Physical Layer in the OSI Model: It’s Functions, component and Protocols.

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Physical Layer in the OSI Model: Functions, component and Protocols

In an OSI (Open Systems Intercommunication) model, the physical layer (Layer 1) is the lowest or bottom most layers of OSI model, which standardizes the functions of a telecommunication or computing system. The primary responsibility of the Physical Layer is to transmit raw bitstreams coming from upper layer (Data link layer) over a physical medium. Physical layer establishes, maintains and deactivates the physical connection.

Learn more about OSI model Click here

What Is computer Network?

Data rate also maintained by the function of the Physical Layer. It defines how two or more devices are connected to a link by line configuration. Physical layer also maintain the Synchronization between sender and receiver. This layer also provide functionality to its upper layer called Data Link Layer (DLL). Physical layer pick data from data link layer and encode it at the sender side and decode data at the receiver side.

Physical layer In OSI model

Physical Layer in the OSI Model: Its Functions

Physical Layer in the OSI Model

Functions of the Physical Layer

The key responsibility of physical layer is sending bits from one node to another node along the network. Its role is determining how physical connections to the network are set up, as well as how bits are represented into signals — as they are transmitted either in the form of electrical signal, optical signal or by radio waves.

To do all this, the physical layer performs a different functions, that are given below:

  1. Bit Transmission: The Physical Layer is responsible for transmitting raw bits (0s and 1s) from one node to another over a physical medium, such as cables, fiber optics, or radio waves.
  2. Signal Encoding: It converts the data bits into signals that can be transmitted over the physical medium. This include encoding bits into electrical, optical, or radio signals depending on the medium used.
  3. Data Rate Control: It determines the rate at which data is transmitted over a physical medium, which is usually measured in bits per second (bps). This data rate can vary depending on the transmission medium and the technologies used.
  4. Topologies: It defines how two or more devices physically and logically connect to make a network. There are six types of topologies such as bus topology, star topology, ring topology, and mesh topology, tree topology and hybrid topologies.

5. Transmission Modes: It describes the direction of the data flow. Transmission modes are classified into three types: Simplex, Half-Duplex, and Full-Duplex.

6. Interfaces and Standards: The Physical Layer defines the hardware specifications and interfaces, including pin layouts, voltage levels, cable types, connectors, and other physical attributes. Examples include RS-232, RJ45, and V.35.

7. Multiplexing: Multiplexing is the process of combining multiple data streams and send it through a single stream for transmission over a communication channel.  It uses different methods like Frequency Division Multiplexing (FDM) or Time Division Multiplexing (TDM) to allow multiple signals to share the same physical medium. Multiplexing is done at the sender side and demultiplexing is done at receiver side.

Components of the Physical Layer

  1. Cables and Connectors: Physical layer use physical media such as twisted pair cables, coaxial cables, optical fiber cables, and wireless media (radio waves, microwaves).
  2. Network Interface Cards (NICs): It is a hardware device that connects a computer to a network.
  3. Repeaters and Hubs: These are the devices that is use to extend the range of a network by amplifying the signals.
  4. Modems: It is a devices that modulate and demodulate signals for transmission over telephone lines or cable systems.

Physical layer Standards and Protocols

  1. Ethernet (IEEE 802.3): It specifies the physical and data link layer’s operation in wired Ethernet networks.
  2. Wi-Fi (IEEE 802.11 ): It governs wireless networking.
  3. Optical Transport Network (ITU-T G.709): it defines the standard for optical fiber networks.
  4. SONET/SDH: It is a standards for synchronous optical networking.

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Examples of physical layer technologies

  1. Ethernet: The most widely used LAN technology that operates at both the data link and physical layers. Uses various media like twisted pair (Cat5e, Cat6) and fiber optics.
  2. Fiber Optics: It uses light signals for high-speed data transmission over long distances with minimal loss.
  3. DSL (Digital Subscriber Line): It uses existing telephone lines to provide high-speed internet access.
  4. Wi-Fi: Wireless technology that provides high-speed internet and network connections.

