11.3 Unicast routing

There are presently four routing protocols defined:

• class Ipv4StaticRouting (covering both unicast and multicast)
• Optimized Link State Routing (a MANET protocol defined in RFC 3626)
• class Ipv4ListRouting (used to store a prioritized list of routing protocols)
• class Ipv4GlobalRouting (used to store routes computed by the global route manager, if that is used)

In the future, this architecture should also allow someone to implement a Linux-like implementation with routing cache, or a Click modular router, but those are out of scope for now.

11.3.1 Ipv4ListRouting

This section describes the current default ns-3 Ipv4RoutingProtocol. Typically, multiple routing protocols are supported in user space and coordinate to write a single forwarding table in the kernel. Presently in ns-3, the implementation instead allows for multiple routing protocols to build/keep their own routing state, and the IPv4 implementation will query each one of these routing protocols (in some order determined by the simulation author) until a route is found.

We chose this approach because it may better faciliate the integration of disparate routing approaches that may be difficult to coordinate the writing to a single table, approaches where more information than destination IP address (e.g., source routing) is used to determine the next hop, and on-demand routing approaches where packets must be cached.

11.3.1.1 Ipv4ListRouting::AddRoutingProtocol

Class Ipv4ListRouting provides a pure virtual function declaration for the method that allows one to add a routing protocol:

  void AddRoutingProtocol (Ptr<Ipv4RoutingProtocol> routingProtocol,
                           int16_t priority);

This method is implemented by class Ipv4ListRoutingImpl in the internet-stack module.

The priority variable above governs the priority in which the routing protocols are inserted. Notice that it is a signed int. By default in ns-3, the helper classes will instantiate a Ipv4ListRoutingImpl object, and add to it an Ipv4StaticRoutingImpl object at priority zero. Internally, a list of Ipv4RoutingProtocols is stored, and and the routing protocols are each consulted in decreasing order of priority to see whether a match is found. Therefore, if you want your Ipv4RoutingProtocol to have priority lower than the static routing, insert it with priority less than 0; e.g.:

  Ptr<MyRoutingProtocol> myRoutingProto = CreateObject<MyRoutingProtocol> ();
  listRoutingPtr->AddRoutingProtocol (myRoutingProto, -10);

Upon calls to RouteOutput() or RouteInput(), the list routing object will search the list of routing protocols, in priority order, until a route is found. Such routing protocol will invoke the appropriate callback and no further routing protocols will be searched.

11.3.2 Optimized Link State Routing (OLSR)

This is the first dynamic routing protocol for ns-3. The implementation is found in the src/routing/olsr directory, and an example script is in examples/simple-point-to-point-olsr.cc.

The following commands will enable OLSR in a simulation.

  olsr::EnableAllNodes ();  // Start OLSR on all nodes
  olsr::EnableNodes(InputIterator begin, InputIterator end); // Start on
    // a list of nodes
  olsr::EnableNode (Ptr<Node> node);  // Start OLSR on "node" only

Once instantiated, the agent can be started with the Start() command, and the OLSR "main interface" can be set with the SetMainInterface() command. A number of protocol constants are defined in olsr-agent-impl.cc.

This document was generated on July, 4 2009 using texi2html 1.78.