Amer Networks SS3GR24i - Manual (Page 45)

SS3GR24i/SS3GR48i Layer3 Stackable Gigabit Switch User’s Guide
Figure 5-3. 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 computer
requesting the file transfer must connect specifically to the FTP
server on the computer that has the file.
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