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The first thing to understand about TANGO Interactive Meeting Engine is that it is NOT an HTTP server.

TANGO Interactive central entity is a conference engine. We call it a Meeting (or Classroom) Engine. The Meeting Engine is somewhat akin to an IP router. It makes sure the messages get to the intended receivers. Unlike a router, though, collaboratory engine accepts permanent connections and it holds a considerable amount of state. The engine works together with all active instances of TANGO Interactive Session Managers to keep and manage the state of the collaboration.

In user terms, an instance of the engine is a meeting point in cyberspace. Each meeting engine can support one or more communities, and multiple engines can support branches of the same community.

On the communication level, each TANGO Interactive meeting engine accepts connections from an arbitrary number of Session Managers. All events created by application modules connected to active Session Managers are sent to the engine and are properly distributed according to system state. There is an analogy between meeting engine and a network router. Both devices basic function is message forwarding or/and replication. The difference is that the routers work on the transport level of the OSI model, while the meeting engines work on the application level layer.

Meeting engine is the system's central point. As such, it is also a single point of failure. At present, TANGO Interactive is not a fault-tolerant system. Hence, great care has been taken to ensure that the TI Meeting Engine is a highly robust module.  Stability of the TI Meeting Engine conforms to the 24x7 operational demands necessary to support ASP operation.

Are all data the applications use going through the engine? Well, no. This would be a non-scalable, low-performance design with a system bottleneck. TANGO Interactive applications  get data either from various Internet servers, or use  separate communication channels to exchange high bit rate or continuous data streams (such as audio and video). The meeting engine just tells the applications how to set up these channels. Once the static bulk of the data is received by an application module, the "changes" to the application state (called "events") are distributed by the engine.

This architecture is extremely robust, and it has been designed to make full use of the available Internet infrastructure. TANGO Interactive is the first, and, so far, the only CSCW system that is fully "Web- aware".

In order to transform the "virtual crowd" into "electronic community", the users must possess permanent electronic identity. This is obviously needed for any business applications, but is also helpful in recreational use of the Web-based communities. TANGO Interactive meetig engine can access user data from repositories such as flat files, HTTP servers, and database backends.  The engine provides services to Session Managers to retrieve user information if necessary.

Another aspect of the community support is security and data encryption. This is also handled by the meeting engine if the community administrator decides that privacy and security is important. Current version of the system supports SOCKS4-based firewalls and it uses SSL to encrypt all data traffic.

Finally, if multiple meeting engines support different branches of one community, it is important for the engines to exchange active user information, so that people can find themselves in the cyberspace. This functionality will be supported by TANGO Interactive engines soon.

In short, think about meeting engine as of a house with rooms  in the virtual space, which provides you with various services to find, meet, and communicate with other electronic users. Behind the walls, there is a maze of pipes and wires, but we don't want you to even think about this. You will never ever need to see them. Enjoy the company and the view from the windows!

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