

This article will help you in preparing your network.

This article provides a guide to the "The essential VoIP bookshelf"



6.  Here's a look at some VoIP players. 


Aspect Communications


Hughes Software Systems


7.  Let's learn how to evaluate IP telephony products

If you've decided to implement an IP Telephony network, but you haven't decided on a vendor yet, you're probably planning to evaluate a lot of IP Telephony hardware and software in the near future. You've got a lot of questions to answer. These include concerns about the hardware and software compatibility with your existing network, and of course, you want to listen to actual phone calls to hear how it sounds for yourself.


You also want to verify interoperability between a number of vendors and product lines.

All of this may be easier said than done. You get some demo equipment from your salesmen, but if you don't already have a network set up, what good is it? If you're trying to set up all the equipment at once and you have issues, it's hard to know which product is misconfigured or at fault. These and other issues can make evals almost pointless.


Related Links:

Here are a few tips for conducting a productive evaluation.



8.  Let's see who's offering VoIP Training

Acquiring the skills to be successful with voice over IP is challenging for most people because it requires a broad knowledge-base in two domains (voice and data networking) plus a functional understanding of the protocols and hardware that connect these two areas (thus the name "convergence").

Fortunately, most people interested in this field start with a reasonably solid grasp of one or the other (voice or data networking). But many people don't know where to begin to find out what they don't know.


There are numerous organizations offer certs in this area, including the likes of Alcatel, Cisco (one of the Cisco qualified specialist credentials focuses on IP telephony), and Nortel, among others.


Given the recent burst of activity around IP telephony, there is an increased demand for certified employees, and workers are beginning to respond to that opportunity.  We recommend you review the various certifications available, and get ready.


Related Links:

Need certification advice? Ask our training and certification expert, Ed Tittel.

Here's more information on certifications.



9. VoIP Words-to-Go Glossary

Browse VoIP vocabulary in this handy printable glossary.


10. Self-assessment

After you've looked at the glossary, quiz yourself to see what you've learned about the basics of VoIP.



This was last published in October 2003

Dig Deeper on Network protocols and standards

Start the conversation

Send me notifications when other members comment.

Please create a username to comment.