OSI model

OSI Model

 

The ISO (International Organization for Standardization) decided to construct a framework of standards in which different vendors would be able to use in order to communicate over a network consisting of diverse equipment and applications.  This framework is now considered the standard for communication of networks.  The OSI is divided into 7 layers, which divides the task into smaller more manageable task groups.  Each task or group of tasks assigned to each layer can also be implemented independently.  This limits complications between layers because the solutions offered by one layer do not adversely affect the other layers.

The 7 layers can be split logically into two subgroups.  Layers 7 thru 4 focus on the end to end communication of data source and destinations.  Layers 3 thru 1 are provide consistent communication between the network devices.  An easier way of looking at the OSI model is dividing the upper layers (7, 6, 5) from the lower layers (4, 3, 2, 1).  The upper layers deal with application issues and are implemented only in software.  The highest layer, the application layer, is the closest to the end user.  The lower layers are responsible for the transportation of the data.  The physical layer and the data link layer are implemented in hardware and software. The lowest layer, the physical layer, is closest to the physical network medium (the wires, for example) and is responsible for placing data on the medium.

The following is a top-down explanation of the OSI Model. It starts with the user's PC and it follows what happens to the user's file as it passes though the different OSI Model layers. The top-down approach was selected specifically (vs. starting at the Physical Layer and working up to the Application Layer) for ease of understanding. It is used here to show how the user's files are transformed (through the layers) into a bit stream for transmission on the network. 

Benefits of the OSI Model

By separating the network communications into logical smaller pieces, the OSI model simplifies how network protocols are designed. The OSI model was designed to ensure different types of equipment (such as network Adapters, hubs, and routers) would all be compatible even if built by different manufacturers. A product from one network equipment vendor that implements OSI Layer 2 functionality, for example, will be much more likely to interoperate with another vendor's OSI Layer 3 product because both vendors are following the same model.

The OSI model also makes network designs more extensible as new protocols and other network services are generally easier to add to a layered architecture than to a monolithic one.

Adapters, hubs, and routers

Physical Layer

At the base of the OSI model is the physical layer. This one is the easiest to understand - it encompasses most of the physical aspects of the network; for example, a repeater (a piece of equipment that amplifies signals) operates at the physical level because it is only concerned with transmitting the electric signal on the wire - it does not try to interfere with, encode/decode, or otherwise logically manipulate the signal. Think of the physical layer as the "electrical" layer of the model - the physical layer is the layer of low-level networking equipment, such as some hubs, cabling, and repeaters . The physical layer is never concerned with protocols or other such higher-layer items.
Examples of hardware in this layer:

• Network adapter
• Repeater
• Network hub
• Modem
• Fiber Media Converter 

 

Data Link Layer

The Data Link Layer transfers data between adjacent nodes in a Wide Area Network, or between nodes on any given Local Area Network. This layer also provides the procedural means to transfer data between network entities and sometimes to detect and correct errors that have occurred within the Physical Layer.
Since the Data Link layer is concerned primarily with local delivery within a LAN, data link frames do not cross the boundaries of a local network segment and instead focus on local delivery, addressing, and media arbitration.
Switches operate in the Data Link layer.

Sublayers

The Data Link Layer is often subdivided into two sublayers, the LLC Sublayer and the MAC Sublayer:

• The LLC (or Logical Link Control) Sublayer multiplexes protocols running atop the Data Link Layer, and provides flow control, acknowledgement, and error control. It also specifies the mechanisms to be used for addressing stations and for controlling the data exchanged between machines.
• The MAC (or Media Access Control) Sublayer determines who is allowed to access the media at any one time (as in CSMA/CD) and provides frame synchronization, which determines where one frame ends and the next begins.

 Protocols

Protocols in the Data Link Layer include:

• Ethernet for LANs
• PPP
• HDLC
• ADCCP for point-to-point connections
• PTPPD Point-to-Point Portal Device

Network Layer 

The Network layer is where the frames of the Data Link layer become packets. It can be described as the puberty of the OSI model. It is where the boys of the Data Link layer become men. The best way to think of the Network layer is as the mailroom clerk of the OSI model. The clerk receives mail and directs it to the appropriate couriers. In similar fashion, the Network layer translates the frames it receives from the Data Link layer into more logical packets which can be routed to other networks (like sending it to a courier). At the Network layer, you can begin to actually communicate across a Network, but the service is called "unreliable" because no connection can be established. Communication over the Network layer is something like throwing a message in a bottle into the sea or hollowing out the wall and writing cryptic references to the Companion Cube at the Aperture Science enrichment center- you cannot verify that the other person ever reads the message. The Network Layer is the layer that uses IP addresses. Most of what we call "routing" occurs at the network layer - that is,network traffic is routed from one network to another at this layer, allowing for inter-network (as opposed to intra-network) communication.

