Criteria for choosing a computer network emulation simulation program. Specialized systems for computer network simulation. Weight coefficient, %

Purpose of the work:

• 1. Introduction to network modeling techniques using Cisco Packet Tracer software.
• 2. Gaining skills in building and modeling networks using hubs, switches, routers.
• 3. Gaining skills to use ping commands, tracert, arp to monitor the state of the computer network.

Theoretical part.

Description of Cisco Packet Tracer.

Cisco Packet Tracer - software product, developed as part of the network academies by Cisco and allows you to design networks, study network equipment, connections between them and configure them.

Figure 1 - Main components Cisco programs Packet Tracer

• 1- Work area where the equipment for organizing the network is located;
• 2- Available equipment (hubs, switches, routers, end devices);
• 3- Object control buttons;
• 4- Select between physical and logical workspace. A special feature of Packet Tracer is that when moving to the physical workspace, you can view the created network at the level from the virtual city to the rack. Move to a lower level by clicking on the object. Return - Back button;
• 5- Window for monitoring and controlling transmitted packets;
• 6- Switching between operating modes - real-time and simulation mode. In simulation mode, all packets sent within the network are displayed graphically (Figure 2). This feature allows you to clearly demonstrate which interface in at the moment the packet is being moved, what protocol is being used, etc. In this mode, you can not only monitor the protocols used, but also see which of the seven layers of the OSI model this protocol enabled by clicking on the square in the Info field (Figure 3).

Figure 2 - Packet transmission in simulation mode

Figure 3 - Layers of the OSI model in Cisco Packet Tracer

You can start working in simulation mode by generating a ping request using or and clicking on the Play button.

Each device can be configured depending on its purpose. For example, by clicking on the computer icon we get to the physical settings area, where appearance equipment and lists the cards that can be added to the device. The Config tab (Figure 4) shows network settings devices (IP, mask, gateway, DNS server).

Figure 4 - Computer network settings

In the Desktop tab there are additional features:

• · IP Configuration - network settings
• · Command Prompt - command line
• · Terminal
• · Browser
• · E-mail and more.

The command line is used to test network health, set settings, and view results. Basic commands when using:

· Ping - sending an echo request

Format: Ping destination_node_address.

Can be with extensions: Ping -t destination_node_address - sending an echo request until interrupted by the Ctrl+C command;

Ping -n count destination_node_address - sending as many echo requests as specified in count.

· Arp - a - view the arp table;

Arp - d - clear the arp table.

· Tracert - determining the route to the destination node.

Format: Tracert destination_node_address.

STP protocol.

Spanning Tree Protocol is a network protocol that operates at the second layer of the OSI model. The main goal of STP is to reduce a multi-link Ethernet network to a tree topology that eliminates packet loops. This happens by automatically blocking currently redundant connections to ensure full port connectivity. The protocol is described in the IEEE 802.1D standard.

CDP protocol.

Cisco Discovery Protocol is a second-level protocol developed by Cisco Systems, which allows you to detect connected (directly or through first-level devices) Cisco network equipment, its name, iOS version and IP addresses. Supported by many company devices, almost not supported by third-party manufacturers.

The information received includes the types of connected devices, the router interfaces to which neighboring devices are connected, the interfaces used to create connections, and device models.

ICMP protocol.

Internet Control Message Protocol - control message protocol.

Using ICMP, hosts and routers communicating over IP can report errors and exchange limited control and status information.

Each ICMP message is sent across the network inside an IP packet (Figure 5). IP packets with ICMP messages are routed just like any other packet, without priority, so they can also be lost. In addition, on a busy network they can cause additional load on routers. To avoid causing an avalanche of error messages, lost IP packets carrying ICMP error messages cannot generate new ICMP messages.

Figure 5 - ICPM packet format

Static and dynamic routing.

Routing is the process of determining the route for information in communication networks. Routes can be specified administratively (static routes) or calculated using routing algorithms based on information about the topology and state of the network obtained using routing protocols (dynamic routes). After determining the route of the packet, it is necessary to send information about this to each transit device. Each message is processed and entered into a routing table, which specifies the interface over which the device should transmit data related to a particular flow.

RIP protocol.

Routing Information Protocol - routing information protocol. Used to change entries in the routing table in automatic mode. To measure the distance to a destination, the number of hops is most often used - the number of intermediate routers that a packet needs to overcome to reach its destination (although there may be other options - network reliability, latency, throughput). Routers send their routing table to neighbors, receive similar messages from them and process them. If the new information has a better metric value, then old post is replaced by a new one, and the router again sends the RIP packet to its neighbors, waits for a response and processes the information.

ARP protocol.

Any device connected to a local network has a unique physical network address specified by hardware. The 6-byte Ethernet address is selected by the manufacturer of the network interface equipment from the address space allocated for it under the license. If the car changes network adapter, then its Ethernet address also changes.

The 4-byte IP address is set by the network manager, taking into account the machine’s position on the Internet. If a machine is moved to another part of the Internet, its IP address must be changed. Converting IP addresses to network addresses is done using the arp table. Each machine on the network has a separate ARP table for each of its network adapters.

