System Development Concept
System
System is a set of interacting or interdependent components forming an integrated whole. A system can be described as a set of objects joined together for a common objective.
Components of system:
-
Hardware: hardware refers to the physical layer of the information system. It includes computers, networks, scanners, digital capture devices, and other technology-based infrastructure.
-
Software: software refers to the logical layer of information system that makes hardware function properly. It includes system software (OS, device driver, etc.) and application software.
-
Data: data is raw facts, figures, and measurements, etc. which are used as input for the system. It may be alphabets, digits, figures and other symbols.
-
Processes: processes, or procedures, describe the tasks that users, managers, and IT staff members perform.
-
People: people refer to users who interact with information system. The users within the organization include mangers, technicians, sales representatives, corporate officers, etc. are called internal users and the users outside the organization include customers, suppliers, etc. are called external users.
Information System
An information system is a computer based system which is an integrated set of different components for collection, process, storage and transmission of data. Simply, it us a system which processes supplied/collected data and generates information that can be used for decision making at different levels for the betterment of an organization. The types of information system are:
-
Transaction processing system: it processes data resulting from business transactions, updates operational database such as sales and inventory processing and accounting systems.
-
Management information system: it is the integrated modern approach of management, information and computerized system. It provides information to support the operations, management, decision making functions of an organization.
-
Decision support system: It is the information system at the organization's senior level management that combines data and sophisticated analytical models or data analysis tools to support semi-structures and unstructured decision makings.
-
Executive support system: it is also known as executive information system. It operates on the executive level of management. It provides critical information from many sources customized to the information needs of executives.
System Analyst
System analyst is a people who is involved in analyzing, designing, implementing and evaluating computer based information to support the decision making and operation of an organization.
The roles of system analyst area as follows:
-
Change event
-
Investigator and event
-
Architect
-
Psychologist
-
Motivator
-
Defining and prioritizing the requirements
-
Analysis and evaluation
-
Designing system
The characteristics of system analyst are as follows:
-
Knowledge of organizations
-
Knowledge of computer system
-
Good inter-personal relation
-
Communication skills
-
Analytical skill
-
Breadth of knowledge
Waterfall model
it is a oldest type of model for software engineering. The fundamental processes of waterfall model are as follows:
-
Requirements analysis and definition: it is the first stage of waterfall model. In this stage, the developer should identify the actual requirements of the given problem.
-
System design: in this stage the systems design process partition the requirements to either hardware or software systems.
-
Implementation and unit system: During this stage, the system design is realized and tested as a complete system to ensure that the software requirements have been met.
-
Operation and maintenance: in this stage, the system is installed to the desire location. The maintenance involves correcting errors which were not discovered in earlier stages of the life cycle, improving the implementation of system units and enhancing the system's service as new requirements are discovered.
Prototyping model
It is the iterative process of system development which is more appropriate for developing new system where there is no clear idea of requirements, inputs and outputs.
-
Identify the user needs: the system analyst interviews the user to obtain an idea of what is required from the system.
-
Develop a prototype: the system analyst, working uses one or more prototyping tools to develop a prototype.
-
Determine if prototype is acceptable: the analyst educates the user in prototype use and provides an opportunity from becoming familiar with the system.
-
Use the prototype: the prototype becomes the operational system.
Spiral system
In this model, process is represented as a spiral rather than as a sequence of activities with backtracking.
-
Planning: the project is reviewed and a decision made whether to continue with a further loop of the spiral. If it is decided to continue, plans are drawn up for the next phase of the project.
-
Risk analysis: for each of the identified project risks, a detailed analysis is carried out. Steps are taken to reduce the risk. For example, if there is a risk that the requirements are inappropriate, a prototype system may be developed.
-
Software development: after risk evaluation, a development model for the system is chosen.
-
User evaluation: specific objectives for the phase of the project are defined by the evaluation of users. Constraints on the process and the product are identified. And a detailed management plan is drawn up.
Prototyping
It is the iterative process of system development which is more appropriate for developing new system where there is no clear idea of requirements, inputs and outputs.
Advantages of Prototyping
-
Communications between the systems analyst and user are improved.
-
The expert system can do a better job of determining the user's needs.
-
The user plays a more active role in system development.
