COMPUTER NETWORKING

Unit-1

Topologies

The arrangement of a network that comprises nodes and connecting lines via sender and receiver is referred to as network topology. The various network topologies are:

  • Mesh Topology
  • Star Topology
  • Ring Topology
  • Tree Topology
  • Bus Topology
  • Hybrid Topology

Mesh Topology:

  • In a mesh topology, every device is connected to another device via a particular channel.
  • Every device is connected to another via dedicated channels. These channels are known as links.

Advantages of this topology:

  • Communication is very fast between the nodes.
  • It is robust.
  • The fault is diagnosed easily. Data is reliable because data is transferred among the devices through dedicated channels or links.
  • Provides security and privacy.

Disadvantages of this topology:

  • Installation and configuration are difficult.
  • The cost of cables is high as bulk wiring is required, hence suitable for less number of devices.
  • The cost of maintenance is high.
  • A common example of mesh topology is the internet backbone, where various internet service providers are connected to each other via dedicated channels.
  • This topology is also used in military communication systems and aircraft navigation systems.

Star Topology:

  • In star topology, all the devices are connected to a single hub through a cable.
  • This hub is the central node and all other nodes are connected to the central node.
  • The hub can be passive in nature i.e., not an intelligent hub such as broadcasting devices, at the same time the hub can be intelligent known as an active hub. Active hubs have repeaters in them.
  • Coaxial cables or RJ-45 cables are used to connect the computers.

Advantages of this topology:

  • If N devices are connected to each other in a star topology, then the number of cables required to connect them is N. So, it is easy to set up.
  • Each device requires only 1 port i.e. to connect to the hub, therefore the total number of ports required is N.
  • It is Robust. If one link fails only that link will affect and not other than that.

Disadvantages of this topology:

  • If the concentrator (hub) on which the whole topology relies fails, the whole system will crash down.
  • The cost of installation is high.
  • Performance is based on the single concentrator i.e. hub.
  • A common example of star topology is a local area network (LAN) in an office where all computers are connected to a central hub.
  • This topology is also used in wireless networks where all devices are connected to a wireless access point.

Bus Topology:

  • Bus topology is a network type in which every computer and network device is connected to a single cable.
  • It is bi-directional.
  • It is a multi-point connection and a non-robust topology because if the backbone fails the topology crashes.

Advantages of this topology:

  • If N devices are connected to each other in a bus topology, then the number of cables required to connect them is 1, known as backbone cable, and N drop lines are required.
  • Coaxial or twisted pair cables are mainly used in bus-based networks that support up to 10 Mbps.
  • The cost of the cable is less compared to other topologies, but it is used to build small networks.
  • Bus topology is familiar technology as installation and troubleshooting techniques are well known.

Disadvantages of this topology:

  • A bus topology is quite simpler, but still, it requires a lot of cabling.
  • If the common cable fails, then the whole system will crash down.
  • If the network traffic is heavy, it increases collisions in the network. To avoid this, various protocols are used in the MAC layer known as Pure Aloha, Slotted Aloha, CSMA/CD, etc.
  • Adding new devices to the network would slow down networks.
  • Security is very low.
  • A common example of bus topology is the Ethernet LAN, where all devices are connected to a single coaxial cable or twisted pair cable.
  • This topology is also used in cable television networks.

Ring Topology:

  • In this topology, it forms a ring connecting devices with exactly two neighboring devices.
  • A number of repeaters are used for Ring topology with a large number of nodes, because if someone wants to send some data to the last node in the ring topology with 100 nodes, then the data will have to pass through 99 nodes to reach the 100th node. Hence to prevent data loss repeaters are used in the network.
  • The data flows in one direction, i.e.., it is unidirectional, but it can be made bidirectional by having 2 connections between each Network Node, it is called Dual Ring Topology.
  • In-Ring Topology, the Token Ring Passing protocol is used by the workstations to transmit the data.
  • A ring topology comprises 4 stations connected with each forming a ring.

Advantages of this topology:

  • The data transmission is high-speed.
  • The possibility of collision is minimum in this type of topology.
  • Cheap to install and expand.
  • It is less costly than a star topology.

Disadvantages of this topology:

  • The failure of a single node in the network can cause the entire network to fail.
  • Troubleshooting is difficult in this topology.
  • The addition of stations in between or the removal of stations can disturb the whole topology.
  • Less secure.
  • A common example of bus topology is the Ethernet LAN, where all devices are connected to a single coaxial cable or twisted pair cable.
  • This topology is also used in cable television networks.

Tree Topology :

  • This topology is the variation of the Star topology.
  • This topology has a hierarchical flow of data.
  • In Tree Topology, protocols like DHCP and SAC (Standard Automatic Configuration ) are used.
  • In this, the various secondary hubs are connected to the central hub which contains the repeater.
  • This data flow from top to bottom i.e. from the central hub to the secondary and then to the devices or from bottom to top i.e. devices to the secondary hub and then to the central hub.
  • It is a multi-point connection and a non-robust topology because if the backbone fails the topology crashes.

Advantages of this topology :

  • It allows more devices to be attached to a single central hub thus it decreases the distance that is traveled by the signal to come to the devices.
  • It allows the network to get isolated and also prioritize from different computers.
  • We can add new devices to the existing network.
  • Error detection and error correction are very easy in a tree topology.

Disadvantages of this topology :

  • If the central hub gets fails the entire system fails.
  • The cost is high because of the cabling.
  • If new devices are added, it becomes difficult to reconfigure.
  • A common example of a tree topology is the hierarchy in a large organization.
  • At the top of the tree is the CEO, who is connected to the different departments or divisions (child nodes) of the company.
  • Each department has its own hierarchy, with managers overseeing different teams (grandchild nodes).
  • The team members (leaf nodes) are at the bottom of the hierarchy, connected to their respective managers and departments.

Hybrid Topology :

  • This topological technology is the combination of all the various types of topologies .
  • It is used when the nodes are free to take any form.
  • It means these can be individuals such as Ring or Star topology or can be a combination of various types of topologies .

Advantages of this topology :

  • This topology is very flexible.
  • The size of the network can be easily expanded by adding new devices.

    • Disadvantages ofthis topology :

    • It is challenging to design the architecture of the Hybrid Network.
    • Hubs used in this topology are very expensive.
    • The infrastructure cost is very high as a hybrid network requires a lot of cabling and network devices.
    • A common example of a hybrid topology is a university campus network.