Address translation is performed by searching the table. This table, called the ARP table, is stored in memory and contains rows for each host on the network. Two columns contain IP and Ethernet addresses. If you need to convert an IP address to an Ethernet address, the entry with the corresponding IP address is searched.

The ARP table is necessary because IP addresses and Ethernet addresses are chosen independently, and there is no algorithm for converting one to the other.

The following types of ARP messages exist: ARP request and ARP reply. The sending system uses an ARP request to request the physical address of the receiving system. The response (the physical address of the destination host) comes in the form of an ARP response.

Before sending the package network layer via Ethernet segment, network stack checks the ARP cache to see if the required information about the recipient host is already registered in it. If there is no such entry in the ARP cache, then an ARP broadcast request is made. The sender will then update its ARP cache and be able to forward the information to the recipient.

The node that needs to map the IP address to local address, generates an ARP request, inserts it into the protocol frame link layer, indicating a known IP address in it, and broadcasts the request.

All hosts on the local network receive an ARP request and compare the IP address specified there with their own.

If they match, the node generates an ARP response, in which it indicates its IP address and its local address and sends it already directed, since in the ARP request the sender indicates its local address.

Computer network simulation

Computer network modeling is a means of system analysis and should be based on a systems approach.

Basic principles of system analysis

Modern research methodology considers any object as a system. By system we mean a set of elements defined in time and space with known properties and ordered connections between elements, focused on fulfilling the main task of this set.

Associated with the system a whole series concepts such as integrity, complexity, structure, goal, subsystem, element, properties, connection, state, external environment.

Integrity establishes that knowledge of a system is achieved through the unity of studying all its elements and therefore the system should in no case be considered as their simple sum. At the same time, when analyzing systems, independent study of its individual parts (decomposition) is allowed, provided that they are functionally independent.

Complexity prescribes taking into account when studying a system the influence on it of both the external environment and internal factors.

Structure reflects the most significant relationships between the elements of the system, which ensure the existence of the system and its basic properties and change little from changes occurring in the system. The structure of the system depends on the depth of display of the object, on the purpose of the creation of the system, and the same system can be represented by several structures.

Target– desired state of the system. The assessment of the degree to which the system achieves the set goal is carried out through the goal criteria, which determine the compliance of the state of the system with the set goal.

Subsystem– this is a relatively independent part of the system, including a set of interconnected elements.

Element represents a conditionally indivisible part of the system. The degree of detail of the system through subsystems and elements is determined by the objectives of the study. A subsystem and an element can fulfill their own goals and objectives, but their functioning is always aimed at fulfilling the main goal (task) of the system.

Theoretical foundations LAN modeling

The main requirement for a LAN is to provide all users with access to shared network resources with a given quality of service (QoS - Quality of Service). One of the main criteria for service quality is performance. The performance indicators used are response time, throughput And transmission delay. Reaction time is the time interval between the occurrence of a user request to a network service and the receipt of a response. The response time depends on the load on the transmission medium segments and active network equipment (switches, routers, servers). Bandwidth– this is the amount of data transmitted per unit of time (bit/s, packets/s). The bandwidth of a composite path in a network is determined by the slowest element (typically a router). Transmission delay– this is the time interval between the moment a packet arrives at the input of a network device and the moment it appears at the output of the device.

To optimize LAN performance, measurement, analysis and modeling methods and tools are used. Client-server architecture and distributed data processing on a LAN complicate modeling tasks.

Analytical modeling of LAN based on the use of queuing system (QS) models and, as a rule, associated with significant simplifications. However, the results of the analytical study can be very valuable, even if they do not take into account all the details of the actual LAN. Such models make it possible to quickly obtain an approximate engineering assessment of the impact of hardware and software characteristics on LAN performance indicators.

The LAN model is built from separate blocks, each of which represents one node or LAN transmission channel. The block consists of a packet buffer storage device and a serving element (Fig. 1). The input of the block receives a stream of packets, characterized by the distribution function of time intervals between the moments of packet arrival A(t). Intensity input packet stream is the average number of packets arriving at the input of a block per unit of time. The reciprocal value 1/ is the average value of the interval between the moments of packet arrival, which is determined by the integral

AND
service intensity block is  the average number of processed packets per unit of time. The reciprocal value 1/ is the average value of the packet service duration, which is determined by the integral

Where B(t) – service duration distribution function. The ratio  =  /  is called block load factor. A real block has a buffer of limited capacity r(see Fig. 2, b). An idealized module can have a buffer of unlimited capacity (see Fig. 2a).

BlockM / M /1. Let's consider the most simple model type M/M/1 (one serving element, unlimited buffer capacity, exponential laws of distribution of time intervals between the moments of packet arrival and service time, FIFO service discipline) for the block shown in Fig. 1, a. In this case A(t)=1– e –  t , B(t)=1–e –  t, average delay time of a packet in a block

Average waiting time in queue W = T– (1/), and the average number of packets in the queue L W =L – .

