Local networks (LAN computers) unite a relatively small number of computers (usually from 10 to 100, although much larger ones are occasionally found) within one room (educational computer class), building or institution (for example, a university). The traditional name - local area network (LAN) - is rather a tribute to those times when networks were mainly used to solve computing problems; today in 99% of cases we're talking about exclusively about the exchange of information in the form of texts, graphic and video images, numerical arrays. The usefulness of drugs is explained by the fact that from 60% to 90% of the information an institution needs circulates within it, without needing to go outside.

The development of drugs was greatly influenced by the creation automated systems enterprise management (ACS). ACS include several automated workstations (AWS), measuring systems, and control points. Another important field of activity in which drugs have proven their effectiveness is the creation of educational classes computer technology(KUVT).

Due to the relatively short lengths of communication lines (usually no more than 300 meters), information can be transmitted via LAN to digital form With high speed transfers. At long distances, this transmission method is unacceptable due to the inevitable attenuation of high-frequency signals; in these cases, it is necessary to resort to additional technical (digital-to-analog conversions) and software (error correction protocols, etc.) solutions.

A characteristic feature of the LAN is the presence of a high-speed communication channel connecting all subscribers for transmitting information in digital form. There are wired and wireless channels. Each of them is characterized by certain values ​​of parameters that are essential from the point of view of drug organization:

• * data transfer speeds;
• * maximum length lines;
• * noise immunity;
• * mechanical strength;
• * convenience and ease of installation;
• * cost.

Territorial distribution networks

Geographically distributed networks provide the same benefits as local ones, but at the same time allow them to cover a larger area. By embedding WAN functionality into core local networks, implemented using a modem or server remote access, you can profitably use external communication technologies. Including:

Sending and receiving messages using electronic mail (e-mail); access to the Internet.

The Internet is a huge public global network, connecting users around the world with repositories of data, images and sound. The rapidly expanding Internet is playing an increasingly important role in business.

Today, the main functions of the Internet remain Email and exchange of information between interest groups and researchers. Networks are becoming more powerful, and an increasing number of companies, their potential customers and suppliers, are connecting to the Internet.

Any computer network is characterized by: topology, protocols, interfaces, network hardware and software.

Introduction

• 1. Types of Internet connection
• 2. Network protocols, used on the Internet
• 3. IP addressing system
• 4. Programs for working on the Internet
• 5. World Wide Web-- The World Wide Web
• 6. FTP - file transfer
• 7. Usenet newsgroups

Lecture 1. Introduction to local networks

Duration 2 hours.

The purpose of this topic is to provide basic understanding of the construction, organization and use of computer networks.

Theoretical material

• 1. Purpose, principles of organizing computer networks. network hardware
• 2. Seven-level OSI model, concept of protocol, message transmission in the network
• 3. Client-server technology

Purpose, principles of organizing computer networks. network hardware

Computer network - is a system distributed processing information consisting of at least two computers interacting with each other using special means communications.

Or in other words, a network is a collection of PCs and other computing devices such as printers, fax machines and modems connected to each other. The network enables individuals in an organization to interact with each other and access shared resources; allows them to access data stored on personal computers V remote offices, and establish relationships with suppliers.

Computers on the network perform the following functions:

Organization of network access

Information transfer control

Providing computing resources and services to network subscribers.

Types of computer networks.

Local and geographically distributed networks

A local area network (LAN) links PCs and printers, usually located in the same building (or complex of buildings). A wide area network (WAN) connects several local networks that are geographically distant from each other.

The local network

Local area networks (LANs), the most basic form of networking, connect a group of PCs together or link them to more powerful computer, acting as a network server (see figure). All PCs on the local network can use specialized applications, stored on a network server, and work with shared devices: printers, faxes and other peripherals. Each PC on a local network is called a workstation or network node.

Local networks allow individual users to communicate with each other easily and quickly. Here are just some of the tasks that LS allows you to perform:

collaboration with documents;

simplification of document flow: you get the opportunity to view, correct and comment on documents without leaving your workplace, without organizing time-consuming meetings;

saving and archiving your work on a server so as not to use up valuable space on your PC hard drive;

easy access to applications on the server;

making it easier for organizations to share expensive resources such as printers, CD-ROM drives, hard disks and applications (eg word processors or software databases).