What is the Physical Layer in the OSI Model?

The Physical Layer is the first and lowest layer of the OSI (Open Systems Interconnection) model. It is responsible for the transmission and reception of raw bit streams over a physical medium, such as cables, optical fibers, or radio waves.

What are the main functions of the Physical Layer?

1. Bit Transmission: Transmits raw bits from one device to another.
2. Signal Encoding: Converts bits into signals suitable for the transmission medium.
3. Data Rate Control: Manages the speed at which data is transmitted.
4. Physical Topologies: Defines the physical layout of network devices.
5. Transmission Modes: Supports simplex, half-duplex, and full-duplex modes.
6. Synchronization: Ensures sender and receiver are synchronized.
7. Multiplexing: Allows multiple signals to share the same medium.
8. Physical Interfaces and Standards: Specifies hardware details like pin layouts and voltage levels.

What are some common physical media used in the Physical Layer?

1. Twisted Pair Cables: Commonly used for Ethernet connections.
2. Coaxial Cables: Used for cable TV and internet.
3. Fiber Optic Cables: Provides high-speed data transmission over long distances.
4. Radio Waves: Used for wireless communications like Wi-Fi and Bluetooth.

What are some devices associated with the Physical Layer?

1. Network Interface Cards (NICs): Connect computers to networks.
2. Repeaters: Amplify signals to extend the range of a network.
3. Hubs: Basic devices that connect multiple Ethernet devices.
4Modems: Modulate and demodulate signals for transmission over telephone lines or cable systems.

The OSI Model: Understanding the 7 Layers of Networking

The OSI (Open Systems Interconnection) model was developed by the International Organization for Standardization (ISO) in 1978 and adopted by all major computer and telecommunication companies since in 1984.

The OSI model is a reference model it is not practically implemented.

The OSI model full form is Open Systems Interconnection define how to transfer data between two systems having different hardware and software across the globe. For example, if two computer having different operating system so, how they communicate with each other, to solve this issue and for successful communication 7 layer OSI model will help.

The OSI mode is a 7 layer architecture, where every layer having his own specific functionality. Here each or every layers interact and help to its lower and upper layer.

Read more What Is Computer Network?

7 Layers of OSI Model

OSI model 7 layers is divided into 3 parts. The upper three layer (Application layer, Presentation layer and Session layer) is called software layers, the lower three layer (Network layer, Datalink layer and Physical layer ) is called hardware layers and the middle layer (Transport layer) is called the heart of the OSI model.

Here’s a detailed explanation of each layer:

Application Layer

The Application Layer (also known as End User layer or desk top layer) is the top most layer of OSI model. It is closest to the end user. It interacts with software applications to implement a communicating component and provides services such as email, file transfer, and network management.

Functions:

  1. It act as an interface between system and the user.
  2. It provide interface through which we ca send data easily.
  3. it Facilitates various protocols and services (e.g., HTTP, FTP, SMTP, Telnet, DNS).

Examples: HTTP (Hyper Text Transfer Protocol), FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), DNS (Domain Name System).

Presentation Layer

The presentation layer is also known as Translation layer. On the sender’s end, the presentation layer translates the data from a user-dependent format to the common binary format. On the receiver’s end, their presentation layer translates it to another, receiver-dependent format.

After translation, presentation layer compress data bit by the process known as data compression and then Encryption and decryption are carried out by the presentation layer to secure data over the computer network. It ensures that only the communicating devices can understand pertinent data.

Functions of the presentation layer

3 main function perform by presentation layer

  1. Data translation and encoding (e.g., ASCII, EBCDIC, Unicode).
  2. Data compression and decompression.
  3. Data encryption and decryption.

Translation : On the sender’s end, the presentation layer translates the data from a user-dependent format to the common binary format. On the receiver’s end, their presentation layer translates it to another, receiver-dependent format.

Data Compression: Data compression is the process of encoding, restructuring or otherwise modifying data to reduce its size. Compression is often used to maximize the use of bandwidth across a network. Data compression id done at sender side and decompression is perform at receiver end.

