Find answers to your most frequently asked VoIP questions
Traditional telephony is giving way to VoIP. Over the past two decades, internet-based calling has gradually replaced older phone systems for businesses around the world.
Voice and data no longer need separate networks. A VoIP PBX uses your existing IP network for calls, making your setup easier to manage, more efficient and simpler to scale.
Phone systems do much more than carry voice calls. As more providers move to IP telephony, businesses are switching to VoIP PBX systems for greater flexibility and features.
VoIP stands for Voice over Internet Protocol. It carries voice calls over IP-based networks rather than the traditional public telephone network, known as the PSTN.
VoIP & IP PBX Basics
Learn about VoIP gateways
A VoIP gateway bridges conventional telephone connections and an IP-based phone system, enabling calls between legacy equipment or networks and VoIP services.
Multi-Line Phone System – A User Guide
Multi-line phone systems let users handle more than one call or line, helping teams manage incoming calls, transfers, and multiple conversations.
PBX vs PABX. What's the difference?
PBX is a general term for a private business telephone exchange, while PABX emphasizes automated switching; in modern usage, the names are often interchangeable.
What are IP phones / IP telephones?
IP phones connect to an IP network to make and receive calls, using a physical desk-phone interface or other network-enabled form factors.
What is a PBX phone system?
A Private Branch Exchange (PBX) is a business telephone system that manages internal extensions and connects users to outside phone networks.
What is a STUN server?
A STUN server helps an internet-connected device discover its public-facing IP address and port mapping when communicating through network address translation.
What is ALG?
An Application Layer Gateway (ALG) inspects or modifies certain application traffic as it passes through a router or firewall; SIP ALG behavior can affect VoIP connectivity.
What is IP telephony?
IP telephony uses internet protocol networks to transmit and manage telephone communications, including business voice calls and associated services.
What is PRI?
Primary Rate Interface (PRI) is an ISDN connection standard that carries multiple voice channels over a digital telephone circuit, often used with traditional business PBXs.
What is PSTN?
The Public Switched Telephone Network (PSTN) is the traditional interconnected telephone network used to route calls through public telephony infrastructure.
What is voice over IP?
Voice over IP (VoIP) converts voice into digital packets and transmits calls over IP networks, including the internet, instead of relying solely on traditional phone lines.
IP PBX Features & Benefits
What are BLF function keys?
Busy Lamp Field (BLF) keys show another extension's status and can provide quick actions such as dialing, transferring, or picking up a call.
What are the advantages of using an IP PBX?
An IP PBX manages calls over data networks, combining business calling features with easier scaling, administration, and potential cost savings compared with traditional systems.
What is a voicemail system?
A voicemail system records messages when calls are not answered and stores them for users to access or receive through other channels.
What is an auto-attendant?
An auto-attendant is an automated phone menu that greets callers and routes them to an extension, department, or queue without requiring a receptionist.
What is Automatic Call Distribution (ACD)?
Automatic Call Distribution routes incoming calls among agents according to rules such as availability, skills, or queue order, helping contact centers manage call traffic.
What is DID – direct inward dialing?
Direct Inward Dialing (DID) assigns an external number to a person or department, allowing callers to reach it directly without passing through the main switchboard.
What is intercom and paging?
Intercom provides direct two-way communication, while paging broadcasts audio announcements to selected phones or groups, often used for internal coordination.
What is IVR?
Interactive Voice Response (IVR) lets callers interact with a recorded menu using keypad input or speech so calls and inquiries can be handled or routed automatically.
What is unified communications?
Unified communications brings calling, messaging, meetings, and related collaboration tools together so teams can communicate through one connected system.
What is voicemail to email?
Voicemail to email sends a user's recorded voicemail, or a notification about it, to their email inbox for easier retrieval and follow-up.
Cloud & Hosted PBX
Hosted PBX vs on-premise
A hosted PBX runs on externally managed infrastructure, while an on-premise PBX runs on equipment maintained by the organization; each differs in control, maintenance, and cost.
