Dial on Demand Routing
When connections between nodes in wide area networks ( WANs ) are only established as required, this is called dial-on-demand routing . This technology saves costs, especially in networks with low data volumes, since no dedicated connections are required between the network nodes .
background
In wide area networks, data is forwarded between individual network areas by routers . To do this, the routers use information that has been statically defined or is constantly exchanged between the routers via existing connections ( see also: Routing ). An important basic principle here is that routers only consider active connections. Inactive connections are considered defective and a diversion is sought around them.
However, if you want to switch a dial-up connection between two network nodes, this leads to a problem with the routing. If the dial-up connection is not established, the routers will see this as a malfunction and will not use the route. If the connection is established manually, for example, the routers will use this connection and exchange their routing data over it. In this case the connection would no longer be cleared down.
Virtual connection
To solve the problems described above, routers can have special virtual connections . With this type of connection, information about the network nodes on the other side of the connection is sent to a router. The router also receives data that allows it to establish a connection automatically if necessary. The router therefore assumes that the connection to the other network nodes is active, because it can establish it if necessary.
Data classification
In order for dial-on-demand routing to work, the router must classify the data to be transmitted. There are roughly two types of data: interesting and uninteresting . If the data is interesting , the connection is established, if not already active. If the connection is already active, an idle timer is reset. No connection is established with uninteresting data. However, they are transmitted when there is a connection. However, the time counter is not reset. If the time counter reaches the value 0 ( timeout ), the connection is cleared down.
Applications
Dial-on-demand routing is often used in smaller private networks. In large networks, branch offices and workplaces that do not depend on a constant connection to the network are connected here. In order to ensure trouble-free operation as possible, DDR is mostly used with fast dial-up networks ( ISDN , ATM , frame relay ).