What is the relationship between tcp and udp packets

DIFFERENCE BETWEEN TCP AND UDP | NETSCOUT

what is the relationship between tcp and udp packets

TCP (Transmission Control Protocol) is connection oriented, whereas UDP (User Datagram Protocol) is connection-less. UDP does not use acknowledgments at all, and is usually used for protocols where a few lost datagrams do not matter. Because of acknowledgments, TCP is considered a. Apr 22, What is the difference between TCP and UDP? TCP is a connection orientated protocol with built in error recovery and re Because there is no connection setup, UDP is faster than TCP and results in less network traffic. Connection-orientation means that the communicating devices should establish a Retransmission of lost packets is possible in TCP, but not in UDP. There is.

Consider a telnet connection to an interactive editor that reacts on every keystroke. Later, when the editor has read the byte, TCP sends a window update, moving the window 1 byte to the right.

This packet is also 40 bytes. Finally, when the editor has processed the character, it echoes the character as a byte packet. In all, bytes of bandwidth are used and four segments are sent for each character typed.

What’s the Difference Between TCP and UDP?

When bandwidth is scarce, this method of doing business is not desirable. One approach that many TCP implementations use to optimize this situation is to delay acknowledgments and window updates for msec in the hope of acquiring some data on which to hitch a free ride. Assuming the editor echoes within msec, only one byte packet now need be sent back to the remote user, cutting the packet count and bandwidth usage in half.

what is the relationship between tcp and udp packets

Although this rule reduces the load placed on the network by the receiver, the sender is still operating inefficiently by sending byte packets containing 1 byte of data. A way to reduce this usage is known as Nagle's algorithm Nagle, What Nagle suggested is simple: Then send all the buffered characters in one TCP segment and start buffering again until they are all acknowledged.

If the user is typing quickly and the network is slow, a substantial number of characters may go in each segment, greatly reducing the bandwidth used. The algorithm additionally allows a new packet to be sent if enough data have trickled in to fill half the window or a maximum segment. Nagle's algorithm is widely used by TCP implementations, but there are times when it is better to disable it.

In particular, when an X Windows application is being run over the Internet, mouse movements have to be sent to the remote computer. Gathering them up to send in bursts makes the mouse cursor move erratically, which makes for unhappy users. Another problem that can degrade TCP performance is the silly window syndrome. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads data 1 byte at a time.

To see the problem, look at the figure below.

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Initially, the TCP buffer on the receiving side is full and the sender knows this i. Then the interactive application reads one character from the TCP stream. This action makes the receiving TCP happy, so it sends a window update to the sender saying that it is all right to send 1 byte. The sender obliges and sends 1 byte. The buffer is now full, so the receiver acknowledges the 1-byte segment but sets the window to 0. This behavior can go on forever. Clark's solution is to prevent the receiver from sending a window update for 1 byte.

Instead it is forced to wait until it has a decent amount of space available and advertise that instead. Specifically, the receiver should not send a window update until it can handle the maximum segment size it advertised when the connection was established or until its buffer is half empty, whichever is smaller. Furthermore, the sender can also help by not sending tiny segments. Instead, it should try to wait until it has accumulated enough space in the window to send a full segment or at least one containing half of the receiver's buffer size which it must estimate from the pattern of window updates it has received in the past.

Nagle's algorithm and Clark's solution to the silly window syndrome are complementary. Nagle was trying to solve the problem caused by the sending application delivering data to TCP a byte at a time. Clark was trying to solve the problem of the receiving application sucking the data up from TCP a byte at a time.

Both solutions are valid and can work together. The goal is for the sender not to send small segments and the receiver not to ask for them.

The receiving TCP can go further in improving performance than just doing window updates in large units. Like the sending TCP, it can also buffer data, so it can block a READ request from the application until it has a large chunk of data to provide. Doing this reduces the number of calls to TCP, and hence the overhead. Of course, it also increases the response time, but for noninteractive applications like file transfer, efficiency may be more important than response time to individual requests.

Another receiver issue is what to do with out-of-order segments. They can be kept or discarded, at the receiver's discretion. Of course, acknowledgments can be sent only when all the data up to the byte acknowledged have been received.

If the receiver gets segments 0, 1, 2, 4, 5, 6, and 7, it can acknowledge everything up to and including the last byte in segment 2. When the sender times out, it then retransmits segment 3. If the receiver has buffered segments 4 through 7, upon receipt of segment 3 it can acknowledge all bytes up to the end of segment 7. Connection Establishment and Termination[ edit ] Establishing a Connection A connection can be established between two machines only if a connection between the two sockets does not exist, both machines agree to the connection, and both machines have adequate TCP resources to service the connection.

If any of these conditions are not met, the connection cannot be made. The acceptance of connections can be triggered by an application or a system administration routine. When a connection is established, it is given certain properties that are valid until the connection is closed. Typically, these will be a precedence value and a security value. These settings are agreed upon by the two applications when the connection is in the process of being established. In most cases, a connection is expected by two applications, so they issue either active or passive open requests.

Figure below shows a flow diagram for a TCP open. The segment that is constructed will have the SYN flag set on set to 1 and will have a sequence number assigned. Any number could have been chosen. Machine B will also set an Initial Send Sequence number of its own.

