affic model from the MOMENTUM project defines a longer mean duration 5 Introduction of Simulation Models for both active and silent periods than the Brady model and it generates a higher traffic. For the UMTS network, it is a more suitable voice traffic model due to its symmetric property and higher traffic demand. Therefore it is chosen to model the voice traffic within this thesis. 5.8.2 Web Browsing Traffic Model A general web browsing traffic model is defined in [ETSI98, TWP*02] as illustrated in Figure 5.9. It is defined on the session level. The session is unidirectional, i.e. in downlink. A web session contains one or several packet calls. Each packet call corresponds to the downloading of a web page. During a packet call several packets may be generated. After the whole web page is entirely downloaded, the user takes a certain amount of time for studying the information before making the request for the next web page. This time interval is called reading time. Start Time of the Session Web Session Web Page Reading Time Figure 5.9: General web traffic model The following parameters are defined to describe the characteristics of the web applications [ETSI98, TWP*02]: Session arrival process It defines how often the service sessions are arriving and set up in the network. Number of packet calls (web pages) per session Usually, a web session contains one or several packet calls where each packet call models a single web page. Reading time between packet calls Reading time starts when the last packet of the packet call is completely received by the user and it ends when the user makes a request for the next packet call. The mean reading time is denoted as MIAT. Number of packets in a packet call According to various networks, different statistical distributions can be used to generate the number of packets. The mean number of packets in a packet call is . 5.8 Traffic Models Inter arrival time between two consecutive packets inside a packet call The interarrival time models the available transmission bandwidth.