Classification of territorial networks. Let's consider territorial networks, which consist of backbone networks and access networks

Global network

A global network is a network whose subscriber systems are located in different countries. They were created as an association of territorial networks. Committed to providing network services and resources to a large number of users led to the unification of territorial networks and the creation of global networks. Thanks to your large sizes each of them provides its users with thousands of Databases (DBs), intercontinental email, the opportunity to study in almost any specialty. In addition, the global network is link large number small networks. A global network consisting of a group of interacting territorial networks is also called a metanetwork. Example: Internet network.

The creation of global networks led to the emergence of computer-network architecture, in which simple and highly efficient network computers have become components of these networks and are designed to take advantage of their greater capabilities. Subscriber systems built on these computers allowed their owners to integrate into the global information infrastructure.

Virtual network

A virtual network is a network whose characteristics are mainly determined by its software.

Reasons for creating virtual networks:

· the need to create operational working groups isolated from other users. Working group is a collection of users who have shared resources and the rights to use these resources are created on the network to perform a specific set of tasks;

· desire to facilitate the procedures for moving and deleting network objects;

desire to provide operational capability changing roles so that the client, when necessary, can act as a server;

· the ability to ensure data security by localizing traffic within an isolated group.

To do this in communication network an intelligent device is installed (switching nodes, hubs, bridges, etc.), which, in accordance with the instructions administrative system connects logical channels to each other, forming a local network closed to other subscribers. In one big association physical networks a significant number of virtual networks can be created that operate independently of each other.

Virtual technology has great flexibility, allowing you to dynamically change the number and composition of virtual networks as many times as you like.

TOPOLOGY OF INFORMATION NETWORKS

Network topology

Topology (configuration) characterizes the properties of networks, systems and programs that do not depend on their size. It studies the structure formed by physical objects and the set of channels or parts of channels connecting them.

The configuration of the connection of elements largely determines many the most important properties networks - reliability (survivability), performance, etc.

According to one approach to configuration classification, networks are divided into two main classes:

· broadcasting;

· consistent.

In broadcast configurations, each subscriber system transmits signals that can be received by other systems. Such configurations include:

1) the common bus (Fig. 1) allows you to significantly simplify the logical and software structure of the network and reduce cable consumption;

2) tree (Fig. 2) is a more developed version of the common bus type configuration. A tree is formed by connecting several buses with active repeaters or network concentrators (“hubs”). It has the necessary flexibility to cover several buildings in a certain area with network means. If there are active repeaters, the failure of one segment does not lead to the failure of the rest. If a repeater fails, the tree is split into two subtrees or two buses;

3) a star (Fig. 3), which can be considered as a tree that has a root with branches to each connected device. In the center of the star there may be a passive connector or hub - quite simple and reliable devices. Star networks are less reliable than bus or tree, but they can be protected from cable disturbances by using a central relay that disconnects failed cable spokes. Such a star requires large quantities cable.

Broadcast configurations must use a relatively more powerful receiver and transmitter that can handle a wide range of signal levels. This problem is partially solved by introducing restrictions on the length of the cable segment and on the number of connections or by using digital repeaters.

In sequential configurations, each physical sublayer transmits information to only one of the subscriber systems. The requirements for transmitters or receivers of systems here are lower than in broadcast systems, and can be used in different parts of the network different types physical environment.

The most common serial configurations are:

1) arbitrary (Fig. 4) ? all devices are connected directly. Each line can use various methods transfers. This method of connecting devices is quite satisfactory for networks with limited number connections. Advantage of this type- simplicity. However, it has a high cost, big number communication channels and the need for information routing;

2) hierarchical (Fig. 5)? intermediate nodes They work on the principle: “accumulate and transfer.” Advantages this method - optimal connection network elements, disadvantages - complexity of logical and program structure, different speed transmission of information to various levels;

3) ring (Fig. 6);

4) chain (Fig. 7);

5) a star with an “intellectual” center (Fig. 8);

6) snowflake (Fig. 9).

Fig.1	Rice. 2	Rice. 3
Rice. 4	Rice. 5	Rice. 6
Rice. 7	Rice. 8	Rice. 9

In these configurations, the network requires Full time job all blocks. To reduce this dependence, a relay is included in each block that blocks the block in case of malfunctions. Disadvantages - slow data transfer (depending on the number of workstations), less reliability. Advantages - simplicity of control methods, high throughput with lower energy consumption, easy network expansion.

