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User Datagram Protocol-Computer Networks-Lecture Slides, Slides of Computer Networks

Anna UniversityComputer Networks

This lecture is part of lecture series delivered by Prof. Deepak Rai at Anna University of Technology for Computer Networks course. Its main points are: User, Datagram, Control, Process-to-process, Communication, Calculate, Checksum, Operation, Modules

Typology: Slides

2011/2012

Uploaded on 07/07/2012

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TCP/IP Protocol Suite 1
Chapter 11
Upon completion you will be able to:
User Datagram
Protocol
• Be able to explain process-to-process communication
• Know the format of a UDP user datagram
• Be able to calculate a UDP checksum
• Understand the operation of UDP
• Know when it is appropriate to use UDP
• Understand the modules in a UDP package
Objectives
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TCP/IP Protocol Suite^1

Chapter 11

Upon completion you will be able to:

User Datagram

Protocol

  • Be able to explain process-to-process communication
  • Know the format of a UDP user datagram
  • Be able to calculate a UDP checksum
  • Understand the operation of UDP
  • Know when it is appropriate to use UDP
  • Understand the modules in a UDP package

Objectives

TCP/IP Protocol Suite^2

Figure 11.1 Position of UDP in the TCP/IP protocol suite

TCP/IP Protocol Suite^4

Figure 11.2 UDP versus IP

TCP/IP Protocol Suite^5

Figure 11.3 Port numbers

TCP/IP Protocol Suite^7

Figure 11.5 ICANN ranges

TCP/IP Protocol Suite^8

The well-known port numbers are less

than 1024.

Note:

TCP/IP Protocol Suite^10

Figure 11.6 Socket address

TCP/IP Protocol Suite^11

11.2 USER DATAGRAM

UDP packets are called user datagrams and have a fixed-size header of 8 bytes.

Note: We are following the terminologies from “Top Down Approach”, where transport layers packets (TCP and UDP) are termed as segments

  • Connectionlessm unreliable transport protocol
    • Packets are independent of each other
    • packets are small
    • packets may be lost or dropped due to error
  • Provide process to process communication
  • Needs a pair of sockets one for client other for server (in client/server model)
  • Limited error checking (Optional)
  • Why use UDP?

TCP/IP Protocol Suite^13

UDP length can also be calculated as

UDP length =

IP length − IP header’s length

Note:

TCP/IP Protocol Suite^14

11.3 CHECKSUM

UDP checksum calculation is different from the one for IP and ICMP. Here the checksum includes three sections: a pseudoheader, the UDP header, and the data coming from the application layer.

The topics discussed in this section include:

Checksum Calculation at Sender Checksum Calculation at Receiver Optional Use of the Checksum

TCP/IP Protocol Suite^16

Figure 11.9 Checksum calculation of a simple UDP user datagram

Checksum Calculation at Sender: Add pseudo header, add padding , make checksum field all zero, sum 2 byte words take complement put in checksum, discard pseudo header and padding

Checksum Calculation at Receiver: Add pseudo header, add padding , sum 2 byte words take 1’s complement if result is non zero there is an error, if zero the packet is ok

TCP/IP Protocol Suite^17

11.4 UDP OPERATION

UDP uses concepts common to the transport layer. These concepts will be discussed here briefly, and then expanded in the next chapter on the TCP protocol.

The topics discussed in this section include:

Connectionless Services Flow and Error Control Encapsulation and Decapsulation Queuing Multiplexing and Demultiplexing

TCP/IP Protocol Suite^19

Figure 11.11 Queues in UDP

Client Side

  • Port no and queues are assigned by Operating System. (incoming and out going queues)
  • All packets coming from different servers will go to same incoming queue

Server Side

  • Port no and queues are assigned by Operating System. (incoming and out going queues)
    • All packets coming from different clients will go to same incoming queue

Common

  • Each incoming packet is placed at the end of the queue
  • Queue may overflow in that case “destination port unreachable ” message goes to client/server by ICMP

TCP/IP Protocol Suite^20

Figure 11.12 Multiplexing and demultiplexing