D-Link DES-3250TG User Manual page 66

DES-3250TG Layer 2 Fast Ethernet Switch User's Guide
Figure 5- 10. Ethernet Packet Header
When a packet is received, the headers are removed. The
Ethernet Network Interface Card (NIC) removes the Ethernet
header and checks the checksum. It then looks at the type
code. If the type code is for IP, the packet is given to IP. IP then
removes the IP header and looks at its protocol field. If the
protocol field is TCP, the packet is sent to TCP. TCP then looks
at the sequence number and uses this number and other data
from the headers to reassemble the data into the original file.
TCP and UDP Well-Known Ports
Application protocols run 'on top of' TCP/IP. When an
application wants to send data or a message, it gives the data
to TCP. Because TCP and IP take care of the networking
details, the application can look at the network connection as a
simple data stream.
To transfer a file across a network using the File Transfer
Protocol (FTP), a connection must first be established. The
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