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Learning Guide: Voice over IP basics

This guide contains all the VoIP basics and essentials you will need when implementing an IP telephony network.

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VoIP (Voice over Internet Protocol)
This guide presents VoIP articles, tutorials, examples, tips, tools, white papers, expert advice and more to pump up your VoIP know-how quickly.

   What is VoIP?
   How does VoIP work?
   Circuit switching vs. packet switching
   H.323 and SIP
   PBXs, IP-PBXs and hybrid systems
   Advantages and disadvantages
   Hosted vs. in-house VoIP
   Regulatory issues/E911
   Securing VoIP
   More Learning Guides

What is VoIP?
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VoIP (Voice over IP ) 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). This guide will help you understand the technology behind VoIP. In addition, this guide delves into key VoIP issues such as; security, regulations, advantages and disadvantages, outsourcing and QoS.

    • Glossary definition: ATM (

    • Guide: Learn IT in 10 easy steps: VoIP (

    • Chapter download: Taking charge of your VoIP project (

    • Quiz: When is it worthwhile to move to VoIP? (Tom Pisello)

    • Tip: 2005 promises yet another 'Year of VoIP' (

    • Tip: Introduction to Internet telephony (

    • Tip: Seven steps to successful VoIP (

    • Article: Voice over what? (

How does VoIP work?
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VoIP works by converting your analog voice into data packets (digital format), sending them over your existing data network and reconverting them to voice at the destination. The benefit of a digital format is that it can be controlled. It can be routed, modified, condensed, expanded and saved. Digital signals are also more noise tolerant than analog. This section will help you to understand the basic processes and functionalities of VoIP.

    • Expert advice: What are the steps involved in designing a VoIP network? (

    • Tip: IP telephony implementation planning (

    • Chapter download: Implementing Voice over IP- Chpt 6: VoIP Deployment in Enterprises (

    • Web resource: Simple explanation of VoIP (Wilco Telephony)

    • Web resource: VoIP 101 (VoIP Now)

Circuit switching vs. packet switching
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Circuit switching was developed for analog-based telephone systems. Circuit switching has been used extensively for the public switched telephone network (PSTN). In circuit switching, users have exclusive use of a connection until the conversation is over and the connection is released. In packet switching, messages are divided into packets, and many users share access to a circuit by taking turns putting their packets onto the channel. Breaking communication down into packets increases capacity. This type of communication between sender and receiver is known as connectionless (rather than dedicated). Most traffic over the Internet uses packet switching.

    • Tip: Bulletproof IP telephony deployment, Part 1 (

    • Tip: Bulletproof IP telephony deployment, Part 3 (

    • Tip: VoIP analysis (

    • Tip: Lowering packet size (

    • Tip: Avaya's management enhances reliability, sets stage for next-generation VoIP (

    • Tip: Duties of an IP telephony gateway when integrating VoIP and the PSTN (

    • Tip: Probing to maximize MTU efficiency and deliver QoS (

    • Article: Alcatel's new switches styled for convergence (

    • Article: Extreme switch aims to cut out the middleman (

    • Web resource (PDF): Making the packet connection with TDM-over-IP (Analog Zone)

H.323 and SIP
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The Session Initiation Protocol (SIP) 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. H.323 is a standard approved by the International Telecommunication Union (ITU) in 1996 to promote compatibility in videoconference transmissions over IP networks.

    • Glossary definition: SIMPLE (

    • Learning Guide: SIP (

    • Expert advice: What is the VoIP future protocol? (Carrie Higbie)

    • Expert advice: SIP advantages and disadvantages (Carrie Higbie)

    • Q & A: SIP to grow leaps, out of VoIP bounds (

    • Tip: VoIP and protocols (Sudha Rani)

    • Tip: SIP, don't gulp (

    • Article: VoIP experts savor SIP's potential (

    • Article: Is SIP a king with no kingdom? (

    • Article: SIP promises sweet taste of interoperability (

    • Chapter download: IP Telephony Demystified - Chapter 4, IP telephony protocols (

    • Chapter download: IP Telephony: Deploying VoIP protocols - Chpt. 3: SIP (

    • Web resource: H.323 overview (International Engineering Consortium)

    • Web resource: VOIP protocols overview (Javvin Technologies, Inc.)

PBXs, IP-PBXs and hybrid systems
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A PBX is a telephone system that switches calls between enterprise users on local lines while allowing all users to share a certain number of external phone lines. The main purpose of a PBX is to save the cost of requiring a line for each user to the telephone company's central office. An IP PBX is a private branch exchange that switches calls between VoIP users on local lines while allowing all users to share a certain number of external phone lines. A typical IP PBX can also switch calls between a VoIP user and a traditional telephone user.

Many major vendors are offering hybrid voice systems that combine elements of VoIP and public switched telephone network (PSTN) systems. These new hybrid systems may give enterprises an opportunity to benefit from VoIP cost savings by combining the traditional telephony hardware with new technologies.

