Transmission Control Protocol (TCP) is a critical protocol that enables communication between computers over a network.
In TCP, data is divided into packets and sent over the network to the receiver.
In this post, we'll explore two TCP flags, PSH and URG, that are used to indicate different types of data.
TCP is a connection-oriented protocol that ensures reliable communication between two devices. In TCP, packets are sent from the sender to the receiver, and the receiver sends an acknowledgement to the sender for each packet received. This process ensures that all packets are received in the correct order, and any lost packets are retransmitted.
TCP uses flags to provide additional information about the packets being sent. There are six flags in TCP, including PSH and URG, which we will discuss in this article.
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TCP Overview
TCP is a reliable, connection-oriented protocol that provides several features, including flow control, congestion control, and error detection. In TCP, data is divided into packets and sent over the network to the receiver.
Each packet contains a header and payload.
The TCP header contains several fields, including the source and destination ports, sequence and acknowledgement numbers, and flags. The payload contains the data being sent.
TCP Flags
TCP uses six flags to indicate different types of packets. These flags are as follows:
- URG – Indicates that the Urgent Pointer field is valid.
- ACK – Indicates that the Acknowledgement Number field is valid.
- PSH – Indicates that the receiver should push the data to the application layer as soon as it is received.
- RST – Indicates that the connection should be reset.
- SYN – Indicates that a connection should be established.
- FIN – Indicates that a connection should be terminated.
In this article, we will focus on the PSH and URG flags.
PSH Flag
The PSH flag indicates that the receiver should push the data to the application layer as soon as it is received, without waiting for more data to arrive. This flag is often used in real-time applications, such as voice and video streaming, where a delay in data transmission can result in poor user experience.
When the PSH flag is set, the receiver pushes the data to the application layer as soon as it is received, even if the buffer is not full. This reduces the latency and ensures that the data is delivered as quickly as possible.
URG Flag
The URG flag indicates that the Urgent Pointer field is valid. The Urgent Pointer field is used to identify a portion of the data that requires immediate attention.
When the URG flag is set, the receiver knows that it should process the urgent data first, before processing the rest of the data. This is useful in situations where certain data requires immediate attention, such as control signals or error messages.
Differences between PSH and URG Flags
The main difference between the PSH and URG flags is the type of data they indicate. The PSH flag indicates that the data should be pushed to the application layer as soon as it is received, while the URG flag indicates that certain data requires immediate attention.
Another difference is the urgency of the data. Data with the PSH flag set is important but not urgent, while data with the URG flag set requires immediate attention.
Use Cases of PSH and URG Flags
The PSH and URG flags are used in different scenarios. The PSH flag is often used in real-time applications, such as voice and video streaming, where a delay in data transmission can result in poor user experience.
The PSH flag ensures that the data is delivered to the application layer as quickly as possible, reducing the latency.
The URG flag is used when certain data requires immediate attention. This is useful in situations where control signals or error messages need to be processed immediately.
For example, when a user enters a URL in a web browser, the browser sends a request to the server using the TCP protocol. The request is divided into packets, and the URG flag is set in the packet that contains the HTTP GET request. This indicates that the HTTP GET request requires immediate attention.
Conclusion
In conclusion, the PSH and URG flags are important TCP flags that indicate different types of data. The PSH flag indicates that the data should be pushed to the application layer as soon as it is received, while the URG flag indicates that certain data requires immediate attention. Both flags are useful in different scenarios, and their proper use can improve the performance of applications that use TCP.
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