Introduction to Computer Communication Network

UNIT - 1

Computer Network

A network is any collection of independent computers that communicate with one another over a shared network medium. A computer network is a collection of two or more connected computers. When these computers are joined in a network, people can share files and peripherals such as modems, printers, tape backup drives, or CD-ROM drives. When networks at multiple locations are connected using services available from phone companies, people can send e-mail, share links to the global Internet, or conduct video conferences in real time with other remote users. When a network becomes open sourced it can be managed properly with online collaboration software. As companies rely on applications like electronic mail and database management for core business operations, computer networking becomes increasingly more important.

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A computer network is an interconnected system of two or more computing devices to transmit and share data, applications, and other resources. These devices can be everything from laptops to desktops to mobile phones to servers. These devices are typically connected with physical wires (e.g., standard cables, fiber optics), but they can also be connected via wireless technology.

Examples of computer networks include a company's private computer network, a utility company's network, and even the whole Internet itself.

 

Every network includes:

•  At least two computers Server or Client workstation.

•  Networking Interface Card's (NIC)

•   A connection medium, usually a wire or cable, although wireless communication between networked computers and peripherals is also possible.

•  Network operating system software, such as Microsoft Windows NT or 2000, Novell NetWare, UNIX and Linux.

 

Key Components of a Computer Network

Most computer networks include all the following components.

 

Network Devices

This is a catch-all term that’s further divided into sub-groups.

·         End devices: This covers computers, smart phones, and other peripheral devices (e.g., printers, fax).

·         Servers: These are the machines dedicated to storage and applications, where all the computations, data processing, and storage happens.

·         Routers: These devices forward packets of data between networks until they reach their destination.

·         Switches: Switches are multi-port bridges. Bridges, in turn, are more intelligent hubs that send data to the destination port. Hubs are repeaters equipped with multiple ports, and repeaters are devices that clean and strengthen received network signals.

 

Links

Links are the methods used to transmit data. They break down into:

·         Wired links. These links include phone lines, coaxial cable, and fiber optics.

·         Non-wired links. Wireless connections include cellular networks, satellites, or other forms of radio or electromagnetic signals.

 

Communication protocols

Communication protocols are sets of rules that all the information-transferring nodes follow. Typical protocols include TCP/IP, wireless LAN, IEEE802, Ethernet, and cellular.

TCP/IP is the predominant model for today’s Internet structure and presents this standard layer configuration for communication links:

·         Network access layer: Defines how the data gets physically transferred.

·         Internet layer: Packages the data into understandable packets so it can be sent and received.

·         Transport layer: Allows the network devices to maintain conversations.

·         Application layer: Establishes how high-level applications access the network for purposes of data transfer.

IEEE802 belongs to the set of IEEE standards and covers local area networks (LAN), and metro area networks (MAN). Wireless LAN is the most recognizable member of the IEEE family and is better known as Wi-Fi.

 

Network Defense

This vital element covers everything needed  to  keep  the  network  safe.  Defenses include firewalls, content filters, load balancers, and intrusion detection and prevention systems.

 

Elementary Terminology of Networks

Nodes (Workstations)

The term nodes refers to the computers that are attached to a network and are seeking to share the resources of the network. Of course, if there were no nodes (also called workstations), there would be no network at all. A computer becomes a workstation of a network as soon as it is attached to a network.

 

Server

Computer that facilitates "the sharing of data" software" and hardware - resources (e.g. "printers" modems etc,) on the network" is termed as a SERVER.

On small networks, sometimes, all the shareable stuff (like files, data, software etc.) is stored on the server. A network can have more than one server also. Each server has a unique name on the network and all users of network identify the server by its unique name. Servers can be of two types: non dedicated and dedicated servers.

 

Network Interface Unit (NIU)

A NETWORK INTERFACE UNIT is an interpreter that helps to establish communication between the server and workstations. The network-interface-unit is a device that is attached to each of the workstations and the server, and helps the workstation to establish the all important connection with the network. Each network-interface-unit that is attached to a workstation has a unique number identifying it which is known as the node address. The NIU is also called Terminal Access Point (TAP). Different manufacturers have different names for the interface.

 

IP address: An IP address is a unique number assigned to every device connected to a network that uses the Internet Protocol for communication. Each IP address identifies the device’s host network and the location of the device on the host network. When one device sends data to another, the data includes a ‘header’ that includes the IP address of the sending device and the IP address of the destination device.