Data Communication Components

  • Data Communication is defined as exchange of data between two devices via some form of transmission media such as a cable, wire or it can be air or vacuum also.
  • For occurrence of data communication, communicating devices must be a part of communication system made up of a combination of hardware or software devices and programs.

There are mainly five components of a data communication system:

  1. Message
  2. Sender
  3. Receiver
  4. Transmission Medium
  5. Set of rules (Protocol)

All above mentioned elements are described below:

Message :

  • This is most useful asset of a data communication system.
  • The message simply refers to data or piece of information which is to be communicated.
  • A message could be in any form, it may be in form of a text file, an audio file, a video file, etc.

    • Sender :

  • To transfer message from source to destination, someone must be there who will play role of a source.
  • Sender plays part of a source in data communication system.
  • It is simple a device that sends data message.
  • The device could be in form of a computer, mobile, telephone, laptop, video camera, or a workstation, etc.

    • Receiver :

  • It is destination where finally message sent by source has arrived.
  • It is a device that receives message.
  • Same as sender, receiver can also be in form of a computer, telephone mobile, workstation, etc.

    • Transmission Medium :

  • In entire process of data communication, there must be something which could act as a bridge between sender and receiver, Transmission medium plays that part.
  • It is physical path by which data or message travels from sender to receiver.
  • Transmission medium could be guided (with wires) or unguided (without wires), for example, twisted pair cable, fiber optic cable, radio waves, microwaves, etc.

    • Set of rules (Protocol) :

  • To govern data communications, various sets of rules had been already designed by the designers of the communication systems, which represent a kind of agreement between communicating devices.These are defined as protocol.
  • In simple terms, the protocol is a set of rules that govern data communication.
  • If two different devices are connected but there is no protocol among them, there would not be any kind of communication between those two devices.
  • Thus the protocol is necessary for data communication to take place.


    • A typical example of a data communication system is sending an e-mail.
    The user which send email act as sender,
    message is data which user wants to send,
    receiver is one whom user wants to send message,
    there are many protocols involved in this entire process,
    one of them is Simple Mail Transfer Protocol (SMTP),
    both sender and receiver must have an internet connection which uses a wireless medium to send and receive email.

    Types of Networks

    A computer network is a cluster of computers over a shared communication path that works for the purpose of sharing resources from one computer to another, provided by or located on the network nodes. Some of the uses of computer networks are the following:

    • Communicating using email, video, instant messaging, etc.
    • Sharing devices such as printers, scanners, etc.
    • Sharing files
    • Sharing software and operating programs on remote systems
    • Allowing network users to easily access and maintain information

    Types of Computer Networks

    • Personal Area Network (PAN)
    • Local Area Network (LAN)
    • Wide Area Network (WAN)
    • Wireless Local Area Network (WLAN)
    • Campus Area Network (CAN)
    • Metropolitan Area Network (MAN)
    • System-Area Network (SAN)

    These are explained as following below.

    Personal Area Network (PAN) :

    • PAN is the most basic type of computer network.
    • This network is restrained to a single person, that is, communication between the computer devices is centered only to an individual’s workspace.
    • PAN offers a network range of 1 to 100 meters from person to device providing communication.
    • Its transmission speed is very high with very easy maintenance and very low cost.
    • This uses BlueTooth, IrDA, and Zigbee as technology.
    • Examples of PAN are USB, computer, phone, tablet, printer, PDA, etc.

    Local Area Network (LAN) :

    • LAN is the most frequently used network.
    • A LAN is a computer network that connects computers together through a common communication path, contained within a limited area, that is, locally.
    • A LAN encompasses two or more computers connected over a server.
    • The two important technologies involved in this network are Ethernet and Wi-fi.
    • It ranges up to 2km & transmission speed is very high with easy maintenance and low cost.
    • Examples of LAN are networking in a home, school, library, laboratory, college, office, etc.

    Wide Area Network (WAN) :

    • WAN is a type of computer network that connects computers over a large geographical distance through a shared communication path.
    • It is not restrained to a single location but extends over many locations.
    • WAN can also be defined as a group of local area networks that communicate with each other with a range above 50km.
    • Here we use Leased-Line & Dial-up technology.
    • Its transmission speed is very low and it comes with very high maintenance and very high cost.
    • The most common example of WAN is the Internet.

    Wireless Local Area Network (WLAN) :

    • WLAN is a type of computer network that acts as a local area network but makes use of wireless network technology like Wi-Fi.
    • This network doesn’t allow devices to communicate over physical cables like in LAN but allows devices to communicate wirelessly.
    • The most common example of WLAN is Wi-Fi.

    Campus Area Network (CAN) :

    • CAN is bigger than a LAN but smaller than a MAN.
    • This is a type of computer network that is usually used in places like a school or colleges.
    • This network covers a limited geographical area that is, it spreads across several buildings within the campus.
    • CAN mainly use Ethernet technology with a range from 1km to 5km.
    • Its transmission speed is very high with a moderate maintenance cost and moderate cost.
    • Examples of CAN are networks that cover schools, colleges, buildings, etc.

    Metropolitan Area Network (MAN) :

    • A MAN is larger than a LAN but smaller than a WAN.
    • This is the type of computer network that connects computers over a geographical distance through a shared communication path over a city, town, or metropolitan area.
    • This network mainly uses FDDI, CDDI, and ATM as the technology with a range from 5km to 50km.
    • Its transmission speed is average. It is difficult to maintain and it comes with high cost.
    • Examples of MAN are networking in towns, cities, a single large city, a large area within multiple buildings, etc.

    Storage Area Network (SAN) :

    • SAN is a type of computer network that is high-speed and connects groups of storage devices to several servers.
    • This network does not depend on LAN or WAN.
    • Instead, a SAN moves the storage resources from the network to its own high-powered network.
    • A SAN provides access to block-level data storage.
    • Examples of SAN are a network of disks accessed by a network of servers.

    OSI Model

    • The Open Systems Interconnection (OSI) Model was developed by International Organization for Standardization (ISO).
    • ISO is the organization, OSI is the model.
    • It was developed to allow systems with different platforms to communicate with each other.
    • Platform could mean hardware, software or operating system.
    • It is a network model that defines the protocols for network communications.
    • It is a hierarchical model that groups its processes into layers.
    • Each layer has specific duties to perform and has to cooperate with the layers above and below it.
    • It has 7 layers as follows: (Top to Bottom)
    1. Application Layer
    2. Presentation Layer
    3. Session Layer
    4. Transport Layer
    5. Network Layer
    6. Data Link Layer
    7. Physical Layer
  • OSI model acts as a reference model and is not implemented on the Internet because of its late invention.
  • The current model being used is the TCP/IP model.

