Unit 4: The Transport Layer (TCP/UDP)
When we talk about networks, we are talking about data transport. The TCP/IP stack provides a TCP/UDP layer that handles the data transport between machines across networks. In this unit, you will learn the TCP and UDP protocols by examining the structure of TCP and UDP segments and identifying how this layer serves as the application layer in the TCP/IP stack.
Each application relies on the transport layer that is described in this unit. It is a key layer in today's networks as it contains all the mechanisms necessary to provide reliable delivery of data over an unreliable network. First, we will develop a simple reliable transport layer protocol. Then, your textbook links you through the details of the TCP and UDP protocols used in TCP/IP networks. We will also study Stream Control Transmission Protocol (SCTP) and Real-Time Transport Protocol (RTP), which are not covered by the textbook. These protocols are the fundamental protocols for modern multimedia applications over the Internet.
Completing this unit should take you approximately 6 hours.
Upon successful completion of this unit, you will be able to:
- describe the use of the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) to transfer data segments;
- explain the use of the TCP and UDP header fields;
- explain the transport layer port addressing scheme and port address assignments;
- describe the Stream Control Transmission Protocol (SCTP) and Real-time Transport Protocol (RTP) and the applications based on these protocols;
- explain the mechanics of a TCP connection establishment (3-way handshake) and release;
- illustrate the TCP transmission policy and window management; and
- illustrate congestion control protocols used by TCP such as Slow Start, Fast Retransmit, Fast Recovery.
4.1: The Transport Layer
This section discusses the transport protocol in perfect and imperfect network service environments in terms of interactions with the Service Data Unit (SDU) at various stages of the transmission between sending and receiving nodes. What happens to your transmission when the environment is perfect? If your data gets corrupted by transmission errors, lost, reordered, or duplicated, then what happens? Explore the links in your textbook for a better understanding of what goes wrong in cyberspace and the mechanisms used to repair impacted activity.
4.2: User Datagram Protocol (UDP)
The UDP allows several applications running on a host to exchange SDUs with several other applications running on remote hosts. This section explores the checksum process and how the UDP accomplishes this multiprocessing.
4.3: Transmission Control Protocol (TCP)
Almost every Internet application relies on the TCP in the transport layer. In this section you will discover how your favorite Internet activity exchanges data around the world. Then in the following subunits, you can travel with your data as it streams to its destination and back.
4.3.1: TCP Connection Establishment
As you read this section, be able to describe the three-way handshake used by TCP to establish a connection.
4.3.2: TCP Connection Release
As you read this section, make sure you are able to identify and explain the two types of connection release.
4.3.3: TCP: A Reliable Data Transport Mechanism
4.3.3.1: TCP Segment Transmission Strategies
This section of your textbook presents the Nagle Algorithm. What is it, and what two strategies does it provide for data transmission?
4.3.3.2: TCP Windows
As you read this section, consider the following questions: What is a TCP window according to the information provided in this section of your textbook? How does a TCP window improve processing in the transport layer?
4.3.3.3: TCP Retransmission Timeout
Follow the path in this section of your textbook to see how the TCP retransmission timeout improves transport performance.
4.3.3.4: Advanced Retransmission Strategies
As you read this section, consider the following questions: What is the exponential back off and how does TCP use it? What is the delayed acknowledgement strategy in TCP? What is the fast retransmit heuristic as utilized by TCP? What is the SACK option?
4.3.3.5: TCP Congestion Control
TCP's congestion control is one of its best performance control features. This section explains this feature and how it improves performance in the transport layer.
Read this tutorial to understand congestion management at different levels: end-to-end, router assisted, and pricing based.
4.4: Stream Control Transmission Protocol (SCTP)
Read this article, which explains why we need the new SCTP protocol and how it works.
4.5: Real Time Transport Protocol (RTP)
Read this webpage to understand how RTP is used for streaming multimedia data. As you read, pay special attention to how RTP protocol is different from TCP protocols and how it is used for multimedia data transport.
4.6: Summary
Read this summary of Chapter 4. The transport layer relies on TCP mechanisms to recover from the errors of the network layer. The chapter 4 summary reviews the strategies at each stage of the transmission.
4.7: Practice Exercises
Read through the practice exercises on pages 113–126. These exercises further expand the key principles in this chapter. If you are a computer professional, you will enjoy the challenges and higher-level discussions in this section. If you are a novice, explore the presentations and spend more time on the topics that are meaningful to you.
Unit 4 Assessment
- Receive a grade
Take this assessment to see how well you understood this unit.
- This assessment does not count towards your grade. It is just for practice!
- You will see the correct answers when you submit your answers. Use this to help you study for the final exam!
- You can take this assessment as many times as you want, whenever you want.