# L18 - Still another way of handling contention is to...

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Still another way of handling contention is to exercise a collision resolution algorithm. My description of this algorithm differs from the one in the text. It is related to “The Adaptive Tree Walk Protocol” described in Section 4.2.4.

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The collision resolution algorithm Efficiency and stability of ALOHA or CSMA/CD can be improved by limiting future transmissions to the colliders until these colliders are successful. Assume time is slotted and all users observe (before next slot) if slot is unused, has a success, or has a collision (number of colliders unknown). Goal: have an algorithm that resolves a collision in as few slots as possible, on average, while also allowing all users to know when the collision has been resolved. The basic idea is called a splitting algorithm .
SPLITTING ALGORITHM Each collider picks a number in a range. The range is divided into two (assumed equal size) subsets, and a collider whose number is in the lower subset retransmits, but those in the upper subset defer. In the event of a success or idle in the permitted subset, the subset is resolved. Only those in the other part remain to be resolved. In the event of a collision in the first subset, that subset is split. Transmission is then restricted to the first subset until it is resolved .

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Illustration of the splitting algorithm Three colliders whose selected numbers are:
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L18 - Still another way of handling contention is to...

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