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 * Copyright 2008 University of Washington

 * 

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 * published by the Free Software Foundation;

 *

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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

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 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

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/**

 * \ingroup internet

 * \defgroup globalrouting Global Routing

 *

 * \section model Model

 *

 * ns-3 global routing performs pre-simulation static route computation

 * on a layer-3 Ipv4 topology.  The user API from the script level is

 * fairly minimal; once a topology has been constructed and addresses

 * assigned, the user may call ns3::GlobalRouteManager::PopulateRoutingTables()

 * and the simulator will initialize the routing database and set up

 * static unicast forwarding tables for each node.

 *

 * The model assumes that all nodes on an ns-3 channel are reachable to

 * one another, regardless of whether the nodes can use the channel

 * successfully (in the case of wireless).  Therefore, this model

 * should typically be used only on wired topologies.  Layer-2 bridge

 * devices are supported.  API does not yet exist to control the subset 

 * of a topology to which this global static routing is applied.

 * 

 * If the topology changes during the simulation, by default, routing

 * will not adjust.  There are two ways to make it adjust.

 * - Set the attribute Ipv4GlobalRouting::RespondToInterfaceEvents to true 

 * - Manually call the sequence of GlobalRouteManager methods to delte global

 *   routes, build global routing database, and initialize routes.

 *   There is a helper method that encapsulates this 

 *   (Ipv4GlobalRoutingHelper::RecomputeRoutingTables())

 * 

 * \section api API and Usage

 * 

 * Users must include ns3/global-route-manager.h header file.  After the

 * IPv4 topology has been built and addresses assigned, users call

 * ns3::GlobalRouteManager::PopulateRoutingTables (), prior to the 

 * ns3::Simulator::Run() call.

 *

 * There are two attributes of Ipv4GlobalRouting that govern behavior.

 * - Ipv4GlobalRouting::RandomEcmpRouting

 * - Ipv4GlobalRouting::RespondToInterfaceEvents

 *

 * \section impl Implementation

 *

 * A singleton object, ns3::GlobalRouteManager, builds a global routing

 * database of information about the topology, and executes a Dijkstra

 * Shortest Path First (SPF) algorithm on the topology for each node, and

 * stores the computed routes in each node's IPv4 forwarding table by

 * making use of the routing API in class ns3::Ipv4.

 *

 * The nodes that export data are those that have had an ns3::GlobalRouter

 * object aggregated to them.  The ns3::GlobalRouter can be thought of

 * as a per-node agent that exports topology information to the 

 * ns3::GlobalRouteManager.  When it comes time to build the global

 * routing database, the list of nodes is iterated and each node with

 * an ns3::GlobalRouter object is asked to export routing information

 * concerning the links to which it is attached.

 *

 * The format of the data exported conforms to the OSPFv2 standard

 * \RFC{2328}.  In particular, the

 * information is exported in the form of ns3::GlobalLSA objects that

 * semantically match the Link State Advertisements of OSPF.

 *

 * By using a standard data format for reporting topology, existing 

 * OSPF route computation code can be reused, and that is what is done

 * by the ns3::GlobalRouteManager.  The main computation functions are

 * ported from the quagga routing suite (http://www.quagga.net).

 * 

 */