So, in the previous article, we figured out why an average user actually needs it. Let's recall the basic concepts of this lesson:
- - a local network is a system of computing devices connected by communication lines, designed to transmit information to a finite number of subscribers;
- - there are three main types of local network topology, on the basis of which more complex local communication structures are built;
- - according to the way computers interact, local networks are peer-to-peer (when all PCs connected to the network are equal) and with a dedicated server.
In this article, we will look at how to create a local network with the same access rights for all its users.
The advantages of such a network include the simplicity of the design (setting up a home network is quite "tough" for a beginner) and the economic availability of equipment, but the range of functionality of such a network is very limited.
So, to create a local area network between computers, we need:
Several computers (in this case, we will consider the option of a network that unites more than two PCs, but we will tell you separately), which will become the nodes of our local network. Each PC needs to check the presence of a network card (although most modern devices are equipped with a built-in "network card", but "what the hell is not kidding ...").
- - Network hardware. To organize local networks, both managed (customizable) and unmanaged network equipment can be used. To make a small home network, a simple unmanaged 4-6 port switch is fine.
- - Network cable to connect each computer with network equipment. The total cable length directly depends on the final number of PCs, their distance from each other and the architecture of the room (building) in which the local network is created.
- - Connectors(RJ-45 connectors), the number of which also depends on the number of computers connected to the network. So, to crimp the cable for each PC, at least 2 connectors are required;
- - Swage(Crimper) - cable termination tool. (In its absence, many craftsmen get by with improvised means (for example, a screwdriver), but it will be quite difficult for a beginner to perform this trick).
Creating and configuring a home network
1. Select the computer from which the creation of the local network will begin, and connect it to the network equipment. For this from both sides crimp the cable and using RJ-45 connectors we connect it to the ports of the switch and the network card of our computer.
The unmanaged switch does not require any additional settings: we only need to register the correct settings for the local network itself in the operating system of each PC
2. To do this, go to the settings of the computer's network card (read, windows 8 and windows XP) and write there IP-the address this PC. Typically, the following IP addresses are used here 192.168.1., 192.168.0;
3. Repeat steps 1-2 for each computer connected to the network.
Important: the last digit of the IP address of each next PC must be different from the previous one (in the above range): for example, if the first computer was assigned IP 192.168.1.1, the second PC will have 192.168.1.2, the third will have 192.168.1.3, and so on.
When all computers are connected, we check our local network for operability.
This can be done in two ways:
Check for other devices connected to the network in the "Network Neighborhood" tab of the control panel of this computer;
Ping any computer on a given network with an ip-address known to us. Pinging is done as follows:
Go to "Start → Run", in the window that opens, assign the command "cmd" and press "Enter";
In the command line window that appears, write ping xxx.xxx.xxx.xxx, where xxx.xxx.xxx.xxx is the IP address of the computer we are looking for.
If, after executing the command, we see a similar picture in the command line window, then the home local network we have created is quite functional, but if the computer displays a message about "the request has exceeded the waiting interval" or that "the specified node is unavailable"
- it is necessary to search for and eliminate technical malfunctions of this network.
Often, during the development of various kinds of projects, a plan is drawn up for the execution of tasks. Microsoft Excel toolkit allows you to create a network diagram, which serves to solve the problem of planning project stages.
Let's create a simple graph using a Gantt chart.
First, you need to create the table itself with columns with appropriate titles.
After that, you can see a new window in which we select the "Alignment" tab. Set the alignment in the fields to "Center", and in the display settings, set the checkbox next to "Wrap by words".
Go to the working window and set the borders of the table. Select the headers and the required number of cells for the table, open the "Home" section, and in it, using the appropriate icon in the list, select the "All borders" item.
As a result, you can see that the wireframe of the table with headers has been created.
The next step is to create a timeline. This is the basic part in network graphics. A certain set of columns corresponds to a particular period in the planning of project tasks. This example will create a 30 day timeline.
For now, let's leave the main table and select thirty columns near its right border in the context of this example. It should be noted that the number of rows = the number of rows in the previously created table.
