The values \u200b\u200bdescribing the efficiency of the computer network:
1. Parameters (primary):
Structural;
Functional;
Load;
2. Characteristics (secondary):
High-quality;
Quantitative.
Network parameters are values \u200b\u200bdescribing the structural and functional organization of the network and its interaction with the external environment.
Network characteristics - describe its efficacy and depend on the parameters. Defined during operation by measurements and in the process of solving system analysis tasks, as the parameter function.
Structural parameters - determine the composition and structure of the network: the number of nodes included in the network and their relationship (network topology); Types of nodes, composition and number of equipment; Technical parameters of devices; Channel bandwidth, etc.
Functional parameters - describe data management strategy in computer network and data processing strategy in nodes. Examples of parameters: Switching method, communication channel access method, algorithm for selecting a route in data transmission on a network, distribution of applications via network nodes, task priorities, etc.
Load parameters - describe network interaction in the external environment. Example: The number of data stream types (audio, video, data, etc.), intensity of receipt of messages (packets or frames), the size of the data transmitted over the network, the resource-intensity of applied tasks.
Qualitative characteristics:
1. Operational features Networks (list of services, services for transmission and data processing);
2. Scalableness - The network's ability to linearly increase its productivity, which can be estimated quantitatively through the ratio of the increase in the performance of the system to increase resources. (The closer to 1, the greater the scalability);
3. manageability - the possibility of administration in order to identify and solve problems arising in network, as well as network development planning and upgrading;
4. Flexibility - Saving the quality of the network functioning when it changes its composition and configuration into the results of equipment failure or add new devices.
Quantitative characteristics:
Computer network performance - Measure of the network power, which determines the amount of work performed by the network per unit of time. Divided by sPD performance - measured by the number of messages (packets, frames, bits) transmitted over the network per unit time, and data processing performance - represents the total performance of data processing.
Features of operationalism - describe delays arising from transmitting and processing data on the network. Divided by time of delivery Messages I. response time.
Characteristics of reliability:
Probability of trouble-free operation of the network;
Failure intensity;
Time of operation for failure - the time interval between two adjacent failures;
Recovery time;
The coefficient of readiness is the share of time during which the network is operational.
Cost Characteristics Network:
- Complete cost of ownership (TSO - Total Cost of Ownership) - costs calculated at all stages of the network life cycle and including the cost of technical, information and software (direct costs) and network operation costs (indirect costs).
The transfer price and data processing on the network is determined by the amount and cost of resources used in the network when transmitting and processing data.
Chapter 3. General Computer Network Information
The material presented earlier will require us to study computer networks, since computer networks are a further development of I / O and allow you to send data between computers, as well as use the total resources of computing systems
Definition, Terminology and Appointment of Computer Networks
Man without communication - what a bird without wings.
In the general case, the communication network is a distributed system of communications that serves to transmit information at a distance. These include television and broadcasting networks, telephone and cellular networks, cable television networks, etc. Synonym for communication - data transmission. The concept of the telecommunications network involves a territorially distributed data network.
A separate computer is an example of a centralized computing system. Unlike centralized, computing network - distributed computing system. This is a combination of computer and communication equipment, communication channels and special software that controls the distributed calculation process between members of this network.
Since recently increased the role of transmitting unlicas information through the computing networks, now the term data network is often used for them. To avoid confusion with a communication network, in which the data is also transmitted, the computer network is used for the computing network.
Computer networks serve to perform the following tasks:
o conducting distributed computing;
o Access organization with centralized (server) information processing;
o general use of hardware resources;
o operational search and receipt of data in corporate resources;
o operational search and receipt of various information in global networks;
o exchange messaging, correspondence, information transmission of various species, etc.
General concepts. Network topologies
Any network consists of knots and connecting their communication lines. Nodes are finite and intermediate. The end node has 1 connection with the line of communication, intermediate - more than one.
Network Networks can be stations (hosts, network computers), or special communication equipment (in Fig. 10 nodes indicated by the "" symbol). The simplest network contains 2 node stations (Fig. 10, a).