B
lokM / G /1. This model is different from the type M/M/1 only because the service time distribution B(t) can be arbitrary. Consider the case when the distribution B(t) is specified for the block by two parameters: service intensity  and service time dispersion

Then the average time a packet spends in the queue is W = (1 + v 2) W P, where W P = (/2)(1–) –1 – the time the packet is in the queue with a constant service duration; v 2 =  2 D – squared coefficient of variation service time. For constant service time v=0, and for the exponential distribution of service time v=1. For model M/G/1 estimate of the time a packet stays in a block T=W + (1/), length of the queue in the buffer L W =W and the total number of packets in the block L = L W + .

BlocksM / M /1/ r And M / G /1/ r. Model type M/G/1/r for the block shown in Fig. 1, b, differs from the model M/G/1 because the buffer capacity is limited by r(it is assumed that the packet being processed is also in the buffer). This model is characterized by the probability of packet loss (denial of service)

where ( r, )=2r/(1+ 2), and   coefficient of variation. Absolute block capacity M/G/1/r

 ABS = (1– P OTK).

At  = 1 formula gives the exact value P QTC for exponential distribution B(t), i.e. for blocks M/M/1/r.

Block networkM / M /1. The LAN model can be represented as a network of blocks (queuing network - SeMO), with many blocks containing buffers. Simple analytical formulas can be obtained for open network blocks M/M/1, an example of which is shown in Fig. 2.

In this network, consisting of three blocks, there are three input streams of packets with intensities  1,  2 and  3, respectively. It is required to estimate the average packet delay for each flow. Queues in this network can be considered individually, with the number of packets in a block j=1...3 is estimated using formula (1), namely

L j =  j / ( j –  j).

Intensity  j flow at the input of each block is equal to the sum of the intensities of elementary flows entering the block in accordance with Fig. 3:

 1 =  1 +  2 ,  2 =  1 +  2 +  3 ,  3 =  2 +  3 .

It can be shown that the average packet delay in the network

de n– number of blocks in the system;  – the sum of the intensities of all flows entering the system. For a single thread i average packet latency on the network

,

Where J i – a subset of blocks involved in processing the stream i. In the example under consideration J 1 ={1, 2, 3}, J 2 =(1, 2) and J 3 ={2, 3}.

Formula (4) is correct under the following assumptions.

 The law of distribution of time intervals between the moments of packet arrival A(t) for individual flows is exponential, and the flows are independent processes. This assumption can be fulfilled in practice.

 Service time distribution law B(t) is also exponential, and the service processes in each queue are independent. This assumption cannot be satisfied, since the service time of a packet is proportional to its length, and, therefore, we cannot talk about the independence of service times in queues.

However, simulation shows that the application of formula (4) gives an acceptable estimate of the average packet delay in the network.

Simulation modeling allows you to simulate the behavior of a real LAN. There are many simulation software available computer networks(GPSS, COMNET III by Caci Products Co., BONeS Designer by Cadence Inc., OPNET by Modeler Mil3 Inc., ns2, etc.).

Literature

Ankudinov G.I., Strizhachenko A.I. Computer networks and telecommunications (architecture and protocols): Textbook. – 2nd ed. St. Petersburg: SZTU, 2003. 72 p.

Olifer V.G., Olifer N.A. Computer networks. Principles, technologies, protocols. – St. Petersburg: Peter, 2002. – 672 p.

Computer networks: Training course/ Per. from English – M.: Channel Trading Ltd LLP, 1997. – 696 p.

Sovetov B.Ya., Yakovlev S.A. Construction of integrated service networks. – L.: Mechanical Engineering, 1990. – 332 p.

English-Russian dictionary of networks and network technologies / Comp. S.B. Orlov. – M.: “Solon”, 1997. – 301 p.

Kulgin M. Technologies corporate networks: Encyclopedia. – St. Petersburg: Publishing House “Peter”, 2000. – 704 p.

Guk M. Local network hardware: Encyclopedia. – St. Petersburg: Publishing House “Peter”, 2000. – 576 p.

Nogl M. TCP/IP: Textbook. - M.: DMK Press, 2001. 480 p.

Novikov Yu.V., Kondratenko S.V. Local networks: architecture, algorithms, design. M.: EKOM Publishing House, 2000. 312 p.

Walrend J. Telecommunications and computer networks: An introductory course / Transl. from English - M.: Postmarket, 2001. 480 p.

Tomashevsky V., Zhdanova E. Simulation modeling in the GPSS environment. - M.: Bestseller, 2003. - 416 p.

Sovetov B.Ya., Yakovlev S.A. Modeling of systems: Textbook. allowance. - M.: Higher. school, 1985.- 271 p.

Petukhov O.A. Models of queuing systems: Textbook. manual.- L.: SZPI, 1989.- 86 p.

Examples of using simulation

modeling

Ensuring accuracy and reliability

simulation results

Number of tests N determines the accuracy of the simulation results. Let it be necessary to determine the accuracy of parameter estimation x random variable x. Probability

P( a –x < ) = ,

Where a– the exact value of the parameter is called reliability of the assessment, and the value  – absolute accuracy of assessment.

Value  0 =  / a called relative accuracy of assessment. Then the reliability of the estimate

P( a –x  / a <  0) = .

Number of realizations for estimating the average value of a random variable

To estimate the average value we use the formula


.

In accordance with the central limit theorem, for large N value x distributed according to the normal law with mathematical expectation a and variance  2 /( N – 1). Then

and the required number of implementations

.

