Many distributed multimedia applications adapt to the network's condition in order to provide an acceptable QoS level at the end systems. On the Internet, practically all adaptation mechanisms are based on packet loss as a sign of congestion which means that congestions actually must be caused before they can be avoided. This situation contrasts with the fact that network administrators can simply ask for information that would drastically facilitate adaptation; therefore, we introduce the Performance Transparency Protocol (PTP), which is trying to bridge that gap by making specific performance parameters available to any Internet application. This approach resembles ATM's Explicit Rate Feedback mechanism.
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