A VoIP Gateway, or Voice over IP Gateway, is a network device which helps to convert voice and fax calls, in real time, between an IP network and Public Switched Telephone Network (PSTN). It is a high performance gateway designed for Voice over IP applications. Typically, a VoIP gateway comes with the ability to support at least two T1/E1 digital channels. Most VoIP gateways feature at least one Ethernet and telephone port. Controlling a gateway can be done with the help of the various protocols like MGCP, SIP;

Foreign eXchange Subscriber (FXS) and Foreign eXchange Office (FXO) are the names of the two most common interfaces (ports or plugs) found in analog telephony environments. 

SIP the session initiation protocol, is the IETF protocol for VoIP and other text and multimedia sessions, like instant messaging, video, voice, Fax, online games and other services.

Today the SIP is the most popular protocol for VoIP solutions and applications, all new features and applications based on SIP in VoIP network,  SIP server as the core in the VoIP phone systems to provide the functions like users authentication, calls route management, billing and so on

T.38 is a protocol that describes how to send a fax over a computer data network. T.38 is needed because fax data can not be sent over a computer data network in the same way as voice communication. In essence, with T.38 a fax is converted to an image, sent to the other T.38 fax device and then converted back to an analog fax signal. Most VoIP SIP Gateways , SIP server and VoIP ATA's now support T38 reliably. An example Realtone's all WSS Series VoIP Gateways support T.38 fax relay very well; have been tested with many SIP server, IPPBX, and VoIP Media trunk gateways;

 A codec (Coder/Decoder) converts analog signals to a digital bitstream, and another identical codec at the far end of the communication converts the digital bitstream back into an analog signal.

IP-PBX business phone systems are designed to meet the voice and data convergence requirements necessary to run your business. With its superior voice quality, IP-PBXs can help your employees connect regardless of where they are physically located. Using Voice-over-IP (VoIP) solutions can keep your employees connected with your customers and each other. Below are some frequently asked questions about IP-PBX, Voice-over-IP, VoIP, and IP telephony.