Go to the "Home" section and select "All borders" in the border icon as well as with the table created earlier.
In this example, we define the plan for June 1-30. And we enter the corresponding dates into the timeline. For this, the "Progression" tool will be used.
After clicking on the item "Progression" a new window will appear. In it, we mark the arrangement by lines (in this example), and select dates as the type. Depending on what time period is used, select the "Day" item. The step value is 1. Set the date June 30 as the final value and confirm the action.
Further, the timeline will be filled with days from the 1st to the 30th. Next, you need to optimize the table for its convenience by selecting the entire time interval and pressing the right mouse button. In the context menu, select "Format cells".
A new window will appear in which you need to open the "Alignment" tab and set the value to 90 degrees. We confirm the action.
But the optimization is not complete. Go to the main section "Home" and click on the "Format" icon and select auto-fit by line height in it.
And to complete the optimization, we do a similar action and select the auto-fit according to the column width.
As a result, the table has acquired a complete look.
The final stage will be filling the first table with the appropriate data. Also, if there is a large amount of data, then by holding down the "Ctrl" key on the keyboard, drag the cursor along the border of the numbering field down the table.
And as a result, the table is ordered. And you can also fill in the rest of the table fields.
In the "Home" section, click on the "Styles" icon and in it click on the "Conditional Formatting" icon. And in the list that appears, select the "Create rule" item.
After this action, a new window will open in which you need to select a rule from the list of rules. We select "Use formula to define formatted cells". A suitable selection rule specifically for our example is shown in the field.
Let's analyze the elements of the formula:
G $ 1> = $ D2 is the first argument that specifies that the value in the timeline is equal to or greater than a specific date. The first part of the element points to the first cell, and the second part to the desired part of the column in relation to the plan.
G $ 1 И - check values for truth
$ - allows you to set values as absolute.
To set the color for the cells, click "Format".
Optimizing the work of a company, especially a manufacturing enterprise, is one of the most important conditions for the existence of a company. Competition is not the only requirement for the smooth flow of the production process. Modern trends in minimizing the cost of manufactured products primarily presuppose the elimination of downtime and the consistency of operations.
To solve these problems, a methodology for optimizing activities and calculating the timing of work is used. The developed network schedule allows you to determine the logical sequence of individual operations, the possibility of combining them in time, as well as the timing of the entire production cycle of work.
What's this?
One of the methods for effective planning of the activities of a manufacturing enterprise is the construction of a network schedule. Initially, it was used in construction and determined not so much the sequence of work as the timing of the exit to the construction site for teams of workers of different specialties. It is called the “work schedule”.
In modern conditions, when large enterprises mass-produce products, the whole process is broken down into simple operations to facilitate and increase productivity. Therefore, the network schedule "migrated" from construction to almost all industries.
So what is displayed in this document? First, all operations necessary for the production of goods (production of services) are listed in detail. Secondly, the logical interdependence between them is determined. And, finally, thirdly, not only the timing of each specific work is calculated, but also the time required for the complete completion of the production process.
By uncovering the internal dependencies of project operations, the network schedule becomes the basis for scheduling the workload of equipment and labor.
Operation in Network Planning
In the network schedule, you can estimate the periods of the beginning (end) of work, the forced downtime and, accordingly, the maximum delay in the production of certain operations. In addition, critical operations are identified - those that cannot be performed outside the schedule.
Understanding the terminology of planning, you need to clearly understand what an operation is. Most often, this is understood as an indivisible part of the work that takes time to complete. Further, we understand that the execution of the operation involves costs: time and resources (both labor and material).
In some cases, you do not need resources to perform any actions, only time is required, which takes into account the network schedule. An example of this is the expectation of concrete hardening (in construction), the cooling time of rolled parts (metallurgy), or simply the approval (signing) of a contract or permits.
Most often, operations in planning are given an imperative name (develop a specification); sometimes verbal nouns are used for names (specification development).
