- Summary of the above results:
- If a wireless node finds the
channel idle,
there is the
possibility
than its transmission will
collide with a
current transmission from a
hidden node...
- If a wireless node finds the channel busy, there is the possibility than the current transmission will not collide with its own transmission...
Conclusion:
- Sensing the carrier is
not 100%
effective
in wireless networks...
(because the information that a node get from sensing the carrier does not tell him whether his transmission will or will not interfere with another transmission)
- But...,
sensing
is not
completely useless !!!!
- especially if there are no hidden nodes !!!
Example:
- If a wireless node finds the
channel idle,
there is the
possibility
than its transmission will
collide with a
current transmission from a
hidden node...
- 802.11 Medium Access Control (MAC)
protocol:
- 802.11 will use
carrier sensing to
reduce
collisions
- In addition,
the 802.11 protocol
will also use:
- Frame acknowledgements
to detect
frame losses
- I.e.: Just like Aloha !!!
- A
military-grade communication
technique
to
overcome
collisions !!!
- 802.11 uses (battle-field-like) anti-jamming communication techniques !!!
- Optionally use a reservation-base protocol to solve the hidden nodes problem
- Frame acknowledgements
to detect
frame losses
- 802.11 will use
carrier sensing to
reduce
collisions