VOIP (Voice Over IP)

Short for Voice over Internet Protocol, a category of hardware and software that enables people to use the Internet as the transmission medium for telephone calls by sending voice data in packets using IP rather than by traditional circuit transmissions of the PSTN. One advantage of VoIP is that the telephone calls over the Internet do not incur a surcharge beyond what the user is paying for Internet access, much in the same way that the user doesn't pay for sending individual e-mails over the Internet.
There are many Internet telephony applications available. Some, like Cool Talk and Net Meeting, come bundled with popular Web browsers. Others are stand-alone products. VoIP also is referred to as Internet telephony, IP telephony, or Voice over the Internet (VOI)
 
Voice over IP has been implemented in various ways using both proprietary and open protocols and standards. Examples of the network protocols used to implement VoIP include:

• H.323
• Media Gateway Control Protocol (MGCP)
• Session Initiation Protocol (SIP)
• Real-time Transport Protocol (RTP)
• Session Description Protocol (SDP)
• Inter-Asterisk eXchange (IAX)
• Jingle XMPP VoIP extensions

The H.323 protocol was one of the first VoIP protocols that found widespread implementation for long-distance traffic, as well as local area network services. However, since the development of newer, less complex protocols such as MGCP and SIP, H.323 deployments are increasingly limited to carrying existing long-haul network traffic. In particular, the Session Initiation Protocol (SIP) has gained widespread VoIP market penetration.
A notable proprietary implementation is the Skype protocol, which is in part based on the principles of peer-to-peer (P2P) networking.

A VoIP phone is necessary to connect to a VoIP service provider. This can be implemented in several ways:

• Dedicated VoIP phones connect directly to the IP network using technologies such as wired Ethernet or wireless Wi-Fi. They are typically designed in the style of traditional digital business telephones.
• An analog telephone adapter is a device that connects to the network and implements the electronics and firmware to operate a conventional analog telephone attached through a modular phone jack. Some residential Internet gateways and cable modems have this function built in.
• A soft phone is application software installed on a networked computer that is equipped with a microphone and speaker, or headset. The application typically presents a dial pad and display field to the user to operate the application by mouse clicks or keyboard input.

 How VoIP Works

To understand how VoIP, short for Voice over Internet Protocol, works, it's helpful to compare it to how conventional phone calls operate. When you place a "regular" phone call using the Public Switched Telephone Network (PSTN), also known as Plain Old Telephone Service (POTS) you use what's called circuit-switched telephony. This system works by setting up a dedicated channel (or circuit) between two points for the duration of the call. These telephony systems are based on copper wires carrying analog voice data over the dedicated circuits.

Sponsored

10 New Reasons to Visualize Your Infrastructure:  

The cost savings that comes with visualization makes an easy selling point, but there are other reasons the technology makes sense.This is in contrast to newer Internet telephony networks based on digital technologies. VoIP, in contrast to PSTN, uses what is called packet-switched telephony. Using this system, the voice information travels to its destination in countless individual network packets across the Internet. This type of communication presents special TCP/IP challenges because the Internet wasn't really designed for the kind of real-time communication a phone call represents.

Individual packets may — and almost always do — take different paths to the same place. It's not enough to simply get VoIP packets to their destination. They must arrive through a fairly narrow time window and be assembled in the correct order to be intelligible to the recipient. VoIP employs encoding schemes and compression technology (see G.7xx for more information) to reduce the size of the voice packets so they can be transmitted more efficiently.

PSTN Versus VoIP: A Feature Comparison

PSTN

VoIP

Dedicated Lines Each line is 64kbps (in each direction) Features such as call waiting, Caller ID and so on are usually available at an extra cost Can be upgraded or expanded with new equipment and line provisioning Long distance is usually per minute or bundled minute subscription Hardwired landline phones (those without an adapter) usually remain active during power outage When placing a 911 call it can be traced to your location

All channels carried over one Internet connection Compression can result in 10kbps (in each direction) Features such as call waiting, Caller ID and so on are usually included free with service Upgrades usually requires only bandwidth and software upgrades Long distance is often included in regular monthly price Lose power, lose phone service without power backup in place 911 emergency calls cannot always be traced to a specific geographic location