 

Ports: A port identifies a specific connection between network devices. Each port is identified by a number. If you think of an IP address as comparable to the address of a hotel, then ports are the suites or room numbers within that hotel. Computers use port numbers to determine which application, service, or process should receive specific messages.

 

Network cable types: The most common network cable types are Ethernet twisted pair, coaxial, and fiber optic. The choice of cable type depends on the size of the network, the arrangement of network elements, and the physical distance between devices.

 

Applications of Computer Networks

·       Marketing and sales: – Computer networks are widely used in both marketing sales firms. These are used by marketing professionals to collect, exchange, and analyzes data relating to customer requirements and product development cycles. Teleshopping is also important part of sales applications that use order-entry computers or telephones connected to an order-processing network, and on-line reservation services for hotels airline and so on.

·       Manufacturing: – Now days, computer networks are used in a several aspects of manufacturing, including the manufacturing process itself. Two applications which use a network to provide necessary services are computer-assisted manufacturing (CAM) and computer –assisted designing (CAD) both of which permit multiple users to work on a project simultaneously.

·       Financial Services: – In Present, Financial services are completely dependent on computer networks. Main applications are credit history searches, foreign exchange and investment services, and Electronic Funds Transfer (EFT) that permits a user to transfer money without going into bank.

·       Teleconferencing: – With The help of teleconferencing conferences are possible to occur without the participants being in the same place. Applications include simple text conferencing, voice conferencing, and video conferencing.

·       Cable Television:-Future Services provided by cable television network can include video on request, as well as the same information, financial and communications services currently provided by the telephone companies and computer networks.

·       Information Services:- Network information services include bulletin boards and data banks. A World Wide Web site offering the technical specifications for a new product is an information service.

·       Electronic Messaging:– Electronic mail (e-mail) is the most widely used network application.

·       Electronic Data Interchange (EDI):– EDI permits business information to be transferred without using paper.

·       Directory services: – By using directory services, it is possible to store the last of files in a central location to speed worldwide search operations.

·       Cellular Telephone: – In the past, two parties desiring to use the services of the telephone company had to be linked by a fixed physical connection. But, in present cellular network make it possible to maintain wireless phone connections even while travelling over large distances.

 

Network Structure

Network structure is a term used to describe the method of how data on a network is organized and viewed. Network structure defined as the physical organization of devices and hardware (protocol), logical design i.e softwares, protocols (computing) and data transmission mode (medium). Network Structure describes the method of how data on a network organized and viewed.

 

Layering Principles and Services

Step by step for successful transmission of data

Protocols and Standards

Rules to be followed for reliable communication.

 

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 most well-known Computer Network Architectures are:

o     Peer-To-Peer network

o     Client/Server network

 

Peer-To-Peer network

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

o     Peer-To-Peer network is useful for small environments, usually up to 10 computers.

o     Peer-To-Peer network has no dedicated server.

o     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:

o     It is less costly as it does not contain any dedicated server.

o     If one computer stops working but, other computers will not stop working.

o     It is easy to set up and maintain as each computer manages itself.

 

Disadvantages Of Peer-To-Peer Network:

o     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.

o     It has a security issue as the device is managed itself.

 

Client/Server Network

o     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.

o     The central controller is known as a server while all other computers in the network

are called clients.

o     A server performs all the major operations such as security and network management.

o     A server is responsible for managing all the resources such as files, directories, printer, etc.

o     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:

o     A Client/Server network contains the centralized system. Therefore we can back up the data easily.

o     A Client/Server network has a dedicated server that improves the overall performance of the whole system.

o     Security is better in Client/Server network as a single server administers the shared resources.

o     It also increases the speed of the sharing resources.

Disadvantages Of Client/Server network:

o     Client/Server network is expensive as it requires the server with large memory.

o     A server has a Network Operating System(NOS) to provide the resources to the clients, but the cost of NOS is very high.

o     It requires a dedicated network administrator to manage all the resources.

 

There are some more lesser known computer architectures:

3.    Centralized Computing Architecture:

 

One powerful computer is utilized to service one or more low-powered computers in centralized computing architecture. The nodes under the centralized architecture are not linked; they are only connected to the server.

The centralized computing architecture includes the following components:

·         The primary, mainframe computer which handles all processing.

