Understanding the Transport Layer: A Beginner’s Guide

Key takeaways

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

• A web developer, who works with the transport layer, makes an annual median total pay of $84,000 [1].

• The transport layer uses multiple internet protocols, including transmission control protocol (TCP) and user datagram protocol (UDP), each of which provides different services.

• You can gain in-demand skills in IT, software development, and programming to understand how the transport layer communicates between users. 

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. Start building in-demand IT and networking skills today with the Google IT Support Professional Certificate. In as little as three months, you’ll gain the skills for an entry-level role in IT. 

What transport layers do: Transport layer protocols

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. 

What is TCP and UDP in transport layer?

TCP and UDP are the two internet protocols that occur in the transport layer. Each protocol provides different services in the transport layer depending on the requirements of the application. Depending on the application's needs, you may want to use the more reliable, but slower TCP connection or the faster, but less reliable UDP connection. Each protocol has its own use cases. TCP is well-suited for the reliability required in the file-transfer protocol (FTP), while UDP is better suited for the needs of video and audio streaming, where packet loss is more tolerable.

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.

All salary information represents the median total pay from Glassdoor as of December 2025. These figures include both base salary and additional pay, which may represent profit-sharing, commissions, bonuses, or other forms of compensation.

Website developer

Median annual total pay (Glassdoor): $84,000 [1] 

Job outlook (projected growth from 2024 to 2034): 7 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

Median annual total pay (Glassdoor): $151,000 [3]

Job outlook (projected growth from 2024 to 2034): 12 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

Median annual total pay (Glassdoor): $121,000 [5]

Job outlook (projected growth from 2024 to 2034): 15 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. 

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