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Topic 2 – Lesson 2 Understanding TCP/IP via an Analogy

Topic 2 – Lesson 2 Understanding TCP/IP via an Analogy. SRA 221. Basic Questions. What is the Internet? How does the Internet work? How do two computers use TCP ports and IP addresses to talk to (or communicate with) each other? . What is the Internet?.

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Topic 2 – Lesson 2 Understanding TCP/IP via an Analogy

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  1. Topic 2 – Lesson 2Understanding TCP/IP via an Analogy SRA 221

  2. Basic Questions • What is the Internet? • How does the Internet work? • How do two computers use TCP ports and IP addresses to talk to (or communicate with) each other?

  3. What is the Internet? • Purpose of the Internet: enable any two computers to talk to each other • Computer 1 and Computer 2 chat online • Computer 1 sends an IM to Computer 2 • The Simplest Internet = Computer 1 (sender) + (a bunch of routers) + Computer 2 (receiver) A bunch of routers Computer 2 Computer 1

  4. How does the Internet work? • The routers relay the message from the sender to the receiver • The message is contained in a packet, which could be viewed as an envelope • The packet could get lost or corrupted during transmission • For reliability, the receiver will typically send an acknowledgement note back • There may exist multiple routes (or paths) from the sender to the receiver

  5. How to use TCP ports and IP addresses (1) When Alice sends a letter to Bob, what to put on the envelope? 404 Alice Room 404 Sheraton Hotel 678 Sunrise Ave Los Angelos, CA xxxxx 101 102 Hilton Hotel 234 Moonrise Ave Boston, MA 02116 404 203 Bob 101 102 Sheraton Hotel 678 Sunrise Ave Los Angelos, CA Envelope

  6. How to use TCP ports and IP addresses (2) When Alice sends a letter to Bob, what to put on the envelope? TCP Port IP address Bob Room 203 Sheraton Hotel 678 Sunrise Ave Los Angelos, CA Envelope

  7. How to use TCP ports and IP addresses (3) 404 Alice TCP Ports 101 102 Hilton Hotel 234 Moonrise Ave Boston, MA 02116 404 IP addresses 203 Bob 101 102 Sheraton Hotel 678 Sunrise Ave Los Angelos, CA

  8. How to use TCP ports and IP addresses (4) When Alice calls Bob, what number to dial? (310) 642-1111 Ext. 203 IP address TCP port number 404 Alice 404 203 Bob 101 102 101 102 Hilton Hotel 234 Moonrise Ave Boston, MA 02116 Sheraton Hotel 678 Sunrise Ave Los Angelos, CA (310) 642-1111

  9. How to use TCP ports and IP addresses (5) • What does a TCP port mean in computer world? • -- Multiple programs are running on a single computer • -- We assign a port number to eachprogram • -- Two types of programs: • -- Service-providing programs • -- Service-requesting programs • -- The first 1,024 ports are reserved for services IE browser program 1 1025 1124 IE program 2 80 Web server program 101 23 Telnet server program Receiver PC IP address: 130.126.2.45

  10. How to use TCP ports and IP addresses (6) When browser X sends a message to the Web server: 130.126.2.45 80 Message content IP address TCP port number The simplest packet 404 Browser Program X 1025 80 Web server program 101 102 101 102 Receiver computer IP address: 130.126.2.45 Sender computer IP address: 162.11.200.5

  11. (7) The simplest packet has a drawback! When browser X sends a message to the Web server: 130.126.2.45 80 Message content IP address TCP port number The simplest packet Drawback: there is NO return address!!! When the receiver sends back the acknowledgement, the receiver will cry – because … 80 Browser Program X Web server program 1025 101 102 Receiver computer IP address: 130.126.2.45 Sender computer IP address: 162.11.200.5

  12. A TCP connection Step 1: establish the connection Step 2: send the messages back and forth Step 3: terminate the connection A phone call session Step 1: Dial the phone number Step 2: do talking Step 3: hang up (8) How to establish a TCP connection between two ports?

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