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Basics of local computer networks

Introduction.

Today there are more than 130 million computers in the world and more than 80% of them are connected into various information and computer networks, from small local networks in offices to global networks such as the Internet. The worldwide trend towards connecting computers into networks is due to a number of important reasons, such as accelerating the transmission of information messages, the ability to quickly exchange information between users, receiving and transmitting messages (faxes, E-Mail letters, etc.) without leaving the workplace, the ability to instantly receive any information from anywhere in the world, as well as the exchange of information between computers of different manufacturers running different software.

Such huge potential opportunities that a computer network carries and the new potential rise that the information complex experiences at the same time, as well as the significant acceleration of the production process, do not give us the right not to accept this for development and not to apply it in practice.

Therefore, it is necessary to develop a fundamental solution to the issue of organizing an information and computer network on the basis of an existing computer park and software package that meets modern scientific and technical requirements, taking into account growing needs and the possibility of further gradual development of the network in connection with the emergence of new technical and software solutions.

The concept of LAN.

What is a local area network (LAN)? A LAN is understood as the joint connection of several separate computer workstations (workstations) to a single data transmission channel. Thanks to computer networks, we have the opportunity to simultaneously use programs and databases by several users.

The concept of local area network - LAN (eng. LAN - Lokal Area Network) refers to geographically limited (territorially or production) hardware and software implementations in which several computer systems are connected to each other using appropriate communications means. Thanks to this connection, the user can interact with other workstations connected to this LAN.

In production practice, LANs play a very important role. Through a LAN, the system combines personal computers located at many remote workplaces, which share equipment, software and information. Workplaces of employees cease to be isolated and are combined into unified system. Let's consider the benefits obtained by networking personal computers in the form of an intra-industrial computer network.

Resource sharing.

Resource sharing allows for efficient use of resources, such as managing peripherals such as laser printers from all connected workstations.

Data separation .

Data sharing provides the ability to access and manage databases from peripheral workstations that require information.

Software separation.

Software separation provides the opportunity to simultaneously use centralized, previously installed software.

Processor resource sharing.

By sharing processor resources, it is possible to use computing power to process data by other systems on the network. The opportunity provided is that the available resources are not “attacked” instantly, but only through a special processor available to each workstation.

Multiplayer mode .

The multi-user properties of the system facilitate the simultaneous use of centralized application software previously installed and managed, for example, if a user of the system is working on another task, the current work in progress is relegated to the background.

One rank network.

In a peer-to-peer network, all computers have equal rights: there is no hierarchy among computers and there is no dedicated server, and, as a rule, each computer functions as both a client and a server. All users independently decide what data on their computer to make available to everyone. A one-rank network is also called a working group. A work group is a small team, so there are no more than 10 computers in a single-rank network.

One thing is that rank networks are relatively simple. Because each computer is both a client and a server, there is no need for a powerful central server or other components required for more complex networks. Single-rank networks are usually cheaper than server-based networks, but require more powerful and expensive computers.

In a peer-to-peer network, the performance and security requirements for network software are generally lower than in networks with a dedicated server. Dedicated servers function solely as servers and not as clients or workstations.

Operating systems such as Microsoft Windows NT Workstation, Microsoft Windows for Workgroups and Microsoft Windows 95 have built-in support for peer-to-peer networks. Therefore, to install a single-rank network, no additional software is required.

One rank computer network looks like this:

Computers are located on users' desktops.

Users themselves act as administrators and ensure the protection of information themselves.

A simple cabling system is used to connect computers into a network.

If these conditions are met, then most likely the choice of a one-rank network will be correct.

Protection involves setting a password for a shared resource, for example a directory. It is very difficult to centrally manage security in a peer-to-peer network, since each user installs it independently, and shared resources can be located on all computers, and not just on the central server. This situation poses a serious threat to the entire network, and some users may not install protection at all.

Server-based networks

If more than 10 users are connected to the network, then a one-rank network, where computers act as clients and servers, may not be sufficiently productive. Therefore, most networks use dedicated servers. A dedicated server is a server that functions only as a server. They are specifically optimized for quickly processing requests from network clients and for managing file and directory protection. Server-based networks have become an industry standard.

As the size of the network and the volume of network traffic increases, it is necessary to increase the number of servers. Distributing tasks across multiple servers ensures that each task is completed in the most efficient manner possible.

The range of tasks that servers must perform is varied and complex. To accommodate increasing user needs, servers in large networks have become specialized. For example, there are different types of servers on a Windows NT network:

File servers and print servers control access to files and printers, respectively; application servers run application parts of client and server applications, and also contain data available to clients. For example, to make data retrieval easier, servers store large amounts of information in a structured manner. These servers are different from file servers and print servers. In print servers, the entire file or data is copied to the requested computer. And in the application server, only the results of the request are sent to the requested computer. A client application on a remote computer accesses data stored on the application server. However, instead of the entire database, only the query results are downloaded to your computer from the server.

In an expanded network, the use of servers of various types becomes most relevant. It is therefore necessary to take into account all sorts of nuances that may appear as the network grows, so that a change in the role of a particular server does not subsequently affect the operation of the entire network.

The main argument when working on a network based on a dedicated server is, as a rule, data protection. On networks such as Windows NT Server, security issues can be handled by a single administrator.

Since vital information is centrally located, that is, concentrated on one or more servers, it is not difficult to ensure its regular backup. Thanks to redundant systems, data on any server can be duplicated in real time, so if the main data storage area is damaged, information will not be lost - it is easy to use a backup copy. Server-based networks can support thousands of users. A network of this size, if it were single-ranked, would be impossible to manage. Since the user's computer does not perform the functions of a server, the requirements for its characteristics depend on the user.

All LANs operate in the same standard adopted for computer networks - the Open Systems Interconnection (OSI) standard.

Basic OSI (Open System Interconnection) model

In order to interact, people use a common language. If they cannot talk to each other directly, they use appropriate aids to convey messages.

The stages shown above are necessary when a message is transferred from the sender to the recipient.

In order to set in motion the process of data transmission, machines were used with the same data encoding and connected to one another. For a unified presentation of data, the communication lines through which information is transmitted, the International Organization for Standardization (ISO - International Standards Organization) was formed.

ISO is intended to provide a model for an international communications protocol within which international standards can be developed. For a clear explanation, let’s break it down into seven levels.

The International Organization for Standardization (ISO) has developed a basic model for open systems interconnection (OSI). This model is an international standard for data transmission.

The model contains seven separate levels:

Level 1: physical- bit protocols for information transfer;

Level 2: duct- formation of personnel, management of access to the environment;

Level 3: network- routing, data flow management;

Level 4: transport- ensuring interaction of remote processes;

Level 5: sessional- support for dialogue between remote processes;

Level 6: presentation data - interpretation of transmitted data;

Level 7: applied- user data management.

The main idea of ​​this model is that each level is assigned a specific role, including the transport environment. Thanks to this, the overall task of data transmission is divided into individual, easily visible tasks. The necessary agreements for communication at one level, for example, upstream and downstream, are called protocol.

Since users need effective management, the computer network system is represented as a complex structure that coordinates the interaction of user tasks.

With the above in mind, the following layer model can be derived with administrative functions running in the user application layer.

The individual layers of the basic model extend downward from the data source (layer 7 to layer 1) and upward from the data sink (layer 1 to layer 7). User data is passed down to the layer below along with a layer-specific header until the last layer is reached.

At the receiving side, incoming data is analyzed and, if necessary, passed on to a higher layer until the information is transferred to the user application layer.

Level 1. Physical.

The physical layer defines the electrical, mechanical, functional, and procedural parameters for physical communication in systems. Physical connectivity and the availability that goes with it is a core function of Level 1. Physical layer standards include CCITT recommendations V.24, EIA RS232 and X.21. The ISDN (Integrated Services Digital Network) standard will play a decisive role in data transfer functions in the future. The data transmission medium is three-core copper wire (shielded twisted pair), coaxial cable, fiber optic conductor and radio relay line.

Level 2. Duct.

The data link layer forms so-called “frames” of a sequence of frames from the data transmitted by the 1st layer. At this level, access control to the transmission medium used by several computers, synchronization, error detection and correction are carried out.

Level 3. Network.

The network layer establishes communication in a computer network between two subscribers. The connection occurs through routing functions that require a network address to be included in the packet. The network layer must also provide error handling, multiplexing, and data flow control. The most well-known standard related to this level is CCITT Recommendation X.25 (for public packet-switched networks).

Level 4. Transport.