Territorial (regional network)

Territorial (regional) refers to networks that usually exist within a city, district, region, or country. They connect subscribers located at a considerable distance from each other. Typically, the distance between subscribers of a regional computer network is tens to hundreds of kilometers. They are a union of several local networks and part of a global one. They are not particularly specific in relation to the global one. Regional computer networks have much in common with local ones, but in many respects they are more complex. For example, in addition to data exchange and voice exchange, regional computer networks can transmit video and audio information. These networks are designed to support long distances than local area networks. They can be used to link multiple local area networks into high-speed integrated network systems. Regional computer networks combine best characteristics local ( low level errors, high transmission speed) with greater geographical extent. IN Lately they began to distinguish the class of corporate networks. They usually cover large corporations. Their scale and structure are determined by the needs of the enterprise owners.

The main task of the federal network is to create a backbone data transmission network with packet switching and provide real-time data transmission services to a wide range of users, which include territorial networks.

Global networks

Global networks provide the ability to communicate by correspondence and teleconference. Global computer network unites subscribers located in various countries, on different continents. Interaction between subscribers of such a network can be carried out on the basis of a telephone line, radio communication and systems satellite communications. Global computer networks make it possible to solve the problem of combining information resources around the world and organizing access to these resources. To connect to remote computers and computer networks, they are used telephone networks. The process of data transmission over telephone lines must occur in the form of electrical oscillations - analogue sound signal, while in a computer information is stored in the form of codes. In order to transmit information from a computer over a telephone line, the codes must be converted into electrical vibrations. This process is called modulation. In order for the recipient to be able to read what was sent to him on his computer, electrical vibrations must be converted back into machine codes- demodulation. A device that converts data from digital form, in which it is stored in a computer, to analog (electrical vibrations), in which it can be transmitted over a telephone line, and vice versa, is called a modem (short for DEModulation Modulator). The computer, in this case, must have a special telecommunications program that controls the modem and also sends and receives signal sequences transmitted information. Global computer networks are created by combining local and regional computer networks. They are a conglomerate various technologies. Compared to a local area network, most global ones are distinguished by slow speed transmissions and higher error rates. New technologies in the field of global computing networks are aimed at solving these problems. Global networks, in addition to covering very large territories, have a number of other features compared to a local network. Global networks are mainly used as communication channels telephone lines- these are slow channels with high level errors. However, high-speed fiber-optic and radio-satellite communication channels are now increasingly being introduced. Computers (PC) are connected to communication channels using special devices called modems. The configuration of such networks can be different and, unlike local networks, is irregular. Various areas covered: for local ones approximately< 10 км, а для глобальных - от сотни и более. В global network between its nodes there are many ways to deliver information, but for local ones there is always one. The speed of information transfer in local networks is higher than in global ones. An example of a global network is the Internet. It differs from a local network in that it has more extensive communications and can include several local ones. A global network usually consists of heterogeneous computing systems And technical means. Therefore, the error rate in them is higher and the exchange protocols are more complex compared to local networks. In global networks, computers are located from each other at distances from several hundred to several tens of thousands of kilometers. In today's understanding, a computer network is a complex structure based on three main principles. The first of them is the presence single center, coordinating the activities and development of the network. The second is the use of a routing system that allows a message to move along a chain of network nodes without additional human intervention. The third is the use of a single standard addressing, making the network “transparent” for external networks, and the latter are accessible to any subscriber point in the system. Significant increase number of global network users per last years has led to the fact that the telephone networks used for data transmission can no longer cope with the entire volume of transmitted information. They are being replaced by satellite communications. In satellite communications, a user, a group of users, or a local network is equipped with a small satellite dish and communicates with each other via a satellite. The advantages of this method of communication include, first of all, high speed communications (up to 8 Mbit/s). Each satellite is capable of supporting up to 5,000 earth stations. This technology communications are developing successfully. Already in 1990 there were about 20,000 small ground stations in the world. In the new century, most global networks will be wireless. From the user's point of view, it is essential to divide all global networks into two categories - commercial and non-commercial. In commercial networks, all services are paid. Typically, the fee is determined by the time the user works on the network and the amount of information he pumps over the network. Tariffs are determined by the type of service. In non-profit networks, all services are free. In Russia, in particular in the North Caucasus, there is non-profit network UniCom/Russia, created by the association of Russian universities and the Russian Academy of Sciences. She is part international network Freenet, which in turn is part of the Internet. Commercial networks also operate in Russia. The most famous among them is Relcom, which is also part of the Internet.

