Transcript Chapter 3: How TCP/IP Works

ITIS 1210
Introduction to Web-Based
Information Systems
Chapter 3. How TCP/IP Works
How TCP/IP Works
 Before there was the Internet there was …
 The telephone company
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Circuit-switched
Connection made for each call
Users “owned” circuit during call
Resources released only when call terminated
How TCP/IP Works
 Internet works differently
 Circuits are permanent
 But not dedicated to a single user
 Messages inhabit a circuit until delivered
 Packet-switched network
 Messages decomposed into subsets
 Packets
 Packets delivered individually to destination
How TCP/IP Works
 TCP/IP enables this process
 TCP – Transmission Control Protocol
 Decomposes messages prior to transmission
 Re-assembles messages at destination
 IP – Internet Protocol
 Routes packets to proper destination
How TCP/IP Works
 TCP decomposes original message into packets
 Packets limited to 1500 characters or less
 Additional data added in a header:
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 Sequence Number
 Checksum
 IP places each packet into an envelope
Additional information added in a header:
 Sender address
 Destination address
 Time to keep until discarded
Packets sent out on Internet
Routers examine addressing information
Best path taken for each packet
Checksums used to detect transmission errors
“Bad” packets discarded
Re-transmission is requested
“Good” packets re-assembled at destination
How TCP/IP Works
 PCs need special software to connect to
the Internet
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Interprets TCP/IP
“Socket” or “TCP/IP stack”
Built-in to all modern computers
Winsock or MacTCP
Without this can’t view Web pages