Computer telecommunications. Telecommunications and computer networks Computing networks and telecommunications
Telecommunication networks currently include:
- * telephone networks;
- * radio network;
- * television networks;
- * computer networks
In all these networks, the resource provided to customers is information.
Telephone networks
Telephone networks provide interactive services, as the two subscribers participating in a conversation (or several subscribers, if this conference) alternately show activity.
The invention in 1876 of the phone marked the beginning of the development of telephone networks that are not ceased to be improved and to the present.
Now, not only speech information (when there is two subscribers' conversation), but also fax messages and digital data are transmitted via public telephone network.
Generally speaking, telephone networks are designed to transmit analog signals on them. Analog signal is continuous and can take values \u200b\u200bfrom a certain range. For example, an analog signal is human speech; In the phone, TV, the radio information also exists in analog form. The disadvantage of such a form of information presentation is its susceptibility to interference.
Radio networks and television networks
The radio networks and television networks provide broadcast services, and information is distributed only in one direction - from the network to subscribers, according to the "one to many" scheme.
The loss of radio networks is the provisions of the Main National Advertising Tool and the offensive of the local radio began in 1948, with the beginning of the television era.
During the 1950s. "Soap operas" "moved" from radio to television, which meant the final "sunset" of the radio network. The next decade, network programs were limited mainly by news and brief coverage of various kinds of events.
Radio network differ in many ways from television networks; The relationship between the radio networks and their branches is also different. In essence, radio networks are program providers, but in contrast to television one radio station can be a member of several radio networks at the same time. For example, a local radio station can broadcast sports reports of one national network, special programs, reports, and news - another, entertainment transfers - the third. If local television stations sell advertising time based on network programs, then in broadcasting, in order to get national advertising support, networks should proceed from local ratings.
Regardless of the differences in the use of network programs with radio stations and many differences with television, radio networks offer certain advantages, some of which are similar to the benefits of televisions. For example, the advertiser prepares one order for advertising schedule for many stations, pays one account and it is guaranteed a single quality of advertising in graphics of all stations. Networks also provide economical coverage and, as radio itself, allow you to establish contacts with those target audience segments, which are often passive users of other media.
The revival of radio networks largely became the result of using satellite communications technologies. The availability of such a connection to developers of national radio programs offers a number of advantages for those who are branches of stations.
Computer networks
Computer networks have become a logical result of the evolution of computer and telecommunication technologies. On the one hand, they are a special case of distributed computer systems, and on the other hand, can be considered as a means of transmitting information over long distances, for which they use coding and multiplexing methods to develop in various telecommunication systems.
Classifying networks by territorial sign, distinguish global (WAN), local (LAN) and urban (MAN) network.
Chronologically first appeared WAN networks. They combine computers dispersed at a distance of hundreds and thousands of kilometers. The first global computer networks have inherited a lot from telephone networks. They often used already existing and not very high-quality communication lines, which led to low data transmission velocities and limited the set of services provided by transferring files in the background and email.
LAN networks are limited to distances a few kilometers; They are built using high-quality communication lines that allow, applying simple data transfer methods than in global networks, reach high data exchange rates to several gigabit per second. Services are provided in connection mode and differ in diversity.
MAN networks are designed to maintain the territory of a major city. With sufficiently large distances between the nodes (tens of kilometers), they have high-quality communication lines and maintain high metabolism. MAN networks provide an economical connection of local networks among themselves, as well as access to global networks.
The most important stage in the development of networks is the emergence of standard network technologies: Ethernet, FDDI, TOKEN Ring, allowing you to quickly and effectively combine computers of various types.
The trend of rapprochement of various types of networks is characteristic not only for local and global computer networks, but also for telecommunication networks of other types: telephone networks, radio networks, television networks. Currently, active work is underway to create universal multiservice networks that can equally effectively transfer information to any type: data, voice and video.
Computer and telecommunication networks
Computer network (COP) -a combination of computers and terminals connected using communication channels into a single system that meets the requirements of distribution data processing.
In general, under telecommunication Network (TC)understanding the system consisting of objects that perform the functions, transformation, storage and consumption of the product by paragraphs (nodes) of the network, and transmission lines (communication, communications, connections), transmitting the product between items.
Considering the dependence of the dismissal product - information, energy, mass - differ accordingly information, energy and real networks.
Information network (IP) - Communication network in which the product of generation, processing, storage and use of information is information. Traditionally, the transmission of sound information uses the phonphon networks, images - the body, the text, the text - the telephone (tel -etype). Today, information is more common integral service networksallowing you to transmit sound, image and data in a single channel.
Computing network (Sun)– information Networkwhich includes computing equipment. Computing network components There are computers and peripheral devices that are sources and data receivers transmitted over the network.
Sun is classified for a number of signs.
1. Given the dependence of the industry between the NLOs of the Sun network, can be divided into three classes:
· local(LAN, LAN - Local Area Network) - covering limited territory (usually within the remoteness of stations not more than several dozen or hundreds of meters from each other, less often on 1 ... 2 km);
· corporate (enterprise scale)- a set of related LANs covering the territory at which one enterprise or an institution in one or several closely located buildings is placed;
· territorial- covering significant geographical space; Among the territorial networks can allocate regional networks (Men - Metropolitan Area Network) and global (WAN - Wide Area Network), having a regional or global scale, respectively.
Especially allocated global Internet.
2. An important feature of the classification of computing networks is their topology that determines the geometric location of the basic resources of computing networks and links between them.
Given the dependence of the otopology, the units of nodes distinguish between the tire (trunk), ring, star, hierarchical, arbitrary structure.
Among the LAN are the most common:
· tire (BUS) - a local network in which the connection between any two stations is set through one common path and data transmitted by any station is simultaneously accessible to all other stations connected to the same data transmission environment;
· ring (Ring)- Nodes are associated with an annular data line (only two lines are suitable for each node). Data passing through the ring, alternately become available in the network nodes;
· star (Star)- There is a central node from which the data transfer lines to each of the other nodes are diverged.
The topological structure of the network has a significant impact on its throughput, the stability of the network to the failures of its equipment, on the logical capabilities and the cost of the network.
3. Considering the dependence of the controls to the network distinguish:
· ''Klent-server''''''''''''- They allocate one or more nodes (their names - servers) performing managers or special service functions on the network, and the rest of the nodes (clients) are terminal, users work in them. Networks' Client-server''' via via the character of the distribution of functions between servers, i.e. by server types (for example, file-servers, database servers). When specializing servers for certain applications we have network distributed computing. Such networks are also distinguished from centralized systems built on mainframes;
· peer-eyed- in them all the nodes are equal. Since in general, under the client, it is customary to understand the object (device or program) requesting some services, and under the server - an object that provides these services, then each node in peer-to-peer networks can perform functions and client and server.
4. Considering the dependence of this, the same or unequal computers are used on the network, distinguish the networks of the same type of computer, called homogeneousand different-type computers - heterogeneous (heterogeneous).In large automated systems, as a rule, networks are inhomogeneous.
5. Considering the addiction to send property on the network they are general Use Networks (Public)or Private (Privat).
Any communication network should include the following main components: transmitter, message, transmission, receiver.
Transmitter -a device that is a data source.
Receiver -device receiving data.
The receiver is a computer, terminal or any digital device.
Message -digital data defined format for transmission.
It should be a database file, a table, response to a query, text or image.
Transmission means -physical transmitting medium and special equipment providing messages.
For messaging in computing networks, various types of communication channels are used. The most common bodies and special channels and special channels for transmitting digital information are most common. Radio channels and satellite channels are also used.
Communication channelcalled the physical environment and hardware, transmitting information between switching nodes.
The needs of the formation of a single global space led to the creation of a global Internet. Today, the Internet attracts users with its informational resources and services (services), which uses about a billion people in the world's countries. Network services include electronic bulletin boards (Bulletin Board System - BBS), email (e-mail), telecomference or newsgroups (News Group), file sharing between computers (FTR), parallel interviews on the Internet (Internet relay Chat - IRC), search engines ''Vecemary web'' '.
Each local or corporate network usually has at least one computer, which has a permanent Internet connection using a high bandwidth line (Internet server).
The Internet provides a person to a person inexhaustible to search for the necessary information of various nature.
Almost all programs contain, besides help system, electronic and printed documentation. This documentation is a source of useful information about the program, and it should not be neglected.
Acquaintance with the program begins with information screens that accompany its installation. While the installation is underway, it should be found as much as possible about the appointment of the program and its capabilities. It helps to understand that you should search for in the program after it is installed.
Print documentation is attached to programs purchased in stores. This is usually quite extensive manuals with a volume of up to several hundred pages. It is the volume of such leadership often suppresses the desire to read it carefully. Indeed, it makes no sense to explore the manual, if the answer to the question can be obtained by simpler means. At the same time in case of difficulty, the program on the program - ϶ᴛᴏ one of the most convenient sources is extremely important.
In many cases, additional reference Information The program is presented in the form of text files that are part of the distribution kit. Historically, these files usually have a readme name, originating from the English phrase:''Read ME (read me) '.
Usually, the README file contains information about the installation of the program, additions and refine the printed guide, as well as any other information. For parliamentary programs and small service programs distributed via the Internet, this file may contain a complete electronic version of the manual.
Programs distributed via the Internet may include other text information files.
In cases where no '-' -'' 'sources do not allow you to get the necessary information about the program, you can refer to the bottomless treasury of information, which is the Internet. The search for information on the Internet is associated with some difficulties, but on the network there are answers to any questions.
All major companies and authors producing programs for computers are presented on the Internet. Using the search engine, it is not difficult to find a web page dedicated to the desired program or a series of programs. Such a page may contain an overview or a brief description, information about the latest version of the program, 'Clocks', associated with the revision of the program or the correction of errors, as well as links to other Web documents on the same issues. Here, often you can find free, conditionally free, demonstration and trial versions programs.
The Internet grows in a very rapid pace, and find the necessary information among billions of web pages and files becomes more difficult. Special search servers are used to search for information, which contain more or less complete and constantly updated information about Web pages, files and other documents stored on tens of millions of Internet servers.
Various search servers can use different search mechanisms, storage and providing information to the user. Internet search servers can be divided into 2 groups:
· Outlook search engines;
· Specialized search engines.
Modern search engines are often information portals that provide users not only to searching for documents on the Internet, but also access to other information resources (news, weather information, currency exchange rate, interactive geographical maps and so on).
General purpose search engines are databases containing thematically grouped information about worldwide web information resources.
Such search engines allow you to find web sites or Web pages by keywords in the database or by searching in the hierarchical catalog system.
The interface of such general purpose systems contains a list of directory partitions and a search field. In the search field, the user can enter keywords to search for the document. And in the directory to select a defined partition, which narrows the search field and thus speeds up the search.
Filling the databases is carried out using special robot programs that periodically 'approach' 'Internet Web servers.
Robots' programs read all the documents that meet keywords allocate them and enter the database containing the URLs - addresses of documents.
Since the information on the Internet is constantly changing (new Web sites and pages are created, the old things are removed, their URLs are changed and so on), search engines do not have time to track all these changes. The information stored in the search engine database may differ from the real internet state and then the user as a result of the search may receive the address of an existing or displaced document.
In order to ensure more compliance between the content of the search engine database and the real state of the Internet, most search engines allow the author of a new or displaced Web site to make information to the database by filling out the registration form. In the process of filling out the profile, the site developer introduces the site͵ of its name, a brief description of the content of the site. And also keywords for which it will be easier to find a site.
