Module 6 Internet Working Notes | EduRev

: Module 6 Internet Working Notes | EduRev

 Page 1


 
 
 
 
 
 
 
 
Module 
6 
  
Internetworking 
Version 2 CSE IIT, Kharagpur 
Page 2


 
 
 
 
 
 
 
 
Module 
6 
  
Internetworking 
Version 2 CSE IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lesson 
3  
 
 
Transport and Application 
Layer Protocols 
 
Version 2 CSE IIT, Kharagpur 
Page 3


 
 
 
 
 
 
 
 
Module 
6 
  
Internetworking 
Version 2 CSE IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lesson 
3  
 
 
Transport and Application 
Layer Protocols 
 
Version 2 CSE IIT, Kharagpur 
Specific Instructional Objectives  
At the end of this lesson, the students will be able to: 
• Explain how UDP allows two applications running in two remote locations can 
communicate  
• State the limitations of UDP 
• Explain how TCP provides connection-oriented service 
• Explain how TCP incorporates reliability in  internet communication  
• Explain how DNS allows the use of symbolic names instead of IP address 
• Explain the use of client-server model for   
o Remote login 
o Mail transfer  
o File transfer 
 
6.3.1 Introduction 
So far we have discussed the delivery of data in the following two ways: 
• Node-to-node delivery: At the data-link level, delivery of frames take place 
between two nodes connected by a point-to-point link or a LAN, by using the 
data-link layers address, say MAC address.  
• Host-to-host delivery: At the network level, delivery of datagrams can take place 
between two hosts by using IP address. 
 
From user’s point of view, the TCP/IP-based internet can be considered as a set of 
application programs that use the internet to carry out useful communication tasks. Most 
popular internet applications include Electronic mail, File transfer, and Remote login. IP 
allows transfer of IP datagrams among a number of stations or hosts, where the datagram 
is routed through the internet based on the IP address of the destination. But, in this case, 
several application programs (processes) simultaneously running on a source host has to 
communicate with the corresponding processes running on a remote destination host 
through the internet. This requires an additional mechanism called process-to-process 
delivery, which is implemented with the help of a transport-level protocol. The transport 
level protocol will require an additional address, known as port number, to select a 
particular process among multiple processes running on the destination host. So, there is 
a requirement of the following third type of delivery system. 
 
• Process-to-process delivery: At the transport level, communication can take 
place between processes or application programs by using port addresses 
 
Basic communication mechanism is shown in Fig. 6.3.1. The additional mechanism 
needed to facilitate multiple application programs in different stations to communicate 
with each other simultaneously can be provided by a transport level protocol such as 
UDP or TCP, which are discussed in this lesson. 
 
 
 
Version 2 CSE IIT, Kharagpur 
Page 4


 
 
 
 
 
 
 
 
Module 
6 
  
Internetworking 
Version 2 CSE IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lesson 
3  
 
 
Transport and Application 
Layer Protocols 
 
Version 2 CSE IIT, Kharagpur 
Specific Instructional Objectives  
At the end of this lesson, the students will be able to: 
• Explain how UDP allows two applications running in two remote locations can 
communicate  
• State the limitations of UDP 
• Explain how TCP provides connection-oriented service 
• Explain how TCP incorporates reliability in  internet communication  
• Explain how DNS allows the use of symbolic names instead of IP address 
• Explain the use of client-server model for   
o Remote login 
o Mail transfer  
o File transfer 
 
6.3.1 Introduction 
So far we have discussed the delivery of data in the following two ways: 
• Node-to-node delivery: At the data-link level, delivery of frames take place 
between two nodes connected by a point-to-point link or a LAN, by using the 
data-link layers address, say MAC address.  
• Host-to-host delivery: At the network level, delivery of datagrams can take place 
between two hosts by using IP address. 
 
From user’s point of view, the TCP/IP-based internet can be considered as a set of 
application programs that use the internet to carry out useful communication tasks. Most 
popular internet applications include Electronic mail, File transfer, and Remote login. IP 
allows transfer of IP datagrams among a number of stations or hosts, where the datagram 
is routed through the internet based on the IP address of the destination. But, in this case, 
several application programs (processes) simultaneously running on a source host has to 
communicate with the corresponding processes running on a remote destination host 
through the internet. This requires an additional mechanism called process-to-process 
delivery, which is implemented with the help of a transport-level protocol. The transport 
level protocol will require an additional address, known as port number, to select a 
particular process among multiple processes running on the destination host. So, there is 
a requirement of the following third type of delivery system. 
 
