Modes of Transmission Medium

1.Simplex mode: In this mode, out of two devices, only one device can transmit the data, and the other device can only
receive the data. Example- Input from keyboards, monitors, TV broadcasting, Radio broadcasting, etc.
2.Half Duplex mode: In this mode, out of two devices, both devices can send and receive the data but only one at a time not
simultaneously. Examples- Walkie-Talkie, Railway Track, etc.
3.Full-Duplex mode: In this mode, both devices can send and receive the data simultaneously. Examples- Telephone
Systems, Chatting applications, etc.
Application of Layered Architecture in computer Networks

OSI
TCP/IP
OSI Model
•OSI stands for Open System Interconnection is a reference model that describes how information from a software
application in one computer moves through a physical medium to the software application in another computer.
•OSI consists of seven layers, and each layer performs a particular network function.

•OSI model was developed by the International Organization for Standardization (ISO) in 1984, and it is now
considered as an architectural model for the inter-computer communications.

•OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task.
•Each layer is self-contained, so that task assigned to each layer can be performed independently.
1. Physical Layer: Physical layer is the lowest layer of OSI model and is responsible for the physical connection
between all the required devices. The information present in physical layer is in the form of bits. Physical
layer performs various functions such as bit rate control, bit synchronization, transmission mode etc.

Functions of a Physical layer:

•Line Configuration: It defines the way how two or more devices can be connected physically.
•Data TransmissionI t defines the transmission mode whether it is simplex, halfduplex or full-duplex mode between the
two devices on the network.
•TopologyI t defines the way how network devices are arranged.
•Signals: It determines the type of the signal used for transmitting the information.

. Data Link Layer: Data Link layer provides with successful delivery of message from one node to the another. It checks
whether this delivery of message is error free. Other functions performed by data link layer are error control, framing, flow
control etc.
•This layer is responsible for the error-free transfer of data frames.
•It defines the format of the data on the network.
•It provides a reliable and efficient communication between two or more devices.
•It is mainly responsible for the unique identification of each device that resides on a local network.
•It contains two sub-layers:
• Logical Link Control Layer
• It is responsible for transferring the packets to the Network layer of the receiver that is receiving.
• It identifies the address of the network layer protocol from the header.
• It also provides flow control.
• Media Access Control Layer
• A Media access control layer is a link between the Logical Link Control layer and the network's physical
layer.
• It is used for transferring the packets over the network.
Functions of the Data-link layer
•Framing: The data link layer translates the physical's raw bit stream into packets known as Frames. The Data link layer
adds the header and trailer to the frame. The header which is added to the frame contains the hardware destination and
source address.
•Physical Addressing: The Data link layer adds a header to the frame that contains a destination address. The frame is
transmitted to the destination address mentioned in the header.
•Flow Control: Flow control is the main functionality of the Data-link layer. It is the technique through which the constant data
rate is maintained on both the sides so that no data get corrupted. It ensures that the transmitting station such as a server with
higher processing speed does not exceed the receiving station, with lower processing speed.
•Error Control: Error control is achieved by adding a calculated value CRC (Cyclic Redundancy Check) that is placed to the
Data link layer's trailer which is added to the message frame before it is sent to the physical layer. If any error seems to occurr,
then the receiver sends the acknowledgment for the retransmission of the corrupted frames.
•Access Control: When two or more devices are connected to the same communication channel, then the data link layer
protocols are used to determine which device has control over the link at a given time.

3. Network Layer: Network Layer is responsible for the transmission of data from one host to the another host that is
connected in different network. It performs other tasks such routing and logical addressing

•It is a layer 3 that manages device addressing, tracks the location of devices on the network.
 •It determines the best path to move data from source to the destination based on the network conditions, the priority of
service, and other factors.
•The Data link layer is responsible for routing and forwarding the packets.

•Routers are the layer 3 devices, they are specified in this layer and used to provide the routing services within an
internetwork.
•The protocols used to route the network traffic are known as Network layer protocols.

Examples of protocols are IP and Ipv6.