Sites in the database are recorded in the number of their poses per day, week or month. Playing sites is determined using special counters that are installed on the site. Counters fix each site poses and transmit information about the number of poses on the search engine server.
The search for a document in the database of the search engine is carried out by entering queries in the search field. A simple request contains one or more keywordswho are the main for this document. You can also use complex queries using logic operations, templates and so on.
Specialized search engines allow you to search for information in other information ''slines' Internet: file archives servers, mail servers, etc.
Computer and telecommunication networks are concepts and types. Classification and features of the category "Computer and telecommunication networks" 2017, 2018.
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All-Russian CauristicFinancial and economic
Institute
Department of Automated Processing
Economic information
COURSE WORK
By discipline « COMPUTER SCIENCE"
on the topic "Computer networks and telecommunications"
Performed:
Plaksina Natalia Nikolaevna
Specialty GMU
Certificate Book No. 07MGB03682
Checked:
Sazonova N.S.
Chelyabinsk - 2009.
- Introduction
- THEORETICAL PART
- 1. Classification of computer networks
- 2. Topology building LAN
- 3. Access methods to the transmitting environment in the LAN
- 4. Corporate Internet
- 5. Principles, Technologies, Internet Protocols
- 6. Trends in the development of the Internet
- 7. Basic components WWW, URL, HTML
- Practical part
- Conclusion
- BIBLIOGRAPHY
Introduction
In recent years, the global Internet network has become a global phenomenon. The network, which, until recently, was used by a limited circle of scientists, civil servants and employees of educational institutions in their professional activities, became accessible to large and small corporations and even for individual users. Computer network LAN Internet
Initially, the Internet was a rather complicated system for an ordinary user. As soon as the Internet has become available to commercial firms and private users, the development of software for working with various useful Internet services, such as FTP, Gopher, Wais and Telnet, has begun. Experts also created a completely new type of service, such as the World Wide Web system, allowing you to integrate text, graphics and sound.
In this paper, I will consider network structures, its tools and technologies and the application of the Internet. The question of it is extremely relevant to me because the Internet today is experiencing a period of explosive growth.
THEORETICAL PART
1. Classification of computer networks
Computer networks have many advantages over the totality of individual systems, including the following:
· Separation of resources.
· Improving the reliability of the system functioning.
· Download allocation.
· Extensibility.
Separation of resources.
Network users can have access to certain resources of all network nodes. Among them, for example, data sets, free memory on remote nodes, the computational power of remote processors, etc. This allows you to save significant funds by optimizing the use of resources and their dynamic redistribution during the work.
Improving the reliability of the system functioning.
Since the network consists of a set of individual nodes, in the event of a failure on one or several nodes, other nodes will be able to take on their functions. At the same time, users may even not notice this- redistribution of tasks will take on the network software.
Download allocation.
In networks with variable upload level, it is possible to redistribute tasks from some network nodes (with high load) to others where there are free resources. Such a redistribution can be carried out dynamically during the work, moreover, users may not even know about network planning features on the network. These functions may take on the network software.
Extensibility.
The network can be easily expanded by adding new nodes. At the same time, the architecture of almost all networks makes it easy to adapt network software to configuration changes. Moreover, it can be done automatically.
However, in terms of security, these advantages turn into vulnerable places, generating serious problems.
Features of the network are determined by its dual character: on the one hand, the network should be considered as a unified system, and on the other, as a set of independent systems, each of which performs its functions; It has its own users. The same duality manifests itself in the logical and physical perception of the network: at the physical level, the interaction of individual nodes is carried out using messages of various types and formats that are interpreted by protocols. On the logical level (i.e., the stroks of the protocols of the upper levels) the network is represented as a set of functions distributed by various nodes, but associated with a single complex.
Networks are divided:
1. On the network topology (classification on the organization of the physical layer).
Total bus.
All nodes are connected to a general high-speed data bush. They are simultaneously configured to receive the message, but each node can only accept the message that is intended for it. The address is identified by the network controller, while only one node with a specified address can be on the network. If two nodes are simultaneously busy transmitting a message (collision of packets), then one of them or they are both stopped, waiting for a random time interval, then a transmission attempted (conflict resolution method). Another case is possible - at the time of transfer to any node of the message over the network, other nodes start the transmission cannot (the method of preventing conflicts). Such a network topology is very convenient: all nodes are equal, the logical distance between any two nodes is 1, the transfer rate is large. For the first time, the organization of the Network Tire network and the relevant lower level protocols were developed jointly by Digital and Rank Xerox, it was called Ethernet.
Ring.
The network is built in the form of a closed circuit of unidirectional channels between stations. Each station takes messages over the input channel, at the beginning of the message contains address and control information. Based on its station makes a decision to make a copy of the message and remove it from the ring or transferred on the output channel to the next node. If no message is currently transmitted, the station itself can transfer the message.
In annular networks used several different ways Management:
Garland - managing information is transmitted by individual sets (circuits) of ring computers;
Managing marker - control information is issued as a specific bit pattern circulating over the ring; Only upon receipt of the marker, the station may issue a message to the network (the most famous method called TKEN Ring);
Segment - over the ring circulates the sequence sequence. Finding empty, the station can put a message in it and transfer to the network;
Inserting registers - the message is loaded into the shift register and is transmitted to the network when the ring is free.
Star.
The network consists of one hub-hub and several terminal nodes connected to it directly between themselves unrelated. One or more terminal nodes may be concentrators of another network, in this case the network acquires a tree topology.
The network management is fully carried out by the hub; Terminal nodes can only communicate through it. Usually, only local data processing is performed on terminal nodes. Processing data relating to the entire network is carried out on a hub. It is called centralized. The network management is usually carried out using the survey procedure: the hub after certain intervals polls in turn terminal stations - is there a message for it. If there is - the terminal station transmits a message to the hub, if not, the following station is surveyed. The hub can be transferred to one or more terminal stations at any time.
2. By network size:
· Local.
· Territorial.
Local.
Data network connecting a number of nodes in one local zone (room, organization); Usually network nodes are equipped with the same type of hardware and software (Although it is optional). Local networks provide high information transfer rates. Local networks are characterized by short (no more than a few kilometers) lines of communication controlled by the working medium, the low probability of errors, simplified protocols. Gateways are used to communicate local networks with territorial areas.
Territorial.
They differ from the local longer length of communication lines (city, area, country, group of countries), which can be provided by telecommunications companies. The territorial network can associate several local networks, separate remote terminals and computers and can be connected to other territorial networks.
Territorial networks rarely use any typical topological structures, as they are intended to perform other, usually specific tasks. Therefore, they are usually built in accordance with arbitrary topology, management is carried out using specific protocols.
3. On the organization of information processing (classification on the logical level of the presentation; here under the system is understood as the entire network as a single complex):
Centralized.
Systems of such an organization are most widespread and familiar. They consist of a central node that implements the entire complex of the functions performed, and the terminals, the role of which comes down to partial input and information conclusion. Basically, the peripheral devices play the role of terminals from which the processing process is managed. The role of terminals can perform display stations or personal computers, both local and deleted. Any processing (including communication with other networks) is performed through the central node. A feature of such systems is a high load on the central node, which is why there should be a highly reliable and high-performance computer. The central node is the most vulnerable part of the system: it fails to fail the entire network. At the same time, the security tasks in centralized systems are solved most simply and actually reduced to the protection of the central node.
Another feature of such systems is the ineffective use of the resources of the central node, as well as the inability of the flexible restructuring of the nature of the work (the central computer should work all the time, which means that it can work out some part). Currently, the share of systems with centralized management gradually falls.
Distributed.
Almost all nodes of this system can perform similar functions, each individual node can use the equipment and software of other nodes. The main part of such a system is a distributed OS, which distributes system objects: files, processes (or tasks), memory segments, other resources. But at the same time, the OS can allocate not all resources or tasks, but only part of them, such as files and free memory on the disk. In this case, the system is still considered distributed, the number of its objects (functions that can be distributed across separate nodes) is called a degree of distribution. Such systems can be both local and territorial. Speaking by the mathematical language, the main function of the distributed system is the display of individual tasks into a plurality of nodes on which their execution occurs. The distributed system must have the following properties:
1. Transparency, that is, the system should ensure the processing of information regardless of its location.
2. The resource allocation mechanism that must perform the following functions: ensure the interaction of processes and remote task call, support virtual channels, distributed transactions and name service.
3. Names service, one for the entire system, including support for the Unified Directory Service.
4. Implementation of homogeneous and heterogeneous networks.
5. Control the functioning of parallel processes.
6. Security. In distributed systems, the security problem goes to qualitatively new levelSince you have to control the resources and processes of the entire system as a whole, as well as the transmission of information between the elements of the system. The main components of protection remain the same - access control and information flow, network traffic control, authentication, operator control and protection management. However, control in this case is complicated.
The distributed system has a number of advantages that do not have any other organization of information processing: the optimality of using resources, resistant to failures (failure of one node does not lead to fatal consequences - it can be easily replaced), etc. However, there are new problems: methods of resource allocation, security, transparency, etc. Currently, all possibilities of distributed systems are not fully implemented.
Recently, the concept of processing the client server receives increasing recognition. This concept is transitional from centralized to distributed and simultaneously unifying both of the latter. However, the client server is not so much a way to organize a network, how much is a way of logical representation and information processing.
The client-server is such an organization of information processing, in which all functions performed are divided into two classes: external and internal. External functions consist of supporting the user interface and information representation functions at the user level. Internal concerns the execution of various requests, process processing process, sorting, etc.
The essence of the client-server concept is that the elements of two levels are allocated in the system: server processing servers (internal functions), and workstations that perform query formation functions and displaying the results of their processing (external functions). From workstations to the server there is a flow of requests, in the opposite direction - the results of their processing. Servers in the system can be several and they can perform various sets of lower level functions (print servers, file and network servers). The main amount of information is processed on servers that play the role in this case. local centers; Information is entered and displayed using workstations.
Distinctive features of systems built on the principle of the client-server, as follows:
The most optimal use of resources;
Partial distribution of information processing process in the network;
Transparent access to remote resources;
Simplified management;
Reduced traffic;
The possibility of more reliable and simple protection;
Great flexibility in the use of the system as a whole, as well as heterogeneous equipment and software;
Centralized access to certain resources,
Separate parts of one system can be built according to various principles and combine using the appropriate matching modules. Each class of networks has its own specific features both in terms of organization and protection plan.
2. Building the construction of the LAN
The term "network topology" refers to the path by which the data is moved over the network. There are three main types of topologies: "Total bus", "Star" and "Ring".
Figure 1. Tire (linear) topology.
The Topology "Total Bus" involves using one cable to which all network computers are connected (Fig. 1). In the case of the "Total Bus" Cable is used together by all stations in turn. Special measures are taken to ensure that computers do not interfere with each other to transmit and receive data when working.
In the Topology "Total Bus" All messages sent by individual computers connected to the network. Reliability here is higher, since the failure of individual computers does not violate the performance of the network as a whole. Troubleshooting in the cable is difficult. In addition, since only one cable is used, in the event of a break, the work of the entire network is violated.
Figure 2. Topology of the "Star" type.
In fig. 2 shows computers connected by a star. In this case, each computer through a special network adapter is connected by a separate cable to a unifying device.