Types of operations
When drawing up a network schedule, several types of work are distinguished:
- merge - this operation is immediately preceded by more than one job;
- parallel operations are performed independently of each other and, at the request of the design engineer, can be performed simultaneously;
- the crushing operation assumes that after its completion, several unrelated works can be performed at once.
In addition, there are a few more concepts that are necessary for planning. The path is the time to complete and the sequence of interdependent operations. And the critical path is called the longest path of the entire system of work. In the event that some operation on this path is performed out of time, the deadlines for the implementation of the entire project are disrupted.
And the last thing: an event. This term usually denotes the beginning or end of an operation. The event does not require resources.
What the graph looks like
Any graph familiar to us is represented by a curve located on a plane (less often in space). But the type of network plan is significantly different.
The network diagram of a project can look like two things: one technique involves the designation of operations in the nodes of the flowchart (DT), the second uses connecting arrows (OS) for this. It is much more convenient to use the first method.
The operation is indicated by a round or rectangular block. The arrows connecting them define the relationships between actions. Since the names of the works can be quite long and voluminous, the numbers of the operations are put down in the blocks, and a specification is drawn up for the schedule.
Schedule development rules
For proper planning, you need to remember a few rules:
- The chart unfolds from left to right.
- Arrows indicate links between operations; they can overlap.
- Each simple work should have its own serial number; any subsequent operation cannot have a number lower than that of the previous one.
- There can be no loops on the chart. That is, any looping of the production process is unacceptable and indicates an error.
- You cannot use conditions when building a network diagram (example of a conditional order: "if an operation is performed .., perform work ... if not, do not take any action").
- To indicate the beginning and end of work, it is more convenient to use one block that defines the initial (final) operations.
Plotting and analyzing a graph
For each job, three points need to be clarified:
- List of operations to be performed prior to this work. They are called prior to the target.
- The list of operations that are performed after a given action. Such works are called the following.
- The list of tasks that can be carried out simultaneously with the given one. These are parallel operations.
All the information obtained provides analysts with the necessary basis for building logical relationships between the operations included in the network graph. An example of how these relationships are built is shown below.
A realistic schedule requires a serious and objective assessment of production times. Determining the time and entering it into the schedule makes it possible not only to calculate the duration of the entire project, but also to identify the most important nodes.
Graph Calculation: Direct Analysis
Estimation of time spent on performing one operation is based on standard labor costs. Thanks to the direct or reverse calculation method, you can quickly navigate the order of work and identify critical steps.
Direct analysis allows you to determine the early start dates for all operations. The reverse - gives an idea of the late dates. In addition, with the help of both methods of analysis, it is possible not only to establish the critical path, but also to identify the time intervals by which it is possible to delay the execution of individual work without disrupting the overall timing of the project.
Direct analysis examines the project from start to finish (if we talk about the drawn up schedule, then the movement along it occurs from left to right). During the movement along all chains of operations, the time for completing the entire complex of works increases. Direct calculation of the network schedule assumes that each subsequent operation begins at the moment when all those preceding it end. It should be remembered that the next work starts at the moment when the longest of the immediately preceding ones ends. At each step of the direct analysis, the execution time of the calculation operation is added. This gives the Early Start (ES) and Early Finish (EF) values.
But you need to be careful: the early end of the previous operation becomes the early start of the next one only if it is not a merge. In this case, the start will be the early end of the longest of the previous works.
Reverse analysis
The reverse analysis takes into account the following network parameters: late completion and late start of work. The name itself suggests that the calculation is carried out from the last operation of the entire project towards the first (from right to left). Moving towards the beginning of work, you should deduct the duration of each action. Thus, the latest dates for the start (LS) and end (LF) of work production are determined. If the project time frame is not initially set, then the calculation starts from the late end of the last operation.
Calculation of temporary reserves
Having calculated the network schedule in both directions, it is easy to determine temporary downtime (sometimes they use the term "fluctuation"). The total time of the possible delay in the execution of an operation is equal to the difference between the early and late start of a particular action (LS - ES). This is the time backlog that will not disrupt the overall timeframe for the project.
