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24-port NWay Ethernet Switch User’s Guide
92 Switch Management and Operating Concepts
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.
IP Level
TCP sends its packets to IP with the source and destination IP
addresses. IP is only concerned with these IP addresses. It is
not concerned with the contents of the packet or the TCP header.
IP finds a route for the packet to get to the other end of the TCP
connection. IP adds its own header to the packet to accomplish
this.
The IP header contains the source and destination addresses, the
protocol number, and another checksum.
The protocol number tells the receiving IP which protocol to give
the packet to. Although most IP traffic uses TCP, other
protocols can be used (such as UDP).
The checksum is used by the receiving IP in the same way as the
TCP checksum.