• Adaptive Routing is a method for transferring data over networks.3d network node image by brunoil from Fotolia.com
  
  "Adaptive Routing" is another name for Dynamic Routing. A distinctive feature of adaptive routing is that, should a selected path be blocked, the routers approaching that link remap the route to find an alternative route. This could involve lots of processing to recalculate a preordained path. However, adaptive routing protocols keep things simple. There is no preordained route; the data packet's route is only set to the next router in the path. Each router makes its own decision on where the next path should be and makes no decision about any further hops.
  
  

Dynamic Routing

• Dynamic-routing algorithms prepare for the task of forwarding packets. They compile a table of possible routes to a destination and order them by distance, direction, the number of links in the path and the throughput of each individual line. With this information stored, the router is ready for an arriving packet. It already has the best route prepared and forwards the data packet onto the neighboring router that's the first hop in the path. It does not pass on instructions on the path it decided was the best, it just passes on the data packet together with the address of its destination. The next router then makes a decision, based on its own knowledge base, where best to send that packet next.
  
  

Link State Routing

• The clearest example of adaptive routing falls in the Link-State routing category. Link-State routing algorithms prioritize possible routes to a destination by taking account of the performance of each link on a previous transmission. If a link fails, the routers feeding into that path make a note of the failure and demote it in their ranking tables.
  
  

Route Propagation

• A new router signals its presence to its immediate neighbors, routers to which it is connected by a cable, but does not communicate any further. The neighboring routers reply by sending copies of their routing tables, and the new router then compiles its own routing table from them. All routers periodically send their routing tables to their neighbors, which adjust their routing tables with the updated information and in turn broadcast their updated tables to their neighbors. By this method, routers all over the world discover each other. However, this information can quickly become out of date; a link can fail on a route before a packet has reached its ultimate destination. This is why routers do not write out the full route for each packet.
  
  

Examples

• The Open Shortest Path First (OSPF) protocol and the Intermediate System to Intermediate System (IS-IS) protocol are the two most popular link-state protocols for wired networks. Wireless networks present a problem for routing, however almost all routing protocols for wireless networks are adaptive. Where individual nodes on a network are independently controlled, there is no knowing when a point in a route will be moved, or switched off. For this reason wireless networking needs to record multiple paths to a destination. A node in the network needs to quickly switch its routing rankings when a favored next hop node suddenly disappears.