Increasing demand for internet services, through mobile networks can be addressed by interworking wireless local area network and universal mobile telecommunication system. Interworking should be carried in such a way that users receive better service. This paper analyses the performance of loose coupling, tight coupling and hybrid coupling interworking architectures in terms of metrics like throughput, media access delay and load through simulation, using OPNET 14.5. The performances of these three interworking architectures are compared. Simulation results show that loose coupling has high throughput, moderate media access delay and moderate load. Tight coupling has low throughput, low media access delay and it handles less load. Hybrid coupling has moderate throughput, high media access delay and high load handling capability than other schemes.