-is defined as a graph of |API_s4u_Tasks| through which circulate Tokens. Tokens
-can carry any user-defined data, using the same internal mechanisms as for the
-other simulated objects. Each Task has to receive a token from each of its
-predecessor to fire a new instance of a |API_s4u_Comm|, |API_s4u_Exec|, or
-|API_s4u_Io| activity. On completion of this activity, the Task propagates tokens
-to its successors, and waits for the next set of tokens to arrive.
+is defined as a graph of |API_s4u_Tasks|, where each |API_s4u_Tasks| has a set of
+successors and predecessors. When a |API_s4u_Tasks| ends it sends a token to each
+of its successors. Each |API_s4u_Tasks| has to receive a token from each of its
+predecessor to start. Tokens can carry any user-defined data.
+
+|API_s4u_Tasks| are composed of several instances: a dispatcher, a collector, and
+instance_0 to instance_n. The dispatcher rely on a load balancing function to select
+the next instance to fire. Once this instance finishes it fires the collector.
+
+Each instance of an |API_s4u_ExecTask| can be placed on a different host.
+|API_s4u_Comm| activities are automatically created when an instance triggers
+another instance on a different host. Each instance has its own parallelism degree
+to scale horizontally on several cores.