Encryption/Decryption : Encryption and decryption are carried out by the presentation layer to secure data over the network. It ensures that only the communicating devices can understand pertinent data.

                                                                       OR

Encryption is the process by which a readable message is converted to an unreadable form to prevent unauthorized parties from reading it. Decryption is the process of converting an encrypted message back to its original (readable) format. The original message is called the plaintext message.

 Protocol Use:  JPEG, MPEG, GIF

Session layer

The session layer establish, controls and maintains connections between two systems to share data. It establishes, maintains, and ends sessions across all channels. In case of a network error, it checks the authenticity and provides recovery options for active sessions.

Functions of the session layer

  1. Session establishment, maintenance, and termination: This layer allows to establish, use, and terminate a connection between the two processes.
  2. 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 be in half-duplex or full-duplex.
  3. 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.

Protocol use: SQL (Structured Query Language) sessions, NetBIOS (Network Basic Input/Output System) sessions.

Transport layer

The transport layer layer is the heart of OSI model. It provides services to the application layer and takes services from the network layer. It receives the data from the session layer (upper layer) and converts them into small-small units known as segments.

This layer provide end-to-end communication and ensures complete data transfer. It manages error detection, data flow control, and retransmission of lost data packets.

Functions of Transport layer

1.Segmentation : Transport layer receives the data from the upper layer (session layer), it divides the data unit 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.

2.Flow Control: The transport layer also responsible for flow control end to end. Flow control define amount of data to be send.

3.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. For error control transport layer use ARQ Algorithm (Automatic Repeat Request ) and check Sum.

4.Connection-oriented and connection less transmission: 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.

Protocols Use: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).

Network Layer

The Network Layer is responsible for determining the best physical path for data to travel from the source to the destination. It manages packet routing, addressing, and forwarding.

Functions of Network layer

  1. Logical Addressing: To identify each and every device in a networks uniquely, the network layer defines an addressing scheme known as logical address or IP addressing. The sender & receiver’s IP addresses are placed in the header by the network layer. Such an IP address distinguishes each and every device uniquely.
  2. Path Determination and Routing: Out of so many paths in inter-network network layer find the best path to reach the destination.
  3. Packetizing: A Network Layer receives the segments from the upper layer (transport layer) and add source and destination IP address to each segment so this segment converts into packets. This process is known as Packetizing. It is achieved by internet protocol (IP).

Protocol Use: IP (Internet Protocol), ICMP (Internet Control Message Protocol), and routers.

The data link layer is responsible for the node-to-node delivery of the data. 

The Data Link Layer ensures reliable data transfer between two physically connected devices. It manages error detection and correction, frame synchronization, and flow control. When a packet arrives in a network, it is the responsibility of the DLL to transmit it to the Host using its MAC address.

  1. Framing: Data Packet coming from upper layer (network layer), data link layer add physical address ( known as MAC address ) of source and destination in header and a tailer in each packet to make a frame.
  2. Physical Addressing: DLL (data link layer) uses MAC (Media Access Control) addresses also known as physical address to ensure that data is sent to the correct destination within the same network segment. MAC addresses is a physical addresses that uniquely identify devices on a local network, enabling proper routing of frames to their intended recipients.
  3. Error Detection and Correction: This layer includes mechanisms to detect and correct errors that may occur during data transmission. A method of detecting errors in transmitted messages by using a checksum. These techniques ensure data integrity by allowing the receiver to detect errors and request retransmission if necessary.
  4. Flow Control: Flow control manage the rate of data transmission between two devices to prevent a fast sender from overwhelming a slow receiver. The technique use for flow control is Stop-and-Wait Protocol and Sliding Window Protocol.
  5. Access Control: These mechanisms ensure that only one device transmits data at a time, reducing the chances of collision and ensuring efficient use of the network medium. Techniques use for access control is Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).

Protocol use: Ethernet (MAC addresses), PPP (Point-to-Point Protocol), and switches.

