Enterprise VoIP glossary

For many immersed in IT, the vocabulary of voice communications may be unfamiliar. Here are some of the most common terms.

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Codec: A compression/decompression algorithm used in IP telephony and other streaming media applications.

G.723.1: An ITU-T Codec, used in many IP telephony systems, that has two associated bit rates: 5.3Kbps and 6.3Kbps.

G.729: An ITU-T Codec, used in many IP telephony systems, that has an 8Kbps bit rate.

Gateway A network device that converts voice and fax calls between the PSTN (public switched telephone network) and an IP network in real time.

H.323: An ITU-T collection of standards used in VoIP (voice over IP) applications to define end points, gateways, and other IP telephony devices and their interaction. Precedes SIP (Session Initiation Protocol).

IP Telephony: The transmission of voice and fax phone calls over a packet-based IP data network; synonymous with VoIP.

IP PBX: The server that provides call control and configuration management for an IP-based phone system.

IP Phone or Handset: A phone system handset that connects to the IP PBX over an IP LAN. IP phones often look and function much like typical legacy corporate phone system handsets, but in some cases they also take on PC-like functionality.

MPLS: Multiprotocol label switching, an IETF set of quality-of-service labeling standards that ISPs use to manage different kinds of data streams based on priority and service plan.

PBX: Private branch exchange, an in-house telephone switching system.

PBX trunk: The shared communications path between the customer's PBX and the public network.

PSTN: Public switched telephone network, which is also called POTS (plain old telephone service).

Q.Sig: Q Signaling, a signaling standard for PBX interoperability used in the United States and Europe.

RTP: Real-Time Transport Protocol, the Internet protocol used by VoIP systems for streaming digitized audio and video across an IP network.

SIP: Session Initiation Protocol, an up-and-coming IETF signaling protocol for Internet conferencing, telephony, presence, events notification, and instant messaging. Competes with H.323.

Softphone: Software that provides IP phone functionality in a PC, notebook, or other computing device.