    • Functions of the Layers

    Physical Layer :

  • Physical characteristics of interfaces and media
  • Representation of bits.
  • Data rate
  • Synchronisation of bits
  • Line configuration (point to point or multipoint)
  • Transmission Mode
  • Physical Topology

    • Data Link Layer :

  • Framing
  • Physical addressing
  • Error control
  • Flow control
  • Access control

    • Network Layer :

  • Routing
  • Congestion control
  • Billing

    • Transport Layer :

  • Service Point addressing
  • Segmentation and reassembly
  • Flow control
  • Error control

    • Session Layer :

  • Dialog control
  • Synchronization

    • Presentation Layer :

  • Data encoding
  • Encryption
  • Compression

    • Application Layer :

  • File Transfer
  • Mail services
  • Directory services

    • TCP/IP

  • The TCP/IP model is a concise version of the OSI model. It contains four layers, unlike the seven layers in the OSI model.
  • The number of layers is sometimes referred to as five or four.
  • The Physical Layer and Data Link Layer are referred to as one single layer as the 'Physical Layer' or 'Network Interface Layer' in the 4-layer reference.
  • The layers are:
    1. Application Layer
    2. Transport Layer(TCP/UDP)
    3. Network/Internet Layer(IP)
    4. Data Link Layer (MAC)
    5. Physical Layer

    Physical Layer:

  • It is a group of applications requiring network communications.
  • This layer is responsible for generating the data and requesting connections.
  • It acts on behalf of the sender and the Network Access layer on the behalf of the receiver.

    • Data Link Layer:

  • The packet's network protocol type, in this case TCP/IP, is identified by the data-link layer.
  • Error prevention and "framing" are also provided by the data-link layer.
  • Point-to-Point Protocol (PPP) framing and Ethernet IEEE 802.2 framing are two examples of data-link layer protocols.

    • Internet Layer:

  • This layer parallels the functions of OSI's Network layer.
  • It defines the protocols which are responsible for the logical transmission of data over the entire network.

    • Transport Layer:

  • The TCP/IP transport layer protocols exchange data receipt acknowledgments and retransmit missing packets to ensure that packets arrive in order and without error.
  • End-to-end communication is referred to as such.
  • Transmission Control Protocol (TCP) and User Datagram Protocol are transport layer protocols at this level (UDP).

    • Application Layer:

  • This layer is analogous to the transport layer of the OSI model.
  • It is responsible for end-to-end communication and error-free delivery of data.
  • It shields the upper-layer applications from the complexities of data.

    • Transmission Media

  • In data communication terminology, a transmission medium is a physical path between the transmitter and the receiver
    i.e. it is the channel through which data is sent from one place to another.
  • Transmission Media is broadly classified into the following types:

    1. Guided Media:

      It is also referred to as Wired or Bounded transmission media.

      2. Signals being transmitted are directed and confined in a narrow pathway by using physical links.

      Features:
      • High Speed
      • Secure
      • Used for comparatively shorter distances

      There are 3 major types of Guided Media:

      1. Twisted Pair Cable
        • It consists of 2 separately insulated conductor wires wound about each other.
        • Generally, several such pairs are bundled together in a protective sheath.
        • They are the most widely used Transmission Media.
        • Twisted Pair is of two types:
        Unshielded Twisted Pair (UTP):
        • UTP consists of two insulated copper wires twisted around one another.
        • This type of cable has the ability to block interference and does not depend on a physical shield for this purpose.
        • It is used for telephonic applications.
        Advantages:
        • Least expensive
        • Easy to install
        • High-speed capacity
          • Disadvantages:
          • Susceptible to external interference
          • Lower capacity and performance in comparison to STP
          • Short distance transmission due to attenuation
          Applications:
          • Used in telephone connections and LAN networks
          Shielded Twisted Pair (STP):
          • This type of cable consists of a special jacket (a copper braid covering or a foil shield) to block external interference.
          • It is used in fast-data-rate Ethernet and in voice and data channels of telephone lines.
          Advantages:
          • Better performance at a higher data rate in comparison to UTP
          • Eliminates crosstalk
          • Comparatively faster
          Disadvantages:
          • Comparatively difficult to install and manufacture
          • More expensive
          • Bulky
          Applications:
          • The shielded twisted pair type of cable is most frequently used in extremely cold climates,
            where the additional layer of outer covering makes it perfect for withstanding such temperatures or for shielding the interior components.
          2. Coaxial Cable
          • It has an outer plastic covering containing an insulation layer made of PVC or Teflon and 2 parallel conductors each having a separate insulated protection cover.
          • The coaxial cable transmits information in two modes: Baseband mode(dedicated cable bandwidth) and Broadband mode(cable bandwidth is split into separate ranges).
          • Cable TVs and analog television networks widely use Coaxial cables.
          Advantages:
          • High Bandwidth
          • Better noise Immunity
          • Easy to install and expand
          • Inexpensive
          Disadvantages:
          • Single cable failure can disrupt the entire network
          Applications:
          • Radio frequency signals are sent over coaxial wire.
          • It can be used for cable television signal distribution, digital audio (S/PDIF), computer network connections (like Ethernet),
            and feedlines that connect radio transmitters and receivers to their antennas.
          3. Optical Fiber Cable
          • It uses the concept of refraction of light through a core made up of glass or plastic.
          • The core is surrounded by a less dense glass or plastic covering called the cladding.
          • It is used for the transmission of large volumes of data.
          Advantages:
          • Increased capacity and bandwidth
          • Lightweight
          • Less signal attenuation
          • Immunity to electromagnetic interference
          • Resistance to corrosive materials
          Disadvantages:
          • Difficult to install and maintain
          • High cost
          • Fragile
          Applications:
          • Medical Purpose: Used in several types of medical instruments.
          • Defence Purpose: Used in transmission of data in aerospace.
          • For Communication: This is largely used in formation of internet cables.
          • Industrial Purpose: Used for lighting purposes and safety measures in designing the interior and exterior of automobiles.

    2. Unguided Media:

      • It is also referred to as Wireless or Unbounded transmission media.
      • No physical medium is required for the transmission of electromagnetic signals.
      Features:
      • The signal is broadcasted through air
      • Less Secure
      • Used for larger distances
      • There are 3 types of Signals transmitted through unguided media:
      1. Radio waves
        • These are easy to generate and can penetrate through buildings.
        • The sending and receiving antennas need not be aligned. Frequency Range:3KHz to 1GHz.
        • AM and FM radios and cordless phones use Radio waves for transmission.

