| Centrex |
Centrex is a set of specialized business solutions for voice service
where the equipment providing the call control and service logic
functions is owned and operated by the service provider and hence is
located on the service provider's premises. |
| Circuit-switched |
Communication system that establishes a dedicated channel for each
transmission. The copper-wire telephone system (POTS) uses circuit-switching, as do
PBX systems. Dedicated channels mean strong reliability and low latency, but the
downside is that only one type of communication can use the channel at any given time. |
| CLEC |
Competitive Local Exchange Carrier. A telephone company that
competes with the larger incumbent carriers (ILECs) through reselling the ILEC
services and/or creating services that use the ILEC's infrastructure. The Regional
Bells are ILECs; local phone companies are frequently CLECs. |
| Compression |
VoIP uses various compression ratios, the highest approximately 12:1.
Compression varies according to available bandwidth. |
| DSP |
Digital Signal Processors. All digital audio systems use DSP technology in order to
differentiate between signal and noise. In telephone communication, too, much noise
creates problems in maintaining connections, and in VoIP systems the DSP component
provides features such as tone generation, echo cancellation, and buffering. |
| E911 |
Enhanced 911. Technology allowing 911 calls from cellular phones to be routed to the
geographically correct emergency station (a.k.a. PSAP: Public Safety Answering Point).
VoIP users currently have limited access to 911 services, and with some providers none,
because VoIP is not geographically based. |
| FCC |
Federal Communications Commission. The regulator of telephone and telecommunications
services in the United States. It's not yet known the full extent to which the FCC will
regulate VoIP communications. Part of the complication lies with determining the
regulation of communications that begin or end on an FCC-regulated system, such as the
standard telephone service. |
| Firewall |
Security software or appliance that sits between the Internet and the individual PC
or networked device. Firewalls can intercept traffic before it reaches network routers
and switches, or between router/switch and PC, or both. Because the job of firewalls
is to prevent access from specific packets over specific network ports, some must be
specially configured to allow VoIP traffic to pass through. |
| FoIP |
Fax over Internet Protocol. The fax counterpart to VoIP, available from some providers
either free or at additional cost. FoIP is actually more reliable than VoIP because of
its tolerance for poor latency. |
| GNU |
GNU is Not Unix. A recursive acronym. The organization behind the GNU
GPL license and advocates open source programming. |
| GPL |
General Public License. The GNU Open Source software license. |
| H.323 |
The standard call protocol for voice and videoconferencing over LANs, WANs, and the
Internet, allowing these activities on a real-time basis as opposed to a packet-switched
network. Initially designed to allow multimedia to function over unreliable networks,
it's the oldest and most established of the VoIP protocols. See also SIP and MGCP. |
| IETF |
The Internet Engineering Task Force is the organization responsible for
defining standards that affect or use the IP network. |
| IP |
Internet Protocol. Internet Protocol is the base protocol upon which
the Internet packet-based network operates. It tracks the Internet
addresses of nodes, routes outgoing messages, and recognizes incoming
messages. |
| IP PBX |
IP PBX is a customer premises telephone system that manages telephones
in the enterprise and acts as the gateway to external networks. Unlike
a conventional PBX that requires two separate networks, one each for
data and voice, an IP PBX is based on converged networks that enable
true one-wire to the desktop connection. |
| ISDN |
Integrated Services Digital Network is a point-to-point signaling protocol
designed to interface PBX equipment with central office switches. |
| ISP |
Internet Service Provider. An organization that provides access to the
Internet. |
| ITSP |
Internet Telephony Service Provider. A company providing VoIP services. |
| Latency |
The time it takes for a packet to travel from its point of origin to its
point of destination. In telephony, the lower the latency, the better the
communication. Latency has always been an issue with telephone communication
taking place over exceptionally long distances (the United States to Europe,
for example). With VoIP, however, latency takes on a new form because of the
splitting of the message into packets (see packet-switched) and network delay
in general. |
| MGCP |
Media Gateway Control Protocol. Another protocol competing with H.323
(see also SIP), MGCP handles the traffic between media gateways and their
controllers. Especially useful in multimedia applications: the media gateway
converts from various formats for the switched-circuit network, and the
controller handles conversion for the packet-switched network. Designed to
take the workload away from IP telephones themselves and thereby make IP
phones less complex and expensive. |
| Packet-switched |
Communication system that chops messages into small packets before sending
them. All packets are addressed and coded so they can be recompiled at their
destination. Each packet can follow its own path and therefore can work around
problematic transmission segments. Packet switching is best when reaching a
destination is the primary concern and latency is permissible, such as sending
e-mail and loading Web pages. |
| PBX |
Private Branch eXchange. An in-house telephone switching system that
interconnects telephone extensions to each other, as well as to the
outside telephone network. It may include functions such as least
cost routing for outside calls, call forwarding, conference calling
and call accounting. |
| PDA |
Personal Digital Assistant. A small lightweight handheld computer. |
| POTS |
Plain Old Telephone Service. Another term for PSTN. |
| PSTN |
Public Switched Telephone Network. The regular old-fashioned telephone system. |
| QOS |
Quality of Service. Refers to the quality of the voice call over a VoIP network.
A major issue in VoIP communications, because the high quality of telephone calls
has always been taken for granted. Latency, packet loss, network jitter, and many
other factors contribute to QOS measurements, and numerous solutions have been
offered by vendors of routers and other network components. |
| RTP |
Real Time Protocol. Also known as Real Time Transport Protocol. Controls the
transmission of packets of data that demands low latency (such as audio and video).
Supports real-time transmission over IP networks and streaming as one means of
delivery. |
| SBC |
Session Border Controller. SBCs are devices that, among other things, allow
VoIP calls to penetrate firewalls and other ”walled-off” areas of Internet.
Other roles of the SBC are topology hiding and protocol translation. |
| SIP |
Session Initiation Protocol. An ASCII-based protocol that provides telephony
services. It creates, modifies, and terminates sessions with one or more
participants. Such sessions include telephony and multimedia conferences.
SIP is a request-response protocol, dealing with requests from clients and
responses from servers. |
| Softphone |
A software based IP telephone not requiring any special hardware. A
softphone can be used on a PC or PDA. |
| Universal Service |
The availability of affordable telecommunications technology for all Americans,
part of the 1966 Telecommunications Act, and regulated by the FCC. Current
discussions revolve around the applicability of VoIP to universal services and
whether or not VoIP providers should be taxed accordingly. |
| Virtual phone number |
A feature of VoIP that allows you to attach additional phone numbers with
different area codes to your basic VoIP service. This feature allows people to
phone you without incurring long-distance charges from the same or adjacent
nontoll area codes. All outgoing calls, however, are billed as if coming from
your main phone number. Virtual phone numbers typically each cost a few extra
dollars per month. |
| WiFi |
Wireless Fidelity. Another term for wireless networks (WLAN). |
| WLAN |
Wireless LAN. A wireless IP network. |
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