op- ment for several years. They consist of an asynchronous exchange of infor- mation. The Internet has been proved to be a powerful tool in developing such asynchronous services, but it can also provide synchronous (real-time) services. Examples include videoconferencing over the Net and live broad- cast on a workstation attached to an IP network. Real-time services are delay sensitive. The information they carry needs to be delivered to its des- tination within a prescribed time limit. If the delay introduced by the net- work is any longer, either the information becomes no longer useful to the receiver or the service quality drops dramatically. It is possible to further classify real-time services into streaming and interactive categories (see Figure 3-4). Streaming services typically have Chapter 3 Figure 3-4 Interactive and streaming real-time services The Internet Real time interactive service The Internet Real time streaming service lower requirements than interactive ones. Consider the transmission of a soccer match as an example of a streaming service. Relatively large delays, in the order of even some seconds, are acceptable for the user as long as the image and sound quality hold up, but probably not vice versa. The industry currently deems it acceptable for users to see a goal on the screen a couple of seconds after it really happened on the soccer field where the match takes place. The Internet Multimedia Conferencing Architecture Services with an interactive flavor have tougher requirements. In a voice conversation over the Internet, the delay must be kept very low. Otherwise it is impossible to undertake a normal conversation. The maximum accept- able delay for this kind of real-time interactive service depends on many factors, but in general, it is lower than the delay for streaming services. According to the International Telecommunication Union Telecommunica- tion Standardization Sector (ITU-T), the maximum acceptable delay for voice conversations is a round-trip delay of 300 ms. The Internet Mu