        Further Categorized as
        1. Terrestrial
        2.Satellite.

      2. Microwaves
        • It is a line of sight transmission i.e. the sending and receiving antennas need to be properly aligned with each other.
        • The distance covered by the signal is directly proportional to the height of the antenna.
        • Frequency Range:1GHz to 300GHz.
        • These are majorly used for mobile phone communication and television distribution.
      3. Infrared
        • Infrared waves are used for very short distance communication.
        • They cannot penetrate through obstacles.
        • This prevents interference between systems.
        • Frequency Range:300GHz to 400THz.
        • It is used in TV remotes, wireless mouse, keyboard, printer, etc.

    Unit-2

    Multiplexing

  • Multiplexing is the sharing of a medium or bandwidth.
  • It is the process in which multiple signals coming from multiple sources are combined and transmitted over a single communication/physical line.

    • Types of Multiplexing

    1. Frequency Division Multiplexing (FDM)
    2. Time-Division Multiplexing (TDM)

    1. Frequency Division Multiplexing :

  • Frequency division multiplexing is defined as a type of multiplexing where the bandwidth of a single physical medium is divided into a number of smaller,
    independent frequency channels.
  • Frequency Division Multiplexing is used in radio and television transmission.
  • In FDM, we can observe a lot of inter-channel cross-talk, due to the fact that in this type of multiplexing the bandwidth is divided into frequency channels.
  • In order to prevent the inter-channel cross talk, unused strips of bandwidth must be placed between each channel.
  • These unused strips between each channel are known as guard bands.
  • In this, a number of signals are transmitted at the same time, and each source transfers its signals in the allotted frequency range.
  • There is a suitable frequency gap between the 2 adjacent signals to avoid over-lapping.
  • Since the signals are transmitted in the allotted frequencies so this decreases the probability of collision.
  • The frequency spectrum is divided into several logical channels, in which every user feels that they possess a particular bandwidth.
  • A number of signals are sent simultaneously at the same time allocating separate frequency bands or channels to each signal.
  • It is used in radio and TV transmission.
  • Therefore to avoid interference between two successive channels Guard bands are used.

    • Application of FDM:
    (i) In the first generation of mobile phones, FDM was used.
    (ii) The use of FDM in television broadcasting
    (iii) FDM is used to broadcast FM and AM radio frequencies.

    2. Time Division Multiplexing :

  • Time-division multiplexing is defined as a type of multiplexing wherein FDM, instead of sharing a portion of the bandwidth in the form of channels, in TDM, time is shared.
  • Each connection occupies a portion of time in the link.
  • In Time Division Multiplexing, all signals operate with the same frequency (bandwidth) at different times.

    • There are two types of Time Division Multiplexing :
    i. Synchronous Time Division Multiplexing
    ii. Statistical (or Asynchronous) Time Division Multiplexing

    Synchronous TDM:
  • The time slots are pre-assigned and fixed.
  • This slot is even given if the source is not ready with data at this time.
  • In this case, the slot is transmitted empty.
  • It is used for multiplexing digitized voice streams.
  • Synchronous TDM is a type of Time Division Multiplexing where the input frame already has a slot in the output frame.
  • Time slots are grouped into frames. One frame consists of one cycle of time slots.
  • Synchronous TDM is not efficient because if the input frame has no data to send, a slot remains empty in the output frame.
  • In synchronous TDM, we need to mention the synchronous bit at the beginning of each frame.
    • Asynchronous (or statistical) TDM:
  • The slots are allocated dynamically depending on the speed of the source or their ready state.
  • It dynamically allocates the time slots according to different input channels’ needs, thus saving the channel capacity.
  • Statistical TDM is a type of Time Division Multiplexing where the output frame collects data from the input frame till it is full, not leaving an empty slot like in Synchronous TDM.
  • In statistical TDM, we need to include the address of each particular data in the slot that is being sent to the output frame.
  • Statistical TDM is a more efficient type of time-division multiplexing as the channel capacity is fully utilized and improves the bandwidth efficiency.

    • Sliding window Protocol

  • Sliding window protocols are data link layer protocols for reliable and sequential delivery of data frames.
  • The sliding window is also used in Transmission Control Protocol.
  • In this protocol, multiple frames can be sent by a sender at a time before receiving an acknowledgment from the receiver.
  • The term sliding window refers to the imaginary boxes to hold frames. Sliding window method is also known as windowing.
  • In these protocols, the sender has a buffer called the sending window and the receiver has buffer called the receiving window.
  • The size of the sending window determines the sequence number of the outbound frames.
  • If the sequence number of the frames is an n-bit field, then the range of sequence numbers that can be assigned is 0 to 2n-1.
  • Consequently, the size of the sending window is 2n-1.
  • Thus in order to accommodate a sending window size of 2n-1, a n-bit sequence number is chosen.
  • The sequence numbers are numbered as modulo-n.

    • For example, if the sending window size is 4,
    then the sequence numbers will be 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, and so on.
    The number of bits in the sequence number is 2 to generate the binary sequence 00, 01, 10, 11.

    The size of the receiving window is the maximum number of frames that the receiver can accept at a time.
    It determines the maximum number of frames that the sender can send before receiving acknowledgment. Example

  • Suppose that we have sender window and receiver window each of size 4.
  • So the sequence numbering of both the windows will be 0,1,2,3,0,1,2 and so on.
  • The following diagram shows the positions of the windows after sending the frames and receiving acknowledgments.

    • Types of Sliding Window Protocols

    Go Back-N ARQ

  • In this protocol, and the frames are sent again if they are lost while being transmitted.
  • The size of the receiver buffer will be one, while the size of the sender buffer is predefined.
  • The receiver cancels the frame if it gets corrupted; when the sender's timer for an acknowledgement to be received expires, the sender sends the same frame again without moving on with different frames.
  • Go - Back - N ARQ provides for sending multiple frames before receiving the acknowledgment for the first frame.
  • It uses the concept of sliding window, and so is also called sliding window protocol.
  • The frames are sequentially numbered and a finite number of frames are sent.
  • If the acknowledgment of a frame is not received within the time period, all frames starting from that frame are retransmitted.

