Why are there single packet collisions in MANET/ WSN?
In networks like Mobile Ad-hoc Networks (MANETs) and Wireless Sensor Networks (WSN), under certain conditions, there is a likelihood of packet collisions.
There are different routing protocols used in these networks like Dynamic Source Routing (DSR), Adhoc On-demand Distance Vector (AODV), Optimized Link State Routing (OLSR), and Zone Routing Protocol (ZRP). The route of a packet from the source to the destination is decided in run-time by these protocols (these routing protocols have functionalities such as Buffering, Route Discovery, Route Maintenance, Route Error, Cache timeouts, etc.,)
In the NetSim Packet Animation, you can observe the errored or collided packets in red color as shown below:
When the animation is played, there will be DSR_RREQ packets transmitted initially which collide.
In the packet trace the Packet status for the first DSR_RREQ packet is shown as Collided
Both the applications start at 0s. Therefore, both the nodes transmit DSR REQ packets for route discovery. This leads to collisions between the two DSR RREQ packets.
This problem can be overcome by enabling random start-up time for both the applications (experiment file attached)
Note that the Animation and Packet Trace files are only written when a packet is received at the receiver. It is not written when a packet is sent by the transmitted. Technically advanced users may note that
- The Received power (in mW) is equal to/ greater than the Receiver Sensitivity (in mW). Hence, the receiver is in range, and the packet is received by marked as collided.
- The Receiver Sensitivity is set to -85 dBm and can be modified by the user. Go to the Physical Layer of Interface Zigbee (in WSN networks)
- There are only PHY_IN events and no MAC_IN events associated with packets marked as collided. This can be observed in the Event Trace.
Useful References:
How do I write code to see the received power in a simple two node wireless system?