After calculating all the fluctuations, they begin to determine the critical path. It will go through all operations for which there is no temporary downtime (LF = EF; and accordingly LF - EF = 0 or LS - ES = 0).
Of course, in theory, everything looks simple and straightforward. The developed network schedule (an example of its construction is shown in the figure) is transferred to production and implemented. But what is behind the numbers and calculations? How to use possible technological downtime or, conversely, to avoid force majeure situations.
Management experts suggest assigning the most experienced staff to perform critical operations. In addition, when assessing the risks of a project, it is necessary to pay special attention not only to these steps, but also to those that directly affect the critical path. If it is not possible to control the progress of work as a whole, then it is necessary to find time to obtain primary information from the operations of the critical path. It is about talking directly to the performers of such works.
The network diagram is a tool for optimizing the company's activities
When it comes to the use of resources (including labor), it is much easier for the manager to dispose of them if there is a network schedule for the production of work. It shows all the downtime and employment of each specific employee (team). The use of an unemployed employee at one facility for the implementation of another allows you to optimize the activities of the company as a whole.
One more practical advice should not be neglected. In reality, project managers are confronted with the “desires of higher management” to see the work done “yesterday”. In order to avoid panic and the release of defects, it is necessary to strengthen resources not so much on the operations of the critical path, but on those directly affecting it. Why? Yes, because there is no downtime on the critical path, and it is often impossible to reduce the production time.
Every project manager is faced with such a typical task for him as building a network diagram. Currently, this process is fully automated and, as a rule, the manager does not have big problems. For a long time there is no need to draw graphs on paper, calculate the early and late beginnings or endings of tasks, connect tasks with arrows, calculate the length of the critical path. PMIS successfully solves all these problems.
However, without understanding the basics and rules for building network diagrams, mistakes are quite often made. Despite the fact that modern ones are quite “smart” and provide insurance to the project manager in many aspects related to the project schedule, nevertheless, there remain “blind” zones that lie only in the area of responsibility of the project manager.
In order to get real benefit from it, it needs to be able to use it competently, like any other tool.
What is a network diagram
Network schedule (eng., Project network) Is a dynamic model of the project, reflecting the dependence and sequence of the work of the project, linking their completion in time, taking into account the cost of resources and the cost of work.
The network graph can be built in two ways:
- The vertices of the graph represent the states of some object (for example, construction), and the arcs represent the work carried out on this object.
- The vertices of the graph represent the activities, and the connections between them represent the dependencies between the activities.
Rules for building network graphics
First of all, building a network diagram consists in the correct connection of events to each other (in the diagram, circles) with the help of works (in the diagram, arrows). The correct connection of the arrows is as follows:
- each work in the network schedule must exit from an event that means the end of all work, the result of which is necessary to start work;
- an event denoting the beginning of a certain work should not include the results of work, the completion of which is not required to start this work;
- the network diagram is built from left to right, and each event with a higher sequence number must be located to the right of the previous one. Arrows representing works should also be positioned from left to right.
Original work
The construction of the graph begins with the image of works that do not require the results of other works to begin. Such works can be called initial, since all other works of the complex will be performed only after they have been fully completed.
Depending on the specifics of the planned complex, there may be several initial works, or there may be only one. When posting initial works, it should be borne in mind that there should be only one initial event on the network diagram.
Figure 1 shows an example of starting a network schedule with one original job (job A), and in Figure 2, an example of the beginning of a network schedule with three initial jobs (jobs A, B, C).
Figure 1. Network diagram with one original job
Figure 2. Network diagram with three original jobs
Sequential work
If work B should only be performed after work has been done A, then on the graph it is depicted as a sequential chain of activities and events.
Figure 3. Sequential work
If to perform several jobs, for example, B and C the result of the same work is required A, then on the graph this is depicted by "parallel" arrows emerging from the event that is the result of the work A.
