# Laboratory work number 7 - Computing systems, networks...

## Laboratory work number 7

Statistics

Goal: using the simulation model from the 6th laboratory work, learn how to work with data and statistics from standard AR1A1 reports.

Work order:

1. Take the model you developed from the 6th laboratory work. Find and/or calculate tasks according to your option, as well as conduct additional compulsory studies to optimize the model. Prove that the model obtained is optimal in terms of parameters.

2. Prepare a report using screen shorts from standard ARENA reports.

Option 1

Find:

1. The average number of jobs in the queue:

• to enter;

• Processing;

• Output.

2. Number of erroneous jobs.

• When typing;

• Output.

Option 2

Find:

1. The average time for the formation of a package of 5 tasks.

3. The average length of the job.

Option 3

Find:

1. Average response time.

2. Total time of all communications channels.

3. Load of computers in centers A, B and C:

• when searching for information;

• When preprocessing.

◘Variant 4

Find:

1. The average number of jobs waiting to be processed by the first and second processors.

2. The number of system crashes.

3. The load of the first and second processor.

◘Variant 5

Find:

1. The average number of messages waiting to be transmitted over the primary communication channel.

2. The number of system crashes.

3. Main and backup channel load.

◘Extension 6

Find:

1. The average number of jobs in the special queue and the average wait time in this queue.

2. The total number of characters processed.

Option 7

Find:

1. The average number of messages in the processing queue for the processor.

2. The number of messages that were rejected.

3. Processor and output line load.

Option 8

Find:

1. The average amount of data to process for the first computer.

2. The number of system crashes.

3. The load of the first and second computers.

4. The total number of data processed.

◘Variant 9

Find:

1. The average waiting time for processing on the first and second computers.

2. Number of users who have been denied service.

3. The load of the first and second computers.

4. Total number of users.

◘ Option 10

Find:

1. The average number of messages in the queue to the computer.

2. The number of messages lost.

6.2. Course design

When students implement the course project, it is suggested to use one of the methods of active learning, namely: working in a team/group. The number of people in the team depends on the amount of work that is being done. Within the framework of this discipline, work is planned in teams of 2 people.

Option 1

The computing system includes three computers. In the system an average of 30 seconds are received tasks that fall into the processing queue to the first computer, where they are processed for about 30 seconds. After that, the task goes simultaneously to the second and third computers.

The second computer can process the task for (14 ± 5) s, and the third - for (16 + 1) s. The end of processing a job on any computer means removing it from a solution from either machine. In their spare time, the second and third computers are busy processing background tasks.

Research the developed model in the following areas:

I. Simulate 4 hours of system operation.

Define:

• the necessary capacity of drives before all computers (maximum and average values);

• load factors of the computer;

• Maintenance time of the main and background tasks (maximum, minimum and average values).

Determine the performance of the second and third computers when solving background problems, provided that one background task is solved for 2 minutes.

2. Analyze the dependence of the above characteristics on the period of receipt for processing of basic and background tasks.

3. Independently to conduct research of any other characteristics of the functioning of this model and their dependencies among themselves.

Option 2

There are 5 computers on the network. From the outside (the time of receipt of messages (5 ± 1) min) the network receives information on three communication channels at the addresses of each computer. Each channel has a transfer rate of 5 Kbytes/min. The intensity of breakages of each channel is 40-80 minutes. When a transmission channel breaks down, the information is transmitted completely over another channel, which is free and functions. If all three channels are broken, the information remains and is transmitted on the first restored channel. The recovery time of each channel is 4-8 minutes.

Computers have unequal opportunities but the reflection of information in hard copy. Therefore, after processing the information (2-6 minutes) by the computer, the processed information is divided into three classes according to the type of printing, depending on the amount of data:

• 1st class - the amount of data in the range of 5 ... 10 Kbytes;

• 2nd class - the amount of data in the interval 10. .. 15 Kbytes;

• 3rd class - the amount of data in the interval 15 ... 20 Kbytes.

Depending on the class, the data is sent over the network to print to the appropriate computer, where the minimum print queue is.

The first and fifth computer can print information of the 1st and 2nd class. The second and fourth computer can print information of the 2nd and 3rd class. The third computer can print the information of the 1st and 3rd class.

If a printer breaks down on the computer where the information was sent, the data is sent back and a similar free printer that can print information is searched. In the absence of such data, the data is sent to the buffer, which is stored until the printer is restored.

The probability of a printer failure is 10%.

Time to send data over the network - 1-2 minutes.

Printer recovery time is 5-15 minutes.

Print time is 5-10 minutes.

The amount of data transferred to the system is 5 ... 20 Kbytes (blocks of 5 Kbytes each).