Physical Layer

This is the lowest layer of the OSI model. This layer is responsible for the physical connection between devices via physical medium. It handles the transmission of raw binary data over a physical medium, such as cables, radio frequencies, or optical fibers.

The function of the physical layer

Line configuration: It defines how two or more devices are connected to a link.

Representation of Bits: It encodes the bit stream into electrical and optical signals. 

Establishment of Physical Connections:

Transmission media: Wired or wireless

Data Rate: How many bits send per second?

Synchronization: The sender and receiver must be synchronized.

Transmission mode: It describes the direction of the data flow.

Topology: the physical and logical arrangement of nodes and connections in a network.

Read more: 8051 Microcontroller

8086 Microprocessor

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What is the OSI model?

The OSI (Open Systems Interconnection) model is a conceptual framework used to understand and standardize the functions of a telecommunication or computing system. It divides the communication process into seven distinct layers

What are the seven layers of the OSI model?

The seven layers of the OSI model are:
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer

What is the function of Physical Layer?

The main functions of physical layer are:
Line configuration: It defines how two or more devices are connected to a link.
Representation of Bits: It encodes the bit stream into electrical and optical signals. 
Establishment of Physical Connections:
Transmission media: Wired or wireless
Data Rate: How many bits send per second?
Synchronization: The sender and receiver must be synchronized.
Transmission mode: It describes the direction of the data flow.
Topology: the physical and logical arrangement of nodes and connections in a network.

What is the function of the Data Link Layer?

The Data Link Layer ensures reliable data transfer across a physical link, do framing, error detection and correction, flow control, and physical addressing (using MAC addresses).

How does the Network Layer differ from the Data Link Layer?

The Network Layer is responsible for determining the best path for data to travel across networks (routing) and logical addressing (using IP addresses), while the Data Link Layer focuses on reliable data transfer between two directly connected devices within the same network segment.

What role does the Transport Layer play?

The Transport Layer provides end-to-end communication services, ensuring complete data transfer with error detection, data flow control, and retransmission of lost packets. It establishes, maintains, and terminates connections between devices.

What is the purpose of the Presentation Layer?

The Presentation Layer translates data between the application layer and the network format, ensuring that data is in a usable format. It handles data encryption, compression, and translation.

What functions are performed by the Application Layer?

The Application Layer provides network services directly to end-users and interfaces with application software. It facilitates various protocols and services like HTTP, FTP, and SMTP.

What Is computer Network ?

Definition: A computer network is a set of nodes connected to each other via communication links for the purpose of sharing there resource or data. The main goal of computer network is the sharing of resources among various devices.

The definition having two key words 1) Nodes 2) Communication links

Nodes: Nodes can be a computer, printer or any other device capable for sending / receiving data generated by other nodes in the network. Example of nodes: Computers, Server, Printer, Security Camera, etc.

Communication links: a link is a communication channel that connects two or more devices for the purpose of data transmission. The link carries the information. A communication link can be wired link or wireless link.

fig 1.1 Types of links

Example of Wire link: Co-axial cable, Optical Fiber Cable.

Example of Wireless link : Air

First computer network is ARPANET (Advance Research Projects Agency Network).

fig 1.2 A sample of Computer Network

In the above figure, how many nodes or devices involved in a network?

In the above figure of computer network, printer is a node, desktop PC is a node, IP phone is a node, scanner, smart phone, laptop PC, router, Wi-Fi router, switches all are called nodes.

In reality all nodes in a network is divided into two types first is End Devices and second is Intermediate Nodes. Where laptop PC, PC, desktop PC, IP phone, smart phone are called end devices because these devices will be either the starting point of communication or the end point of the communication. And router, wi-fi router, switch, server are called intermediate devices. By using Intermediate devices we can easily send or receive data with in a network.

Features of Computer Network

There are number of features of computer network are listed below:

  1. Resource Sharing
  2. Communication Speed
  3. Backup
  4. Scalability
  5. Reliability
  6. Software and hardware sharing
  7. Security

All these features I’ll explain in my next post