Manoj Devare and Ajay Kumar International Journal of Computer Science and Security, Volume (1): Issue (2) 10 Congestion and Flow Control in Homogeneous and Heterogeneous Networks: Discrete Event Simulation Model Manoj Devare manojdeore@rediffmail.com Vidya Pratishthan’s Institute of Information Technology, Baramati (MS),413133- India Ajay Kumar ajay19_61@rediffmail.com Modern College of Engineering, Pune (MS)-411005, India Abstract This Paper provides a study and review of existing congestion control algorithms in various types of homogenous and heterogeneous networks. To test the new methodology for the congestion and flow control we have used the two different discrete event simulation tools. The OPNET simulation tool is used to find out performance of the TCP reliable protocol for built-in congestion control mechanism. The second part is for simulation of existing congestion control algorithm (AIMD-Additive Increase Multiplicative Decrease) and new suggested congestion and flow control algorithm using OMNeT++ discrete event simulation. Keywords: AIMD, discrete event simulation, advertise window, congestion window. 1. INTRODUCTION Congestion control is the efforts made by network nodes to prevent or respond to overload conditions. We use concept of ‘fairness’ i.e. try to share pain among the all users, rather than causing great pain to a few. Many congestion control mechanism having built in notion of resource allocation. Flow control is keeping fast sender form overrunning a slow receiver. Congestion control keeps a set of senders form sending too much data into network because of lack of resources at some point. In other words the bandwidth is also known as throughput. The term throughput is used to measure the performance of the system. Congestion control and resource allocation involves both host and network elements such as routers. Congestion and resource allocation are two sides of same coin involves host and network elements such as routers. The queuing discipline can segregate traffic. As congestion and resource allocation is not isolated to single level of protocol hierarchy. Resource allocation is process by which network elements try to meet the competing demands that application have for network resources. Resources are link bandwidth and buffer space in routers or switches. The problem is for refusing the users. The congestion controlling algorithms are categorized into “box is black”, “box is gray” and “box is green”. This type of categorization is done on the basis of knowledge of it’s state. In case “box is black” category no knowledge of it’s state , other than binary feedback upon congestion. The algorithms AIMD-FC, Binomial mechanism, SIMD, HIGHSPEED-TCP, BIC-TCP and other generations of AIMD are included in this first category. The “Box is Gray” category use