The transport layer supports the continuous transfer of data between two user processes interacting with each other. Transport quality, error-free transmission, independence of computer networks, end-to-end transport service, cost minimization and communication addressing guarantee continuous and error-free data transmission.

Level 5. Sessional.

The session layer coordinates the reception, transmission and delivery of a single communication session. Coordination requires: control of operating parameters, control of data flows of intermediate storage devices and interactive control that guarantees the transfer of available data. In addition, the session layer additionally contains functions for managing passwords, calculating fees for using network resources, managing dialogue, synchronizing and canceling communication in a transmission session after a failure due to errors in lower layers.

Level 6. Data views.

The data presentation layer is for data interpretation; as well as preparing data for the user application layer. At this level, data is converted from frames used to transmit data into screen format or format for printing devices of the end system.

Level 7. Applied.

In the application layer, it is necessary to provide users with already processed information. System and user application software can handle this.

Network devices and communications.

The most commonly used means of communication are twisted pair, coaxial cable, and fiber optic lines. When choosing a cable type, take into account the following indicators:

cost of installation and maintenance,

information transfer speed,

Limitations on the distance of information transmission without additional amplifiers-repeaters (repeaters),

security of data transmission.

The main problem is to simultaneously ensure these indicators, for example, the highest data transfer rate is limited by the maximum possible data transmission distance, which still ensures the required level of data protection. Easy scalability and ease of expansion of the cable system affect its cost.

twisted pair .

The cheapest cable connection is a twisted two-wire connection, often called a twisted pair. It allows you to transmit information at speeds of up to 10 Mbit/s, is easily expandable, but is not protected from interference. The cable length cannot exceed 1000 m at a transmission speed of 1 Mbit/s. The advantages are low price and ease of installation. To increase the noise immunity of information, shielded twisted pair cable is often used, i.e. twisted pair, placed in a shielding sheath, similar to the shield of a coaxial cable. This increases the cost of twisted pair and brings its price closer to the price of coaxial cable.

Ethernet cable.

The Ethernet cable is also a 50 ohm coaxial cable. It is also called thick Ethernet (thick), yellow cable (yellow cable) or 10BaseT5. It uses a 15-pin standard connection. Due to its immunity to noise, it is an expensive alternative to conventional coaxial cables. The maximum available distance without a repeater does not exceed 500 m, and the total distance of the Ethernet network is about 3000 m. The Ethernet cable, due to its backbone topology, uses only one load resistor at the end.

Cheapernet cable.

Cheaper than an Ethernet cable is a Cheapernet cable connection or, as it is often called, thin Ethernet or 10BaseT2. It is also a 50 ohm coaxial cable with an information transfer rate of ten million bits per second.

When connecting Chearenet cable segments, repeaters are also required. Computer networks with Cheapernet cable have a low cost and minimal expansion costs. Network cards are connected using widely used small-sized bayonet connectors (CP-50). No additional shielding is required. The cable is connected to the PC using T-connectors.

The distance between two workstations without repeaters can be a maximum of 300 m, and the total distance for a network on a Cheapernet cable is about 1000 m. The Cheapernet transceiver is located on the network board and both for galvanic isolation between adapters and for amplifying the external signal

Fiber optic lines.

The most expensive are optical conductors, also called fiberglass cable. The speed of information dissemination through them reaches several billion bits per second. The permissible distance is more than 50 km. There is virtually no external interference. This is currently the most expensive LAN connection. They are used where electromagnetic interference fields occur or information transmission over very long distances is required without the use of repeaters. They have anti-frizz properties, since the branching technique in fiber optic cables is very complex. The optical conductors are combined into a JIBC using a star connection.

LAN card

Network adapter cards act as the physical interface, or connection, between the computer and the network cable. The cards are inserted into special sockets (expansion slots) of all computers and servers. To provide a physical connection between the computer and the network, a network cable is connected to the corresponding connector, or port, of the board (after its installation). Purpose of the network adapter card:

preparing data coming from a computer for transmission over a network cable

transferring data to another computer

control the flow of data between the computer and the cable system

The network adapter board receives data from the network cable and translates it into a form understandable by the computer's central processor.

The network adapter card consists of hardware and firmware stored in ROM (read-only memory). These programs implement the functions of the logical communication control sublayers and access control to the OSI model link layer environment.

Splitter(HAB)

The splitter serves as the central node in networks with a star topology.

Repeater

When transmitted over a network cable, the electrical signal gradually weakens (attenuates). And, it is distorted to such an extent that the computer ceases to perceive it. To prevent signal distortion, a repeater is used, which amplifies (restores) the weakened signal and transmits it further along the cable. Repeaters are used in networks with a “bus” topology.

There are a number of principles for constructing a LAN based on the components discussed above. Such principles are also called topologies.

Computer network topologies.

Star topology.

The concept of a star network topology comes from the field of mainframe computers, in which the head machine receives and processes all data from peripheral devices as the active processing node. This principle is used in data communication systems, such as RELCOM e-mail. All information between two peripheral workstations passes through the central node of the computer network.

Star topology

Network throughput is determined by the computing power of the node and is guaranteed for each workstation. There are no data collisions.

Cabling is quite simple as each workstation is connected to a node. Cabling costs are high, especially when the central node is not geographically located in the center of the topology.

When expanding computer networks, previously made cable connections cannot be used: a separate cable must be laid from the center of the network to the new workplace.

The star topology is the fastest of all computer network topologies because data transfer between workstations passes through a central node (if it has good performance) over separate lines used only by these workstations. The frequency of requests to transfer information from one station to another is low compared to that achieved in other topologies.

The performance of a computer network primarily depends on the power of the central file server. It can be a bottleneck in the computer network. If the central node fails, the entire network is disrupted.

The central control node - the file server - can implement the optimal protection mechanism against unauthorized access to information. The entire computer network can be controlled from its center.

Ring topology.

With a ring network topology, workstations are connected to one another in a circle, i.e. workstation 1 with workstation 2, workstation 3

Ring topology

with workstation 4, etc. The last workstation is connected to the first. The communication link is closed in a ring.

Laying cables from one workstation to another can be quite complex and expensive, especially if the workstations are geographically located far from the ring (for example, in a line).

Messages circulate regularly in circles. The workstation sends information to a specific destination address, having previously received a request from the ring. Message forwarding is very efficient since most messages can be sent “on the road” over the cable system one after another. It is very easy to make a ring request to all stations. The duration of information transfer increases in proportion to the number of workstations included in the computer network.

The main problem with a ring topology is that each workstation must actively participate in the transfer of information, and if at least one of them fails, the entire network is paralyzed. Faults in cable connections are easily localized.

Connecting a new workstation requires a short-term shutdown of the network, since the ring must be open during installation. There is no limit on the length of a computer network, since it is ultimately determined solely by the distance between two workstations.

Bus topology.

With a bus topology, the information transmission medium is represented in the form of a communication path accessible to all workstations, to which they all must be connected. All workstations can communicate directly with any workstation on the network.

Bus topology

Workstations can be connected to or disconnected from it at any time, without interrupting the operation of the entire computer network. The functioning of a computer network does not depend on the state of an individual workstation.

In a standard situation, an Ethernet bus network often uses a thin cable or a Cheapernet cable with a T-connector. Shutting down and especially connecting to such a network requires a bus break, which disrupts the circulating flow of information and causes the system to freeze.

Tree structure of LAN.

Along with the well-known topologies of computer networks: ring, star and bus, a combined structure, for example a tree structure, is also used in practice. It is formed mainly in the form of combinations of the above-mentioned computer network topologies. The base of a computer network tree is located at the point (root) at which communication lines of information (tree branches) are collected.

Computer networks with a tree structure are used where direct application of basic network structures in their pure form is not possible.

Types of network construction based on information transmission methods.

Local Token Ring Network

This standard was developed by IBM. The transmission medium used is unshielded or shielded twisted pair (UPT or SPT) or optical fiber. Data transfer speed 4 Mbit/s or 16 Mbit/s. The Token Ring method is used as a method for controlling access of stations to the transmitting medium. The main provisions of this method:

devices are connected to the network using a ring topology;

all devices connected to the network can transmit data only after receiving permission to transmit (token);

At any given time, only one station in the network has this right.

Package types.

IBM Token Ring uses three main types of packets:

control/data package (Data/Command Frame);

token (Token);

reset package (Abort).

Management/Data Package. Using such a packet, data or network control commands are transmitted.

Marker. A station can start transmitting data only after receiving such a packet. There can be only one token in one ring and, accordingly, only one station with the right to transmit data.