Upon receipt, Machine A sends back its own acknowledgment message with the sequence number set to This is ACK in the diagram. Then, having opened and acknowledged the connection, Machine A and Machine B both send connection open messages through the ULP to the requesting applications.

TCP vs UDP -What’s The Difference?

It is not necessary for the remote machine to have a passive open instruction, as mentioned earlier. In this case, the sending machine provides both the sending and receiving socket numbers, as well as precedence, security, and timeout values.

It is common for two applications to request an active open at the same time. This is resolved quite easily, although it does involve a little more network traffic. Data Transfer Transferring information is straightforward, as shown in Figure below. After Machine B receives the message, it acknowledges it with a segment acknowledgment that increments the next sequence number and hence indicates that it received everything up to that sequence number. Figure shows the transfer of only one segment of information - one each way.

The TCP data transport service actually embodies six different subservices: Enables both ends of a connection to transmit at any time, even simultaneously. The use of timers ensures that data is transmitted within a reasonable amount of time. Data sent from one application will be received in the same order at the other end. This occurs despite the fact that the datagrams may be received out of order through IP, as TCP reassembles the message in the correct order before passing it up to the higher layers.

All connections have an agreed-upon precedence and security value. TCP can regulate the flow of information through the use of buffers and window limits. Checksums ensure that data is free of errors within the checksum algorithm's limits. This is shown in Figure 8.

Machine B will then send back an acknowledgment of the request and its next sequence number. Following this, Machine B sends the close message through its ULP to the application and waits for the application to acknowledge the closure. This step is not strictly necessary; TCP can close the connection without the application's approval, but a well-behaved system would inform the application of the change in state.

Finally, Machine A acknowledges the closure and the connection is terminated. An abrupt termination of a connection can happen when one side shuts down the socket. This can be done without any notice to the other machine and without regard to any information in transit between the two.

Aside from sudden shutdowns caused by malfunctions or power outages, abrupt termination can be initiated by a user, an application, or a system monitoring routine that judges the connection worthy of termination. The other end of the connection may not realise an abrupt termination has occurred until it attempts to send a message and the timer expires. To keep track of all the connections, TCP uses a connection table.

Each existing connection has an entry in the table that shows information about the end-to-end connection. The layout of the TCP connection table is shown below- The meaning of each column is as follows: The state of the connection closed, closing, listening, waiting, and so on.

The IP address for the connection. When in a listening state, this will set to 0. The local port number.

  • Communication Networks/TCP and UDP Protocols

The remote's IP address. The port number of the remote connection. But, how does it know when to retransmit the packet already transmitted. It is true that the receiver does acknowledges the received packets with the next expected sequence number.

But what if sender does not receive any ACK. Consider the following two scenarios: In this case the receiver does transmit the cumulative ACK, but this frame gets lost somewhere in the middle. Sender normally waits for this cumulative ACK before flushing the sent packets from its buffer. But for that it has to develop some mechanism by which the sender can take some action if the ACK is not received for too long time.

The mechanism used for this purpose here is the timer. The TCP sets a timer as soon as it transfers the packet. But from where this time-out interval is chosen. Well we will be seeing the procedure to find out this shortly.

In this case the receiver sends the ACK more than one time to the sender for the same packet received. But, ever guessed how can this happen.

9 Difference between TCP and UDP Protocol - Java Network Interview Question

Well, such things may happen due to network problem sometimes, but if receiver does receive ACK more than times there is some sort of meaning attached to this problem. All this problem starts from the receiver side. Receiver keeps on sending ACK to the received frames. In Transmission control protocol, data is sent as a byte stream, and no distinguishing indications are transmitted to signal message segment boundaries. On UDP, Packets are sent individually and are checked for integrity only if they arrived.

Packets have definite boundaries which are honored upon receipt, meaning a read operation at the receiver socket will yield an entire message as it was originally sent. Though TCP will also deliver the complete message after assembling all bytes. Messages are stored on TCP buffers before sending to make optimum use of network bandwidth.

what is the relationship between tcp and udp packets

This cost TCP in terms of speed, that's why UDP is more suitable where speed is a concern, for example, online video streaming, telecast or online multiplayer games. Simple mantra of UDP to deliver a message without bearing any overhead of creating connection and guaranteeing delivery or order guarantee keeps it light weight. This is also reflected in their header sizes, which is used to carry metadata.

Usual header size of a TCP packet is 20 bytes which are more than double of 8 bytes, header size of UDP datagram packet. TCP requires three packets to set up a socket connection before any user data can be sent. TCP handles reliability and congestion control.

On the other hand, UDP does not have an option for flow control. Since TCP provides delivery and sequencing guaranty, it is best suited for applications that require high reliability, and transmission time is relatively less critical. While UDP is more suitable for applications that need fast, efficient transmission, such as games.

UDP's stateless nature is also useful for servers that answer small queries from huge numbers of clients. In practice, TCP is used in finance domain e. In fact, most of the common protocol you are familiar of e. Always remember to mention that TCP is connection oriented, reliable, slow, provides guaranteed delivery and preserves the order of messages, while UDP is connectionless, unreliable, no ordering guarantee, but a fast protocol.

It's worth mentioning that header size of Transmission control protocol is 20 bytes, compared to 8 bytes header of User Datagram protocol. Use TCP, if you can't afford to lose any message, while UDP is better for high-speed data transmission, where loss of a single packet is acceptable e.