Six concepts to understand
Call signaling
Voice media
Encrypted voice media
Cordless handsets and base stations
Interactive voice response
Public/private network translation
Simple definition
3CX is business phone system software that replaces or complements a traditional telephone switchboard. It lets a company make and receive calls on compatible IP desk phones, DECT handsets, desktop and mobile apps or a web client. It manages public phone numbers, internal extensions and call routing.
Technical definition
3CX is a software IP PBX (Internet Protocol Private Branch Exchange). SIP is commonly used to set up and control calls, while RTP or SRTP carries the voice media depending on the configuration. The PBX is not the telephone carrier: calls to and from the public telephone network typically use a compatible SIP trunk provider.
- IP phone Desk phone or app
- IP network LAN / remote access
- 3CX · IP PBX Call routing
- SIP trunk Carrier connection
- Recipient Phone network
SIP establishes the session; RTP or SRTP carries voice media depending on the network and configuration.
- SIP trunk: the connection between the PBX and the phone provider for inbound and outbound calls.
- Extension: an internal number associated with a user, device or PBX function.
- Endpoints: IP desk phones, compatible DECT handsets through a base station, desktop/mobile apps and the web client.
- Call routing: assignment of public DID numbers to extensions, digital receptionists (IVR), ring groups or call queues.
- Remote connectivity: depending on the topology, endpoints may use a 3CX SBC, 3CX tunnel or another supported connection method.
What is 3CX used for?
Companies use 3CX to distribute calls to teams, play an automated greeting, queue callers, transfer conversations and apply office-hour rules. Availability of individual features depends on the license, edition, SIP provider and supported devices.
How does a call flow through 3CX?
- A caller dials a company telephone number; the SIP provider delivers the call through the SIP trunk.
- 3CX matches the incoming DID and routes the call to an extension, ring group, IVR or queue.
- The IP phone, DECT handset or softphone receives the call; SIP signaling negotiates the session.
- After answer, voice media flows according to the deployed network topology and must cross any firewalls, NAT devices and SBCs correctly.
- For outbound calls, dial plans and outbound rules determine the trunk and calling number where user permissions and carrier policies allow.
Practical example
A medical practice has one main phone number and ten extensions. During opening hours, callers hear a menu: press 1 for reception and 2 for technical support. Staff answer on IP phones or mobile apps. Outside business hours, a recording and voicemail take over. A SIP trunk connects the office PBX to its carrier.
Common issues
- SIP trunk not registered or outbound calls blocked: inspect provider status, credentials, dial plans and outbound rules.
- Connected call with one-way audio: inspect RTP paths, NAT, firewall policy, announced media addresses and SIP ALG.
- IP phone or DECT handset not registered: inspect provisioning, extension configuration, DECT base, firmware compatibility and network reachability.
- Incoming calls route to the wrong destination: check DID assignment, hours, ring groups, queues and forwarding rules.
- Choppy audio or delays: measure packet loss, jitter, Wi-Fi coverage, uplink load and traffic prioritization.
First checks when troubleshooting 3CX
- Record the precise scenario: internal, inbound or outbound call; timestamp, extensions and symptoms.
- Check SIP trunk, user extension and endpoint registration status in the 3CX Admin Console.
- Separate call signaling from audio: a call that rings can still have broken media transport.
- Review event logs, call routing and NAT/firewall settings; run 3CX Firewall Checker when applicable.
- Compare a wired desk phone, desktop/mobile app and DECT handset to distinguish endpoint, network and PBX issues.
Security and operational best practices
- Keep 3CX, supported clients and device firmware updated; back up the configuration and test restoration.
- Restrict privileged accounts, use named administrator identities and strong authentication where supported.
- Limit exposed network services, protect SIP trunks and monitor unusual call patterns or toll fraud.
- Use only the firewall rules relevant to the 3CX version, hosting setup and remote endpoint design.
3CX vs SIP vs VoIP
VoIP is voice communication over IP networks. SIP is a signaling protocol often used to set up phone calls. 3CX is the phone system software using those technologies to manage users, devices and call flows. A SIP trunk is the carrier connection, not the PBX.
Related terms
Further reading and official documentation
3CX administration: key concepts and checks
3CX provides IP telephony and unified communications. A typical deployment includes extensions, SIP trunks, softphones, desk phones and possibly DECT systems or session border controllers.
Recommended checks
- Document extension numbering, inbound routing, outbound rules and office hours.
- For one-way or missing audio, check SIP signaling separately from RTP media, NAT and firewall behavior.
- Maintain configuration backups and rehearse the recovery procedure.
- Apply least-privilege administration and secure remote access and authentication.
Frequently asked question
Does a registered extension guarantee working audio? No. SIP registration may succeed while RTP media is blocked or misrouted by a firewall, NAT or network policy.