-
The expert and the user spend less time and effort in developing the system.
-
Implementation is much easier because the user knows what to expect.
-
A system is developed through operational prototyping is capable of easy adaptation.
Disadvantages of Prototyping
-
Because of the iterative nature of prototyping, there is no definite deliverable or competition deadline.
-
Code inefficiencies may be a drawback in terms of functionality.
-
The computer-human interface provided by certain prototyping tools may not reflect good design techniques.
SDLC
SDLC consists of a set of development activities that have a prescribed order. It is the development of software in chronological order.
The different phases of SDLC are as follows:
-
System study: A system is intended to meet the needs of an organization. Thus the first step in the design is to specify these needs or requirements. The top manager of the organization takes the basic decision to use a computer based (information) system for managing the organization.
-
System analysis: system analysis is the dissection of a system into its component pieces to study how those component pieces interact and work. System analysis is a term that collectively describes the early phases of development. It is defined as those phases and activities that focus on the business problem, independent of technology.
-
Feasibility study: feasibility study is the most important activity in the system analysis phase. It analyses the proposed system from different aspects so that it makes us clear that how practical or beneficial the system will be to the organization. So it tells us whether the system is feasible to design nor not.
-
System design: the next step is to develop the logical design of the system. During this phase, the logic of the system, namely, the information requirement of users, and use this to find the necessary database.
-
System development: after designing a logical diagram of a system then next step is to convert into program. This process is called system development. Flowchart, algorithm, Pseudocode, etc. are the outlines the procedures for taking the input data and processing it into usable output.
-
System testing: it is an investigation conducted to provide stakeholders with information about the quality of the product or service under test. System testing also provides an objective, independent view of the software to allow the business to appreciate and understand the risks of software implementation.
-
Implementation: implementation involves testing the installed system, converting from the old system to the new one and training the users. This phase consists of implementation of the system into a production environment, and resolution of the problem identified in testing phase.
-
Maintenance and review: it begins after the system is implemented. Like any system, there is an ageing process that requires periodic maintenance of hardware and software. The content of the review will include objectives met, cost, performance, standards and recommendation.
Feasibility study
Feasibility study is the most important activity in the system analysis phase. It analyses the proposed system from different aspects so that it makes us clear that how practical or beneficial the system will be to the organization. So it tells us whether the system is feasible to design nor not. Thus it is necessary before system design.
The different levels of feasibility study are as:
-
Economical feasibility: it concerns with cost effectiveness of the system. The main objective of economical feasibility is to calculate approximate cost-both the development cost and the operational cost and the benefits from the system.
-
Technical feasibility: it concerns with the availability of the hardware, software and the support equipments for the complete development of the system.
-
Operational feasibility: it concerns with smooth operation of the system. It is all about the problems that may occur during operation of the system after its development.
-
Behavior feasibility: it concerns with behavior of the users and the society towards the new system. Generally, most of the traditional employees are not easily ready to upgrade them with the new system.
-
Schedule feasibility: it is the process of splitting project into tasks and estimate time and resources required to complete each task. It determines the deadline to complete a system and schedule the task accordingly.
-
Legal feasibility: it concerns with legal issue of the system. If the system is illegal then the system designing is meaningless. Everything is measured whether it is legal or illegal. It considers copyright law, foreign law, foreign trade, tax, etc.
System testing
It is an investigation conducted to provide stakeholders with information about the quality of the product or service under test. System testing also provides an objective, independent view of the software to allow the business to appreciate and understand the risks of software implementation.
-
White box testing: white box testing of software is predicted on close examination of procedural details. Logical path through the software and collaborations between components are tested by providing test case that exercises specific sets of conditions or loops. It is used when the tester has access it the internal data structures and algorithms including the code that implement these.
-
Black box testing: black box testing treats the software as a black box –without any knowledge of internal implementation. Black box testing methods include: equivalence partitioning, boundary value analysis, specification based testing, etc. it is also called functional testing because it tests whether a system is functioning or not.
Flowchart
System flowchart describes the internal architecture of a system that describes how data are moved inside the internal components of a system. Program flowchart describes to solve the application types of real world problem. The different symbols used in system flowchart are defined below:
DFD
DFD is the logical diagram to describe the flow of data inside the components of system. It is easier to understand or grasp when being explained and most important to all, it is much more precise and less ambiguous than a narrative one. The main components are: process, data store, data flow, external entities.