Wide Area Networks

Wide-area networks provide the same benefits as local networks, but at the same time allow them to cover a larger area. This is usually done using a switched telephone network. common use(PSTN, Public Switched Telephone Network) with a connection via modem or high-speed digital network lines providing comprehensive services (ISDN, Integrated Services Digital Network). ISDN lines are often used to transfer large files, such as those containing graphic images or video.

By integrating WAN functionality into core local networks, implemented using a modem or remote access server, you can profitably use external communications technologies, including:

sending and receiving messages using electronic mail (e-mail);

access to the Internet.

The Internet is a huge public global network that connects users around the world with repositories of data, images and sound. Expanding rapidly (about 200% per year), the Internet is playing an increasingly important role in business.

Today, the main functions of the Internet remain e-mail and the exchange of information between interest groups and researchers. Networks are becoming more powerful, and more and more companies and individual users are connecting to the Internet. The Internet serves as a link between companies, their potential customers and suppliers. Today, the Internet can support evolving voice and video applications, such as distance learning and remote diagnosis or treatment, providing Internet-based education and medical care to virtually any family or business.

Any computer network is characterized by: topology, protocols, interfaces, network hardware and software.

Topology - computer network reflects the structure of connections between its main functional elements.

Network technical means- This various devices, ensuring the integration of computers into a single computer network.

Network software- manage the operation of the computer network and provide an appropriate interface with users.

Protocols - represent the rules of interaction functional elements networks.

Interfaces are means of connecting functional elements of the network. It should be noted that functional elements can act as individual devices, so software modules. Accordingly, a distinction is made between hardware and software interfaces.

Basic network topologies.

When creating a network, depending on the tasks it will need to perform, one of three network topologies can be implemented.

Bus topology.

Workstations are connected to a common backbone /bus/ (cable) using network adapters. Others are connected to the common line in the same way. network devices. During network operation, information from the transmitting station arrives at the adapters of all workstations, however, it is perceived only by the adapter of that one workstation to whom it is addressed.

Star topology.

Characterized by the presence of a central switching node - a network server to or through which all messages are sent.

Ring topology.

It is characterized by the presence of a closed data transmission channel in the form of a ring or loop. In this case, information is transmitted sequentially between workstations until it is accepted by the recipient and then removed from the network. The disadvantage of this topology is its sensitivity to channel damage.

Network technical means.

Basic components and technologies associated with local or wide area network architectures may include:

Hardware

Network interface cards (NIC, Network Interface Card)

Hubs

Switches

Routers (Wide Area Networks)

Remote access servers (wide-area networks)

Modems (Wide Area Networks)

Structured Cabling Solutions

Structured Wiring System A plan for constructing a cabling system based on modular subsystems and specifying consistent cabling rules and materials.

Old LANs use a bus architecture - all PCs on the network are connected to one long coaxial cable. This organization limits the ability of the company's employees to move within the network. Structured cabling uses a star configuration - a separate segment of low-cost cable connects each user's computer to a central hub (or switch if the network carries large amounts of data). In this case, moving an employee or adding a new user is much easier and less expensive. The employee's new workstation is already cabling, and the user can be moved to a different network segment by simply plugging the end of the cable into a different port on the hub or switch.

Data over the cable is transmitted in the form of packets sent from one network device to another. There are several types of cables, each of which has its own advantages.

twisted pair

Cable type " twisted pair"(TP, Twisted Pair) comes in two types: shielded twisted pair (STP, Shielded Twisted Pair) and unshielded twisted pair (UTP, Unshielded Twisted Pair). Both types of cable consist of a pair of twisted copper wires. Unshielded twisted pair cable has become most popular due to its low cost, flexibility and ease of installation. The only drawback of such a cable is its vulnerability to electrical interference and "noise" on the line. Twisted pair cables come in different categories (3, 4 or 5). The higher the category number, those higher speed transmission supports cable.

Thin and thick coaxial cable

These cable types are similar to standard television cable. Because such cables are more difficult to work with, new installations almost always use twisted pair or fiber optic cable.

Fiber optic cable

Fiber optic cable supports data transfer rates (in packet form) of 10, 100, or 1000 Mbps. Data is transmitted using light pulses traveling along an optical fiber. Although this cable is much more expensive and more difficult to install than UTP, it is often used in central backbone networks because it provides full protection from electrical interference and allows you to transmit information over very long distances. In addition, thanks to improvements in fiber optic technology this cable is becoming more and more affordable.

