OSI Transport Layer

1. OSI Transport Layer Network Fundamentals – Chapter 4

2. Objectives • Explain the need for the Transport layer. • Identify the role of the Transport layer as it provides the end-to-end transfer of data between applications. • Describe the role of two TCP/IP Transport layer protocols: TCP and UDP. • Explain the key functions of the Transport layer, including reliability, port addressing, and segmentation. • Explain how TCP and UDP each handle key functions. • Identify when it is appropriate to use TCP or UDP and provide examples of applications that use each protocol.

3. Course Index • 4.1 Roles of the Transport Layer • 4.2 The TCP Protocol – Communicating with Reliability • 4.3 Managing TCP Sessions • 4.4 The UDP Protocol - Communicating with Low Overhead • 4.5 Lab Activities

4. 4.1 Roles of the Transport Layer

5. 4.1.1 Purpose of the Transport Layer • Tracking Individual Conversations • Segmenting Data • Reassembling Segments • Identifying the Applications

6. 4.1.2 Controlling the Conversations • The Primary function of Transport layer protocols • Segmentation and Reassembly • Conversation Multiplexing • Other function of Transport layer protocols • Connection-oriented conversations • Reliable delivery • Ordered data reconstruction • Flow control

7. 4.1.3 Supporting Reliable Communication

8. 4.1.4 TCP and UDP • TCP • Connection-oriented • Reliable delivery • Flow control • Applications that use TCP: • Web Browsers; E-mail • File Transfers • UDP • Simple • Connectionless • Low overhead • Best effort • Applications that use UDP: • Domain Name System (DNS); Video Streaming; Voice over IP (VoIP)

9. 4.1.5 Port Addressing • Used for Identifying the Conversations

10. 4.1.5 Port Addressing • Types of port numbers

11. 4.1.5 Port Addressing • netstat Command

12. 4.1.6 Segmentation and Reassembly • Ensures that data is transmitted within the limits of the media • Ensures that data from different applications can be multiplexed on to the media • TCP and UDP Handle Segmentation Differently

13. 4.2 The TCP Protocol – Communicating with Reliability

14. 4.2.1 TCP – Making Conversations Reliable • TCP segment

15. 4.2.2 TCP Server Process

16. 4.2.3 TCP Connection Establishment and Termination • Establishment of TCP sessions

17. 4.2.3 TCP Connection Establishment and Termination • Termination of TCP sessions

18. 4.3 Managing TCP Sessions

19. 4.3.1 TCP Segment Reassembly • Use the sequence number

20. 4.3.2 TCP Acknowledgement with Windowing • Use the acknowledgement number • It’s expectational acknowledgement

21. 4.3.3 TCP retransmission • TCP usually only acknowledges data for contiguous sequence bytes • Selective Acknowledgements is an optional feature

22. 4.3.4 TCP Congestion Control – Minimizing Segment Loss • Window size—flow and congestion control

23. 4.4 The UDP Protocol - Communicating with Low Overhead

24. 4.4.1 UDP – Low Overhead vs. Reliability • UDP • Provides the basic Transport layer functions • Lower overhead • It is not connection-oriented and does not provide the sophisticated retransmission, sequencing, and flow control mechanisms Application that use UDP include: Domain Name System (DNS) Simple Network Management Protocol (SNMP) Dynamic Host Configuration Protocol (DHCP) Routing Information Protocol (RIP) Trivial File Transfer Protocol (TFTP) Online games

25. 4.4.2 UDP Datagram Reassembly • UDP protocol reassembles PDUs in the order that it was received.

26. 4.4.3 & 4.4.4 UDP Processes • Also use port numbers to identify a specified application layer process and direct segments to the proper service or application

27. Summary