Magnitude t is taken for a given confidence  from the normal distribution table.

Since the dispersion of the estimated value is unknown, it is necessary to conduct 50-100 preliminary tests and estimate the value of .

For variance  2, estimation accuracy
, where  4 is the central moment of the fourth order of the random variable x. For a normal distribution  4 =3 4.

Example 1.

Given:

block diagram computing system (providing part of local information technology);

batch operation mode computing system;

input flow intensity tasks  = 0.2 (exponential distribution);

decision time tasks in the computer system should not exceed

T extra= 30 s for 90% of tasks;

mathematical model computing system in the form of a single-threaded single-line queuing system of the type M/M/1/ (Fig. 1).

N IT:

parameter value – the average intensity of servicing requests in the device , at which the residence time of any request in the QS t will not exceed the specified value (30 s) for 90% of applications:

P( t30) = 0.9

based on what was found  calculate the system characteristics of the QS;

Based on what was found, determine the appropriate type of computing system and its performance indicators that provide the required time for solving the problem.

Restrictions:

Solution:

Equation (1) determines the value of the probability distribution function (PDF) of the random variable t at point 28.5, equal to 0.9. For system M/M/1/ (and only for it) the analytical expression for the PDF t is known. Then, to find the unknowns  and , you can create a system of nonlinear equations:

Solution of the nonlinear system of equations (2):

-( – )30 = ln 0.1,

 = - ln 0.1/30+0.2 = 0.276753,

 = / = 0.2 / 0.276753 = 0.722.

Let's choose  = /0.7 = 0.2/0.7 = 0.285714.

Then the calculated values ​​of the average packet delay time in the QS:

T= 1/ ( – ) = 11.67 s.

Average number of transactions in QS:

L =  / ( – ) = 2.334.

Average number of transactions in queue:

L W = L–  = 2.334 – 0.722 = 1.612.

To select a suitable computing system (server), we will set the parameters of the software package for processing. Let any package contain 100 programs of 10,000 statements each. Then the total volume of the package in operators will be Q=10 6 operations. In this case, the required performance of the computing system (server) will be equal to V=Q=10 6 0.285714 300 thousand op./s. To determine a suitable computing system(server) we will use the data in Table 1.

Table 1. Performance of INTEL processors

Processor type	Clock frequency, MHz	Performance, million op./s

From the list of processors, the youngest processor model, 8086, meets the specified requirements.

Received by mathematical models the results do not always adequately reflect the actual operation of a computing system of a given structure, since the calculated analytical formulas are derived and correct only under simplifying assumptions (or assumptions) regarding the structure, flow and service distributions, and others. An alternative approach to solving the problem is direct imitation on a PC (simulation modeling) of the process of executing a package in a computer system of a given structure using the GPSS modeling system.

EXPON FUNCTION RN1,C24

TABLA TABLE M1.0.3500000.15

GENERATE 5000000,FN$EXPON 1/ =1/ 0.2= 5.0

* 1 modem time unit = 1 µs

ADVANCE 3500000,FN$EXPON 1/ =3.5 s

The simulation results (see Listing 1) are summarized in Table 2.

Table 2

(device)	Parameter	Meaning	Interpretation
	(load factor)
	AVERAGE TIME/XACT (average service time per transaction)		T S = 1/  =
(queue)	AVERAGE CONTENTS (medium length)		L W = 1.634
	MAXIMUM CONTENTS (max. length)		L W max =29
	AVERAGE TIME/UNIT (average waiting time)		W=8.261344 s
(tabular data for full time in SMO)	(average time in QS per 1 transaction)		T= 11.759 s
	STANDARD DEVIATION (rms time deviation in QS for 1 transaction)

The simulation results are in good agreement with the calculated values.

Example 2.

Let's consider solving the problem for the interactive mode of operation of a local computer system.

Given:

operating mode- interactive;

reaction time dialogue subscriber (thinking time) 1/=10s;

decision time tasks (response time to a request from the terminal) should not exceed T d additional=1 s for 90% of tasks;

number of usersn=20;

mathematical model computing system in the form of a closed queuing network (Fig. 2).

R is. 2

In this model there are constantly circulating n applications (transactions).

Find:

value of queuing network parameters , at which

t T d extra1 s for 90% of interactive requests, i.e.

P( t 1 c ) = 0.9;

using the found  and , calculate the system and network characteristics of SeMO;

determine the appropriate type of computing system and its performance indicators that provide the required response time to a request from the terminal.

Restrictions:

Solution:

To solve the problem, an approximate method is used, based on the decomposition of the computing system into a processing subsystem and a terminal subsystem (and their “independent” consideration) with the subsequent balance of flows in these subsystems. Then, to find the unknowns , we can create a system of equations:

1 – e - ( – ) Td extra =P

From the first equation

For P = 0.9, T d extra= 1 s, 1/ = 10 s, n=20 we get:

 = 20 / (10 – 1 / ln (1–0.9)) = 2.09080,

 =  - ln(1– P) / T d extra= 2.09080 – ln (1–0.9) / 1 = 4.39339,

 =  /  = 0.475897 – load factor.