Which cable to choose?

The table shows which cable should be used for different LAN technologies (10 Mbps Ethernet, 100 Mbps Fast Ethernet, or 1000 Mbps Gigabit Ethernet). In general, all new installations use Category 5 UTP cable to connect desktop PCs and create a workgroup network.

A server in a client/server network is a PC with hard drive large capacity, on which you can store applications and files that are accessible to other PCs on the network. The server can also control access to peripheral devices (such as printers) and is used to run a network operating system (NOS, Network Operating System).

Network interface cards

Network interface cards (NIC, Network Interface Card) are installed on desktop and laptop PCs. They are used to interact with other devices on the local network. There is a whole range of network cards for various PCs that have specific performance requirements. They are characterized by data transfer speed and methods of connecting to the network.

If we consider simply the method of receiving and transmitting data on PCs connected to the network, then modern network cards (network adapters) play an active role in improving performance, prioritizing critical traffic (transmitted/received information) and monitoring traffic on the network. In addition, they support features such as remote activation from a central workstation or remote configuration changes, which significantly saves administrators time and effort in ever-growing networks.

Hubs

In a structured cabling configuration, all PCs on the network communicate with a hub (or switch).

Hab (hub; hub) is a multiple access device that acts as a central connection point in a physical star topology. Along with the traditional name “hub”, the term “hub” is also found in the literature.

PCs connected to the hub form one LAN segment. This scheme simplifies connection to the network large number users, even if they move frequently. The main function of a hub is to connect users into one network segment. There are hubs different types and sizes and provide connection for a different number of users - from a few employees in a small company to hundreds of PCs in a network covering a complex of buildings. The functions of these devices are also different: from simple wireline concentrators to large devices that perform the functions of a central network node, supporting management functions and a number of standards (Ethernet, Fast Ethernet, Gigabit Ethernet, FDDI, etc.). There are also hubs that play an important role in network security.

Hub entry level(basic hub) is simple, standalone device, which can be a good starting point for many organizations.

Stackable hubs allow you to gradually increase the size of your network. Such hubs are connected to each other flexible cables extensions are stacked one on top of the other and function as one hub. Due to their low cost per port, stackable hubs have become particularly popular.

How does a hub work?

When using a hub, all users share the network bandwidth. A packet received on one of the hub ports is broadcast to all other ports that analyze this packet (whether it is intended for them or not). With a small number of users, this system works great. Meanwhile, as the number of users increases, competition for bandwidth begins to take effect, which slows down traffic on the local network.

Traditional hubs support only one network segment, giving all users connecting to them the same bandwidth. Port-switching hubs or segmented hubs (such as the SuperStack II PS Hub family) allow you to combine this problem at a minimum, by allocating users to any of the four internal segments of the hub (each of these segments has a bandwidth of 10 Mbps). This scheme makes it possible to flexibly distribute bandwidth between users and balance the network load.

Dual-speed hubs can be advantageously used to create modern networks with shared network segments. They support existing Ethernet channels 10 Mbit/s and new Fast networks Ethernet 10 Mbps, automatically detecting connection speed, eliminating manual configuration. This simplifies connection upgrades - moving from Ethernet networks to Fast Ethernet when support for new bandwidth-intensive applications or segments with a large number of users is required.

Hubs also provide a central point for connecting cables, changing configurations, troubleshooting and centralized management, simplifying all these operations.

Switches

Switch (switch) 1. A multiport device that provides high-speed packet switching between ports. 2. In a packet switching network, a device that routes packets, usually to one of the nodes in the backbone network. Such a device is also called a data switch (data PABX).

A switch provides each device (server, PC, or hub) connected to one of its ports with the entire network bandwidth. This improves performance and reduces network response time by reducing the number of users per segment. Like dual-speed hubs, the latest switches are often designed to support 10 or 100 Mbps, depending on the maximum speed connected device. If they are equipped with automatic baud rate detection, they can adjust themselves to optimal speed- There is no need to change the configuration manually.

How does a switch work?