If necessary, you can combine several networks with the "Star" topology, with branched network configurations.
From the point of view of reliability, this topology is not
the best solution, since the failure of the central node will stop the entire network. However, when using the topology "Star" easier to find a malfunction in the cable network.
The Topology "Ring" is also used (Fig. 3). In this case, the data is transmitted from one computer to another as if on the relay. If the computer receives data intended for another computer, it transmits them further along the ring. If the data is intended for the computer received them, they are no further transmitted.
The local network can use one of the listed topologies. It depends on the number of computers united, their mutual location and other conditions. You can also combine several local networks made using different topologies into a single local network. Maybe, for example, a tree topology.
Figure 3. Ring topology.
3. Access methods to the transmitting environment in the LAN
Undoubted advantages of information processing in computer networks are wrapped in considerable difficulties in organizing their protection. We note the following main problems:
Separation of shared resources.
Due to the sharing of a large number of resources by various network users, possibly located at a high distance from each other, the risk of NSDs is greatly increasing - it can be made easier and more accurate in the network.
Expansion of the control zone.
The administrator or operator of a separate system or subnet must control the activities of users who are out of reach, possibly in another country. At the same time, it must maintain working contact with his colleagues in other organizations.
Combination of various software and hardware.
The connection of several systems, even if homogeneous according to the characteristics, the network increases the vulnerability of the entire system as a whole. The system is configured to perform its specific security requirements that may be incompatible with the requirements on other systems. In the case of the combination of heterogeneous systems, the risk rises.
Unknown perimeter.
Easy expansion of networks leads to the fact that it is sometimes difficult to determine the network boundaries; The same node can be available for users of various networks. Moreover, for many of them, it is not always possible to determine how many users have access to a specific node and who they are.
Many attack points.
In the networks, the same data set or message can be transmitted through several intermediate nodes, each of which is a potential source of threat. Naturally, this cannot contribute to an increase in network security. In addition, many modern networks can be accessed with switched communication lines and modem, which increases many times the number of possible attack points. This method is simple, easy to implement and difficult to control; Therefore, it is considered one of the most dangerous. The list of network vulnerable places also feature communication lines and various types of communication equipment: signal amplifiers, repeaters, modems, etc.
The complexity of control and control access to the system.
Many network attacks can be carried out without physical access to a specific node - using a network from remote points. In this case, the identification of the intruder may be very difficult, if not impossible. In addition, the time of attack may be too small for adequate measures.
In essence, the problem of network protection is due to the dual character of the latter: we talked about it above. On the one hand, the network has a single system with a single information processing rules, and on the other, is a set of separate systems, each of which has its own rules for processing information. In particular, this duality refers to the problems of protection. The network attack can be carried out from two levels (there is a combination of them):
1. Upper - the attacker uses network properties to penetrate another node and perform certain unauthorized actions. The protection measures undertaken are determined by the potential possibilities of the attacker and the reliability of the protection of individual nodes.
2. Nizhny - The attacker uses the properties of network protocols to violate the confidentiality or integrity of individual messages or flow as a whole. Violation of the message flow may result in leakage of information and even loss of network control. The protocols used must ensure the protection of messages and their flow as a whole.
Protection of networks, as well as the protection of individual systems, has three goals: maintaining confidentiality transmitted and processed in the network information, integrity and availability of resources and network components.
These goals determine the actions on the organization of protection against attacks from the top level. Specific tasks that get up when organizing network protection are caused by the capabilities of the high-level protocols: the wider these possibilities, the more tasks have to be solved. Indeed, if the network capabilities are limited to sending data sets, the main problem of protection is to prevent NSD to data sets available for shipment. If the network capabilities allow you to organize a remote launch of programs, work in the virtual terminal mode, then you need to implement a full range of protective measures.
Network protection should be planned as a single set of measures covering all the features of information processing. In this sense, the Network Protection Organization, the Development Policy Development, its implementation and management are subject to the general rules that were discussed above. However, it must be borne in mind that each network node must have individual protection depending on the functions performed and the network capabilities. In this case, the protection of a separate node must be part overall protection. Each separate node must be organized:
Access control to all files and other data sets available from the LAN and other networks;
Control processes activated from remote nodes;
Network chart control;
Efficient identification and authentication of users receiving access to this node from the network;
Control access to the resources of the local node available for use by network users;
Control over the dissemination of information within the local network and related other networks.
However, the network has a complex structure: to transfer information from one node to another, the latter passes several stages of transformations. Naturally, all these transformations should contribute to the protection of the transmitted information, otherwise the attack from the lower level can jeopardize the network protection. Thus, network protection as a single system is consisted of measures to protect each individual node and protocol protection functions of this network.
The need for data protection protocol protection functions is again caused by the dual character of the network: it represents a set of separate systems that exchange information using messages. On the way from one system to other, these messages are converted by protocols of all levels. And since they are the most vulnerable network element, the protocols should provide for ensuring their security to support the confidentiality, integrity and availability of information transmitted on the network.
Network software should be included in the network node, otherwise disruption of the network and its protection is possible by changing programs or data. At the same time, the protocols must implement the security requirements for the transmitted information that are part of the general security policy. Below is a classification of threats specific to networks (threats of lower level):
1. Passive threats (violation of the confidentiality of data circulating in the network) - view and / or record data transmitted over lines of communication:
Viewing Messages - An attacker can view the content of the message transmitted over the network;
Analysis of the schedule - an attacker can view the headlines of packets circulating on the network and on the basis of the service information contained in them to make conclusions about senders and recipients of the package and transmission conditions (departure time, message class, security category, etc.); In addition, it can find out the length of the message and the scope of the schedule.
2. Active threats (violation of the integrity or availability of network resources) - unauthorized use of devices that have access to the network to change individual messages or flow of messages:
Refusal of messaging services - an attacker can destroy or delay individual messages or a full flow of messages;
- "Masquerade" - an attacker can assign a foreign identifier to his node or repeater and receive or send messages from someone else's name;
The introduction of network viruses - transmission over a virus body network with its subsequent activation by the user of a remote or local node;
Modification of the message flow - an attacker can selectively destroy, modify, delay, reordering and duplicate messages, as well as insert fake messages.
It is clear that any manipulation described above with individual messages and flow as a whole can lead to network disorders or leakage of confidential information. This is especially true of service messages carrying information about the network status or individual nodes, about the events on individual nodes (remote launch of programs, for example) - active attacks on such messages may lead to a loss of network control. Therefore, protocols that form messages and put them into the stream should take measures to protect them and imprudent delivery to the recipient.
The tasks solved by the protocols are similar to the tasks solved when protected local systems: ensuring the confidentiality of the information being processed and transmitted to the network integrity and availability of the network (components) of the network. The implementation of these functions is carried out using special mechanisms. These include:
Encryption mechanisms that ensure confidentiality of data transmitted and / or data flow information. The encryption algorithm used in this mechanism can use the secret or public key. In the first case, the presence of keys management and distribution mechanisms are assumed. There are two encryption methods: channel, implemented using a channel-level protocol, and terminal (subscriber), implemented using the applied or, in some cases, a representative level.
In the case of channel encryption, the entire information transmitted over the communication channel is protected, including service. This method has the following features:
Opening the encryption key for one channel does not compromise information in other channels;
All transmitted information, including service messages, service fields of data messages, securely protected;
All information is open on intermediate nodes - strokes, gateways, etc.;
The user does not participate in the operations performed;
For each pair of nodes, your key is required;
Encryption algorithm must be sufficiently racks and provide encryption speed at the level bandwidth channel (otherwise there will be a delay of messages, which can lead to blocking system or a significant reduction in its performance);
The previous feature leads to the need to implement the encryption algorithm by hardware, which increases the cost of creating and maintaining the system.
Terminal (subscriber) encryption allows you to ensure the confidentiality of data transmitted between two applied objects. In other words, the sender encrypts data, the recipient - decipheres. This method has the following features (compare with channel encryption):
Only the content is protected; All service information remains open;
No one besides the sender and recipient to restore information (if the encryption algorithm used is sufficiently racks);
Transmission route is incomplete - in any channel information will remain protected;
For each pair of users, a unique key is required;
The user must know the procedures for encrypting and distributing keys.
The selection of this or that method of encryption or their combination depends on the results of risk analysis. The question is as follows: which is more vulnerable - directly a separate communication channel or the content of the message transmitted through various channels. Channel encryption is faster (other, faster, algorithms are used), transparent to the user requires less keys. Terminal encryption is more flexible, it can be used selectively, but requires user participation. In each case, the question must be solved individually.
Digital signature mechanisms that include closing data blocking procedures and checking a closed data block. The first process uses secret key information, the second - open, not allowing to restore the secret data. Using secret information, the sender forms a service data block (for example, based on a unilateral function), the recipient based on publicly available information checks the adopted block and determines the authenticity of the sender. To form a genuine unit can only a user having an appropriate key.
Access control mechanisms.
Carry out the authority of the network object to access resources. The authority check is made in accordance with the rules of the developed security policies (selective, authorized or any other) and implementing its mechanisms.
Mechanisms to ensure the integrity of the transmitted data.
These mechanisms provide both the integrity of the individual block or the data field and the data stream. The integrity of the data block is provided by transmitting and receiving objects. The transmit object adds a feature to the data block, the value of which is a function from the data themselves. The receiving object also calculates this function and compares it from the resulting. In case of failure, the decision is made on the violation of integrity. Detection of changes may entail data recovery actions. In the case of a deliberate disorder of integrity, the value of the control attribute may be appropriately changed (if the algorithm of its formation is known), in this case the recipient will not be able to establish integrity disorders. Then it is necessary to use the algorithm for generating a test indication as a data function and a secret key. In this case, the correct change in the control feature without knowledge of the key will be impossible and the recipient will be able to establish whether these modifications were subjected.
Protection of the integrity of data streams (from reordering, adding, repeats or deleting messages) is carried out using additional numbering forms (control of the message numbers in the stream), time stamps, etc.
The desired network protection components are the following mechanisms:
Authentication mechanisms of network objects.
To ensure authentication, passwords are used, checking the characteristics of the object, cryptographic methods (similar digital signatures). These mechanisms are usually used to authenticate single-level network objects. The methods used can be combined with a "triple handshake" procedure (triple messaging between the sender and the recipient with authentication and confirmation parameters).
Text fill mechanisms.
Used to ensure protection against schedule analysis. As such a mechanism, for example, generation of fictitious messages can be used; In this case, traffic has a constant intensity in time.
Route control mechanisms.
Routes can be selected dynamically or in advance in order to use physically safe subnets, repeaters, channels. Terminal systems When setting up attempts to impose a connection on another route. In addition, selective routing can be used (that is, part of the route is set by the sender explicitly - bypassing hazardous sites).
Experience mechanisms.
Data characteristics transmitted between two and more objects (integrity, source, time, recipient) can be confirmed by the inspection mechanism. Confirmation is provided by a third party (arbiter), which is trusted by all interested parties and which has the necessary information.
In addition to the above-listed protection mechanisms implemented by the protocols of various levels, there are two more, non-specific levels. They are similar to their intended control mechanisms in local systems:
Detection and processing of events (Analogue of hazardous events control means).
