Original requests may ask for several services. They may then split into specific single service requests or trigger the generation of secondary requests in servers and services. The arrival of the last response of such a series is considered as the completion of this particular request. Requests and responses traveling in the model form the model traffic. They are temporary stored in the node memories which may model different queuing and scheduling strategies.
Messages compete for the memory space or link bandwidth.
As a result of such competition, congestions and bottlenecks may occur. Different types of messages may have different priorities to solve the conflicts. The sessions are generated with some interarrival time and each session initiates a series of request messages. Some termination condition defines when a session is completed. To prevent overcrowding at services, an admission control for sessions may be used in servers.