 Transport Layer 

At the Transport layer, the Network layer's packets are sorted and organized into "segments." This is different from the idea of packets in the Network layer in one fundamental way: the segments of data over the Transport layer contain information on the connection and the transmission of data. The Transport layer removes the uncertainty of "throwing the message in the bottle" that we experience over the Network layer by attaching to segments (which are basically continued packets) information about the state of a connection. Thus, the Transport layer uses the LLC sub-layer of the Data Link layer to establish connections between hosts. The protocols that are typically associated with the Transport layer are:

• TCP: Connection-Oriented, reliable - unlike the "message in the bottle," or "hidden Companion Cube reference," it can verify that a segment or packet reaches the location, or note failure
• UDP: Connectionless, unreliable - it is like a "smarter" message in the bottle service; it makes a best-effort delivery but does not establish a connection or verify receipt

Session Layer 

The Session layer is the layer that initiates and terminates the transport layer connection-oriented services . While the Session layer is not widely used by protocols, it is important in that it is responsible for managing the connections that we value and that the Transport layer provides. In other words, the Session layer is like the GLaDOS of the transport layer, just like GLaDOS tells the robots what to do and promises them eternal damnation in case of insubordination, the Session layer also bosses the Transport layer around.

Presentation Layer 

The Presentation layer translates the segments of information from the Transport layer into data that can be used at the Application layer. It is like the C3-PO of the OSI model. It is something of an intermediary between the network node's processing area and the network node's actual networking area - it can interpret the segments or packets it receives and change them into "data formats" that we all know and that the PC can recognize.

 Application Layer 

This is the top of our cake, utilizes the layers below it, and includes the functions that we are most familiar with - the end-user application protocols such as FTP and HTTP, the vital services like DHCP and DNS, and several obscure applications. This is where the sockets are defined. The Application layer does indeed cover a wide variety of protocols and services, but don't let this overwhelm you. In general, when trying to decide if a service or protocol is an application level one, ask: "Does this facilitate networking, or does networking facilitate the service?" If the answer is the latter, you know it is an Application layer service.

 

 

operating system

Operating System

An operating system is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs.

The operating system is the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.

For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.

An operating system, or "OS," is software that communicates with the hardware and allows other programs to run. It is comprised of system software, or the fundamental files your computer needs to boot up and function. Every desktop computer, tablet, and Smartphone includes an operating system that provides basic functionality for the device.

Common desktop operating systems include Windows, Mac OS X, and Linux. While each OS is different, they all provide a graphical user interface, or GUI, that includes a desktop and the ability to manage files and folders. They also allow you to install and run programs written for the operating system. While Windows and Linux can be installed on standard PC hardware, Mac OS X can only run on Macintosh computers. Therefore, the hardware you choose affects what operating system(s) you can run.

Mobile devices, such as tablets and Smartphone’s also include operating systems that provide a GUI and can run applications. Common mobile OSes include Android, iOS, and Windows Phone. These OSes are developed specifically for portable devices and therefore are designed around touchscreen input. While early mobile operating systems lacked many features found in desktop OSes, they now include advanced capabilities, such as the ability to run third-party apps and run multiple apps at once.

Since the operating system serves as a computer's fundamental user interface, it significantly affects how you interact with the device. Therefore, many users prefer to use a specific operating system. For example, one user may prefer to use a computer with Mac OS X instead of a Windows-based PC. Another user may prefer an Android-based Smartphone instead of an iPhone, which runs the iOS.

When software developers create applications, they must be write and compile them for a specific operating system. This is because each OS communicates with the hardware differently and has a specific application program interface, or API, that the programmer must use. While many popular programs are crossplatform, meaning they have been developed for multiple OSes, some are only available for a single operating system. Therefore, when choosing a computer, it is important to make sure the operating system supports the programs you want to run.

ERP

                                                                

ERP is an acronym for "Enterprise Resource Planning". An ERP attempts to integrate all departments and functions across a company onto a single computer system that can serve all those different department's particular needs.

E: Enterprise is a huge business Organisation.
R: Resources are Money, Material, Man power, Machinery, and Methods
P: Planning for optimal Utilization of resource for a huge business Organisation implementation

Enterprise resource planning software, or ERP, doesn’t live up to its acronym. Forget about planning—it doesn’t do much of that—and forget about resource, a throwaway term. But remember the enterprise part. This is ERP’s true ambition. It attempts to integrate all departments and functions across a company onto a single computer system that can serve all those different departments’ particular needs.
That is a tall order, building a single software program that serves the needs of people in finance as well as it does the people in human resources and in the warehouse. Each of those departments typically has its own computer system optimized for the particular ways that the department does its work. But ERP combines them all together into a single, integrated software program that runs off a single database so that the various departments can more easily share information and communicate with each other.
That integrated approach can have a tremendous payback if companies install the software correctly.
Take a customer order, for example. Typically, when a customer places an order, that order begins a mostly paper-based journey from in-basket to in-basket around the company, often being keyed and rekeyed into different departments’ computer systems along the way. All that lounging around in in-baskets causes delays and lost orders, and all the keying into different computer systems invites errors. Meanwhile, no one in the company truly knows what the status of the order is at any given point because there is no way for the finance department, for example, to get into the warehouse’s computer system to see whether the item has been shipped. "You’ll have to call the warehouse" is the familiar refrain heard by frustrated customers.
ERP vanquishes the old standalone computer systems in finance, HR, manufacturing and the warehouse, and replaces them with a single unified software program divided into software modules that roughly approximate the old standalone systems. Finance, manufacturing and the warehouse all still get their own software, except now the software is linked together so that someone in finance can look into the warehouse software to see if an order has been shipped. Most vendors’ ERP software is flexible enough that you can install some modules without buying the whole package. Many companies, for example, will just install an ERP finance or HR module and leave the rest of the functions for another day.