The calculation can be simplified somewhat if we consider that T d extra  T d/2 (for P= 0.9), where T d=1/( – ) - average response time. Then T d  2T d extra And

.  20/(10-2*1) = 2.5.

Simulation program in GPSS/H language (student version).

SPACE STORAGE 20

EXPON FUNCTION RN1,C24

0,0/.1,.104/.2,.222/.3,.355/.4,.509/.5,.69/.6,.915/

7,1.2/.75,1.38/.8,1.6/.84,1.85/.88,2.12/.9,2.3/

92,2.52/.94,2.81/.95,2.99/.96,3.2/.97,3.5/.98,3.9/

99,4.6/.995,5.3/.998,6.2/.999,7/.9998,8

QTIME QTABLE QU1,0,200,20

SYS0 ENTER SPACE

ADVANCE 10000000,FN$EXPON

ADVANCE 250000,FN$EXPON

TEST E X6,0,SYS0

The simulation results for 4 values ​​of  are summarized in Table 3 (see Listing 2 for  = 4).

Table 3

	Simulation results					T S +T w [s]
		T S[With]	L W	L W MAX	T w [With]

In this table

T S– average request processing time;

L W– average queue length;

L W MAX – maximum queue length;

T w – average waiting time for a request in the queue;

T S + T w – average response time.

To select a suitable computing system (server), you should select the option with

 = 4 or 5.

Example 3.

Let us consider solving the problem for a mixed operating mode of a local computing system, when for one group of subscribers the computer system model is represented as a closed interactive SeMO (SMO network), and for another group - as an open SeMO.

Modeling a future network is a mandatory part of any information and telecommunications network project.

The goals of modeling can be:

Determination of optimal topology;

Choice network equipment;

Determination of network performance characteristics;

Checking the characteristics of new protocols.

Using the model, you can check the impact of load bursts and the impact of a large flow of broadcast requests, which is unlikely to be something anyone can afford on a working network.

The listed tasks impose different requirements on programs that simulate the functioning of the network. At the same time, determining the characteristics of the network before it is put into operation is of paramount importance, since it allows you to adjust the characteristics of the local network at the design stage. Solving this problem is possible through analytical or statistical modeling.

Analytical network modeling is a set of mathematical relationships that connect the input and output characteristics of the network. When deriving such relationships, one has to neglect some unimportant details or circumstances.

Simulation (statistical) modeling is used to analyze the system in order to identify critical network elements. This type of modeling is also used to predict future system performance. The modeling process includes creating a model, debugging the modeling program, and checking the correctness of the selected model. The last stage usually consists of comparing the calculated results with experimental data obtained for a real network.

Different modeling approaches are possible. The classic approach is to reproduce events on the network as accurately as possible and model the consequences of these events step by step.

Another approach could be a method where for each logical segment (collision zone) a queue of events is first simulated.

A complete network simulation based on production applications assumes the following characteristics:

Node characteristics;

Connection characteristics;

Protocols used;

Characteristics of sent packets.

Protocol characteristics:

The length of the packet sent by each node (message length + address part length + length of additional attached information);

Message length;

Temporal distribution of packet sending moments.

The structure of the description of each node includes:

Node number (identifier);

Node type code;

MAC address;

IP address;

Status byte (node ​​is transmitting; someone else’s packet has reached the node;...);

Code of the protocol used (IPv4 or IPv6; TCP, UDP, ICMP, etc.);

Input/output buffer volume. Buffer type (FIFO, LIFO, etc.).

Each of the existing modeling methods has its drawbacks. When building a network, it is necessary to remember what results this model should lead to.

For more detailed analysis it was decided to use statistical presentation models. The results obtained by modeling all processes in the network will be a sufficient basis for assessing the quality of the constructed network of the Lux company. This model involves modeling processes on a network using special software.

PacketTrecer simulation program

PacketTracer is a program that is a data network emulator. Allows you to create workable network models, configure (using Cisco IOS commands) routers and switches, and interact between several users (via the cloud). Includes the Cisco 1800, 2600, 2800 series of routers and 2950, ​​2960, 3650 switches. In addition, there are DHCP, HTTP, TFTP, FTP servers, workstations, various modules for computers and routers, WiFi devices, various cables. The program allows you to successfully create even complex network layouts and check the functionality of the topology.

A fully assembled enterprise LAN model in the emulator and configured to full functionality is shown in Figure 6.

Figure 6. General diagram of the information and telecommunications network.

The server room houses the database server and web server; a router to provide the backbone and distribution layer, connected to the Internet provider; access level switches that physically unite 50 end users into a single local network, as well as a network printer and access point. User workstations are indicated schematically. Routers connect to the Internet provider via high-speed communication lines to provide high speed data transfer. Each department of the company is defined in a separate virtual local network using routers, which facilitates network administration.

The network is built using a star topology. Traffic on the network is used to transfer data between users and file servers, as well as for transmitting data to the Internet. Internet access is provided using PAT technology, using a single IP address provided by the provider.

Types of computer networks

Purpose of a computer network

The main purpose of computer networks is the sharing of resources and the implementation of interactive communication both within one form and beyond. Resources are data, applications and peripherals such as external drive, printer, mouse, modem or joystick. The concept of interactive communication between computers implies the exchange of messages in real time.

