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The transport layer 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.
Where does this topic fit? • Internet concepts • Applications • Technology (communication) • Implications • Internet skills • Application development • Content creation • User skills
TCP/IP from the outside Application Program, for example, a Web client Application Program, for Example, a Web server A TCP/IP network
Key TCP functions Establish connections Check for errors A C B → A B C Reorder packets Slow transmission Which program (port)? ftp, web, send email, read email, iTunes, … (Transmission control protocol)
Which destination program (port)? Program 1 11101 Program 2 TCP … Program n
Key UDP functions Establish connections Which application (port)? ftp, web, send email, read email, iTunes, … (Transmission control protocol)
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?
Summary A C B → A B C ftp, web, send email, read email, iTunes, …
Self study questions We mentioned five key functions of TCP – what were they? UDP only performs two of those functions, which ones? What is the purpose of the port number in TCP header? Would UDP also use port numbers? Explain your answer. What is the purpose of the IP address in a TCP header? Would UDP also use IP addresses? Explain your answer. Would a video conferencing application use UDP or TCP for transport? Explain your answer. 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.