Voice over Internet Protocol (Voice over IP, VoIP)
is a family of technologies, methodologies, communication
protocols, and transmission techniques for the
delivery of voice
communications and multimedia sessions over Internet
Protocol (IP) networks, such as the Internet. Other terms frequently encountered and often used synonymously with
VoIP are IP telephony, Internet telephony, voice
over broadband (VoBB), broadband
telephony, and broadband phone.
Internet
telephony refers to communications services—Voice, fax, SMS, and/or
voice-messaging applications—that are transported via the Internet, rather than
the public switched telephone network (PSTN). The steps involved in originating a VoIP telephone call are
signaling and media channel setup, digitization of the analog voice signal,
encoding, packetization, and transmission as Internet
Protocol (IP) packets over a packet-switched network. On the receiving side,
similar steps (usually in the reverse order) such as reception of the IP
packets, decoding of the packets and digital-to-analog conversion reproduce the
original voice stream. Even though IP Telephony and VoIP are terms that are
used interchangeably, they are actually different; IP telephony has to do with
digital telephony systems that use IP protocols for voice communication while
VoIP is actually a subset of IP Telephony. VoIP is a technology used by IP
telephony as a means of transporting phone calls.
VoIP systems employ session control
protocols to control the set-up and tear-down of calls as well as audio codecs which encode speech allowing transmission over an IP network as digital audio via an audio stream. The codec used is varied between different implementations of VoIP
(and often a range of codecs are used); some implementations rely on narrowband and compressed speech, while others support high fidelity stereo codecs.
There are three types of VoIP tools that
are commonly used; IP Phones,Software VoIP and Mobile and Integrated VoIP. The
IP Phones are the most institutionally established but still the least obvious
of the VoIP tools. The use of software VoIP has increased during the global
recession of 2008-2010, as many persons, looking for ways to cut costs have
turned to these tools for free or inexpensive calling or video
conferencing applications. Software VoIP can be
further broken down into three classes or subcategories; Web Calling, Voice and
Video Instant Messaging and Web Conferencing. Mobile and Integrated VoIP is
just another example of the adaptability of VoIP. VoIP is available on many smartphones and
internet devices so even the users of portable devices that are not phones can
still make calls or send SMS text messages over 3G or WIFI.
PROTOCOLS
Voice
over IP has been implemented in various ways using both proprietary and open protocols and
standards. Examples of technologies used to implement Voice over IP include:
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.
IMPLEMENTATION
A major
development that started in 2004] was the
introduction of mass-market VoIP services that utilize existing broadband Internet access, by which subscribers place and receive
telephone calls in much the same manner as they would via the public switched telephone
network (PSTN). Full-service VoIP phone
companies provide inbound and outbound service with Direct Inbound Dialing. Many offer unlimited domestic calling
for a flat monthly subscription fee. This sometimes includes international
calls to certain countries. Phone calls between subscribers of the same
provider are usually free when flat-fee service is not available.
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 cablemodems have this function built in.
§ A softphone 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.
CORPORATE USE
Because of the bandwidth efficiency and low costs that VoIP
technology can provide, businesses are migrating from traditional copper-wire
telephone systems to VoIP systems to reduce their monthly phone costs. In 2008,
80% of all new PBX lines installed internationally were VoIP.
VoIP
solutions aimed at businesses have evolved into "unified
communications" services that treat all communications—phone
calls, faxes, voice mail, e-mail, Web conferences and more—as discrete units
that can all be delivered via any means and to any handset, including
cellphones. Two kinds of competitors are competing in this space: one set is
focused on VoIP for medium to large enterprises, while another is targeting the
small-to-medium business (SMB) market.
VoIP allows both voice and data communications to be
run over a single network, which can significantly reduce infrastructure costs.
The prices of extensions on VoIP are lower than for PBX
and key systems. VoIP switches may run on commodity hardware, such as PCs or
Linux systems. Rather than closed architectures, these devices rely on standard
interfaces.
VoIP devices have simple, intuitive user interfaces, so
users can often make simple system configuration changes. Dual-mode cellphones
enable users to continue their conversations as they move between an outside
cellular service and an internal Wi-Finetwork, so that it is no longer necessary to carry
both a desktop phone and a cellphone. Maintenance becomes simpler as there are
fewer devices to oversee.
Skype, which originally
marketed itself as a service among friends, has begun to cater to businesses,
providing free-of-charge connections between any users on the Skype network and
connecting to and from ordinary PSTN telephones for a charge.
In the United States the Social Security Administration
(SSA) is converting its field offices of 63,000 workers from traditional phone
installations to a VoIP infrastructure carried over its existing data network.
BENEFITS
VoIP
can be a benefit for reducing communication and infrastructure costs. Examples
include:
§ Routing phone calls over existing data networks to
avoid the need for separate voice and data networks.
§ Conference calling, IVR, call forwarding, automatic
redial, and caller ID features that traditional telecommunication
companies (telcos) normally
charge extra for, are available free of charge from open source VoIP implementations.
VoIP
can facilitate tasks and provide services that may be more difficult to
implement using the PSTN. Examples include:
§ The ability to transmit more than one telephone call
over a single broadband connection.
§ Secure calls using standardized protocols (such as Secure Real-time Transport Protocol). Most of the difficulties of creating a secure telephone connection over traditional phone lines, such as
digitizing and digital transmission, are already in place with VoIP. It is only
necessary to encrypt and authenticate the existing data stream.
§ Location independence. Only a sufficiently fast and
stable Internet connection is needed to get a connection from anywhere to a
VoIP provider.
§ Integration with other services available over the
Internet, including video conversation, message or data file exchange during
the conversation, audio conferencing, managing address books, and passing
information about whether other people are available to interested parties.
§ Unified Communications, the integration of VoIP with
other business systems including E-mail, Customer Relationship Management
(CRM), and Web systems.
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