Network topology is a graph of computer network links, that is, the type of connection of nodes and communication lines. The following main network topologies distinguish (Fig. 10):
o Typical: a) point-point - contains 2 nodes; b) tire (linear network) - contains only two terminal nodes, any number of intermediate nodes and has only one way between any two nodes; c) the star - the network in which there is only one intermediate node; d) a tree (hierarchical star) - a network that contains more than two terminal nodes and at least two intermediate nodes, and in which there is only one path between two nodes; e) Ring - a network in which only two branches are attached to each node;
o Derivatives: E) Mixed (combined) - formed by a typical connection; g) complete connection - each node is connected to all the others; h) cellular - a network that contains at least two nodes having two or more paths between them (the type of mixed, in which the separation for typical topologies is not clearly visible);
Fig. 10 Main network topologies.
Lines connecting data network nodes are called data transmission channels or communication channels. The physical environments used for communication channels will be discussed in this chapter below.
Some important concepts.
Traffic Called the data flow through the communication channel or via the network device, as well as the volume of this flow in bytes.
Protocol The rules for transferring information on the network are called.
Address Network Network (network address) is called its unique identifier, describing the location of the network node and allows you to send information to this particular node.
The refined definition of the protocol and in more detail about addressing in computer networks will be told in this chapter when learning the OSI model.
Classification and characteristics of computer networks
Diameter The network is called the distance between the two stations of this network most remote from each other.
Computer networks are divided depending on the diameter of the network and the type of equipment used on the following types (the approximate range of diameters is indicated in brackets):
o Local (1-3000 m) - combine computers within a few buildings;
o Campus (100-10000 m) - Local Networks of the Scale "Campus" - a small town;
o urban (5-20 km) - high-speed communication channels within the big city;
o Regional (territorial) (100-1000 km) - combine computers of the geographical area;
o Global (10,000-20000 km) - combining computers in various parts of the world (Internet).
The most important characteristic of the computer network is its bandwidth. The bandwidth (bit rate of information) is the amount of information that can be transmitted on this network per unit of time. The bandwidth is measured in the bit / s. 1 bit / s is 1 bits of information transmitted for 1 s. Multiple units are used: Kbps, Mbit / s, Gb / s.
Depending on the nature of the distribution of functions distinguish:
o. peer-to-peer networks - small local networks, in which all computers are functionally equal; Usually include up to 15 stations;
o. networks with selected servers (Double networks) - medium and large networks in which part of the functions performed by the stations are assigned to the servers.
Networks with selected servers are characterized by the types of network services used in them (servers), which will be described below.
Data transfer media
Electromagnetic signals in the form of oscillations of different frequencies are used as media in modern communication technology. Under the data transmission medium (communication), the physical environment is understood by the signal at its passage along the communication line.
In communication lines, 2 main technologies are used: conductor and wireless.
ConditionsUsed in computer networks are divided into:
1. 1) copper electrical conductors. The most common transmission environment. A variable electrical current of different frequencies and signal forms is used as a medium of information. The most common types of cables used in computer networks:
o. coaxial cable - isolated copper veins, shielded with metal braid;
o shielded or unshielded twisted pair - a pair of isolated twisted wires;
o General use telephone lines (TFOP) - two-housing insulated wires of subscriber lines and multi-cable telephone communications cables.
2. 2) fiber optic (fiber optic) lines (WOLS) are a hollow flexible conductor (light guide), coated from the inside by reflective substance. A modulated light beam is used as a carrier, emitted by a laser.
For wireless communication As an environment, surrounding air, water, vacuum or other medium, not delaying electromagnetic waves, are used, which are the carrier of information in this case. In the frequency range, wireless communication is divided into:
o radio communication - used in satellite communications and with remote access;
o infrared - is used mainly to communicate with wireless peripheral devices;
o optical - it is rarely used due to the presence of interference on the signal propagation path;
o Ultrahigh-frequency (microwave) - used in local networks.
The quality of the network is characterized by the following properties: performance, reliability, compatibility, handling, security, expandability and scalability.
There are two main approaches to providing the quality of the network. The first is that the network guarantees the user to comply with some numerical value of the quality of service. For example, Frame Relay and ATM networks can guarantee the user a given bandwidth. With the second approach (BEST EFFORT), the network is trying to better serve the user if possible, but nothing guarantees.
