What are the differences between UDP and TCP?

We often hear about UDP and TCP communication protocols. Both are used for transmitting data, and both operate on a server-client model. So, if these two communication protocols are used for data transmission, what are the differences that set them apart, and in which situations should we use each communication protocol?

2 / 2

Reliability

UDP sends data without a control mechanism. What does this mean? Unlike TCP, when we send data with TCP, we can receive a response to confirm whether the data has been delivered or not. However, UDP doesn’t work this way. UDP sends data without worrying about whether it reaches its destination or not. This is actually the reason we often hear the phrase, ‘TCP is more reliable.’ So, if TCP is more reliable and UDP doesn’t care if the data goes through, wouldn’t it be more logical to always use TCP?

Not necessarily. TCP constantly listens for a response after sending data, and if the data didn’t reach its destination correctly, it informs the client. However, this continuous checking can significantly slow down the process and reduce efficiency. This is where UDP makes more sense. UDP sends the data without waiting for a response, which makes it much more efficient. The risk here is that if the recipient is not listening or if the data sent is incorrect, UDP won’t notify the client. So, you need to think about the specific task at hand. Is it a situation where you need to know whether the sent data has reached its destination, or are you just streaming a video that needs to be shared?

Data Transmission Methods

UDP sends data without establishing a connection, while TCP uses a mechanism called HANDSHAKE to do so. UDP simply sends the data to a specific address and port, but TCP operates differently. For TCP to be able to transmit data (when two computers are communicating), there needs to be a mechanism called HANDSHAKE that connects the two computers.

The client first initiates a connection request to the server (SYN flag). The flag it sends includes a sequence number. The server responds to this request, and if it accepts the connection request, it sends an ACK flag back to the client along with its own sequence number using a SYN flag. The client then responds to this acknowledgment with an ACK flag, and at this point, the two computers are connected and ready for data transmission. This mechanism is entirely aimed at ensuring security in data transmission, and it is not present in UDP.

General Differences:

UDP uses a data type called a datagram, while TCP sends packets. In TCP, data is sent sequentially, while in UDP, data is not sent sequentially.