Special Issue Advanced Technologies and Solutions toward Ubiquitous Network Society Communication Door: Real-Time Communication Middleware By Masahiro TABUCHI,* Kazuaki NAKAJIMA,* Akiko KAWAMOTO,* Takashi OSHIBA* and Shujun YOSHIZAKA* We describe a real-time communication middleware system that enables solution providers to ABSTRACT construct various applications, such as web conferencing systems and IP-based call centers. The middleware platform, called Communication Door, is a web-based application platform for real-time groupware. It includes a real-time web sharing function implemented with an HTTP-based push protocol and an audio-video communication function. By using this middleware, many real-time groupware applications can be customized by rewriting their designs and functionalities through a server-side web application while utilizing thin clients. Solution providers can customize the user interface design and the functions of real-time groupware by revising their server-side web applications. In this paper, we describe the architecture of the middleware and its applications. KEYWORDS Real-time communication, Web conferencing, Groupware, Web application, Middleware 1. INTRODUCTION lutions in the same manner as the development of web applications. It supports three major features: This paper describes a real-time communication 1) real-time synchronization of contents among web middleware platform called Communication Door. browsers connected to the same web application; This system enables solution providers to develop 2) real-time voice and video communication; and tailored solutions, such as VoIP (Voice over IP), web 3) an HTTP-based push server that can autono- conferencing, and call center applications, for various mously send differences in data maintained by the customers. server to web browsers connected to the application Recent progress in network access technologies (as compared to a general HTTP server, which can such as ADSL (Asymmetric Digital Subscriber Line) send data only when a web browser requests it). By and FTTH (Fiber To The Home) has increased the use utilizing these capabilities of Communication Door, of broadband Internet connections. Broadband various communication services can be developed. Internet is becoming a new infrastructure for commu- nication services, and it is reducing the costs of voice 2. OUTLINE OF COMMUNICATION DOOR communication. Customers also now require commu- nication services that provide higher value than con- Communication Door is a middleware application ventional voice services. To satisfy various require- supporting various interactive communication forms ments for communication services, solution providers via broadband Internet. It offers solution providers should rapidly deploy tailored solutions to their cus- various functions for real-time communication. tomers. Since conventional communication services, such as telephone service, require both dedicated ter- 2.1 Purpose minals and a dedicated network in general, it is too The purpose of Communication Door is to provide expensive to rapidly satisfy varied customer require- leverage to enlarge communication solutions in busi- ments. ness by integrating information technology with net- Communication Door is a middleware platform working technology. that enables solution providers to develop custom so- As a new infrastructure for communication ser- vices, broadband Internet reduces the cost of voice communication, as in the case of telephone service. As a result, customers require higher value communica- *Internet Systems Research Laboratories tion services, such as web conferencing and 176 NEC J. of Adv. Tech., Summer 2004 Communication Door: Real-Time Communication Middleware web-based call centers, as compared with voice com- Many desktop conferencing systems based on ITU munication services. standards such as H.323 and T.120[9] have been de- To satisfy these requirements, solution providers veloped. NetMeeting[10], developed by Microsoft Cor- must rapidly develop various solutions suited to their poration, is an example of a desktop conferencing customers’ businesses. Therefore, solution providers application based on the H.323 standard. Recently, require middleware enabling this sort of rapid devel- other desktop conferencing systems have been based opment based on their customers’ requirements. on proprietary protocols. Examples include Macromedia’s Flash Communication Server[11] and 2.2 Related Work and Issues Microsoft’s Office Live Communications Server. Several researchers[1-5] have proposed various These systems have rich functionality but require a communication functions that will be required in a higher level of expertise for solution providers to uti- real-time groupware system. These previous ap- lize them in customizing applications. proaches have been implemented as dedicated sys- tems. Therefore, custom applications based on these 2.3 Concept of Communication Door systems cannot work in a general-purpose system. As described above, the purpose of Communication Other researchers[6,7] have proposed web-based Door is to enable solution providers to develop com- groupware systems. The benefit of this approach is munication systems in the manner of web develop- the ease of customizing applications by using develop- ment rather than the development of dedicated sys- ment tools for web applications. Web-based applica- tems. Users of web applications can select services tions, however, cannot support real-time functions according to their businesses by specifying URLs because of the standard behavior of HTTP. Specifi- (Uniform Resource Locators) in their web browsers. cally, HTTP is a transactional protocol, meaning that Users of Communication Door can thus select real- a web browser can update contents on-screen only by time communication services in this way, by specify- accessing an HTTP server. ing URLs. Another previously proposed approach, called “e- Figure 1 shows the relationship between real- office”[8], supports real-time web conferencing but time communication services and Communication requires a dedicated server for real-time communica- Door. Such real-time communication services as TV tion. In this system, a user’s view is produced by a telephony, web conferencing, and call centers can be web application, but the application program has to implemented as applications based on Communica- be implemented as a client program of the dedicated tion Door. Communication Door supports the common server. functions of real-time communication, including voice Fig. 1 Outline of Communication Door. NEC Journal of Advanced Technology, Vol. 1, No. 3 177 Special Issue and video communication, real-time sharing, and con- browsers. Communication Door supports functions tent synchronization. for propagating the differences in web contents, i.e., The advantages of Communication Door are that it HTML documents, to reduce the time for sending supports flexible customization and ensures real-time data. When Push Server sends both an identifier and performance. the differences in an HTML document to a web browser, LiveComm, running on the web browser, can (1) Flexible Customization identify parts of the HTML document from the identi- Communication Door is designed to support flex- fier. Then, LiveComm replace the specified parts in ible customization as a middleware platform for web the document with the differences sent by Push applications. The methodology of developing web ap- Server. plications is widely accepted as providing such flex- ibility. Conventional web applications, however, do 3. ARCHITECTURE not support real-time updating of the contents of web browsers. Our middleware extends to both server Communication Door is designed as a system plat- technology and client technology. The server technol- form for web-based real-time communication applica- ogy, called Push Server, pushes data from a web tions. application to web browsers. The client technology, called LiveComm, receives the data sent by Push 3.1 Overview Server and updates the contents of a web browser. Communication Door consists of a web server, A web application based on Communication Door Push Server, and web browsers. It is characterized by can update the contents of all connected web browsers the establishment of a persistent, real-time connec- in real time. Thus, by utilizing the APIs (Application tion over HTTP with low latency time. Applications Programming Interfaces) of Push Server and based on Communication Door can support real-time LiveComm, solution providers can develop real-time communication with voice, video, image, and text communication services as web applications synchro- data over HTTP. nizing among web browsers. Communication Door provides solution venders with server-side modules and ActiveX controls run- (2) Ensuring Real-Time Performance ning in web browsers, as shown in Fig. 2. By using Communication Door is designed to ensure the the APIs of these modules, solution venders can de- real-time performance of web applications. As men- velop web applications based on ASP (Active Server tioned above, Push Server can send any data to web Pages) to control the modules. Fig. 2 System architecture. 178 NEC J. of Adv. Tech., Summer 2004 Communication Door: Real-Time Communication Middleware 3.2 ASP Applications and COM Interfaces cation, it downloads an HTML document with a script The ASP applications are implemented on a web program calling the control. After downloading the server, by applying IIS (Internet Information