ER diagram
The E-R diagram is an overall logical structure of a database that can be expressed graphically. It was developed to facilitated database design and the simplicity and pictorial clarity of this diagramming technique have done great help in the designing part of database. The main components are attributes, entities and relationship.
Case diagram
computer aided software engineering tool is automatic computer based program that helps for software engineering and SDLC process. It us very fast and effective tools for the development of big scale software. It helps in analysis, design, implementation, testing and maintenance.
UML
Unified Modelling Language is a standardized general purpose modelling language in the field of object-oriented software engineering. The standard is managed, and was created by, the object management group. UML includes a set of graphic notation techniques to create visual models of object-oriented software.
System flowchart
System flowchart describes the internal architecture of a system that describes how data are moved inside the internal components of a system. Program flowchart describes to solve the application types of real world problem.
Database
Relational Database Management System (RDBMS)
The database system which stores and displays data in tabular format of rows and columns, like spreadsheet, is known as Relational Database Management System.
Different between Database and DBMS
Database: it is a collection of related information about a subject organized in a useful manner that provides a base or foundation for procedure, such as retrieving information, drawing conclusion and make decision.
DBMS: A DBMS is a set of programs that manages the database files. It allows accessing the files, updating the records and retrieving data as requested.
The technique for designing a database using top-down methods is to write a main database parts that names all the major storage and retrievals it will need. Later, the programming team looks at the requirements of each of those database components and the process is repeated.
The top-down method starts from the general and moves to the specific. Basically, you start with a general idea of what is needed for the system and then ask the end-users what data they need to store. The analyst will then work with the users to determine what data should be kept in the database. Using the top-down method requires that the analyst has a detailed understanding of the system. The top-down method also can have shortcomings. In some cases, top-down design can lead to unsatisfactory results because the analyst and end-users can miss something that is important and is necessary for the system.
Different database models
-
HierarchicDal database model: this is one of the oldest type of database models. In this model data is represented in the form of records. Each record has multiple fields. All records are arranged in database as tree like structure. The relationship between the records is called parent child relationship in which any child record relates to only a single parent type record.
-
Network database model: it replaced hierarchical network database model due to some limitations on the model. Suppose, if an employee relates to two departments, then the hierarchical database model cannot able to arrange records in proper place. So network, database model was emerged to arranged non-hierarchical database. The structure of database is more like graph rather than tree structure.
-
Relational database model: in this model, the data is organized into tables which contain multiple rows ad columns. These tables are called relations. A row in a table represents a relationship among a set of values. Since a table is a collection of such relationships, it is generally referred to the mathematical term relation, from which the relational database model derives its name.
-
Entity-Relationship database model: this model is based on perception of a real world that contains a collection of basic objects, called entities and of relationship among these objects and characteristics of an entity. It shows relationship between different entities.
Advantages of the database being centralized
-
easier to organize, edit, update and back-up the data
-
less data duplication - data is only entered once but can be accessed by many users
-
data integrity - because data is stored once different data is no longer held in different databases in various departments around the organization
Advantages of database
-
Sharing data
-
Reduced data redundancy
-
Data backup and recovery
-
Inconsistency avoided
-
Data integrity
-
Data security
-
Data independence
-
Multiple user interfaces
-
Process complex query
Domains and Tuples
In data management and database analysis, a data domain refers to all the values which a data element may contain. The rule for determining the domain boundary may be as simple as a data type with an enumerated list of values.
Tuple is the collection of information about the attributes of table for single instance. In simple this also can be called as a 'row' in a Table.
Different between centralize and distributed database system
Centralized database system |
Distributed database system |
Simple type |
Complex type |
Located on particular location |
Located in many geographical locations. |
Consists of only one server |
Contains servers in several locations |
Suitable for small organizations |
Suitable for large organizations |
Less chance of data lost |
More chances of data hacking, lost |
Maintenance is easy and security is high |
Maintenance is not easy and security is low |
Failure of system makes whole system down |
Failure of one server does not make the whole system down |
There is no feature of load balancing |
There is feature of load balancing |
Data traffic rate is high |
Data traffic rate is low |
Cost of centralized database system is low |
Cost of distributed database system is high |
DBA and responsibilities of DBA
DBA is the most responsible person in an organization with sound knowledge of DBMS. He/she is the overall administrator of the system. He/she has the maximum amount of privileges (permission to access the database) for accessing the database, settings up system and defining the role of the employees which use the system.