Let's consider territorial networks that consist of backbone networks and access networks

It is advisable to divide territorial networks into two large categories:

· backbone networks;

· access networks.

Backbone wide-area networks are used to form peer-to-peer connections between large local networks belonging to large departments of the enterprise. Backbone territorial networks must provide high throughput, since the backbone combines the flows of a large number of subnets. In addition, backbone networks must be constantly available, that is, provide a very high availability factor, since they carry the traffic of many business-critical applications. Due to the special importance of highways, they can be forgiven for their high cost. Since a company usually does not have much large networks, then the backbone networks are not required to maintain an extensive access infrastructure.

Typically, digital dedicated channels with speeds from 2 to 622 Mbit/s are used as backbone networks, through which packet-switched network traffic is transmitted. frame relay, ATM, X.25 or TCP/IP. In the presence of dedicated channels, a mixed redundant topology of connections is used to ensure high availability of the backbone, as shown in Fig. 4.

Rice. 4. Structure of the global enterprise network

Under access networks understands the territorial networks necessary for connecting small local networks and individual remote computers with the central local network of the enterprise. If the organization of trunk connections when creating corporate network always paid great attention to the organization remote access employees of the enterprise became strategically important issues only recently. Fast access To corporate information from any geographic location determines the quality of decision-making by its employees for many types of enterprise activities. The importance of this factor is growing with the increase in the number of employees working at home (telecommuters) who are often on business trips, and with the increase in the number of small branches of enterprises located in different cities and, perhaps, different countries.

ATMs or cash registers , requiring access to a central database to obtain information about legal clients of the bank, whose plastic cards must be authorized on site. ATMs or cash registers usually designed to interact with central computer over X.25 network, which at one time was specially developed as a network for remote access of non-intelligent terminal equipment to a central computer.

Access networks have requirements that are significantly different from those for backbone networks. Since an enterprise can have a lot of remote access points. One of the main requirements is the presence of an extensive access infrastructure that can be used by enterprise employees both when working at home and on business trips. In addition, the cost of remote access must be moderate to economically justify the cost of connecting tens or hundreds of remote subscribers. In this case, the bandwidth requirements of an individual computer or local network, consisting of two or three clients, usually fall within the range of several tens of kilobits per second (if such speed does not fully satisfy remote client, then usually the convenience of its operation is sacrificed for the sake of saving money for the enterprise).

Analogue telephone networks, ISDN networks and, less commonly, frame relay networks are usually used as access networks.. When connecting local branch networks, dedicated channels with speeds from 19.2 to 64 Kbps are also used. A qualitative leap in expanding the capabilities of remote access occurred due to the rapid growth in the popularity and prevalence of the Internet. Internet transport services are cheaper than long-distance and international telephone networks, and their quality is rapidly improving.

Software and hardware that provide connection of computers or local networks of remote users to the corporate network are called remote access means. Typically, on the client side, these facilities are represented by a modem and associated software.

The organization of mass remote access from the central local network is ensured by remote access server (RAS). A remote access server is a software and hardware complex that combines the functions of a router, bridge and gateway. The server performs one or another function depending on the type of protocol it operates on remote user or remote network. Remote access servers typically have quite a few low-speed ports to connect users via analogue telephone networks or ISDN.

Internet resources

Self-test questions

1. Describe the concepts: information, source of information, consumer of information, message, data format, information network object, user, subscriber.

2. Describe open information systems.

3. Give a classification information networks according to various criteria.

Target: study the models and basic structures of information networks, as well as their informational resources.

Tasks:

ü study the purpose and main characteristics of information networks;

ü study the basic topologies of information networks;

ü review and study information resources of networks.

After studying the topic you should know:

ü purpose and main characteristics of information networks.

ü basic topologies of information networks;

ü information resources of networks.

Local area network (LAN)- a distributed data processing system covering a small area (up to 10 km in diameter) inside institutions, research institutes, universities, banks, offices, etc. The channels of such a network have high quality connections and belong to the same organization.

Two network architectures are used:

Client-server architecture (allows efficient use of network resources). In such a network, one or more control and service nodes are allocated, the remaining nodes are terminal.

By functionality they stand out: file server, print server, communication server, application server, database server.

One-rank architecture involves the interaction of peer subscriber systems, where each node can perform the functions of both a client and a server. The problem with peer-to-peer networks is their security, since there are no network-scale security measures. At the same time, individual resources individual computers can be protected by a password system, and only those users who know the password can access the resources. This type of network can work on small networks, but also requires users to know and remember different passwords for each shared resource in the network. As the number of users and resources increases, the single-rank network becomes inoperable. This is not because the network cannot function correctly, but because users are unable to cope with the complexity of the network.

