S-MAC Message Passing

S-MAC Message Passing:

S-MAC Message Passing
S-MAC Message Passing

To develop application-level performance, S-MAC uses message passing.

Messages get subdivided into small messages. 

These small messages are sent in a single burst.

The pieces of message are sent using only one RTS/CTS swap between transmitter and receiver nodes.

At the finish of this swapping, the channel is reserved till to the transfer of the whole message is finished successfully. 

Each piece of message holds the time required to send all the subsequent pieces and their relating acknowledgments in its duration field.

This procedure is shown in the image.

Upon sending a fragment the transmitter waits for an acknowledgment from the receiving node.

If the sender is not able to get an acknowledgment, the transmitter increases the time needed to finish transmission of the fragment it also includes the time to send one more fragment and its relating acknowledgment and resends the unacknowledged frame immediately.

The sleeping nodes can listen to this extension if they listen to extended fragments or their relating acknowledgments. 

The nodes heard RTS and CTS packet exchange stay unaware of the transmission extension.

S-MAC has the ability to obtain significant energy savings.

S-MAC is well suited for such applications where fairness is not an important design goal and increased delay is acceptable.

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