Amer Networks SS3GR24i - Manual (Page 42)

SS3GR24i/SS3GR48i Layer3 Stackable Gigabit Switch User’s Guide
Figure 5-1. 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 number in the window field. In practice, a single packet can
acknowledge the receipt of data and give permission for more data
to be sent.
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