The present disclosure is directed to aspects of assessing performance of a session between an OTT service provider endpoint and an OTT service recipient endpoint in regard of a particular OTT service. The performance assessment is based on a series of data records generated for the session. Data record generation includes monitoring, at a network site between the two endpoints and during successive periods of time, at least one transport layer connection of the session. The monitoring is performed to determine, for each period of time, an activity metric indicative of a pending transport layer activity of the session in the respective period of time. This activity metric is then evaluated in connection with service performance assessment.