·         Terminals are connected to a central computer and function as input/output devices.

·         Linking of at least two mainframe computers together via networks. Terminals communicate solely with the mainframe and never with one another.

4.    Distributed Computing Architecture:

 

 

 

 

 

 

 

 

 

 

A distributed architecture connects one or more nodes, which are personal computers. It supports a variety of functions, including file sharing, hardware sharing, and network sharing. The nodes in the distributed architecture can manage their own data and rely on the network for administration rather than data processing.

The following components are found in distributed computing architecture:

·         Different computers are effective at performing independently.

·         Completion of tasks on multiple computers locally.

·         Networks enable computers to exchange data and services, but they do not offer processing help.

 

5.   
Collaborative Computing Architecture:

The collaborative computing architecture is a hybrid of centralised and decentralised computing. Individual members of a network can process their users’ fundamental needs under the collaborative model.

A database server, such as an MSSQL server or an ORACLE server, for example, observes or manages all database-related operations on all network nodes. The model will, however, execute requests that are not from the database.

 

Topology

Topology is derived from two Greek words topo and logy, where topo means 'place' and logy means 'study'. In computer networks, a topology is used to explain how a network is physically connected and the logical flow of information in the network. A topology mainly describes how devices are connected and interact with each other using communication links.

 

In computer networks, there are mainly two types of topologies, they are:

Physical Type

A physical topology describes the way in which the computers or nodes are connected with each other in a computer network. It is the arrangement of various elements (link, nodes, etc.), including the device location and code installation of a computer network. In other words, we can say that it is the physical layout of nodes, workstations, and cables in the network. It also refers to the transmission medium of the signal. Examples – Bus topology, Star topology, Ring topology, Tree topology, Mesh Topology, Point-to-Point topology, and Hybrid Topology

 

Logical Type

A logical topology describes the way, data flow from one computer to another. It is bound to a network protocol and defines how data is moved throughout the network and which path it takes. In other words, it is the way in which the devices communicate internally.

 

Network Topology

Network topology describes the physical and logical relationship of nodes in a network, the schematic arrangement of the links and nodes, or some hybrid combination thereof.

Network topology defines the layout(arrangement), virtual(real) shape, or structure of the network, not only physically but also logically. A network can have one physical topology and multiple logical topologies at the same time.

 

In a computer network, there are mainly seven types of physical topology, they are:

1.       Point to Point Topology

2.       Bus Topology

3.       Ring Topology

4.       Star Topology

5.       Mesh Topology

6.       Hybrid Topology

7.       Tree Topology

 

Point to Point

Point-to-Point topology is the simplest topology that connects two nodes directly together with a common link. The entire bandwidth(maximum amount of data is transmitted over internet) of the common link is reserved for transmission between those two nodes. The point-to-point connections use an actual length of wire or cable to connect the two ends, but other options, such as satellite links, or microwaves are also possible.

When you  change  TV  channels  by  remote,  you  are  establishing  a point-to-

point connection between the remote control and the TV’s control system.

 

 

 

 

 

 

 

 

 

 

 

The transfer of data in a point-to-point topology can be in multiple ways across the network: in a simplex, in full duplex, or half duplex.

·         In Simplex mode of communication, signal flows in ONE direction and only one node transmit and the other receives.(tv, radio)

·         In Half duplex mode of communication, each node can transmit and receive but NOT at the same time (walkie-talkie).

 

·              In     Full-duplex mode  of   communication, both    stations   transmit           and   receive simultaneously (telephone).

 

Advantages

1.    Highest Bandwidth because there is only two nodes having entire bandwidth of a link

2.    Very fast compared to other topologies network because it can access only two nodes.

3.    Very simple connectivity

4.    It provides low Latency(delay in netwok communication)

5.    Easy to handle and maintain

6.    Node Can be Replaced in few seconds

Disadvantages

1.    This topology is only used for small areas where nodes are closely located.

2.    The entire network depends on the common channel in case of link broken entire network will become dead.

3.    There is another major drawback of this topology there are only two nodes if any of the node stops working, data cannot be transfer across the network.

 

Bus

· In bus topology there is a main cable and all the devices are connected to this main cable through drop lines.

· There is a device called tap that connects the drop line to the main cable.

· Since all the data is transmitted over the main cable, there is a limit of drop lines and the distance a main cable can have.