The main characteristics of the network performance include: reaction time, which is defined as time between the emergence of a request to any network service and receiving an answer to it; The bandwidth, which reflects the amount of data transmitted by the network per unit of time, and the transmission delay, which is equal to the interval between the moment of receipt of the package to the input of any network device and the moment of its appearance at the output of this device.
To assess the reliability of networks, various characteristics are used, including: the coefficient of readiness, meaning a time share during which the system can be used; Safety, that is, the ability of the system to protect data from unauthorized access; Failure tolerance - the ability of the system to work in the conditions of refusing to some of its elements.
Extensibility It means the possibility of relatively easy to add separate network elements (users, computers, applications, services), building the length of the network segments and replacing the existing hardware to be more powerful.
Scalabilityit means that the network allows you to increase the number of nodes and the length of the links in very wide limits, while the network performance does not deteriorate.
Transparency - The network property hide the details of your internal device from the user, thereby simplifying its operation on the network.
Network handling It implies the ability to centrally monitor the state of the main network elements, detect and resolve problems arising during network operation, perform performance analysis and plan network development.
Compatibility This means that the network is capable of include the most diverse software and hardware.
Topology- configuration of physical connections between network nodes. Network characteristics depend on the type of topology installed. In particular, the choice of one or another topology affects:
On the composition of the necessary network equipment;
Network equipment capabilities;
Network expansion capabilities;
Method of network management.
Under the term "Topology" COP may imply physical topology (configuration of physical connections) or logical topology - signal transmission routes between network nodes. The physical and logical topology of the COP may coincide or vary. Local networks are built on the basis of three basic topologies known as:
· Total bus (BUS);
· Star (star)
In order for the network successfully coped with the task, it must meet the requirements for productivity, reliability, etc.
Network performance determines The amount of transmitted data and the time required for their transmission. Numerical characteristics are used to evaluate performance - network reaction time, average bandwidth, maximum capacity, transmission delay.
Reliability means the likelihood that the network performs its functions. The reliability of technical devices is usually characterized by the time of operation for failure and the readiness ratio (the percentage of time during which the system can be used). The reliability of complex systems is also characterized by the probability of delivery of the message to the addressee.
Safety Indicates the impossibility of unauthorized access to data and ensuring reliability and resistance to deliberate destructive actions.
Extensibility- The possibility of relatively easy to add new network elements.
Scalability - The ability to significantly increase the size of the network, including by increasing the number of segments.
Transparency - The ability to use network resources in the same way, regardless of their actual placement - on the local computer or online. At the same time, the user as if "does not notice" the network, working directly with the resources.
Support for various types of traffic - The ability to combine the functions of various networks, such as television, telephone, computer.
Controllability - the ability to centralized detection and troubleshooting, distribution of resources and powers between users.
Compatibility - Ability to interact with various equipment and software.
On the territorial sign of the network divide on local, regional and global.
Regional networks Covers the city, district, region, a small republic. Sometimes there are corporate networks, where it is important to protect information from unauthorized access (for example, a network of the Ministry of Defense, banking networks, etc.). A corporate network can combine thousands and tens of thousands of computers posted in various countries and cities (a network of Microsoft Corporation can be brought as an example).
Local networks (LAN) . The main purpose of any computer network is the provision of information and computing resources connected to it users.
From this point of view, the LAN can be viewed as a set of servers and workstations.
Server- A computer connected to the network and providing its users with certain services.
Servers can store data, managing databases, remote task processing, print jobs and a number of other functions, the need for users can occur in the network. Server - Network resource source.
Work station - Personal computer connected to the network through which the user gets access to its resources.
The network workstation functions both in the network and local mode. It is equipped with its own OS, provides the user with all the necessary tools to solve applied tasks.
Special attention should be paid to one of the types of servers - file server.
It stores network user data and provides them with access to these data. This is a computer with a large capacitance of OP, high-capacity hard drives and additional magnetic tape drives (strimmers).
It works under the control of a special OS, which provides simultaneous access to network users to the data located on it.
The file server performs the following functions: data storage, data archiving, data transmission.
For many tasks, the use of one server file is insufficient. Then the network may include multiple servers.
Computer networks implement distributed data processing. Data processing in this case is distributed between two objects: client and server.
