- The algorithm to
transmit a
new frame is
as follows:
Explanation:
- When a node transmits
a new frame
(i.e., a frame for the
first time:
- The node always reset the the random number range (CW (collision window) to the initial value (CWmin)
- Before the
node can
transmit
the frame:
- The node must "defer" (= listen) for a DIFS seconds (to let high priority frames like ACK frames) go first)
- If the node did
not sense (=
receive) any
transmissions for
DIFS duration:
- The node will transmit the data frame
- Wait for an ACK frame !!!
If the node received an ACK frame, it is done
Otherwise (no ACK received):
- The node waits until the current transmission (if any) has ended
- Then the node will execute a binary exponential back off algorithm (discussed after this)
- If the node
senses
(= receives) a
transmission during its
DIFS sense period:
- The node waits until the current transmission (if any) has ended
- Then the node will execute a binary exponential back off algorithm (discussed after this)
Note:
- The node porforms a binary exponential back off to minimize the collision probability
- When a node transmits
a new frame
(i.e., a frame for the
first time: