Computer Networks:It is the interconnection of multiple devices, generally termed as Hosts connected using multiple paths for the purpose of sending/receiving data or media. There are also multiple devices or mediums which helps in the communication between two different devices which are known as Network devices. Ex: Router, Switch, Hub, Bridge.

Goals of Computer Networks:   The following are some important goals of computer networks:1. Resource Sharing –

Many organization has a substantial number of computers in operations, which are located apart. Ex. A group of office workers can share a common printer, fax, modem, scanner etc.

2. High Reliability –If there are alternate sources of supply, all files could be replicated on two or, machines. If one of them is not available, due to hardware failure, the other copies could be used.

3. Inter-process Communication –Network users, located geographically apart, may converse in an interactive session through the network. In order to permit this, the network must provide almost error-free communications.

4. Flexible access –Files can be accessed from any computer in the network. The project can be begun on one computer and finished on another.

Network Applications:

1. Resource Sharing Hardware(Computing resources, Disks, Printers) Software(Application software)

2. Information Sharing Easy Accessibility from anywhere(files, databases) Search Capability(WWW)

3. Communication Email Messsage Broadcast

4. Remote Computing5. Distributed Processing(GRID Computing)

Unique Identifiers of Network: Host name:

Each device in the network is associated with a unique device name known as Hostname.Type “hostname” in the command prompt(Administrator Mode) and press ‘Enter’, this displays the hostname of your machine.

Protocol:A protocol is the set of rules or algorithms which define the way how two entities can communicate across the network and there exists different protocol defined at each layer of the OSI model. Few of such protocols are TCP, IP, UDP, ARP, DHCP, FTP and so on.

IP Address (Internet Protocol address):Also, known as the Logical Address, is the network address of the system across the network.To identify each device in the world-wide-web, Internet Assigned Numbers Authority (IANA) assigns IPV4 (Version 4) address as a unique identifier for each device on the Internet.Length of the IP address is 32-bits. (Hence we have 232 IP addresses available.)Type “ipconfig” in the command prompt and press ‘Enter’, this gives us the IP address of the device.

MAC Address (Media Access Control address):Also known as physical address, is the unique identifier of each host and is associated with the NIC (Network Interface Card). MAC address is assigned to the NIC at the time of manufacturing.

Length of the MAC address is : 6 bytes/ 48 bitsType “ipconfig/all” in the command prompt and press ‘Enter’, this gives us the MAC address.

Port:Port can be referred as a logical channel through which data can be sent/received to an application. Any host may have multiple applications running, and each of this application is identified using the port number on which they are running.Port number is a 16-bit integer, hence we have 216 ports available which are categorized as shown below:

PORT TYPES RANGE

Well known Ports 0 – 1023

Registered Ports

1024 – 49151

Ephemeral Ports

49152 – 65535

Type “netstat -a” in the command prompt and press ‘Enter’, this lists all the ports being used.

Socket:The unique combination of IP address and Port number together are termed as Socket.

DNS Server:DNS stands for Domain Name system. DNS is basically a server which translates web addresses or URL (ex: www.google.com) into their corresponding IP addresses. We don’t have to remember all the IP addresses of each and every website.The command ‘nslookup’ gives you the IP address of the domain you are looking for. This also provides the information of our DNS Server.

ARP:ARP stands for Address Resolution Protocol. It is used to convert the IP address to its corresponding Physical Address(i.e.MAC Address). ARP is used by the Data Link Layer to identify the MAC address of the Receiver’s machine.RARP:RARP stands for Reverse Address Resolution Protocol. As the name suggests, it provides the IP address of the device given a physical address as input. But RARP has become obsolete since the time DHCP has come into the picture.

Computer Network Architecture:

Computer Network Architecture is defined as the physical and logical design of the software, hardware, protocols, and media of the transmission of data. Simply we can say that how computers are organized and how tasks are allocated to the computer.

The two types of network architectures are used:

Peer-To-Peer network

Peer-To-Peer network is a network in which all the computers are linked together with equal privilege and responsibilities for processing the data.

Peer-To-Peer network is useful for small environments, usually up to 10 computers. Peer-To-Peer network has no dedicated server. Special permissions are assigned to each computer for sharing the resources, but this can lead to a problem if

the computer with the resource is down.

Advantages Of Peer-To-Peer Network: It is less costly as it does not contain any dedicated server. If one computer stops working but, other computers will not stop working. It is easy to set up and maintain as each computer manages itself.

Disadvantages Of Peer-To-Peer Network: In the case of Peer-To-Peer network, it does not contain the centralized system . Therefore, it cannot

back up the data as the data is different in different locations. It has a security issue as the device is managed itself.

Client/Server Network

Client/Server network is a network model designed for the end users called clients, to access the resources such as songs, video, etc. from a central computer known as Server.

The central controller is known as a server while all other computers in the network are called clients. A server performs all the major operations such as security and network management. A server is responsible for managing all the resources such as files, directories, printer, etc. All the clients communicate with each other through a server. For example, if client1 wants to send some

data to client 2, then it first sends the request to the server for the permission. The server sends the response to the client 1 to initiate its communication with the client 2.

Advantages Of Client/Server network: A Client/Server network contains the centralized system. Therefore we can back up the data easily. A Client/Server network has a dedicated server that improves the overall performance of the whole system. Security is better in Client/Server network as a single server administers the shared resources. It also increases the speed of the sharing resources.

Disadvantages Of Client/Server network: Client/Server network is expensive as it requires the server with large memory. A server has a Network Operating System(NOS) to provide the resources to the clients, but the cost of NOS

is very high. It requires a dedicated network administrator to manage all the resources.

Types of Network:

PAN (Personal Area Network)PAN is a computer network formed around a person. It generally consists of a computer, mobile, or personal digital assistant. PAN can be used for establishing communication among these personal devices for connecting to a digital network and the internet.Characteristics of PAN

It is mostly personal devices network equipped within a limited area. Allows you to handle the interconnection of IT devices at the surrounding of a single user. PAN includes mobile devices, tablet, and laptop. It can be wirelessly connected to the internet called WPAN. Appliances use for PAN: cordless mice, keyboards, and Bluetooth systems.

Advantages of PAN PAN networks are relatively secure and safe It offers only short-range solution up to ten meters Strictly restricted to a small area

Disadvantages of PAN It may establish a bad connection to other networks at the same radio bands. Distance limits.

LANA Local Area Network (LAN) is a group of computer and peripheral devices which are connected in a limited area such as school, laboratory, home, and office building. It is a widely useful network for sharing resources like files, printers, games, and other application. The simplest type of LAN network is to connect computers and a printer in someone's home or office. In general, LAN will be used as one type of transmission medium.It is a network which consists of less than 5000 interconnected devices across several buildings.Characteristics of LAN

It is a private network, so an outside regulatory body never controls it. LAN operates at a relatively higher speed compared to other WAN systems. There are various kinds of media access control methods like token ring and ethernet.

Advantages of LAN Computer resources like hard-disks, DVD-ROM, and printers can share local area networks. This

significantly reduces the cost of hardware purchases. You can use the same software over the network instead of purchasing the licensed software for each client

in the network. Data of all network users can be stored on a single hard disk of the server computer. You can easily transfer data and messages over networked computers. It will be easy to manage data at only one place, which makes data more secure. Local Area Network offers the facility to share a single internet connection among all the LAN users.

Disadvantages of LAN LAN will indeed save cost because of shared computer resources, but the initial cost of installing Local Area

Networks is quite high. The LAN admin can check personal data files of every LAN user, so it does not offer good privacy. Unauthorized users can access critical data of an organization in case LAN admin is not able to secure

centralized data repository. Local Area Network requires a constant LAN administration as there are issues related to software setup and

hardware failures

WANWAN (Wide Area Network) is another important computer network that which is spread across a large geographical area. WAN network system could be a connection of a LAN which connects with other LAN's using telephone lines and radio waves. It is mostly limited to an enterprise or an organization.Characteristics of LAN:

The software files will be shared among all the users; therefore, all can access to the latest files. Any organization can form its global integrated network using WAN.

Advantages of WAN WAN helps you to cover a larger geographical area. Therefore business offices situated at longer distances

can easily communicate. Contains devices like mobile phones, laptop, tablet, computers, gaming consoles, etc. WLAN connections work using radio transmitters and receivers built into client devices.

Disadvantage of WAN The initial setup cost of investment is very high. It is difficult to maintain the WAN network. You need skilled technicians and network administrators. There are more errors and issues because of the wide coverage and the use of different technologies. It requires more time to resolve issues because of the involvement of multiple wired and wireless

technologies. Offers lower security compared to other types of networks.

MANA Metropolitan Area Network or MAN is consisting of a computer network across an entire city, college campus, or a small region. This type of network is large than a LAN, which is mostly limited to a single building or site. Depending upon the type of configuration, this type of network allows you to cover an area from several miles to tens of miles.Characteristics of MAN

It mostly covers towns and cities in a maximum 50 km range Mostly used medium is optical fibers, cables Data rates adequate for distributed computing applications.

Advantages of MAN It offers fast communication using high-speed carriers, like fiber optic cables. It provides excellent support for an extensive size network and greater access to WANs. The dual bus in MAN network provides support to transmit data in both directions concurrently. A MAN network mostly includes some areas of a city or an entire city.

Disadvantages of MAN You need more cable to establish MAN connection from one place to another. In MAN network it is tough to make the system secure from hackers.

Transmission Mode:Transmission mode means transferring of data between two devices. It is also known as communication mode. Buses and networks are designed to allow communication to occur between individual devices that are interconnected. There are three types of transmission mode:-

Simplex Mode Half-Duplex Mode

Full-Duplex Mode

Simplex ModeIn Simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit, the other can only receive. The simplex mode can use the entire capacity of the channel to send data in one direction. Example: Keyboard and traditional monitors. The keyboard can only introduce input, the monitor can only give the output.

Half-Duplex ModeIn half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa. The half-duplex mode is used in cases where there is no need for communication in both direction at the same time. The entire capacity of the channel can be utilized for each direction. Example of half duplex is a walkie- talkie in which message is sent one at a time but messages are sent in both the directions.

Full Duplex ModeIn full duplex system we can send data in both the directions as it is bidirectional at the same time in other words, data can be sent in both directions simultaneously.Example of Full Duplex is a Telephone Network in which there is communication between two persons by a telephone line, using which both can talk and listen at the same time.

In full duplex system there can be two lines one for sending the data and the other for receiving data.

Transmission Medium:

In data communication terminology, a transmission medium is a physical path between the transmitter and the receiver i.e it is the channel through which data is sent from one place to another. Some factors need to be considered for designing the transmission media:

Bandwidth: All the factors are remaining constant, the greater the bandwidth of a medium, the higher the data transmission rate of a signal.

Transmission impairment: When the received signal is not identical to the transmitted one due to the transmission impairment. The quality of the signals will get destroyed due to transmission impairment.

Interference: An interference is defined as the process of disrupting a signal when it travels over a communication medium on the addition of some unwanted signal.

Causes Of Transmission Impairment:

Attenuation: Attenuation means the loss of energy, i.e., the strength of the signal decreases with increasing the distance which causes the loss of energy.

Distortion: Distortion occurs when there is a change in the shape of the signal. This type of distortion is examined from different signals having different frequencies. Each frequency component has its own propagation speed, so they reach at a different time which leads to the delay distortion.

Noise: When data is travelled over a transmission medium, some unwanted signal is added to it which creates the noise.

Guided Media

It is defined as the physical medium through which the signals are transmitted. It is also known as Bounded media.

Types Of Guided media:

Twisted pair:

Twisted pair is a physical media made up of a pair of cables twisted with each other. A twisted pair cable is cheap as compared to other transmission media. Installation of the twisted pair cable is easy, and it is a lightweight cable. The frequency range for twisted pair cable is from 0 to 3.5KHz. The degree of reduction in noise interference is determined by the number of turns per foot. Increasing the number of turns per foot decreases noise interference.

Types of Twisted pair:

Unshielded Twisted Pair:

An unshielded twisted pair is widely used in telecommunication. This type of cable has the ability to block interference and does not depend on a physical shield for this purpose. Following are the categories of the unshielded twisted pair cable:

Category 1: Category 1 is used for telephone lines that have low-speed data. Category 2: It can support upto 4Mbps. Category 3: It can support upto 16Mbps. Category 4: It can support upto 20Mbps. Therefore, it can be used for long-distance communication. Category 5: It can support upto 200Mbps.

Advantages Of Unshielded Twisted Pair:

It is cheap. Installation of the unshielded twisted pair is easy. It can be used for high-speed LAN.

Disadvantage:

This cable can only be used for shorter distances because of attenuation.

Shielded Twisted PairA shielded twisted pair is a cable that contains the mesh surrounding the wire that allows the higher transmission rate. It is used in fast-data-rate Ethernet and in voice and data channels of telephone lines.

Characteristics Of Shielded Twisted Pair:

The cost of the shielded twisted pair cable is not very high and not very low. An installation of STP is easy. It has higher capacity as compared to unshielded twisted pair cable. It has a higher attenuation. It is shielded that provides the higher data transmission rate.

Disadvantages

It is more expensive as compared to UTP and coaxial cable. It has a higher attenuation rate.

Coaxial Cable

Coaxial cable is very commonly used transmission media, for example, TV wire is usually a coaxial cable. The name of the cable is coaxial as it contains two conductors parallel to each other. It has a higher frequency as compared to Twisted pair cable. The inner conductor of the coaxial cable is made up of copper, and the outer conductor is made up of copper

mesh. The middle core is made up of non-conductive cover that separates the inner conductor from the outer conductor.

The middle core is responsible for the data transferring whereas the copper mesh prevents from the EMI(Electromagnetic interference).

Coaxial cable is of two types:

1. Baseband transmission: It is defined as the process of transmitting a single signal at high speed.2. Broadband transmission: It is defined as the process of transmitting multiple signals simultaneously.

Advantages of Coaxial cable:

The data can be transmitted at high speed. It has better shielding as compared to twisted pair cable. It provides higher bandwidth.

Disadvantages of Coaxial cable:

It is more expensive as compared to twisted pair cable. If any fault occurs in the cable causes the failure in the entire network.

Fiber Optic

Fiber optic cable is a cable that uses electrical signals for communication. Fiber optic is a cable that holds the optical fibers coated in plastic that are used to send the data by pulses of

light. The plastic coating protects the optical fibers from heat, cold, electromagnetic interference from other types

of wiring. Fiber optics provide faster data transmission than copper wires.

Diagrammatic representation of fibre optic cable:

Basic elements of Fiber optic cable:

Core: The optical fiber consists of a narrow strand of glass or plastic known as a core. A core is a light transmission area of the fiber. The more the area of the core, the more light will be transmitted into the fiber.

Cladding: The concentric layer of glass is known as cladding. The main functionality of the cladding is to provide the lower refractive index at the core interface as to cause the reflection within the core so that the light waves are transmitted through the fiber.

Jacket: The protective coating consisting of plastic is known as a jacket. The main purpose of a jacket is to preserve the fiber strength, absorb shock and extra fiber protection.

Following are the advantages of fiber optic cable over copper:

Greater Bandwidth: The fiber optic cable provides more bandwidth as compared copper. Therefore, the fiber optic carries more data as compared to copper cable.

Faster speed: Fiber optic cable carries the data in the form of light. This allows the fiber optic cable to carry the signals at a higher speed.

Longer distances: The fiber optic cable carries the data at a longer distance as compared to copper cable. Better reliability: The fiber optic cable is more reliable than the copper cable as it is immune to any

temperature changes while it can cause obstruct in the connectivity of copper cable. Thinner and Sturdier: Fiber optic cable is thinner and lighter in weight so it can withstand more pull

pressure than copper cable.

Unguided Transmission

An unguided transmission transmits the electromagnetic waves without using any physical medium. Therefore it is also known as wireless transmission.

In unguided media, air is the media through which the electromagnetic energy can flow easily.

Unguided transmission is broadly classified into three categories:

Radio waves

Radio waves are the electromagnetic waves that are transmitted in all the directions of free space. Radio waves are omnidirectional, i.e., the signals are propagated in all the directions. The range in frequencies of radio waves is from 3Khz to 1 khz. In the case of radio waves, the sending and receiving antenna are not aligned, i.e., the wave sent by the

sending antenna can be received by any receiving antenna. An example of the radio wave is FM radio.

Applications of Radio waves:

A Radio wave is useful for multicasting when there is one sender and many receivers. An FM radio, television, cordless phones are examples of a radio wave.

Advantages of Radio transmission:

Radio transmission is mainly used for wide area networks and mobile cellular phones. Radio waves cover a large area, and they can penetrate the walls. Radio transmission provides a higher transmission rate.

Microwaves

Terrestrial Microwave Transmission Terrestrial Microwave transmission is a technology that transmits the focused beam of a radio signal from

one ground-based microwave transmission antenna to another. Microwaves are the electromagnetic waves having the frequency in the range from 1GHz to 1000 GHz. Microwaves are unidirectional as the sending and receiving antenna is to be aligned, i.e., the waves sent by

the sending antenna are narrowly focused. In this case, antennas are mounted on the towers to send a beam to another antenna which is km away. It works on the line of sight transmission, i.e., the antennas mounted on the towers are the direct sight of

each other.

Characteristics of Microwave:

Frequency range: The frequency range of terrestrial microwave is from 4-6 GHz to 21-23 GHz. Bandwidth: It supports the bandwidth from 1 to 10 Mbps. Short distance: It is inexpensive for short distance. Long distance: It is expensive as it requires a higher tower for a longer distance. Attenuation: Attenuation means loss of signal. It is affected by environmental conditions and antenna size.

Advantages Of Microwave:

Microwave transmission is cheaper than using cables. It is free from land acquisition as it does not require any land for the installation of cables. Microwave transmission provides an easy communication in terrains as the installation of cable in terrain is

quite a difficult task. Communication over oceans can be achieved by using microwave transmission.

Disadvantages of Microwave transmission:

Eavesdropping: An eavesdropping creates insecure communication. Any malicious user can catch the signal in the air by using its own antenna.

Out of phase signal: A signal can be moved out of phase by using microwave transmission. Susceptible to weather condition: A microwave transmission is susceptible to weather condition. This

means that any environmental change such as rain, wind can distort the signal. Bandwidth limited: Allocation of bandwidth is limited in the case of microwave transmission.

Satellite Microwave Communication A satellite is a physical object that revolves around the earth at a known height. Satellite communication is more reliable nowadays as it offers more flexibility than cable and fiber optic

systems. We can communicate with any point on the globe by using satellite communication.

How Does Satellite work?

The satellite accepts the signal that is transmitted from the earth station, and it amplifies the signal. The amplified signal is retransmitted to another earth station.

Advantages of Satellite Microwave Communication:

The coverage area of a satellite microwave is more than the terrestrial microwave. The transmission cost of the satellite is independent of the distance from the centre of the coverage area. Satellite communication is used in mobile and wireless communication applications. It is easy to install. It is used in a wide variety of applications such as weather forecasting, radio/TV signal broadcasting, mobile

communication, etc.

Disadvantages Of Satellite Microwave Communication:

Satellite designing and development requires more time and higher cost. The Satellite needs to be monitored and controlled on regular periods so that it remains in orbit. The life of the satellite is about 12-15 years. Due to this reason, another launch of the satellite has to be

planned before it becomes non-functional.

Infrared

An infrared transmission is a wireless technology used for communication over short ranges. The frequency of the infrared in the range from 300 GHz to 400 THz. It is used for short-range communication such as data transfer between two cell phones, TV remote

operation, data transfer between a computer and cell phone resides in the same closed area.

Characteristics Of Infrared:

It supports high bandwidth, and hence the data rate will be very high. Infrared waves cannot penetrate the walls. Therefore, the infrared communication in one room cannot be

interrupted by the nearby rooms. An infrared communication provides better security with minimum interference. Infrared communication is unreliable outside the building because the sun rays will interfere with the

infrared waves.

Network Topology:

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

a) Mesh Topology :

In mesh topology, every device is connected to another device via particular channel.

Every device is connected with another via dedicated channels. These channels are known as links. If suppose, N number of devices are connected with each other in mesh topology, then total number of ports that

is required by each device is N-1. In the Figure 1, there are 5 devices connected to each other, hence total number of ports required is 4.

If suppose, N number of devices are connected with each other in mesh topology, then total number of dedicated links required to connect them is NC2 i.e. N(N-1)/2. In the Figure 1, there are 5 devices connected to each other, hence total number of links required is 5*4/2 = 10.

Advantages of this topology : It is robust. Fault is diagnosed easily. Data is reliable because data is transferred among the devices through dedicated

channels or links. Provides security and privacy.Problems with this topology : Installation and configuration is difficult. Cost of cables are high as bulk wiring is required, hence suitable for less number of devices. Cost of maintenance is high.

b) Star Topology :

In star topology, all the devices are connected to a single hub through a cable. This hub is the central node and all others nodes are connected to the central node. The hub can be passive in nature i.e. not intelligent hub such as broadcasting devices, at the same time the hub can be intelligent known as active hubs. Active hubs have repeaters in them.

Advantages of this topology : If N devices are connected to each other in star topology, then the number of cables required to connect them is

N. So, it is easy to set up. Each device require only 1 port i.e. to connect to the hub.Problems with this topology : If the concentrator (hub) on which the whole topology relies fails, the whole system will crash down.

Cost of installation is high. Performance is based on the single concentrator i.e. hub.

c) Bus Topology :

Bus topology is a network type in which every computer and network device is connected to single cable. It transmits the data from one end to another in single direction. No bi-directional feature is in bus topology.

Advantages of this topology : If N devices are connected to each other in bus topology, then the number of cables required to connect them is 1

which is known as backbone cable and N drop lines are required. Cost of the cable is less as compared to other topology, but it is used to built small networks.Problems with this topology : If the common cable fails, then the whole system will crash down. If the network traffic is heavy, it increases collisions in the network. To avoid this, various protocols are used in

MAC layer known as Pure Aloha, Slotted Aloha, CSMA/CD etc.

d) Ring Topology :

In this topology, it forms a ring connecting a devices with its exactly two neighbouring devices.

The following operations takes place in ring topology are :1. One station is known as monitor station which takes all the responsibility to perform the operations.2. To transmit the data, station has to hold the token. After the transmission is done, the token is to be released for

other stations to use.3. When no station is transmitting the data, then the token will circulate in the ring.4. There are two types of token release techniques : Early token release releases the token just after the

transmitting the data and Delay token release releases the token after the acknowledgement is received from the receiver.

Advantages of this topology : The possibility of collision is minimum in this type of topology. Cheap to install and expand.Problems with this topology : Troubleshooting is difficult in this topology. Addition of stations in between or removal of stations can disturb the whole topology.

e) Hybrid Topology :

This topology is a collection of two or more topologies which are described above. This is a scalable topology which can be expanded easily. It is reliable one but at the same it is a costly topology.

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

1. Circuit Switching Circuit switching is a switching technique that establishes a dedicated path between sender and receiver. In the Circuit Switching Technique, once the connection is established then the dedicated path will remain to

exist until the connection is terminated. Circuit switching in a network operates in a similar way as the telephone works. A complete end-to-end path must exist before the communication takes place. In case of circuit switching technique, when any user wants to send the data, voice, video, a request signal is

sent to the receiver then the receiver sends back the acknowledgment to ensure the availability of the dedicated path. After receiving the acknowledgment, dedicated path transfers the data.

Circuit switching is used in public telephone network. It is used for voice transmission. Fixed data can be transferred at a time in circuit switching technology.

Communication through circuit switching has 3 phases: Circuit establishment Data transfer Circuit Disconnect

Advantages Of Circuit Switching: In the case of Circuit Switching technique, the communication channel is dedicated. It has fixed bandwidth.

Disadvantages Of Circuit Switching: Once the dedicated path is established, the only delay occurs in the speed of data transmission. It takes a long time to establish a connection approx 10 seconds during which no data can be transmitted. It is more expensive than other switching techniques as a dedicated path is required for each connection. It is inefficient to use because once the path is established and no data is transferred, then the capacity of the

path is wasted. In this case, the connection is dedicated therefore no other data can be transferred even if the channel is free.

2. Message Switching Message Switching is a switching technique in which a message is transferred as a complete unit and routed

through intermediate nodes at which it is stored and forwarded. In Message Switching technique, there is no establishment of a dedicated path between the sender and

receiver. The destination address is appended to the message. Message Switching provides a dynamic routing as the

message is routed through the intermediate nodes based on the information available in the message. Message switches are programmed in such a way so that they can provide the most efficient routes. Each and every node stores the entire message and then forward it to the next node. This type of network is

known as store and forward network. Message switching treats each message as an independent entity.

Advantages Of Message Switching Data channels are shared among the communicating devices that improve the efficiency of using available

bandwidth. Traffic congestion can be reduced because the message is temporarily stored in the nodes. Message priority can be used to manage the network. The size of the message which is sent over the network can be varied. Therefore, it supports the data of

unlimited size.Disadvantages Of Message Switching

The message switches must be equipped with sufficient storage to enable them to store the messages until the message is forwarded.

The Long delay can occur due to the storing and forwarding facility provided by the message switching technique.

3. Packet Switching The packet switching is a switching technique in which the message is sent in one go, but it is divided into

smaller pieces, and they are sent individually. The message splits into smaller pieces known as packets and packets are given a unique number to identify

their order at the receiving end. Every packet contains some information in its headers such as source address, destination address and

sequence number.

Packets will travel across the network, taking the shortest path as possible. All the packets are reassembled at the receiving end in correct order. If any packet is missing or corrupted, then the message will be sent to resend the message. If the correct order of the packets is reached, then the acknowledgment message will be sent.

Approaches Of Packet Switching:There are two approaches to Packet Switching:Datagram Packet switching: It is a packet switching technology in which packet is known as a datagram, is considered as an independent entity.

Each packet contains the information about the destination and switch uses this information to forward the packet to the correct destination.

The packets are reassembled at the receiving end in correct order. In Datagram Packet Switching technique, the path is not fixed. Intermediate nodes take the routing decisions to forward the packets. Datagram Packet Switching is also known as connectionless switching.Virtual Circuit Switching Virtual Circuit Switching is also known as connection-oriented switching. In the case of Virtual circuit switching, a preplanned route is established before the messages are sent. Call request and call accept packets are used to establish the connection between sender and receiver. In this case, the path is fixed for the duration of a logical connection.Let's understand the concept of virtual circuit switching through a diagram:

Differences b/w Datagram approach and Virtual Circuit approach

Datagram approach Virtual Circuit approach

Node takes routing decisions to forward Node does not take any routing decision.

the packets.

Congestion cannot occur as all the packets travel in different directions.

Congestion can occur when the node is busy, and it does not allow other packets to pass through.

It is more flexible as all the packets are treated as an independent entity.

It is not very flexible.

Advantages of Packet Switching: Cost-effective: In packet switching technique, switching devices do not require massive secondary storage

to store the packets, so cost is minimized to some extent. Therefore, we can say that the packet switching technique is a cost-effective technique.

Reliable: If any node is busy, then the packets can be rerouted. This ensures that the Packet Switching technique provides reliable communication.

Efficient: Packet Switching is an efficient technique. It does not require any established path prior to the transmission, and many users can use the same communication channel simultaneously, hence makes use of available bandwidth very efficiently.

Disadvantages of Packet Switching: Packet Switching technique cannot be implemented in those applications that require low delay and high-

quality services. The protocols used in a packet switching technique are very complex and requires high implementation cost. If the network is overloaded or corrupted, then it requires retransmission of lost packets. It can also lead to

the loss of critical information if errors are nor recovered.

Network Devices:1.Repeater – A repeater operates at the physical layer. Its job is to regenerate the signal over the same network

before the signal becomes too weak or corrupted so as to extend the length to which the signal can be transmitted over the same network. When the signal becomes weak, they copy the signal bit by bit and regenerate it at the original strength. It is a 2 port device.

 2. Hub –  A hub is basically a multiport repeater. A hub connects multiple wires coming from different branches, for example, the connector in star topology which connects different stations. Hubs cannot filter data, so data packets are sent to all connected devices.  Types of Hub Active Hub:- These are the hubs which have their own power supply and can clean, boost and relay the signal

along with the network. It serves both as a repeater as well as wiring centre. These are used to extend the maximum distance between nodes.

Passive Hub :- These are the hubs which collect wiring from nodes and power supply from active hub. These hubs relay signals onto the network without cleaning and boosting them and can’t be used to extend the distance between nodes.

 3. Bridge – A bridge operates at data link layer. A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of source and destination. It is also used for interconnecting two LANs working on the same protocol. It has a single input and single output port, thus making it a 2 port device.

4. Switch – A switch is a multiport bridge with a buffer and a design that can boost its efficiency(a large number of ports imply less traffic) and performance. A switch is a data link layer device. The switch can perform error checking before forwarding data, that makes it very efficient as it does not forward packets that have errors and forward good packets selectively to correct port only.

5. Routers – A router is a device like a switch that routes data packets based on their IP addresses. Router is mainly a Network Layer device. Routers normally connect LANs and WANs together and have a dynamically updating routing table based on which they make decisions on routing the data packets. Router divide broadcast domains of hosts connected through it.

6. Gateway – A gateway, as the name suggests, is a passage to connect two networks together that may work upon different networking models. They basically work as the messenger agents that take data from one system, interpret it, and transfer it to another system. Gateways are also called protocol converters and can operate at any network layer. Gateways are generally more complex than switch or router. 

OSI Model:

OSI stands for Open Systems Interconnection. It has been developed by ISO – ‘International Organization of Standardization‘, in the year 1984. It is a 7 layer architecture with each layer having specific functionality to perform. All these 7 layers work collaboratively to transmit the data from one person to another across the globe.

Physical Layer (Layer 1) :The lowest layer of the OSI reference model is the physical layer. It is responsible for the actual physical connection between the devices. The physical layer contains information in the form of bits. It is responsible for the actual

physical connection between the devices. When receiving data, this layer will get the signal received and convert it into 0s and 1s and send them to the Data Link layer, which will put the frame back together.The functions of the physical layer are :

1. Bit synchronization: The physical layer provides the synchronization of the bits by providing a clock. This clock controls both sender and receiver thus providing synchronization at bit level.

2. Bit rate control: The Physical layer also defines the transmission rate i.e. the number of bits sent per second.3. Physical topologies: Physical layer specifies the way in which the different, devices/nodes are arranged in a

network i.e. bus, star or mesh topolgy.4. Transmission mode: Physical layer also defines the way in which the data flows between the two connected

devices. The various transmission modes possible are: Simplex, half-duplex and full-duplex.* Hub, Repeater, Modem, Cables are Physical Layer devices. Network Layer, Data Link Layer and Physical Layer are also known as Lower Layers or Hardware Layers.

Data Link Layer (DLL) (Layer 2) :The data link layer is responsible for the node to node delivery of the message. The main function of this layer is to make sure data transfer is error free from one node to another, over the physical layer. When a packet arrives in a network, it is the responsibility of DLL to transmit it to the Host using its MAC address.Data Link Layer is divided into two sub layers :

1. Logical Link Control (LLC)2. Media Access Control (MAC)

The packet received from Network layer is further divided into frames depending on the frame size of NIC(Network Interface Card). DLL also encapsulates Sender and Receiver’s MAC address in the header.The functions of the data Link layer are :

1. Framing: Framing is a function of the data link layer. It provides a way for a sender to transmit a set of bits that are meaningful to the receiver. This can be accomplished by attaching special bit patterns to the beginning and end of the frame.

2. Physical addressing: After creating frames, Data link layer adds physical addresses (MAC address) of sender and/or receiver in the header of each frame.

3. Error control: Data link layer provides the mechanism of error control in which it detects and retransmits damaged or lost frames.

4. Flow Control: The data rate must be constant on both sides else the data may get corrupted thus , flow control coordinates that amount of data that can be sent before receiving acknowledgement.

5. Access control: When a single communication channel is shared by multiple devices, MAC sub-layer of data link layer helps to determine which device has control over the channel at a given time.

* Packet in Data Link layer is referred as Frame. Switch & Bridge are Data Link Layer devices.

Network Layer (Layer 3) :Network layer works for the transmission of data from one host to the other located in different networks. It also takes care of packet routing i.e. selection of the shortest path to transmit the packet, from the number of routes available. The sender & receiver’s IP address are placed in the header by network layer.The functions of the Network layer are :

1. Routing: The network layer protocols determine which route is suitable from source to destination. This function of network layer is known as routing.

2. Logical Addressing: In order to identify each device on internetwork uniquely, network layer defines an addressing scheme. The sender & receiver’s IP address are placed in the header by network layer. Such an address distinguishes each device uniquely and universally.

* Segment in Network layer is referred as Packet. Network layer is implemented by networking devices such as routers.

Transport Layer (Layer 4) :Transport layer provides services to application layer and takes services from network layer. The data in the transport layer is referred to as Segments. It is responsible for the End to End delivery of the complete message. Transport layer also provides the acknowledgment of the successful data transmission and re-transmits the data if an error is

found.• At sender’s side:Transport layer receives the formatted data from the upper layers, performs Segmentation and also implements Flow & Error control to ensure proper data transmission. It also adds Source and Destination port number in its header and forwards the segmented data to the Network Layer.Note: The sender need to know the port number associated with the receiver’s application.Generally, this destination port number is configured, either by default or manually. For example, when a web application makes a request to a web server, it typically uses port number 80, because this is the default port assigned to web applications. Many applications have default port assigned.• At receiver’s side:Transport Layer reads the port number from its header and forwards the Data which it has received to the respective application. It also performs sequencing and reassembling of the segmented data.The functions of the transport layer are :

1. Segmentation and Reassembly: This layer accepts the message from the (session) layer , breaks the message into smaller units . Each of the segment produced has a header associated with it. The transport layer at the destination station reassembles the message.

2. Service Point Addressing: In order to deliver the message to correct process, transport layer header includes a type of address called service point address or port address. Thus by specifying this address, transport layer makes sure that the message is delivered to the correct process.

The services provided by transport layer :1. Connection Oriented Service: It is a three-phase process which include

– Connection Establishment– Data Transfer– Termination / disconnectionIn this type of transmission, the receiving device sends an acknowledgment, back to the source after a packet or group of packet is received. This type of transmission is reliable and secure.

2. Connection less service: It is a one phase process and includes Data Transfer. In this type of transmission, the receiver does not acknowledge receipt of a packet. This approach allows for much faster communication between devices. Connection oriented Service is more reliable than connection less Service.

* Data in the Transport Layer is called as Segments.Transport layer is operated by the Operating System. It is a part of the OS and communicates with the Application Layer by making system calls. Transport Layer is called as Heart of OSI model.

Session Layer (Layer 5) :This layer is responsible for establishment of connection, maintenance of sessions, authentication and also ensures security.The functions of the session layer are :

1. Session establishment, maintenance and termination: The layer allows the two processes to establish, use and terminate a connection.

2. Synchronization : This layer allows a process to add checkpoints which are considered as synchronization points into the data. These synchronization point help to identify the error so that the data is re-synchronized properly, and ends of the messages are not cut prematurely and data loss is avoided.

3. Dialog Controller : The session layer allows two systems to start communication with each other in half-duplex or full-duplex.

Presentation Layer (Layer 6) :Presentation layer is also called the Translation layer.The data from the application layer is extracted here and manipulated as per the required format to transmit over the network.The functions of the presentation layer are :

1. Translation : For example, ASCII to EBCDIC.2. Encryption/ Decryption : Data encryption translates the data into another form or code. The encrypted data

is known as the cipher text and the decrypted data is known as plain text. A key value is used for encrypting as well as decrypting data.

3. Compression: Reduces the number of bits that need to be transmitted on the network.

Application Layer (Layer 7) :At the very top of the OSI Reference Model stack of layers, we find Application layer which is implemented by the network applications. These applications produce the data, which has to be transferred over the network. This layer also serves as a window for the application services to access the network and for displaying the received information to the user.Ex: Application – Browsers, Skype Messenger etc. Application Layer is also called as Desktop Layer.

The functions of the Application layer are :1. Network Virtual Terminal2. FTAM-File transfer access and management3. Mail Services4. Directory Services

TCP/IP Model:It stands for Transmission Control Protocol/Internet Protocol. The TCP/IP model is a concise version of the OSI model. It contains four layers, unlike seven layers in the OSI model. The layers are:1. Process/Application Layer2. Host-to-Host/Transport Layer3. Internet Layer4. Network Access/Link Layer

1. Network Access Layer –

This layer corresponds to the combination of Data Link Layer and Physical Layer of the OSI model. It looks out for hardware addressing and the protocols present in this layer allows for the physical transmission of data.We just talked about ARP being a protocol of Internet layer, but there is a conflict about declaring it as a protocol of Internet Layer or Network access layer. It is described as residing in layer 3, being encapsulated by layer 2 protocols.

2. Internet Layer –

This layer parallels the functions of OSI’s Network layer. It defines the protocols which are responsible for logical transmission of data over the entire network. The main protocols residing at this layer are :1. IP – stands for Internet Protocol and it is responsible for delivering packets from the source host to the

destination host by looking at the IP addresses in the packet headers. IP has 2 versions:IPv4 and IPv6. IPv4 is the one that most of the websites are using currently. But IPv6 is growing as the number of IPv4 addresses are limited in number when compared to the number of users.

2. ICMP – stands for Internet Control Message Protocol. It is encapsulated within IP datagrams and is responsible for providing hosts with information about network problems.

3. ARP – stands for Address Resolution Protocol. Its job is to find the hardware address of a host from a known IP address. ARP has several types: Reverse ARP, Proxy ARP, Gratuitous ARP and Inverse ARP.

3. Host-to-Host Layer –

This layer is analogous to the transport layer of the OSI model. It is responsible for end-to-end communication and error-free delivery of data. It shields the upper-layer applications from the complexities of data. The two main protocols present in this layer are :1. Transmission Control Protocol (TCP) – It is known to provide reliable and error-free communication between

end systems. It performs sequencing and segmentation of data. It also has acknowledgment feature and controls the flow of the data through flow control mechanism. It is a very effective protocol but has a lot of overhead due to such features. Increased overhead leads to increased cost.

2. User Datagram Protocol (UDP) – On the other hand does not provide any such features. It is the go-to protocol if your application does not require reliable transport as it is very cost-effective. Unlike TCP, which is connection-oriented protocol, UDP is connectionless.

4. Process Layer –

This layer performs the functions of top three layers of the OSI model: Application, Presentation and Session Layer. It is responsible for node-to-node communication and controls user-interface specifications. Some of the protocols present in this layer are: HTTP, HTTPS, FTP, TFTP, Telnet, SSH, SMTP, SNMP, NTP, DNS, DHCP, NFS. HTTPS – HTTP stands for Hypertext transfer protocol. It is used by the World Wide Web to manage

communications between web browsers and servers. HTTPS stands for HTTP-Secure. It is a combination of HTTP with SSL(Secure Socket Layer). It is efficient in cases where the browser need to fill out forms, sign in, authenticate and carry out bank transactions.

SSH – SSH stands for Secure Shell. It is a terminal emulations software similar to Telnet. The reason SSH is more preferred is because of its ability to maintain the encrypted connection. It sets up a secure session over a TCP/IP connection.

NTP – NTP stands for Network Time Protocol. It is used to synchronize the clocks on our computer to one standard time source. It is very useful in situations like bank transactions. Assume the following situation without the presence of NTP. Suppose you carry out a transaction, where your computer reads the time at 2:30 PM while the server records it at 2:28 PM. The server can crash very badly if it’s out of sync.

ISDN:The main feature of ISDN is that it can integrate speech and data on the same lines, which were not available in the classic telephone system.

The Integrated Services of Digital Networking, in short ISDN is a telephone network based infrastructure that allows the transmission of voice and data simultaneously at a high speed with greater efficiency. This is a circuit switched telephone network system, which also provides access to Packet switched networks.

The model of a practical ISDN is as shown below.

ISDN supports a variety of services like Voice calls, Videotext, Teletext, Electronic Mail, Database access etc.

Types of ISDN

Among the types of several interfaces present, some of them contains channels such as the B-Channels or Bearer Channels that are used to transmit voice and data simultaneously; the D- Channels or Delta Channels that are used for signaling purpose to set up communication.

The ISDN has several kinds of access interfaces such as −

Basic Rate Interface (BRI) Primary Rate Interface (PRI) Narrowband ISDN

Broadband ISDN

Basic Rate Interface (BRI)

The Basic Rate Interface or Basic Rate Access, simply called the ISDN BRI Connection uses the existing telephone infrastructure. The BRI configuration provides two data or bearer channels at 64 Kbits/sec speed and one control or delta channel at 16 Kbits/sec. This is a standard rate.

The ISDN BRI interface is commonly used by smaller organizations or home users or within a local group, limiting a smaller area.

Primary Rate Interface (PRI)

The Primary Rate Interface or Primary Rate Access, simply called the ISDN PRI connection is used by enterprises and offices. The PRI configuration is based on T-carrier or T1 in the US, Canada and Japan countries consisting of 23 data or bearer channels and one control or delta channel, with 64kbps speed for a bandwidth of 1.544 M bits/sec. The PRI configuration is based on E-carrier or E1 in Europe, Australia and few Asian countries consisting of 30 data or bearer channels and two-control or delta channel with 64kbps speed for a bandwidth of 2.048 M bits/sec.

The ISDN BRI interface is used by larger organizations or enterprises and for Internet Service Providers.

Narrowband ISDN

The Narrowband Integrated Services Digital Network is called the N-ISDN. This can be understood as a telecommunication that carries voice information in a narrow band of frequencies. This is actually an attempt to digitize the analog voice information. This uses 64kbps circuit switching.

The narrowband ISDN is implemented to carry voice data, which uses lesser bandwidth, on a limited number of frequencies.

Broadband ISDN

The Broadband Integrated Services Digital Network is called the B-ISDN. This integrates the digital networking services and provides digital transmission over ordinary telephone wires, as well as over other media. The CCITT defined it as, “Qualifying a service or system requiring transmission channels capable of supporting rates greater than primary rates.”

The broadband ISDN speed is around 2 MBPS to 1 GBPS and the transmission is related to ATM, i.e., Asynchronous Transfer Mode. The broadband ISDN communication is usually made using the fiber optic cables.

As the speed is greater than 1.544 Mbps, the communications based on this are called  Broadband Communications. The broadband services provide a continuous flow of information, which is distributed from a central source to an unlimited number of authorized receivers connected to the network. Though a user can access this flow of information, he cannot control it.

Advantages of ISDN

ISDN is a telephone network based infrastructure, which enables the transmission of both voice and data simultaneously. There are many advantages of ISDN such as −

As the services are digital, there is less chance for errors. The connection is faster. The bandwidth is higher. Voice, data and video − all of these can be sent over a single ISDN line.

Disadvantages of ISDN

The disadvantage of ISDN is that it requires specialized digital services and is costlier.

However, the advent of ISDN has brought great advancement in communications. Multiple transmissions with greater speed are being achieved with higher levels of accuracy.

Delay Analysis:

Two hosts A and B are connected over a transmission link / transmission media. A data packet is sent by the Host A to Host B.

 Following different types of delay occur during transmission-

 

 

 

Transmission Delay- Time taken to put the data packet on the transmission link is called as transmission delay. Mathematically,

 

Propagation Delay-Time taken for one bit to travel from sender to receiver end of the link is called as propagation delay

 

 

Queuing Delay-Time spent by the data packet waiting in the queue before it is taken for execution is called as queuing delay. It depends on the congestion in the network.

 

Processing Delay- Time taken by the processor to process the data packet is called as processing delay. It depends on the speed of the processor. Processing of the data packet helps in detecting bit level errors that occurs during transmission

Total delay in sending one data packet or End to End time = Transmission delay + Propagation delay + Queuing delay + Processing delay

 

In optical fiber, transmission speed of data packet = 2.1 x 108 m/sec

 

In optical fiber, signals travel with 70% speed of light(3 x 108  m/sec). So, consider transmission speed = 2.1 x 108  m/sec for calculations when using optical fiber.Bandwidth is always expressed in powers of 10 and data is always expressed in powers of 2.