Responsibilities of DBA:
-
DBA defines data security, schemas, forms, reports, relationships and user privileges.
-
DBA has responsibility to install. Monitor and upgrade database server.
-
DBA provides different facilities for data retrieving and making reports as required.
-
DBA has responsibility to maintain database security, backup-recovery strategy, and documentation of data recovery.
-
DBA supervises all the activities in the system: addition, modification and deletion data from the database.
State and different types of data integrity
Mainly there are 3 types of data integrity constraints used in the database system. They are as:
-
Domain integrity constraints: it defines a set range of data values for given specific data field. And also determines whether null values are allowed or not in the data field.
-
Entity integrity constraints: it specify that all rows in a table have a unique identifier, known as the primary key value and it never be null i.e. blank.
-
Referential integrity constrains: it exists in a relationship between the two tables in a database. It ensures that the relationship between the primary keys in the master table and foreign key in child table are always maintained.
Normalization and normalization process
Normalization is a database design process in which complex database table is broken down into simple separate tables. It makes data model more flexible and easier to maintain. There are two goals of the normalization process: eliminating redundant data and ensuring data dependencies make sense.
For example: the table shown is our database without normalized. Here in table we can see that for the large records of this table, there would be multiple data row of same values especially in the country and city column. So, we can normalize the table by splitting it into two tables where one table only stores the location area of each person name and could be referenced by some unique id. Say Area code.
id |
country |
city |
Name |
15 |
Nepal |
Kathmandu |
Alex |
16 |
India |
Delhi |
Martin |
17 |
Nepal |
Kathmandu |
Melman |
18 |
Japan |
Tokyo |
Gloria |
The above table can be normalized in two tables as below:
country |
city |
Area code |
Nepal |
Kathmandu |
N1 |
India |
Delhi |
I1 |
Japan |
Tokyo |
J1 |
Id |
Area code |
Name |
15 |
N1 |
Alex |
16 |
I1 |
Martin |
17 |
N1 |
Melman |
18 |
J1 |
Gloria |
Data and information: Data is defined as the raw facts and figures. It could be any numbers, alphabets or any combination of it.
When data are processed using a database program or software, they are converted to the meaningful result, called information.
Field and record: A column in a table is called field and it contains specific piece of information within a record.
A row in a table is called record and it contains information about person, event, etc. Another name of record is tuple.
Data dictionary: A data dictionary is a file which contains meta-data that is data about data. It also called information system catalogue. It keeps all the data information about the database system such as location, size of the database, tables, records, fields, user information, recovery system, etc.
DDL: DDL is used by the database designers and programmers to specify the content and structure of the table. It is used to define the physical characteristics of records. It includes commands that manipulate the structure of objects such as views, tables, and indexes, etc.
DML: DML is related with manipulation of records such as retrieval, sorting, display and deletion of records of data. It helps user to use query and display reports of the table. So it provides technique for processing the database.
Primary key: the field or fields that contain the unique value can be set as primary key. It does not permit duplicate or null values.
Relationship: A relationship is an association among several entities and represents meaningful dependencies between them. It is represented by diamond. There are 3 types of relationship:
-
One to one
-
One to many
-
Many to many
Communication and Networking
Computer Network
It is defined as the collection of two or more autonomous computers which are interconnected together for sharing resources with the help of transmission media and set of protocols.
Advantages of Computer Network
-
Sharing resources: hardware resources such as processor, storage devices, printers, scanner, etc. can be shared among us using computer network. It helps to minimize the operational cost of an organization.
-
Faster and cheaper communication: communication in modern days has become very faster and cheaper to send information to a long distance through network.
-
Centralized control: all network resources such as computers, printer file , database , etc can be managed and controlled by a central connecting computer also known as the server.
-
Backup and recovery: server is used to keep data as backup. It maintains backup of all individual computer’s information.
-
Remote and mobile access: a remote user can access resources from the distance using computer network.
