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3CX SIP Server Software

3CX is a SIP server that works with popular VoIP Gateways and SIP phones to allow you to setup a complete IP PBX in a matter of minutes. 3CX’s SIP server is quickly downloaded and installed on Windows or Linux. Configuration is performed via an easy to use Web interface.

Download Your Free Licence of 3CX SIP Server

You can get a free 3CX licence for up to 16 simultaneous calls, 25 web conferencing participants and an unlimited number of extensions. There are 3 commercial editions available of the 3CX SIP Server which include call reporting, presence, fax to email, CRM integrations, advanced call center features (wallboard) and much more. Download your free SIP server today here.

Key 3CX SIP Server Features

  • Supports SIP 2.0
  • Supports the use of standard PSTN/Telephone lines via SIP Gateways such as Patton, and Audiocodes
  • Supports the use of SIP Trunks and SIP providers
  • Supports main codecs including G711, GSM, IspeeX and ILBLC
  • Available as a free edition supporting an unlimited number of extensions

The SIP Protocol

The Session Initiation Protocol (SIP) is a protocol for establishing real time communication sessions with one or more participants. Its most frequently used for voice communications but it can handle video as well as future applications. SIP was designed to be independent of the transport layer, i.e it can work on UDP, TCP or STCP. All voice/video communications take place via another protocol, usually RTP.

There are many RFCs surrounding SIP, but the most important one is RFC 3261.

SIP is a text based protocol that looks and acts very much like the HTTP protocol. The original designers (Henning Schulzrinne & Mark Handley) wanted to make a protocol that had its roots in the IP world, rather then in the telecoms world. SIP has been an amazing success, and has become the major driver in the adoption of VoIP and Internet Telephony in recent years. All major manufacturers have adopted the standard, and SIP software and SIP hardware, as well as SIP service providers are ubiquitous.

SIP servers are responsible for setting up calls between SIP devices. SIP servers usually combine several of the SIP server functions such as SIP proxy and SIP registrar into one piece of software. 3CX is both a SIP proxy and a SIP registrar as well as a media server in order to also handle real time voice communications.

Free for up to 1 year! Select preferred deployment:


for Linux on a $200 appliance or as a VM

Get the ISO


for Windows as a VM

Download the setup file

On the cloud

In your Google, Amazon, Azure account

Take the PBX Express