1. ITIS 1210 Introduction to Web-Based Information Systems Chapter 3. How TCP/IP Works

2. How TCP/IP Works  Before there was the Internet there was …  The telephone company  Circuit-switched  Connection made for each call  Users “owned” circuit during call  Resources released only when call terminated

3. 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

4. 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

5. How TCP/IP Works  TCP decomposes original message into packets  Packets limited to 1500 characters or less  Additional data added in a header:  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

6. How TCP/IP Works  PCs need special software to connect to the Internet  Interprets TCP/IP  “Socket” or “TCP/IP stack”  Built-in to all modern computers  Winsock or MacTCP  Without this can’t view Web pages