Printers and other peripherals

Before the advent of computer networks, each user had to have his own printer, plotter and other peripheral devices. To share a printer, the only way was to sit at a computer connected to that printer.

Networks now allow multiple users to simultaneously “own” data and peripheral devices. If several users need to print a document, they can all access a network printer.

Data

Before the advent of computer networks, people exchanged information something like this:

transmitted information orally (oral speech)

wrote notes or letters (written speech)

wrote information onto a floppy disk, took the floppy disk to another computer and copied the data to it

Computer networks simplify this process by giving users access to almost any type of data.

Applications

Networks provide excellent conditions for unifying applications (for example, a word processor). This means that all computers on the network are running the same type of application and the same version. Usage single application will help simplify the support of the entire network. Indeed, it is easier to learn one application than to try to master four or five at once. It is also more convenient to deal with one version of the application and configure computers in the same way.

SCS is the basis of a computer local network (LAN)

SCS is the basis of a local network

For the organization to operate, a local network is required that connects computers, telephones, and peripheral equipment. You can do without a computer network. It’s just inconvenient to exchange files using floppy disks, line up near the printer, and access the Internet through one computer. The solution to these problems is provided by technology, abbreviated SCS.

A structured cabling system is a universal telecommunications infrastructure of a building/building complex that provides transmission of signals of all types, including voice, information, and video. SCS can be installed before user requirements, data transfer rates, and the type of network protocols are known.

SCS creates the basis of a computer network integrated with the telephone network. The collection of telecommunications equipment of a building/building complex, connected through a structured cabling system, is called a local area network.

SKS or computer plus telephone network

Structured cabling systems provide long term services, combining ease of use, quality of data transmission, and reliability. The implementation of SCS creates the basis for increasing the efficiency of the organization, reducing operating costs, improving interaction within the company, and ensuring the quality of customer service.

A structured cabling system is built in such a way that each interface (connection point) provides access to all network resources. In this case, two lines are enough at the workplace. One line is computer, the second is telephone. The lines are interchangeable. Cables connect TP workplaces to the ports of distribution points. Distribution points are connected by trunk lines according to the “hierarchical star” topology.

SKS is an integrated system. Let's compare SCS with the outdated computer plus telephone network model. A number of advantages are obvious.

an integrated local network allows you to transmit different types of signals;

SCS ensures the operation of several generations of computer networks;

SCS interfaces allow you to connect any equipment of local networks and voice applications;

SCS implements a wide range of data transfer rates from 100 Kbit/s for voice applications to 10 Gbit/s for information applications;

administration of SCS reduces labor costs for maintaining the local network due to ease of operation;

a computer network allows the simultaneous use of different types of network protocols;

standardization plus competition in the SCS market ensures lower prices for components;

local network allows you to realize the freedom of movement of users without changing personal data (addresses, telephone numbers, passwords, access rights, classes of service);

SCS administration ensures transparency of the computer and telephone network - all SCS interfaces are marked and documented. The work of the organization does not depend on the employee monopolist of telephone network connections.

A reliable, long-lasting SCS is the foundation of a local network. However, every dignity has a downside. SCS standards recommend redundancy of quantitative system parameters, which entails significant one-time costs. But you can forget about the nightmare of permanent renovation of an existing office to expand a computer network to meet current needs.

SCS standards

The standards define the structure of SCS, operating parameters of structural elements, design principles, installation rules, measurement techniques, administration rules, telecommunications grounding requirements.

SCS administration includes marking of ports, cables, panels, cabinets, and other elements, as well as a recording system supplemented with links. Together with the thoughtful organization of cables laid down at the stage of creating the SCS, the administration system allows you to maintain good organization local network. The 2007 SCS standards consider the presence of administration as one of the conditions for SCS compliance with the requirements of the standards.

SCS are determined by international, European and national standards. SKS standards are addressed to professional builders. In Russia, SCS is more often created by organizations specializing in computer networks and security systems.

Russia is a member of the International Organization for Standardization (ISO), and therefore is guided by international standards. This information reflects the requirements of the international standard ISO/IEC 11801.

SCS subsystems

The ISO/IEC 11801 standard divides structured cabling into three subsystems:

main subsystem of the building complex;

main building subsystem;

horizontal subsystem.

SCS backbone subsystem and telephone network

The backbone subsystem of the building complex connects the cable systems of the buildings.

The backbone subsystem of the building connects the distribution points of the floors.

The trunk subsystem includes information and speech subsystems of the SCS. The main transmission medium of the information subsystem is optical fiber (single-mode or multimode), supplemented by symmetrical four-pair cables. If the length of the main line does not exceed 90 meters, symmetrical cables of category 5 and higher are used. For longer lengths, information applications, i.e. computer networks, require fiber optic cables.

Building backbone speech applications operate over multi-pair cables. Speech applications that create a telephone network belong to the lower classes of SCS. This allows you to increase the length of the backbone subsystem lines created by multi-pair cables to two to three kilometers.

