- Physics of
wireless transmissions:
- The signal strength
of wireless transmission
attenuates (= weakens)
very rapidly:
- Signal strength decreases at a rate of 1/r3 where r is the distance to the source
Example:
- The signal strength
of wireless transmission
attenuates (= weakens)
very rapidly:
- Rapid signal strength attenuation
results in:
- a limited range of reception.
Example:
Notes:
- The letters indicate the physical location of each node
- The circles
indicate the transmission range
of each node
- Node B is in A's range.
- Nodes A and C are in B's range.
- Nodes B and D are in C's range.
- Node C is in D's range.
- Range of 802.11 devices:
- The range
is relatively short:
- about a hundred of feet.
- The range
is relatively short:
- Because
of the short distance:
- A dode's transmissions
will
reach
other
nodes
almost instantaneously
- Nodes will still be transmitting (a frame) when other nodes detect the transmission
In other words:
-
Channel sensing
can
help you
avoid
collisions !!!
(Just like Ethernet)
- A dode's transmissions
will
reach
other
nodes
almost instantaneously
- Fact:
- Due to rapid signal attenuation
(= weakening of the
transmission signal) in
wireless transmission:
- The effectiveness of channel sensing is diminished
- Due to rapid signal attenuation
(= weakening of the
transmission signal) in
wireless transmission:
- Problems that
wireless networks
have to deal with:
- The
hidden node
problem:
- A node that is out of range can interfere with your transmissions
- The
exposed node
problem:
- A transmitting node that is in range but do not interfere with your transmissions
- The
hidden node
problem: