Comtech EF Data CDD-880, Installation And Operation Manual

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CDD-880 Multi Receiver Router MN-CDD880
Appendix D Revision 2
D–10
The backoff is based on contention levels of 2
n
(where
n
= 0 to 4; i.e. 2
0
=1, 2
1
=2, 2
2
=4, 2
3
=8, and
2
4
=16). The Contention Level always starts at 0 , which means the CDM-840 transmits in the next
frame when it receives a TAP message. If the transmission is not detected, the CDM-840 goes to
Contention Level
1
and picks a random slot in one of the next two frames. If it is
still
not
detected, Contention Level goes to 3 and the CDM-840 randomly picks a slot in one of the next
four frames.
If the CDM-840 is not detected by Contention Level 4 (16 frames), it then resets to Contention
Level 0 and tries again – the CDM-840 uses one random number to select a frame at the current
contention level and another random number to select a slot within the frame.
Since the CDM-840s are not aware of each other, their Contention Levels are
independent and determined only by when they were initially ready to transmit.