Horizontal subsystem of SCS and computer network

The horizontal subsystem of the SCS includes distribution panels, patch cables of floor distribution points, horizontal cables, consolidation points, and telecommunication connectors. The horizontal subsystem provides a local network for subscribers and provides access to backbone resources. The transmission medium of the horizontal subsystem is symmetrical cables of at least category 5. The 2007 SCS standards provide for data processing centers to select SCS of at least category 6. For information technology(computer plus telephone network) of private homes, new standards recommend the use of category 6 / 7. Broadcast transmission medium communication technologies(television, radio) private houses / apartments - symmetrical protected cables with a frequency band of 1 GHz, plus coaxial cables up to 3 GHz. The use of optical fiber is also allowed.

The horizontal subsystem of SCS is dominated by a computer network. This results in a limitation on the maximum length of the channel - 100 meters, regardless of the type of medium. To extend the service life without modifications, the horizontal subsystem of the SCS must provide redundancy and reserve parameters.

Work area in the structure of the horizontal subsystem of SCS

The SCS work area is the premises (part of the premises) where users work with terminal (telecommunications, information, speech) equipment.

The work area does not belong to the horizontal subsystem of the SCS. Functional element The horizontal subsystem of the SCS is the telecommunications connector - TR.

Workstations are equipped with sockets that include two or more telecommunications connectors. The work area equipment is connected using subscriber cables. Subscriber / network cables are outside the scope of SCS, but they allow you to create channels whose parameters are determined by SCS standards. SCS includes patch cables / jumpers used for connections between panel ports / cross-connect contacts.

More than 90% of SCS cables are in the horizontal subsystem. The cables of the horizontal subsystem are maximally integrated into the building infrastructure. Any changes in the horizontal subsystem affect the work of the organization. Therefore, redundancy of the horizontal subsystem is so important, ensuring trouble-free long-term operation of the local network.

There are two methods of laying cables - hidden and open. For hidden installation, the construction of walls, floors, and ceilings is used. However, this is not always possible. The most common option for cable channels is plastic boxes.

Options for open laying of cable harnesses include trays, boxes, mini-columns. Hidden cable routing provides for the installation of built-in sockets and installation of floor hatches.

SCS distribution points – local network nodes

SKS distribution points are the ends of horizontal and main lines, which are fixed on panels or cross-connections for ease of use. Floor/wall cabinets and telecommunication racks are used to install panels, cross-connects, and network equipment. The distribution point can occupy part of a cabinet or several cabinets. The premises of distribution points are called telecommunications premises, literally – telecommunication closets. It is recommended to install one floor control panel on each floor of the building. If the office floor area exceeds 1000 square meters, an additional distribution center is provided, connected by main channels.

SCS distribution points create local network nodes where network and server equipment are compactly located.

Floor-standing cabinets allow you to place hundreds of line terminations, equipment, and PBX units. Telecommunications racks provide cabinet capacity at a lower cost. They are used when additional protection of local network equipment or special operating conditions is not required. It is recommended to choose wall-mounted cabinets if there are a small number of lines and there is no telecommunications room. The cabinet equipment is cooled by fans.

Today, like 10 years ago, there are two types of networks - peer-to-peer and server-based networks. Each of them has both advantages and disadvantages.

A peer-to-peer network is likely to appeal to users who want to try out the network first or who can only afford the low cost of building and maintaining a network. A server-based network is used where complete control over all workstations is important. It may be small home network, and volumetric corporate system networks united into one common one.

These two different types networks have common roots and principles of operation, which, in case of necessary modernization, makes it possible to move from more simple option– peer-to-peer network – to more complex – server-based network.

Peer-to-peer network

It is very easy to build a peer-to-peer network. The most important characteristic of such a network is that all the computers included in it work on their own, that is, no one controls them.

In fact, a peer-to-peer network looks like a number of computers connected using one of the types of communications. It is the absence of a control computer – a server – that makes its construction cheap and quite effective. However, the computers themselves that are part of the peer-to-peer network must be powerful enough to cope with all basic and additional tasks (administrative, virus protection, etc.).

Any computer on such a network can be called either a worker or a server, since there is no specific dedicated computer that exercises administrative or other control. A computer on such a network is monitored by the user (or users) who works on it. This is where it lies main drawback peer-to-peer network - its user must not only be able to work on a computer, but also have an understanding of administration. In addition, he himself has to cope with emergency situations that arise during the operation of the computer and protect it from a variety of troubles, from viruses to possible software and hardware problems.

As expected, a peer-to-peer network uses shared resources, files, printers, modems, etc. However, due to the absence of a control computer, each user of the shared resource must independently establish the rules and methods for its use.

You can use any operating system to work with peer-to-peer networks. Peer-to-peer network support is implemented in Microsoft Windows, starting with Windows 95, so no additional software not required.

A peer-to-peer network is usually used when you need to connect several (usually up to 10) computers into a network using the simplest cable connection system and do not need to use strict data protection. More It is not recommended to connect computers, since the lack of “controlling authorities” sooner or later leads to various problems. After all, because of one uneducated or lazy user, the protection and operation of the entire network is jeopardized!

If you are interested in a more secure and controlled network, then create a server-based network.

Server based network

A server-based network is the most common type of network, which is used both in full-fledged home networks and offices, as well as in large enterprises.