    • Selective Repeat ARQ

  • This protocol also provides for sending multiple frames before receiving the acknowledgment for the first frame.
  • However, here only the erroneous or lost frames are retransmitted, while the good frames are received and buffered.
  • Selective repeat automatic repeat request works with the data link layer and uses the sliding window method to send frames.
  • Only the corrupted frame during transmission is sent again in its execution, while the further requests get acknowledged.
  • The window size in both the sender and receiver is the same.
  • This protocol helps in saving on bandwidth as compared to Go Back-N ARQ, which processed the whole frames again without selectively choosing to send the faulty frames.

    • Hamming Code

  • Hamming code is a block code that is capable of detecting up to two simultaneous bit errors and correcting single-bit errors. It was developed by R.W. Hamming for error correction.
  • In this coding method, the source encodes the message by inserting redundant bits within the message.
  • These redundant bits are extra bits that are generated and inserted at specific positions in the message itself to enable error detection and correction.
  • When the destination receives this message, it performs recalculations to detect errors and find the bit position that has error.
    • Encoding a message by Hamming Code

    The procedure used by the sender to encode the message encompasses the following steps
    Step 1 - Calculation of the number of redundant bits.
    Step 2 - Positioning the redundant bits.
    Step 3 - Calculating the values of each redundant bit.

  • Once the redundant bits are embedded within the message, this is sent to the user.

    • Decoding a message in Hamming Code
     Once the receiver gets an incoming message, it performs recalculations to detect errors and correct them.
    The steps for recalculation are
    Step 1 - Calculation of the number of redundant bits.
    Step 2 - Positioning the redundant bits.
    Step 3 - Parity checking.
    Step 4 - Error detection and correction

    Error Detection Techniques

  • A condition when the receiver's information does not match with the sender's information.
  • During transmission, digital signals suffer from noise that can introduce errors in the binary bits travelling from sender to receiver.
  • That means a 0 bit may change to 1 or a 1 bit may change to 0.
  • Basic approach used for error detection is the use of redundancy bits, where additional bits are added to facilitate detection of errors.
  • Some popular techniques for error detection are:

    • 1. Simple Parity check
    2. Two-dimensional Parity check
    3. Checksum
    4. Cyclic redundancy check

    Simple Parity check

  • Blocks of data from the source are subjected to a check bit or parity bit generator form, where a parity of :
  • 1 is added to the block if it contains odd number of 1's, and 0 is added if it contains even number of 1's
  • This scheme makes the total number of 1's even, that is why it is called even parity checking.

    • Two-dimensional Parity check

  • Parity check bits are calculated for each row, which is equivalent to a simple parity check bit.
  • Parity check bits are also calculated for all columns, then both are sent along with the data.
  • At the receiving end these are compared with the parity bits calculated on the received data.

    • Checksum

  • In checksum error detection scheme, the data is divided into k segments each of m bits.
  • In the sender's end the segments are added using 1's complement arithmetic to get the sum. The sum is complemented to get the checksum.
  • The checksum segment is sent along with the data segments.
  • At the receiver's end, all received segments are added using 1's complement arithmetic to get the sum. The sum is complemented.
  • If the result is zero, the received data is accepted; otherwise discarded.

    • Cyclic redundancy check (CRC)

  • Unlike checksum scheme, which is based on addition, CRC is based on binary division.
  • In CRC, a sequence of redundant bits, called cyclic redundancy check bits, are appended to the end of data unit so that the resulting data unit becomes exactly divisible by a second, predetermined binary number.
  • At the destination, the incoming data unit is divided by the same number. If at this step there is no remainder, the data unit is assumed to be correct and is therefore accepted.
  • A remainder indicates that the data unit has been damaged in transit and therefore must be rejected.

    • Unit-3

    IEEE 802

  • IEEE 802.3 is a set of standards and protocols that define Ethernet-based networks.
  • Ethernet technologies are primarily used in LANs, though they can also be used in MANs and even WANs.
  • IEEE 802.3 defines the physical layer and the medium access control (MAC) sub-layer of the data link layer for wired Ethernet networks.
  • IEEE 802.3 Popular Versions There are a number of versions of IEEE 802.3 protocol.
  • The most popular ones are.

    • i. IEEE 802.3
    ii.IEEE 802.3a
    iii.IEEE 802.3

    Token Ring
  • Token ring (IEEE 802.5) is a communication protocol in a local area network (LAN) where all stations are connected in a ring topology and pass one or more tokens for channel acquisition.
  • A token is a special frame of 3 bytes that circulates along the ring of stations.
  • A station can send data frames only if it holds a token.
  • The tokens are released on successful receipt of the data frame.

    • Token Passing Mechanism in Token Ring

  • If a station has a frame to transmit when it receives a token, it sends the frame and then passes the token to the next station; otherwise it simply passes the token to the next station.
  • Passing the token means receiving the token from the preceding station and transmitting to the successor station.
  • The data flow is unidirectional in the direction of the token passing.
  • In order that tokens are not circulated infinitely, they are removed from the network once their purpose is completed.
    • Token Bus
  • Token Bus (IEEE 802.4) is a standard for implementing token ring over virtual ring in LANs.
  • The physical media has a bus or a tree topology and uses coaxial cables.
  • A virtual ring is created with the nodes/stations and the token is passed from one node to the next in a sequence along this virtual ring.
  • Each node knows the address of its preceding station and its succeeding station.
  • A station can only transmit data when it has the token.
  • The working principle of token bus is similar to Token Ring.

    • Token Passing Mechanism in Token Bus

  • A token is a small message that circulates among the stations of a computer network providing permission to the stations for transmission.
  • If a station has data to transmit when it receives a token, it sends the data and then passes the token to the next station; otherwise, it simply passes the token to the next station.

    • CSMA

  • CSMA is a mechanism that senses the state of the shared channel to prevent or recover data packets from a collision.
  • It is also used to control the flow of data packets over the network so that the packets are not get lost, and data integrity is maintained.
  • In CSMA, when two or more data packets are sent at the same time on a shared channel, the chances of collision occurred.
  • Due to the collision, the receiver does not get any information regarding the sender's data packets.
  • And the lost information needs to be resented so that the receiver can get it.
  • Therefore we need to sense the channel before transmitting data packets on a network.
  • It is divided into two parts, CSMA CA (Collision Avoidance) and CSMA CD (Collision Detection).

