By introducing a virtual computing session abstraction to network computing infrastructure, and slightly extending its underlying remote display protocol, we propose VICOS (virtual computing session): a framework of session management which provides session-level manageability, and allows multiple user to access the computing service on the server simultaneously. The virtual computing session abstraction also supports user roaming among desktops, i.e. user mobility. This framework isolates user's computing session from network or desktop failure. The session-level management mechanism provided by this framework improves the service availability and reliability. We have implemented our VICOS prototype in Linux. We demonstrate that our Linux VICOS prototype can provide general-purpose computing service with low overhead.