Quality of Service (QoS) is the description or measurement of the overall performance of a service, particularly the performance seen by the users of the network. Simulation experimentis applied in Asynchronous Transfer Mode or ATM network. ATM network is a network that integrated some traffic like voice, video, and data, refers to bandwidth allocation and data speed as the user request. The purpose of this research is to analyze QoS performance of ATM network. Experiment method by simulating OPNET Modeler 14.5. OPNET is simulator application which to design a network model and simulate it bygenerating a graph. The network service is Voice, Video, File Transfer Protocol (FTP), and Email. QoS parameter is Cell Transfer Delay (CTD), Cell Delay Variation (CDV), and Cell Loss Ratio (CLR). Experiment result shows that if the number of user is higher, resulting that the value of CTD, CDV, and CLS are higher. Refers to the theory that if the number of user is higher, so many cells is generated and transmitted by the network and make the network is traffic jam and full memory buffer, consequently make the cells need more time to destination. The imbalance traffic has an effect to network performance, the value of CTD, CDV, and CLR is higher. That is due to the single server has high congestion and the client request the service in single server, and for random server, client can request the service in any server.

Keywords : ATM, QoS, CTD, CDV, CLR, OPNET Modeler 14.5.