    • CSMA CD

  • The Carrier Sense Multiple Access/ Collision Detection protocol is used to detect a collision in the media access control (MAC) layer.
  • Once the collision was detected, the CSMA CD immediately stopped the transmission by sending the signal so that the sender does not waste all the time to send the data packet.
  • Suppose a collision is detected from each station while broadcasting the packets.
  • In that case, the CSMA CD immediately sends a jam signal to stop transmission and waits for a random time context before transmitting another data packet.
  • If the channel is found free, it immediately sends the data and returns it.
  • Carrier Sense Multiple Access (CSMA) is a random-access protocol (multiple access protocol) that is used to minimise the chance of collision and increase performance.
  • The main principle used is 'sense before transmit'.
  • CSMA is using a shared medium which means any data passed with a common interconnection network.

    • There are mainly two conditions for the carrier, which are as follows
    i. Carrier is busy transmission take place
    ii.Carrier is idle -no transmission takes place.

    Advantages of CSMA CD:

  • It is used for collision detection on a shared channel within a very short time.
  • CSMA CD is better than CSMA for collision detection.
  • CSMA CD is used to avoid any form of waste transmission.
  • When necessary, it is used to use or share the same amount of bandwidth at each station.
  • It has lower CSMA CD overhead as compared to the CSMA CA.

    • Disadvantage of CSMA CD

  • It is not suitable for long-distance networks because as the distance increases, CSMA CD' efficiency decreases.
  • It can detect collision only up to 2500 meters, and beyond this range, it cannot detect collisions.
  • When multiple devices are added to a CSMA CD, collision detection performance is reduced.

    • CSMA/CA

  • CSMA stands for Carrier Sense Multiple Access with Collision Avoidance.
  • It means that it is a network protocol that uses to avoid a collision rather than allowing it to occur, and it does not deal with the recovery of packets after a collision.
  • It is similar to the CSMA CD protocol that operates in the media access control layer.
  • In CSMA CA, whenever a station sends a data frame to a channel, it checks whether it is in use.
  • If the shared channel is busy, the station waits until the channel enters idle mode.
  • It reduces the chances of collisions and makes better use of the medium to send data packets more efficiently.
  • Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is a network protocol for carrier transmission that operates in the Medium Access Control (MAC) layer.
    • Algorithms
    1. When a frame is ready, the transmitting station checks whether the channel is idle or busy.
    2. If the channel is busy, the station waits until the channel becomes idle.
    3. If the channel is idle, the station starts transmitting and continually monitors the channel to detect collision.
    4. If a collision is detected, the station starts the collision resolution algorithm.
    5. The station resets the retransmission counters and completes frame transmission.

    The algorithm of Collision Resolution is:

    1. The station continues transmission of the current frame for a specified time along with a jam signal, to ensure that all the other stations detect collision.
    2. The station increments the retransmission counter.
    3. If the maximum number of retransmission attempts is reached, then the station aborts transmission.
    4. Otherwise, the station waits for a backoff period which is generally a function of the number of collisions and restart main algorithm.
    5. Though this algorithm detects collisions, it does not reduce the number of collisions.
    6. It is not appropriate for large networks performance degrades exponentially when more stations are added.

      7. Advantage of CSMA CA

      1. When the size of data packets is large, the chances of collision in CSMA CA is less.
      2. It controls the data packets and sends the data when the receiver wants to send them.
      3. It is used to prevent collision rather than collision detection on the shared channel.
      4. CSMA CA avoids wasted transmission of data over the channel.
      5. It is best suited for wireless transmission in a network.
      6. It avoids unnecessary data traffic on the network with the help of the RTS/ CTS extension.

      Disadvantage of CSMA CA

      1. Sometime CSMA/CA takes much waiting time as usual to transmit the data packet.
      2. It consumes more bandwidth by each station.
      3. Its efficiency is less than a CSMA CD.

    Switching Methods

    • In large networks, there can be multiple paths from sender to receiver.
    • The switching technique will decide the best route for data transmission.
    • Switching technique is used to connect the systems for making one-to-one communication.
    Classification Of Switching Techniques

    Circuit Switching

    • Circuit switching is a switching technique that establishes a dedicated path between sender and receiver.
    • In the Circuit Switching Technique, once the connection is established then the dedicated path will remain to exist until the connection is terminated.
    • Circuit switching in a network operates in a similar way as the telephone works.
    • A complete end-to-end path must exist before the communication takes place.
    • In case of circuit switching technique, when any user wants to send the data, voice, video, a request signal is sent to the receiver then the receiver sends back the acknowledgment to ensure the availability of the dedicated path.
    • After receiving the acknowledgment, dedicated path transfers the data.
    • Circuit switching is used in public telephone network. It is used for voice transmission.

    Advantages Of Circuit Switching:

    1. In the case of Circuit Switching technique, the communication channel is dedicated.
    2. It has fixed bandwidth.

    Disadvantages Of Circuit Switching:

    1. Once the dedicated path is established, the only delay occurs in the speed of data transmission.
    2. It takes a long time to establish a connection approx 10 seconds during which no data can be transmitted.
    3. It is more expensive than other switching techniques as a dedicated path is required for each connection.
    4. It is inefficient to use because once the path is established and no data is transferred, then the capacity of the path is wasted.
    5. In this case, the connection is dedicated therefore no other data can be transferred even if the channel is free.

    Message Switching

    • Message Switching is a switching technique in which a message is transferred as a complete unit and routed through intermediate nodes at which it is stored and forwarded.
    • In Message Switching technique, there is no establishment of a dedicated path between the sender and receiver.
    • The destination address is appended to the message. Message Switching provides a dynamic routing as the message is routed through the intermediate nodes based on the information available in the message.
    • Message switches are programmed in such a way so that they can provide the most efficient routes.
    • Each and every node stores the entire message and then forward it to the next node.
    • This type of network is known as store and forward network.
    • Message switching treats each message as an independent entity.

    Advantages Of Message Switching

    1. Data channels are shared among the communicating devices that improve the efficiency of using available bandwidth.
    2. Traffic congestion can be reduced because the message is temporarily stored in the nodes.
    3. Message priority can be used to manage the network.
    4. The size of the message which is sent over the network can be varied. Therefore, it supports the data of unlimited size.

    Disadvantages Of Message Switching

    1. The message switches must be equipped with sufficient storage to enable them to store the messages until the message is forwarded.
    2. The Long delay can occur due to the storing and forwarding facility provided by the message switching technique.