Client - Task, workstation or computer network user.
In the processing process, the client can form a request to the server to perform complex procedures, reading a file, search for information in the database, etc.
The server executes a request received from the client. The results of the execution of the request are transmitted to the client. The server provides storage of public data, organizes access to this data and transmits data to the client.
The client processes the data obtained and represents the processing results in a convenient for the user. In principle, data processing can be performed on the server. For such systems, the terms are taken - systems client-server. or architecture client-server..
Architecture client-server. It can be used both in peer-to-peer LAN and on a network with a dedicated server.
Single Network - There is no single working stations interaction management center and there is no single storage device. The network user is available all devices connected to other stations (discs, printers).
Dignity - Low cost and high reliability.
disadvantages - dependence of the efficiency of the network from the number of stations; The complexity of network management; the complexity of ensuring information protection; Difficulties of updating and changing stations software.
Network with a dedicated server - On the network, one of the computers performs data storage features intended for all workstations, interaction management between workstations and a number of service functions.
Such a computer is called the network server. It is installed on it the network OS, all shared external devices are connected to it - hard drives, printers, modems.
Dignity - a reliable information protection system; high speed; lack of restrictions on the number of workstations; Easy control compared to peer-to-peer networks.
disadvantages - high cost due to the selection of one computer under the server; dependence of the speed and reliability of the network from the server; Ligger flexibility compared to peer-to-peer network.
Similar information.
The network is a plurality of nodes combined with each other. Railways where the nodes are stations and stations, and connections - rails, serve as an example of transport networks organized to solve transport problems. To provide information processes, use a personal computer with which it is possible to solve a wide range of tasks. But there are also a number of important and responsible processes that cannot be solved with a single computer. For example, this is the flight of rockets, the assembly of a complex design at the factory, a nuclear reaction at a nuclear power plant, etc. To solve such problems in the network, several computers connect, duplicating the main and increasing the reliability of work.
Also the most important component of human activity is the exchange of information and the establishment of communication relations. Already traditional telecommunications (from Greek Tele - "distance, far" and lat. Communicato - "Communication"), which serve the exchange of information at a distance. The most familiar examples of technical means of telecommunications are radio transmitter, telephone, telegraph, television, fax machine, television and mail. Computers are now widespread, which led to the creation of computer communications (networks), which have already displaced facsimile and teletype bond.
Assigning computer networks.
Computer (electronic) network is an information exchange system between different computers at a distance, which gives users to apply them as means of transmitting and receiving information. The electronic network combines computers of different types with different operating systems. Computer networks include computing networks intended for distributed data processing (sharing of computing power), and information networks intended for sharing information resources. Thus, users or subscribers of a computer network are able to share its software, technical, information and organizational resources.
The feasibility of creating a computer network is determined by as follows:
- - the possibility of using territorially distributed software, information databases and databases of knowledge from various users;
- - the possibility of organizing distributed data processing by attracting resources of many computing machines;
- - operational redistribution of the load between computers included in the network and eliminate peak load due to the redistribution of it, taking into account time zones;
- - specialization of individual machines at work with unique programs that need a number of network users;
- - collectivization of resources, especially expensive peripheral equipment, which is economically impractical to equip each compartment;
Computer networks are a complex of technical, software and information funds. Technical means - this is a computer of various types (from micro to super email); data transfer systems, including communication channels, modems and network adapters for connecting computers to communication lines; Gateways, distributors, routers and other equipment. Information tools are a single information fund containing data from different types for general and individual applications: databases, knowledge bases - local and distributed. Networking software are designed to organize collective access to its resources, dynamic distribution and redistribution of network resources, to optimally load technical means, coordinating the operation of the main network links.
Almost any network is based on several powerful computers, called servers (from English. Serve - to serve). These servers are usually connected to the second order network (regional), third order (sectoral or corporate) and fourth order (local), and users of individual computers are usually connected. Computer networks transmit data in various environments - houses, minor firms and huge corporations, in which there is a large number of divisions separated by geographically.