Depending on the physical means of connection used, wired and wireless local networks are distinguished.

Territorial network is a network whose systems are located in different geographical points. It covers large space(from region to group of countries). Characteristic feature is the use of extended broadband channels, a large number of switching nodes or communication satellites.

It must satisfy the following basic requirements:

Include a large number of subscriber systems (up to several thousand);

Cover a large geographical area;

Provide broadcasting and delivery of messages to groups and individual recipients;

Have high throughput (up to tens of Gbit/s);

Have great reliability in operation;

Guarantee data security;

Transfer various types of data: texts, sound, images.

Figure 3 shows the classification of territorial networks.

Rice. 3. Classification of territorial networks

Global network is a network whose subscriber systems are located in different countries. They were created as an association of territorial networks.

A global network consisting of a group of interacting territorial networks is also called a metanetwork, for example: the Internet. The creation of global networks led to the emergence of computer-network architecture, in which simple and highly efficient networked computers became components of these networks and were designed to take advantage of their greater capabilities. Subscriber systems built on these computers allowed their owners to integrate into the global information infrastructure.

Virtual network is a network whose characteristics are mainly determined by its software.

The virtual network must provide:

The work of operational working groups isolated from other users. A work group is a collection of users who have common resources and the rights to use these resources, created on the network to perform a specific set of tasks;

Procedures for moving, deleting network objects, the ability to change roles so that the client, when necessary, can act as a server;

The ability to ensure data security by localizing traffic within an isolated group.

To do this, an intelligent device (switching nodes, hubs, bridges, etc.) is installed in the communication network, which, in accordance with the instructions of the administrative system, connects logical channels to each other, forming a local network closed to other subscribers.

Communication network topology defines the layout of communication lines and switches (this can be, for example, a ring or a lattice). The topology of networks is usually depicted in the form of graphs in which arcs correspond to communication lines, and nodes correspond to switches. Each node in the network (or in the corresponding graph) is associated with specific set communication lines.

Classification of networks by topology (configuration of elements in the network):

Broadcast;

Consistent.

In broadcast configurations Each subscriber system transmits signals that can be perceived by other systems. Such configurations include:

1) the common bus (Fig. 4, a) allows you to significantly simplify the logical and software structure of the network and reduce cable consumption;

2) tree (Fig. 4, b) is a more developed version of the common bus type configuration. A tree is formed by connecting several buses with active repeaters or network concentrators (“hubs”). It has the necessary flexibility to cover several buildings in a certain area with network means. If there are active repeaters, the failure of one segment does not lead to the failure of the rest. If a repeater fails, the tree is split into two subtrees or two buses;

3) a star (Fig. 4, c), which can be considered as a tree that has a root with branches to each connected device. In the center of the star there may be a passive connector or hub - quite simple and reliable devices. Star networks are less reliable than bus or tree, but they can be protected from cable disturbances by using a central relay that disconnects failed cable spokes. Such a star requires a large amount of cable.

In serial configuration information is routed, data is transferred sequentially from one station to the neighboring one, and can be used in different parts of the network different kinds physical transmission medium.

The most common serial configurations are:

1) arbitrary (Fig. 4, d) - all devices are connected directly. Each line can use different transmission methods. This method of connecting devices is quite satisfactory for networks with a limited number of connections. The advantage of this type is simplicity. However, it has a high cost, a large number of communication channels and the need for information routing;

2) hierarchical (Fig. 4, e) intermediate nodes work according to the principle: “accumulate and transmit”. The advantages of this method are the optimal connection of network elements, the disadvantages are the complexity of the logical and program structure, different speeds of information transfer at different levels;

3) ring (Fig. 4, f);

4) chain (Fig. 4g);

5) a star with an “intellectual” center (Fig. 4h);

6) snowflake (Fig. 4i).

In these configurations, the correct functioning of the network requires constant operation of all units. To reduce this dependence, a relay is included in each block that blocks the block in case of malfunctions. Disadvantages - slow data transfer (depending on the number of workstations), less reliability. Advantages: simplicity of control methods, high throughput with lower energy consumption, ease of network expansion.

There are three main goals in choosing the optimal topology:

providing alternative routing, maximum reliability of data transmission;

Choice optimal route transmission of data blocks (minimizing the number of channels of forming sequences);

Providing acceptable response time and required bandwidth.

Rice. 4. Basic network topologies

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