Disadvantages of Computer Network
-
Expensive: In order to install computer network, we require some extra cost to purchase networking devices such as hubs, switch, cables, etc.
-
Security problems: network security is the most challenging job for network administrator in order to protect network resources from authorized users and physical destructions.
-
Needs technical person: it is very difficult to install and operate good computer network.
Types of Computer Network
On the basis of size computer networks can be classified into three categories:
-
Local Area Network (LAN): A LAN is privately owned small size network. It spans only in small geographical area such as within a room, office, buildings or up to few kilometers (2 to 3 Km). it connects the network resources such as computers, faxes, printers and various networking devices.
-
Metropolitan Area Network (MAN): A MAN can be either public or privately owned network. Its size is bigger than LAN and smaller than WAN. It spans within one metropolitan city or larger geographical area. It can connect large number of computers and heterogeneous multiple LANs within a city maximum, up to 100Km.
-
Wide Area Network (WAN): A WAN is basically public type heterogeneous network. It is the largest sized network and connects millions of computers, thousands of LANs, hundreds of MANs around the countries, continents and even the whole world.
Difference between LAN and WAN
LAN |
WAN |
LAN (Local Area Network) is a computer network covering a small geographic area, like a home, office, school, or group of buildings. |
WAN (Wide Area Network) is a computer network that covers a broad area (e.g., any network whose communications links cross metropolitan, regional, or national boundaries over a long distance). |
High speed (1000 mbps) |
Less speed (150 mbps) |
Network in an organization can be a LAN |
Internet is a good example of a WAN |
If there is a need to set-up a couple of extra devices on the network, it is not very expensive to do that. |
For WANs since networks in remote areas have to be connected the set-up costs are higher. However WANs using public networks can be setup very cheaply using just software (VPN etc). |
LAN covers 100 m |
WAN covers more than 100 m |
Experiences fewer data transmission errors |
Experiences more data transmission errors as compared to LAN |
Typically owned, controlled, and managed by a single person or organization. |
WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management over long distances. |
Network topology and it's types
Network topology refers to the physical layout of the network. It shows the geometrical representation of all links and linking devices, also called nodes. Its types are as:
-
Bus topology: computers are connected to a single continuous cable that is called bus. A bus must be terminated on both sides to prevent signal bounce and computers are connected to the bus with the help of drop line and T-connector.
-
Star topology: Many home networks use the star topology. A star network features a central connection point called a "hub node" that may be a network hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.
-
Ring topology: In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.
-
Mesh topology: Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.
-
Tree topology: Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the root of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.
-
Hybrid topology: if two or more topologies are combined together then it is called hybrid topology. So it is very difficult to design and to implement the hybrid topology. It is expensive too.
Network architecture
Network architecture refers to the various services provided by the network and it also deals with how data is transmitted from one computer to others.
Client server network: The client/server topology is the model for vertical scaling, where clients typically host a small subset of the data in the application process space and delegate to the server system for the rest. Compared to peer-to-peer by itself, the client/server architecture provides better data isolation, high fetch performance, and more scalability. If you expect data distribution to put a very heavy load on the network, client/server architecture usually gives better performance. In any client/server installation, the server system is itself a peer-to-peer system, with data distributed between servers. Client systems have a connection pool, which it uses to communicate with servers and other Gem Fire members. A client may also contain a local cache.
Peer-peer network: The peer-to-peer distributed system is the building block for all Gem Fire installations. Peer-to-peer alone is the simplest topology. Each cache instance, or member, directly communicates with each every other member in the distributed system. This cache configuration is primarily designed for applications that want to embed a cache within the application process space and participate in a cluster. A typical application example would be an application server cluster where the application and the cache are co-located and share the same heap.