The principles of functioning of various electronic networks are approximately the same, since they all represent an information system folding from computers (as sources of information), a communication channel by which information in the form of a material and energy signal can enter the addressee address, as well as some agreement ( code), which will allow a computer-addressing computer to convert a perceived signal to a clear consumer-person. The computer network will allow collectively solving various applied tasks, increases the use of resources available on the network (information, computing, communication) and provides remote access to them. For efficient networking, special operating systems are used (network OS), which, unlike personal operating systems, are intended to solve special tasks for managing the operation of the computer network. They are installed on specially dedicated computers.
Network applications are applied software complexes that expand the capabilities of the network OS. Among them, you can select mail programs (e-mail, web browser, Instant Messaging), teamwork systems (Collaboration), network databases, etc.
Computer networks are local, sectoral, regional, global. Local computing network (LAN - Local Area Network) combines computers more often than one organization located compact in one or several buildings. Its throughput reaches 10 Gbps, and the size does not exceed a few kilometers. High quality data transfer makes it possible to provide a wide range of services: print, fax, scanner, file service, email, databases and other services, the implementation of which is very expected separately on the local computer. Communication channels can be used together by many network computers.
The Global Computing Network (WAN - Wide Area Network) combines computers that are located in different countries, on various continents. The interaction between subscribers of such a network can be carried out on the basis of existing communication lines, such as telephone lines, radio communications and satellite communication systems. Since these lines were laid for purposes other than computer data transfer, their quality, as well as the data exchange rate, is often very low, which requires the use of special complex algorithms and data transfer procedures and expensive equipment.
Computer network functional components.
All devices connected to the network can be divided into three functional groups, in terms of their relationship to resources:
- · Workstations;
- · Servers;
- · Communication nodes;
Workstation (Workstation) is a PC connected to the network on which the network user performs its work. Each workstation processes its local files and uses its operating system. But the user also has access to the network. You can select three types of workstations: a workstation with a local disk (OS is loaded from this local disk), a diskless workstation (OS is loaded from a file server disk) and a remote workstation (connects to a local network through telecommunication channels of communication - for example, using telephone network).
Server (from eng. Serve - "service") is a computer connected to the network and providing certain services to network users. For example, storing public data, processing a request to the DBMS, print jobs, etc.
Communication nodes. Communication network nodes include devices such as: switches, bridges, repeaters, marchutizers, hubs, gateways. A part of the network in which the extension device is not included is called the network segment.
- - Repeater (REPEATER) - a device designed to enhance or regenerate the signal that has come to it. In all the reinforced segments, the exchange of data is maintained only between two stations;
- - Hub (HUB) - a device that allows you to combine several workstations into one network segment;
- - The gateway is a special software and hardware complex designed to ensure compatibility between networks for which information is not possible to standard means. The gateway converts data and protocols of their transfer to a single standard. It is usually implemented on the basis of a certain nodal computer. Using gateways expands network subscribers;
- - Switches (Switch);
- - router (Router);
Physical components of the network.
There are 4 main categories of network physical components:
1. Computer (Eng. Computer - "Computer"). This device or system capable of performing a specified, clearly defined sequence of operations. This is most often the operation of numerical calculations and data manipulation, however, there are both I / O operations. The description of the sequence of operations is called the program.
The electronic computing machine (computers) is synonymous with a computer. This is a complex of technical means designed to automatically process information in the process of solving computing and informational tasks. EUM implies the use of electronic components as its functional nodes, but the computer can be arranged on other principles - it can be mechanical, biological, optical, quantum, etc. By type of functioning, the computing machine may be digital (TSM) and analog (AVM);
computer network software scanned
Figure 1. Personal computer diagram.
1. Monitor; 2. Motherboard; 3. Processor; 4. Port Ata; 5. RAM; 6. Expansion cards; 7. Computer power supply; 8. Drive; 9. Hard disk; 10. Keyboard; 11. Computer mouse;
Interconnections are a component that transmits data from one point of the network to another. This category includes the following types of components:
- - network adapters (network cards) - convert data processed by a computer into a format suitable for transmission over the local network;
- - cables or wires for which signals are transmitted from one network adapter to another;
- - Connectors - Cable and Wiring Points;
Switch, or Svish (from English Switch - Switch). These are devices that combine terminal devices and intelligently transmit data between them. Switches simultaneously supports multiple data exchange processes for each pair of stations of different segments. Switches were developed using bridge technologies and are therefore often treated as multiport bridges. The switch transmits the data only directly to the recipient (the exception is broadcast traffic to all network nodes and traffic for devices for which the outgoing port of the switch is not known);
Network switch on 48 ports (with sockets for four additional ports).
