An end to end (e2e) packet delay variations (jitter) has a negative impact on the offered QoS in IP networks. Therefore, in this paper we clarify this passive impact, and discuss the delay jitter that is based on the analysis done in [x]. However, here we focus on the expedited forwarding (EF) class in the differentiated services network (DiffServ). EF flows are represented by renewal periodic ON-OFF flows, and the background (BG) flows by Poisson process. We analyze the jitter effects of these BG flows on EF flows patterns when they are serviced by a single class scheduling discipline, such as FIFO, and a multicalss scheduling discipline, such as static priority service discipline (SPS). Thus, we have simulated a DiffServ network, where different users were provided with different service classes. Consequently, along the simulations different scenarios were formed to see the impact of BG flows and their characteristics on EF flows. As a result, we have found out from these simulations that the EF Per-Hop Behaviors (PHBs) configuration according to RFC 2598 can’t stand alone in guaranteeing the EF flows delay jitter. Therefore, playout buffers must be added to the DiffServ network for handling the EF delay jitter problem.