Data Communication Overview


Data Communication Oversee

A system of interconnected complaceers and complaceerized peripherals such as printers is called complaceer ne2rk. This wislimterinterconnection among complaceers facilitates information sharing among all of all of them. Complaceers may connect to every other by possibly wicrimson or cableless media.

Clbumification of Complaceer Ne2rks

Complaceer ne2rks are courseified based on various fworkors.They includes:

  • Geographical span
  • Inter-connectivity
  • Administration
  • Architecture

Geographical Span

Geographically a ne2rk can be seen in one of the folloearng categories:

  • It may be spanned acombination your table, among Bluetooth enabled devices,. Ranging not more than couple of meters.
  • It may be spanned acombination a whole produceing, including intermediate devices to connect all floors.
  • It may be spanned acombination a whole city.
  • It may be spanned acombination multiple ciconnects or provinces.
  • It may be one ne2rk covering whole world.


Components of a ne2rk can be connected to every other variously in some fashion. By connectedness we mean possibly logically , physically , or both ways.

  • Every performle device can be connected to every other device on ne2rk, macalifornia king the ne2rk mesh.
  • All devices can be connected to a performle medium but geographically disconnected, produced bus like structure.
  • Each device is connected to it is left and proper peers only, creating rangear structure.
  • All devices connected collectively with a performle device, creating star like structure.
  • All devices connected arbitrarily uperform all previous ways to connect every other, resulting in a hybrid structure.


From an administrator’s stage of see, a ne2rk can be private ne2rk which bedurationys a performle autonomous system and cannot be accessed awaypart it is physical or logical domain.A ne2rk can be public which is accessed by all.

Ne2rk Architecture

    Complaceer ne2rks can be discriminated into various types such as Care locatednt-Server,peer-to-peer or hybrid, depending upon it is architecture.

  • There can be one or more systems worcalifornia king as Server. Other being Care locatednt, requests the Server to serve requests.Server considers and processes request on behalf of Care locatednts.
  • Two systems can be connected Point-to-Point, or in back-to-back fashion. They both repart at the exwork exaction same level and called peers.
  • There can be hybrid ne2rk which involves ne2rk architecture of both the above types.

Ne2rk Applications

Complaceer systems and peripherals are connected to form a ne2rk.They provide numerou advantages:

  • Resource sharing such as printers and storage devices
  • Exmodify of information by means of e-Mails and FTP
  • Information sharing by uperform Web or Internet
  • Interworkion with other users uperform dynamic web pages
  • IP phones
  • Video conferences
  • Parallel complaceing
  • Instant messaging

Complaceer Ne2rk Types

Generally, ne2rks are distinguished based on their particular geographical span. A ne2rk can be as small as distance between your mobile phone and it is Bluetooth mindphone and as big as the internet it iself, covering the whole geographical world,

Personal Area Ne2rk

A Personal Area Ne2rk (PAN) is smallest ne2rk which is very private to a user. This may include Bluetooth enabled devices or infra-crimson enabled devices. PAN has connectivity range up to 10 meters. PAN may include cableless complaceer keytable and mouse, Bluetooth enabled mindphones, cableless printers and TV remotes.

Personal Area Ne2rk

For example, Piconet is Bluetooth-enabled Personal Area Ne2rk which may contain up to 8 devices connected collectively in a master-slave fashion.

Local Area Ne2rk

A complaceer ne2rk spanned inpart a produceing and operated below performle administrative system is generally termed as Local Area Ne2rk (LAN). Usually,LAN covers an body body organization’ away fromices, colleges, colleges or universit down downies. Number of systems connected in LAN may vary from as minimumern as 2 to as a lot as 16 million.

LAN provides a useful way of sharing the resources between end users.The resources such as printers, file servers, scanners, and internet are easily sharable among complaceers.

Local Area Ne2rk

LANs are composed of inexpensive ne2rcalifornia king and rawaying equipment. It may contains local servers serving file storage and other locally shacrimson applications. It the majority ofly operates on private IP adoutfites and does not involve weighty rawaying. LAN works below it is own local domain and manageled centrally.

LAN uses possibly Ethernet or Token-ring technology. Ethernet is the majority of widely employed LAN technology and uses Star topology, while Token-ring is rarely seen.

LAN can be wicrimson,cableless, or in both forms at once.

Metropolitan Area Ne2rk

The Metropolitan Area Ne2rk (MAN) generally expands throughaway a city such as cable TV ne2rk. It can be in the form of Ethernet,Token-ring, ATM, or Fiber Distributed Data Interface (FDDI).

Metro Ethernet is a service which is provided by ISPs. This service enables it is users to expand their particular Local Area Ne2rks. For example, MAN can help an body body organization to connect all of it is away fromices in a city.

Metropolitan Area Ne2rk

Backbone tissue tissue of MAN is high-capacity and high-speed fiber optics. MAN works in between Local Area Ne2rk and Wide Area Ne2rk. MAN provides uplink for LANs to WANs or internet.

Wide Area Ne2rk

As the name suggests,the Wide Area Ne2rk (WAN) covers a wide area which may span acombination provinces and also a whole councheck. Generally, telecommunication ne2rks are Wide Area Ne2rk. These ne2rks provide connectivity to MANs and LANs. Since they are equipped with very high speed backbone tissue tissue, WANs use very expensive ne2rk equipment.

Wide Area Ne2rk

WAN may use advanced technologies such as Asynchronous Transfer Mode (ATM), Frame Relay, and Synchronous Optical Ne2rk (SONET). WAN may be managed by multiple administration.


A ne2rk of ne2rks is called an interne2rk, or simply the internet. It is the bigst ne2rk in existence on this particular planet.The internet hugely connects all WANs and it can have interconnection to LANs and Home ne2rks. Internet uses TCP/IP protocol suite and uses IP as it is addresperform protocol. Present day, Internet is widely implemented uperform IPv4. Because of shortage of adoutfit spaces, it is gradually migrating from IPv4 to IPv6.

Internet enables it is users to share and access enormous amount of information worldwide. It uses WWW, FTP, email services, audio and video streaming etc. At huge level, internet works on Care locatednt-Server model.

Internet uses very high speed backbone tissue tissue of fiber optics. To inter-connect various continents, fibers are laid below ocean belowstandn to us as submarine communication cable.

Internet is widely deployed on World Wide Web services uperform HTML linked pages and is accessible by care locatednt smoothware belowstandn as Web Brangesers. When a user requests a page uperform some web brangeser located on some Web Server any kind ofwhere in the world, the Web Server responds with the proper HTML page. The communication delay is very low.

Internet is serving many kind of proposes and is wislimvolved in many kind of aspects of life. Some of all of all of them are:

  • Web sit down downes
  • E-mail
  • Instant Messaging
  • Blogging
  • Social Media
  • Marketing
  • Ne2rcalifornia king
  • Resource Sharing
  • Audio and Video Streaming

Ne2rk LAN Technologies

Let us go through various LAN technologies in short:


Ethernet is a widely deployed LAN technology.This technology was invented by Bob Metcalfe and D.R. Boggs in the calendar 12 months 1970. It was standardized in IEEE 802.3 in 1980.

Ethernet shares media. Ne2rk which uses shacrimson media has high probcapcapability of data collision. Ethernet uses Carrier Sense Multi Access/Collision Detection (CSMA/CD) technology to detect collisions. On the occurrence of collision in Ethernet, all it is hosts roll back, wait for some random amount of time, and then re-transmit the data.

Ethernet connector is,ne2rk interface card equipped with 48-bit is MAC adoutfit. This helps other Ethernet devices to identify and communicate with remote devices in Ethernet.

Traditional Ethernet uses 10BASE-T specifications.The number 10 depicts 10MBPS speed, BASE stands for baseband, and T stands for Thick Ethernet. 10BASE-T Ethernet provides transmission speed up to 10MBPS and uses coaxial cable or Cat-5 twisted pair cable with RJ-45 connector. Ethernet follows star topology with segment duration up to 100 meters. All devices are connected to a hub/switch in a star fashion.


To encomcomppermite need of fast emerging smoothware and hardware technologies, Ethernet extends it iself as Fast-Ethernet. It can operate on UTP, Optical Fiber, and cablelessly too. It can provide speed up to 100 MBPS. This standard is named as 100BASE-T in IEEE 803.2 uperform Cat-5 twisted pair cable. It uses CSMA/CD technique for wicrimson media sharing among the Ethernet hosts and CSMA/CA (CA stands for Collision Avoidance) technique for cableless Ethernet LAN.

Fast Ethernet on fiber is degreatd below 100BASE-FX standard which provides speed up to 100 MBPS on fiber. Ethernet over fiber can be extended up to 100 meters in half-duplex mode and can revery maximum of 2000 meters in comppermite-duplex over multimode fibers.


After being introduced in 1995, Fast-Ethernet could enjoy it is high speed status only for 3 calendar 12 monthss till Giga-Ethernet introduced. Giga-Ethernet provides speed up to 1000 mbit is/seconds. IEEE802.3ab standardize Giga-Ethernet over UTP uperform Cat-5, Cat-5e and Cat-6 cables. IEEE802.3ah degreats Giga-Ethernet over Fiber.

Virtual LAN

LAN uses Ethernet which in turn works on shacrimson media. Shacrimson media in Ethernet produce one performle Broadcast domain and one performle Collision domain. Introduction of switches to Ethernet has removed performle collision domain issue and every device connected to switch works in it is separate collision domain. But also Switches cannot divide a ne2rk into separate Broadcast domains.

Virtual LAN is a solution to divide a performle Broadcast domain into multiple Broadcast domains. Host in one VLAN cannot speak to a host in an additional. By default, all hosts are placed into the exwork exaction same VLAN.

Virtual LAN

In this particular diagram, various VLANs are depicted in various colour codes. Hosts in one VLAN, also if connected on the exwork exaction same Switch cannot see or speak to other hosts in various VLANs. VLAN is Layer-2 technology which works close uply on Ethernet. To rawaye packets between 2 various VLANs a Layer-3 device such as Rawayer is requicrimson.

Complaceer Ne2rk Toplogies

A Ne2rk Topology is the arrangement with which complaceer systems or ne2rk devices are connected to every other. Topologies may degreat both physical and logical aspect of the ne2rk. Both logical and physical topologies can be exwork exaction same or various in a exwork exaction same ne2rk.


Point-to-stage ne2rks contains exworkly 2 hosts such as complaceer, switches or rawayers, servers connected back to back uperform a performle piece of cable. Often, the receiving end of one host is connected to sending end of the other and vice-versa.

If the hosts are connected stage-to-stage logically, then may have multiple intermediate devices. But the end hosts are unaware of belowlying ne2rk and see every other as if they are connected immediately.

Bus Topology

In case of Bus topology, all devices share performle communication range or cable.Bus topology may have issue while multiple hosts sending data at the exwork exaction same time. Therefore, Bus topology possibly uses CSMA/CD technology or recognises one host as Bus Master to solve the issue. It is one of the fundamental forms of ne2rcalifornia king where a failure of a device does not affect the other devices. But failure of the shacrimson communication range can produce all other devices quit functioning.

Bus Topology

Both ends of the shacrimson channel have range terminator. The data is sent in only one immediateion and as soon as it reveryes the extreme end, the terminator removes the data from the range.

Star Topology

All hosts in Star topology are connected to a central device, belowstandn as hub device, uperform a stage-to-stage interconnection. Thead wear is, there exists a stage to stage interconnection between hosts and hub. The hub device can be any kind of of the folloearng:

  • Layer-1 device such as hub or repeater
  • Layer-2 device such as switch or bridge
  • Layer-3 device such as rawayer or gateway

Star Topology

As in Bus topology, hub works as performle stage of failure. If hub fails, connectivity of all hosts to all other hosts fails. Every communication between hosts, considers place through only the hub.Star topology is not expensive as to connect one more host, only one cable is requicrimson and configuration is fundamental.

Ring Topology

In ring topology, every host machine connects to exworkly 2 other machines, creating a circular ne2rk structure. When one host tries to communicate or send message to a host which is not adjacent to it, the data travels through all intermediate hosts. To connect one more host in the existing structure, the administrator may need only one more extra cable.

