network: Update queue documentation

src/network/doc/queue.rst

@@ -7,8 +7,11 @@ Queues
    ============= Subsection (#.#.#)
    ############# Paragraph (no number)
 
-This section documents the queue object, typically associated with
-NetDevice models, that is maintained as part of the ``network`` module:
+This section documents the queue object, which is typically used by NetDevices
+and QueueDiscs to store packets.
+
+Packets stored in a queue can be managed according to different policies.
+Currently, the following policies are available:
 
 * DropTail
 
@@ -17,7 +20,7 @@ Model Description
 
 The source code for the new module lives in the directory ``src/network/utils``.
 
-ns-3 provides a couple of classic queue models and the ability to
+ns-3 provides the classic droptail queue model and the ability to
 trace certain queue operations such as enqueuing, dequeuing, and dropping.
 These may be added to certain NetDevice objects that take a Ptr<Queue>
 pointer.
@@ -27,6 +30,8 @@ In particular, WiFi, WiMax, and LTE use specialized device queues.
 The queue models described here are more often used with simpler ns-3 
 device models such as PointToPoint and Csma.
 
+All the queuing disciplines, instead, make use of the queue model defined here.
+
 Design
 ======
 
@@ -49,6 +54,14 @@ There are three trace sources that may be hooked:
 * ``Dequeue``
 * ``Drop``
 
+Also, three attributes are defined in the Queue base class:
+
+* ``Mode``: whether the capacity of the queue is measured in packets or bytes
+* ``MaxPackets``: the maximum number of packets accepted by the queue in packet mode
+* ``MaxBytes``: the maximum number of bytes accepted by the queue in byte mode
+
+The Enqueue method does not allow to store a packet if the queue capacity is exceeded.
+
 DropTail
 ########