This document provides an overview of the User Datagram Protocol (UDP). It discusses several key points: - UDP is a connectionless, unreliable transport protocol that performs limited error checking and uses minimal overhead. It is suitable for applications that need simple request-response communication and do not require reliability. - UDP packets, called user datagrams, have a fixed 8-byte header containing source/destination port numbers, length, and checksum fields. Port numbers identify the sending/receiving processes and range from 0-65,535. - The checksum field is used to detect errors over the entire datagram (header and data). It allows the receiver to verify no errors by checking if the checksum equals 0.

1. Computer Networks
User Datagram Protocol
Prepared by,
P.Nivetha,
Asst.Prof,
Dept. of BCA,
Bon Secours College for Women,
Thanjavur

2. UDP
• It is a connectionless, unreliable transport
protocol.
• It performs very limited error checking.
• UDP is a very simple protocol using a minimum of
overhead.
• If a process wants to send a small message it can
use UDP and does not care much about
reliability.
• UDP takes much less interaction between the
sender and receiver than using TCP or SCTP.

3. 1. User Datagram
• UDP packets, called user datagram's, have a
fixed-size header of 8 bytes.
The fields are as follows:
1. Source port number.
2. Destination port number.
3. Length.
4. Checksum.

4. i)Source port number
• It used by the process running on the source
host.
• It is 16 bits long, which means that the port
number can range from 0 to 65,535.
• If source host is the client(sending a Req)- is
called as ephemeral port number requested
by the process.
• If the source host is the server(Sending a
Resp)- known as well-known port number.

5. ii) Destination port number
• It used by the process running on the
destination host.
• It is also 16 bits long.
• If the destination host is the server(sending a
request)- known as well-known port number.
• If the destination host is the client(sending a
response)- called as ephemeral port number.

6. iii) Length
• 16-bit field that defines the total length of the
user datagram, header & data.
• Has a total length of 0 to 65,535 bytes.
• A user datagram is encapsulated in an IP
datagram.
• There is a field in the IP datagram that defines the
total length.
• There is another field in the IP datagram that
defines the length of the header.
UDP length = IP length - IP header's length

7. iv) Checksum
• It used to detect errors over the entire user datagram ,header &data.
• The checksum is used in the Internet by several protocols.
Example 10.18
 Suppose our data is a list of five 4-bit numbers that we want to send
to a destination.
 In addition to sending these numbers, we send the sum of the
numbers.
 For example, if the set of numbers is (7, 11, 12, 0, 6), we send (7, 11,
12,0,6,36), where 36 is the sum of the original numbers.
 The receiver adds the five numbers and compares the result with the
sum.
 If the two are the same, the receiver assumes no error, accepts the
five numbers, and discards the sum.
 Otherwise, there is an error somewhere and the data are not
accepted.

8. Continued…
Example 10.19
 We can make the job of the receiver easier if
we send the negative (complement) of the
sum, called the checksum.
In this case, we send (7, 11, 12,0,6, -36).
 The receiver can add all the numbers received
(including the checksum).
 If the result is 0, it assumes no error;
otherwise, there is an error.

9. 2. UDP Operation
• UDP uses concepts common to the transport
layer.
1. Connectionless Services.
2. Flow and Error Control.
3. Encapsulation and Decapsulation.
4. Queuing

10. Use of UDP
• UDP is suitable for a process that requires simple
request-response communication.
• UDP is suitable for a process with internal flow
and error control mechanisms.
• UDP is a suitable transport protocol for
multicasting.
• UDP is used for management processes such as
SNMP.
• UDP is used for some route updating protocols
such as Routing Information Protocol (RIP).

11. Thank You