How can I get a free cloud PBX?
A free cloud PBX option lets a business start with hosted calling and essential features without an initial software charge, subject to the provider's current plan limits.
What is a cloud contact center?
A cloud contact center provides customer service tools, such as call distribution and multichannel communication, from hosted infrastructure accessible online.
What is a cloud PBX?
A cloud PBX delivers business call handling from infrastructure hosted in the cloud, enabling remote administration and access through internet-connected devices.
What is a hosted PBX?
A hosted PBX is a business phone system operated on a provider-managed server rather than equipment maintained on company premises.
What is a Hosted Phone System and how does it work?
A hosted phone system places core telephony functions on a remote server, allowing employees to make and receive business calls through connected phones or apps.
What is a virtual call center?
A virtual call center lets agents handle customer interactions from different locations through internet-based calling, call routing, and management tools.
What is a virtual PBX?
A virtual PBX supplies phone system functions such as extensions, transfers, and call routing without requiring a traditional physical PBX at the business site.
What is a Virtual Phone System & how does it work?
A virtual phone system uses internet-based services and devices to manage a business's incoming and outgoing calls, extensions, and routing.
Contact Center
How does a helpdesk ticketing system work?
A helpdesk ticketing system turns customer requests into tracked tickets that support agents can assign, prioritize, update, and resolve.
Live Chat – frequently asked questions
Live chat gives website visitors a way to message a business in real time; the FAQ covers how it works and how organizations can use it for customer conversations.
The 15 best call center software options for 2025
This comparison explores call center software options and features to consider, such as call routing, agent tools, reporting, integrations, and deployment.
The benefits of a helpdesk ticketing tool
Helpdesk ticketing tools organize support requests, improve accountability, and make it easier to monitor customer issues through resolution.
What is a multichannel contact center?
A multichannel contact center supports customer service through several channels, such as calls, email, and live chat, which may operate separately.
What is an omnichannel contact center?
An omnichannel contact center connects customer conversations across channels so agents can retain context as customers move between phone, chat, and other touchpoints.
Video Conferencing
How to host a webinar?
Hosting a webinar involves planning an online presentation, inviting attendees, setting up audio and video, and using meeting tools to deliver and manage the session.
PDF sharing in online meetings
PDF sharing lets meeting participants present document pages directly in an online conference, helping everyone follow the same material.
What are the benefits of encryption?
Encryption turns communications data into a protected form so unauthorized parties cannot easily read it, improving privacy and security in online calls and meetings.
What is desktop sharing?
Desktop sharing allows a participant to show their computer desktop to others during an online meeting, making demonstrations and collaboration easier.
What is DTLS?
Datagram Transport Layer Security (DTLS) secures datagram-based communication and can help establish cryptographic keys for real-time media sessions.
What is screen sharing?
Screen sharing broadcasts a device's screen or selected application to other meeting participants for presentations, troubleshooting, and collaboration.
What is SRTP?
Secure Real-time Transport Protocol (SRTP) protects audio and video streams by providing encryption, authentication, and replay protection for real-time media.
What is VP8?
VP8 is an open-source video compression codec used in real-time communications, including WebRTC, to encode and transmit video efficiently.
What is web conferencing?
Web conferencing lets people hold online meetings using audio, video, screen sharing, and other collaborative tools through internet-connected devices.
What is WebRTC?
Web Real-Time Communication (WebRTC) enables browsers and apps to exchange live audio, video, and data, often without installing extra plugins.
Why use remote desktop?
Remote desktop gives an authorized user access to another computer's screen and controls over a network, supporting remote assistance and administration.
Fax over VoIP
Fax work in VoIP environments
Fax over VoIP can be sensitive to delay, packet loss, and audio compression, so supported gateways, codecs, and protocols such as T.38 can improve reliability.
What is fax to email?