 

·         The main cable that is connected to the devices on the network using drop line is called backbone cable.

·         The main cable broadcast the message to all the devices connected to it.

·         When a device wants to sends a message, it transmits the message to the backbone cable. All the other devices connected to the backbone cable receives the message whether they are intended(purpose) to receive the message or not.

·         The most common access method of the bus topologies is CSMA (Carrier Sense Multiple Access). This method is used to prevent the collision of data as two or more devices can send the data to main cable at the same time.

 

CSMA: This method is developed to decrease the chance of collisions when two or more devices starts sending the signal at the same time.

 

CSMA CD (Carrier Sense Multiple Access with Collision Detection): In this method, a device monitors the transmission medium after it sends the data to see if the transmission was successful. If successful, the device marks the communication successful else it sends the data again.

CSMA CA (Carrier Sense Multiple Access with Collision Avoidance): This method tries

 

to prevent the collision from happening. In this method, before sending the data, the device checks the transmission medium to see if it is busy or not. If busy, then the sender device waits until the transmission medium becomes idle.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Advantages of bus topology

·         Easy installation, each cable needs to be connected with backbone cable.

·         Less Expensive: Less cables are required than Mesh and star topology

·         Limited failure: The connection failure of one device doesn’t affect the connections of other devices on network.

Disadvantages of bus topology

·         Difficultly in fault detection.

·         Not scalable (no changing of size) as there is a limit of how many nodes you can connect with backbone cable.

·         Difficult to troubleshoot: It is difficult to identify the cause of failure.

·         Data collision: When two or more devices send the data simultaneously then there is a chance of data collision. However this can be solved by implementing CSMA techniques that we discussed above.

 

Ring

In ring topology each device is connected with the two devices on either side of it.

There are two dedicated point to point links a device has with the devices on the either side of it. This structure forms a ring thus it is known as ring topology.

If a device wants to send data to another device then it sends the data in one direction, each device in ring topology has a repeater, if the received data is intended for other device then repeater forwards this data until the intended device receives it.

·         Data flow is unidirectional in ring topology.

·         This topology doesn’t have any end points as nodes are connected in circular fashion.

·         The data transfers in ring topology in clockwise direction.

 

·         The popular access method used in ring topology is token passing method. The word token describes segment of data send through the network. There are multiple tokens available on the network, the device that successfully acquires the token attaches the data to the token. The device that successfully decodes the token, receives the data.

 

Advantages of Ring Topology

·         Easy to install.

·         Managing is easier as to add or remove a device from the topology only two links are required to be changed.

·         Less expensive: Generally Twisted pair cabling is used in ring topology which is

inexpensive and easily available.

·         Easy maintenance: The network in ring topology is easy to maintain as a system failure doesn’t affect other systems on network, the failed system can be easily removed and installed again after fixing the issue.

Disadvantages of Ring Topology

·         A link failure can fail the entire network as the signal will not travel forward due to failure.

·         Data traffic issues, since all the data is circulating in a ring.

 

Star

In star topology each device in the network is connected to a central device

called hub. Unlike Mesh topology, star topology doesn’t allow direct communication between devices, a device must have to communicate through hub.

If one device wants to send data to other device, it has to first send the data to hub and then the hub transmit that data to the designated device.

 

The central device is known as hub and other devices connected to hub are called clients. Generally Coaxial cable or RJ-45 cables are used to connect the clients to the hub.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Advantages of Star topology

·         Less expensive: Less expensive because each device only need one I/O port and needs to be connected with hub with one link.

·         Easier to install

·         Cost effective: Less amount of cables required because each device needs to be connected with the hub only.

·         Robust: If one link fails, other links will work just fine.

·         Easy to troubleshoot: Easy fault detection because the link can be easily identified.

·         Reliable: Each device is separately connected to the hub, so a connection failure between a device and hub doesn’t affect the connection of the other devices.

Disadvantages of Star topology

·         If hub goes down everything goes down, none of the devices can work without hub.

·         Hub requires more resources and regular maintenance because it is the central system of star topology.

·         Not Scalable: There is a limit to add new devices as each device increase the load on

the central unit (hub or switch). This is why it is not suitable for the large networks.

 

Mesh

In mesh topology each device is  connected to every other device on the network

through a dedicated point-to-point link. When we say dedicated it means that the link only carries data for the two connected devices only. Lets say we have n devices in the network then each device must be connected with (n-1) devices of the network. Number of links in a mesh topology of n devices would be n(n-1)/2.

