Network monitoring is essential to ensure network performance, integrity and security. However, with the growth of link rates and simultaneous number of flows, real-time traffic monitoring is challenging because it requires network devices that perform operations on a time scale very reduced and, possibly, with a small amount of memory to store measurement data. Among the available metrics to asses network performance, this thesis refers to the round-trip time (RTT) of data flows, i.e. packets sharing the same flowID. To comply with the aforementioned constraints, the measurement device should be equipped with a very efficient data structure both for recording the time each outgoing packet enters the system and for querying it at the reception of its response to calculate their RTT.