This paper describes establishment of SIP service on the Restcomm communication platform. Main purpose is to show and explain establishment and communication flow between Restcomm platform and calling user. Restcomm platform is designed to enable its users multimedia communication over Internet, because todays user-to-user communication is more than just simply texting and calling. Restcomm platform also enables creating of own service easily by using drag and drop abilities. Once created Restcomm service, can be called from any device whose communication is based on SIP signalizing protocol. SIP protocol is created after HTTP and SMTP protocols, belongs to OSI session layer and relies on TCP and UDP protocols of the transport layer. One of the main purposes of SIP protocol is to establish and keep track of communication flow between calling users. It is text-based protocol and in its messages, which are exchanged within the UDP or TCP datagrams, are headers that represents the stream of communication. In this paper communication between user and Restcomm platform is established with Linphone. Linphone is open source software phone also based on SIP protocol. Restcomm-user communication is designed as question-answer process. When user calls Restcomm service, it responds based on the created modules. Response can be simple or structured. In this project is created Restcomm service which contains two modules. First module contains record variable for collecting data, and second contains external service variable which is used for establishment of HTTP connection with external server. As an external server is used XAMPP, which contains PHP data processing scripts that are additionally associated with APIs such as IBM WATSON, TMDB and OMDb. After the scripts handles the user's query, the response is returned back to the Restcomm service. There, the response is further processed by converting from text to speech after which is interpreted to the user. Question response makes the end of call. The call flow and protocols that are being exchanged are followed by the Wireshark program. Restcomm platform is built on the Docker virtual system, as the operating system is used Linux Ubuntu 16.04 LTS. Docker and Linphone are also available on Windows operating systems.