There are two types of Mesh topology:

1.       Full Mesh Topology: In this topology each device is connected to all the devices available on the network.

2.       Partial Mesh Topology: In partial mesh topology, each device is connected to only those devices, to which they communicate frequently. This reduces redundant links and saves the setup cost.

 

 

Advantages of Mesh topology

1.   No data loss: No data traffic issues as there is a dedicated link between two devices which means the link is only available for those two devices.

2.   Reliable: Mesh topology is reliable and robust as failure of one link doesn’t affect other links and the communication between other devices on the network.

3.   Secure: Mesh topology is secure because there is a point to point link thus unauthorized access is not possible.

4.   Easy to troubleshoot: Fault detection is easy as there is a separate connection between each devices.

5.   Fast communication: As there is a dedication connection between two devices on a network, the communication is fast.

 

Disadvantages of Mesh topology

1.   Amount of wires required to connected each system is tedious and headache.

2.  Since each device needs to be connected with other devices, number of I/O ports required must be huge.

3.  Scalability issues because a device cannot be connected with large number of devices with a dedicated point to point link.

 

Hybrid

A combination of two or more topology is known as hybrid topology. For example a combination of star and bus topology is known as star bus hybrid topology, this topology is shown in the above diagram.

 

Advantages of Hybrid topology

·         We can choose the topology based on the requirement for example, scalability is our concern then we can use star topology instead of bus technology.

·         Scalable as we can further connect other computer networks with the existing networks with different topologies.

Disadvantages of Hybrid topology

·         Fault detection is difficult.

·         Installation is difficult.

·         Design is complex so maintenance is high thus expensive.

 

Tree

·         Tree topology is an example of hybrid topology as it is a combination of star topology and bus topology that forms a tree like structure.

·         The devices are connected to each other in hierarchical manner. Each node has arbitrary number of child nodes. The device at the top of the hierarchy is known as root node and other devices that are lower in hierarchy known as descendants of the root node.

·         There is a single path between two devices and this is the path of the communication between devices.

·         Tree topology is also called star-bus topology.

Advantages of Tree topology

·         Easy error detection.

·         Expendable: It is easy to add new devices to the network in tree topology.

·         Easy maintenance: Devices are grouped in small star networks and these star networks are connected to each other using bus topology. It is easy to manage a device in small star network.

 

·         Reliable: One system failure doesn’t bring the whole network down. The failed system can be easily managed.

·         Supports broadband(high bandwidth) transmissions: It supports broadband transmission that is reason this topology is frequently used in corporate networks.

 

Disadvantages of Tree topology

·         Cost: Cost of broadband transmission is high.

·         Dependant on backbone cable of bus topology: All the devices connected in star networks are connected with other devices using backbone cable of bus topology. Failure in this main cable can affect the whole network.

·         PAN (Personal Area Network)

·         LAN (Local Area Network)

·         MAN (Metropolitan Area Network)

·         WAN (Wide Area Network)

 

PAN (Personal Area Network) 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

Below are the main 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.

 

LAN (Local Area Network)

A 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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Local Area Network (LAN)

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(like server).

·         Local Area Network requires a constant LAN administration as there are issues related to software setup and hardware failures

 

MAN (Metropolitan Area Network)?

A 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.

 

 

 

 

 

 

 

 

 

 

 

 

Metropolitan Area Network (MAN)

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

 

WAN (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.

Wide Area Network (WAN)

Characteristics of WAN

·         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.

Disadvantages 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 network in computer.

 

Other Types of Computer Networks

Apart from above mentioned computer networks, here are some other important types of networks:

·         WLAN (Wireless Local Area Network)

·         Storage Area Network

·         System Area Network

·         Home Area Network

·         POLAN- Passive Optical LAN

·         Enterprise private network

·         Campus Area Network

·         Virtual Area Network

1)   WLAN

WLAN (Wireless Local Area Network) helps you to link single or multiple devices using wireless communication within a limited area like home, school, or office building. It gives users an ability to move around within a local coverage area which may be connected to the network. Today most modern day’s WLAN systems are based on IEEE 802.11 standards.

2)   Storage-Area Network (SAN)

A Storage Area Network is a type of network which allows consolidated, block-level data storage. It is mainly used to make storage devices, like disk arrays, optical jukeboxes, and tape libraries.