Functions of Network Layer:

•Internetworking: An internetworking is the main responsibility of the network layer. It provides a logical connection between
different devices.
•Addressing: A Network layer adds the source and destination address to the header of the frame. Addressing is used to
identify the device on the internet.
•Routing: Routing is the major component of the network layer, and it determines the best optimal path out of the multiple
paths from source to the destination.
•Packetizing: A Network Layer receives the packets from the upper layer and converts them into packets. This process is
known as Packetizing. It is achieved by internet protocol (IP).
4. Transport Layer

•The Transport layer is a Layer 4 ensures that messages are transmitted in the order in which they are sent and there is no
duplication of data.
•The main responsibility of the transport layer is to transfer the data completely.

•It receives the data from the upper layer and converts them into smaller units known as segments.
•This layer can be termed as an end-to-end layer as it provides a point-to-point connection between source and destination to

.
deliver the data reliably

The two protocols used in this layer are:

•Transmission Control Protocol

• It is a standard protocol that allows the systems to communicate over the internet.

• It establishes and maintains a connection between hosts.

• When data is sent over the TCP connection, then the TCP protocol divides the data into smaller units known as
segments. Each segment travels over the internet using multiple routes, and they arrive in different orders at the
destination. The transmission control protocol reorders the packets in the correct order at the receiving end.
•User Datagram Protocol

• User Datagram Protocol is a transport layer protocol.

• It is an unreliable transport protocol as in this case receiver does not send any acknowledgment when the packet is
received, the sender does not wait for any acknowledgment. Therefore, this makes a protocol unreliable.
Functions of Transport Layer:

•Service-point addressing: Computers run several programs simultaneously due to this reason, the transmission of data
from source to the destination not only from one computer to another computer but also from one process to another process.
The transport layer adds the header that contains the address known as a service-point address or port address. The
responsibility of the network layer is to transmit the data from one computer to another computer and the responsibility of
the transport layer is to transmit the message to the correct process.
•Segmentation and reassembly: When the transport layer receives the message from the upper layer, it divides the message
into multiple segments, and each segment is assigned with a sequence number that uniquely identifies each segment. When
the message has arrived at the destination, then the transport layer reassembles the message based on their sequence
numbers.
•Connection control: Transport layer provides two services Connection-oriented service and connectionless service. A
connectionless service treats each segment as an individual packet, and they all travel in different routes to reach the
destination. A connection-oriented service makes a connection with the transport layer at the destination machine before
delivering the packets. In connection-oriented service, all the packets travel in the single route.
•Flow control: The transport layer also responsible for flow control but it is performed end-to-end rather than across a single
link.
•Error control: The transport layer is also responsible for Error control. Error control is performed end-to-end rather than
across the single link. The sender transport layer ensures that message reach at the destination without any error.
5. Session Layer

•It is a layer 3 in the OSI model.

•The Session layer is used to establish, maintain and synchronizes the interaction between communicating devices.
Functions of Session layer:
 •Dialog control: Session layer acts as a dialog controller that creates a dialog between two processes or we can say that it
allows the communication between two processes which can be either half-duplex or full-duplex.
•Synchronization: Session layer adds some checkpoints when transmitting the data in a sequence. If some error occurs in
the middle of the transmission of data, then the transmission will take place again from the checkpoint. This process is
known as Synchronization and recovery.
7 .Presentation Layer

•A Presentation layer is mainly concerned with the syntax and semantics of the information exchanged between the two
systems.
•It acts as a data translator for a network.
•This layer is a part of the operating system that converts the data from one presentation format to another format.
•The Presentation layer is also known as the syntax layer.
Functions of Presentation layer:
•Translation: The processes in two systems exchange the information in the form of character strings, numbers and so on.
Different computers use different encoding methods, the presentation layer handles the interoperability between the different
encoding methods. It converts the data from sender-dependent format into a common format and changes the common format
into receiver-dependent format at the receiving end.

•Encryption: Encryption is needed to maintain privacy. Encryption is a process of converting the sender-transmitted
information into another form and sends the resulting message over the network.
•Compression: Data compression is a process of compressing the data, i.e., it reduces the number of bits to be transmitted.
Data compression is very important in multimedia such as text, audio, video.