Figure 4. Work performed after the same work
If to get the job done C result of work is required A and B, then on the graph this is depicted by "parallel" arrows entering the event, after reaching which the work follows C.
Figure 5. Work performed after several jobs
If to perform work B and C an intermediate result of work is required A then work A is divided into subtasks in such a way that its first subtask ( A1) was executed until the intermediate result required to start work was obtained B, and the second subtask was performed until the intermediate result required to start work was obtained C, the subsequent part A3, can be performed in parallel with the work A1 and A2.
Figure 6. Work performed after partial completion of other work
Two adjacent events can be combined by one and only one job. To depict parallel jobs on a network diagram, a so-called intermediate event and fictitious job are introduced.
Figure 7. Jobs with common start and end events
If doing work D possible only after receiving the cumulative result of work A and B, and the execution of work C- after receiving only the result of work A, then it is necessary to enter an additional event and fictitious work in the network schedule.
Figure 8. Using fictitious jobs
"Tails" and "dead ends"
There should be no dead ends in the network, i.e. intermediate events from which no work comes out. In Figure 9, the dead-end event is the event 6.
Also, there should be no "tails", i.e. intermediate events that are not preceded by at least one job. In Figure 9, the tail event is the event 3 .
Figure 9. "Tails" and "dead ends" in the network diagram
Cycles
The network diagram should not have cycles consisting of interconnected activities that create a closed circuit - a chain of activities D-> F-> G in Figure 10. This situation most likely indicates an error in compiling a list of works and determining their relationships.
Figure 10. Cycle on a network graph
In this case, it is necessary to analyze the initial data and, depending on the conclusions drawn from the analysis, either redirect the work that creates the cycle to another event (if the work starting in this event requires its result, or if it is part of the overall result), or completely exclude it from the complex (if it is revealed that its result is not required).
Figure 11 shows an example of loop elimination when work G becomes part of the overall result.
Figure 11. Eliminating a loop on a network graph
Job naming and event numbering
Each work in the network schedule should be uniquely identified, only by its inherent pair of events, as it should not be on the schedule of events with the same numbers.
For the correct numbering of events, proceed as follows: the numbering of events begins with the original event, which is given a number 0 ... All outgoing jobs are deleted from the original event, and an event is found again on the remaining network that does not include any jobs. This event is given a number 1 ... Then cross out the works coming out of the event 1 , and again find an event on the rest of the network that does not include any work, it is assigned a number 2 , and so on until the final event.
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On this page you will find solved typical tasks from the control tests on network planning - the section of economic and mathematical methods and models.
As part of the study of network analysis, students usually learn: build a network graph according to a tabular or verbal description of the project (and vice versa), find early and late start and finish dates, reserves, critical path and the minimum time to complete the project. More complex tasks imply various options for adjusting and optimizing the network schedule (with an increase in time and a decrease in costs, or vice versa, with a decrease in time and an increase in costs), resource allocation tasks. Various graphical methods of displaying both a network graph (see tasks below) and other charts for a project (Gantt chart, line chart) are studied.
Examples of solutions to problems of network planning online
Objective 1. For a given network model of a certain set of works, determine the time and the critical path.
Objective 2. The publisher has a contract with the author to publish his book. Below is a sequence of (simplified) processes leading up to a book publishing project. It is necessary to develop a network for this project.
Objective 3. 1. For a given list of works, build a network schedule.
2. Determine the duration of the full paths of the schedule.
3. Identify and highlight the critical path.
4. Determine the reserve time for each path.
5. Determine the coefficients of the path tension.
6. Determine early and late start and end dates of work.
7. Determine the full reserve of time for each job.
Task 5. On the network diagram, find the early and late dates of the occurrence of events, determine the critical path and time reserves for each event.
Task 6. Build a network diagram. Solve the problem of optimal resource allocation for jobs at constant intensities. Availability of resource R = 10. The works do not allow a break in their execution.
Task 7. According to the option, it is required:
1) build a network model;
2) identify the critical paths of the model;
3) to carry out the maximum possible reduction of the project completion time with the minimum possible additional costs
