# ABORt: Acknowledgement-Based Opportunistic Routing Protocol for High Data Rate Multichannel WSNs
## 4 Simulations Environment and Performance Evaluation
### Overhead  
At the network set-up phase, nodes need to exchange control messages (beacon frames) to discover their neighborhood, in order to build the network and also to allocate channels in the cases of ABORt, M-HopCount and M-HopCount-Sync. The use of control messages leads to a certain amount of overhead, which has a direct impact on channel congestion and energy consumption. Figures 11-13 present the number of generated beacon frames for each protocol according to the number of nodes and packet generation rate. Notice that CoLBA overhead increases with the number of nodes and packet generation rate. This is because, when the traffic load becomes high, more packets are enqueued and CoLBA metric value varies more often. Thus, each node needs to transmit additional beacon frames to inform its neighbors about its new metric value or to alert them about the risk of its queue overflow. We also notice that, in the scenarios with less nodes and light traffic, CoLBA has less overhead than the other protocols because the medium is less occupied and CoLBA metric value is almost stable with a low risk of queue overflow.  
Results also show that the overhead of RPL, ABORt and M-HopCount are almost the same for each network size regardless of the packet generation rate. In RPL, the overhead is mainly due to DIO, Destination Advertisement Object (DOA), DAO-ACK and Destination oriented directed acyclic graph Information Solicitation (DIS) messages. The number of DIO messages is largely higher than the others because DIO messages are used to build and maintain the network topology. DIO messages generation is governed by the trickle algorithm [24] timer regardless of the data traffic generation rate. This is why the overhead of RPL is not much affected by the packet generation rate. Thus, the overhead of RPL remains stable for the same number of nodes. In M-HopCount, beacon frames are generated only at the network start-up phase. However, in ABORt, in addition to the set-up phase, beacon frames can be generated during the data transmission in case of a high risk of queue overflow. In that case, beacon frames are sent to alert neighbor nodes to stop transmitting packets to overloaded neighbors. In all three packet generation rates, most of the time, ABORt generates more beacon frames than M-HopCount. In some scenarios, M-HopCount has slightly more overhead than ABORt essentially due to the random behavior of beacon frames transmissions during the start-up phase using CSMA/CA. In M-HopCount-Sync, beacon frames are generated at the network start-up phase and also during each synchronization phase used for routing metric exchange. This is why M-HopCount-Sync has more overhead than ABORt and M-HopCount where the synchronization phase is not needed because the routing metric information is disseminated using ACK frames. In conclusion, the approach used by ABORt and M-HopCount, which consists of using ACK frames for routing metric dissemination helps to reduce the network overhead.  
Figure 11: Overhead for 1 pkt/sec/node.