D-Link DES-3326 User Manual - page 99
DES-3326 Layer 3 Fast Ethernet Switch User’s Guide
Switch Management and Operating Concepts
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Figure 5-12. TCP Packet Header
When packets have been successfully received, TCP sends an
acknowledgement. This is simply a packet that has the
acknowledgement number field filled in.
An acknowledgement number of 1000 indicates that all of the data
up to octet 1000 has been received. If the transmitting TCP does
not receive an acknowledgement in a reasonable amount of time,
the data is resent.
The window field controls the amount of data being sent at any one
time. It would require too much time and overhead to acknowledge
each packet received. Each end of the TCP connection declares
how much data it is able to receive at any one time by writing this
number of octets in the window field.
The transmitting TCP decrements the number in the window field
and when it reaches zero, the transmitting TCP stops sending data.
When the receiving TCP can accept more data, it increases the