3)   System-Area Network

System Area Network is used for a local network. It offers high-speed connection in server- to-server and processor-to-processor applications. The computers connected on a SAN network operate as a single system at quite high speed.

4)   Passive Optical Local Area Network

POLAN is a networking technology which helps you to integrate into structured cabling. It allows you to resolve the issues of supporting Ethernet protocols and network apps.

POLAN allows you to use optical splitter which helps you to separate an optical signal from a single-mode optical fiber. It converts this single signal into multiple signals.

 

5)   Home Area Network (HAN):

A Home Area Network is always built using two or more interconnected computers to form a local area network (LAN) within the home. For example, in the United States, about 15 million homes have more than one computer.

These types of network connections help computer owners to interconnect with multiple computers. This network allows sharing files, programs, printers, and other peripherals.

6)   Enterprise Private Network :

Enterprise private network (EPN) networks are build and owned by businesses that want to securely connect numerous locations in order to share various computer resources.

7)   Campus Area Network (CAN):

A Campus Area Network is made up of an interconnection of LANs within a specific geographical area. For example, a university campus can be linked with a variety of campus buildings to connect all the academic departments.

8)   Virtual Private Network:

A VPN is a private network which uses a public network to connect remote sites or users together. The VPN network uses “virtual” connections routed through the internet from the enterprise’s private network or a third-party VPN service to the remote site.

It is a free or paid service that keeps your web browsing secure and private over public WiFi hotspots.

OSI Reference Model

o         OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer.

o         It was the first standard model for network communications, adopted by all major

computer and telecommunication companies in the early 1980s

o         The modern Internet is not based on OSI, but on the simpler TCP/IP model. However, the OSI 7-layer model is still widely used, as it helps visualize and communicate how networks operate, and helps isolate and troubleshoot networking problems.

o         OSI was introduced in 1983 by representatives of the major computer and telecom companies, and was adopted by ISO as an international standard in 1984.

o         The Open Systems Interconnection (OSI) model describes seven layers that computer systems use to communicate over a network.

o         OSI consists of seven layers, and each layer performs a particular network function.

 

The OSI model is divided into two layers: upper layers and lower layers.

o         The upper layer of the OSI model mainly deals with the application related issues, and they are implemented only in the software. The application layer is closest to the end user. Both the end user and the application layer interact with the software applications. An upper layer refers to the layer just above another layer.

o         The lower layer of the OSI model deals with the data transport issues. The data link layer and the physical layer are implemented in hardware and software. The physical layer is the lowest layer of the OSI model and is closest to the physical medium. The physical layer is mainly responsible for placing the information on the physical medium.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

OSI Model Explained: The OSI 7 Layers

 

7. Application Layer

The application layer is used by end-user software such as web browsers and email clients. It provides protocols that allow software to send and receive information and present meaningful data to users. A few examples of application layer protocols are the Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS).

6. Presentation Layer

The presentation layer prepares data for the application layer. It defines how two devices should encode, encrypt, and compress data so it is received correctly on the other end. The presentation layer takes any data transmitted by the application layer and prepares it for transmission over the session layer.

5. Session Layer

The session layer creates communication channels, called sessions, between devices. It is responsible for opening sessions, ensuring they remain open and functional while data is being transferred, and closing them when communication ends. The session layer can also set checkpoints during a data transfer—if the session is interrupted, devices can resume data transfer from the last checkpoint.

4. Transport Layer

The transport layer takes data transferred in the session layer and breaks it into “segments” on the transmitting end. It is responsible for reassembling the segments on the receiving end, turning it back into data that can be used by the session layer. The transport layer carries out flow control, sending data at a rate that matches the connection speed of the receiving device, and error control, checking if data was received incorrectly and if not, requesting it again.

3. Network Layer

The network layer has two main functions. One is breaking up segments into network packets, and reassembling the packets on the receiving end. The other is routing packets by discovering the best path across a physical network. The network layer uses network addresses (typically Internet Protocol addresses) to route packets to a destination node.

2. Data Link Layer

The data link layer establishes and terminates a connection between two physically- connected nodes on a network. It breaks up packets into frames and sends them from source to destination. This layer is composed of two parts—Logical Link Control (LLC), which identifies network protocols, performs error checking and synchronizes frames, and Media Access Control (MAC) which uses MAC addresses to connect devices and define permissions to transmit and receive data.

