In passive monitoring, performance measurements are obtained by carrying out passive measurements within the network. In contrast, subscriber terminal-based monitoring characterises subscriber satisfaction by carrying out performance measurements directly in the terminal of a subscriber.
By way of example, for passive measurement in the network, the network traffic may be captured at certain interfaces in the network, and performance indicators may be obtained by processing this information. Performance indicators are possible to define such that end-user perceived quality is well-approximated by the indicators.
Even though subscriber-perceived performance can generally be best observed in the subscriber terminal, a passive monitoring system for carrying out measurement in the network may have the following advantages:                no specific terminals are needed;        all terminals in a live network can be observed;        cost-efficient large-scale monitoring is possible, because a few measurement points can cover a large part of a network;        not only user-perceived performance can be observed, but also the traffic composition and volume (e.g., the most popular applications, the traffic demands of typical or power users, etc.); and        by appropriate placing of the measurement points, it is possible to localize faults or find the cause of performance degradations (e.g., bottlenecks).        
Passive monitoring-based performance/fault analysis and traffic modeling is therefore becoming an increasingly important part of network audit and management services.
However, as access rates increase and prices of services fall, an increased number of subscribers start to use more bandwidth-hungry applications. Consequently, passive monitoring becomes more difficult.
It is an object of the present application to provide improved systems and methods for monitoring transport of data in a generalised communications system wherein data packets conform to a layered transmission protocol.