Ring Topology

Failure of any kind of host results in failure of the whole ring.Thus, every interconnection in the ring is a stage of failure. There are methods which employ one more backup ring.

Mesh Topology

In this particular type of topology, a host is connected to one or multiple hosts.This topology has hosts in stage-to-stage interconnection with every other host or may also have hosts which are in stage-to-stage interconnection to couple of hosts only.

Full Mesh Topology

Hosts in Mesh topology also work as relay for other hosts which do not have immediate stage-to-stage links. Mesh technology comes into 2 types:

  • Full Mesh: All hosts have a stage-to-stage interconnection to every other host in the ne2rk. Thus for every brand new host n(n-1)/2 interconnections are requicrimson. It provides the the majority of reliable ne2rk structure among all ne2rk topologies.
  • Partially Mesh: Not all hosts have stage-to-stage interconnection to every other host. Hosts connect to every other in some arbitrarily fashion. This topology exists where we need to provide relicapcapability to some hosts away of all.

Tree Topology

Also belowstandn as Hierarchical Topology, this particular is the the majority of common form of ne2rk topology in use presently.This topology imitates as extended Star topology and inherit is properconnects of bus topology.

This topology divides the ne2rk in to multiple levels/layers of ne2rk. Mainly in LANs, a ne2rk is bifurcated into three types of ne2rk devices. The lowerthe majority of is access-layer where complaceers are attached. The middle layer is belowstandn as distribution layer, which works as mediator between upper layer and lower layer. The highest layer is belowstandn as core layer, and is central stage of the ne2rk, i.e. fundamental of the tree from which all nodes fork.

Tree Topology

All neighbouring hosts have stage-to-stage interconnection between all of all of them.Similar to the Bus topology, if the fundamental goes down, then the entire ne2rk suffers also.though it is not the performle stage of failure. Every interconnection serves as stage of failure, failing of which divides the ne2rk into unreveryable segment.

Daisy Chain

This topology connects all the hosts in a rangear fashion. Similar to Ring topology, all hosts are connected to 2 hosts only, other than the end hosts.Means, if the end hosts in daisy chain are connected then it represents Ring topology.

Daisy Chain Topology

Each link in daisy chain topology represents performle stage of failure. Every link failure split is the ne2rk into 2 segments.Every intermediate host works as relay for it is immediate hosts.

Hybrid Topology

A ne2rk structure whose style contains more than one topology is said to be hybrid topology. Hybrid topology inherit is merit is and demerit is of all the incorporating topologies.

Hybrid Topology

The above picture represents an arbitrarily hybrid topology. The combining topologies may contain attributes of Star, Ring, Bus, and Daisy-chain topologies. Most WANs are connected by means of Dual-Ring topology and ne2rks connected to all of all of them are the majority ofly Star topology ne2rks. Internet is the best example of bigst Hybrid topology

Complaceer Ne2rk Models

Ne2rcalifornia king engineering is a complicated task, which involves smoothware, firmware, chip level engineering, hardware, and electric pulses. To reare locatedve ne2rk engineering, the whole ne2rcalifornia king concept is divided into multiple layers. Each layer is wislimvolved in some particular task and is wislimdependent of all other layers. But as a whole, althe majority of all ne2rcalifornia king tasks depend on all of these layers. Layers share data between all of all of them and they depend on every other only to consider inplace and send awayplace.

Layecrimson Tasks

In layecrimson architecture of Ne2rk Model, one whole ne2rk process is divided into small tasks. Each small task is then bumigned to a particular layer which works dedicatedly to process the task only. Every layer does only specific work.

In layecrimson communication system, one layer of a host deals with the task done by or to be done by it is peer layer at the exwork exaction same level on the remote host. The task is possibly initiated by layer at the lowest level or at the top the majority of level. If the task is wislimitiated by the-top the majority of layer, it is comppermiteed on to the layer below it for further procesperform. The lower layer does the exwork exaction same slimg, it processes the task and comppermitees on to lower layer. If the task is wislimitiated by lower the majority of layer, then the reverse path is considern.

Layecrimson Tasks

Every layer clubs collectively all procedures, protocols, and methods which it requires to execute it is piece of task. All layers identify their particular counterparts by means of encapsulation minder and tail.

OSI Model

Open System Interconnect is an open up standard for all communication systems. OSI model is established by International Standard Organization (ISO). This model has salso layers:

OSI Model

  • Application Layer: This layer is responsible for providing interface to the application user. This layer encomcomppermitees protocols which immediately interwork with the user.

  • Presentation Layer: This layer degreats how data in the native format of remote host need to be presented in the native format of host.

  • Session Layer: This layer maintains sessions between remote hosts. For example, once user/comppermiteword authentication is done, the remote host maintains this particular session for a while and does not ask for authentication again in thead wear time span.

  • Transslot Layer: This layer is responsible for end-to-end delivery between hosts.

  • Ne2rk Layer: This layer is responsible for adoutfit bumignment and uniquely addresperform hosts in a ne2rk.

  • Data Link Layer: This layer is responsible for reading and writing data from and onto the range. Link errors are detected at this particular layer.

  • Physical Layer: This layer degreats the hardware, cabling wiring, power awayplace, pulse rate etc.

Internet Model

Internet uses TCP/IP protocol suite, also belowstandn as Internet suite. This degreats Internet Model which contains four layecrimson architecture. OSI Model is general communication model but Internet Model is exworkly exactionly whead wear the internet uses for all it is communication.The internet is wislimdependent of it is belowlying ne2rk architecture so is it is Model. This model has the folloearng layers:

Internet Model

  • Application Layer: This layer degreats the protocol which enables user to interwork with the ne2rk.For example, FTP, HTTP etc.

  • Transslot Layer: This layer degreats how data need to flow between hosts. Major protocol at this particular layer is Transmission Control Protocol (TCP). This layer ensures data delivecrimson between hosts is wislim-order and is responsible for end-to-end delivery.

  • Internet Layer: Internet Protocol (IP) works on this particular layer. This layer facilitates host addresperform and recognition. This layer degreats rawaying.

  • Link Layer: This layer provides mechanism of sending and receiving workual data.Unlike it is OSI Model counterpart, this particular layer is wislimdependent of belowlying ne2rk architecture and hardware.

Complaceer Ne2rk Security

During preliminary days of internet, it is use was limited to military and universit down downies for rereoceanrch and producement purpose. Later when all ne2rks merged collectively and formed internet, the data useds to travel through public transit down down ne2rk.Common people may send the data thead wear can be highly sensit down downive such as their particular bank ccrimsonentials, username and comppermitewords, private documents, onrange shopping details, or confidential documents.

All security threats are intentional i.e. they occur only if intentionally triggecrimson. Security threats can be divided into the folloearng categories:

  • Interruption

    Interruption is a security threat in which availcapcapability of resources is attacked. For example, a user is unable to access it is web-server or the web-server is hijacked.

  • Privacy-Brevery

    In this particular threat, the privacy of a user is compromised. Someone, who is not the authorised person is accesperform or intercepting data sent or received by the unique authenticated user.

  • Integrity

    This type of threat includes any kind of alteration or modification in the unique context of communication. The attacker intercepts and receives the data sent by the sender and the attacker then possibly modifies or generates false data and sends to the receiver. The receiver receives the data bumuming thead wear it is being sent by the unique Sender.

  • Authenticity

    This threat occurs when an attacker or a security violator, poses as a authentic person and accesses the resources or communicates with other authentic users.

No technique in the present world can provide 100% security. But steps can be considern to secure data while it travels in unsecucrimson ne2rk or internet. The the majority of widely used technique is Cryptography.


Cryptography is a technique to enweeppt the fundamental-text data which produces it difficult to belowstand and interpret. There are some weepptographic algorithms available present day as described below:

  • Secret Key

  • Public Key

  • Message Digest

Secret Key Enweepption

Both sender and receiver have one secret key. This secret key is used to enweeppt the data at sender’s end. After the data is enweeppted, it is sent on the public domain to the receiver. Because the receiver belowstands and has the Secret Key, the enweeppted data packets can easily be deweeppted.

Example of secret key enweepption is Data Enweepption Standard (DES). In Secret Key enweepption, it is requicrimson to have a separate key for every host on the ne2rk macalifornia king it difficult to manage.

Public Key Enweepption

In this particular enweepption system, every user has it is own Secret Key and it is not in the shacrimson domain. The secret key is never revealed on public domain. Adurationy with secret key, every user has it is own but public key. Public key is always made public and is used by Senders to enweeppt the data. When the user receives the enweeppted data, he can easily deweeppt it by uperform it is own Secret Key.

Example of public key enweepption is Rivest-Shamir-Adleman (RSA).

Message Digest

In this particular method, workual data is not sent, instead a hash value is calculated and sent. The other end user, complacees it is own hash value and compares with the one simply received.If both hash values are go withed, then it is accepted otherwise rejected.

Example of Message Digest is MD5 hashing. It is the majority ofly used in authentication where user comppermiteword is combination checked with the one saved on the server.

Physical Layer – Introduction

Physical layer in the OSI model plays the role of interworcalifornia king with workual hardware and signaling mechanism. Physical layer is the only layer of OSI ne2rk model which workually deals with the physical connectivity of 2 various stations. This layer degreats the hardware equipment, cabling, wiring, frequencies, pulses used to represent binary signals etc.

Physical layer provides it is services to Data-link layer. Data-link layer hands over frames to physical layer. Physical layer converts all of all of them to electrical pulses, which represent binary data.The binary data is then sent over the wicrimson or cableless media.


When data is sent over physical medium, it needs to be very first converted into electromagnetic signals. Data it iself can be analog such as individual voice, or digital such as file on the disk.Both analog and digital data can be represented in digital or analog signals.

  • Digital Signals

    Digital signals are discrete in character and represent sequence of voltage pulses. Digital signals are used wislim the circuicheck of a complaceer system.

  • Analog Signals

    Analog signals are in continuous wave form in character and represented by continuous electromagnetic waves.

Transmission Impairment

When signals travel through the medium they tend to deteriorate. This may have many kind of reasons as given:

  • Attenuation

    For the receiver to interpret the data precisely, the signal must be sufficiently strong.When the signal comppermitees through the medium, it tends to get weaker.As it covers distance, it loses strength.

  • Dispersion

    As signal travels through the media, it tends to spread and overlaps. The amount of dispersion depends upon the frequency used.

  • Delay distortion

    Signals are sent over media with pre-degreatd speed and frequency. If the signal speed and frequency do not go with, there are possibiliconnects thead wear signal reveryes destination in arbitrary fashion. In digital media, this particular is very critical thead wear some bit is revery earare locatedr than the previously sent ones.

  • Noise

    Random disturbance or fluctuation in analog or digital signal is said to be Noise in signal, which may distort the workual information being carried. Noise can be charworkerized in one of the folloearng course:

    • Thermal Noise

      Heat agitates the digital conductors of a medium which may introduce sound in the media. Up to a specific level, thermal sound is unavoidable.

    • Intermodulation

      When multiple frequencies share a medium, their particular interference can cause sound in the medium. Intermodulation sound occurs if 2 various frequencies are sharing a medium and one of all of all of them has excessive strength or the component it iself is not functioning properly, then the resultant frequency may not be delivecrimson as expected.

    • Crosstalk

      This sort of sound happens when a foreign signal enters into the media. This is because signal in one medium affects the signal of second medium.

    • Impulse

      This sound is wislimtroduced because of irregular disturbances such as lightening, electricity, short-circuit, or faulty components. Digital data is the majority ofly affected by this particular sort of sound.

Transmission Media

The media over which the information between 2 complaceer systems is sent, called transmission media. Transmission media comes in 2 forms.

  • Guided Media

    All communication cables/cables are guided media, such as UTP, coaxial cables, and fiber Optics. In this particular media, the sender and receiver are immediately connected and the information is send (guided) through it.

  • Unguided Media

    Wireless or open up air space is said to be unguided media, because there is no connectivity between the sender and receiver. Information is spread over the air, and any kind ofone including the workual recipient may collect the information.

Channel Capacity

The speed of transmission of information is said to be the channel capacity. We count it as data rate in digital world. It depends on numerous fworkors such as:

  • Bandwidth:  The physical limitation of belowlying media.