Unlike hubs, which broadcast all packets received on any port, switches transmit packets only to the target device (addressee), since they know the MAC (Media Access Control) address of each connected device (similar to how a postman broadcasts postal address determines where the letter should be delivered). The result is reduced traffic and increased overall throughput, both of which are critical given the growing network bandwidth demands of today's complex business applications.

Switching is gaining popularity as a simple, low-cost method of increasing the available network bandwidth. Modern switches often support features such as traffic prioritization (which is especially important when transmitting voice or video over the network), network management functions, and multicast control.

Routers

Routers can perform the following simple functions:

Connecting local networks (LAN) to wide area networks (WAN).

Connection of several local networks.

Routers depend on the protocol used (for example, TCP/IP, IPX, AppleTalk) and, unlike bridges and switches, which operate at Layer 2, operate at Layer 3 or Layer 7 of the OSI model. A router's performance in terms of data transferred per second is usually proportional to its cost. Because a router is protocol-based, it can decide on the best route to deliver data based on factors such as cost, delivery speed, etc. Routers also allow you to efficiently manage broadcast traffic, ensuring that data is sent only to the required ports.

Layer 3 Switches

These switches are so called because they operate at the third layer of the seven-layer model. Like routers, they depend on the protocol used, but they are much faster and cheaper. Typically, Layer 3 switches are designed to interconnect multiple LANs and do not support WAN connections.

Remote access servers

If you need to provide network access to remote users establishing a dial-up connection from home or while traveling, you can install a remote access server. This device allows multiple users to connect to a network over a telephone line (by dialing one phone number) and contact network resources just like when working in an office. In addition, such servers may provide protection against unauthorized user access.

Routers move data by figuring out the best route from sender to recipient. Here, the local network LAN 1 transmits through LAN 3 to LAN 5, however, if the connection between LAN 1 and LAN 3 fails, the data can be sent through LAN 4.

Modems allow PC users to exchange information and connect to the Internet via regular telephone lines. The name "modem" comes from the function of the device and means "modulator/demodulator". Modem modulates digital signals, coming from the PC, in analog signals, transmitted by telephone network public, and another modem demodulates these signals at the receiving end, converting them back into digital form.

Unlike routers, which provide shared external access to users, a modem supports only one connection at a time. In this case, the payment is the same as for a telephone, including the cost of services long distance communication. Installing modems on a central network server can allow them to be shared. For PCs, built-in and external modems are used, and for laptop computers Typically PC Card format modems are used. The fastest modern modems support speeds of 56 Kbps.

Network software.

The basic components and technologies associated with local or wide area network architecture also include:

Software includes

Network operating system

Network management software

Network operating system

A network operating system (NOS, Network Operating System) is software used on every PC connected to a network. It manages and coordinates access to network resources. The network OS is responsible for routing messages on the network, resolving contention for network devices, and running a PC operating system such as Windows 95, Windows NT, UNIX, Macintosh, or OS/2.

Network OS provides working together with files and applications. Such resources located on one workstation can be shared, transferred, or modified from another workstation. The main part of the network OS is located on the network server, and its other components operate on all workstations on the network.

The network operating system recognizes all devices on the network and controls priority access to shared peripheral devices if multiple workstations attempt to access them simultaneously. The network OS acts as a traffic regulator, provides a directory service, provides control of credentials in the security system, and implements network management functions. Popular network operating systems include Windows NT Server, Novell NetWare, and Banyan VINES.

Network Management Software

Network management software plays an increasingly important role in monitoring, managing and protecting your network. It provides proactive control, which makes it possible to avoid network downtime and the occurrence of bottlenecks in it, and reduce the total cost of ownership of the network (TCO, Total Cost of Ownership).

From a management workstation or via the World Wide Web, network administrators can monitor traffic patterns, identify trends leading to segment congestion, monitor and resolve problems, and reconfigure the network to maximize network performance. As networks grow in size and complexity, monitoring tools such as RMON and RMON2 help administrators maintain control over their network environment. These monitoring tools allow you to get detailed information from the edge of the network, identify a potential problem in time so that the network administrator can take preventive action.

In addition, the management software protects data transmitted over the network. From the management workstation, network administrators can set passwords, determine which resources users have the right to access, and log “intrusion attempts” by unauthorized users.

