1. Skills: Concepts: layered protocols, transport layer functions, TCP and UDP protocols, isochronous applications This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License. The transport layer

2. Where does this topic fit? Internet concepts – Applications – Technology (communication) – Implications Internet skills – Application development – Content creation – User skills

3. TCP/IP from the outside Application Program, for example, a Web client Application Program, for Example, a Web server A TCP/IP network

4. The transport layer LayerFunction ApplicationDo useful work like Web browsing, email, and file transfer TransportTransport data between application programs running on two hosts InternetRoute packets between networks (inter network) Data linkSend data within the local area network PhysicalSpecify hardware characteristics and ways to differentiate between ones and zeros

5. A C B → A B C Key TCP functions Establish connections Slow transmission Check for errors Reorder packets Which program (port)? ftp, web, send email, read email, iTunes, … (Transmission control protocol)

6. Program 1 Program 2 Program n … TCP 11101 Which destination program (port)?

7. Key UDP functions Establish connections Which application (port)? ftp, web, send email, read email, iTunes, … (Transmission control protocol)

8. UDP sounds lame Web clients and servers use TCP. File transfer clients and servers use TCP. But Streaming video clients and servers use UDP. Internet telephony clients and servers use UDP. Why?

9. Isochronous applications

10. Summary A C B → A B C ftp, web, send email, read email, iTunes, …

11. Self study questions 1.We mentioned five key functions of TCP – what were they? 2.UDP only performs two of those functions, which ones? 3.What is the purpose of the port number in TCP header? 4.Would UDP also use port numbers? Explain your answer. 5.What is the purpose of the IP address in a TCP header? 6.Would UDP also use IP addresses? Explain your answer. 7.Would a video conferencing application use UDP or TCP for transport? Explain your answer. 8.We say that TCP makes connections. Making a connection is just two computers exchanging IP addresses and agreeing on which port numbers to use during their conversation. Explain that statement.