Understanding the Transport Layer: A Beginner’s Guide

The transport layer ensures data moves accurately between sending and receiving computers and connected devices. 

Computers and the internet help billions of people daily. When you use your devices, you rely on a complex system that makes things seem simple. Thanks to transport layers, reliable end-to-end data transportation happens over wired and wireless networks. Continue reading to learn more about transport layers and gain a deeper understanding of the transport level in computer systems to help you succeed in a computing career. 

What transport layers do

Transport layers work with other layers of complex computer systems to transmit data. Understanding the basics of computer networking requires knowledge of each layer in different models, including the open systems interconnection (OSI) model and the transmission control protocol/internet protocol (TCP/IP) model.

In both models, the transport layer services the sender and the receiver. It receives data from the sender’s application layer and readies it for delivery to the network layer. Vice versa, the transport layer reassembles the delivered data from the network layer and sends it to the recipient’s application layer. 

For example, when you navigate to www.coursera.org, you want to see the website on your device's browser. For instance, it would be strange and unexpected if your computer displayed a binary DNS response. The transport layer ensures you get where you intend to be, which in this case is HTML-formatted data in the shape of a website. The transport layer delivers your request to the web server and returns the web page to your browser (often instantaneously). 

Succinctly summarized, transport layers provide delivery services, flow, and traffic control, and data integrity support in both models. Explore these functions in more detail after placing the transport layer in each primary communication system model.

Read more: What Is Computer Science? Meaning, Jobs, and Degrees

The transport layer in the OSI model

The transport layer comes fourth in the seven-layer OSI model. As the conduit between the application and network layer, the transport layer handles end-to-end delivery of messages.

The transport layer in the TCP/IP model

You’ll find the transport layer first or second from the top in the four-layer TCP/IP model or within the process layer or host-to-host layer. The layer it uses depends on whether or not you're using a connectionless user data protocol (UDP) transport layer protocol. 

The TCP/IP model provides a simplified view of the OSI model. TCP/IP works to transfer data from one device to another. Each TCP/IP stack layer serves a specific purpose, with the transport layer playing a pivotal role in ensuring that accurate, reliable data flows from the sender to the recipient. 

Services that transport layers provide

The transport layer establishes, uses, and terminates the connection between sender and receiver applications and networks. Its protocols support smooth, reliable end-to-end communication through several essential services.

Delivery

Put simply, when you get an email from a friend or coworker, that data has to go through the transport layer to get to you. Your friend writes the email on their application, and it goes through the transport layer to get out to the network and reach you. The transport layer segments the data. 

You might have heard of data packets, the smaller components of overall communication. The transport layer makes those packets. It also adds source and destination data to help the data go where it needs to be. If something happens, it will re-transmit that data until a successful transmission is acknowledged.

Data integrity 

Transport-level protocols ensure data packets arrive accurately and in order. This layer accepts the packet data from the sender and reassembles it for the recipient. It performs sequencing, exchanges data receipt acknowledgments, and retransmits any missing data packets.

Flow control

The individual devices in a network connection can’t know each other’s capabilities for data throughput. As a result, the transport layer takes on that responsibility. It can send data faster if the receiving device proves capable or slow the data flow if needed. By controlling the flow, the transport layer helps avoid network performance issues and manages data flow to work for both ends of the network connection.

Traffic control

As with flow control, the transport layer also tackles traffic control to avoid network congestion. With digital communications subject to bandwidth and processing speed restrictions, the transport layer identifies potential overloads and reduces flow rates accordingly. 

Multiplexing

In the TCP/IP model, the transport layer also performs multiplexing duties. Imagine filling out a web form and sending emails on the same desktop. The computer must handle multiple communications simultaneously, a process known as multiplexing. It can accomplish this because of the transport layer’s work.

What professions use transport layers? 

Knowing data and network communication, particularly the transport layer, can set you up for success in several professions, including computer programming, computer network architecture, and software development. Discover more about three such job titles, including average salary and how to start.

Website developer

Average annual salary in the US: $65,768 [1] 

Job outlook (projected growth from 2023 to 2033): 8 percent [2]

As a web developer, you will help design and create websites. You may also help maintain existing sites or work with clients to add updates and functionality. In this role, you’ll work in a team and seek feedback from different departments to prototype and design an optimized website to help your company meet its goals. 

Computer network architect

Average annual salary in the US: $112,238 [3]

Job outlook (projected growth from 2023 to 2033): 13 percent [4]

As a computer network architect, you’ll use your expertise to establish the IT infrastructure and ensure efficient, effective, and secure network communications. Demand for computer network architects continues to grow.

Software developer

Average annual salary in the US: $102,344 [5]

Job outlook (projected growth from 2023 to 2033): 17 percent [6]

Understanding the transport layer can help your work as a software developer. In this role, you’ll work to build, test, and deploy the specific applications your clients desire. 

Read more: 5 Entry-Level Programming Jobs + How to Get One

Continue learning about computer systems on Coursera.

The transport layer helps facilitate communication between processes, such as sending an email and ensuring the data reaches its intended destination. When using a web browser, the transport layer responds to the request to deliver access. Understanding the transport layer can help, but you’ll learn much more about networking, operating systems, and programming. 

For example, you might begin with an Information Technology (IT) and Cloud Fundamentals Specialization offered by IBM on Coursera. You can also try Google’s Connect and Protect: Networks and Network Security as part of the Google Cybersecurity Professional Certificate.