  • Error-rate:  Inproper reception of information because of sound.

  • Encoding:  The number of levels used for signaling.


Multiplexing is a technique to mix and send multiple data streams over a performle medium. This technique requires system hardware called multiplexer (MUX) for multiplexing the streams and sending all of all of them on a medium, and de-multiplexer (DMUX) which considers information from the medium and distributes to various destinations.


Switching is a mechanism by which data/information sent from source towards destination which are not immediately connected. Ne2rks have interconnecting devices, which receives data from immediately connected sources, stores data, analyze it and then forwards to the next interconnecting device close upst to the destination.

Switching can be categorized as:


Digital Transmission

Data or information can be stocrimson in 2 ways, analog and digital. For a complaceer to use the data, it must be in discrete digital form.Similar to data, signals can also be in analog and digital form. To transmit data digitally, it needs to be very first converted to digital form.

Digital-to-Digital Conversion

This section exfundamentals how to convert digital data into digital signals. It can be done in 2 ways, range coding and block coding. For all communications, range coding is essential whereas block coding is optional.

Line Coding

The process for converting digital data into digital signal is said to be Line Coding. Digital data is found in binary format.It is represented (stocrimson) internally as series of 1s and 0s.

Line Coding

Digital signal is denoted by discreet signal, which represents digital data.There are three types of range coding schemes available:

Line Coding

Uni-polar Encoding

Unipolar encoding schemes use performle voltage level to represent data. In this particular case, to represent binary 1, high voltage is transmitted and to represent 0, no voltage is transmitted. It is also called Unipolar-Non-return-to-zero, because there is no rest condition i.e. it possibly represents 1 or 0.

UniPolar NRZ Encoding

Polar Encoding

Polar encoding scheme uses multiple voltage levels to represent binary values. Polar encodings is available in four types:

  • Polar Non-Return to Zero (Polar NRZ)

    It uses 2 various voltage levels to represent binary values. Generally, posit down downive voltage represents 1 and negative value represents 0. It is also NRZ because there is no rest condition.

    NRZ scheme has 2 variants: NRZ-L and NRZ-I.

    Unipolar NRZ

    NRZ-L modifys voltage level at when a various bit is encountecrimson whereas NRZ-I modifys voltage when a 1 is encountecrimson.

  • Return to Zero (RZ)

    Problem with NRZ is thead wear the receiver cannot conclude when a little ended and when the next bit is started, in case when sender and receiver’s clock are not synchronized.


    RZ uses three voltage levels, posit down downive voltage to represent 1, negative voltage to represent 0 and zero voltage for none. Signals modify during bit is not between bit is.

  • Manchester

    This encoding scheme is a combination of RZ and NRZ-L. Bit time is divided into 2 halves. It transit down downs in the middle of the bit and modifys phase when a various bit is encountecrimson.

  • Differential Manchester

    This encoding scheme is a combination of RZ and NRZ-I. It also transit down down at the middle of the bit but modifys phase only when 1 is encountecrimson.

Bipolar Encoding

Bipolar encoding uses three voltage levels, posit down downive, negative and zero. Zero voltage represents binary 0 and bit 1 is represented by altering posit down downive and negative voltages.

Block Coding

To ensure accuracy of the received data frame crimsonundant bit is are used. For example, in also-parity, one parity bit is added to produce the count of 1s in the frame also. This way the unique number of bit is is wislimcrreare locatedved. It is called Block Coding.

Block coding is represented by slash notation, mB/nB.Means, m-bit block is substituted with n-bit block where n > m. Block coding involves three steps:

  • Division,
  • Substitution
  • Combination.

After block coding is done, it is range coded for transmission.

Analog-to-Digital Conversion

Miplantshones produce analog voice and camera produces analog videos, which are treated is analog data. To transmit this particular analog data over digital signals, we need analog to digital conversion.

Analog data is a continuous stream of data in the wave form whereas digital data is discrete. To convert analog wave into digital data, we use Pulse Code Modulation (PCM).

PCM is one of the the majority of commonly used method to convert analog data into digital form. It involves three steps:

  • Sampling
  • Quantization
  • Encoding.



The analog signal is sampled every T interval. Most imslotant fworkor in sampling is the rate at which analog signal is sampled. According to Nyquist Theorem, the sampling rate must be at minimumern 2 times of the highest frequency of the signal.



Sampling yields discrete form of continuous analog signal. Every discrete pattern shows the amplitude of the analog signal at thead wear instance. The quantization is done between the maximum amplitude value and the minimum amplitude value. Quantization is approximation of the immediateaneous analog value.



In encoding, every approximated value is then converted into binary format.

Transmission Modes

The transmission mode decides how data is transmitted between 2 complaceers.The binary data in the form of 1s and 0s can be sent in 2 various modes: Parallel and Serial.

Parallel Transmission

Parallel Transmission

The binary bit is are body body organised in-to groups of fixed duration. Both sender and receiver are connected in parallel with the equal number of data ranges. Both complaceers distinguish between high order and low order data ranges. The sender sends all the bit is at once on all ranges.Because the data ranges are equal to the number of bit is in a group or data frame, a compenablee group of bit is (data frame) is sent in one go. Advantage of Parallel transmission is high speed and didepresperformvantage is the cost of cables, as it is equal to the number of bit is sent in parallel.

Serial Transmission

In serial transmission, bit is are sent one after an additional in a queue manner. Serial transmission requires only one communication channel.

Serial Transmission

Serial transmission can be possibly asynchronous or synchronous.

Asynchronous Serial Transmission

It is named so because there’is no imslotance of timing. Data-bit is have specific pattern and they help receiver recognise the start and end data little’s.For example, a 0 is prefixed on every data byte and one or more 1s are added at the end.

Two continuous data-frames (bytes) may have a gap between all of all of them.

Synchronous Serial Transmission

Timing in synchronous transmission has imslotance as there is no mechanism followed to recognise start and end data little’s.There is no pattern or prefix/suffix method. Data little’s are sent in burst mode withaway maintaining gap between bytes (8-bit is). Single burst of data little’s may contain lots of bytes. Therefore, timing becomes very imslotant.

It is up to the receiver to recognise and separate bit is into bytes.The advantage of synchronous transmission is high speed, and it has no overmind of extra minder and footer bit is as in asynchronous transmission.

Analog Transmission

To send the digital data over an analog media, it needs to be converted into analog signal.There can be 2 cases according to data formatting.

Bandcomppermite:The filters are used to filter and comppermite frequencies of curiosit down downy. A bandcomppermite is a band of frequencies which can comppermite the filter.

Low-comppermite: Low-comppermite is a filter thead wear comppermitees low frequencies signals.

When digital data is converted into a bandcomppermite analog signal, it is called digital-to-analog conversion. When low-comppermite analog signal is converted into bandcomppermite analog signal, it is called analog-to-analog conversion.

Digital-to-Analog Conversion

When data from one complaceer is sent to an additional via some analog carrier, it is very first converted into analog signals. Analog signals are modified to reflect digital data.

An analog signal is charworkerized by it is amplitude, frequency, and phase. There are three kinds of digital-to-analog conversions:

  • Amplitude Shift Keying

    In this particular conversion technique, the amplitude of analog carrier signal is modified to reflect binary data.

    Amplitude Shift Keying

    When binary data represents digit 1, the amplitude is held; otherwise it is set to 0. Both frequency and phase remain exwork exaction same as in the unique carrier signal.

  • Frequency Shift Keying

    In this particular conversion technique, the frequency of the analog carrier signal is modified to reflect binary data.

    Frequency Shift Keying

    This technique uses 2 frequencies, f1 and f2. One of all of all of them, for example f1, is chosen to represent binary digit 1 and the other one is used to represent binary digit 0. Both amplitude and phase of the carrier wave are kept intwork.

  • Phase Shift Keying

    In this particular conversion scheme, the phase of the unique carrier signal is altecrimson to reflect the binary data.

    Phase Shift Keying

    When a brand new binary symbol is encountecrimson, the phase of the signal is altecrimson. Amplitude and frequency of the unique carrier signal is kept intwork.

  • Quadrature Phase Shift Keying

    QPSK alters the phase to reflect 2 binary digit is at once. This is done in 2 various phases. The main stream of binary data is divided equally into 2 sub-streams. The serial data is converted in to parallel in both sub-streams and then every stream is converted to digital signal uperform NRZ technique. Later, both the digital signals are merged collectively.

Analog-to-Analog Conversion

Analog signals are modified to represent analog data. This conversion is also belowstandn as Analog Modulation. Analog modulation is requicrimson when bandcomppermite is used. Analog to analog conversion can be done in three ways:

Analog Modulation

  • Amplitude Modulation

    In this particular modulation, the amplitude of the carrier signal is modified to reflect the analog data.

    Amplitude Modulation

    Amplitude modulation is implemented by means of a multipare locatedr. The amplitude of modulating signal (analog data) is multipare locatedd by the amplitude of carrier frequency, which then reflects analog data.

    The frequency and phase of carrier signal remain unmodifyd.

  • Frequency Modulation

    In this particular modulation technique, the frequency of the carrier signal is modified to reflect the modify in the voltage levels of the modulating signal (analog data).

    Frequency Modulation

    The amplitude and phase of the carrier signal are not altecrimson.

  • Phase Modulation

    In the modulation technique, the phase of carrier signal is modulated in order to reflect the modify in voltage (amplitude) of analog data signal.

    Phase Modulation

    Phase modulation is prworkically similar to Frequency Modulation, but in Phase modulation frequency of the carrier signal is not incrreare locatedved. Frequency of carrier is signal is modifyd (made dense and sparse) to reflect voltage modify in the amplitude of modulating signal.

Transmission Media

The transmission media is noslimg but the physical media over which communication considers place in complaceer ne2rks.

Magnetic Media

One of the the majority of convenient way to transfer data from one complaceer to an additional, also before the birth of ne2rcalifornia king, was to save it on some storage media and transfer physical from one station to an additional. Though it may seem old-fashion way in today’s world of high speed internet, but when the dimension of data is huge, the magnetic media comes into play.

For example, a bank has to handle and transfer huge data of it is customer, which stores a backup of it at some geographically far-away place for security reasons and to maintain it from unspecific calamiconnects. If the bank needs to store it is huge backup data then it is,transfer through internet is not feasible.The WAN links may not supslot such high speed.Even if they do; the cost too high to afford.

In these cases, data backup is stocrimson onto magnetic tapes or magnetic discs, and then shifted physically at remote places.

Twisted Pair Cable

A twisted pair cable is made of 2 pfinalic insulated copper cables twisted collectively to form a performle media. Out of these 2 cables, only one carries workual signal and an additional is used for ground reference. The twists between cables are helpful in crimsonucing sound (electro-magnetic interference) and combinationtalk.

There are 2 types of twisted pair cables:

  • Shielded Twisted Pair (STP) Cable

  • Unshielded Twisted Pair (UTP) Cable

STP cables comes with twisted cable pair covecrimson in steel foil. This produces it more invarious to sound and combinationtalk.

UTP has salso categories, every suitable for specific use. In complaceer ne2rks, Cat-5, Cat-5e, and Cat-6 cables are the majority ofly used. UTP cables are connected by RJ45 connectors.

Coaxial Cable

Coaxial cable has 2 cables of copper. The core cable are locateds in the centre and it is made of solid conductor.The core is enclose upd in an insulating sheath.The second cable is wrapped around over the sheath and thead wear too in turn encased by insulator sheath.This all is covecrimson by pfinalic cover.

Coaxial Cable

Because of it is structure,the coax cable is capable of carrying high frequency signals than thead wear of twisted pair cable.The wrapped structure provides it a great shield against sound and combination talk. Coaxial cables provide high bandwidth rates of up to 450 mbps.

There are three categories of coax cables namely, RG-59 (Cable TV), RG-58 (Thin Ethernet), and RG-11 (Thick Ethernet). RG stands for Radio Government.

Cables are connected uperform BNC connector and BNC-T. BNC terminator is used to terminate the cable at the far ends.

Power Lines

Power Line communication (PLC) is Layer-1 (Physical Layer) technology which uses power cables to transmit data signals.In PLC, modulated data is sent over the cables. The receiver on the other end de-modulates and interprets the data.