Designed to detect events that lead or can lead to a violation of network security policies. The list of these events complies with the list for individual systems. In addition, events may include events indicating violations in the work of the above-mentioned protection mechanisms. Actions taken in this situation may include various recovery procedures, event logging, unilateral disconnection, local or peripheral event report (log entry), etc.
Security verification report (analogue of verification using a system log).
Security verification is an independent verification of system entries and activities for compliance with the specified security policy.
The protection functions of each level protocols are determined by their assignment:
1. Physical level - control of electromagnetic emission of communication lines and devices, support for communication equipment in working condition. Protection at this level is provided by shielding devices, interference generators, physical protection of the transmitting medium.
2. Channel level - an increase in the reliability of protection (if necessary) by encrypting the data transmitted over the channel. In this case, all transmitted data is encrypted, including service information.
3. Network level - the most vulnerable level in terms of protection. All routing information is formed on it, the sender and the recipient appear explicitly, the flow control is carried out. In addition, the network-level protocols packets are processed on all routers, gateways, etc. Intermediate nodes. Almost all specific network violations are carried out using the protocols of this level (reading, modification, destruction, duplication, reorientation of individual messages or flow as a whole, disguise to another node, etc.).
Protection against all such threats is carried out by the protocols of the network and transport levels and with the help of cryptocrustics. At this level can be implemented, for example, selective routing.
4. Transport level - monitors network-level functions at the receiving and transmitting nodes (the traffic level protocol does not function on intermediate nodes). Transport leveling mechanisms check the integrity of individual data packets, packet sequences, traveled route, sending and delivery time, identification and authentication of the sender and recipient, etc. Functions. All active threats become visible at this level.
The guarantor of the integrity of the transmitted data is cryptotes of data and official information. Nobody besides the secret key of the recipient and / or the sender can not read or change the information so that the change remains unnoticed.
An analysis of the schedule is prevented by transmitting messages that do not contain information that, however, look like real. Adjusting the intensity of these messages, depending on the amount of information transmitted, you can constantly achieve a uniform schedule. However, all these measures cannot prevent the threat to destroying, reorienting or delaying the message. The only protection against such violations can be parallel delivery of duplicate messages on other ways.
5. Upper level protocols ensure control of the interaction of adopted or transmitted information with the local system. The protocols of the session and representative level of protection functions are not performed. The application-level protocol protection function includes access control to specific data sets, identification and authentication of certain users, as well as other functions defined by a specific protocol. More complex these features are in the event of a security policy security policy.
4. Corporate Internet
The corporate network is private case Corporate network of a large company. Obviously, the specificity of the activity places strict requirements for information protection systems in computer networks. An equally important role in building a corporate network plays the need to ensure trouble-free and uninterrupted work, since even a short-term failure in its work can lead to gigantic losses. And finally, it is required to ensure fast and reliable transmission of a large amount of data, since many application programs must operate in real time.
Corporate network requirements
The following main requirements for the corporate network can be distinguished:
The network combines into a structured and managed closed system. All owned company information devices: separate computers and local computing networks (LAN), host servers, workstations, telephones, faxes, office PBX.
The network provides reliability of its operation and powerful information protection systems. That is, the system is guaranteed to be sure to work as in personnel errors and in the case of an attempt unauthorized access.
There is a well-established communication system between separations of different levels (both with urban and non-residential branches).
In connection with modern development trends, a need for specific decisions appears. An essential role is acquired by the organization of the operational, reliable and secure access of the remote client to modern services.
5. Principles, Technologies, Internet Protocols
The main thing that distinguishes the Internet from other networks is its protocols - TCP / IP. In general, the term TCP / IP usually means everything connected with the interaction protocols between computers in the Internet. It covers a whole family of protocols, applied programs, and even the network itself. TCP / IP is a mechanical interaction technology, Internet technology. The network that uses the Internet technology is called "Internet". If we are talking about a global network that combines multiple networks with Internet technology, it is called the Internet.
The TCP / IP protocol received its name from two communication protocols (or communication protocols). This TRANSMISSION CONTROCOL (TCP) and INTERNET PROTOCOL (IP). Despite the fact that the Internet uses a large number of other protocols, the Internet is often called a TCP / IP network, since these two protocols are definitely the most important.
As in every other network in the Internet, there are 7 levels of interaction between computers: physical, logical, network, transport, communication session, representation and applied level. Accordingly, each interaction level corresponds to a set of protocols (i.e. interaction rules).
Physical layer protocols determine the type and characteristics of communication lines between computers. Internnet uses almost all currently known methods of communication from simple wire (twisted pair) to fiber optic communication lines (Vols).
For each type of lines of communication, the appropriate logical level protocol is developed, managing the transfer of information on the channel. The logical level protocols for telephone lines include SLIP (Serial Line Interface Protocol) and PPP (POINT TO POINT PROTOCOL). To communicate via a local network cable - this is batch drivers for LAN boards.
The network layer protocols are responsible for transmitting data between devices in different networks, that is, they are engaged in the network route. The network layer protocols belong to IP (Internet Protocol) and ARP (Address Resolution Protocol).
Transport level protocols manage data transfer from one program to another. TCP and UDP (User Datagram Protocol) are belonging to the Transmission Control Protocol.
Communication session protocols are responsible for the installation, maintenance and destruction of the corresponding channels. On the Internet, these are already mentioned TCP and UDP protocols, as well as the UUCP protocol (UNIX TO UNIX Copy Protocol).
Executive Level Protocols are engaged in servicing application programs. Executive Level Programs own programs running, for example, on a UNIX server, to provide various services to subscribers. Such programs include: Telnet Server, FTP Server, Gopher Server, NFS Server, NNTP (Simple Mail Transfer Protocol), POP2 and POP3 (Post Office Protocol), etc.
Applied level protocols include network services and programs for their provision.
6. Trends in the development of the Internet
In 1961, Darpa (Defence Advanced Research Agensy) on the task of the US Department of Defense began a project to create an experimental packet transmission network. This network, called Arpanet, was originally intended to study methods for ensuring reliable communication between computers of various types. Many data transfer methods through modems were developed in Arpanet. Then the data transfer protocols on the network were also developed - TCP / IP. TCP / IP is a lot of communication protocols that determine how computers of various types can communicate with each other.
An experiment with Arpanet was so successful that many organizations wanted to enter it, for the purpose of using for daily data transmission. And in 1975, Arpanet turned from the experimental network in working network. Responsibility for network administration took on DCA (Defence Communication Agency), currently called DISA (Defence Information Systems Agency). But the development of Arpanet did not stop at this; TCP / IP protocols continued to develop and improve.
In 1983, the first standard for TCP / IP protocols was entered in Military Standarts (MIL STD), i.e. In military standards, and everyone who worked on the network was obliged to go to these new protocols. To facilitate this transition, Darpa turned with a proposal to the company managers to implement TCP / IP protocols in Berkeley (BSD) UNIX. From this, the Unix and TCP / IP Union began.
After some time, TCP / IP was adapted to the usual, that is, the public standard, and the term internet went into universal use. In 1983, Milnet stood from Arpanet, which began to refer to the US Department of Defense. The term Internet began to be used to designate a single network: Milnet plus Arpanet. And although in 1991, Arpanet ceased to exist, the Internet network exists, its size is much higher than the initial, as it combined many networks around the world. Figure 4 illustrates an increase in the number of hosts connected to the Internet with 4 computers in 1969 to 8.3 million in 1996. The host on the Internet is called computers operating in a multi-tasking operating system (UNIX, VMS) supporting TCP \\ IP protocols and providing Users of any network services.
7. Basic components WWW, URL, HTML
World Wide Web is translated into Russian as a "World Wide Web". And, in essence, this is true. WWW is one of the most advanced tools for working in the global world Internet network. This service appeared relatively recently and still continues to grow rapidly.
The greatest number of developments are related to the homeland of WWW - CERN, European Particle Physics Laboratory; But it would be a mistake to assume that the Web is a tool developed by physicists and physicists. The fruitfulness and attractiveness of the ideas based on the project turned WWW into a global scale system that provides information hardly in all areas of human activity and covering approximately 30 million users in 83 countries of the world.
The main difference of WWW from the remaining tools for working with the Internet is that WWW allows you to work with almost all available now on the computer type of documents: it can be text files, illustrations, sound and video rollers, etc.
What is WWW? This is an attempt to organize all the information in the Internet, plus any local information For your choice, as a set of hypertext documents. You move over the network, moving from one document to another by reference. All these documents are written on a special language specifically designed for this, which is called HyperText Markup Language (HTML). He reminds of something that is used to write text documents, only HTML easier. Moreover, you can use not only the information provided by the Internet, but also to create your own documents. In the latter case, there are a number of practical recommendations for writing them.
All the benefits of a hypertext is to create hypertext documents if you are interested in any item in such a document, then you can poke there with a cursor to get the necessary information. Also in one document it is possible to make links to others written by other authors or even located on another server. While it seems to you as one.
Hypermedia is a hypertext suggestion. In hypermedia, operations are made not only over text but also over the sound, images, animation.
There are WWW servers for UNIX, Macintosh, MS Windows and VMS, most of them apply to free. By installing the www server, you can solve two tasks:
1. Provide information to external consumers - information about your company, product catalogs, technical or scientific information.
2. Provide its employees convenient access to the internal information resources of the organization. This can be the latest manual order, internal telephone directory, answers to frequently asked questions for users of applied systems, technical documentation and everything that tells the imaging of administrator and users. The information you want to provide WWW users is drawn up in the form of files in HTML. HTML is a simple markup language that allows you to marry text fragments and set references to other documents, allocate the headers of several levels, break the text on paragraphs, centen them, etc., turning the simple text into a formatted hypermedia document. It is enough to create an HTML file manually, however, there are specialized editors and file converters from other formats.
The main components of the World Wide Web technology
By 1989, the hypertext represented a new, promising technology that had a relatively large number of implementations on the one hand, and on the other hand, an attempt was made to construct formal models of hypertext systems, which were rather descriptive in nature and were inspired by the success of the relational description approach. The idea of \u200b\u200bT. Bernes-Lee was to apply a hypertext model to information resources distributed on the network, and to make it the most simple way. He laid three cornerstone of the system of the four existing now, developing:
hypertext Marking of HTML documents (Hypertext Markup Lan-Guage);
* universal way Addressing resources in the URL network (Universal Resource Locator);
* HTTP hypertext information exchange protocol (HYPERTEXT TRANSFER PROTOCOL).
* CGI Universal Gateway Interface (Common Gateway Interface).
HTML idea is an example of an extremely successful solution to the problem of building a hypertext system using a special display control tool. For the development of a language of hypertext marking, two factors were significantly influenced: studies in the field of hypertext interfaces and a desire to ensure a simple and fast way to create a hypertext database distributed on the network.
In 1989, the problem of the interface of hypertext systems was actively discussed, i.e. Methods of displaying hypertext information and navigation in the hypertext network. The value of hypertext technology was compared with the value of typography. It was alleged that the paper sheet and computer display / playbacks are seriously different from each other, and therefore the form of information presentation should also differ. Contextual hypertext references were recognized as the most effective form of a hypertext organization, and in addition, division was recognized on references associated with all the document as a whole and individual parts.
The easiest way to create any document is its packing in a text editor. The experience of creating well-fitted documents for the subsequent display in CERN_E was it difficult to find physics that would not use the Tex or LaTEX system. In addition, by the time there was a markup language standard - Standard Generalized Markup Language (SGML).
