Common Time Reference for Interactive Multimedia Applications

A delay of about 100 ms gives human communicators the feeling of live interaction. Since in a global network the propagation delay alone is about 100 ms, every other delay component, such as processing and queuing, should be kept as short as possible. Moreover, the deployment of new high bandwidth multimedia applications will boost network traffic and consequently the demand for very high capacity transmission technologies, such as Wavelength Division Multiplexing (WDM). Networks will suffer (i) electronic switching bottlenecks among high-speed links and (ii) communications link bottlenecks between high capacity core technologies and low speed access technologies. This paper addresses the design of interactive systems for applications such as toll quality telephony, videotelephony and videoconferencing, highlighting the benefits brought by the availability of global common time reference derived from GPS (Global Positioning System). Common time reference is essential to keep the user perceived delay within the 100 ms bound while avoiding the two above mentioned bottlenecks. The proposed solution can be applied to both IP and ATM networks, does not require changes to any of the existing protocols, and enables traffic aggregation in the core of the network–thus not requiring nodes to keep state information on microflows–while providing a guaranteed quality service to individual applications.