Learning Objectives

After successfully completing this unit, you should be able to

  1. explain the principles of the transport layer.
  2. list and describe the services the transport layer provides to the upper layer.
  3. explain how the transport layer is related to the layers above and below in the Internet protocol stack.

Learning Tasks

Required:

  1. Watch the slideshow for this section.
  2. Study the following sections in the textbook:

3.1 Introduction and Transport Layer Services
3.2 Multiplexing and Demultiplexing 

Terms and Topics

Section 1 – Transport Layer Principles and Services

Transport-layer services
Logical communication between application layer processes
Segments
Relationship between transport layer and network layer
Internet as TCP/IP network
TCP (transport layer protocol)
TCP Connection-oriented
TCP reliable data transfer
TCP congestion control
UDP (user datagram protocol)
Connectionless
IP service as best-effort delivery service

IP service as unreliable service
Transport-layer multiplexing
Transport-layer demultiplexing
Transport-layer segment format
Source port number field
Destination port number field
Well-known port numbers
UDP sockets and TCP sockets
DNS runs on UDP
Popular Internet applications and their underlying transport protocols

Leading Questions

  1. What services does the transport layer provide?
  2. What principles are suggested for use in designing transport layer protocols?
  3. What is the relationship between the transport layer and the network layer?
  4. What are protocol data units (PDUs) called in TCP and UDP respectively?
  5. What is a best-effort delivery service?
  6. What are the multiplexing and demultiplexing applications?
  7. Why is the IP service model called best-effort delivery service?
  8. Why is IP also called an unreliable service?
  9. How does TCP provide reliable data transfer?
  10. What services do TCP provide?
  11. What is multiplexing and demultiplexing respectively?
  12. How are multiplexing and demultiplexing done in TCP?
  13. What are sockets? How are sockets related to ports?
  14. What are some well-known port numbers?
  15. What are connectionless multiplexing/demultiplexing and connection-oriented multiplexing/demultiplexing, respectively? What are the differences?
  16. How are Web servers and TCP related?