Reset Pack. Sending such a packet signals the termination of all transmissions.

You can connect computers in a network using a star or ring topology.

Ethernet LAN

The Ethernet specification was proposed by Xerox Corporation in the late seventies. Later, Digital Equipment Corporation (DEC) and Intel Corporation joined this project. In 1982, the Ethernet specification version 2.0 was published. Based on Ethernet, the IEEE 802.3 standard was developed by the IEEE Institute. The differences between them are minor.

Basic operating principles.

At the logical level, Ethernet uses a bus topology:

all devices connected to the network have equal rights, i.e. any station can start transmitting at any time (if the transmitting medium is free);

Data transmitted by one station is available to all stations in the network.

Rules for installing the cable part of a LAN.

10 BaseT

In 1990, IEEE released the 802.3 specification for twisted-pair Ethernet networks. 10 BaseT (10 – transmission speed 10 Mbps, Base – narrowband, T – twisted pair) is an Ethernet network that usually uses unshielded twisted pair (UTP) to connect computers. Most networks of this type are built in the form of a star, but the signal transmission system is a bus, like other Ethernet configurations. Typically, a 10BaseT network splitter acts as a multiport repeater. Each computer connects to the other end of a cable connected to a splitter and uses two pairs of wires: one for receiving and one for transmitting.

The maximum length of a 10BaseT segment is 100 m. The minimum cable length is 2.5 m. A 10BaseT LAN can serve up to 1024 computers.

To build a 10BaseT network use:

RJ – 45 connectors at the ends of the cable,

The distance from the workstation to the splitter is no more than 100 m.

10Base2

According to the IEEE 802.3 specification, this topology is called 10Base2 (10 - 10 Mbps transmission rate, Base - narrowband transmission, 2 - transmission over a distance of approximately twice 100 m (actual distance 185 m).

A network of this type is focused on a thin coaxial cable, or thin Ethernet, with a maximum segment length of 185 m. The minimum cable length is 0.5 m. In addition, there is a limit on the maximum number of computers that can be connected on a 185-meter cable segment - 30 things.

Thin Ethernet cable components:

BNC barrel – connectors (connectors);

BNC T – connectors;

BNC – terminators;

Thin Ethernet networks typically have a bus topology. IEEE standards for thin Ethernet do not require the use of a transceiver cable between the T connector and the computer. Instead, the T-connector is placed directly on the network adapter board.

BNC barrel connector, connecting cable segments, allows you to increase its total length. However, their use should be kept to a minimum as they degrade signal quality.

Thin Ethernet networking is a cost-effective way to implement networks for small office workgroups. The cable used in this type of network is relatively inexpensive, easy to install, and easy to configure. A thin Ethernet network can support up to 30 nodes (computers and printers) per segment.

A thin Ethernet network can consist of a maximum of five cable segments connected by four repeaters, but only three segments can be connected to workstations. Thus, two segments remain reserved for repeaters, they are called inter-repeater links. This configuration is called the 5 – 4 – 3 rule.

10Base5.

According to the IEEE specification, this topology is called 10Base5 (10 - 10 Mbit/s transmission rate, Base - narrowband transmission, 5 - 500 meter segments (5 times 100 meters)). There is another name for it - standard Ethrnet.

Networks on thick coaxial cable (thick Ethrnet) usually use a “bus” topology. Thick Ethrnet can support up to 100 nodes (workstations, repeaters, etc.) per backbone segment. The trunk, or trunk segment, is the main cable to which transceivers with workstations and repeaters connected to them are connected. A thick Ethernet segment can be 500 meters long for a total network length of 2500 meters. The distances and tolerances for thick Ethernet are greater than for thin Ethernet.

Cable system components:

Transceivers. Transceivers, providing communication between the computer and the main LAN cable, are combined with a “vampire tooth” connected to the cable.

Transceiver cables. The transceiver cable (drop cable) connects the cable to the network adapter board.

DIX – connector, or AUI – connector. This connector is located on the transceiver cable.

Topic 3.3: Applications for creating websites

Topic 3.4: Application of the Internet in the economy and information protection

Local computer networks

3.1. Network technologies. Local area networks

3.1.1. Basics of Local Area Networks

Currently, LANs are widely used in enterprises and institutions, the main purpose of which is to provide access to network-wide (information, software and hardware) resources. In addition, LANs allow enterprise employees to quickly exchange information with each other.

LANs are used to solve problems such as:

1. Data distribution. Data in local network stored on a central PC and can be accessed on workstations. In this regard, there is no need to have drives for storing the same information at each workplace.
2. Resource distribution. Peripheral devices can be accessed by all LAN users. Such devices can be, for example, a scanner or laser printer.
3. Distribution of programs. All LAN users can share access to programs that have been centrally installed on one of the computers.

A local area network (LAN) is a connection between multiple PCs using appropriate hardware and software. In local networks, the data transfer speed is high, the protocols are relatively simple compared to the protocols of global networks, and there is no redundancy of communication channels.

Local networks, depending on the administrative relationships between computers, are divided into:

• hierarchical or centralized;
• peer-to-peer.

Local networks, depending on the physical and logical relationships between computers, differ in architecture (Ethernet, Token Ring, FDDI, etc.) and topology (bus, ring, star, etc.).

Local networks implement client-server technology. The server is an object (computer or program) that provides services, and the client is an object (computer or program) that requests the server to provide these services.

In peer-to-peer networks, the server can simultaneously be a client, i.e. use the resources of another PC or the same PC to which it itself provides resources.

A server in hierarchical networks can only be a client of a server more high level hierarchy. Hierarchical networks are called dedicated server networks. The computers that make up a local network are called nodes. Each node can be a server or a workstation.

Peer-to-peer (one-level) local network

A peer-to-peer network is a network of peer computers (workstations), each of which has a unique name and password to log into the computer. A peer-to-peer network does not have a central PC (Fig. 1).

Rice. 1.

In a peer-to-peer network, each workstation can share all of its resources with other workstations on the network. Work station may share some resources, or may not provide any resources to other stations at all. For example, some hardware (scanners, hard drive printers, CD-ROM drives, etc.) connected to individual PCs is shared at all workstations.

Each user of a peer-to-peer network is an administrator on his or her own PC. Peer-to-peer networks are used to network small number of computers– no more than 10-15. Peer-to-peer networks can be organized, for example, using an operating system Windows systems 95, 98, 2000, Windows XP and other OS.

To access the resources of workstations in a peer-to-peer network, you must enter the Network Neighborhood folder by double-clicking the Network Neighborhood icon and select the Show workgroup computers command. After this, the computers that are part of the peer-to-peer network will be displayed on the screen; by clicking on the computer icons you can open logical drives and folders with network-wide resources.

Hierarchical (multi-level) local networks

Hierarchical local networks are local networks in which there are one or more special computers– servers that store information shared between different users. Hierarchical local networks are, as a rule, a LAN with a dedicated server (Fig. 2), but there are also networks with a non-dedicated server. In networks with a non-dedicated server, the functions of the workstation and server are combined. Workstations included in a hierarchical network can simultaneously organize a peer-to-peer local network among themselves.

Rice. 2.

Dedicated servers are usually high-performance computers with hard drives large capacity. A network operating system is installed on the server, everyone connects to it external devices(printers, scanners, hard drives, modems, etc.). Provision of server resources in a hierarchical network is done at the user level.

Each user must be registered by the network administrator under a unique name (login) and users must assign themselves a password under which they will log into the PC and the network. In addition, when users register, the network administrator assigns them the necessary resources on the server and access rights to them.

The computers from which information on the server is accessed are called workstations, or clients. They install a stand-alone operating system and a client part of a network operating system. The local operating systems Windows 95, 98, 2000, Windows XP include the client part of such network operating systems as: Windows NT Server, Windows 2003 Server.

Depending on how the server is used in hierarchical LANs, the following types of servers are distinguished.

File server . In this case, the server contains shared files and shared programs.

Database server. The server hosts a network database. The database on the server can be replenished from various workstations and provide information upon requests from workstations.

Access Server– a dedicated computer on the local network for remote processing of tasks. The server executes the task received from the remote workstation and sends the results to the remote workstation. In other words, the server is designed for remote access(for example, from a mobile PC) to local network resources.

Server - print. A fairly powerful printer is connected to a low-power computer, which can print information from several workstations at once. The software organizes a queue of print jobs.

Mail server . The server stores information sent and received both over the local network and externally via a modem. The user can view the information received in his name or send via mail server your information.