It should also be taken into account that according to its proposals of Berners-Lee, it was assumed to combine the available CERN information resources to the unified system, and the first demonstration systems were to become the system for Next and Vax / VMS.
Typically, hypertext systems have special software for the construction of hypertext links. Hypertext links themselves are stored in special formats or even make up special files. This approach is good for the local system, but not for distributed on a variety of different computer platforms. In HTML, hypertext links are built into the body of the document and stored as part of it. Often in systems use special data storage formats to increase access efficiency. In WWW, documents are ordinary ASCII files that can be prepared in any text editor. Thus, the problem of creating a hypertext database was solved extremely simple.
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Introduction .. 65.
2 cables and interfaces ... 10
3 Data exchange online .. 15
6 Internet Services .. 40
8 WEB LOOKING Tools 54
Introduction .. 6.
1 Network Concepts and Terms ... 7
1.1 Basic concepts. 7.
1.2 Classification of networks on scale. 7.
1.3 Classification of networks for server availability. 7.
1.3.1 peer-to-peer networks. 7.
1.3.2 networks with a dedicated server. eight
1.4 Network selection. nine
2 cables and interfaces ... 10
2.1 Types of cables. 10
2.1.1 Twisted Pair Type Cable - Twisted Pair 10
2.1.2 Coaxial cable. eleven
2.1.3 Fiber optic cable. 12
2.2 Wireless technology. 12
2.2.1 Radio communication. 13
2.2.2 Communication in the microwave range. 13
2.2.3 Infrared communication. 13
2.3 Cable Parameters. 13
3 Data exchange online .. 15
3.1 General concepts. Protocol. Stack of protocols. fifteen
3.2 Model ISO / OSI 16
3.3 ISO / OSI model level functions
3.4 Application interaction protocols and transport subsystem protocols. 21.
3.5 Functional compliance of modes of communication equipment Levels of model OSI 22
3.6 IEEE 802 specification. 24
3.7 on the protocol stack. 25.
4 Network equipment and topology .. 27
4.1 Network components. 27.
4.1.1 Network cards. 27.
4.1.2 Repeators and amplifiers. 28.
4.1.3 Hubs. 29.
4.1.4 Bridges. 29.
4.1.5 Routers. thirty
4.1.6 gateways. thirty
4.2 Types of network topology. 31.
4.2.1 Tire. 31.
4.2.2 Ring. 32.
4.2.3 Star. 32.
4.2.5 Mixed topologies. 33.
5 Global Internet Internet .. 36
5.1 Theoretical foundations of the Internet. 36.
5.2 Work with Internet services. 37.
6 Internet Services .. 40
6.1 Terminal mode. 40.
6.2 Email (E-Mail) 40
6.4 Teleconference Service (UseNet) 41
6.5 Service WORLD WIDE WEB (WWW) 43
6.6 Domain Names Service (DNS) 45
6.7 File Transfer Services (FTP) 48
6.8 Internet Relay Chat 49
6.9 ICQ service. 49
7 Connecting to the Internet .. 51
7.1 Basic concepts. 51.
7.2 Installing the modem. 52.
7.3 Connecting to the Internet service provider. 53.
8 WEB LOOKING Tools 54
8.1 Concept of browsers and their functions. 54.
8.2 Working with the program Internet Explorer. 54
8.2.1 Opening and viewing Web pages. 56.
8.2.3 Browser control techniques. 57.
8.2.4 Working with multiple windows. 58.
8.2.5 Setting the properties of the browser. 58.
8.3 Search for information in the World Wide Web. 60.
8.4 Receive files from the Internet. 62.
9 Working with emails .. 64
9.1 Sending and receiving messages. 64.
9.2 Working with the Outlook Express program. 65.
9.2.1 Create an account. 65.
9.2.2 Creating an email message. 66.
9.2.3 Preparation of responses to messages. 66.
9.2.4 Reading teleconferencing messages. 67.
9.3 Working with the address book. 67.
Introduction
The material under consideration in this abstract is not about a specific operating system and not even about a specific type of operating system. In it, operating systems (OS) are considered from the most common positions, and the fundamental concepts described and the principles of construction are fair for most OS.
1 Network Concepts and Terms
1.1 Basic concepts
The network is a connection between two and more computers, allowing them to share resources.
1.2 Network Classification
The local network Local Area Network) is a set of computers connected to a network located within a small physical region, for example, a single building.
This is a set of computers and other connected devices that fit into the action zone of one physical network. Local networks are basic blocks for the construction of united and global networks.
Global networks (Wide Area Network) can connect networks worldwide; For firewalls, third-party communications tools are commonly used.
Connections in global networks can be very expensive, since the cost of communication is growing with increasing bandwidth. Thus, only a small number of connections in global networks support the same bandwidth as the usual local networks.
Regional networks Metropolitan Area Network) use global networking technologies to combine local networks in a particular geographic region, such as city.
1.3 Classification of server availability
1.3.1 peer-to-peer networks
Computers in peer-to-peer networks can act as the role of clients and the role of servers. Since all computers in this type of networks are equal, then peer-to-peer networks do not have centralized resource separation management. Any computers in this network can share their resources with any computer from the same network. A peer-to-peer relationship also mean that no computer has neither the highest priority for access, nor high responsibility for providing resources into sharing.
Advantages of peer-to-peer networks:
- They are easy to install and configure;
- individual machines do not depend on the selected server;
- Users are able to control their own resources;
- inexpensive type of networks in the acquisition and operation;
- no additional equipment or software, except the operating system;
- No need to hire a network administrator;
- Well suits the number of users not exceeding 10.
Disadvantages of peer-to-peer networks:
- application of network security simultaneously only to one resource;
- Users must remember so many passwords as there are separated resources;
- It is necessary to back up separately on each computer to protect all the joint data;
- when accessing access to a resource, on a computer on which this resource is located, the drop in productivity is felt;
- There is no centralized organizational scheme for searching and managing access to data.
1.3.2 networks with a dedicated server
Microsoft prefers Server-Based term. The server is a machine (computer) whose main task is the reaction to client requests. Servers are rarely managed by someone directly - just to install, configure or serve.
Advantages of networks with a dedicated server:
- they provide a centralized management of user accounts, security and access, which simplifies network administration;
- more powerful equipment means more efficient access to network resources;
- users to enter the network you need to remember only one password, which allows them to access all resources that have the right;
- Such networks are better scaled (grow) with an increase in the number of customers.
Disadvantages of networks with a dedicated server:
- Server malfunction can make a network inoperable, at best - loss of network resources;
- Such networks require qualified personnel to accompany the complex specialized software;
- The cost of the network increases, due to the need for specialized equipment and software.
1.4 Network selection
The choice of network depends on a number of circumstances:
- the number of computers on the network (up to 10 - peer-to-peer networks);
- financial reasons;
- availability of centralized management, safety;
- access to specialized servers;
- Access to the global network.
2 Cables and Interfaces
At the lowest level of network communications there is a carrier for which data is transmitted. With regard to data transfer, the term Media (medium, data transfer environment) may include both cable and wireless technology.
2.1 Cable types
There are several different types of cables used in modern networks. Various network situations may require different types of cables.
2.1.1 "Twisted Pair" type cable - Twisted Pair
It is a network media used in many network topologies, including Ethernet, ArcNet, IBM Token Ring.
Twisted pair is two species.
1. Unshielded twisted pair.
There are five categories of unshielded twisted pair. They are numbered in order of quality increase from Cat1 to Cat5. Highly category cables usually contain more conductor pairs, and these conductors have more turns per unit length.
CAT1 - telephone cable, does not support digital data transfer.
Cat2 - is a rarely used old type of unshielded twisted pair. It supports data transfer rate up to 4 Mbps.
Cat3 - the minimum level of unshielded twisted pair required for today's digital networks has a bandwidth of 10 Mbps.
CAT4 - Intermediate cable specification that supports data transfer rate up to 16 Mbps.
Cat5 is the most efficient type of unshielded twisted pair that supports data transfer rate up to 100 Mbps.
Unshielded twisted pair cables connect the network card of each computer with a power panel or with a network hub using the RJ-45 connector for each connection point.
An example of such a configuration is the standard on ethernet network 10Base-T, which is characterized by a unshielded twisted pair cable (from Cat3 to Cat5) and using the RJ-45 connector.
Disadvantages:
- sensitivity to interference from the external electromagnetic sources;
- mutual overlay signal between adjacent wires;
- unshielded twisted pair vulnerable to intercept the signal;
- a large attenuation of the signal along the way (restriction up to 100 m).
2. Shielded twisted pair.
It has a similar design as the previous one, obeys the same 100 meter restriction. Usually contains four or more pairs of twisted copper insulated wires, as well as an electrically grounded woven copper mesh or aluminum foil, creating a screen from an external electromagnetic effect.
Disadvantages:
- cable less flexible;
- requires electrical grounding.
2.1.2 Coaxial Cable
This type of cable consists of a central copper conductor, thicker than wires in a cable type of twisted pair. The central conductor is coated with a layer of foamy plastic insulating material, which in turn is surrounded by a second conductor, usually a wicker copper mesh or aluminum foil. The external conductor is not used for data transmission, and acts as a ground.
Coaxial cable can transmit data from speed up to 10 Mbps at the maximum distance from 185 m to 500 m.
The two main types of coaxial cable used in local networks is the "thick Ethernet" (ThinkNet) and "Thin Ethernet".
Also known as the RG-58 cable is the most used. It is most flexible from all types of coaxial cables, has a thickness of about 6 mm. It can be used to connect each computer with other computers on the local network using the T-connector, British Naval Connector (BNC) -connector and 50-ohm plugs (Terminator Terminators). Used mainly for 10Base-2 Ethernet networks.
This configuration supports data transmission with a speed of up to 10 Mb / s to a maximum distance of up to 185 m between repeaters.
It is a thicker and more expensive coaxial cable. By design, it is similar to the previous, but less flexible. Used as the basis for 10Base-5 Ethernet networks. This cable has a RG-8 or RG-11 marking, approximately 12 mm in diameter. It is used in the form of a linear tire. To connect to each network board, a special external AUI transceiver and a vampire (branch), permeating cable shell to gain access to the wire.
It has a thick central conductor, which provides reliable data transmission at a distance of up to 500 m per cable segment. It is often used to create connecting highways. Data transfer rate up to 10 Mbps.
2.1.3 Fiber optic cable
Provide excellent information transfer rate over long distances. They are not susceptible to electromagnetic noise and overheard.
It consists of a central glass or plastic conductor surrounded by another layer of glass or plastic coating, and an external protective shell. The data is transmitted via cable using a laser or LED transmitter, which sends unidirectional light pulses through central glass fiber. Glass coating helps maintain light focusing in an internal conductor. At the other end of the conductor, the signal is received by a photodiode receiver, converting light signals into an electrical signal.
Data transfer rate for fiber optic cable reaches from 100 Mbps to 2Gbps. Data can be securely transferred to a distance of up to 2 km without repeaters.
Light pulses move only in one direction, so you need to have two conductor: incoming and outgoing cables.
This cable is folded in the installation, is the most expensive type of cable.
2.2 Wireless technology
Wireless data transmission methods are a more convenient form. Wireless technologies differ by signals, frequency, transmission distance.
Three main types of wireless data transmission are: radio communication, microwave communication, infrared communication.
