What is Transmission Control Protocol (TCP)?

by Jim Donnelly | February 18, 2022

The Transmission Control Protocol (TCP) is one of those things that pretty much everyone should know about – yet very few people actually do.

People should know more about it because Transmission Control Protocol is essentially the backbone of the modern-day internet.

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What is the Transmission Control Protocol

Also known as TCP/IP (Internet Protocol) or the Internet Protocol Suite, TCP is a widely-used protocol that governs how computers talk to each other when exchanging data. However, TCP’s sheer ubiquity, doesn’t mean it’s the only data transfer protocol out there.

Other standards – such as User Datagram Protocol (UDP) or Open Systems Interconnection (OSI) – are also used in various circumstances.   

But how does TCP work? And what’s it used for?

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How Does Transmission Control Protocol Work?

Being one the main data transfer protocols on the internet, TCP’s job is relatively simple:

It’s there to ensure all data sent by one computer to another is received successfully, without errors or glitches, and in the correct order.

That means whenever you browse a webpage with all the information right-side up, or an email that’s not complete gibberish, you can thank TCP.

On the other hand, how it accomplishes this task isn’t quite so rudimentary. Because it’s a connection-oriented protocol, TCP must first acknowledge the existence of a session between the two computers before doing any communicating.

Here’s how TCP establishes a connection between two computers (a process known as a “three-way handshake” ????):

1. One computer (the sender) makes an initial message to the receiving computer to formally request that a connection be established. This is known as a SYN message (short for synchronize).

2. The receiving computer must then send acknowledgement of the SYN (what is known as a SYN ACK message). 

3. Finally, the sender must then acknowledge the acknowledgement (known as an ACK RECEIVED message).

After these three steps have successfully completed, data transfer can begin. 

If you think that’s a lot of steps simply to establish a communication channel, you’re right. It’s one reason why TCP connections are generally slower than UDP-based connections. They simply have to go through more steps before communicating.

TCP can also be combined with other protocols such as Microsoft’s Server Message Block (SMB) for connections to remote servers

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The Four Layers of TCP

TCP is composed of four different layers: application, transport, internet, and network access. Let’s go through them:

1. Application layer. This is the layer of TCP that applications, such as web browsers, interact with (the application layer includes further protocols such as HTTPS and SMTP).

2. Transport layer. After the application receives the data from a web browser (for example), it then talks to the transport layer via a port. In a web browser’s case, this would be Port 80.

The transport layer then slices and dices the received data into individual packets, which each take the fastest route to the destination. Each packet also comes with a header with instructions around how to deliver the packet payload (ie. the data being sent).

3. Internet layer. Packets are next pushed to this layer, which uses the Internet Protocol to tag each packet with origin and destination IP addresses.

4. Network layer. Finally! This is the layer in which actual data is converted into electrical impulses and sent out into the world. The network layer handles information such as media access control (MAC) addresses, which ensures each packet goes to the right computer.

Read More: How to Upload Faster From a Browser (Send and Receive Large Files Quickly)

Why is TCP used?

It’s probably obvious by now, but TCP is used in instances when all transmitted data absolutely must arrive (and with no errors). Indeed, the inherent value of TCP is that it guarantees the integrity of all data delivered. If there’s an error, TCP resends the data.

That’s why other high-level protocols that require perfection – such as Secure Shell (SSH), File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), Internet Message Access Protocol (IMAP), and HTTP – all use TCP.

Some large file transfer solutions, such as MASV, also use accelerated TCP-based technology because it delivers all your data in order and doesn’t require firewall changes.

TCP vs. UDP

One issue with TCP is latency, especially through the public internet. This is largely due to all those steps I mentioned above, including data retransmittances and packet reordering.

That’s why a different protocol, UDP, exists. It is often used for real-time online gaming, streaming, voice over IP (VoIP), and other applications that require fast speeds but can live with some data being incomplete or missing.

However, UDP is not a connection-oriented protocol. Unlike TCP, it doesn’t establish a session between computers or guarantee the integrity of data delivered. So, dropped packets can be a common occurrence. Each data packet sent via UDP contains less header information, and if packets are lost in transit, they’re gone forever.

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Why MASV is TCP-based and Not UDP-Based

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Although some popular file transfer solutions such as Aspera, Signiant, and File Catalyst are UDP-based (either point-to-point using on-premises servers or over the cloud), many use TCP technology.

MASV uses TCP technology by choice, for several reasons. It allows our service to be much easier to set up and run, since no firewall changes are required. Our TCP-based transfers also guarantee file and folder trees arrive in exactly the same structure as they’re sent

Although TCP is slower than UDP, MASV gets around this by using an accelerated private network of more than 150 servers in all corners of the world. That means your file packages only need to travel a short distance before they start riding our accelerated network. And they always arrive at your client’s or partner’s machines exactly how they were sent.

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