Peer-to-peer and hierarchical local networks have their advantages and disadvantages. The choice of the type of local network depends on the requirements for its cost, reliability, data processing speed, information secrecy, etc.

MINISTRY OF AGRICULTURE
RUSSIAN FEDERATION

Federal State Educational Institution of Higher Professional Education "VORONEZH STATE"
AGRICULTURAL UNIVERSITY NAMED AFTER K.D. GLINKI"

DEPARTMENT OF INFORMATION SUPPORT
AND MODELING OF AGRO-ECONOMIC SYSTEMS

Course work

on the topic "Local computer networks"

completed by: student E-2-1
Bespakhotnykh L.A.

Checked by: Ph.D., Associate Professor
Kulneva. ON THE..

Voronezh
2007

Introduction 4

Theoretical basis organizing local networks 6

1.1 General information about networks 6

1.2 Network topology 11

1.3 Basic exchange protocols in computer networks 14

Software overview 17

1.5 Installation and configuration of network protocols 20

Conclusions and suggestions 24

References 27

Appendix 28

Introduction

Russia's entry into the global information space entails the widespread use of the latest information technologies, and first of all, computer networks. At the same time, the user’s capabilities sharply increase and qualitatively change both in providing services to their clients and in solving their own organizational and economic problems.

It is appropriate to note that modern computer networks are a system whose capabilities and characteristics generally significantly exceed the corresponding indicators of the simple sum of the constituent elements of a network of personal computers in the absence of interaction between them.

The advantages of computer networks have led to their widespread use in information systems credit and financial sphere, government and local governments, enterprises and organizations. Therefore, the purpose of this course work is to become familiar with the basics of building and operating computer networks, to achieve this goal it is necessary to solve a number of problems:

Introduction to computer networks, highlighting their features and differences;

Characteristics of the main methods of constructing networks (network topology);

Familiarity with methods of protection against unauthorized access to network resources;

Brief description of the main network protocols that ensure consistent interaction between users on the network;

Summing up the results of the work and making suggestions on this topic.

When solving problems, the main method is to analyze the literature on this topic.

Theoretical foundations of organizing local networks

1.1General information about networks

Modern production requires high speeds of information processing, convenient forms of its storage and transmission. It is also necessary to have dynamic ways of accessing information, ways of searching for data in given time intervals; implement complex mathematical and logical data processing. Managing large enterprises and managing the economy at the country level require the participation of fairly large teams in this process. Such groups can be located in different areas of the city, in different regions of the country, and even in different countries. To solve management problems that ensure the implementation of economic strategy, the speed and convenience of information exchange, as well as the possibility of close interaction between all those involved in the process of developing management decisions, become important and relevant.

The principle of centralized data processing did not meet the high requirements for the reliability of the processing process, hampered the development of systems and could not provide the necessary time parameters for interactive data processing in multi-user mode. A short-term failure of a centralized computer led to fatal consequences for the system as a whole, since it was necessary to duplicate the functions of the central computer, significantly increasing the costs of creating and operating data processing systems.

The emergence of small computers, microcomputers and personal computers required a new approach to the organization of data processing systems and the creation of new information technologies. A logically justified requirement arose to move from the use of individual computers in centralized data processing systems to distributed data processing, i.e. processing performed on independent but interconnected computers representing a distributed system.

To implement distributed data processing, multi-machine associations were created, the structure of which is developed in one of the following areas:

multi-machine computing systems (MCCs) – a group of computers installed nearby, united using special interface tools and jointly performing the information and computing process;

computer (computer) networks – a set of computers and terminals connected via communication channels into a single system that meets the requirements of distributed data processing.

Computer networks are the highest form of multi-machine associations. The main differences between a computer network and a multi-machine computing complex are highlighted.

The first difference is dimension. A multi-machine computing complex usually includes two, maximum three computers, located mainly in one room. A computer network can consist of tens or even hundreds of computers located at a distance from each other from several meters to thousands of kilometers.

The second difference is the division of functions between computers. If in a multi-machine computing complex the functions of data processing, transmission and system control can be implemented in one computer, then in computer networks these functions are divided between different computers.

The third difference is the need to solve the problem of message routing in the network. A message from one computer to another can be transmitted along different routes depending on the state of the communication channels connecting the computers to each other.

Depending on the territorial location of subscriber systems, computer networks can be divided into three main classes:

global networks (WAN – Wide Area Network);

regional networks (MAN - Metropolitan Area Network);

local networks (LAN – Local Area Network).

A local area network unites subscribers located within a small area. Currently, there are no clear restrictions on the territorial dispersion of subscribers. Typically, such a network is tied to a specific location. The length of such a network can be limited to 2 – 2.5 km.

The main purpose of any computer network is to provide information and computing resources to users connected to it.

From this point of view, a local area network can be considered as a collection of servers and workstations.

Server is a computer connected to a network and providing its users with certain services. Servers can perform data storage, database management, remote job processing, job printing, and a number of other functions that network users may need. The server is the source of network resources.

A workstation is a personal computer connected to a network through which the user gains access to its resources. A network workstation operates in both network and local modes. It is equipped with its own operating system (MS DOS, Windows, etc.) and provides the user with all the necessary tools for solving applied problems.

Computer networks, as mentioned above, implement distributed data processing. Data processing in this case is distributed between two objects: client and server.

Client – ​​a task, workstation or computer network user. During data processing, the client can create a request to the server to perform complex procedures, read files, search for information in a database, etc.

The server defined earlier fulfills the request received from the client. The results of the request are transmitted to the client. The server provides storage of public data, organizes access to this data, and transmits the data to the client.

The client processes the received data and presents the processing results in a form convenient for the user. For such systems, the terms adopted are systems or client-server architecture.

The client-server architecture can be used both in peer-to-peer networks and in networks with a dedicated server.

A peer-to-peer network in which there is no single center for managing the interaction of workstations and no single center for storing data. The network operating system is distributed across workstations. Each network station can perform the functions of both a client and a server. It can service requests from other workstations and forward its own service requests to the network. The network user has access to all devices connected to other stations.

Advantages of peer-to-peer networks:

low cost;

high reliability.

Disadvantages of peer-to-peer networks:

dependence of network efficiency on the number of stations;

complexity of network management;

difficulty in ensuring information security;

difficulties in updating and changing station software.

The most popular are peer-to-peer networks based on the network operating systems LANtastic and NetWare Lite.

In a network with a dedicated server, one of the computers performs the functions of storing data intended for use by all workstations, managing interaction between workstations, and a number of service functions.

Such a computer is usually called a network server. A network operating system is installed on it, and all shared external devices are connected to it - hard drives, printers and modems.

Interaction between workstations on a network is usually carried out through a server.

Advantages of a network with a dedicated server:

reliable information security system;

high performance;

no restrictions on the number of workstations;

ease of management compared to peer-to-peer networks.

Network disadvantages:

high cost due to the allocation of one computer per server;

dependence of performance and reliability on the server;

less flexibility compared to peer-to-peer networks.

Dedicated server networks are the most common among computer network users. Network operating systems for such networks are LANServer (IBM), Windows NT Server versions 3.51 and 4.0, and NetWare (Novell).

1.2Network topology

The topology of a network is determined by the placement of nodes in the network and the connections between them. From the many possible constructions, the following structures are distinguished.

Star topology. Each computer is connected via a network adapter with a separate cable to the unifying device. All messages pass through a central device, which processes incoming messages and forwards them to the desired or all computers (Fig. 1).

A star-shaped structure most often involves the location of a specialized computer or hub in the central node.

Advantages of a “star”:

simplicity of peripheral equipment;

each user can work independently of other users;

high level of data protection;

easy detection of faults in the cable network.

Disadvantages of a "star":

failure of the central device leads to the shutdown of the entire network;

high cost of the central device;

network performance decreases as the number of computers connected to the network increases.

Ring topology. All computers are connected to each other in a ring. Here, network users have equal rights. Information over the network is always transmitted in one direction (Fig. 2). A ring network requires special repeaters, which, having received information, transmit it further as if in a relay race; copy into their memory (buffer) if the information is intended for them; change some service ranks if they are allowed to do so. Information is removed from the ring by the node that sent it.

Advantages of the “ring”:

lack of an expensive central device;

easy search for faulty components;

there is no routing problem;

Network bandwidth is shared among all users, so all users are guaranteed to consistently access the network;

ease of error control.

Disadvantages of the "ring":

it is difficult to connect new computers to the network;

each computer must actively participate in the transfer of information, this requires resources so that there are no delays in the main operation of these computers;

If just one computer or piece of cable fails, the entire network is paralyzed.