2.2.1 Radioculum
Radiocommunication technologies ship data on radio frequencies and practically does not have a distance restrictions. Used to connect local networks on large geographic distances.
Disadvantages:
- radio transmission has a high cost,
- subject to state regulation,
- extremely sensitive to electronic or atmospheric influence,
- susceptible to interception, so requires encryption.
2.2.2 Communication in the Microwave Range
Supports data transfer in the microwave range, uses high frequencies and is used both at short distances and in global communications.
Restriction: The transmitter and the receiver must be in the direct visibility of each other.
It is widely used in the global transmission of information using satellites and ground satellite antennas.
2.2.3 Infrared communication
Functions at high frequencies approaching visible light frequencies. Can be used to establish a double-sided or broadcast data transfer to close distances. Typically use LEDs to transmit infrared waves receiver.
These waves can be physically blocked and experiencing interference with a bright light, therefore the transmission is limited to small distances.
2.3 Cable Parameters
When planning a network or expansion existing network It is necessary to clearly consider several issues related to cables: cost, distance, data transfer rate, ease of installation, number of supported nodes.
Comparison of cable types for data transfer speed, cable costs, installation complexity, maximum data transmission distance is presented in Table 2.1.
The number of nodes to the segment and nodes in the network in the construction of networks with various use of cables is presented in Table 2.2.
Table 2.1 - Comparative characteristics Cables
Table 2.2 - the number of nodes depending on the type of network
3 Data exchange online
3.1 General concepts. Protocol. Stack of protocols.
The main goal, which is prosecuted when connecting computers to the network is the ability to use each computer resources by all users of the network. In order to implement this feature, computers connected to the network must have the interaction tool with other network computers for this.
The task of separating network resources includes a solution to a variety of problems - selecting the method of addressing computers and coordinating electrical signals when installing electrical communication, ensuring reliable data transmission and processing error messages, generating sent and interpretation of received messages, as well as many other equally important tasks.
The usual approach in solving a complex problem is its partition to several private problems - subtasks. To solve each subtask, some module is assigned. At the same time, the functions of each module and the rules for their interaction are clearly defined.
A special case of the task decomposition is a multi-level representation, in which all many modules solving subtasks are divided into hierarchically ordered groups - levels. For each level, a set of query functions is defined, with which modules of this level can apply the modules above the underlying level to solve their tasks.
Such a set of functions performed by this level for above the underlying level, as well as the formats of messages that are exchanged by two neighboring levels during their interaction, is called an interface.
The rules for the interaction of two machines can be described as a set of procedures for each level. Such formalized rules that determine the sequence and format of the messages that are exchanged network components lying on the same level, but in different nodes are called protocols.
The agreed set of protocols of different levels, sufficient for the organization of firewall, is called stack of protocols.
When organizing interaction, two main types of protocols can be used. IN connection Protocols (Connection-Oriented Network Service, Cons) Before the exchange of data, the sender and recipient must first set the logical connection, that is, to agree on the parameters of the exchange procedure, which will act only within this compound. After completing the dialogue, they must break this compound. When a new connection is established, the negotiation procedure is re-made.
Second group of protocols - protocols without prior connection Connectionless Network Service, ClnS). Such protocols are also called datagram protocols. The sender simply transmits a message when it is ready.
3.2 ISO / OSI model
From the fact that the protocol is an agreement adopted by two interacting objects in this case, two computers working on the network, it does not undermine what it is necessarily a standard. But in practice, when implementing networks, the standard protocols seek to use. These may be branded, national or international standards.
International Standards Organization, ISO) has developed a model that clearly defines various levels of system interaction, gives them standard names and indicates what operation should each level. This model is called an open system interaction model (OPEN System InterConnection, OSI) or ISO / OSI model.
In the OSI model, the interaction is divided into seven levels or layers (Fig. 1). Each level deals with one specific interaction aspect. Thus, the problem of interaction is decomposed by 7 private problems, each of which can be solved independently of others. Each level supports interfaces with the above and underlying levels.
The OSI model describes only the system of interaction, without touching end-user applications. Applications implement their own interaction protocols, referring to the system tools. It should be borne in mind that the application can take on the functions of some upper levels of the OSI model, in which case, if necessary, it is referred to the system tools that perform the functions of the remaining lower levels of the OSI model.
The end-user application can use system tools of interaction not only to organize a dialogue with another application running on another machine, but also simply to obtain services for a network service.
So, let the application refers to the request to the application layer, for example, to the file service. Based on this request, the application-level software generates a standard format message to which the service information (title) places and, possibly transmitted data. Then this message is sent to the representative level.
The representative level adds its header to the message and transmits the result of a session level, which in turn adds its heading, etc.
Finally, the message reaches the lowest, physical layer, which really transmits it over lines of communication.
When a message on the network enters another machine, it is sequentially moving up from a level to level. Each level analyzes, processes and deletes a header of its level, performs the corresponding function to this level and transmits the message by the above level.
In addition to the term "Message" (Message), there are other names used by network specialists to indicate the data exchange unit. In ISO standards, such a term is used for protocols of any level as the Protocol Data Block - Protocol Data Unit (PDU). In addition, the names of the frame (FRAME), Packa (Datagram) are often used.
3.3 ISO / OSI level level functions
Physical level. This level is dealing with bits in physical channels, such as a coaxial cable, a twisted pair or fiber optic cable. The characteristics of the physical data transmission media are related to this level, such as bandwidth, noise immunity, wave resistance and others. At the same level, the characteristics of electrical signals are determined, such as requirements for pulse fronts, voltage levels or transmitting current, coding type, signal transmission rate. In addition, the types of connectors and the purpose of each contact are standardized here.
Functions of the physical layer are implemented in all devices connected to the network. On the computer, the physical layer function is performed by a network adapter or serial port.
Channel level. One of the tasks of the channel level is to check the availability of the transmission medium. Another channel level task is to implement detection and error correction mechanisms. To do this, on the channel bits, the bits are grouped into kits, called frames (Frames). The channel level ensures the correctness of the transmission of each frame, placing a special sequence of bits to the beginning and end of each frame to mark it, and also calculates the checksum, summing up all the frame bytes in a certain way and adding the checksum to the frame. When the frame comes, the recipient again calculates the checksum of the obtained data and compares the result with the checksum from the frame. If they coincide, the frame is considered correct and accepted. If the checksums do not match, the error is fixed.
In the channel level protocols used in local networks, a certain structure of connections between computers and the methods of their addressing are laid. Although the channel level and ensures the delivery of the frame between any two nodes of the local network, it makes it only on a network with a completely defined linking topology, it is the topology for which it has been developed. Such standard topologies supported by the channel level of local networks include a common tire, ring and star. Examples of channel level protocols are Ethernet, Token Ring, FDDI, 100VG-AnyLAN protocols.
Network level. This level is used to form a single transport system that combines several networks with various information transmission principles between end nodes.
Network level messages are invited to name packets. When organizing package delivery on the network level, the concept of "network number" is used. In this case, the recipient's address consists of a network number and a computer number in this network.
In order to transfer a message from the sender located on the same network, the recipient, located on another network, you need to make a certain number of transit gears (HOPS) between networks, each time choosing the appropriate route. Thus, the route is a sequence of routers through which the package passes.
The problem of choosing the best path is called routing and its solution is the main task of the network level. This problem is complicated by the fact that the shortest path is not always the best. Often the criterion when choosing a route is the data transfer time on this route, it depends on the bandwidth of the communication channels and the traffic intensity that can change over time.
At the network level, two types of protocols are determined. The first view refers to the definition of packet transmission rules with the data of the end nodes from the node to the router and between routers. It is these protocols that usually mean when they talk about network-level protocols. The network layer includes another type of protocols called the exchange protocols of route information. Using these protocols, routers collect information about the topology of firewalls. Network Level Protocols are implemented software modules operating system, as well as software and hardware of routers.
Examples of the network level protocols are the TCP / IP IP Stack IP and the NOVEll IPX Stack Schedule Protocol.
Transport level. On the way from the sender to the recipient, packages can be distorted or lost. Although some applications have their own error handling tools, there are also those who prefer to immediately deal with a reliable connection. The operation of the transport level is to provide applications or upper stack levels - applied and session - data transfer with that degree of reliability that they need. The OSI model defines five service classes provided by the transport level.
As a rule, all protocols starting from the transport level and above are implemented software End nodes of the network - components of their network operating systems. As an example of transport protocols, the TCP and UDP TCP / IP stack and the Novell SPX protocol can be given.
Session level. The session level provides a dialogue management in order to record which of the parties is active at the moment, and also provides synchronization tools. The latter allow you to insert control points into long transmissions so that in case of refusal it was possible to go back to the last checkpoint, instead of starting everything from the beginning. In practice, few applications use a session level, and it is rarely implemented.
Presentation level. This level ensures a guarantee that the information transmitted by the application level will be understood by the application level in another system. If necessary, the view level performs the conversion of data formats into some common representation format, and at the reception, respectively, performs the reverse transformation. Thus, application levels can overcome, for example, syntactic differences in data representation. At this level, encryption and decryption data can be performed, thanks to which the secrecy of data exchange is provided immediately for all application services. An example of a protocol operating at the presentation level is the Secure Socket Layer (SSL) protocol, which provides secret messaging for the TCP / IP stack application level protocols.
Applied level. Applied level is in reality just a set of diverse protocols by which network users get access to shared resources, such as files, printers, or hypertext web pages, and also organize their collaboration, for example, using the email protocol. A data unit that operates the application level is commonly called message (Message).
There is a very large variety of application-level protocols. We give as examples at least some of the most common implementations of file services: NCP in the Novell NetWare operating system, SMB in Microsoft Windows NT, NFS, FTP and TFTP included in the TCP / IP stack.
3.4 Application Interaction Protocols and Transport Subsystem Protocols
The functions of all levels of the OSI model can be attributed to one of the two groups: either to features depending on the specific technical implementation of the network, or to function-oriented features.
Three lower levels - physical, channel and network - are simulated, that is, the protocols of these levels are closely related to the technical implementation of the network, with the communication equipment used.
Three upper levels are a session, level of presentation and applied - applications are focused and few depend on the technical features of the network construction. No changes in the topology of the network, replacing the equipment or the transition to another network technology do not affect the protocols of these levels.
The transport level is intermediate, it hides all the details of the functioning of the lower levels from the upper levels. This allows you to develop applications that are independent of technical means directly involved in transportation of messages.
Figure 2 shows the levels of the OSI model on which various network elements work.
The computer, with the network OS installed on it, interacts with another computer using the protocols of all seven levels. This interaction computers are carried out through various communication devices: hubs, modems, bridges, switches, routers, multiplexers. Depending on the type, the communication device can work either only at the physical level (repeater), or on the physical and channel (bridge and switch), or on the physical, channel and network, sometimes capturing and transport level (router).
3.5 Functional compliance of modes of communication equipment levels of the OSI model
Best way To understand the differences between network adapters, repeaters, bridges / switches and routers is the consideration of their work in terms of the OSI model. The ratio between the functions of these devices and the levels of the OSI model is shown in Figure 3.
Repeater that regenerates signals, due to which it allows you to increase the length of the network, works at the physical level.
The network adapter works on the physical and channel levels. The physical layer includes that part of the network adapter functions, which is associated with the reception and transmission of signal signals, and get access to the shared transmission medium, the recognition of the computer's MAC address is already a channel level function.
