The key difference between TCP and UDP is that TCP provides a wide variety of services to applications, whereas UDP does not. For example, routers discard packets for many reasons, including bit errors, congestion, and instances in which no correct routes are known. As you have read already, most data-link protocols notice errors (a process called error detection) but then discard frames that have errors. TCP provides retransmission (error recovery ) and helps to avoid congestion (flow control), whereas UDP does not. As a result, many application protocols choose to use TCP.
Each TCP/IP application typically chooses to use either TCP or UDP based on the application’s requirements. For example, TCP provides error recovery, but to do so, it consumes more bandwidth and uses more processing cycles. UDP does not perform error recovery, but it takes less bandwidth and uses fewer processing cycles. Regardless of which of these two TCP/IP transport layer protocols the application chooses to use, you should understand the basics of how each of these transport layer protocols works.
TCP relies on IP for end-to-end delivery of the data, including routing issues. In other words, TCP performs only part of the functions necessary to deliver the data between applications. Also, the role that it plays is directed toward providing services for the applications that sit at the endpoint computers. Regardless of whether two computers are on the same Ethernet, or are separated by the entire Internet, TCP performs its functions the same way.
Compare TCP and UDP Protocol
TCP/IP helps you to determine how a specific computer should be connected to the internet and how you can transmit data between them. It helps you to create a virtual network when multiple computer networks are connected. TCP/IP stands for Transmission Control Protocol/ Internet Protocol. It is specifically designed as a model to offer highly reliable and end-to-end byte stream over an unreliable internetwork.
UDP is a Datagram oriented protocol. It is used for broadcast and multicast type of network transmission. The full form of UDP is User Datagram Protocol (A datagram is a transfer unit associated with a packet-switched network.) The UDP protocol works almost similar to TCP, but it throws all the error-checking stuff out, all the back-and-forth communication and deliverability.
| TCP | UDP |
|---|---|
| It is a connection-oriented protocol. | It is a connectionless protocol. |
| TCP reads data as streams of bytes, and the message is transmitted to segment boundaries. | UDP messages contain packets that were sent one by one. It also checks for integrity at the arrival time. |
| TCP messages make their way across the internet from one computer to another. | It is not connection-based, so one program can send lots of packets to another. |
| TCP rearranges data packets in the specific order. | UDP protocol has no fixed order because all packets are independent of each other. |
| The speed for TCP is slower. | UDP is faster as error recovery is not attempted. |
| Header size is 20 bytes. | Header size is 8 bytes. |
| TCP is heavy-weight. TCP needs three packets to set up a socket connection before any user data can be sent. | UDP is lightweight. There are no tracking connections, ordering of messages, etc. |
| TCP does error checking and also makes error recovery. | UDP performs error checking, but it discards erroneous packets. |
| Acknowledgment segments. | No Acknowledgment segments. |
| Using handshake protocol like SYN, SYN-ACK, ACK. | No handshake (so connectionless protocol). |
| TCP is reliable as it guarantees delivery of data to the destination router. | The delivery of data to the destination can’t be guaranteed in UDP. |
| TCP offers extensive error checking mechanisms because it provides flow control and acknowledgment of data. | UDP has just a single error checking mechanism which is used for checksums. |
TCP Connection Establishment and Termination (3 Way handshake)
TCP connection establishment occurs before any of the other TCP features can begin their work. Connection establishment refers to the process of initializing Sequence and Acknowledgment fields and agreeing on the port numbers used.
This three-way connection establishment flow (also called a three-way handshake) must complete before data transfer can begin. The connection exists between the two sockets, although the TCP header has no single socket field. Of the three parts of a socket, the IP addresses are implied based on the source and destination IP addresses in the IP header. TCP is implied because a TCP header is in use, as specified by the protocol field value in the IP header. Therefore, the only parts of the socket that need to be encoded in the TCP header are the port numbers.
TCP signals connection establishment using 2 bits inside the flag fields of the TCP header. Called th e SYN and ACK flags, these bits have a particularly interesting meaning. SYN means “synchronize the sequence numbers,” which is one necessary component in initialization for TCP.
This four-way termination sequence is straightforward and uses an additional flag, called the FIN bit. (FIN is short for “finished,” as you might guess.) One interesting note: Before the device on the right sends the third TCP segment in the sequence, it notifies the application that the connection is coming down. It then waits on an acknowledgment from the application before sending the third segment in the figure. Just in case the application takes some time to reply, the PC on the right sends the second flow in the figure, acknowledging that the other PC wants to take down the connection. Otherwise, the PC on the left might resend the first segment repeatedly.
TCP establishes and terminates connections between the endpoints, whereas UDP does not. Many protocols operate under these same concepts, so the terms connection-oriented and connectionless are used to refer to the general idea of each. More formally, these terms can be defined as follows:
- Connection-oriented protocol: A protocol that requires an exchange of messages before data transfer begins, or that has a required pre-established correlation between two endpoints.
- Connectionless protocol: A protocol that does not require an exchange of messages and that does not require a pre-established correlation between two endpoints.