    • Expert advice: What are IP PBXs? (Patrick Ferriter)

    • Article: A hazy future for the IP-PBX (

    • Article: Opportunities abound for hybrid voice systems (

    • Tip: Hosted PBX lets small businesses act big (

Advantages and disadvantages
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VoIP technologies can reduce telecommunication and networking costs and offer new voice capabilities. However, it is important that you understand the advantages and disadvantages of VoIP before you begin an implementation. Some advantages include; reduction of intra-office toll charges, lower hardware costs, productivity benefits for remote and traveling workers, improved security and reduced system downtime. Some of the risks involved with a VoIP project can include; quality of service/performance issues, cost and resources needed for user and administrative training and proprietary vs. open systems interoperability. This section takes a closer look at the good, bad and ugly of VoIP.

    • Tip: Before deploying VoIP consider this (

    • Expert advice: How do I know if VoIP is right for my business? (Tom Pisello)

    • Case study: TCF Financial Corp. (

    • Case study: Johns Hopkins Bloomberg School of Public Health (

    • Article: VoIP 2005: Better watch what you say (

    • Article: Vendors 'lying' about VoIP cost savings (

    • Article: VoIP can cut costs, but capable of much more (

Hosted vs. in-house VoIP
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Many carriers are now offering low-maintenance hosted VoIP services for enterprises. Is hosted VoIP right for your company? There are many things to consider when making the choice between hosted and in-house VoIP. Quality of service (QoS) issues, hardware stability, network monitoring and latency are all very important factors to look at. This section will help you better understand the pros and cons of both options.

    • Expert advice: Why should we use a hosted voice service? (John Blake)

    • Article: Making the case for VoIP outsourcing (

    • Article: Hosted VoIP has its advantages, risks (

    • Web resource: Presentation on hosted IP services vs. managed IP services (Broadsoft)

    • Web resource: The slow rise of managed voice services (Outsourcing Pipeline)

    • Web resource: Hosted voice services (Telecommunications Magazine )

Regulatory issues/E911
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In many countries, VoIP is illegal. In many others (including the United States) telecom regulations are changing faster than you can say 911. Recently, the Supreme Court ruled to uphold FCC regulations permitting cable operators to block rivals from using their infrastructures. This could hurt VoIP providers and increase costs significantly. In addition, the FCC has set a mandate for VoIP providers to get E911 services up and running soon. This section will help you sort through the intricate web of VoIP regulations.

    • Expert advice: Impact of VoIP E911 (Patrick Ferriter)

    • Tip: The trouble with 911 and VoIP (

    • Article: VoIP regulatory issues concern Interop attendees (

    • Article: VoIP industry preps for regulatory battles, new competition (

    • Article: Industry coalition seeks to head off VoIP 911 requirements (

    • Article: Enterprises answer FCC's 911 call (

    • Web resource: Get to know VoIP regulations (

    • Web resource: VoIP regulations kick in (TechWeb)

Securing VoIP
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Deploying effective VoIP security is challenging. Since telephony traffic must travel over the IP network between gateways, stations, servers and proxies, there are plenty of places to attack. The list of possible threats includes; toll fraud, impersonation, hijacking of calls, session replay, media tampering, denial of service and SPIT. This section will help you avoid some security pitfalls.

    • VoIP Security Resource Guide (

    • Expert advice: How will a service provider ensure security and QoS? (John Blake)

    • Tip: Employ fuzzing to test VoIP security (

    • Tip: Stolen voices: The challenge of securing VoIP (

    • Tip: Don't forget to secure the signaling (

    • Tip: M2M issues in VoIP security (

    • Tip: Mitigating VoIP deployment risks with route analytics (

    • Article: VoIP could bring new security threats (

    • Article: VoIP security details make or break implementation (

    • Article: Gartner underscores five overblown threats (

    • Article: Can VoIP ever be as secure as Ma Bell's creation? (

    • Article: VoIP security, 'spit' concern experts (

    • Article: VoIP demands more from a firewall (

    • Q & A: Avoiding a VoIP security 'judgment day' (

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A big component of VoIP infrastructure is effectively deploying a Quality of Service (QoS) model. QoS is the idea that transmission rates, error rates and other characteristics can be measured, improved, and to some extent, guaranteed in advance. QoS is of particular concern for the continuous transmission of high-bandwidth video and multimedia information. There are many ways to ensure QoS. This section will help you decide which QoS method is right for you.

    • Expert advice: Measuring quality of service (Patrick Ferriter)

    • Expert advice: QoS in a VoWLAN (Joel Vincent)

    • Expert advice: Challenges of QoS for large IP networks (Carrie Higbie)

    • Expert advice: How successful is E-Model, a tool for measuring QoS for VoIP? (Patrick Ferriter)

    • Tip: VoIP product development issues (

    • Tip: Elements of VoIP QoS (

    • Tip: QoS classification and marking for VoIP infrastructures (

    • Tip: A closer look at QoS components (

    • Tip: Tools for VoIP planning, monitoring and management (

    • Tip: Link efficiency within QoS (

More Learning Guides
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Check out this collection of related learning tools and guides.

    • Learning Guide: SIP (

    • VoIP Security Resource Guide (

    • Firewall Resource Guide (

This was last published in May 2004

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