Bridges perform most of their work on the channel level. For them, the network is presented by a set of MAC addresses. They remove these addresses from the headers added to the packages on the channel level, and use them during processing packets to make a decision on which port to send a particular package. Bridges do not have access to information about network addresses related to higher levels. Therefore, they are limited to making solutions about possible ways or routes for moving packets over the network.
Routers operate on the OSI network level. For routers, the network is a set of device network addresses and multiple network paths. Routers analyze all possible paths between any two network nodes and choose the shortest of them. Other factors, such as the status of intermediate nodes and communication lines, lines bandwidth or data transfer costs, can also be selected.
In order for the router to perform the functions assigned to it, more detailed network information should be available than the one that is available to the bridge. In the header of the network layer package, in addition to the network address, there are data, for example, the criteria that should be used when choosing a route, about the lifetime of the package in the network, about which top-level protocol belongs to the package.
Thanks to the use of additional information, the router can carry out more operations with packages than the bridge / switch. Therefore, the software required for the router is more complex.
Figure 3 shows another type of communication devices - a gateway that can operate at any level of the OSI model. Gateway (Gateway) is a device that translocates the protocols. The gateway is located between the interacting networks and serves as an intermediary that translates messages coming from one network into the format of another network. The gateway can be implemented both pure software installed on the usual computer and on the basis of a specialized computer. The broadcast of one stack of protocols to the other is a complex intelligent task that requires the most complete network information, so the gateway uses the headers of all translated protocols.
3.6 IEEE 802 Specification
At about the same time, when the OSI model appeared, the IEEE 802 specification was published, which actually expands the OSI network model. This extension occurs on channel and physical levels, which are defined as more than one computer can access the network, avoiding conflicts with other network computers.
This standard details these levels by splitting the channel level by 2 sublayers:
- Logical Link Control (LLC) - Logic connection management fairy. Controls the links between data channels and determines the use of the dots of the logical interface called Services Access Point (service points for services), which other computers can be used to transfer information to the upper levels of the OSI model;
- Media Access Control (Mac) - Contact Access Control Site. Provides parallel access for multiple network adapters on the physical level, has direct interaction with the computer's network card and is responsible for providing error-free data transmission between computers on the network.
3.7 on the protocol stack
A set of protocols (or protocol stack) is a combination of protocols that work together to provide network interaction. These protocol sets are usually divided into three groups corresponding to the OSI network model:
- Network;
- transport;
- Applied.
Network protocols provide the following services:
- addressing and routing of information;
- verification for errors;
- Request request;
- Setting the interaction rules in a specific network environment.
Popular Network Protocols:
- DDP (Delivery Datagram Protocol - Datagram Delivery Protocol). Transmission protocol apple dataUsed in AppleTalk.
- IP (Internet Protocol - Internet Protocol). Part of the TCP / IP protocol set, providing address information and routing information.
- IPX (Internetwork Packet Exchange - Firewall Schemes) and NWLink. Novell NetWare Network Protocol (and implementing this protocol by Microsoft) used to routing and directions of packages.
- NetBeui. Developed jointly IBM and Microsoft, this protocol provides transport services for NetBIOS.
Transport protocols are responsible for ensuring reliable transportation of data between computers.
Popular Transport Protocols:
- ATP (AppleTalk Transaction Protocol - AppleTalk Transaction Protocol) and NBP (Name Binding Protocol - Name Link Protocol). AppleTalk session and transport protocols.
- NetBIOS / NetBeui. The first - establishes a connection between computers, and the second - provides data services for this compound.
- SPX (Sequenced Packet Exchange - sequential exchange of packages) and NWLink. Connect-oriented Novell Protocol, used to provide data delivery (and implementing this protocol by Microsoft).
- TCP (Transmission Control Protocol - Transmission Management Protocol). Part of the TCP / IP protocol set is responsible for reliable data delivery.
Application protocols responsible for the interaction of applications.
Popular Applied Protocols:
- AFP (AppleTalk File Protocol - Filelock AppleTalk protocol). Macintosh remote control protocol.
- FTP (FILE TRANSFER PROTOCOL - Data Transmission Protocol). Another TCP / IP protocol dialing member used to provide file transmission services.
- NCP (NetWare Core Protocol - NetWare Basic Protocol). Shell and redirector customers Novell.
- SMTP (Simple Mail Transport Protocol - Simple Mail Transfer Protocol). TCP / IP dial member responsible for email transmission.
- SNMP (Simple Network Management Protocol - Simple Network Management Protocol). TCP / IP protocol used to manage and monitor network devices.
4 Network Equipment and Topologies
4.1 Network components
There are many network devices that can be used to create, segment and enhance the network.
4.1.1 Network cards
Network adapter (NETWORK INTERFACE Card, Nic.) - This is a computer peripheral device directly interacting with the data transmission medium that directly or through other communication equipment connects it to other computers. This device solves the task of a reliable exchange of binary data represented by the corresponding electromagnetic signals, according to external communication lines. Like any computer controller, the network adapter runs running the operating system driver.
In most modern standards for local networks, it is assumed that a special communication device (hub, bridge, switch or router) is installed between network adapters of interacting computers, which takes some functions to control the data stream.
The network adapter usually performs the following functions:
– Registration of transmitted information as a frame form of a specific format. The frame includes several service fields, including a destination computer address and a frame checksum.
– Access to data transfer environment. In local networks, the communication channels (total bus, ring) are mainly used, access to which is provided by a special algorithm (the most frequently applied the random access method or method with the transmission of the access marker).
– Coding the sequence of the frame bit by a sequence of electrical signals during data transmission and decoding when taken. Coding should provide the transmission of initial information on communication lines with a specific bandwidth and a certain level of interference so that the receiving party can recognize with a high degree of probability sent information.
– Converting information from parallel shape to serial and back. This operation is associated with the fact that in computing networks the information is transmitted in a sequential form, bit beyond the bit, and not tolerately, as inside the computer.
– Synchronization of bits, bytes and frames. For sustainable reception of the transmitted information, it is necessary to maintain the permanent synchronism of the receiver and the information transmitter.
Network adapters differ in the type and bit of the internal data bus used in the computer - ISA, EISA, PCI, MCA.
Network adapters also differ by type of network technology adopted in the network - Ethernet, token Ring, FDDI, etc. Usually, specific model The network adapter works on a specific network technology (for example, Ethernet).
Due to the fact that for each technology it is possible to use different transmission media, the network adapter can support both one and at the same time several media. In the case when the network adapter supports only one data transfer medium, and the other, transceivers and converters are used.
Transceiver (Transmitter, Transmitter + Receiver) - This is part of the network adapter, its terminal device overlooking the cable. In Ethernet versions, "but it turned out to be convenient to release network adapters with the AUI port to which the transceiver can be attached for the desired environment.
Instead of selecting a suitable transceiver, you can use converterwhich can match the output of a transceiver intended for one environment, with a different data transfer medium (for example, a watery output is converted to an output to the coaxial cable).
4.1.2 Repeaters and amplifiers
As mentioned earlier, the signal when moving over the network weakens. To prevent this weakening, you can use repeaters and (or) amplifiers that enhance the signal passing through them.
Repeater (REPEATER) are used in networks with a digital signal to combat the attenuation (weakening) of the signal. When the repeater gets a loose signal, it clears this signal, enhances and sends the next segment.
Amplifier (amplifier), although they have a similar purpose, are used to increase the transmission range in networks using an analog signal. This is called broadband. The media is divided into several channels, so different frequencies can be transmitted in parallel.
Usually the network architecture determines the maximum number of repeaters that can be installed in a separate network. The reason for this is a phenomenon known as "distribution delay". The period required by each repeater for cleaning and amplifying a signal multiplied by the number of repeaters can lead to noticeable data transmission delays over the network.
4.1.3 Hubs
The hub (HUB) is a network device acting on the physical level of the OSI network model, which serves as central point Connections and connecting line in the "Star" network configuration.
There are three main types of hubs:
- Passive (passive);
- active (ACTIVE);
- Intellectual (Intelligent).
Passive hubs do not require electricity and act as a physical connection point, without adding anything to the passing signal).
Active require the energy that is used to restore and amplify the signal.
Intelligent hubs can provide services such as Packet Switching and Traffic Redirection (Traffic Riuting).
4.1.4 Bridges
Bridge (Bridge) is a device used to connect network segments. Bridges can be viewed as an improvement of repeaters, as they reduce the network load: Bridges read the address network card (Mac Address) Recipient Computer from each incoming data packet and view special tables to determine what to do with a package.
The bridge functions on the channel level of the OSI network model.
The bridge functions as a repeater, it receives data from any segment, but it is more picking than the repeater. If the recipient is in the same physical segment as the bridge, the bridge knows that the package is no longer needed. If the recipient is in another segment, the bridge knows that the package must be sent.
This processing allows you to reduce the network load, since the segment will not receive messages that do not belong to it.
Bridges can connect segments that use different carriers (10Baset, 10Base2), as well as with different media access schemes (Ethernet, Token Ring).
4.1.5 Routers
Router (Router) is a network communication device operating on the network-level network model, and can bind two or more network segments (or subnets).
It functions like a bridge, but to filter traffic, it uses not the address of the computer's network card, but information about the network address transmitted to the packet relating to the network layer.
After receiving this information, the router uses the routing table to determine where to send the Package.
There are two types of routing devices: static and dynamic. The first use the static routing table, which must create and update the network administrator. The second - create and update their tables themselves.
Routers can reduce network load, increase bandwidth, as well as increase the reliability of data delivery.
The router can be both a special electronic device and a specialized computer connected to several network segments using multiple network cards.
It can associate several small subnets using various protocols if the protocols used are supported by routing. Route protocols have the ability to redirect data packets to other network segments (TCP / IP, IPX / SPX). Not routable protocol - NetBeui. He cannot work outside his own subnet.
4.1.6 gateways
Gateway (Gateway) is a communication method between two and more network segments. Allows you to interact in incomplete systems on the network (Intel and Macintosh).
Another gateway function is the protocol conversion. The gateway can get the IPX / SPX protocol to the client using the TCP / IP protocol on the remote segment. The gateway converts the source protocol to the required recipient protocol.
The gateway operates at the transport level of the network model.
4.2 Types of network topology
Under the topology of the network it is understood as a description of its physical location, that is, how computers are connected ones with each other and with the help of which devices are included in the physical topology.
There are four main topologies:
- bus (tire);
- Ring (ring);
- Star (Star);
- Mesh (cell).
The physical topology of the tire, referred to as the linear tire, consists of a single cable to which all the computers of the segment are attached (Fig. 4.1).
Messages are sent over the line to all connected stations, regardless of who is a recipient. Each computer checks each package in the wire to determine the package recipient. If the package is intended for another station, the computer rejects it. If the package is designed to this computer, it will receive and process it.
Figure 4.1 - Topology "Tire"
The main tire cable, known as the highway, has at both ends of the plug (terminators) to prevent signal reflection. Usually, two types of media are used in networks with tire topology: thick and thin Ethernet.
Disadvantages:
- It is difficult to isolate the station or other network component;
- Problems in the main cable can lead to the failure of the entire network.
4.2.2 Ring
The Ring Topology (Ring) is used mainly in TECK Ring and FDDI networks (fiber optic).