Because power ranges are widely deployed, PLC can produce all powecrimson devices manageled and monitocrimson. PLC works in half-duplex.

There are 2 types of PLC:

  • Narrange band PLC

  • Broad band PLC

Narrange band PLC provides lower data rates up to 100s of kbps, as they work at lower frequencies (3-5000 kHz).They can be spread over some kilometers.

Broadband PLC provides higher data rates up to 100s of Mbps and works at higher frequencies (1.8 – 250 MHz).They cannot be as a lot extended as Narrangeband PLC.

Fiber Optics

Fiber Optic works on the properconnects of light. When light ray hit is at critical angle it tends to refrworks at 90 degree. This home has been used in fiber optic. The core of fiber optic cable is made of high quality cup or pfinalic. From one end of it light is emitted, it travels through it and at the other end light detector detects light stream and converts it to electric data.

Fiber Optic provides the highest mode of speed. It comes in 2 modes, one is performle mode fiber and second is multimode fiber. Single mode fiber can carry a performle ray of light whereas multimode is capable of carrying multiple beams of light.

Fiber Optics

Fiber Optic also comes in uniimmediateional and biimmediateional capabiliconnects. To connect and access fiber optic special type of connectors are used. These can be Subscriber Channel (SC), Straight Tip (ST), or MT-RJ.

Wireless Transmission

Wireless transmission is a form of unguided media. Wireless communication involves no physical link established between 2 or more devices, communicating cablelessly. Wireless signals are spread over in the air and are received and interpreted by appropriate antennas.

When an antenna is attached to electrical circuit of a complaceer or cableless device, it converts the digital data into cableless signals and spread all over wislim it is frequency range. The receptor on the other end receives these signals and converts all of all of them back to digital data.

A small part of electromagnetic spectrum can be used for cableless transmission.

Electromagnetic Spectrum

Radio Transmission

Radio frequency is easier to generate and because of it is big waveduration it can penetrate through walls and structures alike.Radio waves can have waveduration from 1 mm – 100,000 km and have frequency ranging from 3 Hz (Extremely Low Frequency) to 300 GHz (Extremely High Frequency). Radio frequencies are sub-divided into six bands.

Radio waves at lower frequencies can travel through walls whereas higher RF can travel in straight range and bounce back.The power of low frequency waves decrreare locatedves razor-razor-sharply as they cover durationy distance. High frequency stereo waves have more power.

Lower frequencies such as VLF, LF, MF bands can travel on the ground up to 1000 kilometers, over the earth’s surface.

Radio wave - grounded

Radio waves of high frequencies are prone to be absorbed by rain and other obstacles. They use Ionosphere of earth atmosphere. High frequency stereo waves such as HF and VHF bands are spread upwards. When they revery Ionosphere, they are refrworked back to the earth.

Radio wave - Ionosphere

Micrangeave Transmission

Electromagnetic waves above 100 MHz tend to travel in a straight range and signals over all of all of them can be sent by beaming those waves towards one particular station. Because Micrangeaves travels in straight ranges, both sender and receiver must be aligned to be rigorously in range-of-sight.

Micrangeaves can have waveduration ranging from 1 mm – 1 meter and frequency ranging from 300 MHz to 300 GHz.

Personal Area Ne2rk

Micrangeave antennas concentrate the waves macalifornia king a beam of it. As shown in picture above, multiple antennas can be aligned to revery farther. Micrangeaves have higher frequencies and do not penetrate wall like obstacles.

Micrangeave transmission depends highly upon the climate conditions and the frequency it is uperform.

Infracrimson Transmission

Infracrimson wave are locateds in between noticeable light spectrum and micrangeaves. It has waveduration of 700-nm to 1-mm and frequency ranges from 300-GHz to 430-THz.

Infracrimson wave is used for very short range communication purposes such as television and it’s remote. Infracrimson travels in a straight range hence it is immediateional by character. Because of high frequency range, Infracrimson cannot combination wall-like obstacles.

Light Transmission

Highest the majority of electromagnetic spectrum which can be used for data transmission is light or optical signaling. This is achieved by means of LASER.

Because of frequency light uses, it tends to travel rigorously in straight range.Hence the sender and receiver must be in the range-of-sight. Because laser transmission is uniimmediateional, at both ends of communication the laser and the photo-detector needs to be installed. Laser beam is generally 1mm wide hence it is a work of precision to align 2 far receptors every stageing to lasers source.

Light Transmission

Laser works as Tx (transmitter) and photo-detectors works as Rx (receiver).

Lasers cannot penetrate obstacles such as walls, rain, and solid fog. Additionally, laser beam is distorted by earnd, atmosphere temperature, or variation in temperature in the path.

Laser is secure for data transmission as it is very difficult to tap 1mm wide laser withaway interrupting the communication channel.


Multiplexing is a technique by which various analog and digital streams of transmission can be simultaneously processed over a shacrimson link. Multiplexing divides the high capacity medium into low capacity logical medium which is then shacrimson by various streams.

Communication is probable over the air (stereo frequency), uperform a physical media (cable), and light (optical fiber). All mediums are capable of multiplexing.

When multiple senders check to send over a performle medium, a device called Multiplexer divides the physical channel and allocates one to every. On the other end of communication, a De-multiplexer receives data from a performle medium, identifies every, and sends to various receivers.

Frequency Division Multiplexing

When the carrier is frequency, FDM is used. FDM is an analog technology. FDM divides the spectrum or carrier bandwidth in logical channels and allocates one user to every channel. Each user can use the channel frequency independently and has exclusive access of it. All channels are divided in such a way thead wear they do not overlap with every other. Channels are separated by guard bands. Guard band is a frequency which is not used by possibly channel.

Frequency Division Multiplexing

Time Division Multiplexing

TDM is appare locatedd primarily on digital signals but can be appare locatedd on analog signals as well. In TDM the shacrimson channel is divided among it is user by means of time slot. Each user can transmit data wislim the provided time slot only. Digital signals are divided in frames, equivalent to time slot i.e. frame of an optimal dimension which can be transmitted in given time slot.

TDM works in synchronized mode. Both ends, i.e. Multiplexer and De-multiplexer are timely synchronized and both switch to next channel simultaneously.

Time Division Multiplexing

When channel A transmit is it is frame at one end,the De-multiplexer provides media to channel A on the other end.As soon as the channel A’s time slot expires, this particular part switches to channel B. On the other end, the De-multiplexer works in a synchronized manner and provides media to channel B. Signals from various channels travel the path in interdepartd manner.

Waveduration Division Multiplexing

Light has various waveduration (colours). In fiber optic mode, multiple optical carrier signals are multiplexed into an optical fiber by uperform various wavedurations. This is an analog multiplexing technique and is done conceptually in the exwork exaction same manner as FDM but uses light as signals.

Waveduration Division Multiplexing

Further, on every waveduration time division multiplexing can be incorporated to accommodate more data signals.

Code Division Multiplexing

Multiple data signals can be transmitted over a performle frequency by uperform Code Division Multiplexing. FDM divides the frequency in smaller channels but CDM enables it is users to comppermite bandwidth and transmit signals all the time uperform a unique code. CDM uses orthogonal codes to spread signals.

Each station is bumigned with a unique code, called chip. Signals travel with these codes independently, inpart the whole bandwidth.The receiver belowstands beforehand the chip code signal it has to receive.

Ne2rk Switching

Switching is process to forward packets coming in from one slot to a slot leading towards the destination. When data comes on a slot it is called ingress, and when data departs a slot or goes away it is called egress. A communication system may include number of switches and nodes. At wide level, switching can be divided into 2 major categories:

  • Connectionless: The data is forwarded on behalf of forwarding tables. No previous handshacalifornia king is requicrimson and acbelowstandladvantagements are optional.

  • Connection Oriented:  Before switching data to be forwarded to destination, there is a need to pre-establish circuit adurationy the path between both endstages. Data is then forwarded on thead wear circuit. After the transfer is compenableed, circuit is can be kept for future use or can be turned down immediately.

Circuit Switching

When 2 nodes communicate with every other over a dedicated communication path, it is called circuit switching.There 'is a need of pre-specified rawaye from which data will travels and no other data is permitted.In circuit switching, to transfer the data, circuit must be established so thead wear the data transfer can consider place.

Circuit is can be permanent or temporary. Applications which use circuit switching may have to go through three phases:

  • Establish a circuit

  • Transfer the data

  • Disconnect the circuit

Circuit Switching

Circuit switching was styleed for voice applications. Telephone is the best suitable example of circuit switching. Before a user can produce a call, a virtual path between caller and callee is established over the ne2rk.

Message Switching

This technique was somewhere in middle of circuit switching and packet switching. In message switching, the whole message is treated as a data device and is switching / transfercrimson in it is entirety.

A switch worcalifornia king on message switching, very first receives the whole message and buffers it until there are resources available to transfer it to the next hop. If the next hop is not having sufficient resource to accommodate big dimension message, the message is stocrimson and switch wait is.

Message Switching

This technique was conpartcrimson substitute to circuit switching. As in circuit switching the whole path is blocked for 2 enticonnects only. Message switching is replaced by packet switching. Message switching has the folloearng drawbacks:

  • Every switch in transit down down path needs sufficient storage to accommodate entire message.

  • Because of store-and-forward technique and wait is included until resources are available, message switching is very slower.

  • Message switching was not a solution for streaming media and real-time applications.

Packet Switching

Shortcomings of message switching provided birth to an idea of packet switching. The entire message is broken down into smaller chunks called packets. The switching information is added in the minder of every packet and transmitted independently.

It is easier for intermediate ne2rcalifornia king devices to store small dimension packets and they do not consider a lot resources possibly on carrier path or in the internal memory of switches.

Packet Switching

Packet switching enhances range efficiency as packets from multiple applications can be multiplexed over the carrier. The internet uses packet switching technique. Packet switching enables the user to variousiate data streams based on prioriconnects. Packets are stocrimson and forwarded according to their particular priority to provide quality of service.

Data-link Layer Introduction

Data Link Layer is second layer of OSI Layecrimson Model. This layer is one of the the majority of complicated layers and has complex functionaliconnects and liabiliconnects. Data link layer hides the details of belowlying hardware and represents it iself to upper layer as the medium to communicate.

Data link layer works between 2 hosts which are immediately connected in some sense. This immediate interconnection can be stage to stage or widecast. Systems on widecast ne2rk are said to be on exwork exaction same link. The work of data link layer tends to get more complex when it is dealing with multiple hosts on performle collision domain.

Data link layer is responsible for converting data stream to signals bit by bit and to send thead wear over the belowlying hardware. At the receiving end, Data link layer picks up data from hardware which are in the form of electrical signals, bumembles all of all of them in a recognizable frame format, and hands over to upper layer.

Data link layer has 2 sub-layers:

  • Logical Link Control: It deals with protocols, flow-manage, and error manage

  • Media Access Control: It deals with workual manage of media

Functionality of Data-link Layer

Data link layer does many kind of tasks on behalf of upper layer. These are:

  • Framing

    Data-link layer considers packets from Ne2rk Layer and encapsulates all of all of them into Frames.Then, it sends every frame bit-by-bit on the hardware. At receiver’ end, data link layer picks up signals from hardware and bumembles all of all of them into frames.

  • Addresperform

    Data-link layer provides layer-2 hardware addresperform mechanism. Hardware adoutfit is bumumed to be unique on the link. It is encoded into hardware at the time of manufworkuring.

  • Synchronization

    When data frames are sent on the link, both machines must be synchronized in order to transfer to consider place.

  • Error Control

    Sometimes signals may have encountecrimson issue in transit down downion and the bit is are flipped.These errors are detected and attempted to recover workual data little’s. It also provides error resloting mechanism to the sender.

  • Flow Control

    Stations on exwork exaction same link may have various speed or capacity. Data-link layer ensures flow manage thead wear enables both machine to exmodify data on exwork exaction same speed.

  • Multi-Access

    When host on the shacrimson link tries to transfer the data, it has a high probcapcapability of collision. Data-link layer provides mechanism such as CSMA/CD to equip capcapcapability of accesperform a shacrimson media among multiple Systems.

