The recent remarkable advances in information systems require that networks satisfy the demands of multimedia transmission. 100Base-T is a high-speed extended version of 10Base-T and is being introduced extensively. In this paper, we are concerned with the performance of standard 100Base-T networks and 100Base-T networks that have been modified for the integrated transmission of motion picture and computer data. The modified 100Base-T is one of a number of 1-persistent CSMA/CD (Carrier Sense Multiple Access with Collision Detection) systems which can reduce both the expectation and variance of transmission delays. We evaluate the performance of both CSMA/CD systems and discuss the improvement obtained by the modified system.