Routers (from English Router) carry out efficient data transfer between networks (analyzes the destination address and sends data to the optimally selected route). The router is a specialized network computer that has at least one network interface and forwarding data packets between different network segments.
The router operates on a higher "network" level 3 than a switch (or a network bridge) and a hub (hub) that operate, respectively, at 2 and level 1 of the OSI model. When running the router uses the recipient's address specified in the batch data, and determines the path to the routing table by which the data should be transmitted. If there is no route in the routing table for the address, the package is discarded.
Software components are network operating systems and network applications. Network administration includes configuration, monitoring and malfunctional detection, as well as the expansion and development of the network with an increase in the number of users or communication requirements. Computer network management tools are network monitoring programs, protocol analyzers, sniffers (network traffic analyzer, a program or software and hardware device, designed to intercepted and subsequent analysis, or only network traffic analysis for other nodes) and network management programs. Many large companies offer a network management system, including Microsoft Systems Management Server (SMS), IBM (Tivoli Enterprise) and Hewlett-Packard (OpenView.
The capabilities of the computer network are determined by the characteristics of the computers included in the network. To describe and compare networks, many parameters can be used, but from the point of view of execution and structure, they are described by the following parameters:
- - speed. This parameter shows how fast the data is transmitted over the network. More accurate characteristic is throughput;
- - Protection. This parameter shows how reserved the network itself and the data transmitted in it. The concept of protection is very important in the computer network. Protection must be thought out before any changes affecting the network;
- - Handling. This parameter provides the ability to affect the operation of any network element. Network management is engaged in the network administrator or the user who is entrusted with these functions. The usual user, as a rule, has no administrative rights. Also, controllability helps to identify problems in the computer network or its individual segments, work out management actions to solve identified problems and makes it possible to automate these processes when solving similar problems in the future;
- - Availability indicates how much the network will be available to use if necessary. For a network, which should work 24 hours a day, 7 days a week, 365 days a year Availability is calculated by dividing the time it was really available for work on a full time and multiplication by 100 to obtain a percentage indicator;
- - Cost. This parameter shows the full cost of components, installation and support of the network;
- - Performance. It is determined by such indicators as the system reaction time (time between the moment of the request and the moment of receipt of the response) and the bandwidth (determined by the number of information transmitted via the network or its segment per unit of time; is defined in bits per second);
- - Extensibility, or scalability. Any computer network is a developing object, and not only in terms of upgrading its elements, but also in terms of its physical expansion, adding new network elements (users, computers, services). The existence of such opportunities, the complexity of their implementation is included in the concept of extensibility. Another similar characteristic is the scalability of a network that shows how easy the network can serve more users or transmit more data without a significant reduction in performance. If the network has been designed and optimized only for current requirements, when changes or expansion will be required, it will be too difficult and expensive;
- - Reliability. This characteristic shows the reliability of the components (routers, switches, personal computers, etc.), component network and measures the ability to accidentally. MTBF (Mean Time Between Failure) - average time between accidents;
- - The network transparency involves hiding (invisibility) network features from the end user. The user appeals to the network resources as the usual local resources of the computer on which it works. Another important side of the network transparency is the ability to parallelize the work between different elements of the network. Destination of individual parallel tasks to individual network devices should also be hidden from the user and resolve automatically;
- - Integrability is the possibility of connecting a variety of and dirty equipment, software from different manufacturers to the computer network. The coexistence of two types of data with opposite requirements of the transmission process is a challenge, the solution of which is a necessary condition for the computing network with good integrability. If such an inhomogeneous computing network successfully performs its functions (standardization of networks, their elements and components), then we can say that it has good integrability;
- - topology. In the description of the networks, 2 types of topologies are used: physical (cable location, network devices and terminal systems) and logical (paths by which signals are transmitted over the network);
Some of these characteristics (requirements) are laid in international or national standards, others serve as subject to interfirm agreements and additions.
