This report covers one of the most demanding issues of network users i.e. network testing. Network testing in this study is about performance evaluation of networks, by putting traffic load gradually to determine the queuing delay for different traffics. Testing of such operations is becoming complex and necessary due to use of real time applications such as voice and video traffic, parallel to elastic data of ordinary applications over WAN links. Huge size elastic data occupies almost 80% resources and causes delay for time sensitive traffic. Performance parameters like service outage, delay, packet loss and jitter are tested to assure the reliability factor of provided Quality of Service (QoS) in the Service Level Agreements (SLAs). Normally these network services are tested after deployment of physical networks. In this case most of the time customers have to experience unavailability (outage) of network services due to increased levels of load and stress. According to user-centric point of view these outages are violation and must be avoided by the net-centric end. In order to meet these challenges network SLAs are tested on simulators in lab environment. This study provides a solution for this problem in a form of testbed simulator named Combinatorial TestBed Simulator (CTBS). Prototype of this simulator is developed for conducting experiment. It provides a systematic approach of combinatorial structures for finding such traffic patterns that exceeds the limit of queuing delay, committed in SLAs. Combinatorics is a branch of mathematics that deals with discrete and normally finite elements. In the design of CTBS, technique of combinatorics is used to generate a variety of test data that cannot be generated manually for testing the given network scenario. To validate the design of CTBS, results obtained by pilot runs are compared with the results calculated using timeline. After validation of CTBS design, actual experiment is conducted to determine the set of traffic patterns that exceeds the threshold value of queuing delay for Voice over Internet Protocol (VOIP) traffic. / 14:36 Folkparksvagan Ronneby 372 40 Sweden