Today, most companies at a certain stage of development are faced with the task of creating the most flexible and efficient system for managing branches and office sites, creating unified system document flow and operational collection of information, centralized management of information and financial flows, etc. The creation of a unified information system for the operation of such geographically distributed business applications is ensured by a corporate data transmission network.
Geographically distributed KSPD, As a rule, they unite offices, divisions and other structures of the company that are located at a distance from each other. In this case, nodes are often corporate network find themselves located in different cities and sometimes countries. The principles by which such a network is built are: differ from those used to create local networks.

The main difference is that Wide-area networks use leased communication lines, the rental fee for the use of which constitutes a significant part of the cost of the entire network and increases with the increase in the quality and speed of data transmission. Therefore, the organization of communication channels is the first task that must be solved when creating geographically distributed corporate networks. If within one city it is possible to rent leased lines, including high-speed ones, then when moving to geographically distant nodes, the cost of renting channels becomes significant, and their quality and reliability may be low.

A possible solution to the problem of organizing communication channels between remote nodes of a company’s corporate network is to use already existing global private networks. In this case, it is necessary to provide channels from the company's offices to the nearest nodes of the global private network. Private networks may contain communication channels different types: cable optical and electrical, including telephone, wireless radio and satellite channels, having different throughputs.
When connecting company offices via global private networks remote users do not feel isolated from information systems they access, the company's remote locations can exchange information immediately, and all transmitted information remains secret. However, establishing communication links over global private networks can also be expensive.
Provide many of the benefits of private networks virtual private network technology (VPN, Virtual Private Network) allows for a lower cost. VPN is logical private network, organized on top of a public network, usually the Internet. Following the same functional principles Just like leased lines, a VPN allows you to establish a secure digital connection between two remote locations (or local networks). Despite the fact that communications over public networks are carried out using insecure protocols, encryption creates closed information exchange channels that ensure the security of transmitted data.

Virtual private networks allow you to combine geographically distributed offices of an organization into single network and thus provide a single LAN address space, a single corporate numbering telephone communication, common base data, etc. In other words, a unified network infrastructure is organized and information space company, access to which is equally possible from anywhere in the corporate network.

Geographically distributed KSPD, built on the basis VPN technologies, are the foundation for the implementation of all subsequent additional services, such as voice over IP, video conferencing, business applications and services, as well as for organizing prompt and confidential communication with all branches of the company and significantly reducing the volume of long-distance and international traffic by transmitting telephone calls over DSPD channels.

An integral part of a unified information environment educational institution based on a computer network is the school intranet.

An intranet is a local or geographically distributed network, closed from external access from the Internet, based on Internet technology.

The school local area network (LAN), like any LAN, according to one apt remark, is the blood vessels of the educational environment.

There are three aspects to the school Intranet:

New methods of information management and their positive impact on educational process in a modern school.

The ability to solve organizational, methodological and administrative issues of school information management in the context of the use of information and communication technologies.

Solving issues of architecture, system-technical infrastructure and technological means of building Intranet systems in relation to an educational institution.

One of the significant features of a LAN is that all personal computers (in this case they are also called workstations) connected to the network use the potential capabilities of other network devices. Thanks to this, it is possible to work simultaneously and even jointly with any program, exchange files and letters, and reduce the number of peripheral devices (printers, drives, etc.).

One of the options for using the Intranet is work related to the joint processing of text, graphic and other materials, calculations, and database access. That is, the work that is performed collectively, but is distributed in space and time in such a way that only communication between computers allows the results of collective work to be quickly used. In this case, computers on the network have an equal position, and each user can, if they have access rights, obtain information or use the resources of another computer.

Most often, the information environment of an educational institution is organized on the basis of a network with a dedicated server. In general, this is a network of various equipment, not grouped in one room.

In this case, it is possible to divide computers by types of tasks (for example, educational - separately, administrative - separately) or, if there are several computer classes, by type educational tasks. To do this, it is necessary to establish a differentiation of user rights, define a hierarchy of access to information, and organize multi-level group work on the network.

Basis for information flows, reflecting the most important production processes and processes of additional support for the activities of an educational institution, is certain basic information. An integral part of the basic information is the so-called general (collective) access information and special access information. Information flows, reflecting the main production processes of an educational institution, closely interact with each other, while the results of planning, organizing and managing the educational process serve as support for administration processes and content provision processes.