• Process-to-process delivery: At the transport level, communication can take 
place between processes or application programs by using port addresses 
 
Basic communication mechanism is shown in Fig. 6.3.1. The additional mechanism 
needed to facilitate multiple application programs in different stations to communicate 
with each other simultaneously can be provided by a transport level protocol such as 
UDP or TCP, which are discussed in this lesson. 
 
 
 
Version 2 CSE IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 6.3.1 Communication mechanism through the internet 
 
6.3.2 User Datagram protocol (UDP) 
UDP is responsible for differentiating among multiple source and destination processes 
within one host. Multiplexing and demultiplexing operations are performed using the port 
mechanism as depicted in Fig. 6.3.2.  
 
 
 
Figure 6.3.2 Multiplexing and demultiplexing mechanism of UDP 
 
 
 
 
Version 2 CSE IIT, Kharagpur 
Page 5


 
 
 
 
 
 
 
 
Module 
6 
  
Internetworking 
Version 2 CSE IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Lesson 
3  
 
 
Transport and Application 
Layer Protocols 
 
Version 2 CSE IIT, Kharagpur 
Specific Instructional Objectives  
At the end of this lesson, the students will be able to: 
• Explain how UDP allows two applications running in two remote locations can 
communicate  
• State the limitations of UDP 
• Explain how TCP provides connection-oriented service 
• Explain how TCP incorporates reliability in  internet communication  
• Explain how DNS allows the use of symbolic names instead of IP address 
• Explain the use of client-server model for   
o Remote login 
o Mail transfer  
o File transfer 
 
6.3.1 Introduction 
So far we have discussed the delivery of data in the following two ways: 
• Node-to-node delivery: At the data-link level, delivery of frames take place 
between two nodes connected by a point-to-point link or a LAN, by using the 
data-link layers address, say MAC address.  
• Host-to-host delivery: At the network level, delivery of datagrams can take place 
between two hosts by using IP address. 
 
From user’s point of view, the TCP/IP-based internet can be considered as a set of 
application programs that use the internet to carry out useful communication tasks. Most 
popular internet applications include Electronic mail, File transfer, and Remote login. IP 
allows transfer of IP datagrams among a number of stations or hosts, where the datagram 
is routed through the internet based on the IP address of the destination. But, in this case, 
several application programs (processes) simultaneously running on a source host has to 
communicate with the corresponding processes running on a remote destination host 
through the internet. This requires an additional mechanism called process-to-process 
delivery, which is implemented with the help of a transport-level protocol. The transport 
level protocol will require an additional address, known as port number, to select a 
particular process among multiple processes running on the destination host. So, there is 
a requirement of the following third type of delivery system. 
 
• Process-to-process delivery: At the transport level, communication can take 
place between processes or application programs by using port addresses 
 
Basic communication mechanism is shown in Fig. 6.3.1. The additional mechanism 
needed to facilitate multiple application programs in different stations to communicate 
with each other simultaneously can be provided by a transport level protocol such as 
UDP or TCP, which are discussed in this lesson. 
 
 
 
Version 2 CSE IIT, Kharagpur 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 6.3.1 Communication mechanism through the internet 
 
6.3.2 User Datagram protocol (UDP) 
UDP is responsible for differentiating among multiple source and destination processes 
within one host. Multiplexing and demultiplexing operations are performed using the port 
mechanism as depicted in Fig. 6.3.2.  
 
 
 
Figure 6.3.2 Multiplexing and demultiplexing mechanism of UDP 
 
 
 
 
Version 2 CSE IIT, Kharagpur 
Port Numbers 
Transport layer address is specified with the help a 16-bit Port number in the range of 0 
and 65535. Internet Assigned Number Authority (IANA) has divided the addresses in 
three ranges: 
• Well-known ports: The ports in the range from 0 to 1023 are assigned and controlled 
by IANA. These port numbers are commonly used as universal port numbers in the 
servers for the convenience of many clients the servers serve. Some commonly used 
well-known ports used with UDP is given in Table 6.3.1. 
• Registered ports: Registered ports in the range from 1024 to 49151 are not assigned 
or controlled by IANA. However, they can only be registered with IANA to avoid 
duplication. 
• Dynamic ports: Dynamic ports (49152 to 65535) are neither controlled by IANA nor 
need to be registered. They can be defined at the client site and chosen randomly by 
the transport layer software. 
 
Table 6.3.1 Well-known ports used by UDP 
       
 
Version 2 CSE IIT, Kharagpur 
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