Error Detection and Correction

There are many kind of reasons such as sound, combination-talk etc., which may help data to get corrupted during transmission. The upper layers work on some generalized see of ne2rk architecture and are not aware of workual hardware data procesperform.Hence, the upper layers expect error-free transmission between the systems. Most of the applications would not function expectedly if they receive erroneous data. Applications such as voice and video may not be thead wear affected and with some errors they may still function well.

Data-link layer uses some error manage mechanism to ensure thead wear frames (data little streams) are transmitted with specific level of accuracy. But to belowstand how errors is manageled, it is essential to belowstand exworkly exactionly whead wear types of errors may occur.

Types of Errors

There may be three types of errors:

  • Single bit error

    Single bit error

    In a frame, there is only one bit, any kind ofwhere though, which is corrupt.

  • Multiple bit is error

    Multiple bit is error

    Frame is received with more than one bit is in corrupted state.

  • Burst error

    Burst error

    Frame contains more than1 consecutive bit is corrupted.

Error manage mechanism may involve 2 probable ways:

  • Error detection

  • Error properion

Error Detection

Errors in the received frames are detected by means of Parity Check and Cyclic Redundancy Check (CRC). In both cases, couple of extra little’s are sent adurationy with workual data to confirm thead wear bit is received at other end are exwork exaction same as they were sent. If the counter-check at receiver’ end fails, the bit is are conpartcrimson corrupted.

Parity Check

One extra little is sent adurationy with the unique bit is to produce number of 1s possibly also in case of also parity, or odd in case of odd parity.

The sender while creating a frame counts the number of 1s in it. For example, if also parity is used and number of 1s is also then one bit with value 0 is added. This way number of 1s remains also.If the number of 1s is odd, to produce it also a little with value 1 is added.

Even Parity

The receiver simply counts the number of 1s in a frame. If the count of 1s is also and also parity is used, the frame is conpartcrimson to be not-corrupted and is accepted. If the count of 1s is odd and odd parity is used, the frame is still not corrupted.

If a performle bit flips in transit down down, the receiver can detect it by counting the number of 1s. But when more than one bit is are erro neous, then it is very difficult for the receiver to detect the error.

Cyclic Redundancy Check (CRC)

CRC is a various approach to detect if the received frame contains valid data. This technique involves binary division of the data little’s being sent. The divisor is generated uperform polynomials. The sender performs a division operation on the bit is being sent and calculates the remainder. Before sending the workual bit is, the sender adds the remainder at the end of the workual bit is. Actual data little’s plus the remainder is called a codeword. The sender transmit is data little’s as codewords.


At the other end, the receiver performs division operation on codewords uperform the exwork exaction same CRC divisor. If the remainder contains all zeros the data little’s are accepted, otherwise it is conpartcrimson as there some data corruption occurcrimson in transit down down.

Error Correction

In the digital world, error properion can be done in 2 ways:

  • Backward Error Correction  When the receiver detects an error in the data received, it requests back the sender to retransmit the data device.

  • Forward Error Correction  When the receiver detects some error in the data received, it executes error-propering code, which helps it to auto-recover and to proper some kinds of errors.

The very first one, Backward Error Correction, is fundamental and can only be effectively used where retransmitting is not expensive. For example, fiber optics. But in case of cableless transmission retransmitting may cost too a lot. In the latter case, Forward Error Correction is used.

To proper the error in data frame, the receiver must belowstand exworkly which bit in the frame is corrupted. To locate the bit in error, crimsonundant bit is are used as parity bit is for error detection.For example, we consider ASCII words (7 bit is data), then there can be 8 kind of information we need: very first salso bit is to tell us which bit is error and one more bit to tell thead wear there is no error.

For m data little’s, r crimsonundant bit is are used. r bit is can provide 2r combinations of information. In m+r bit codeword, there is possibility thead wear the r bit is all of all of themselves may get corrupted. So the number of r bit is used must inform abaway m+r bit locations plus no-error information, i.e. m+r+1.

Requicrimson bit is

Data-link Control and Protocols

Data-link layer is responsible for implementation of stage-to-stage flow and error manage mechanism.

Flow Control

When a data frame (Layer-2 data) is sent from one host to an additional over a performle medium, it is requicrimson thead wear the sender and receiver need to work at the exwork exaction same speed. Thead wear is, sender sends at a speed on which the receiver can process and accept the data. Whead wear if the speed (hardware/smoothware) of the sender or receiver differs? If sender is sending too fast the receiver may be overloaded, (swamped) and data may be lost.

Two types of mechanisms can be deployed to manage the flow:

  • Stop and Wait

    This flow manage mechanism forces the sender after transmitting a data frame to quit and wait until the acbelowstandladvantagement of the data-frame sent is received.

    Stop and Wait

  • Sliding Window

    In this particular flow manage mechanism, both sender and receiver concur on the number of data-frames after which the acbelowstandladvantagement need to be sent. As we find outt, quit and wait flow manage mechanism wastes resources, this particular protocol tries to produce use of belowlying resources as a lot as probable.

Error Control

When data-frame is transmitted, there is a probcapcapability thead wear data-frame may be lost in the transit down down or it is received corrupted. In both cases, the receiver does not receive the proper data-frame and sender does not belowstand any kind ofslimg abaway any kind of loss.In such case, both sender and receiver are equipped with some protocols which helps all of all of them to detect transit down down errors such as loss of data-frame. Hence, possibly the sender retransmit is the data-frame or the receiver may request to resend the previous data-frame.

Requirements for error manage mechanism:

  • Error detection  – The sender and receiver, possibly both or any kind of, must bumpecific thead wear there is some error in the transit down down.

  • Posit down downive ACK  – When the receiver receives a proper frame, it need to acbelowstandladvantage it.

  • Negative ACK  – When the receiver receives a damaged frame or a duplicate frame, it sends a NACK back to the sender and the sender must retransmit the proper frame.

  • Retransmission:  The sender maintains a clock and sets a timeaway period. If an acbelowstandladvantagement of a data-frame previously transmitted does not arrive before the timeaway the sender retransmit is the frame, pondering thead wear the frame or it’s acbelowstandladvantagement is lost in transit down down.

There are three types of techniques available which Data-link layer may deploy to manage the errors by Automatic Repeat Requests (ARQ):

  • Stop-and-wait ARQ

    Stop and Wait ARQ

    The folloearng transit down downion may occur in Stop-and-Wait ARQ:

    • The sender maintains a timeaway counter.
    • When a frame is sent, the sender starts the timeaway counter.
    • If acbelowstandladvantagement of frame comes in time, the sender transmit is the next frame in queue.
    • If acbelowstandladvantagement does not come in time, the sender bumumes thead wear possibly the frame or it is acbelowstandladvantagement is lost in transit down down. Sender retransmit is the frame and starts the timeaway counter.
    • If a negative acbelowstandladvantagement is received, the sender retransmit is the frame.
  • Go-Back-N ARQ

    Stop and wait ARQ mechanism does not utilize the resources at their particular best.When the acbelowstandladvantagement is received, the sender sit down downs idle and does noslimg. In Go-Back-N ARQ method, both sender and receiver maintain a earndow.

    Go-back-n ARQ

    The sending-earndow dimension enables the sender to send multiple frames withaway receiving the acbelowstandladvantagement of the previous ones. The receiving-earndow enables the receiver to receive multiple frames and acbelowstandladvantage all of all of them. The receiver maintains track of incoming frame’s sequence number.

    When the sender sends all the frames in earndow, it checks up to exworkly exactionly whead wear sequence number it has received posit down downive acbelowstandladvantagement. If all frames are posit down downively acbelowstandladvantaged, the sender sends next set of frames. If sender finds thead wear it has received NACK or has not receive any kind of ACK for a particular frame, it retransmit is all the frames after which it does not receive any kind of posit down downive ACK.

  • Selective Repeat ARQ

    In Go-back-N ARQ, it is bumumed thead wear the receiver does not have any kind of buffer space for it is earndow dimension and has to process every frame as it comes. This enforces the sender to retransmit all the frames which are not acbelowstandladvantaged.

    In Selective-Repeat ARQ, the receiver while maintaining track of sequence numbers, buffers the frames in memory and sends NACK for only frame which is misperform or damaged.

    The sender in this particular case, sends only packet for which NACK is received.

Ne2rk Layer Introduction

Layer-3 in the OSI model is called Ne2rk layer. Ne2rk layer manages options pertaining to host and ne2rk addresperform, managing sub-ne2rks, and interne2rcalifornia king.

Ne2rk layer considers the responsibility for rawaying packets from source to destination wislim or awaypart a subnet. Two various subnet may have various addresperform schemes or non-compatible addresperform types. Same with protocols, 2 various subnet may be operating on various protocols which are not compatible with every other. Ne2rk layer has the responsibility to rawaye the packets from source to destination, chartping various addresperform schemes and protocols.

Layer-3 Functionaliconnects

Devices which work on Ne2rk Layer mainly focus on rawaying. Rawaying may include various tasks aimed to achieve a performle goal. These can be:

  • Addresperform devices and ne2rks.

  • Populating rawaying tables or static rawayes.

  • Queuing incoming and awaygoing data and then forwarding all of all of them according to quality of service constraints set for those packets.

  • Interne2rcalifornia king between 2 various subnets.

  • Delivering packets to destination with best efforts.

  • Provides interconnection oriented and interconnection less mechanism.

Ne2rk Layer Features

With it is standard functionaliconnects, Layer 3 can provide various features as:

  • Quality of service management

  • Load balancing and link management

  • Security

  • Interrelation of various protocols and subnets with various schema.

  • Different logical ne2rk style over the physical ne2rk style.

  • L3 VPN and tunnels can be used to provide end to end dedicated connectivity.

Internet protocol is widely respected and deployed Ne2rk Layer protocol which helps to communicate end to end devices over the internet. It comes in 2 flavours. IPv4 which has ruled the world for decades but now is operatening away of adoutfit space. IPv6 is produced to replace IPv4 and hopecomppermitey mitigates limitations of IPv4 too.

Ne2rk Addresperform

Layer 3 ne2rk addresperform is one of the major tasks of Ne2rk Layer. Ne2rk Adoutfites are always logical i.e. these are smoothware based adoutfites which can be modifyd by appropriate configurations.

A ne2rk adoutfit always stages to host / node / server or it can represent a whole ne2rk. Ne2rk adoutfit is always configucrimson on ne2rk interface card and is generally chartped by system with the MAC adoutfit (hardware adoutfit or layer-2 adoutfit) of the machine for Layer-2 communication.

There are various kinds of ne2rk adoutfites in existence:

  • IP

  • IPX

  • AppleTalk

We are discusperform IP here as it is the only one we use in prworkice these days.

Ne2rk Addresperform

IP addresperform provides mechanism to variousiate between hosts and ne2rk. Because IP adoutfites are bumigned in hierarchical manner, a host always reparts below a specific ne2rk.The host which needs to communicate awaypart it is subnet, needs to belowstand destination ne2rk adoutfit, where the packet/data is to be sent.

Hosts in various subnet need a mechanism to locate every other. This task can be done by DNS. DNS is a server which provides Layer-3 adoutfit of remote host chartped with it is domain name or FQDN. When a host acquires the Layer-3 Adoutfit (IP Adoutfit) of the remote host, it forwards all it is packet to it is gateway. A gateway is a rawayer equipped with all the information which leads to rawaye packets to the destination host.

Rawayers consider help of rawaying tables, which has the folloearng information:

  • Method to revery the ne2rk

Rawayers upon receiving a forwarding request, forwards packet to it is next hop (adjacent rawayer) towards the destination.

The next rawayer on the path follows the exwork exaction same slimg and alsotually the data packet reveryes it is destination.

Ne2rk adoutfit can be of one of the folloearng:

  • Unicast (destined to one host)

  • Multicast (destined to group)

  • Broadcast (destined to all)

  • Anycast (destined to nearest one)

A rawayer never forwards widecast traffic by default. Multicast traffic uses special treatment as it is the majority of a video stream or audio with highest priority. Anycast is simply similar to unicast, other than thead wear the packets are delivecrimson to the nearest destination when multiple destinations are available.

