Tcp how does it work

Cloud-native visibility, detection, and response for the hybrid enterprise. Find white papers, reports, datasheets, and more by exploring our full resource archive. Even if you haven't heard of TCP, you've heard of what runs on it, including the world wide web, e-mail, and peer-to-peer file sharing, among others.

While TCP is used to connect network devices to the internet, it can also be used as a communication protocol for a private intranet or extranet. The following flags are either set or not set for these actions:. Window size 16 bits : This field specifies the number of bytes that the sender is willing to receive.

Checksum 16 bits : The Transmission Control Protocol can reliably detect transmission errors. The checksum calculated from the header, the payload data and the pseudo-header is used for this purpose.

Urgent pointer 16 bits : The urgent pointer indicates the position of the first byte after the payload data that is to be processed urgently. As a result, this field is only valid and relevant if the URG flag is set. The length of the options must always be a multiple of 32, otherwise zero-bit padding is required. Even before the first data is transmitted, the sender and receiver typically agree on the maximum size of the TCP segments to be sent MSS.

By default, up to 1, bytes per segment are possible, with at least 20 bytes for the TCP header and a further 20 bytes for the IP header, leaving 1, bytes for payload data.

In order to protect your privacy, the video will not load until you click on it. With the maximum segment size minus the headers, a TCP packet can only transmit 1. Segmentation is used to exchange web content like images, which are sometimes several hundred kilobytes in size, via the TCP protocol. In this case, the application data is divided into several blocks of data before transport, numbered and then sent in random sequence.

Since the receiver must acknowledge the receipt of each segment and can reconstruct the actual sequence based on the sequence numbers, the receiver can easily completely reassemble the received payload data after the TCP transmission. If the sender does not receive acknowledgment for a transmitted segment, the retransmission timeout RTO technique is used. If this timer expires after a packet is sent before a response is transmitted, the packet is automatically retransmitted.

The duration of the timer is dynamically adjusted by an algorithm and depends on the individual transmission speed. The TCP protocol has shaped the history and development of computer networks for nearly a half a century.

The most important features can be summarized as follows:. But the topic also has its drawbacks: what else are IP addresses used for, besides websites and emails? Protocols control communication on the Internet. Doors have to be opened so that packages of data can get into systems and come out of them. These ports are an important aspect of the Internet.

There are over 65, possible UDP and TCP ports, which are broken down into well-known ports, registered ports, and dynamic ports. Which ports are important? Slow start, described in RFC forces TCP senders to set a congestion window variable limiting the amount of data a sender can push into the network before receiving an acknowledgement from a receiver. Slow start also prescribes an algorithm for senders to carefully probe the network to see how much data they should be sending. At the beginning of a new network connection, there is no way for a sender to know the available bandwidth of the network.

After an acknowledgement is received, the sender can transmit eight TCP segments. This pattern continues so that for every acknowledged packet, two new packets can be sent, up to the receive window limit specified by the receiver. From this, we can derive a new rule for TCP senders: the maximum amount of data that is unacknowledged is the minimum of the receive window and the congestion window.

After each successful roundtrip, the congestion window is doubled. The TCP protocol can only ever estimate the bandwidth available in the underlying network, and must use packet loss and the congestion window variables to regulate packet flow. If packet loss occurs, the TCP congestion avoidance algorithm starts.

Congestion avoidance is designed with the assumption that packet loss is an indicator of an overloaded network, and the solution is to limit the amount of data sent by resetting the congestion window variable that senders use to regulate data flow. Once the congestion window is reset, congestion avoidance specifies its own algorithms for how to grow the window to minimize further loss.

At a certain point, another packet loss event will occur, and the process will repeat once over. When packet loss does occur, TCP undergoes a congestion detection phase, followed by a congestion avoidance phase.

In the congestion detection phase, the congestion window is reduced, and in the congestion avoidance phase the congestion window is slowly increased. The original TCP algorithm specified a multiplicative decrease , halving the size of the congestion window when congestion is detected, followed by an additive increase , that slowly increases the size of the congestion window by one each round trip.

The following figure, from ResearchGate , shows the varying size of the congestion window in response to packet loss and the multiplicative decrease, additive increase algorithm. The congestion detection and avoidance algorithm is a key feature of TCP, and its implementation has a large effect on network performance. In many cases, this algorithm is too conservative, and new algorithms have been developed up to 13 at this point. Congestion detection and avoidance are still an area of ongoing research.

TCP is a wonderful thing. It completes a difficult task in a way that is completely transparent to the application. And even though it is complex, the core principles can be easily explained. In particular, the TCP protocol can be distilled down to a few items:. There are a lot of details in each individual item, but the essence of the protocol remains simple.

TCP has a long history, and because it is a cornerstone of the internet, it is an area of continued interest and research, culminating in many RFCs and a few good books:. TCP also sends and receives packets from the network layer, handles the transmission of any dropped packets, manages flow control, and ensures all packets reach their destination. A good example of how this works in practice is when an email is sent using SMTP from an email server. To start the process, the TCP layer in the server divides the message into packets, numbers them, and forwards them to the IP layer, which then transports each packet to the destination email server.

Both the device and server must synchronize and acknowledge packets before communication begins, then they can negotiate, separate, and transfer TCP socket connections. The model represents how data is exchanged and organized over networks. It is split into four layers, which set the standards for data exchange and represent how data is handled and packaged when being delivered between applications, devices, and servers. For this reason, it is vital to avoid using public Wi-Fi networks for sending private data and to ensure information is encrypted.

Finding a public IP address is a simple process that can be discovered using various online tools. Fortinet's high-performance, scalable crypto VPNs protect organizations and their users from advanced cyberattacks, such as man-in-the-middle MITM attacks, and the threat of data loss while data is in motion at high speed.

They establish secure connections by encrypting the data being transmitted between applications and devices. It is designed to break down a message, such as an email, into packets of data to ensure the message reaches its destination successfully and as quickly as possible. TCP meaning Transmission Control Protocol, is a communications standard for delivering data and messages through networks.

TCP is a basic standard that defines the rules of the internet and is a common protocol used to deliver data in digital network communications. TCP is a protocol or standard used to ensure data is successfully delivered from one application or device to another. Department of Defense to support the construction of the internet. UDP is an alternative to TCP that does not provide error correction, is less reliable, and has less overhead, which makes it ideal for streaming.