  Why ERP-

There are five major reasons why companies undertake ERP.

Ø  Integrate financial Information

Ø  Integrate Customer Order Information

Ø  Standardize and speed up manufacturing processes

Ø  Reduce inventory

Ø  Standardize HR information.

ERP is used for planning resources [Money, Material, Man power, Machinery and Methods] to get maximum profits with minimum Efforts.  For this, all the business functions and processes need to be atomised and integrated.   The common business functions of any large enterprise are-

                                                                                                                                 

 FICO -Financial Accounting & Controlling, HR -Human resources,

PP-Production planning, MM -Material Management, SD -Sales and distribution
PM -Plant Maintenance, QM -Quality Management, etc depending on the enterprise.

ERP Implementation -

No matter what type of business you're in, implementing an ERP solution is a critical project that must be taken seriously. From concerns about cost and demonstrating ROI, to practical considerations about who will manage the process at your company, ERP implementation efforts require commitment by a project team and support by business leaders to ensure success.
There's no getting around the fact that ERP deployment is a major undertaking, but the process doesn't have to be painful. With proper planning and execution, implementing an ERP system should be a smooth process and quickly improve efficiency across your business. Here are some critical ERP implementation best practices to consider when selecting and deploying a solution.

Select the Best ERP Implementation

Given the range of functions that ERP encompasses, it should come as no surprise that there are multiple types of ERP implementations. You can choose to build your own custom ERP and program it from the bottom up, though the cost and complexity of taking on such a huge project can make a do-it-yourself approach a poor one.
Or you can purchase on-premise ERP software and install it on your company's computers and servers. Before investing in an on-site ERP solution, however, consider this sobering fact: Two-thirds of mid-size businesses are running old versions of their ERP software. ¹Why the lag? Organizations often decide that the pain required to re-implement incremental releases is too great—especially since each upgrade means the business risks losing critical customizations and integrations. Keeping ERP technology current is key to maximizing its potential, so it's essential to choose a system deployment option that's easy to update and will preserve custom features.
There's a third alternative: a cloud-based ERP solution like NetSuite. Because the system is cloud-based and managed entirely off site by the ERP provider, a cloud-based solution means you don't have to make expensive upfront investments in IT hardware and servers, nor worry about dedicating significant personnel resources to managing it. In addition, cloud-based implementations are usually much faster and easier to deploy than on-site deployments, and maintenance is much easier since the cloud-based ERP provider is responsible for keeping the technology up to date. Most importantly, with cloud technology, product enhancements are painless—customizations and integrations automatically update with system upgrades—so you can always be assured that your business is running with the most advanced capability.

 Consensus around ERP Implementation

Getting buy-in from company executives means more than just getting a signature to approve investment in an ERP solution (though that is certainly important); it means educating leadership about what ERP implementation means for the company. More than just software, ERP technology can transform the business, an idea that executives must support before moving forward with any deployment effort. Frequent communication from executives about ERP implementation plans and changing processes are vital to helping build consensus—and even excitement—across your company.

Set Realistic Expectations for ERP Implementation

ERP software is powerful technology that can streamline processes, improve visibility, reduce costs, and completely change the way that your company does business—but it won't happen overnight. ERP solutions encompass many complex front- and back-office systems, from accounting and inventory management to ecommerce and CRM, which need to be integrated to create a seamless experience for end users.
This takes careful planning and time to execute. To accelerate the implementation process, make sure your project is scoped appropriately and consider working with an experienced, knowledgeable ERP expert. The average NetSuite customer is typically able to implement its ERP system within three months—much less than the on-premise ERP implementation industry average of a year and a half.

Focus on Staff Resources and  Project Management

Before starting any ERP implementation, make sure that your company has the staff resources in place to see the project through to completion. This may seem like an obvious point, but many companies begin deployment without resourcing it adequately, resulting in overworked, unhappy employees and a less-than-optimal installation.Identifying a dedicated project leader and a team for your ERP implementation will help ensure that the project goes smoothly. For ERP team members, consider reassigning or removing some of their normal job duties so they have enough time to concentrate on the task at hand. Identify a team leader with strong project management skills who can facilitate team communication, address any issues that may arise, and keep the implementation on schedule.
Keeping these best practices in mind will help you launch your deployment on the right track and keep it there throughout the entire process. Researching the best ERP implementation option for your business, building consensus around the effort, setting realistic expectations, and giving your staff the support they need—these steps take more time, but they result in a more effective ERP experience and a better-run business in the long term.