Ne2rk Layer Rawaying

When a device has multiple paths to revery a destination, it always selects one path by preferring it over others. This selection process is termed as Rawaying. Rawaying is done by special ne2rk devices called rawayers or it can be done by means of smoothware processes.The smoothware based rawayers have limited functionality and limited scope.

A rawayer is always configucrimson with some default rawaye. A default rawaye tells the rawayer where to forward a packet if there is no rawaye found for specific destination. In case there are multiple path existing to revery the exwork exaction same destination, rawayer can produce decision based on the folloearng information:

  • Hop Count

  • Bandwidth

  • Metric

  • Prefix-duration

  • Delay

Rawayes can be statically configucrimson or dynamically find outt. One rawaye can be configucrimson to be prefercrimson over others.

Unicast rawaying

Most of the traffic on the internet and intranets belowstandn as unicast data or unicast traffic is sent with specified destination. Rawaying unicast data over the internet is called unicast rawaying. It is the fundamentalst form of rawaying because the destination is already belowstandn. Hence the rawayer simply has to look up the rawaying table and forward the packet to next hop.

Unicast rawaying

Broadcast rawaying

By default, the widecast packets are not rawayed and forwarded by the rawayers on any kind of ne2rk. Rawayers produce widecast domains. But it can be configucrimson to forward widecasts in some special cases. A widecast message is destined to all ne2rk devices.

Broadcast rawaying can be done in 2 ways (algorithm):

  • A rawayer produces a data packet and then sends it to every host one by one. In this particular case, the rawayer produces multiple copies of performle data packet with various destination adoutfites. All packets are sent as unicast but because they are sent to all, it simulates as if rawayer is widecasting.

    This method consumes lots of bandwidth and rawayer must destination adoutfit of every node.

  • Secondly, when rawayer receives a packet thead wear is to be widecasted, it simply floods those packets away of all interfaces. All rawayers are configucrimson in the exwork exaction same way.

    Broadcast rawaying

    This method is easy on rawayer's CPU but may cause the issue of duplicate packets received from peer rawayers.

    Reverse path forwarding is a technique, in which rawayer belowstands beforehand abaway it is pcrimsonecessor from where it need to receive widecast. This technique is used to detect and discard duplicates.

Multicast Rawaying

Multicast rawaying is special case of widecast rawaying with significance difference and challenges. In widecast rawaying, packets are sent to all nodes also if they do not want it. But in Multicast rawaying, the data is sent to only nodes which wants to receive the packets.

Multicast rawaying

The rawayer must belowstand thead wear there are nodes, which wish to receive multicast packets (or stream) then only it need to forward. Multicast rawaying works spanning tree protocol to avoid looping.

Multicast rawaying also uses reverse path Forwarding technique, to detect and discard duplicates and loops.

Anycast Rawaying

Anycast packet forwarding is a mechanism where multiple hosts can have exwork exaction same logical adoutfit. When a packet destined to this particular logical adoutfit is received, it is sent to the host which is nearest in rawaying topology.

Anycast rawaying

Anycast rawaying is done with help of DNS server. Whenever an Anycast packet is received it is enquicrimson with DNS to where to send it. DNS provides the IP adoutfit which is the nearest IP configucrimson on it.

Unicast Rawaying Protocols

There are 2 kinds of rawaying protocols available to rawaye unicast packets:

  • Distance Vector Rawaying Protocol

    Distance Vector is fundamental rawaying protocol which considers rawaying decision on the number of hops between source and destination. A rawaye with less number of hops is conpartcrimson as the best rawaye. Every rawayer advertises it is set best rawayes to other rawayers. Ultimately, all rawayers produce up their particular ne2rk topology based on the advertisements of their particular peer rawayers,

    For example Rawaying Information Protocol (RIP).

  • Link State Rawaying Protocol

    Link State protocol is slightly complicated protocol than Distance Vector. It considers into account the states of links of all the rawayers in a ne2rk. This technique helps rawayes produce a common graph of the entire ne2rk. All rawayers then calculate their particular best path for rawaying purposes.for example, Open Shorcheck Path First (OSPF) and Intermediate System to Intermediate System (ISIS).

Multicast Rawaying Protocols

Unicast rawaying protocols use graphs while Multicast rawaying protocols use trees, i.e. spanning tree to avoid loops. The optimal tree is called shorcheck path spanning tree.

  • DVMRP  – Distance Vector Multicast Rawaying Protocol

  • MOSPF  – Multicast Open Shorcheck Path First

  • CBT  – Core Based Tree

  • PIM  – Protocol independent Multicast

Protocol Independent Multicast is commonly used now. It has 2 flavours:

  • PIM Dense Mode

    This mode uses source-based trees. It is used in dense environment such as LAN.

  • PIM Sparse Mode

    This mode uses shacrimson trees. It is used in sparse environment such as WAN.

Rawaying Algorithms

The rawaying algorithms are as follows:


Flooding is fundamentalst method packet forwarding. When a packet is received, the rawayers send it to all the interfaces other than the one on which it was received. This produces too a lot burden on the ne2rk and lots of duplicate packets wandering in the ne2rk.

Time to Live (TTL) can be used to avoid infinite looping of packets. There exists an additional approach for flooding, which is called Selective Flooding to crimsonuce the overmind on the ne2rk. In this particular method, the rawayer does not flood away on all the interfaces, but selective ones.

Shorcheck Path

Rawaying decision in ne2rks, are the majority ofly considern on the basis of cost between source and destination. Hop count plays major role here. Shorcheck path is a technique which uses various algorithms to decide a path with minimum number of hops.

Common shorcheck path algorithms are:

  • Dijkstra's algorithm

  • Bellman Ford algorithm

  • Floyd Warshall algorithm

Interne2rcalifornia king

In real world scenario, ne2rks below exwork exaction same administration are generally scattecrimson geographically. There may exist requirement of connecting 2 various ne2rks of exwork exaction same kind as well as of various kinds. Rawaying between 2 ne2rks is called interne2rcalifornia king.

Ne2rks can be conpartcrimson various based on various parameters such as, Protocol, topology, Layer-2 ne2rk and addresperform scheme.

In interne2rcalifornia king, rawayers have belowstandladvantage of every other’s adoutfit and adoutfites beyond all of all of them. They can be statically configucrimson go on various ne2rk or they can find out by uperform interne2rcalifornia king rawaying protocol.


Rawaying protocols which are used wislim an body body organization or administration are called Interior Gateway Protocols or IGP. RIP, OSPF are examples of IGP. Rawaying between various body body organizations or administrations may have Exterior Gateway Protocol, and there is only one EGP i.e. Border Gateway Protocol.


If they are 2 geographically separate ne2rks, which want to communicate with every other, they may deploy a dedicated range between or they have to comppermite their particular data through intermediate ne2rks.

Tunneling is a mechanism by which 2 or more exwork exaction same ne2rks communicate with every other, by comppermiteing intermediate ne2rcalifornia king complexiconnects. Tunneling is configucrimson at both ends.


When the data enters from one end of Tunnel, it is tagged. This tagged data is then rawayed inpart the intermediate or transit down down ne2rk to revery the other end of Tunnel. When data exists the Tunnel it is tag is removed and delivecrimson to the other part of the ne2rk.

Both ends seem as if they are immediately connected and tagging produces data travel through transit down down ne2rk withaway any kind of modifications.

Packet Fragmentation

Most Ethernet segments have their particular maximum transmission device (MTU) fixed to 1500 bytes. A data packet can have more or less packet duration depending upon the application. Devices in the transit down down path also have their particular hardware and smoothware capabiliconnects which tell exworkly exactionly whead wear amount of data thead wear device can handle and exworkly exactionly whead wear dimension of packet it can process.

If the data packet dimension is less than or equal to the dimension of packet the transit down down ne2rk can handle, it is processed neutrally. If the packet is bigr, it is broken into smaller pieces and then forwarded. This is called packet fragmentation. Each fragment contains the exwork exaction same destination and source adoutfit and rawayed through transit down down path easily. At the receiving end it is bumembled again.

If a packet with DF (don’t fragment) bit set to 1 comes to a rawayer which can not handle the packet because of it is duration, the packet is fallped.

When a packet is received by a rawayer has it is MF (more fragments) bit set to 1, the rawayer then belowstands thead wear it is a fragmented packet and parts of the unique packet is on the way.

If packet is fragmented too small, the overmind is wislimcrreare locatedves. If the packet is fragmented too big, intermediate rawayer may not be able to process it and it may get fallped.

Ne2rk Layer Protocols

Every complaceer in a ne2rk has an IP adoutfit by which it can be uniquely identified and adoutfited. An IP adoutfit is Layer-3 (Ne2rk Layer) logical adoutfit. This adoutfit may modify every time a complaceer restarts. A complaceer can have one IP at one instance of time and an additional IP at some various time.

Adoutfit Resolution Protocol(ARP)

While communicating, a host needs Layer-2 (MAC) adoutfit of the destination machine which bedurationys to the exwork exaction same widecast domain or ne2rk. A MAC adoutfit is physically burnt into the Ne2rk Interface Card (NIC) of a machine and it never modifys.

On the other hand, IP adoutfit on the public domain is rarely modifyd. If the NIC is modifyd in case of some fault, the MAC adoutfit also modifys. This way, for Layer-2 communication to consider place, a chartping between the 2 is requicrimson.

ARP Mechanism

To belowstand the MAC adoutfit of remote host on a widecast domain, a complaceer wishing to initiate communication sends away an ARP widecast message ascalifornia king, “Who has this particular IP adoutfit?” Because it is a widecast, all hosts on the ne2rk segment (widecast domain) receive this particular packet and process it. ARP packet contains the IP adoutfit of destination host, the sending host wishes to speak to. When a host receives an ARP packet destined to it, it repare locateds back with it is own MAC adoutfit.

Once the host gets destination MAC adoutfit, it can communicate with remote host uperform Layer-2 link protocol. This MAC to IP chartping is saved into ARP cache of both sending and receiving hosts. Next time, if they require to communicate, they can immediately refer to their particular respective ARP cache.

Reverse ARP is a mechanism where host belowstands the MAC adoutfit of remote host but requires to belowstand IP adoutfit to communicate.

Internet Control Message Protocol (ICMP)

ICMP is ne2rk diagnostic and error resloting protocol. ICMP bedurationys to IP protocol suite and uses IP as carrier protocol. After constructing ICMP packet, it is encapsulated in IP packet. Because IP it iself is a best-effort non-reliable protocol, so is ICMP.

Any give food toback abaway ne2rk is sent back to the originating host. If some error in the ne2rk occurs, it is resloted by means of ICMP. ICMP contains dozens of diagnostic and error resloting messages.

ICMP-echo and ICMP-echo-reply are the the majority of commonly used ICMP messages to check the reverycapcapability of end-to-end hosts. When a host receives an ICMP-echo request, it is bound to send back an ICMP-echo-reply. If there is any kind of issue in the transit down down ne2rk, the ICMP will reslot thead wear issue.

Internet Protocol Version 4 (IPv4)

IPv4 is 32-bit addresperform scheme used as TCP/IP host addresperform mechanism. IP addresperform enables every host on the TCP/IP ne2rk to be uniquely identifiable.

IPv4 provides hierarchical addresperform scheme which enables it to divide the ne2rk into sub-ne2rks, every with well-degreatd number of hosts. IP adoutfites are divided into many kind of categories:

  • Clbum A  – it uses very first octet for ne2rk adoutfites and final three octets for host addresperform

  • Clbum B  – it uses very first 2 octets for ne2rk adoutfites and final 2 for host addresperform

  • Clbum C  – it uses very first three octets for ne2rk adoutfites and final one for host addresperform

  • Clbum D  – it provides flat IP addresperform scheme in contrast to hierarchical structure for above three.

  • Clbum E  – It is used as experimental.

IPv4 also has well-degreatd adoutfit spaces to be used as private adoutfites (not rawayable on internet), and public adoutfites (provided by ISPs and are rawayable on internet).

Though IP is not reliable one; it provides ‘Best-Effort-Delivery’ mechanism.

Internet Protocol Version 6 (IPv6)

Exhaustion of IPv4 adoutfites provided birth to a next generation Internet Protocol version 6. IPv6 adoutfites it is nodes with 128-bit wide adoutfit providing plenty of adoutfit space for future to be used on entire planet or beyond.

