Signal Stability-based Adaptive Routing Protocol

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The Signal Stability-based Adaptive Routing Protocol ( SSA ) tries to find stronger routes based on the signal strength and location stability of the nodes . SSA is partly based on DSR . The main goal of SSA is that only routes that have stronger connections are chosen.

SSA, like Associativity-Based Routing Protocol (ABR), is beacon-based, which means that the signal strength of the beacons (special messages) is measured in order to measure the connection stability between the nodes. The spatial stability defines paths that have existed for a long time. With the help of the connection stability and location stability, the connections are classified as stable or unstable.

The signal strength of the neighboring nodes is stored in a table called SST ( signal stability table ). Each node permanently renews its SST with the help of the beacon packets received. The information from the SST is used to forward the route request messages to the destination, but only via stable connections.

One difference between SSA and ABR is that nodes forward route request messages only if they have received them over a stable connection. Otherwise the corresponding packets are discarded. Furthermore, SSA only uses one metric : the signal strength between the nodes.

Building a route

Example for SSA: Route request packets are only forwarded via stable links (path: 1-2-4-8-13-15)

Before SSA is used, the initiator checks whether a route to the destination is available in its route cache . SSA is only used if no such route exists.

  1. First, the network is flooded with route request packets .
  2. When a node receives such a packet, it checks whether the packet was sent to it over a stable connection. All packets that it received over an unstable connection or received twice are discarded. The address of each intermediate node of the previous route is stored in the route request packet (i.e. it is modified before each further transmission).
  3. When the first route request packet arrives at the destination via a connection classified as stable, the destination immediately sends a route reply packet to inform the source of the selected route. The route reply packet is sent back via the same path.

Maintaining a Route

Example of new routing at SSA: Broken connection: 2-4, new stable route: 1-5-4-8-13-15
  1. As soon as a connection is interrupted, the two intermediate nodes concerned send a corresponding message to the start node and the destination node.
  2. The start node floods the network again with route request messages in order to find another stable route.
  3. Older routes are only deleted if the data packet with the route information does not reach the next node.
  4. If no path can be found via stable connections (and only then), unstable connections are also used.

advantages

The main advantage of SSA is that it finds more stable routes to its destination than DSR does. The shortest path is not necessarily the best. By checking the signal strength via beacons, SSA can find a stable route.

disadvantage

Broken connections are discovered locally, but not repaired. Multiple flooding of the network with route request messages limits the bandwidth of the network. In addition, route request packets over weak connections are not taken into account, but are directly discarded.

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