Exponential backoff

Old stateRandom delayNew state
0+1..2 slots1
1+1..4 slots2
2+1..8 slots3
3+1..16 slots4
4+1..32 slots5
5+1..64 slots6
6+1..128 slots7
7+1..256 slots8
8+1..512 slots9
9+1..1024 slots10
10+1..1024 slots11
11+1..1024 slots12
12+1..1024 slots13
13+1..1024 slots14
14+1..1024 slots15
15discard frame-

In the exponential backoff simulation the notation 'C2+5' means that host C currently being in the backoff state 2 is not able to send its frame either due to a collision or an occupied channel and therefore chooses a random delay of 5 slots from the range 1..8 and transits into the new backoff state 3.

Number of hosts

The number of hosts that want to send an Ethernet frame simultaneously can be chosen between 1 and 26. Each host is assigned a capital letter from the set 'A'..'Z'.

Frame size

SlotsFrame size
164 bytes
2128 bytes
4256 bytes
8512 bytes
161024 bytes
241536 bytes

The frame size is given in slots of 64 bytes. The maximum Ethernet frame size is 1518 bytes which corresponds to about 24 slots.


The backoff delays are derived from a pseudo-random generator which is initialized with a seed value. Changing the seed changes the backoff simulation scenario.


By default a single scenario for a given seed is executed. The resulting slot occupancy is shown in full detail. If several runs are chosen then only the slot statistics are shown for each run. The seed value is incremented by one with each run, resulting in different outcomes. The statistics of the best and worst case scenarios are given as well as the average statistics over all runs.


The bit times for 10 Mbit/s and 100 Mbit/s Ethernet are 100 ns and 10 ns, respectively. This results in slot times of 51.2 µs and 5.12 µs, respectively.

© 2007 Institute for Internet Technologies and Applications - HSR