Evaluate the performance of the system within two days by parameters:

computer;

• the number of times the information channels fail;

• the amount of information transmitted on each channel;

• Number of times the printer failed;

Independently to conduct research of any other characteristics of the functioning of this model and their dependencies among themselves.

Option 3

Computer company assembles and sells computers on a daily basis. Work on the assembly of 3 people. The wizard can collect and check from 10 to 15 computers per day. Each of his two assistants - from 5 to 10 computers per day.

The components are distributed in the following categories: processors, motherboards, video cards, sound cards, RAM, hard disks. When checking collected, not all computers are in working order (on average, one of the 10 assembled computers does not work). If the computer is assembled by the master, then it performs diagnostics and determines which part is faulty (there can be any or several parts that are defective at the same time). If the computer assembled by one of the helpers is faulty, then they give it to the master for diagnostics.

The frequency of hit of faulty components is distributed as follows:

• Hard disks - 1-3 of 55,

• motherboards - 1 of 20,

• sound cards - 1 out of 30,

• processors - 2-3 out of 100,

• Video cards - 1 of 40.

1. Determine (per day):

• how many computers are assembled;

• how many faulty computers are assembled (and repaired accordingly);

• how many faulty parts (and to which categories these parts belong) are detected during checks;

• how much is needed for the component firm of all categories;

• how many computers each collector collects.

2. Investigate the above characteristics, depending on the change in the number of computers collected by each collector and the percentage of faulty parts.

3. Independently to conduct research of any other characteristics of the functioning of this model and their dependencies among themselves.

◘Variant 4

The data link consists of two channels (main and backup) and a common storage. During normal operation, messages are transmitted over the main channel after (7 ± 3) s. In the main channel failures occur at time intervals (200 ± 35) s. If a failure occurs during transmission, a spare channel is started for 2 seconds, which transmits the interrupted message from the very beginning.

The restoration of the main channel takes (23 ± 7) s. After restoration, the backup channel is turned off and the main channel continues to work with the next message.

Messages are sent through (9 ± 4) s and remain in the drive (buffer) until the transfer is complete. In case of a failure, the transmitted message is duplicated by a spare channel.

Research the developed model in the following areas:

1. Simulate the work of the data transmission line within 10 hours. Determine if the initial data available in the job:

• frequency of failures of the main channel;

• number of interrupted messages;

• The average time that messages are sent.

Do ten experiments and find the mean values ​​of the required parameters.

2. Collect statistics for parameters:

• average time of message passing;

• The maximum message queue length in the buffer.

3. Independently to conduct research of any other characteristics of the functioning of this model and their dependencies among themselves.

◘Variant 5

In order to unload the main channel, the ISP provider connects its subscribers to the outside world via a proxy server.

The proxy server is designed to keep on its hard drives all the information that was requested and received by some subscriber (that is, the proxy server writes all the web pages on its magnetic media, which were disclosed by the client, and all received files). When a subscriber receives an application for receiving a data packet (when a user dials any address on the Internet or when a link is triggered), all information on the proxy server is checked first. If there are no files on it, this link is sent to a specific requested server via a common communication channel with the World Wide Web.

Suppose, in our case, we have three telephone lines for modem connection with the provider. Each line is constantly in an active state, i.e. the client can at any time send an application.

Let's assume that all lines of modem connection of subscribers with the provider have the same transmission speed - 33600 bps.

As you enter the proxy server, requests from each client are queued.

Scanning the disk space of the proxy server takes approximately 2-8 seconds.

If a necessary data packet is found on the proxy server, the data on the modem line is transferred to the client. The probability that the requested data packet is on the proxy server is 30%. In the absence of the necessary information, the application is sent to the Internet via a common channel.

Let the speed of information exchange in the network at the moment is only 1.5 Kb/s. The client in response to his application receives over the network the package he needs (from 10 to 100 Kbytes) or, in case of failure, a failure. The probability of failure is 10%. It is necessary to take into account the fact that the client can not send a new application without receiving the requested data or a refusal indication from the previous application.

Data packets are firstly sent to the provider's server via a common channel, and then via a telephone line (modem link) to one of the clients.

1. Simulate the work of the data transmission line within 10 hours.

2. Determine if the initial data is available in the job:

• the number of packets transmitted over a common transmission channel;

• The amount of information received by each client.

3. Depending on the probability of finding the requested data packet on the proxy server, determine:

• The load of the shared channel;

• The workload of each station receiving information.

4. Independently to conduct research of any other characteristics of the functioning of this model and their dependencies among themselves.

As a result of the project the student must prepare a report containing:

• title page;

• Introduction;

• statement of the problem;

• a brief theoretical part;

• a general description of the model logic and the model itself;

• a description of each module and the module itself with its parameters;

• A separate section on conducting experiments and collecting statistics;

• a conclusion containing conclusions on the work done;

• list of sources used.

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