/**

 * @anchor modules_anchor

 *

 * @defgroup core Core

 * \brief The "core" module contains:

 *    - a time management class to hold a time and convert between various time units: ns3::Time 

 *    - a scheduler base class used to implement new simulation event schedulers:       

 *      ns3::Scheduler and ns3::SchedulerFactory 

 *    - a simulator class used to create, schedule and cancel events: ns3::Simulator

 *    - a Functor class: ns3::Callback  

 *    - an os-independent interface to get access to the elapsed wall clock time: ns3::SystemWallClockMs 

 *    - a class to register regression tests with the test manager: ns3::Test and ns3::TestManager

 *    - debugging facilities: \ref logging, \ref assert

 *    - \ref randomvariable

 *    - a base class for objects which need to support per-instance "attributes" and

 *      trace sources: ns3::ObjectBase

 *    - a base class for objects which need to support reference counting

 *      and dynamic object aggregation: ns3::Object

 *    - a smart-pointer class ns3::Ptr designed to work together with ns3::Object

 *    - a configuration class used to set and control all attributes and trace sources

 *      in a simulation: ns3::Config.

 *

 * @defgroup network Network

 * The "network" module contains: 

 *    - a packet class to create and manipulate simulation packets: 

 *      ns3::Packet, ns3::Header,  and ns3::Trailer. This packet class 

 *      also supports per-packet ns3::Tag which are  globs of data 

 *      which can be attached to any packet.

 *    - a ns3::Node base class which should be subclassed by any new type of

 *      network Node.

 *    - models which abstract the MAC-layer from the IP layer protocols:

 *      ns3::NetDevice and ns3::Channel. 

 *    - models which abstract the application-layer API: ns3::Application,

 *      ns3::Socket, ns3::SocketFactory, and, ns3::Udp

 * 

 * @defgroup internet Internet

 * 

 * The "internet" module contains:

 *    - an Ipv4 stack

 *    - an Ipv6 stack

 *    - an ARP module

 *    - a UDP and a TCP implementation

 *    

 * @defgroup routing Routing

 *

 * @defgroup applications Applications

 *

 * @defgroup mobility Mobility

 *

 * @defgroup constants Constants

 * @brief Constants you can change

 *

 * @defgroup utils Utils

 * @brief The utils directory is for various programs and scripts related 

 * to code coverage, test suites, style checking, and benchmarking.

 */