VoIP Glossary

IP Telephony Glossary

As you investigate IP Telephony solutions for your organization, you will run across many unfamiliar terms. Some of them are related to your communications system and others to the underlying network. Here is a glossary of many terms you will need to know.

Term	Definition
Auto attendant	An automated attendant allows calls to be routed to a user’s extension without intervention of a receptionist.
Conferencing	The ability to connect three or more callers in one phone conversation
Call forwarding	The ability of a telephone system to redirect a call that would otherwise go unanswered to another extension or phone number.
Call parking	A telephony function that allows a call to be suspended for retrieval by another station
Call transfer	A function that allows redirecting a call from one station to another.
Call waiting	A telephony feature that allows a callee to suspend an existing call to answer another.
CODEC	Compressor/Decompressor. A technology for compressing and decompressing data. For Voice over IP, an analog voice signal is converted to digital form and compressed for transmission to conserve bandwidth. It is decompressed and converted to analog on the receiving end. Common CODECS for VoIP include G.711 (μ-law and a-law), G.726, G.729, GSM, iLBC, ADPCM. Each has represents tradeoffs between fidelity and bandwidth utilization.
Content filtering	Content filters are used to block unwanted content, generally malevolent content such as malware and unwanted electronic mail or undesirable content such as pornography or hate materials.
Converged Network	A modern Local or Wide Area Network that carries data, voice, and video over the same cabling.
DDOS	Distributed Denial of Service
Distributed Denial of Service	An concerted malevolent attempt using multiple points of origin to deny services to a computer or network.
Firewall	A firewall regulates traffic between networks of differing security levels.
Group paging	The use of a telephone system to broadcast a message to a group of extensions.
Hunt group	A telephony function that allows a call to a single destination to be redirected to a series of extensions.
Internet Protocol	Strictly speaking, Internet Protocol or IP is a network layer protocol for routing packets of data over a packet switched network. A more general acronym, TCP/IP is used to refer to suite of protocols involved in communicating data over networks. The Internet and most commercial network implement TCP/IP.
Internet Telephony Service Provider	A service provider who provides Voice over IP connectivity over the Internet.
Intrusion prevention	An intrusion prevention system monitors network or system activities for malicious or unwanted behavior and can react in real-time to block or prevent those activities.
ITSP	Internet Telephony Service Provider
Key System	Multiline telephone system typically used in small office environments. Also called a key telephone system. Key systems typically have some number of buttons on the telephone set with the same line or lines s shared on each set.
LAN	Local Area Network
Local Area Network	A computer network that covers a small geographic area such as a home, building, or small group of buildings.
Network Switch	Network switches inspect data packets for origin and destination and direct them appropriately within a local network.
PBX	Private Branch Exchange.
PoE	Power over Ethernet
POTS	Plain Old Telephone System. Traditional telephone service over analog lines. More properly referred to as the Public Switched Telephone Network
Power over Ethernet	A system to transmit electrical power over a standard twisted pair Ethernet cable.
Private Branch Exchange	A telephone exchange that serves a particular business or office, as opposed to one that a common carrier or telephone company operates for many businesses or for the general public. They are also sometimes referred to as Private Automated Branch Exchange (PABX) or Electronic Private Automated Branch Exchange (EPABX).
Public Switched Telephone Network	Traditional telephone service over analog lines. Sometimes called POTS for Plain Old Telephone Service. The PSTN uses TDM communications to carry signaling and voice traffic.
PSTN	Public Switched Telephone Network.
QoS	Quality of Service
Quality of Service	A means of identifying the importance of traffic on a network and assigning a priority value to better reserve bandwidth in an attempt to guarantee a level of performance.
Shared line appearance	A phone line that appears on more than one device.
Real-time Transfer Protocol	A standardized protocol that defines a packet format for delivering audio and video over a computer network. The voice component of Voice over IP uses RTP.
Router	A computing device used to direct packets between networks.
RTP	Real-time Transfer Protocol
SDP	Session Description Protocol.
Session Description Protocol	A protocol describing multimedia communications sessions for purposes of session announcement or invitation and for other forms of initiating multimedia sessions.
Session Initiation Protocol	A signaling protocol designed to allow for setting up a media stream, such as a voice telephone conversation, between network devices.
Simple Network Management Protocol	A protocol for monitoring devices on a network for conditions requiring administrative attention.
SIP	Session Initiation Protocol
SNMP	Simple Network Management Protocol
SPI	Stateful Packet Inspection
Switch	See Network Switch or Telephone Switch.
Stateful Packet Inspection	The capability of a firewall to track of the state of network connections. Only packets matching a known connection state will be allowed by the firewall to pass. All others will be rejected.
TCP/IP	A collective term for a suite of communications protocols used for computer networking. These protocols allow computers with like or different wired connections to share information either on a LAN or over a WAN. The specifications for TCP/IP are contained in Requests for Comment (RFC). Adoption is managed by the Internet Engineering Task Force (IETF).
TDM	Time Division Multiplexing.
Time Division Multiplexing	A means of establishing communications over the PSTN using two or more signaling channels to carry messages or voice over a single communications path.
Telephone Switch	A system of electronic components that connects calls over analog telephone lines.
Virtual Private Network	A connection tunneled over one network, commonly the Internet, for access into another. Most often used to create a secure connection into a private network. The connection is made over an encrypted channel.
Voice over Internet Protocol	A collection of protocols for transmitting voice signals over an Internet Protocol based network.
VoIP	Voice over Internet Protocol
VPN	Virtual Private Network
WAN	Wide Area Network
Wide Area Network	A computer network that covers a broad geographic area, typically with communication links spanning metropolitan, regional, or even national boundaries. The best known example of a WAN is the Internet.
WiFi	Wireless Fidelity. Radio based protocols for extending Local Area Networks to unwired devices such as computers or Personal Digital Assistants.
Wireless-G	A WiFi protocol allowing communications over a wireless network up to 54 megabits per second.
Wireless-N	A WiFi protocol allowing communications over a wireless network at greater speeds than previous protocols. It is still draft and subject to minor changes.

Other Terminology

SIP endpoints, i.e., phones, gateways, etc., are identifies as User Agents.

SIP Servers perform a variety of functions. They are not necessarily separate physical system, but are logical roles in a telephony system.

Registrar Servers are used by User Agents to announce their presence
Proxy Servers process call routing requests
Redirect Servers provide call routing information to User Agents
Location Database Servers store the locations in the network for User Agents