    Packet Switching

    • The packet switching is a switching technique in which the message is sent in one go, but it is divided into smaller pieces, and they are sent individually.
    • The message splits into smaller pieces known as packets and packets are given a unique number to identify their order at the receiving end.
    • Every packet contains some information in its headers such as source address, destination address and sequence number.
    • Packets will travel across the network, taking the shortest path as possible.
    • All the packets are reassembled at the receiving end in correct order.
    • If any packet is missing or corrupted, then the message will be sent to resend the message.
    • If the correct order of the packets is reached, then the acknowledgment message will be sent.

    Advantages Of Packet Switching:

    1. Cost-effective
    2. Reliable
    3. Efficient

    Disadvantages Of Packet Switching:

    1. Packet Switching technique cannot be implemented in those applications that require low delay and high-quality services.
    2. The protocols used in a packet switching technique are very complex and requires high implementation cost.
    3. If the network is overloaded or corrupted, then it requires retransmission of lost packets.
    4. It can also lead to the loss of critical information if errors are nor recovered.

    Unit-4

    Networking Devices & Internetworking Devices

  • The devices employed for interaction between various hardware in the computer network are known as networking devices.
  • Every networking device works in a different computer network segment and performs unique functions.

    • Networking devices

    Repeaters
  • Repeaters are network devices operating at physical layer of the OSI model that amplify or regenerate an incoming signal before retransmitting it.
  • They are incorporated in networks to expand its coverage area.
  • They are also known as signal boosters.
    • Types of Repeaters According to the types of signals that they regenerate, repeaters can be classified into two categories
  • Analog Repeaters They can only amplify the analog signal.
  • Digital Repeaters They can reconstruct a distorted signal.
    • According to the types of networks that they connect, repeaters can be categorized into two types
  • Wired Repeaters They are used in wired LANs.
  • Wireless Repeaters They are used in wireless LANs and cellular networks.
    • According to the domain of LANs they connect, repeaters can be divided into two categories
  • Local Repeaters They connect LAN segments separated by small distance.
  • Remote RepeatersThey connect LANs that are far from each other.

    • Advantages of Repeaters

  • Repeaters are simple to install and can easily extend the length or the coverage area of networks.
  • They are cost effective.

    • Disadvantages of Repeaters

  • Repeaters cannot connect dissimilar networks.
  • They cannot differentiate between actual signal and noise.
  • They cannot reduce network traffic or congestion.

    • Bridges
  • Bridges are used to connect two subnetworks that use interchangeable protocols.
  • It combines two LANs to form an extended LAN.
  • The main difference between the bridge and repeater is that the bridge has a penetrating efficiency.
  • A bridge accepts all the packets and amplifies all of them to the other side.
    • Types of Bridges Transparent Bridges
  • It is also called learning bridges.
  • Bridge construct its table of terminal addresses on its own as it implements connecting two LANs.
  • It facilitates the source location to create its table. It is self-updating. It is a plug and plays bridge.
    • Source Routing Bridge
  • This sending terminal means the bridges that the frames should stay.
  • This type of bridge is used to prevent looping problem.
    • Uses of Bridges
  • Bridges are used to divide large busy networks into multiple smaller and interconnected networks to improve performance.
  • Bridges also can increase the physical size of a network.
  • Bridges are also used to connect a LAN segment through a synchronous modem relation to another LAN segment at a remote area.
  • Bridges are used to connect two subnetworks that use interchangeable protocols.

    • Internetworking Devices

    Gateways
  • A device that can bridge several network structure is called a gateway.
  • Thus gateways can link two dissimilar LANs.
  • The major difference between gateways and routers is that routers operate at the OSI model’s network layer.
  • Gateways operate from the lowest to the topmost layer, i.e., the application layer to the OSI model’s network layer.
  • Gateways and routers are used correspondently.
  • It can change data packets from one protocol structure to another before forwarding them to connect two different networks.
  • Hence it incorporates a protocol conversion function at the application layer.
  • A gateway is a connecting device that can relate to multiple networks.
  • They perform at the application layer of the OSI model.
  • They manage messages, locations, and protocol conversion to deliver a packet to its terminal between two connections.
  • The main disadvantage of the gateway is that gateways are slow because they need to perform intensive conversions.

    • Routers
  • Routers are networking devices operating at layer 3 or a network layer of the OSI model.
  • They are responsible for receiving, analysing, and forwarding data packets among the connected computer networks.
  • When a data packet arrives, the router inspects the destination address, consults its routing tables to decide the optimal route and then transfers the packet along this route.
  • A router is a layer 3 or network layer device.
  • It connects different networks together and sends data packets from one network to another.
  • A router can be used both in LANs (Local Area Networks) and WANs (Wide Area Networks).
  • Routers provide protection against broadcast storms.
  • Routers are more expensive than other networking devices like hubs,bridges and switches.

    • Types of Routers

    1. Wireless Router
      • They provide WiFi connection WiFi devices like laptops, smartphones etc.
      • They can also provide standard Ethernet routing.
      • For indoor connections, the range is 150 feet while its 300 feet for outdoor connections.
    2. Broadband Router
      • They are used to connect to the Internet through telephone and to use voice over Internet Protocol (VoIP) technology for providing high-speed Internet access.
      • They are configured and provided by the Internet Service Provider (ISP).
    3. Core Routers
      • They can route data packets within a given network, but cannot route the packets between the networks.
      • They helps to link all devices within a network thus forming the backbone of network.
      • It is used by ISP and communication interfaces.
    4. Edge Routers
      • They are low-capacity routers placed at the periphery of the networks.
      • They connect the internal network to the external networks, and are suitable for transferring data packets across networks.
      • They use Border Gateway Protocol (BGP) for connectivity.
    5. Brouters
      • Brouters are specialised routers that can provide the functionalities of bridges as well.
      • Like a bridge, brouters help to transfer data between networks.
      • And like a router, they route the data within the devices of a network.

    Transport Layer

  • The transport layer (Layer 4) is responsible for delivery of an entire message from an application program on the source device to a similar application program on the destination device.
    • The main functions of the transport layer are as follows
  • It delivers a message from a specific process of one computer to a specific process in another computer.
  • The transport layer adds a port address to the header of the data packet. It divides a message into smaller segments such that each segment contains a sequence number along with the port address.
  • It ensures that the segments arrive correctly at the receiver’s end and then reassembles them.
  • It provides an error-free point-to-point channel for both connectionless and connection-oriented services.
  • It isolates the upper layers, i.e., the user support layers from any changes in hardware technology in the lower layers, i.e., network support layers.
  • It identifies errors like damaged packets, lost packets, and duplication of packets, and provides adequate error-correction techniques.