Common bus topology. The shared bus is most widely used in local area networks. The “common bus” topology involves the use of one cable (bus), to which all computers on the network are directly connected (Fig. 3). In this case, the cable is used by all stations in turn, i.e. Only one station can occupy the bus at a time. Access to the network (cable) is carried out through competition between users. The network takes special measures to ensure that when working with a common cable, computers do not interfere with each other’s data transfer. Conflicts that arise are resolved by appropriate protocols. Information is transmitted to all stations at once.

Advantages of the “common bus”:

ease of network construction;

the network is easily expanded;

Channel capacity is used efficiently;

reliability is higher, because Failure of individual computers will not disrupt the functionality of the network as a whole.

Disadvantages of the “common bus”:

limited tire length;

there is no automatic confirmation of receiving messages;

the possibility of collisions on the bus when several stations try to transmit information at once;

low data protection;

failure of any section of the cable leads to disruption of the network;

difficulty finding the break point.

Tree topology. This structure allows you to combine several networks, including those with different topologies, or split one large network into a number of subnetworks (Fig. 4).

Partitioning into segments will allow you to select subnetworks within which there is intensive exchange between stations, separate data flows and thus increase the performance of the network as a whole. The connection of individual branches (networks) is carried out using devices called bridges or gateways. The gateway is used when connecting networks with different topologies and various protocols. Bridges connect networks with the same topology, but can convert protocols. The network is divided into subnets using switches and routers.

1.3 Basic exchange protocols in computer networks

To ensure consistent operation in data networks, various data communication protocols are used - sets of rules that the sending and receiving parties must adhere to for consistent data exchange. Protocols are sets of rules and procedures that govern how some communication occurs. Protocols are rules and technical procedures that allow multiple computers, when networked, to communicate with each other.

There are many protocols. And although they all participate in the implementation of communication, each protocol has different goals, performs different tasks, and has its own advantages and limitations.

Protocols operate at different levels of the OSI/ISO open systems interaction model (Fig. 5). The functions of a protocol are determined by the layer at which it operates. Multiple protocols can work together. This is the so-called stack, or set, of protocols.

Just as network functions are distributed across all layers of the OSI model, protocols operate together at different layers of the protocol stack. The layers in the protocol stack correspond to the layers of the OSI model. Taken together, the protocols provide a complete description of the functions and capabilities of the stack.

Data transmission over a network, from a technical point of view, must consist of successive steps, each of which has its own procedures or protocol. Thus, a strict sequence in performing certain actions is maintained.

In addition, all these steps must be performed in the same sequence on each network computer. On the sending computer, actions are performed in a top-down direction, and on the receiving computer, from bottom to top.

The sending computer, in accordance with the protocol, performs the following actions: Breaks the data into small blocks called packets that the protocol can work with, adds address information to the packets so that the receiving computer can determine that this data is intended for it, prepares the data for transmission through the network adapter card and then via the network cable.

The recipient computer, in accordance with the protocol, performs the same actions, but only in reverse order: it receives data packets from network cable; transmits data to the computer via the network adapter card; removes from the packet all service information added by the sending computer, copies the data from the packet into a buffer - to combine it into the original block, transfers this data block to the application in the format that it uses.

Both the sending computer and the receiving computer need to perform each action in the same way so that the data received over the network matches the data sent.

If, for example, two protocols have different ways of breaking up data into packets and adding information (packet sequencing, timing, and error checking), then a computer running one of those protocols will not be able to successfully communicate with a computer running the other protocol. .

Until the mid-80s, most local networks were isolated. They served individual companies and were rarely combined into large systems. However, when local networks reached a high level of development and the volume of information transmitted by them increased, they became components of large networks. Data transmitted from one local network to another along one of the possible routes is called routed. Protocols that support data transfer between networks over multiple routes are called routed protocols.

Among the many protocols, the most common are the following:

IPX/SPX and NWLmk;

Kit OSI protocols.

Each protocol stack will be discussed in more detail in the next chapter.

Software overview

1.4 Authentication and authorization. Kerberos system

Kerberos is a network service designed to centrally solve authentication and authorization problems in large networks. It can run on many popular operating systems. This rather cumbersome system is based on several simple principles.

In networks using Kerberos security, all authentication procedures between clients and servers on the network are performed through an intermediary who is trusted by both parties to the authentication process, with the Kerberos system itself being such an authoritative arbiter.

In a Kerberos system, a client must prove its authenticity to access each service it invokes.

All data exchanges on the network are carried out securely using an encryption algorithm.

The Kerberos network service is built on a client-server architecture, which allows it to work in the most complex networks. The Kerberos client is installed on all computers on the network that can access any network service. In such cases, the Kerberos client, on behalf of the user, transmits the request to the Kerberos server and maintains a dialogue with it necessary to perform the functions of the Kerberos system.

So, in the Kerberos system there are the following participants: Kerberos server, Kerberos client and resource servers (Fig. 6). Kerberos clients try to access network resources - files, applications, printers, etc. This access can be granted, firstly, only to legal users, and secondly, if the user has sufficient authority, determined by the authorization services of the corresponding resource server - file server, application server, print server. However, in a Kerberos system, resource servers are prohibited from “directly” accepting requests from clients, and are only allowed to begin processing a client request when authorized to do so by the Kerberos server. Thus, the client path to a resource in a Kerberos system consists of three stages:

Determining the legality of the client, logical entry into the network, obtaining permission to continue the process of gaining access to the resource.

Obtaining permission to access the resource server.

Obtaining permission to access a resource.

To solve the first and second tasks, the client contacts the Kerberos server. Each of these tasks is solved by a separate server that is part of the Kerberos server. Performing initial authentication and issuing permission to continue the process of gaining access to a resource is carried out by the so-called authentication server (Authentication Server, AS). This server stores information about user IDs and passwords in its database.

The second task, related to obtaining permission to access the resource server, is solved by another part of the Kerberos server - the Ticket-Granting Server (TGS). The receipt server for legal clients performs additional verification and gives the client permission to access the resource server he needs, for which he provides him with an electronic receipt form. To perform its functions, the receipt server uses copies secret keys all resource servers that are stored in its database. In addition to these keys, the TGS server has another secret DES key, which it shares with the AS server.

The third task - obtaining permission to access the resource directly - is solved at the resource server level.

When studying the rather complex mechanism of the Kerberos system, one cannot help but wonder: what effect do all these numerous encryption and key exchange procedures have on network performance, what part of the network resources do they consume and how does this affect it? bandwidth?

The answer is quite optimistic - if Kerberos is implemented and configured correctly, it will slightly reduce network performance. Because receipts are reused, the network resources spent on receipt requests are small. Although the transmission of a receipt during login authentication reduces some throughput, such an exchange should be carried out when using any other authentication systems and methods. Additional costs are insignificant. Experience with implementing the Kerberos system has shown that response times with Kerberos installed do not differ significantly from response times without it - even in very large networks with tens of thousands of nodes. This efficiency makes Kerberos very promising.

Among vulnerabilities Kerberos systems can be called a centralized storage of all secret keys of the system. A successful attack on a Kerberos server, which contains all the information critical to the security system, leads to the collapse of the information protection of the entire network. An alternative solution could be a system built on the use of pairwise key encryption algorithms, which are characterized by distributed storage of secret keys.

Another weakness of the Kerberos system is that the source code of those applications accessed through Kerberos must be modified accordingly. This modification is called “kerberization” of the application. Some vendors sell "kerberized" versions of their applications. But if there is no such version and no source code, then Kerberos cannot provide access to such an application.

1.5 Installation and configuration of network protocols

As mentioned above, among the many protocols, the most common ones can be identified.

NetBEUI is an extended NetBIOS interface. Initially, NetBEUI and NetBIOS were closely related and considered as one protocol, then manufacturers separated them and now they are considered separately. NetBEUI is a small, fast and efficient transport layer protocol that comes with all Microsoft networking products. NetBEUI's advantages include small stack size, high data transfer speeds, and compatibility with all Microsoft networks. The main disadvantage is that it does not support routing, this limitation applies to all Microsoft networks.

The Xerox Network System (XNS) was developed by Xerox for its Ethernet networks. Its widespread use began in the 80s, but gradually it was replaced by the TCP/IP protocol. XNS is a large and slow protocol, and it also uses a significant number of broadcast messages, which increases network traffic.