As the name suggests, this network uses one or more servers that monitor all workstations. As a rule, a server is characterized by high power and speed necessary to perform assigned tasks, be it working with a database or servicing other user requests. The server is optimized for quickly processing requests from users and has special mechanisms software protection and control. Sufficient server power allows you to reduce the power requirement of the client machine. The operation of a server-based network is usually monitored by a special person - system administrator. He is responsible for regularly updating anti-virus databases, troubleshooting problems, adding and monitoring shared resources, etc.

The number of workstations in such a network can vary - from several to hundreds or thousands of computers. In order to maintain network performance at the required level as the number of connected users increases, additional servers are installed. This allows for optimal distribution of computing power.

Not all servers do the same job. There are specialized servers that allow you to automate or simply facilitate the execution of certain tasks.

File server. Designed mainly for storing a variety of data, from office documents to music and video. Typically, personal user folders are created on such a server, to which only they (or other users who have received the right to access documents in this folder) have access. To manage such a server, use any network operating system, equivalent to Windows NT 4.0.

Print server. The main task of this server is maintenance network printers and ensuring access to them. Very often, in order to save money, a file server and a print server are combined into one server.

Database server. The main task of such a server is to provide maximum speed searching and recording the necessary data into the database or obtaining data from it and then transmitting it to the network user. These are the most powerful of all servers. They have maximum performance, since the comfort of all users depends on this.

Application server. This is an intermediate server between the user and the database server. As a rule, those queries that require maximum performance and must be transmitted to the user without affecting either the database server or the user's computer. This can be either frequently requested data from the database or any program modules.

Other servers. In addition to those listed above, there are other servers, such as mail, communication, gateway servers, etc.

A server-based network provides a wide range of services and capabilities that are difficult or impossible to achieve from a peer-to-peer network. In addition, a peer-to-peer network is inferior to such a network in terms of security and administration. Having a dedicated server or servers makes it easy to provide backup, which is a priority if there is a database server on the network.

Local network

Network concept

The simplest network consists of at least two computers connected to each other by cable. This allows them to share the data. All networks are based on this simple principle. Although the idea of ​​connecting computers using a cable does not seem particularly remarkable to us, it was a significant advance in the field of communications in its time.

A network is a group of connected computers and other devices. The concept of computers connected and sharing resources is called networking.

Computers on the network can share:

data

printers

fax machines

modems

other devices

This list is constantly replenished, because new ways are emerging sharing resources

Local area networks

Initially, computer networks were small and connected up to ten computers into one printer. The technology limited the size of the network, including the number of computers on the network and its physical length. For example, in the early 1980s, the most popular type of network consisted of no more than 30 computers, and its cable length did not exceed 185 m.

Network problems

Choosing a network that is not suitable for the company can lead to problems. The most common situation is when a peer-to-peer network is selected when the network should be server-based. Network layout problems may also arise if topology constraints prevent the network from operating in some configurations.

Peer-to-peer networks

In peer-to-peer networks, or workgroups, problems may arise due to unplanned interference in the operation of the network station. Signs that a peer-to-peer network does not meet the company's requirements are:

difficulties associated with the lack of centralized data protection

constantly arising situations when users turn off their computers, which act as servers.

Networks with a bus topology

In networks with a "bus" topology, situations are possible when - for various reasons - the bus is not connected to the terminator. And this, as you know, stops the operation of the entire network.

The cable may break

Breaking the cable will result in its two ends being free, i.e. without terminators. Electrical signals will begin to reflect and the network will stop working.

The cable may become disconnected from the T-connector

The computer is disconnected from the network, and the cable also has a free end. Signals begin to be reflected, therefore the entire network stops functioning

The cable may lose its terminator

If the terminator is lost, the end of the cable becomes free. The signals begin to be reflected, which leads to the failure of the entire network.

Wireless networks

Wireless environment

The wireless environment is gradually entering our lives. As soon as the technology is finally formed, manufacturers will offer a wide selection of products at reasonable prices, which will lead to both an increase in demand for it and an increase in sales. In turn, this will drive further improvement and development of the wireless environment. The phrase "wireless environment" can be misleading because it means there are no wires on the network, but in reality this is not the case. Typically, wireless components interact with a network that uses cable as the transmission medium; such a network with mixed components is called a hybrid one.

Possibilities

The idea of ​​a wireless environment is very attractive because its components are:

Provide temporary connection to the existing cable network.

Help organize backup to existing cable network

Guarantees a certain level of mobility

Allows you to remove restrictions on the maximum network length imposed by copper or even fiber optic cables.

Signal transmission

To transmit encoded signals via cable, two technologies are used - narrowband transmission and wideband transmission.

Narrowband transmission

Narrowband systems transmit data as a digital signal of a single frequency. The signals are discrete electrical or light pulses. With this method, the entire capacity of the communication channel is used to transmit one pulse, or, in other words, digital signal uses the entire cable bandwidth. Bandwidth is the difference between the maximum and minimum frequency that can be transmitted over a cable.

Broadband transmission

Broadband systems transmit data in the form of an analog signal that uses a certain frequency range. The signals are continuous electromagnetic or optical waves. With this method, signals are transmitted through the physical medium in one direction.