Enterasys VH-2402-L3 Management Manual page 160

contain are. If there are 100 octets of data in each packet,
the first packet is numbered 0, the second 100, the third 200,
etc.
To insure that the data in a packet is received uncorrupted,
TCP adds the binary value of all the octets in the packet and
writes the sum in the checksum field. The receiving TCP
recalculates the checksum and if the numbers are different,
the packet is dropped.
Figure 2-10. 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.
152 VH-2402-L3 Management Guide 9033691-01