Develop Online Messenger including IM /Audio / Video Call across devices

Chat Requirement ------------------------------------------------------------------------------------- General Guidance: * Technology should be develop using MVC ASP.net,SQL, HTML5, CSS3, Javascript, Angular Framework. * it should working across devices such different browser in computer (Chrome,Explore,Firefox,safari), iOS, Android and windows Mobile. * the solution should not depend on paid service and it should not include any licensing cost to achieve the requirement. * No plugin or install should required, it should work with native browser, except unsupported browser where Flash can be used, and automatically run the native one if bower start supporting it. * Interface Design should be responsive, and should cater for different devices and resolutions. * there should not be any security Holes in the client/server design such changing the username in JavaScript and getting connect as other online users. 1) Employee Login to Server.. 2) Employee session get created including employeeID,Name,Company,other information 3) Active Users shows all online users who logged in. 4) any logged in person can select a user and/or add additional user to chat. 5) Chat should include emoji and sharing files, drag-drop for files computer to chat option too. 6) any logged in person can call any online user and the person should be able to pick the call or ignore it. 7) when person is currently in a call it should show busy status. 8) the user can add more participant to the call. 9) the user can initiate video/audio call and other parties can accept or reject. 10) the user can add more participants to video call. 11) the user should be able to convert audio call to video call and other parties should accept or reject that. 12) the user should be able to modify the setting such mute sound/ change his status. 13) the code should handle multiple page login for the same user, and send same chat data to all. 14) UX design should be perfect across devices. -----------------------------------------------------------------------------------