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slotted ring

With the slotted ring, the time axis is divided into time slices(slots) of fixed length. The slots then correspond to circulating message containers.

A status indicator is assigned to each slot, indicating whether the slot is currently free or occupied. Messages can be inserted into free slots by stations willing to transmit. Either the station empties the slot on return reception of its own messages and may immediately insert new messages on this occasion, or it empties the slot after return reception, but may not then transmit again immediately, but passes the transmitting right indirectly to the following station.

Slot types

Slot types

The first version is only feasible if there are more slots than stations. This is because a station is able to monopolize a slot for itself. Thus, with fewer slots than stations, some stations can be permanently excluded from traffic.

Slotted-Aloha Phases

Slotted-Aloha Phases

The second version corresponds to an indirect token procedure and, like it, guarantees access to the transmission medium for all stations in a fair manner. The disadvantage is that in borderline situations only every second slot can be used for transmission in the second version, whereas in the first version every slot can be used. The borderline situation occurs exactly when one station transmits everything and the others are only receivers.

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Englisch: slotted ring
Updated at: 04.08.2016
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Translations: DE