to number and acknowledge the data. For example, TCP provides error recovery and
defines a TCP header. The headers used by that protocol have some numbering and
acknowledgment fields to both acknowledge data and notice when it has been lost in
transmission. The endpoints that are sending and receiving data use the fields in this
header to identify that data was sent and to signify that data was received.
error-recovery algorithms require the sender to send all data, starting with the lost data. To
limit the negative effect of having to resend lots of data, a window of unacknowledged
data, which can be dynamic in size, is defined. This window defines the maximum amount
of data that can be sent without getting an acknowledgment.
same way. Generically, the transmitted data is labeled or numbered. After receipt, the receiver
signals back to the sender that the data was received, using the same label or number to identify
the data. Figure 3-7 summarizes the operation.
numbers are placed into the header used by that particular protocol; for example, the TCP
header contains similar numbering fields. When Barney sends his next frame to Fred, Barney
acknowledges that all three frames were received by setting his acknowledgment field to 4. The
number 4 refers to the next data to be received, which is called forward acknowledgment. This
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