IN physical topology "Ring" data transfer lines actually form a logical ring to which all network computers are connected (Fig. 4.2).
Figure 4.2 - Topology "Ring"
Access to the carrier in the ring is carried out through markers (TOKEN), which are started in a circle from the station to the station, giving them the opportunity to send the package if necessary. A computer can only send data when owning a marker.
Since each computer with this topology is part of the ring, it has the ability to send any data packets received by another station.
Disadvantages:
- malfunctions at one station can lead to the failure of the entire network;
- When reconfiguring any part of the network, it is necessary to temporarily disable the entire network.
4.2.3 Star
In the Star Topology (Star), all computers in the network are connected to each other with a central hub (Fig. 4.3).
All data that the station sends is sent directly to the hub that sends the package in the direction of the recipient.
In this topology, only one computer can send data at a specific point in time. With a simultaneous attempt of two and more computers, send data, they will all get a failure and will be forced to wait for a random time interval to repeat the attempt.
These networks are better scaled than other networks. Maltages at one station do not fail the entire network. The presence of a central hub facilitates the addition of a new computer.
Disadvantages:
- requires more cable than other topologies;
- The failure of the concentrator will invalid the entire network segment.
Figure 4.3 - Star Topology
The MESH topology (cell) connects all computers pairwise (Fig. 4.4).
Figure 4.4 - Topology "Cell"
Mesh networks use a much larger cable than other topologies. These networks are much more difficult to install. But these networks are resistant to failures (capable of working with damage).
4.2.5 Mixed topologies
In practice, there are many combinations of main network topologies. Consider the main of them.
Star Bus.
The Mixed Star Bus Topology (Star on the Tire) combines the topology of the bus and a star (Fig. 4.5).
Star Ring Topology (Star on the Ring) is also known as Star-Wired Ring, since the hub itself is made as a ring.
This network is identical to the topology "Star", but in fact the hub is connected by wires as a logical ring.
Also, as in the physical ring, markers are sent in this network to determine the procedure for transmitting data to computers.
Figure 4.5 - Topology "Star on Tire"
Hybrid Mesh.
Since the implementation of the real MESH topology in large networks can be expensive, the Hybrid Mesh topology network can provide some of the significant advantages of this MESH network.
Mainly applies to connecting servers that store critical data (Fig. 4.6).
Figure 4.6 - Topology "Hybrid Cell"
5 Global Internet Network
5.1 Theoretical Basics of the Internet
Early transmission experiments and reception with computers began in the 50s and had a laboratory. Only in the late 1960s, the Agency of the Agency of the Prospective Development of the US Department of Defense was created network Network. She got a name Arpanet.. This network associated several large scientific, research and educational centers. Its main task was to coordinate groups of groups working on unified scientific and technical projects, and the main purpose was exchanged by email files with scientific and design documentation.
ARPANET network earned in 1969. The few nodes included in it at the time were associated with dedicated lines. Reception and transmission of information were provided by programs running on nodal computers. The network gradually expanded due to the connection of new nodes, and by the beginning of the 80s, on the basis of the largest nodes, their regional networks were created, recreating the overall architecture of the Arpanet at a lower level (in a regional or local scale).
For real born internet It is considered to be 1983. This year, revolutionary changes in computer communication software occurred. The day of the Internet in a modern understanding of this word was the date standardization of the TCP / IP communication protocol underlying the worldwide network to this day.
TCP / IP is not one network protocol, but several protocols lying at different levels of the OSI network model (this is the so-called protocol stack). Of these, the TCP protocol is a transport level protocol. It controls how information is transmitted. Protocol IP address. It belongs to the network layer and determines where the transfer takes place.
Introduction
Computer network - Association of several computers to jointly solve information, computational, educational and other tasks.
One of the first to develop computer equipment Tasks required to create a network of at least two computers - providing many times more than one machine, reliability when managing a responsible process in real time. Thus, when the spacecraft is launched, the necessary reaction rate to external events exceed human capabilities, and the failure of the control computer faces irreparable consequences. In the simplest scheme, the operation of this computer duplicates the second same, and with a failure of the active machine, the contents of its processor and RAM is very quickly transferred to the second, which picks up control (in real systems, everything, of course, is significantly more complicated).
Here are examples of other, very dissimilar, situations in which the combining of several computers is necessary.
A. In the simplest, cheapest educational computer class, only one inspector - the teacher's workplace - has a drive that allows you to save the program on the disk and the data of the entire class, and the printer, with which you can print texts. For the exchange of information between the workplace of the teacher and the workplaces of students, we need a network.
B. For the sale of railway or air tickets, in which hundreds of cashiers participate throughout the country at the same time, we need a network connecting hundreds of computers and remote terminals at ticket sales points.
B. Today, there are many computer databases and data banks on a variety of aspects of human activity. For access to the stored information in them, you need a computer network.
EUM networks are rushing into the life of people - both in professional activities and in life - the most unexpected and massive way. Knowledge of networks and skills of work in them become the necessary multitude of people.
Computer networks have created substantially new information processing technologies -Setheye technology. In the simplest case, network technologies make it possible to share resources - high-capacity drives, printing devices, Internet access, databases and data banks. The most modern and promising approaches to networks are associated with the use of collective division of labor when working together with information - the development of various documents and projects, management of the institution or enterprise, etc.
The simplest view of the network is the so-called peer-to-associate network. personal computers end users and allows you to share drives, printers, files.
More advanced networks besides computers of end-users of erectors - include special selected computers - servers. The server is a computer. Performing special functions of servicing other network computers - workstations. there is different types Servers: File, Telecommunication servers, servers for mathematical calculations, database servers.
Very popular today and extremely perspective technology Information processing on the network is called "client - server". The "Client-Server" methodology is assumed to be a deep separation of computer functions on the network. At the same time, in the "client" function (under which a computer with the relevant software is understood)
Providing a user interface focused on certain production duties and user powers;
The formation of requests to the server, and not necessarily informing the user; Ideally, the user does not delve into the computer communication technology, which it works, with the server;
Analysis of server responses to requests and serve them. The main function of the server is to perform specific actions at customer requests (for example, solving a complex mathematical problem, data search in the database, a client compound with another client, etc.); At the same time, the server itself does not initiate any interactions with the client. If the server to which the client addressed is not able to solve the task due to the lack of resources, then ideally he finds another, more powerful, server and transfers the task to him, becoming, in turn, the client, but not informing about it without The needs of the initial client. We note that the "client" is not at all the submissive server terminal. Customer can be quite powerful computerThat, by virtue of its capabilities, solves the task yourself.
Computer networks and network information processing technologies have become the basis for building modern information systems. The computer now should be considered not as a separate processing device, but as a "window" in computer networks, a tool for communications with network resources and other users of networks.
Local networks
HARDWARE
Local Networks (LAN Computer) are combined with a relatively small number of computers (usually from 10 to 100, although occasionally occur and much large) within one room (educational computer class), buildings or institutions (for example, university). The traditional name is a local computing network (LAN) - rather tribute, in the time, when networks were mainly used to solve computational tasks; Today, in 99% of cases, we are talking exclusively about the exchange of information in the form of texts, graphic and video images, numerical arrays. The usefulness of the LS is due to the fact that from 60% to 90% of the necessary institution of information circulates inside it, without needing output.
The creation of automated enterprises management systems (ACS) has great impact on the development of drugs. The ACS includes several automated jobs (AWP), measuring complexes, control points. Another crucial field of activity in which LS has proven its effectiveness -Creeding class of educational computers (KUVT).
Due to the relatively small lengths of communication lines (as a rule, no more than 300 meters), you can transfer information in a digital form with a high transmission rate. At long distances, such a 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-analog transformations) and software (error correction protocols, etc.) solutions.
The characteristic feature of the LS is the presence of binding all subscribers of the high-speed communication channel for transmitting information in digital form. There are wired and wireless (radio) channels. Each of them is characterized by certain values \u200b\u200bof the parameters of the parameters substantial in terms of the organization:
Data transfer speeds;
Maximum line length;
Noise immunity;
Mechanical strength;
Convenience and ease of installation;
Cost.
Currently use four types of network cables:
Coaxial cable;
Unprotected twisted pair;
Protected twisted pair;
Fiber optic cable.
The first three types of cables transmit electrical signal over copper conductors. Fiber optic cables transmit light on glass fiber.
Most networks allow multiple cable connections.
Coaxial cables consist of two conductors surrounded by insulating layers. The first insulation layer surrounds the central copper wire. This layer is braided outside an external shielding conductor. The most common coaxial cables are fat and thin Ethernet cables. This design provides good noise immunity and small signal attenuation at distances.
There are thick (about 10 mm in diameter) and thin (about 4 mm) coaxial cables. With advantages on noise immunity, strength, length of lines, a thick coaxial cable is more expensive and harder in the installation (it is more difficult to stretch through the cable channels) than thin. Until recently, the thin coaxial cable was a reasonable compromise between the main parameters of the LAN communication lines and in Russian conditions most often used to organize large LANs of enterprises and institutions. However, more expensive thick cables provide better data transmission for greater distance and less sensitive to electromagnetic interference.
Twisted couples are two occasions twisted together with six inch turns to ensure protection against electromagnetic interference and the coordination of impedance or electrical resistance. Another name, usually used for such a wire, is "IBM Type-3". In the US, such cables are placed when building buildings to provide telephone communication. However, the use of a telephone wire, especially when it is already placed in the building, can create big problems. First, unprotected twisted pairs are sensitive to electromagnetic interference, such as electrical noise generated by luminescent lamps and moving elevators. Interference can also create signals transmitted via a closed loop in telephone lines passing along the local network cable. In addition, the twisted pairs of poor quality can have variable numelists per inch, which distorts the calculated electrical resistance.
It is also important to note that the telephone wires are not always laid in a straight line. Cable connecting two nearby rooms can actually get around half of the building. The underestimation of the length of the cable in this case may lead to the fact that it will actually exceed the maximum allowable length.
Protected twisted pairs are similar to unprotected, except that they use thicker wires and are protected from external exposure to the insulator layer. The most common type of such cable used in local networks, "IBM Type-1" is a secure cable with two twisted pairs of continuous wire. In the new buildings, the best option can be the "type-2" cable, as it includes, in addition to the data line, four unprotected pairs of continuous wire for transferring telephone negotiations. Thus, "Type-2" allows you to use one cable for transmalethephon negotiations and data on the local network.
Protection and careful observance of the number of obes make a secure cable with twisted pairs with reliable alternative cable connections. However, this reliability leads to an increase in value.
Fiber optic cables transmit data in the form of light pulses along glass "wires". Most local network systems are currently supported by a fiber optic cable connection. The fiber optic cable has significant advantages compared to any variants of the copper cable. Fiber optic cables provide the highest transfer rate; they are more reliable because not subject to losses information bags Due to electromagnetic interference. The optical cable is very thin and flexible, which makes it transporting it more convenient compared to a heavier copper cable. However, the most important thing is that only the optical cable has sufficient bandwidth, which in the future will be required for faster networks.
While the price of a fiber-optic cable is significantly higher than copper. Iproof with a copper cable Installation of an optical cable more time consuming, since it should be carefully polished and aligned to ensure a reliable connection. However, now there is a transition to fiber-optic lines, absolutely surrendered interferences and competing for bandwidth. The cost of such lines is steadily declining, the technological difficulties of the optical fiber docking are successfully overcome.