  The Asynchronous Transfer Mode (ATM) network is crucial due to its ability to
efficiently transmit data, provide reliable connections, and support various
service classes with specific Quality of Service (QoS) requirements. In this
paper, we utilize the OPNET network simulation software to model an ATM network
and analyze the impact of QoS classification on network performance. We
investigate the effects of Constant Bit Rate (CBR), Variable Bit Rate (VBR),
Available Bit Rate (ABR) and Unspecified Bit Rate (UBR) models on various
network traffic types such as voice, video and data. For voice traffic, we
examine key QoS parameters including Jitter, Packet Delay Variation and
End-to-End Delay. For video traffic, we evaluate Packet Delay Variation and
End-to-End Delay. Additionally, we analyze Download Response Time for data
traffic to assess the influence of QoS on the ATM network. Our results
demonstrate that CBR and VBR are preferred for real-time traffic like voice and
video, providing low delay and jitter. The simulation approach enables us to
test various configurations and gain insights not possible in hardware tests.
Our findings can help network operators determine the optimal QoS settings and
tradeoffs when deploying ATM for modern multi-service networks.