    • Responsibilities of a Transport Layer:

    Process to process delivery:
  • While Data Link Layer requires the MAC address (48 bits address contained inside the Network Interface Card of every host machine)
    of source-destination hosts to correctly deliver a frame and the Network layer requires the IP address for appropriate routing of packets,
    in a similar way Transport Layer requires a Port number to correctly deliver the segments of data to the correct process amongst the multiple processes running on a particular host.
  • A port number is a 16-bit address used to identify any client- server program uniquely.
    • End-to-end Connection between hosts:
  • The transport layer is also responsible for creating the end-to-end Connection between hosts for which it mainly uses TCP and UDP.
  • TCP is a secure, connection-orientated protocol that uses a handshake protocol to establish a robust connection between two end hosts.
  • TCP ensures reliable delivery of messages and is used in various applications.
  • UDP, on the other hand, is a stateless and unreliable protocol that ensures best-effort delivery.
  • It is suitable for applications that have little concern with flow or error control and requires sending the bulk of data like video conferencing.It is often used in multicasting protocols.
    • Multiplexing and Demultiplexing:
  • Multiplexing allows simultaneous use of different applications over a network that is running on a host.
  • The transport layer provides this mechanism which enables us to send packet streams from various applications simultaneously over a network.
  • The transport layer accepts these packets from different processes differentiated by their port numbers and passes them to the network layer after adding proper headers.
  • Similarly, Demultiplexing is required at the receiver side to obtain the data coming from various processes.
  • Transport receives the segments of data from the network layer and delivers it to the appropriate process running on the receiver’s machine.
    • Congestion Control:
  • Congestion is a situation in which too many sources over a network attempt to send data and the router buffers start overflowing due to which loss of packets occur.
  • As a result retransmission of packets from the sources increases the congestion further.
  • In this situation, the Transport layer provides Congestion Control in different ways.
  • It uses open loop congestion control to prevent the congestion and closed- loop congestion control to remove the congestion in a network once it occurred.
  • TCP provides AIMD- additive increase multiplicative decrease, leaky bucket technique for congestion control.
    • Data integrity and Error correction:
  • The transport layer checks for errors in the messages coming from the application layer by using error detection codes, computing checksums,
    it checks whether the received data is not corrupted and uses the ACK and NACK services to inform the sender if the data has arrived or not and checks for the integrity of data.
    • Flow control:
  • The transport layer provides a flow control mechanism between the adjacent layers of the TCP/IP model.
  • TCP also prevents data loss due to a fast sender and slow receiver by imposing some flow control techniques.
  • It uses the method of sliding window protocol which is accomplished by the receiver by sending a window back to the sender informing the size of data it can receive.

    • Session Layer

  • The session layer services are provided by a functional unit set, which constitutes the session layer.
  • The session layer can be understanding as a general-purpose tool kit out of which the user selects the tools to be used.
    • The functions provided by the session layers are as follows:
  • The session layer’s primary function is to provide and establish connections between communicating users, known as sessions.
  • It can transfer the data over these sessions in a reliable and orderly way.
  • It can settle a session between two computers for communication, file transfer, remote login, or other purposes.
  • The exchange of data between user entities can either be a two-way alternate (half-duplex) or two ways simultaneous (full-duplex).
  • In the half-duplex mode, only one user has the exclusive right to initiate the transfer of data.
  • For releasing the session connection, one of the following four variations are used:
    1. User abort
    2. Provider abort
    3. Orderly release
    4. Negotiated release
  • Synchronisation
  • Resynchronisation
  • Reporting

    • Application Layer

  • The application layer in the OSI model is the closest layer to the end user which means that the application layer and end user can interact directly with the software application.
  • The application layer programs are based on client and servers.

    • The Application layer includes the following functions:

  • The application layer identifies the availability of communication partners for an application with data to transmit.
  • The application layer determines whether sufficient network resources are available for the requested communication.
  • All the communications occur between the applications requires cooperation which is managed by an application layer.
  • An application layer allows a user to log on to a remote host.
  • File Transfer, Access, and Management (FTAM): An application allows a user to access files in a remote computer, to retrieve files from a computer and to manage files in a remote computer.
  • To obtain communication between client and server, there is a need for addressing.
  • Mail Services: An application layer provides Email forwarding and storage.
  • Directory Services: An application contains a distributed database that provides access for global information about various objects and services.
  • Authentication: It authenticates the sender or receiver's message or both.

    • Presentation Layer

  • Presentation Layer is the 6th layer in the Open System Interconnection (OSI) model.
  • This layer is also known as Translation layer, as this layer serves as a data translator for the network.
  • The data which this layer receives from the Application Layer is extracted and manipulated here as per the required format to transmit over the network.
  • The main responsibility of this layer is to provide or define the data format and encryption.
  • The presentation layer is also called as Syntax layer since it is responsible for maintaining the proper syntax of the data which it either receives or transmits to other layers.

    • Functions of Presentation Layer :

    Data from Application Layer <=> Presentation layer <=> Data from Session Layer
  • The presentation layer, being the 6th layer in the OSI model, performs several types of functions, which are described below
  • Presentation layer format and encrypts data to be sent across the network.
  • This layer takes care that the data is sent in such a way that the receiver will understand the information (data) and will be able to use the data efficiently and effectively.
  • This layer manages the abstract data structures and allows high-level data structures (example- banking records), which are to be defined or exchanged.
  • This layer carries out the encryption at the transmitter and decryption at the receiver.
  • This layer carries out data compression to reduce the bandwidth of the data to be transmitted (the primary goal of data compression is to reduce the number of bits which is to be transmitted).
  • This layer is responsible for interoperability (ability of computers to exchange and make use of information) between encoding methods as different computers use different encoding methods.
  • This layer basically deals with the presentation part of the data.
  • Presentation layer, carries out the data compression (number of bits reduction while transmission), which in return improves the data throughput.
  • This layer also deals with the issues of string representation.
  • The presentation layer is also responsible for integrating all the formats into a standardized format for efficient and effective communication.
  • This layer encodes the message from the user-dependent format to the common format and vice-versa for communication between dissimilar systems.
  • This layer deals with the syntax and semantics of the messages.
  • This layer also ensures that the messages which are to be presented to the upper as well as the lower layer should be standardized as well as in an accurate format too.
  • Presentation layer is also responsible for translation, formatting, and delivery of information for processing or display.
  • This layer also performs serialization (process of translating a data structure or an object into a format that can be stored or transmitted easily).