The Exposed Terminal Problem occurs in wireless networks when a device is unable to transmit data due to interference from another device that is transmitting to a different destination.
This problem results in inefficient use of the network medium, as the exposed terminal unnecessarily defers its transmission.
Example Scenario
Devices A and B are within range of each other and communicating with Device C and Device D, respectively.
If Device A wants to transmit data to Device C, but Device B is already transmitting to Device D, Device A might be unable to transmit even though Device B’s transmission does not interfere with Device A’s intended communication.
Causes
Overhearing Transmissions: Device A defers its transmission because it hears Device B’s transmission, even though it does not interfere with Device A’s communication with Device C.
Medium Reservation: Device A is incorrectly prevented from using the medium due to the reservation made by Device B for its own communication.
Impact
Inefficient Medium Utilization: The network medium is underutilized because devices are unnecessarily prevented from transmitting data.
Reduced Throughput: Overall network performance and throughput may be decreased due to the incorrect deferral of transmissions.
Solutions
Network Protocols
Network Protocol Enhancements:
Use of protocols that better manage medium access and reduce the impact of the exposed terminal problem.
Implement mechanisms that allow devices to determine whether a transmission will actually cause interference.
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
CSMA/CA Adjustments:
Improve the CSMA/CA protocol to handle situations where transmissions are unnecessarily deferred.
Directional Antennas
Directional Antennas:
Use directional antennas to limit the transmission range and reduce interference with devices outside the intended communication area.
Summary
The Exposed Terminal Problem results from a device deferring its transmission due to perceived interference from a transmission that does not actually impact its communication.
Solutions involve enhancing network protocols, adjusting CSMA/CA, and using directional antennas to improve medium utilization and network efficiency.