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Steve McQuerry. Interconnecting Cisco Network Devices. (Cisco Press: 2000) pages 163-165.
Q. 126
What is a backoff on an 802.3 network?
A. It is latency in store and forward switching.
B. It is the time used for token passing for machine to machine.
C. It is the retransmission delay that is reinforced when a collision occurs.
D. It is the result of two nodes transmitting at a same time the frames from each transmitting device
collide and are damaged.
Answer: C
Explanation: Backoff is done when a collision occurs. Those trying to transmit at the same time “back-off” and
attempt to retransmit at a later time. A 802.3 network uses collision detection, so that the transmitters are
notified of the collision. Then using a random calculated wait time, re-transmission occurs. By using a random
wait time, hopefully both transmitter wait a different amount of time and do not attempt simultaneous
transmission again.
Incorrect Answers:
A is incorrect; back off occurs after a collision has occurred and is not latency stored and forward switching.
B is incorrect; has nothing to do with the passing of the token.
D is incorrect; back off is used to prevent another collision.
Steve McQuerry. Interconnecting Cisco Network Devices. (Cisco Press: 2000) pages 16-17.
Q. 127
You have just issued an erase startup-config command and reloaded your router. In which mode will
your router be when you reboot?
A. Setup.
B. Startup.
C. User EXEC.
D. User privileged.
E. Global configuration.
Answer: A
Explanation: When a router is booted, it will copy the startup-config from NVRAM to the RAM and begin
execution. Since the erase wiped out the startup configuration, the router can’t start. This forces the router into
setup mode, where a configuration has to be built from by scratch.