The OSI protocol suite is a complete protocol stack, where each protocol corresponds to a specific layer of the OSI model. The suite contains routing and transport protocols, the IEEE Project 802 series of protocols, the session layer protocol, the presentation layer protocol, and several protocols. application level. They provide full network functionality, including file access, printing, etc.

Particular attention should be paid to the IPX/SPX protocol stack. This stack is the original Novell protocol stack, which it developed for its NetWare network operating system back in the early 80s. The Internetwork Packet Exchange (IPX) and Sequenced Packet Exchange (SPX) protocols, which give the stack its name, are direct adaptations of Xerox's XNS protocols, which are much less common than IPX/SPX. In terms of installations, IPX/SPX protocols are the leaders, and this is due to the fact that the NetWare OS itself occupies a leading position with a share of installations worldwide of approximately 65%.

The Novell protocol family and their correspondence to the ISO/OSI model are presented in Fig. 7

At the physical and data link levels, Novell networks use all popular protocols of these levels (Ethernet, Token Ring, FDDI and others).

At the network level, the Novell stack runs the IPX protocol, as well as the RIP and NLSP routing information exchange protocols. IPX is a protocol that deals with addressing and routing packets on Novell networks. IPX routing decisions are based on the address fields in its packet header as well as information from routing information exchange protocols. For example, IPX uses information provided by either RIP or NLSP (NetWare Link State Protocol) to forward packets to the destination computer or the next router. The IPX protocol supports only the datagram method of message exchange, due to which it economically consumes computing resources. So, the IPX protocol provides three functions: setting an address, establishing a route, and sending datagrams.

The transport layer of the OSI model in the Novell stack corresponds to the SPX protocol, which carries out connection-oriented message transfer.

The NCP and SAP protocols operate at the upper application, representative and session levels. NCP (NetWare Core Protocol) is a protocol between the NetWare server and the workstation shell. This application layer protocol implements the client-server architecture at the upper layers of the OSI model. Using the functions of this protocol, the workstation connects to the server, maps the server directories to local drive letters, scans the server file system, copies remote files, changes their attributes, etc., and also shares a network printer between workstations.

SAP (Service Advertising Protocol) - service advertising protocol - is conceptually similar to the RIP protocol. Just as RIP allows routers to exchange routing information, SAP allows network devices to exchange information about available network services.

Servers and routers use SAP to advertise their services and network addresses. The SAP protocol allows network devices to constantly update information about what services are currently available on the network. At startup, servers use SAP to notify the rest of the network about their services. When a server shuts down, it uses SAP to notify the network that its services have ceased.

On Novell networks, NetWare 3.x servers send out SAP broadcast packets every minute. SAP packets significantly clog the network, so one of the main tasks of routers that access global communications is to filter traffic from SAP packets and RIP packets.

The features of the IPX/SPX stack are due to the features of the NetWare OS, namely the orientation of its early versions to work in local networks small sizes, consisting of personal computers with modest resources. Therefore, Novell needed protocols that required a minimum amount of RAM and that would run quickly on low-power processors. As a result, the IPX/SPX stack protocols until recently worked well in local networks and not so well in large corporate networks, since they overloaded slow global links with broadcast packets that are intensively used by several protocols in this stack (for example, to establish communications between clients and servers).

This circumstance, as well as the fact that the IPX/SPX stack is the property of Novell and requires a license to implement it, has for a long time limited its distribution only to NetWare networks. However, by the time NetWare 4.0 was released, Novell had made and continues to make major changes to its protocols aimed at adapting them to work in corporate networks. Now the IPX/SPX stack is implemented not only in NetWare, but also in several other popular network operating systems - SCO UNIX, Sun Solaris, Microsoft Windows NT.

Conclusions and offers

Based on the results of the work done, we can give a brief description of the organization of local networks.

Firstly, local networks implement distributed information processing; accordingly, processing is distributed among all computers on the network, which allows increasing computer performance.

Secondly, local networks come in two types:

A peer-to-peer network in which there is no single center for managing the interaction of workstations and no single center for storing data.

A network with a dedicated server, i.e. The server performs the functions of storing information, managing interactions within the network, and a number of service functions.

Thirdly, according to their structure, the entire variety of networks can be divided into the following types:

star topology, i.e. Each computer is connected via a network adapter with a separate cable to the unifying device. All messages pass through a central device, which processes incoming messages and forwards them to the desired or all computers

“ring” topology, i.e. all computers are connected in series, and information is transmitted in one direction, passing through each network node;

“common bus” topology, i.e. all computers are connected to a common bus (cable);

The tree topology allows you to combine networks with different topologies.

Fourthly, to ensure consistent operation within the network, protocols are used - this is a set of rules that regulate order in the network at different levels of interaction. The main protocol stacks were reviewed and a brief description of them was given.

Fifthly, the Kerberos system was considered, which, through authentication, provides protection against unauthorized access to the network and use of its resources.

As a conclusion of all the work, we can say that a local network is not just a mechanical sum of personal computers, it significantly expands the capabilities of users. Computer networks at a qualitatively new level make it possible to provide the following basic characteristics:

maximum functionality, i.e. suitability for most different types operations,

integration, which consists in concentrating all information in a single center,

efficiency of information and management, determined by the possibility 24/7 work in real time,

functional flexibility, i.e. the ability to quickly change system parameters,

developed infrastructure, i.e. prompt collection, processing and presentation to a single center of all information from all departments,

minimized risks through comprehensive security of information that is exposed to accidental and intentional threats.

The last point is very important, since the network may contain data that can be used during competition, but, in general, if security is at the proper level, local networks become simply necessary in modern economic and management conditions.

List of used literature

Gerasimenko V.G., Nesterovsky I.P., Pentyukhov V.V. and others. Computer networks and means of their protection: Textbook / Gerasimenko V.G., Nesterovsky I.P., Pentyukhov V.V. and others - Voronezh: VSTU, 1998. - 124 p.

Kamalyan A.K., Kulev S.A., Nazarenko K.N. etc. Computer networks and information security tools: Tutorial/Kamalyan A.K., Kulev S.A., Nazarenko K.N. and others - Voronezh: VSAU, 2003.-119p.

Kurnosov A.P. Workshop on Informatics/Ed. Kurnosova A.P. Voronezh: VSAU, 2001.- 173 p.

Makarova N.V. Informatics /ed. Prof. N.V. Makarova. - M.: Finance and Statistics, 1997. - 768 p.: ill.

Malyshev R.A. Local computer networks: Textbook / RGATA. – Rybinsk, 2005. – 83 p.

Olifer V.G., Olifer N.A. Network operating systems/ V.G. Olifer, N.A. Olifer. – St. Petersburg: Peter, 2002. – 544 p.: ill.

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

Simonovich S.V. Informatics. Basic course/Simonovich S.V. and others - St. Petersburg: Peter Publishing House, 2000. - 640 pp.: ill.

PART 1

BASICS OF BUILDING COMPUTER NETWORKS

BASIC CONCEPTS

A computer network is a collection of nodes (computers, terminals, peripheral devices) that have the ability to information interaction with each other using special communication equipment and software. The sizes of networks vary widely - from a couple of interconnected computers standing on neighboring tables, to millions of computers scattered around the world (some of them may be located in space objects). Based on the breadth of coverage, networks are divided into several categories. Local area networks, LAN or LAN(Local-Area Network), allow you to connect computers located in a limited space. For local networks, as a rule, a specialized cable system is laid, and the position possible points subscriber connections are limited to this cable system. Sometimes in local networks they use wireless communication(wireless), but even at the same time the possibilities of moving subscribers are very limited. Local networks can be combined into larger-scale formations - CAN(Campus-Area Network - campus a network that connects local networks of nearby buildings), MAN(Metropolitan-Area Network - city-scale network), WAN(Wide-Area Network) GAN(Global-Area Network - global network). The network of networks in our time is called the global network - the Internet. For more large networks special wired or wireless lines communication or the infrastructure of existing public communication means is used. In the latter case, computer network subscribers can connect to the network at relatively arbitrary points covered by a telephony, ISDN or cable television network.

Concept intranet(intranet) refers to the internal network of an organization, where two points are important: 1) isolation or protection of the internal network from the external one (Internet); 2) use of the IP network protocol and Web technologies (application HTTP protocol). In the hardware aspect, the use of intranet technology means that all network subscribers mainly exchange data with one or more servers on which the main information resources of the enterprise are concentrated.

Networks use various network technologies, of which the most common in local networks are Ethernet, Token Ring, l00VG-AnyLAN, ARCnet, FDDI, discussed in Chapters 6-9. WANs use other technologies, briefly discussed in Chapters 10 and 11. Each technology has its own types of equipment.