Fax to email converts incoming fax transmissions into digital files, often PDFs, and delivers them to a recipient's email inbox.
What is FoIP – Fax over IP?
Fax over IP (FoIP) sends fax information using IP networks rather than a conventional telephone connection, often using T.38 for fax transport.
What is T38 fax?
T.38 is a protocol designed to transport fax data across IP networks more reliably than sending fax tones through ordinary voice compression.
SIP & VoIP Phones
Can you list all known SIP responses?
SIP response codes indicate the status of a signaling request, from provisional progress messages to success, redirection, and error outcomes.
SIP methods / Requests and responses?
SIP uses request methods such as INVITE, ACK, BYE, and REGISTER, together with response codes, to control how sessions are created and ended.
SIP phones / VoIP phones types
VoIP phones can include physical IP desk phones, wireless models, and softphones, enabling calls over an IP connection rather than only traditional lines.
What are SIP phones?
SIP phones use the Session Initiation Protocol to establish and manage voice calls over IP networks, as desk phones or software-based clients.
What are SIP trunks?
SIP trunks connect a business phone system to a telephony provider over IP, replacing or supplementing traditional telephone circuits for external calls.
What is a SIP server?
A SIP server processes signaling used to register endpoints and establish, route, or terminate calls between SIP devices and services.
What is a SIP-URI?
A SIP URI is an address used to identify a communication endpoint or service in SIP, commonly following a format similar to sip:user@domain.
What is an IP Phone MAC address?
An IP phone's MAC address is a unique network interface identifier commonly used when recognizing or provisioning a phone on a local network.
What is SIP forking?
SIP forking sends an incoming call invitation to multiple registered endpoints so more than one device can ring for the same user or address.
What is SIP?
Session Initiation Protocol (SIP) is a signaling protocol used to initiate, manage, and end voice, video, and other real-time communication sessions.
VoIP Protocols
What is H323?
H.323 is a family of protocols for establishing and managing multimedia communications, including voice and video, across packet-based networks.
What is RCS?
Rich Communication Services (RCS) is an enhanced messaging standard that supports richer conversations, media, and interactive messaging features beyond basic SMS.
What is RTCP?
Real-time Transport Control Protocol (RTCP) complements RTP by reporting media delivery and quality information such as packet loss and timing.
What is RTP?
Real-time Transport Protocol (RTP) carries audio and video media streams across IP networks, typically working alongside signaling and control protocols.
What is SDP?
Session Description Protocol (SDP) describes media session details, such as codecs, addresses, and ports, so communication endpoints can negotiate an audio or video session.
Telephony Technology & Terms
Different types of CODECS?
A codec encodes and decodes audio or video for transmission; different codecs balance bandwidth, compression efficiency, latency, and perceived media quality.
What do FXS and FXO mean?
FXS ports supply the phone line signal to analog devices, while FXO ports connect to an existing analog telephone line, enabling integration with VoIP equipment.
What does ENUM mean?
ENUM maps telephone numbers to internet-based communication identifiers using DNS, helping services discover ways to reach a telephone number over IP.
What is a TDM PBX?
A Time Division Multiplexing (TDM) PBX is a traditional telephone system that switches voice calls using allocated time slots on digital circuits.
What is ECHO cancellation?
Echo cancellation detects and reduces reflected audio during a telephone or video call, improving the clarity of both sides of a conversation.
Internet Protocol was originally designed for data networking. Once it became the global standard, it was adapted to carry voice calls over the same type of network too.
With VoIP, you can still use your existing phone lines. A VoIP gateway connects traditional PSTN lines to your VoIP system when you need extra reliability and availability.
A VoIP PBX makes it easier for employees to work from anywhere. It grows with your business, is simpler to manage than a traditional PBX and helps reduce administration costs.
3CX supports a wide range of hardware, so you aren't locked into one supplier or proprietary contracts. Explore our VoIP FAQs below for answers to common questions.