The underlying infrastructure of ns-2 does not support multiple interfaces for a single node. To get around this limitation, our approach allows the general support for logically multihoming nodes that have a multihomed transport layer, such as SCTP. Each multihomed node is actually made up of more than one node. As shown in Figure 36.1, a logically multihomed node is made up of a single "core node" and multiple "interface nodes", one for each simulated interface. The core node is connected to each interface node via a uni-directional link towards the interface node, but traffic never traverses these links. These links are only in place for the core node to make routing decisions. An SCTP agent simultaneously resides on all these nodes (i.e., the core and interface nodes), but actual traffic only goes to/from the interface nodes. Whenever the SCTP agent needs to send data to a destination and does not know which outgoing interface to use, the agent firsts consults with the core node for a route lookup. Then, the SCTP agent performs the send from the appropriate interface node. Incoming data is received at one of the interface nodes directly and passed up to the SCTP agent. This solution is applicable to any transport protocol that requires multihoming functionality in ns-2. Note: the user must configure multihomed nodes using commands in Section 36.1.2 (an example is shown in Section 36.5.2).

Figure 36.1: Example of a Multihomed Node

Tom Henderson 2011-11-05