Network equipment is divided into active - computer interface cards, repeaters, hubs, etc. and passive - cables, connectors, patch panels, etc. In addition, there are auxiliary equipment - uninterruptible power supply devices, air conditioning devices and accessories - mounting racks, cabinets, cable ducts of various types. From a physics point of view, active equipment is a device that requires energy to generate signals; passive equipment does not require energy.

Computer network equipment is divided into end systems (devices) that are sources and/or consumers of information, and intermediate systems that ensure the passage of information through the network. TO end systemsES(End Systems), include computers, terminals, network printers, fax machines, cash registers, barcode readers, voice and video communications and any other peripheral devices equipped with one or another network interface. TO intermediate systemsIS(Intermediate Systems), include hubs (repeaters, bridges, switches), routers, modems and other telecommunications devices, as well as the cable and/or wireless infrastructure connecting them.

The activity that is “useful” to users is the exchange of information between end devices. The flow of information transmitted over a network is called network traffic. Traffic except useful information includes its service part - inevitable overheads to organize the interaction of network nodes. Bandwidth communication lines, also called bandwidth(bandwidth), defined as the amount of information passing through the line per unit of time. Measured in bit/s (bps - bit per second), kbit/s (kbps), Mbit/s (Mbps), Gbit/s (Gbps), Tbit/s (Tbps)... Here, as a rule, the prefixes are kilo -, mega-, giga-, tera - have a decimal value (103, 106, 109, 1012) rather than a binary value (210, 220, 230, 240). For active communication equipment, the concept applies performance, and in two various aspects. In addition to the “gross” amount of unstructured information transmitted by the equipment per unit of time (bit/s), they are also interested in the speed of processing packets (pps - packets per second), frames (fps - frames per second) or cells (cps - cells per second). Naturally, the size of the structures (packets, frames, cells) for which the processing speed is measured is also specified. Ideally, the performance of communications equipment should be so high that it provides information processing, arriving at all interfaces (ports) at their full speed (wire speed).

To organize information exchange, a set of software and hardware must be developed, distributed across different network devices. At first, developers and suppliers of networking tools tried to follow their own path, solving the whole range of problems using their own set of protocols, programs and equipment. However, solutions from different vendors turned out to be incompatible with each other, which caused a lot of inconvenience for users who, for various reasons, were not satisfied with the set of capabilities provided by only one of the vendors. As technology develops and the range of services provided expands, there is a need to decomposition network task - breaking it down into several interrelated subtasks with defining the rules of interaction between them. Task breakdown and standardization protocols allows you to take part in its decision a large number parties - developers of software and hardware, manufacturers of communication and auxiliary (for example, test) equipment and installers, who bring all these fruits of progress to end consumers. The use of open technologies and adherence to generally accepted standards allows us to avoid the effect Babylonian pandemonium. Of course, at some point the standard becomes a brake on development, but someone makes a breakthrough, and his new proprietary technology eventually develops into a new standard.

This chapter will define the basic concepts needed to describe specific network technologies and types of active equipment.

1.1. Basic model open systems interactionsOSI

ISO has developed an open systems interconnection model to describe how network devices communicate. BOS -OSI(Open System Interconnection). It is based on level protocols, which allows us to provide:

· logical decomposition of a complex network into observable parts - levels;

standard interfaces between network functions;

· symmetry in relation to the functions implemented in each network node (similarity of functions of the same level in each network node);

4. Transport layer(transport layer) is responsible for transmitting data from source to recipient with the quality level (throughput, transmission delay, reliability level) requested by the session layer. If the data blocks transmitted from the session layer are larger than the allowed packet size for a given network, they are broken into several numbered packets. At this level, transmission paths are determined, which may be different for neighboring packets. At the receiving end, packets are collected and transmitted in the proper sequence to the session layer (in a large routed network, packets may reach the receiver out of the order in which they were transmitted, and may be duplicated and lost).

The transport layer is border and connecting between the upper layers, which are highly dependent on applications, and the lower ones (subnet layers - layers below the transport layer), tied to a specific network. Relative to this boundary, they are determined IS - intermediate systems that provide packet transmission between source and destination using lower layers, and ES - end systems operating at upper levels.

Lower layers may or may not provide reliable transmission, in which the recipient is handed an error-free packet or the sender is notified that the transmission could not be transmitted.

The lower levels of service can be connection oriented. In this case, at the beginning of communication, a connection is established between the source and the receiver, and transmission can proceed without numbering the packets, since each of them follows its predecessor along the same path. When the transfer is completed, the connection is terminated. Connectionless communication requires numbering of packets, since they can be lost, repeated, or received out of order. Transport layer protocols depend on the service of lower layers:

· TRO...TP4 (Transport Protocol Class 0...4) - classes of protocols of the OSI model, focused on various types of lower-level services.

· TCP (Transmission Control Protocol) - connection-based data transfer protocol.

· UDP (User Datagram Protocol) is a connectionless data transfer protocol.

· SPX (Sequenced Packet Exchange) - Novell NetWare connection-based data transfer protocol.

3. Network layer(network layer) formats the transport layer data and supplies it with the information necessary for routing (finding a path to the recipient). The level is responsible for addressing (translation of physical and network addresses, ensuring internetworking); finding a path from a source to a destination or between two intermediate devices; establishing and maintaining logical connections between nodes to establish both connection-oriented and non-connection-oriented communications. Data formatting is carried out in accordance with communication technology(local networks, global networks). Examples of network layer protocols:

· ARP (Address Resolution Protocol) - mutual conversion of hardware and network addresses.

IP ( Internet Protocol) - datagram delivery protocol, the basis of the TCP/IP stack.

· IPX (Internetwork Packet Exchange) - the basic NetWare protocol responsible for addressing and routing packets, providing service for SPX.

2. Link layer(data link layer), also called the data link layer. Provides the formation of frames - frames transmitted through the physical layer, error control and data flow control. The data link layer is designed to hide details from higher-ups technical implementation networks (for local networks, for example, the network layer will not “see” the differences between Ethernet, Token Ring, ARCnet, FDDI).

IEEE in its network model 802 introduced an additional division link layer on 2 sublevel(sublayers):

· SublevelLLC(Logical-Link Control) is a standard (IEEE 802.2) interface with a network layer independent of network technology.

· SublevelMAC(Media Access Control - media access control) provides access to the level of physical coding and signal transmission. Applied to Ethernet technologies The MAC layer of the transmitter arranges the data coming from the LLC into frames suitable for transmission. Next, waiting for the channel (transmission medium) to become free, it transmits the frame to the physical layer and monitors the result of the work physical level. If the frame is transmitted successfully ( collisions no), it reports this to the LLC sublayer. If a collision is detected, it retries the transmission several times and, if the transmission still fails, reports this to the LLC sublayer. On the receiving side, the MAC layer receives the frame, checks it for errors (if only all network adapters did this honestly!) and, freeing it from the service information of its layer, transmits it to the LLC.

1. Physical layer(physical layer) - the lower level that provides physical coding frame bits into electrical (optical) signals and transmitting them over communication lines. Defines the type of cables and connectors, pin assignments, and physical signal format.

Examples of physical layer specifications:

· EIA/TIA-232-D - revision and expansion of RS-232C (V.24+V.28), 25-pin connector and serial synchronous/asynchronous communication protocol.

· IEEE 802.5 defining physical connection for Token Ring.

· IEEE 802.3, which defines types of Ethernet (10 Mbit/s). Here the physical level is divided into 4 more sublevels:

1. PLS(Physical Layer Signaling) - signals for the transceiver cable;

2. AUI(Attachment Unit Interface) - transceiver cable specifications (AUI interface);

3. RMA(Physical Medium Attachment) - transceiver functions;

4. MDI(Medium Dependent Interface) - specifications for connecting the transceiver to a specific type of cable (IOBase5, IOBase2).

Network technology (in relation to local networks, these are all types of Ethernet, Token Ring, ARCnet, FDDI) covers channel and physical

model level. Intermediate systems (devices) are described by protocols of several levels, starting from the 1st and reaching the 3rd and sometimes 4th levels.

IN real networks Various protocol stacks are used, and it is not always possible to practically separate systems into layers of the OSI model with the ability for applications to access each of them. To improve productivity, the number of levels is reduced to 3-4, combining the functions of adjacent levels (at the same time, the share of overhead to cross-layer interfaces). However, correlating functional modules with model levels helps to understand the possibilities of interaction between heterogeneous systems. With all the variety of approaches to implementing the upper levels of stacks, standardization at the physical, data link and network levels is observed quite strictly. The need to ensure compatibility of network devices from different manufacturers, without which they market position unstable.