•An application layer serves as a window for users and application processes to access network service.
•It handles issues such as network transparency, resource allocation, etc.
•An application layer is not an application, but it performs the application layer functions.
•This layer provides the network services to the end-users.

•File transfer, access, and management (FTAM): An application layer allows a user to access the files in a remote computer,
to retrieve the files from a computer and to manage the files in a remote computer.
•Mail services: An application layer provides the facility for email forwarding and storage.
•Directory services: An application provides the distributed database sources and is used to provide that global information
about various objects.

TCP/IP model

Functions of TCP/IP layers:

The TCP/IP model refers to the Transmission Control Protocol/Internet Protocol Model.
This model is a part of the network domain designed specifically for efficient and error-free transmission of data.
The model works on a four-layered architecture model.

The network access layer.

The internet layer.

The transport layer.

The application layer.

1. Network Access Layer

• This layer is the combination of data-link and physical layer, where it is responsible for maintaining the task of sending
and receiving data in raw bits, i.e., in binary format over the physical communication modes in the network channel.
• It uses the physical address of the system for mapping the path of transmission over the network channel.
The internet layer

The Internet layer performs the task of controlling the transmission of the data over the network modes .
This layer performs many important functions in the TCP/IP model, some of which are:
1.It is responsible for specifying the path that the data packets will use for transmission.
2.This layer is responsible for providing IP addresses to the system for the identification matters over the network channel.
Some of the protocols applied in this layer are:
•IP: This protocol assigns your device with a unique address; the IP address is also responsible for routing the data over the
communication channel.
•ARP: This protocol refers to the Address Resolution Protocol that is responsible for finding the physical address using the IP
address.
The transport layer:
This layer is responsible for establishing the connection between the sender and the receiver device and also performs the
task of dividing the data from the application layer into packets, which are then used to create sequences .
It also performs the task of maintaining the data, i.e., to be transmitted without error, and controls the data flow rate over
the communication channel for smooth transmission of data.
The protocols used in this layer are:
•TCP: Transmission Control Protocol is responsible for the proper transmission of segments over the communication
channel. It also establishes a network connection between the source and destination system.
UDP: User Datagram Protocol (UDP) is a communications protocol for timesensitive applications like gaming, playing
videos. UDP results in speedier communication because it does not spend time forming a firm connection with the
destination before transferring the data. Because establishing the connection takes time, eliminating this step results in
faster data transfer speeds.
However, UDP can also cause data packets to get lost as they go from the source to the destination.
 This is the topmost layer which indicates the applications and programs that utilize the TCP/IP model for communicating with
the user through applications and various tasks performed by the layer, including data representation for the applications
executed by the user and forwards it to the transport layer.
The application layer

The application layer maintains a smooth connection between the application and user for data exchange and offers
various features as remote handling of the system, e-mail services, etc.

Some of the protocols used in this layer are:

•HTTP: Hypertext transfer protocol is used for accessing the information available on the internet.
•SMTP: Simple mail transfer protocol, assigned the task of handling e-mail-related steps and issues.
•FTP: This is the standard protocol that oversees the transfer of files over the network channel.

Differences between OSI Model and TCP/IP Model

OSI Model TCP/IP Model

It stands for Open System Interconnection. It stands for Transmission Control Protocol.

OSI model hasbeendeveloped by ISO It was developed by ARPANET (Advanced Research Proje
(International Standard Organization). Agency Network).

In the OSI model, the transport layer provides a guarantee for the The transport layer does not provide the surety for the delivery o
delivery of the packets. packets. But still, we can say that it is a reliable model.

In this model, the session and presentation layers are separated, i.e., In this model, the session and presentation layer are not differe
both the layers are different. layers. Both layers are included in the application layer.
In this model, the network layer provides both connection-oriented The network layer provides only connectionless
and connectionless service. service.

Protocols in the OSI model are hidden and can be easily replaced In this model, the protocol cannot be easily replaced.
when the technology changes.

It consists of 7 layers. It consists of 4 layers.

The usage of this model is very low. This model is highly used.