External access - HNA

A MANET can exist isolated, independent of other computer networks. However, the option to connect to other networks should be offered on some level since this is very likely to be a requirement in many situations. Internet access in MANETs has been documented in [20] and [57].

OLSR offers this kind of external connectivity at the routing protocol level. A host can announce itself as a gateway to specific networks using Host and Network Association(HNA) messages. Fig 4.1 illustrates a typical HNA scenario. A node has an Ethernet link on which it has Internet access. This node wishes to offer Internet connectivity to the other nodes in the MANET. This is done by sending HNA messages.

Due to OLSRs default forwarding algorithm, all nodes does not need to support the HNA functionality for HNA messages to be flooded throughout the MANET. But all nodes must support HNA processing and route calculation for the actual HNA routing to work. If a node routes Internet traffic to an intermediate neighbor based on HNA information, the intermediate neighbor must also have set up an Internet route for the traffic to be routed. Therefore, in the general case, the neighbor must support HNA functioning.

Figure: A node in the MANET announces itself as a gateway to Internet for the nodes in the MANET. This is done by HNA messaging.

Andreas 2004-07-29