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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.

SearchNetworking editorial team

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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.

TABLE OF CONTENTS
   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
   QoS
   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.

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.

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.

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.

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.

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.

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.

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.

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.

QoS
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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.

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

This was last published in May 2004

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