IPv6 has introduced Anycast addresperform but has removed the concept of widecasting. IPv6 enables devices to self-acquire an IPv6 adoutfit and communicate wislim thead wear subnet. This auto-configuration removes the dependcapcapability of Dynamic Host Configuration Protocol (DHCP) servers. This way, also if the DHCP server on thead wear subnet is down, the hosts can communicate with every other.

IPv6 provides brand new feature of IPv6 mobility. Mobile IPv6 equipped machines can roam around withaway the need of changing their particular IP adoutfites.

IPv6 is still in transit down downion phase and is expected to replace IPv4 compenableely in coming calendar 12 monthss. At present, there are couple of ne2rks which are operatening on IPv6. There are some transit down downion mechanisms available for IPv6 enabled ne2rks to speak and roam around various ne2rks easily on IPv4. These are:

  • Dual stack implementation
  • Tunneling
  • NAT-PT

Transslot Layer Introduction

Next Layer in OSI Model is recognised as Transslot Layer (Layer-4). All modules and procedures pertaining to transslotation of data or data stream are categorized into this particular layer. As all other layers, this particular layer communicates with it is peer Transslot layer of the remote host.

Transslot layer provides peer-to-peer and end-to-end interconnection between 2 processes on remote hosts. Transslot layer considers data from upper layer (i.e. Application layer) and then breaks it into smaller dimension segments, numbers every byte, and hands over to lower layer (Ne2rk Layer) for delivery.


  • This Layer is the very first one which breaks the information data, suppare locatedd by Application layer in to smaller device’s called segments. It numbers every byte in the segment and maintains their particular accounting.

  • This layer ensures thead wear data must be received in the exwork exaction same sequence in which it was sent.

  • This layer provides end-to-end delivery of data between hosts which may or may not bedurationy to the exwork exaction same subnet.

  • All server processes intend to communicate over the ne2rk are equipped with well-belowstandn Transslot Service Access Points (TSAPs) also belowstandn as slot numbers.

End-to-End Communication

A process on one host identifies it is peer host on remote ne2rk by means of TSAPs, also belowstandn as Port numbers. TSAPs are very well degreatd and a process which is checcalifornia king to communicate with it is peer belowstands this particular withbeforehand.


For example, when a DHCP care locatednt wants to communicate with remote DHCP server, it always requests on slot number 67. When a DNS care locatednt wants to communicate with remote DNS server, it always requests on slot number 53 (UDP).

The 2 main Transslot layer protocols are:

  • Transmission Control Protocol

    It provides reliable communication between 2 hosts.

  • User Datagram Protocol

    It provides unreliable communication between 2 hosts.

Transmission Control Protocol

The transmission Control Protocol (TCP) is one of the the majority of imslotant protocols of Internet Protocols suite. It is the majority of widely used protocol for data transmission in communication ne2rk such as internet.


  • TCP is reliable protocol. Thead wear is, the receiver always sends possibly posit down downive or negative acbelowstandladvantagement abaway the data packet to the sender, so thead wear the sender always has bproper clue abaway whether the data packet is reveryed the destination or it needs to resend it.

  • TCP ensures thead wear the data reveryes intended destination in the exwork exaction same order it was sent.

  • TCP is interconnection oriented. TCP requires thead wear interconnection between 2 remote stages be established before sending workual data.

  • TCP provides error-checcalifornia king and recovery mechanism.

  • TCP provides end-to-end communication.

  • TCP provides flow manage and quality of service.

  • TCP operates in Care locatednt/Server stage-to-stage mode.

  • TCP provides comppermite duplex server, i.e. it can perform roles of both receiver and sender.


The duration of TCP minder is minimum 20 bytes durationy and maximum 60 bytes.

TCP Header

  • Source Port (16-bit is)  – It identifies source slot of the application process on the sending device.

  • Destination Port (16-bit is) - It identifies destination slot of the application process on the receiving device.

  • Sequence Number (32-bit is) - Sequence number of data bytes of a segment in a session.

  • Acbelowstandladvantagement Number (32-bit is)  – When ACK flag is set, this particular number contains the next sequence number of the data byte expected and works as acbelowstandladvantagement of the previous data received.

  • Data Offset (4-bit is)  – This field impare locateds both, the dimension of TCP minder (32-bit words) and the away fromset of data in current packet in the whole TCP segment.

  • Reserved (3-bit is)  – Reserved for future use and all are set zero by default.

  • Flags (1-bit every)

    • NS – Nonce Sum bit is used by Explicit Congestion Notification signaling process.

    • CWR – When a host receives packet with ECE bit set, it sets Congestion Windows Reduced to acbelowstandladvantage thead wear ECE received.

    • ECE -It has 2 meanings:

      • If SYN bit is clear to 0, then ECE means thead wear the IP packet has it is CE (congestion encounter) bit set.

      • If SYN bit is set to 1, ECE means thead wear the device is ECT capable.

    • URG – It indicates thead wear Urgent Pointer field has significan’t data and need to be processed.

    • ACK – It indicates thead wear Acbelowstandladvantagement field has significance. If ACK is cleacrimson to 0, it indicates thead wear packet does not contain any kind of acbelowstandladvantagement.

    • PSH – When set, it is a request to the receiving station to PUSH data (as soon as it comes) to the receiving application withaway buffering it.

    • RST – Reset flag has the folloearng features:

      • It is used to refuse an incoming interconnection.

      • It is used to reject a segment.

      • It is used to restart a interconnection.

    • SYN – This flag is used to set up a interconnection between hosts.

    • FIN – This flag is used to relreare locatedve a interconnection and no more data is exmodifyd thereafter. Because packets with SYN and FIN flags have sequence numbers, they are processed in proper order.

  • Windows Size  – This field is used for flow manage between 2 stations and indicates the amount of buffer (in bytes) the receiver has allocated for a segment, i.e. how a lot data is the receiver expecting.

  • Checksum - This field contains the checksum of Header, Data and Pseudo Headers.

  • Urgent Pointer  – It stages to the urgent data byte if URG flag is set to 1.

  • Options  – It facilitates additional options which are not covecrimson by the regular minder. Option field is always described in 32-bit words. If this particular field contains data less than 32-bit, padding is used to cover the remaining bit is to revery 32-bit boundary.


TCP communication between 2 remote hosts is done by means of slot numbers (TSAPs). Ports numbers can range from 0 – 65535 which are divided as:

  • System Ports (0 – 1023)
  • User Ports ( 1024 – 49151)
  • Private/Dynamic Ports (49152 – 65535)

Connection Management

TCP communication works in Server/Care locatednt model. The care locatednt initiates the interconnection and the server possibly accepts or rejects it. Three-way handshacalifornia king is used for interconnection management.

TCP Handshake


Care locatednt initiates the interconnection and sends the segment with a Sequence number. Server acbelowstandladvantages it back with it is own Sequence number and ACK of care locatednt’s segment which is one more than care locatednt’s Sequence number. Care locatednt after receiving ACK of it is segment sends an acbelowstandladvantagement of Server’s response.

Relreare locatedve

Either of server and care locatednt can send TCP segment with FIN flag set to 1. When the receiving end responds it back by ACKnowledging FIN, thead wear immediateion of TCP communication is close upd and interconnection is relreare locatedved.

Bandwidth Management

TCP uses the concept of earndow dimension to accommodate the need of Bandwidth management. Window dimension tells the sender at the remote end, the number of data byte segments the receiver at this particular end can receive. TCP uses slower start phase by uperform earndow dimension 1 and incrreare locatedves the earndow dimension exponentially after every successful communication.

For example, the care locatednt uses earndows dimension 2 and sends 2 bytes of data. When the acbelowstandladvantagement of this particular segment received the earndows dimension is doubled to 4 and next sent the segment sent will be 4 data bytes durationy. When the acbelowstandladvantagement of 4-byte data segment is received, the care locatednt sets earndows dimension to 8 and so on.

If an acbelowstandladvantagement is missed, i.e. data lost in transit down down ne2rk or it received NACK, then the earndow dimension is crimsonuced to half and slower start phase starts again.

Error Control &and Flow Control

TCP uses slot numbers to belowstand exworkly exactionly whead wear application process it needs to handover the data segment. Adurationy with thead wear, it uses sequence numbers to synchronize it iself with the remote host. All data segments are sent and received with sequence numbers. The Sender belowstands which final data segment was received by the Receiver when it gets ACK. The Receiver belowstands abaway the final segment sent by the Sender by referring to the sequence number of currently received packet.

If the sequence number of a segment currently received does not go with with the sequence number the receiver was expecting, then it is discarded and NACK is sent back. If 2 segments arrive with the exwork exaction same sequence number, the TCP timestamp value is compacrimson to produce a decision.


The technique to combine 2 or more data streams in one session is called Multiplexing. When a TCP care locatednt preliminaryizes a interconnection with Server, it always refers to a well-degreatd slot number which indicates the application process. The care locatednt it iself uses a randomly generated slot number from private slot number pools.

Uperform TCP Multiplexing, a care locatednt can communicate with lots of various application process in a performle session. For example, a care locatednt requests a web page which in turn contains various types of data (HTTP, SMTP, FTP etc.) the TCP session timeaway is wislimcrreare locatedved and the session is kept open up for durationyer time so thead wear the three-way handshake overmind can be avoided.

This enables the care locatednt system to receive multiple interconnection over performle virtual interconnection. These virtual interconnections are not great for Servers if the timeaway is too durationy.

Congestion Control

When big amount of data is fed to system which is not capable of handling it, congestion occurs. TCP manages congestion by means of Window mechanism. TCP sets a earndow dimension telling the other end how a lot data segment to send. TCP may use three algorithms for congestion manage:

  • Additive incrreare locatedve, Multiplicative Decrreare locatedve

  • Slow Start

  • Timeaway Rework

Timer Management

TCP uses various types of timer to manage and management various tasks:

Keep-alive timer:

  • This timer is used to check the integrity and validity of a interconnection.

  • When maintain-alive time expires, the host sends a probe to check if the interconnection still exists.

Retransmission timer:

  • This timer maintains stateful session of data sent.

  • If the acbelowstandladvantagement of sent data does not receive wislim the Retransmission time, the data segment is sent again.

Persist timer:

  • TCP session can be paused by possibly host by sending Window Size 0.

  • To resume the session a host needs to send Window Size with some bigr value.

  • If this particular segment never reveryes the other end, both ends may wait for every other for infinite time.

  • When the Persist timer expires, the host re-sends it is earndow dimension to enable the other end belowstand.

  • Persist Timer helps avoid deadlocks in communication.


  • After releaperform a interconnection, possibly of the hosts wait is for a Timed-Wait time to terminate the interconnection compenableely.

  • This is wislim order to produce sure thead wear the other end has received the acbelowstandladvantagement of it is interconnection termination request.

  • Timed-away can be a maximum of 240 seconds (4 moments).

Crash Recovery

TCP is very reliable protocol. It provides sequence number to every of byte sent in segment. It provides the give food toback mechanism i.e. when a host receives a packet, it is bound to ACK thead wear packet having the next sequence number expected (if it is not the final segment).

When a TCP Server crashes mid-way communication and re-starts it is process it sends TPDU widecast to all it is hosts. The hosts can then send the final data segment which was never unacbelowstandladvantaged and carry onwards.

User Datagram Protocol

The User Datagram Protocol (UDP) is fundamentalst Transslot Layer communication protocol available of the TCP/IP protocol suite. It involves minimum amount of communication mechanism. UDP is said to be an unreliable transslot protocol but it uses IP services which provides best effort delivery mechanism.

In UDP, the receiver does not generate an acbelowstandladvantagement of packet received and in turn, the sender does not wait for any kind of acbelowstandladvantagement of packet sent. This shortcoming produces this particular protocol unreliable as well as easier on procesperform.

