UDP (User Datagram Protocol) is a simple OSI transport layer protocol for client/server network applications based on Internet Protocol (IP). UDP is the main alternative toTCP and one of the oldest network protocols in existence, introduced in 1980.
UDP is often used in videoconferencing applications or computer games specially tuned for real-time performance. To achieve higher performance, the protocol allows individual packets to be dropped (with no retries) and UDP packets to be received in a different order than they were sent as dictated by the application.
THE USER DATAGRAM PROTOCOL (UDP):
TCP/IP contains two transport protocols:
• UDP
• TCP
UDP:
UDP is less complex
and easier to unders tand. It does not provide the type of
service a typical application expects.
CHARACTERISTICS OF UDP:
UDP has the following characteristics.
• It is an
end-to-end protocol . It provides application-to -application communication.
• It provides
connectionless service.
• It is a
Message-Oriented protocol.
• It uses
best-effort delivery service.
• It follows
arbitrary interaction.
• It is operating
system independent.
THE CONNECTIONLESS PARADIGM:
UDP does not need to
pre-establish communication and also there is no need to
terminate communication. UDP allows an app lication to delay
long intervals between two
messages. There are no Control Messages; only Data Messages.
So it has very low
overhead.
MESSAGE-ORIENTED INTERFACE:
UDP offers application
programs a Message -Oriented Interface. It does not divide
messages into packets for transmission and does not combine
messages for delivery.
Let’s discuss its advantages and disadvantages.
ADVANTAGES:
• Applications can
depend on protoc ol to preserve data boundaries.
DISADVANTAGES:
• Each UDP message
must fit into a single IP datagram.
• It can result to
an inefficient use of the underlying
network.
•
UDP COMMUNICATION SEMANTICS:
UDP uses IP for all
delivery, that is, same best effort delivery as IP.
To use UDP, an application must either be immune to the
problems or
programmer must take additional steps to detect and correct
problems.
EXAMPLES:
• Audio transmission
• On-line shopping
application
ARBITRARY INTERACTION:
UDP follows four
types of interaction
• 1-to-1: One application can communicate with one
application.
• 1-to-many: One application can communicate with many
applications.
• Many-to-1: Many applications can communication with one
application.
• Many-to-many: Many applications can communicate with many
applications.
UDP Datagrams
UDP network traffic is organized in the form ofdatagrams. A datagram comprises one message unit. The first eight (8) bytes of a datagram contain header information and the remaining bytes contain message data.
A UDP datagram header consists of four (4) fields of two bytes each:
- source port number
- destination port number
- datagram size
- checksum
The UDP datagram size is a count of the total number of bytes contained in header and data sections. As the header length is a fixed size, this field effectively tracks the length of the variable-sized data portion (sometimes called payload). The size of datagrams varies depending on the operating environment but has a maximum of 65535 bytes.
UDP checksums protect message data from tampering. The checksum value represents an encoding of the datagram data calculated first by the sender and later by the receiver. Should an individual datagram be tampered with or get corrupted during transmission, the UDP protocol detects a checksum calculation mismatch. In UDP, checksumming is optional as opposed to TCP where checksums are mandatory.
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