A typical SimGrid simulation is composed of several |Actors|_, that
execute user-provided functions. The actors have to explicitly use the
-S4U interface to express their computation, communication, disk usage
+S4U interface to express their
+:ref:`computation <exhale_class_classsimgrid_1_1s4u_1_1Exec>`,
+:ref:`communication <exhale_class_classsimgrid_1_1s4u_1_1Comm>`,
+:ref:`disk usage <exhale_class_classsimgrid_1_1s4u_1_1Io>`,
and other |Activities|_, so that they get reflected within the
-simulator. These activities take place on resources: |Hosts|_,
-|Links|_, |Storages|_ and |VirtualMachines|_. SimGrid predicts the
-time taken by each activity and orchestrates accordingly the actors
-waiting for the completion of these activities.
+simulator. These activities take place on resources such as |Hosts|_,
+|Links|_ and |Storages|_. SimGrid predicts the time taken by each
+activity and orchestrates accordingly the actors waiting for the
+completion of these activities.
+
+
+When **communicating**, data is not directly sent to other actors but
+posted onto a |Mailbox|_ that serve as rendez-vous point between
+communicating actors. This means that you don't need to know who you
+are talking to, you just put your communication `Send` request in a
+mailbox, and it will be matched with a complementary `Receive`
+request. Alternatively, actors can interact through **classical
+synchronization mechanisms** such as |Barrier|_, |Semaphore|_,
+|Mutex|_ and |ConditionVariable|_.
+
+Each actor is located on a simulated |Host|_. Each host is located
+itself in a |NetZone|_, that route communications through the
+links. Each NetZone is included in another one, forming a tree of
+NetZones which root zone contains the whole platform.
+
+The :ref:`simgrid::s4u::this_actor
+<namespace_simgrid__s4u__this_actor>` namespace provides many helper
+functions to simplify the code of actors.
+
+- **Global Classes**
+
+ - :ref:`class s4u::Actor <exhale_class_classsimgrid_1_1s4u_1_1Actor>`:
+ Active entities executing your application.
+ - :ref:`class s4u::Engine <exhale_class_classsimgrid_1_1s4u_1_1Engine>`
+ Simulation engine (singleton).
+ - :ref:`class s4u::Mailbox <exhale_class_classsimgrid_1_1s4u_1_1Mailbox>`
+ Communication rendez-vous.
+
+- **Platform Elements**
+
+ - :ref:`class s4u::Host <exhale_class_classsimgrid_1_1s4u_1_1Host>`:
+ Actor location, providing computational power.
+ - :ref:`class s4u::Link <exhale_class_classsimgrid_1_1s4u_1_1Link>`
+ Interconnecting hosts.
+ - :ref:`class s4u::NetZone <exhale_class_classsimgrid_1_1s4u_1_1NetZone>`:
+ Sub-region of the platform, containing resources (Hosts, Link, etc).
+ - :ref:`class s4u::Storage <exhale_class_classsimgrid_1_1s4u_1_1Storage>`
+ Resource on which actors can write and read data.
+ - :ref:`class s4u::VirtualMachine <exhale_class_classsimgrid_1_1s4u_1_1VirtualMachine>`:
+ Execution containers that can be moved between Hosts.
+
+- **Activities** (:ref:`class s4u::Activity <exhale_class_classsimgrid_1_1s4u_1_1Activity>`):
+ The things that actors can do on resources
+
+ - :ref:`class s4u::Comm <exhale_class_classsimgrid_1_1s4u_1_1Comm>`
+ Communication activity, started on Mailboxes and consuming links.
+ - :ref:`class s4u::Exec <exhale_class_classsimgrid_1_1s4u_1_1Exec>`
+ Computation activity, started on Host and consuming CPU resources.
+ - :ref:`class s4u::Io <exhale_class_classsimgrid_1_1s4u_1_1Io>`
+ I/O activities, started on and consumming Storages.
+
+- **Synchronization Mechanisms**: Classical IPC that actors can use
+
+ - :ref:`class s4u::Barrier <exhale_class_classsimgrid_1_1s4u_1_1Barrier>`
+ - :ref:`class s4u::ConditionVariable <exhale_class_classsimgrid_1_1s4u_1_1ConditionVariable>`
+ - :ref:`class s4u::Mutex <exhale_class_classsimgrid_1_1s4u_1_1Mutex>`
+ - :ref:`class s4u::Semaphore <exhale_class_classsimgrid_1_1s4u_1_1Semaphore>`
-Each actor executes a user-provided function on a simulated |Host|_,
-with which it can interact using the :ref:`simgrid::s4u::this_actor
-<namespace_simgrid__s4u__this_actor>` namespace. **Communications**
-are not directly sent to actors, but posted onto a |Mailbox|_ that
-serve as rendez-vous point between communicating actors. Actors can
-also interact through **classical synchronization mechanisms** such as
-|Barrier|_, |Semaphore|_, |Mutex|_ and |ConditionVariable|_.
-
-.. todo:: Add NetZone
-
.. |Actors| replace:: **Actors**
.. _Actors: api/classsimgrid_1_1s4u_1_1Actor.html
.. |Mailbox| replace:: **Mailbox**
.. _Mailbox: api/classsimgrid_1_1s4u_1_1Mailbox.html
+.. |NetZone| replace:: **NetZone**
+.. _NetZone: api/classsimgrid_1_1s4u_1_1NetZone.html
+
.. |Barrier| replace:: **Barrier**
.. _Barrier: api/classsimgrid_1_1s4u_1_1Barrier.html
