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VOIP Glossary of Terms

Bad Frame Interpolation -

Interpolates lost/corrupted packets by using the previously received voice frames. It

increases voice quality by making the voice transmission more robust in bursty error environments.

Bandwidth -

The transmission capacity of a communications line. It is a factor in determining the amount of

information and the speed at which a medium can transmit data or voice.

Bps (bits per second) -

A unit to measure the speed at which data bits can be transmitted or received.

Cable Connections -

Cable modems allow a PC or networked computer to transmit and receive data over a cable TV

network (CATV). Because existing CATV networks already employ high-bandwidth coaxial cable into the home or

of ce, these modems are much faster than dial-up analog modems offering speeds from 3 to 10M bps.

Central Of ce (CO) -

The lowest, or most basic level of switching in the PSTN network. A business PBX or any

residential phone connects to the PSTN at a central of ce.

Circuit-switched Network -

A technology used by the PSTN that allocates a pair of conductors for the exclusive use

of one communication path. Circuit switching provides a temporary connection of two or more communications

channels using a  xed, non-shareable path through the network. Users have full use of the circuit until the

connection is terminated.

CODEC -

Coder-decoder compression scheme or technique. In Voice over IP, it speci es the voice coder rate of speech

for a dial peer.

Compression -

Used at anywhere from 1:1 to 12:1 ratios in VOIP applications to consume less bandwidth and leave

more for data or other voice/fax communications. The voice quality may decrease with increased compression

ratios.

DiffServ (Differentiated Services) -

Is a quality of service protocol that prioritizes IP voice traf c to help preserve

voice quality even when network traf c is heavy.

DSL (Digital Subscriber Line) -

A technology that allows a provider to use the excess bandwidth found in a copper

line for the provision of data services. Its maximum download speed is 1.5M bps.

E&M (Ear and Mouth) -

The interface on a VOIP device that allows it to be connected to analog PBX trunk ports (tie

lines).

Echo Cancellation -

The elimination of an echo in a two-way transmisison.

Ethernet -

A 10-megabit/100-megabit baseband local area network that allows multiple stations to access the

transmission medium at will without prior coordination.

Forward Error Correction -

Increases voice quality by recovering lost or corrupted packets.

Frame -

A group of data bits in a speci c format to help network equipment recognize what the bits mean and how

to process them. The bits are sent serially, with a  ag at each end, signifying the start and end of the frame.

Frame Relay -

A fast-packet data communications standard that allows a network to carry data frames in packets

of varying length; usually used to connect LANs or for LAN-to-WAN connections. They are protocol independent

making it a less expensive, high-speed network.

FXO (foreign exchange of ce) -

The interface on a VOIP device for connecting to an analog PBX extension.

FXS (foreign exchange station) -

The interface on a VOIP device for connecting directly to phones, fax machines, and

CO ports on PBXs or key telephone systems.

H.323 -

An industry-standard call setup protocol designed to standardize VOIP communications between other

H.323 telephony solutions.

ITU (International Telecommunications Union) -

A civil international organization established to promote

standardized telecommunications on a worldwide basis.

Internet -

Refers to the computer network of many millions of university, government and private users around the

world. Each user has a unique Internet address (IP address).