1.2. StandardsIEEE802.x

The IEEE 802.1-802.12 group of standards and working group reports primarily refers to the lower layers of the networking model. Some of these standards formed the basis for similar specifications ISO 8802.1-8802.11. The structure of these standards is illustrated in Fig. 1.2.

LLC MAC Physical

Rice. 1.2. Structure of 802.x standards

802.1 standards group refers to the management of network devices at the hardware level, as well as to the provision of internetworking. These include:

· 802.1d - bridge/switch operation logic; Spanning Tree algorithm, which eliminates loops in redundant connections of Ethernet switches.

· 802.1h - broadcast bridge (between different technologies, for example Ethernet-Token Ring).

· 802.1p - additions to the logic of MAC bridges of local networks and MAN, providing traffic prioritization and dynamic filtering of group traffic broadcasting. Relies on additional frame fields introduced in 802.Q.

· 802.1Q - construction of virtual local networks, VLAN (VLAN), using bridges. Here, an extension of the Ethernet frame format (tagged frames) is defined, which is used to mark whether a frame belongs to an overhead network and for other purposes (traffic prioritization).

802.2 standard describes the operation of the LLC sublayer, under which local network technologies are combined (see Fig. 1.2), including FDDI technology, standardized by ANSI. The LLC sublayer provides three types of service:

LLCI - without establishing a connection or confirmation.

· LLC2 - with connection establishment and confirmation.

LLC3 - without establishing a connection, with confirmation.

End systems can support multiple types of service. Class 1 devices support only LLCI, class II - LLCI and LLC2, class III - LLCI and LLC3, class IV - all three types.

LLC sublayer frames have a unified format and contain the following fields:

· DSAP (Destination Service Access Point - destination service access point), 1 byte.

· SSAP (Source Service Access Point), 1 byte.

· Control specifies the LLC frame type.

· Data - a field for storing data from upper-level protocols (may be absent in some frames).

The DSAP and SSAP fields identify the upper-level protocol that uses the LLC service, and the receiving party uses them to determine where to send the received frame. Together with the Control field, they form the LLC frame header.

Standard 8023 describes the physical layer and MAC sublayer of technology with the CSMA/CD access method: Ethernet, Fast Ethernet (802.3u), Gigabit Ethernet(802.3z and 802.3ab), full duplex flow control (802.3x). They are described in detail in Chapter 6.

802.4 standard describes the physical layer and MAC sublayer of the technology with bus topology and token passing. This class includes the MAP (Manufacturing Automation Protocol) protocol for connecting industrial automation devices and Token Bus technology. ARCnet networks using the same access method are not subject to the 802.4 standard.

802.5 standard describes the physical layer and MAC sublayer of a technology with a ring topology and access token passing. It corresponds to IBM's Token Ring technology (see Chapter 7).

802.6 standard refers to urban-scale networks MAN (Metropolitan-Area Network), the nodes of which are scattered over distances of more than 5 km.

802.7 is the report of a technical meeting on broadband transmission.

802.8 refers to fiber optic technology used in networks defined by 802.3-802.6.

802.9 refers to integrated voice and data communications. The specifications are ISDN compatible.

802.10 relates to the security (confidentiality) of networks: data encryption, network management for architectures compatible with the OSI model. Sometimes the ideas of this specification are used to build virtual local networks (to transmit information about belonging to a specific VLAN).

802.11 refers to wireless (wireless) data transmission technologies (see 12.6).

802.12 standard defines a transmission technology with the Demand Priority access method. The l00VG-AnyLAN technology works using this method and in accordance with this standard (see 9.1).

1.3. Classification of topological network elements

Local networks consist of end devices and intermediate devices connected by a cable system. Let's define some basic concepts.

Network nodes(nodes) - end devices and intermediate devices endowed with network addresses. Network nodes include computers with a network interface that act as workstations, servers, or both; network peripheral devices (printers, plotters, scanners); network telecommunication devices (modem pools, shared modems); routers.

· Cable segment- a piece of cable or a chain of pieces of cables electrically (optically) connected to each other, providing a connection between two or more network nodes. Sometimes, in relation to a coaxial cable, this is also the name for a section of cable terminated with connectors, but we will use the broader interpretation given above.

· Network segment(or simply a segment) is a collection of network nodes using a common (shared) transmission medium. In relation to Ethernet technology, this is a set of nodes connected to one coaxial cable segment, one hub (repeater), as well as to several cable segments and/or hubs interconnected by repeaters. In relation to Token Ring, this is one ring.

· Net(logical) - a set of network nodes that have a unified third-level addressing system of the OSI model. Examples would be IPX network, IP network. Each network has its own own address, these addresses are used by routers to transmit packets between networks. The network can be divided into subnets, but this is a purely organizational division with addressing at the same third level. A network can consist of many segments, and the same segment can be part of several different networks.

· Cloud(cloud) - a communication infrastructure with homogeneous external interfaces, the details of the organization of which are not interested. An example of a cloud would be city-long-distance-international telephone network: anywhere you can connect a telephone and contact any subscriber.

According to the method of using cable segments, they are distinguished:

· Point-to-point connections(pomt-to-point connection) - between two (and only two!) nodes. For such connections, symmetrical electrical (twisted pair) and optical cables are mainly used.

· Multipoint connections(multi point connection) - more than two nodes are connected to one cable segment. A typical transmission medium is an unbalanced electrical cable (coaxial cable); other cables, including optical ones, can also be used. Connecting devices with cable segments one after another is called daisy chaining. It is possible to connect multiple devices to one piece of cable using the tap method.

Communication between end nodes connected to different cable and logical segments is provided by intermediate systems - active communication devices. These devices have at least two ports (interfaces). Based on the OSI model layers they use, these devices are classified as follows:

· Repeater(repeater) - a physical layer device that allows you to overcome the topological limitations of cable segments. Information is transmitted from one cable segment to another bit by bit, no information analysis is performed.

· Bridge(bridge) - a means of combining network segments that provides transmission personnel from one segment to another (others). A frame coming from one segment can be forwarded to another or filtered. The decision to forward (transfer to another segment) or filter (ignore) a frame is made based on level 2 information:

1. BridgeMAC-sublevel(MAC Bridge) allows you to combine network segments within one technology.

2. BridgeLLC-sublevel(LLC Bridge), also known as a translating bridge, allows you to combine network segments with different technologies(For example, Ethernet-Fast Ethernet, Ethernet-Token Ring, Ethernet-FDDI).

For network nodes, the bridge can be “transparent”; the presence of such a bridge does not in any way affect the actions of the nodes. The bridge itself determines whether and in which frame it is necessary to transfer a frame from one segment to another. Transparent bridges are characteristic of Ethernet technology. In contrast to transparent ones, there are also source routing bridges (SRB - Source Routing Bridge). To use these bridges, the source of the frame must specify the transmission route. SRB bridges are specific to Token Ring. A combination of these frame routing methods is also possible (see 7.5). In the forwarded frame, the bridge can only modify information of the second level; it is not interested in the third level. Based on second-level information, the bridge can perform filtering according to administratively defined rules.

A bridge can be local, remote, or distributed. Local bridge- a device with two or more interfaces to which connected segments of local networks are connected. Remote bridges connect network segments that are significantly distant from each other through a communication line. To connect remote segments, bridges are installed in pairs, with a device at each end of the line. Distributed Bridge is a set of interfaces of some communication cloud to which segments of the connected networks are connected.

· Switch(switch) of the second level (MAC and LLC) performs functions similar to those of bridges, but is used for segmentation - partitioning networks into small segments in order to increase throughput. Smart switches are used to build VLANs (VLAN - Virtual LAN, virtual local area networks). When microsegmentation(a microsegment containing just one node is connected to each port), the switch must forward every frame received by each port to the other port(s), which places high demands on its performance.

· Router(router) operates at layer 3 and is used for transmission packages between networks. Routers are oriented towards a specific protocol stack (TCP/IP, IPX/SPX, AppleTalk); Multiprotocol routers can serve multiple protocols. According to the rules of the protocol used, the router modifies some fields of the Layer 3 header in forwarded packets. The router performs filtering based on Layer 3 (and higher) information. Unlike repeaters and bridges/switches, the presence of a router is known to hosts on the networks connected to its interfaces. Each router port has its own network address, nodes send packets destined for nodes on other networks to this address.