PBX and VoIP glossary
Plain-English definitions of the terms you meet when choosing a phone system.
- ACD
- Automatic Call Distribution. Routes incoming calls to the best available agent.
- ATA
- Analog Telephone Adapter. Connects an analog phone or fax machine to a VoIP system.
- Asterisk
- An open-source telephony engine used to build PBX systems.
- Auto attendant
- A menu that greets callers and routes them without a receptionist.
- CDR
- Call Detail Record. A log entry with time, numbers and duration of each call.
- Codec
- Software that compresses voice for sending over the internet, such as G.711 or Opus.
- DID
- Direct Inward Dialing. A phone number that rings straight to an extension.
- DTMF
- The tones sent when you press keys on a phone, used in IVR menus.
- ECM
- Error Correction Mode. Helps fax pages arrive clean over poor lines.
- Extension
- A short internal number for a user or phone on the PBX.
- Fax server
- Software that sends and receives fax and delivers it by email.
- FreeSWITCH
- An open-source telephony platform used for PBX and call center systems.
- FXO and FXS
- Analog ports. FXS connects phones; FXO connects to a phone line.
- G.711
- A common uncompressed voice codec using about 64 kbps.
- G.729
- A compressed codec using about 8 kbps.
- Hosted PBX
- A PBX run by a provider in the cloud instead of on your premises.
- IP PBX
- A phone system that routes calls over an IP network.
- IVR
- Interactive Voice Response. A menu callers use with keypad or voice.
- Jitter
- Variation in packet arrival time that can make audio choppy.
- MOS
- Mean Opinion Score. A 1 to 5 rating of call quality.
- NAT
- Network Address Translation. A common cause of one-way audio in VoIP.
- On-premise PBX
- A PBX installed on your own server or hardware.
- Opus
- A flexible, high-quality voice codec.
- Packet loss
- Lost audio packets, which cause gaps in calls.
- PBX
- Private Branch Exchange. A business phone system that connects internal and external calls.
- Predictive dialer
- Software that dials many numbers and connects answered calls to agents.
- PSTN
- The public switched telephone network.
- QoS
- Quality of Service. Settings that give voice traffic priority.
- Queue
- A waiting line for callers until an agent is free.
- Ring group
- A set of phones that ring together or in order.
- RTP
- The protocol that carries voice audio in a VoIP call.
- SBC
- Session Border Controller. Protects and connects VoIP networks.
- SIP
- Session Initiation Protocol. The standard way VoIP calls are set up.
- SIP trunk
- A virtual phone line that connects your PBX to the phone network.
- Softphone
- A phone app on a computer or mobile.
- T.38
- A protocol for sending fax reliably over IP networks.
- UCaaS
- Unified Communications as a Service. Cloud calling, chat and meetings.
- VoIP
- Voice over IP. Phone calls over the internet.
- WebRTC
- Technology that lets browsers make calls without plugins.
- White-label PBX
- A PBX you can resell under your own brand.
Start here: What is a PBX? The complete guide.