cnp3-ebook/principles/reliability

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196 ../../principles/reliability.rst:1038

	English Reliable protocols often need to send data in both directions. To reduce the overhead caused by the acknowledgments, most reliable protocols use `piggybacking`. Thanks to this technique, a datalink entity can place the acknowledgments and the receive window that it advertises for the opposite direction of the data flow inside the header of the data frames that it sends. The main advantage of piggybacking is that it reduces the overhead as it is not necessary to send a complete frame to carry an acknowledgment. This is illustrated in the figure below where the acknowledgment number is underlined in the data frames. Piggybacking is only used when data flows in both directions. A receiver will generate a pure acknowledgment when it does not send data in the opposite direction as shown in the bottom of the figure. 821/10000 · 821
197 ../../principles/reliability.rst:1044

	English Piggybacking example 20/10000 · 20
198 ../../principles/reliability.rst:1052

	English SDU is the acronym of Service Data Unit. We use it as a generic term to represent the data that is transported by a protocol. 125/10000 · 125
199 ../../principles/reliability.rst:1054

	English The size of the sliding window can be either fixed for a given protocol or negotiated during the connection establishment phase. Some protocols allow to change the maximum window size during the data transfer. We will explain these techniques with real protocols later. 269/10000 · 269
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