The paper presents a modeling and evaluation study of the characteristics of SMTP and HTTP applications in terms of user behavior, nature of contents transferred and application layer protocol exchanges. Results are reported on measuring, modeling and analysis of application level traces collected, at client and server ends, from different environments such as university networks and commercial Frame Relay networks. The methodologies used for capturing traffic flows and for modeling are reported. Statistical models have been developed for diverse parameters of applications, which can be useful for building synthetic workloads for simulation and benchmarking purposes. Both applications possess a session oriented structure. Within each session, a number of transactions may occur, and this number has been modeled as well.