The Impact of the DOCSIS 1.1/2.0 MAC Protocol on TCP

The number of broadband cable access subscribers in the United States is rapidly approaching 30 million. However there is very little research that has evaluated TCP/IP in modern cable environments. We have developed a model of the data over cable system interface specification (DOCSIS) 1.1/2.0 MAC and physical layers using the 'ns' simulation package. In this paper we show that the interaction of the MAC layer on downstream TCP Web traffic leads to poor network performance as the number of active users grow. We provide an intuitive explanation of this result and explore several possible improvements.