In this paper, p-persistent carrier sense multiple access protocols, with and without collision detection (CSMA/CD & CSMA), were analyzed based on the consideration of realistic network structure; i.e., there is a finite population of users, and each of them has a finite capacity of buffers. By constructing a two-dimentional semi-markov chain and examining th state of the system immediately after a transmission period, we can obtain a solution of the system.