1. Physical Layer

The physical layer is responsible for the physical cable or wireless connection between network nodes. It defines the connector, the electrical cable or wireless technology connecting the devices, and is responsible for transmission of the raw data, which is simply a series of 0s and 1s, while taking care of bit rate control.

 

Advantages of OSI Model

The OSI model helps users and operators of computer networks:

·  Determine the required hardware and software to build their network.

·  Understand and communicate the process followed by components communicating across a network.

·  Perform troubleshooting, by identifying which network layer is causing an issue and focusing efforts on that layer.

The OSI model helps network device manufacturers and networking software vendors:

·  Create devices and software that can communicate with products from any other vendor, allowing open interoperability

·  Define which parts of the network their products should work with.

·  Communicate to users at which network layers their product operates – for example, only at the application layer, or across the stack.

 

The TCP/IP Reference Model

TCP/IP means Transmission Control Protocol and Internet Protocol. It is the network model used in the current Internet architecture as well. Protocols are set of rules which govern every possible communication over a network. These protocols describe the movement of data between the source and destination or the internet. They also offer simple naming and addressing schemes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Protocols and networks in the TCP/IP model:

 

Overview of TCP/IP reference model

TCP/IP that is Transmission Control Protocol and Internet Protocol was developed by Department of Defence's Project Research Agency (ARPA, later DARPA) as a part of a research project of network interconnection to connect remote machines.

The features that stood out during the research, which led to making the TCP/IP reference model were:

·         Support for a flexible architecture. Adding more machines to a network was easy.

·         The network was robust, and connections remained intact untill the source and destination machines were functioning.

The overall idea was to allow one application on one computer to talk to(send data packets) another application running on different computer.

 

Different Layers of TCP/IP Reference Model

The 4 layers that form the TCP/IP reference model:

Layer 1: Host-to-network Layer

·  Lowest layer of the all.

·  Protocol is used to connect to the host, so that the packets can be sent over it.

·  Varies from host to host and network to network.

Layer 2: Internet layer

·  Selection of a packet switching network which is based on a connectionless internetwork layer is called a internet layer.

·  It is the layer which holds the whole architecture together.

·  It helps the packet to travel independently to the destination.

·  Order in which packets are received is different from the way they are sent.

·  IP (Internet Protocol) is used in this layer.

·  The various functions performed by the Internet Layer are:

o     Delivering IP packets

o     Performing routing

o     Avoiding congestion

Layer 3: Transport Layer

·  It decides if data transmission should be on parallel path or single path.

·  Functions such as multiplexing, segmenting or splitting on the data is done by transport layer.

·  The applications can read and write to the transport layer.

·  Transport layer adds header information to the data.

·  Transport layer breaks the message (data) into small units so that they are handled more efficiently by the network layer.

·  Transport layer also arrange the packets to be sent, in sequence.

 

Layer 4: Application Layer

The TCP/IP specifications described a lot of applications that were at the top of the protocol stack. Some of them were TELNET, FTP, SMTP, DNS etc.

·  TELNET is a two-way communication protocol which allows connecting to a remote machine and run applications on it.

·  FTP(File Transfer Protocol) is a protocol, that allows File transfer amongst computer users connected over a network. It is reliable, simple and efficient.

·  SMTP(Simple Mail Transport Protocol) is a protocol, which is used to transport electronic mail between a source and destination, directed via a route.

·  DNS(Domain Name Server) resolves an IP address into a textual address for Hosts connected over a network.

·  It allows peer entities to carry conversation.

·  It defines two end-to-end protocols: TCP and UDP

o     TCP(Transmission Control Protocol): It is a reliable connection-oriented protocol which handles byte-stream from source to destination without error and flow control.

o     UDP(User-Datagram Protocol): It is an unreliable connection-less protocol

that do not want TCPs, sequencing and flow control. Eg: One-shot request- reply kind of service.

 

Merits of TCP/IP model

·  It operated independently.

·  It is scalable.

·  Client/server architecture.

·  Supports a number of routing protocols.

·  Can be used to establish a connection between two computers.

Demerits of TCP/IP

·  In this, the transport layer does not guarantee delivery of packets.

·  The model cannot be used in any other application.

·  Replacing protocol is not easy.

·  It has not clearly separated its services, interfaces and protocols.