Class 32: TCP

Held Wednesday, April 19, 2000

Overview

Today we visit one of the preeminent transport-layer protocols: TCP.

Notes

• Upcoming events:
  • Thursday night's Africana studies conference
  • Cool talk on bias in standardized testing Thursday at 4:30.
• On Monday, April 24th at 7 p.m. in South Lounge, Katie Koestner, a nationally recognized, outspoken survivor of college date rape and sexual assault prevention specialist, will present a program for students and community members.
• After class, we'll go over assignment 6.
• Are there questions on:
  • Assignment 7 (due Friday)
  • Assignment 8 (due Monday)
• New assignment (due Friday):
  • Assignment 9B

Contents

• Homework 9A
• TCP
• Setting Up TCP Connections

Summary

Homework 9A

I understand that a number of you had some problems with the assignment for today, so we'll spend some time going over it. I'll start and end with questions for you:

Start: What is a protocol?

End: Why do you think the book asked these questions?

TCP

• Transmission Control Protocol
• Connection-oriented reliable byte streams
• Alternatives?
  • Message streams
  • Unreliable
  • Connectionless
• Standard Unix interface: sockets
  • Hence, a lot like any other file descriptor
  • Potentially one of the main design issues
• First design issues: How do you form connections?
• Second design issues: How do you delete connections?
• Third design issue: How to turn bytes into packets?
• I'm sick of headers, so we won't discuss the TCP header format.

Setting Up TCP Connections

• Lots of handshaking described in the diagram.
• Nonuniform: Designated server and client.
• The server sits there, listening for connections.
  • How does it know to do so? The application tells it to.
• Eventually the client connects using a SYN message.
  • How does it know to do so? The application tells it to.
• The server acknowledges the SYN message and sends its own.
• Eventually, the client acknowledges the SYN message and both can start sending data.
• What happens if packets are lost?