Congestion control remains an important topic for today's Internet protocols. Congestion is generally bad for users, applications and networks. Several mechanisms were proposed by researchers to improve congestion control. These mechanisms include TCP Tahoe, Reno, Vegas, SACK, and NewReno. In this paper, we evaluate the current congestion control protocols considering throughput, losses, delay, and fairness that provided by each variant. This study is done using the well known network simulator NS-2 and a realistic topology generator called GT-ITM.