The work reported here addresses the modeling and simulation of a hybrid network that conforms to Hybrid Internet Service, which is an Internet access currently commercialized by Hughes Network Systems. The objective is to research and discover performance enhancement techniques for Hybrid Internet Service. Hybrid Internet Service intends to provide Internet end users with high bandwidth by delivering packets over a satellite channel. It takes advantage of the fact that the vast majority of Internet end-users don't send as much data as they receive. However, long delays experienced over the satellite channel (in the case of a GEO satellite) have catastrophic consequences on the overall throughput with Commercial-Off-The-Shelf TPC/IP stacks. This problem is addressed by the Asymmetric TCP/IP protocol implemented within a gateway, the hybrid gateway. The hybrid gateway acts as a go-between for the server and the end user. The hybrid gateway both acknowledges packets on behalf of the end user and advertises a larger window to the server. We have implemented the Asymmetric TCP/IP within the hybrid gateway with OPNET, which is an industrial-strength, popular network modeling and simulation software. A discussion of the current results of the simulation in the broader perspective of hybrid networks development is provided following the presentation of both Hybrid Internet Service and OPNET along with the various built-in OPNET models used in the course of the simulation. The methodology we have followed is also included in this report.