Requirement of UDP

A question may arise, why do we need an unreliable protocol to transslot the data? We deploy UDP where the acbelowstandladvantagement packets share significan’t amount of bandwidth adurationy with the workual data. For example, in case of video streaming, thougreat sands of packets are forwarded towards it is users. Acbelowstandledging all the packets is troublesome and may contain huge amount of bandwidth wastage. The best delivery mechanism of belowlying IP protocol ensures best efforts to deliver it is packets, but also if some packets in video streaming get lost, the impwork is not calamitous and can be ignocrimson easily. Loss of couple of packets in video and voice traffic occasionally goes unnoticed.


  • UDP is used when acbelowstandladvantagement of data does not hold any kind of significance.

  • UDP is great protocol for data floearng in one immediateion.

  • UDP is fundamental and suitable for query based communications.

  • UDP is not interconnection oriented.

  • UDP does not provide congestion manage mechanism.

  • UDP does not guarantee ordecrimson delivery of data.

  • UDP is stateless.

  • UDP is suitable protocol for streaming applications such as VoIP, multimedia streaming.

UDP Header

UDP minder is as fundamental as it is function.

UDP Header

UDP minder contains four main parameters:

  • Source Port  – This 16 bit is information is used to identify the source slot of the packet.

  • Destination Port  – This 16 bit is information, is used identify application level service on destination machine.

  • Length  – Length field specifies the entire duration of UDP packet (including minder). It is 16-bit is field and minimum value is 8-byte, i.e. the dimension of UDP minder it iself.

  • Checksum  – This field stores the checksum value generated by the sender before sending. IPv4 has this particular field as optional so when checksum field does not contain any kind of value it is made 0 and all it is bit is are set to zero.

UDP application

Here are couple of applications where UDP is used to transmit data:

  • Domain Name Services

  • Simple Ne2rk Management Protocol

  • Trivial File Transfer Protocol

  • Rawaying Information Protocol

  • Kerberos

Application Layer Introduction

Application layer is the top the majority of layer in OSI and TCP/IP layecrimson model. This layer exists in both layecrimson Models because of it is significance, of interworcalifornia king with user and user applications. This layer is for applications which are involved in communication system.

A user may or may not immediately interworks with the applications. Application layer is where the workual communication is wislimitiated and reflects. Because this particular layer is on the top of the layer stack, it does not serve any kind of other layers. Application layer considers the help of Transslot and all layers below it to communicate or transfer it is data to the remote host.

When an application layer protocol wants to communicate with it is peer application layer protocol on remote host, it hands over the data or information to the Transslot layer. The transslot layer does the rest with the help of all the layers below it.

Application Layer

There’is an ambiguity in belowstanding Application Layer and it is protocol. Not every user application can be place into Application Layer. other than those applications which interwork with the communication system. For example, styleing smoothware or text-editor cannot be conpartcrimson as application layer programs.

On the other hand, when we use a Web Brangeser, which is workually uperform Hyper Text Transfer Protocol (HTTP) to interwork with the ne2rk. HTTP is Application Layer protocol.

Another example is File Transfer Protocol, which helps a user to transfer text based or binary files acombination the ne2rk. A user can use this particular protocol in possibly GUI based smoothware like FileZilla or CuteFTP and the exwork exaction same user can use FTP in Command Line mode.

Hence, irrespective of which smoothware you use, it is the protocol which is conpartcrimson at Application Layer used by thead wear smoothware. DNS is a protocol which helps user application protocols such as HTTP to accomplish it is work.

Care locatednt Server Model

Two remote application processes can communicate mainly in 2 various fashions:

  • Peer-to-peer: Both remote processes are executing at exwork exaction same level and they exmodify data uperform some shacrimson resource.

  • Care locatednt-Server: One remote process works as a Care locatednt and requests some resource from an additional application process worcalifornia king as Server.

In care locatednt-server model, any kind of process can work as Server or Care locatednt. It is not the sort of machine, dimension of the machine, or it is complaceing power which produces it server; it is the capcapability of serving request thead wear produces a machine a server.

A system can work as Server and Care locatednt simultaneously. Thead wear is, one process is worcalifornia king as Server and an additional is worcalifornia king as a care locatednt. This may also happen thead wear both care locatednt and server processes repart on the exwork exaction same machine.


Two processes in care locatednt-server model can interwork in various ways:

  • Sockets

  • Remote Procedure Calls (RPC)


In this particular paradigm, the process worcalifornia king as Server open ups a socket uperform a well-belowstandn (or belowstandn by care locatednt) slot and wait is until some care locatednt request comes. The second process worcalifornia king as a Care locatednt also open ups a socket but instead of waiting for an incoming request, the care locatednt processes ‘requests very first’.

When the request is reveryed to server, it is served. It can possibly be an information sharing or resource request.

Remote Procedure Call

This is a mechanism where one process interworks with an additional by means of procedure calls. One process (care locatednt) calls the procedure lying on remote host. The process on remote host is said to be Server. Both processes are allocated stubs. This communication happens in the folloearng way:

  • The care locatednt process calls the care locatednt stub. It comppermitees all the parameters pertaining to program local to it.

  • All parameters are then packed (marshalled) and a system call is made to send all of all of them to other part of the ne2rk.

  • Kernel sends the data over the ne2rk and the other end receives it.

  • The remote host comppermitees data to the server stub where it is unmarshalled.

  • The parameters are comppermiteed to the procedure and the procedure is then executed.

  • The result is sent back to the care locatednt in the exwork exaction same manner.

Application Protocols

There are some protocols which work for users in Application Layer. Application layer protocols can be widely divided into 2 categories:

  • Protocols which are used by users.For email for example, eMail.

  • Protocols which help and supslot protocols used by users.For example DNS.

Few of Application layer protocols are described below:

Domain Name System

The Domain Name System (DNS) works on Care locatednt Server model. It uses UDP protocol for transslot layer communication. DNS uses hierarchical domain based naming scheme. The DNS server is configucrimson with Fully Qualified Domain Names (FQDN) and email adoutfites chartped with their particular respective Internet Protocol adoutfites.

A DNS server is requested with FQDN and it responds back with the IP adoutfit chartped with it. DNS uses UDP slot 53.

Simple Mail Transfer Protocol

The Simple Mail Transfer Protocol (SMTP) is used to transfer digital mail from one user to an additional. This task is done by means of email care locatednt smoothware (User Agents) the user is uperform. User Agents help the user to type and format the email and store it until internet is available. When an email is submitted to send, the sending process is handled by Message Transfer Agent which is normally comes inbuilt in email care locatednt smoothware.

Message Transfer Agent uses SMTP to forward the email to an additional Message Transfer Agent (Server part). While SMTP is used by end user to only send the emails, the Servers normally use SMTP to send as well as receive emails. SMTP uses TCP slot number 25 and 587.

Care locatednt smoothware uses Internet Message Access Protocol (IMAP) or POP protocols to receive emails.

File Transfer Protocol

The File Transfer Protocol (FTP) is the the majority of widely used protocol for file transfer over the ne2rk. FTP uses TCP/IP for communication and it works on TCP slot 21. FTP works on Care locatednt/Server Model where a care locatednt requests file from Server and server sends requested resource back to the care locatednt.

FTP uses away-of-band manageling i.e. FTP uses TCP slot 20 for exchanging manageling information and the workual data is sent over TCP slot 21.

The care locatednt requests the server for a file. When the server receives a request for a file, it open ups a TCP interconnection for the care locatednt and transfers the file. After the transfer is compenablee, the server close ups the interconnection. For a second file, care locatednt requests again and the server reopen ups a brand new TCP interconnection.

Post Office Protocol (POP)

The Post Office Protocol version 3 (POP 3) is a fundamental mail retrieval protocol used by User Agents (care locatednt email smoothware) to retrieve mails from mail server.

When a care locatednt needs to retrieve mails from server, it open ups a interconnection with the server on TCP slot 110. User can then access his mails and download all of all of them to the local complaceer. POP3 works in 2 modes. The the majority of common mode the deenablee mode, is to deenablee the emails from remote server after they are downloaded to local machines. The second mode, the maintain mode, does not deenablee the email from mail server and gives the user an option to access mails later on mail server.

Hyper Text Transfer Protocol (HTTP)

The Hyper Text Transfer Protocol (HTTP) is the foundation of World Wide Web. Hypertext is well body body organised documentation system which uses hyperlinks to link the pages in the text documents. HTTP works on care locatednt server model. When a user wants to access any kind of HTTP page on the internet, the care locatednt machine at user end initiates a TCP interconnection to server on slot 80. When the server accepts the care locatednt request, the care locatednt is authorised to access web pages.

To access the web pages, a care locatednt normally uses web brangesers, who are responsible for initiating, maintaining, and cloperform TCP interconnections. HTTP is a stateless protocol, which means the Server maintains no information abaway earare locatedr requests by care locatednts.

HTTP versions

  • HTTP 1.0 uses non persistent HTTP. At the majority of one object can be sent over a performle TCP interconnection.

  • HTTP 1.1 uses persistent HTTP. In this particular version, multiple objects can be sent over a performle TCP interconnection.

Ne2rk Services

Complaceer systems and complaceerized systems help individual beings to work effectively and explore the unslimkable. When these devices are connected collectively to form a ne2rk, the capabiliconnects are enhanced multiple-times. Some fundamental services complaceer ne2rk can provide are.

Directory Services

These services are chartping between name and it is value, which can be variable value or fixed. This smoothware system helps to store the information, body body organise it, and provides various means of accesperform it.

  • Accounting

    In an body body organization, lots of users have their particular user names and comppermitewords chartped to all of all of them. Directory Services provide means of storing this particular wislimformation in weepptic form and produce available when requested.

  • Authentication &and Authorization

    User ccrimsonentials are checked to authenticate a user at the time of login and/or periodically. User accounts can be set into hierarchical structure and their particular access to resources can be manageled uperform authorization schemes.

  • Domain Name Services

    DNS is widely used and one of the essential services on which internet works. This system charts IP adoutfites to domain names, which are easier to remember and recall than IP adoutfites. Because ne2rk operates with the help of IP adoutfites and individuals tend to remember websit down downe names, the DNS provides websit down downe’s IP adoutfit which is chartped to it is name from the back-end on the request of a websit down downe name from the user.

File Services

File services include sharing and transferring files over the ne2rk.

  • File Sharing

    One of the reason which provided birth to ne2rcalifornia king was file sharing. File sharing enables it is users to share their particular data with other users. User can upload the file to a specific server, which is accessible by all intended users. As an alternative, user can produce it is file shacrimson on it is own complaceer and provides access to intended users.

  • File Transfer

    This is an workivity to duplicate or move file from one complaceer to an additional complaceer or to multiple complaceers, with help of belowlying ne2rk. Ne2rk enables it is user to locate other users in the ne2rk and transfers files.

Communication Services

  • Email

    Electronic mail is a communication method and someslimg a complaceer user cannot work withaway. This is the basis of today’s internet features. Email system has one or more email servers. All it is users are provided with unique IDs. When a user sends email to other user, it is workually transfercrimson between users with help of email server.

  • Social Ne2rcalifornia king

    Recent technologies have made technical life social. The complaceer savvy peoples, can find other belowstandn peoples or friends, can connect with all of all of them, and can share thoughts, pictures, and videos.

  • Internet Chead wear

    Internet chead wear provides immediate text transfer services between 2 hosts. Two or more people can communicate with every other uperform text based Internet Relay Chead wear services. These days, voice chead wear and video chead wear are very common.

  • Discussion Boards

    Discussion tables provide a mechanism to connect multiple peoples with exwork exaction same curiosit down downys.It enables the users to place queries, questions, suggestions etc. which can be seen by all other users. Other may respond as well.

  • Remote Access

    This service enables user to access the data residing on the remote complaceer. This feature is belowstandn as Remote desktop. This can be done via some remote device, e.g. mobile phone or home complaceer.

Application Services

These are noslimg but providing ne2rk based services to the users such as web
services, database managing, and resource sharing.

  • Resource Sharing

    To use resources effectively and economically, ne2rk provides a mean to share all of all of them. This may include Servers, Printers, and Storage Media etc.

  • Databases

    This application service is one of the the majority of imslotant services. It stores data and information, processes it, and enables the users to retrieve it effectively by uperform queries. Databases help body body organizations to produce decisions based on statistics.

  • Web Services

    World Wide Web has become the synonym for internet.It is used to connect to the internet, and access files and information services provided by the internet servers.