Difference analog and digital single
Analog signal |
Digital signal |
Analog signal is a continuous signal which represents physical measurements. |
Digital signals are discrete time signals generated by digital modulation. |
Subjected to deterioration by noise during transmission and write/read cycle. |
Can be noise-immune without deterioration during transmission and write/read cycle. |
More likely to get affected reducing accuracy |
Less affected since noise response are analog in nature |
Stored in the form of wave signal |
Stored in the form of binary bit |
Low cost and portable |
Cost is high and not easily portable |
Example: Human voice in air, analog electronic devices. |
Example: Computers, CDs, DVDs, and other digital electronic devices. |
Difference between Internaet and Intranet
Internet |
Intranet |
The Internet is a worldwide, publicly accessible series of interconnected computer networks transmit data by packet switching using the standard Internet Protocol |
An intranet is a private computer network that uses Internet protocols, network connectivity to securely share part of an organization's information or operations |
This is the base, independent of the World Wide Web |
Independent of the internet; however, internet is also used parallel |
The Internet allows computer users to connect to other computers & information stores easily across the world; it is also used in marketing, online chat, file transfer, etc. |
Intranets are being used to deliver tools & applications, helps to improve the services provided to the users, increases employees' ability to perform their jobs faster, etc. |
Internet is a public computer network |
Intranet is a private computer network |
Signal modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal (high frequency signal), with a modulating signal that typically contains information to be transmitted.
Three forms of modulations are possible. They are as:
-
Amplitude Modulation (AM): Amplitude modulation is an increase or decrease of the carrier voltage (Ec), will all other factors remaining constant.
-
Frequency Modulation (FM): Frequency modulation is a change in the carrier frequency (fc) with all other factors remaining constant.
-
Phase Modulation (PM): Phase modulation is a change in the carrier phase angle (θ). The phase angle cannot change without also affecting a change in frequency. Therefore, phase modulation is in reality a second form of frequency modulation.
Transmission media
A transmission media is defined as the means of communication between two networking devices that helps to transfer data from sender to receiver and vice versa.
Transmission media is broadly classified into two groups.
-
Wired or Guided Media or Bound Transmission Media: Bound transmission media are the cables that are tangible or have physical existence and are limited by the physical geography. Popular bound transmission media in use are twisted pair cable, co-axial cable and fiber optical cable. Each of them has its own characteristics like transmission speed, effect of noise, physical appearance, cost etc.
-
Wireless or Unguided Media or Unbound Transmission Media: Unbound transmission media are the ways of transmitting data without using any cables. These media are not bounded by physical geography. This type of transmission is called Wireless communication. Nowadays wireless communication is becoming popular. Wireless LANs are being installed in office and college campuses. This transmission uses Microwave, Radio wave, Infra red are some of popular unbound transmission media.
Switching system
It provides a path between the two devices in a network. The process of transferring data blocks from one node to another node is called data switching.
Types of switching system are as follows:
-
Circuit switching: It is the most familiar technique used to build a communication network. Used in ordinary telephone lines and it allows communications equipment and circuits to be shared among users. Each user has the sole access to a circuit during network use.
-
Message switching: Message switching is a network switching technique in which data is routed in its entirety from the source node to the destination node, one hope at a time. During message routing, every intermediate switch in the network stores the whole message. If the entire network's resources are engaged or the network becomes blocked, the message-switched network stores and delays the message until ample resources become available for effective transmission of the message.
-
Packet switching: A network technology that breaks up a message into small packets for transmission, unlike circuit switching, which requires the establishment of a dedicated point to point connections each packet in a packed switched network contains a destination address. Thus all packets in a single message do not have to follow the same path. Packet can arrive out of order. Destination computer reassembles the packets into their proper sequence.
OSI reference model
It is based on a proposal developed by the international organization for standardization (ISO). The model is called ISO OSI reference model, because it deals with connecting open system i.e. the system that are open for communication with other system.
1. Physical Layer: This layer concerned with transmission of bit it determines voltage level for 0 & 1. It also determines the data rate of the system. This layer involves standardized protocol dealing with electrical & signaling interface.
2. Data Link Layer: It handles error in physical layer. This layer ensures the correct delivery of frame to the destination address. It consists of 2 parts or 2 sub-layers. i.e.
-
Logic Link Control
-
Media Access Control
3. Network Layer: This layer is concerned with transmission of packet. N/w layer protocol chooses the best path to send a package called routing. Two protocols are widely used in n/w layer.
-
X.25 Protocol
-
Internet Protocol
4. Transport Layer: It provides the mechanism for the exchange of data between end systems. It ensures that the data received is in fact in order. Following jobs are performed by this layer.
-
Port Addressing
-
Segmentation & Reassemble
-
Connection Control