To support user mobility across different devices, communication session continuity should be enabled at session initiation and during a session. The session continuity can be managed by either a user or dedicated network nodes such as back-to-back user agent (B2BUA) in IP Multimedia Subsystem (IMS) architecture. When network manages the session continuity, user experience is enriched because users do not need to know how to perform session transfer. However, in IMS architecture, three different network nodes (SIP forking proxy, SIP registrar and B2BUA) need to cooperate for session continuity. When single user (callee) logs in from different devices, it is very hard to achieve cooperation. In addition, these network nodes should be scalable when many users request this service simultaneously. This paper proposes a general architecture that supports the user mobility and how the general architecture can be realized into a Web-based communication system. Our initial analytical result shows that the usage of computing resources (e.g. CPU) is reduced while supporting scalability, thanks to the simple Web client service infrastructure and Web Socket connections on top of HTTP