Symantec Norton Personal Firewall 2003, User Manual

Page: 119 / 151

About the Internet
How information is transmitted over the Internet
119
The Internet is a packet switching network . Every communication is broken
into packets by TCP (Transmission Control Protocol). Each packet contains
the addresses of the sending and receiving computers along with the
information to be communicated.
IP (Internet Protocol) is responsible for routing the packets to their
destinations. Each packet may take a different route across the Internet,
and packets may be broken up into
fragments . Packets travel across the
Internet, moving from one router to another. Routers look at the destination
address and forward the packet to the next router. IP does not guarantee
the delivery of every packet.
On the destination computer, TCP joins the packets into the complete
communication. TCP may have to reorder the packets if they are received
out of order, and it may have to reassemble fragmented packets. TCP
requests retransmission of missing packets.
TCP/IP is often used to refer to a group of protocols used on the Internet,
including UDP (User Datagram Protocol), ICMP (Internet Control Message
Protocol), and IGMP (Internet Group Membership Protocol).
Router
Router
Router
Router
Router
Router
Router
Sending
computer
Receiving
computer
Routes that a packet or fragments of a packet may take