LOCAL COMPUTER NETWORKS (LKS)

GLOBAL COMPUTER NETWORKS

INTRODUCTION

Today, there are more than 130 million computers in the world, and more than 80% of them are united in various information and computer networks from small local area networks in offices to global networks such as the Internet, FidoNet, FREEnet, etc. The worldwide trend towards connecting computers in a network is due to a number of important reasons, such as the acceleration of the transfer of information messages, the possibility quick exchange information between users, receiving and transmitting messages (faxes, E – Mail letters, electronic conferences, etc.) without leaving the workplace, the ability to instantly receive any information from anywhere in the world, as well as the exchange of information between computers different firms manufacturers working under different software.

Such huge potential opportunities that the computer network carries and the new potential rise that the information complex is experiencing, as well as significant acceleration production process do not give us the right to ignore and not apply them in practice.

Often there is a need to develop a fundamental solution to the issue of organizing an information and computing network (ICT) on the basis of an already existing computer park and software complex that meets modern scientific and technical requirements, taking into account increasing needs and the possibility of further gradual development of the network in connection with the emergence of new technical and software solutions.

PRINCIPLE OF CONSTRUCTION OF COMPUTER NETWORKS

A computer network is a collection of computers and various devices that provide information exchange between computers in a network without using any intermediate storage media.

All the variety of computer networks can be classified according to a group of features:

1) Territorial prevalence;

2) Departmental affiliation;

3) Speed ​​of information transfer;

4) Type of transmission medium;

In terms of territorial distribution, networks can be local, global, and regional. Local - these are networks that cover an area of ​​no more than 10 m 2, regional - located on the territory of a city or region, global on the territory of a state or a group of states, for example, worldwide network Internet.

Departmental and state networks are distinguished by affiliation. Departmental belong to one organization and are located on its territory. Government networks - networks used in government structures.

According to the speed of information transfer, computer networks are divided into low-, medium- and high-speed.

By the type of transmission medium, they are divided into coaxial, twisted-pair, fiber-optic networks, with the transmission of information over radio channels, in the infrared range.

Computers can be connected by cables, forming a different network topology (star, bus, ring, etc.).

A distinction should be made between computer networks and terminal networks (terminal networks). Computer networks connect computers, each of which can work autonomously. Terminal networks usually connect powerful computers (mainframes), and in some cases PCs with devices (terminals), which can be quite complex, but outside the network, their work is either impossible or even meaningless. For example, a network of ATMs or ticket offices for the sale of air tickets. They are built on principles completely different from computer networks and even on other computer technology.

In the classification of networks, there are two main terms: LAN and WAN.

LAN (Local Area Network) - local area networks with a closed infrastructure before reaching service providers. The term "LAN" can describe a small office network, and a network of the level of a large plant covering several hundred hectares. Foreign sources even give a close estimate - about six miles (10 km) in radius; use of high-speed channels.

WAN (Wide Area Network) is a global network that covers large geographic regions, including both local networks and other telecommunication networks and devices. An example of a WAN is a packet-switched network (Frame Relay) through which various computer networks can "talk" to each other.

The term "corporate network" is also used in the literature to refer to the interconnection of several networks, each of which can be built on different technical, software and information principles.

The types of networks considered above are closed-type networks, access to them is allowed only to a limited number of users, for whom work in such a network is directly related to their professional activities. Global networks are focused on serving any user.

In Figure 1, consider the methods of switching computers and types of networks.

Figure 1 - Methods of switching computers and types of networks .

LOCAL COMPUTER NETWORKS (LKS)

LCS classification

Local area networks are divided into two radically different classes: peer-to-peer (single-level or Peer to Peer) networks and hierarchical (multi-level) networks.

Peer-to-peer networks.

A peer-to-peer network is a network of peer-to-peer computers, each with a unique name (computer name) and usually a password to log into it at boot time. The login name and password are assigned by the PC owner by means of the OS. Peer-to-peer networks can be organized using such operating systems as LANtastic, Windows'3.11, Novell NetWare Lite. These programs work with both DOS and Windows. Peer-to-peer networks can also be organized on the basis of all modern 32-bit operating systems - Windows'95 OSR2, Windows NT Workstation versions, OS / 2) and some others.

Hierarchical networks.

In hierarchical local area networks, there are one or more special computers - servers that store information shared by different users.

A server in hierarchical networks is a persistent repository of shared resources. The server itself can only be a client of a server at a higher level of the hierarchy. Therefore, hierarchical networks are sometimes referred to as dedicated server networks. Servers are usually high-performance computers, possibly with several parallel processors, with hard drives large capacity, with a high-speed network card (100 Mbps or more). The computers from which the information on the server is accessed are called stations or clients.

LKS are classified by purpose:

· Terminal service networks. They include a computer and peripheral equipment used in exclusive mode by the computer to which it is connected, or to be a shared network resource.

· Networks on the basis of which the production management systems and office activities are built. They are united by the IDA / TOP group of standards. IDA describes the standards used by industry. TOP describe the standards for networks used in office networks.

· Networks that integrate automation and design systems. Workstations of such networks are usually based on sufficiently powerful personal computers, for example from Sun Microsystems.

· Networks on the basis of which distributed computing systems are built.

According to the classification criterion, local computer networks are divided into ring, bus, star-shaped, tree-like;

based on speed - to low-speed (up to 10 Mbps), medium-speed (up to 100 Mbps), high-speed (over 100 Mbps);

by type of access method - random, proportional, hybrid;

by the type of physical transmission medium - twisted pair, coaxial or fiber-optic cable, infrared channel, radio channel.

LKS structure

The way computers are connected is called the structure or topology of the network. Ethernet networks can be in both bus and star topologies. In the first case, all computers are connected to one common cable (bus), in the second, there is a special central device (hub), from which "rays" go to each computer, i.e. each computer is connected to its own cable.

The bus structure, Figure 2 (a), is simpler and more economical because it does not require an additional device and uses less cable. But it is very sensitive to cabling faults. If the cable is damaged at least in one place, then problems arise for the entire network. The location of the malfunction is difficult to locate.

In this sense, the "star", Figure 2 (b), is more stable. A damaged cable is a problem for one specific computer; it does not affect the operation of the network as a whole. No effort is required to isolate the fault.

In a network with a “ring” type structure, Figure 2 (c), information is transmitted between stations along a ring with a relay in each network controller. Re-reception is carried out through buffer drives made on the basis of random access memory devices, therefore, when one of them fails, network controller the operation of the entire ring may be disrupted.

The advantage of the ring structure is the ease of implementation of the devices, and the disadvantage is low reliability.

All considered structures are hierarchical. However, thanks to the use of bridges, special devices combining local networks with different structures, networks with a complex hierarchical structure can be built from the above types of structures.

a B C)

Figure 2 - structure of construction (a) bus, (b) ring, (c) star
Physical transmission medium in local networks

Very important point- consideration of the factors influencing the choice of the physical transmission medium (cable system). Among them are the following:

1) Required bandwidth, network transmission speed;

2) The size of the network;

3) The required set of services (data, voice, multimedia, etc.), which must be organized.

4) Requirements for the level of noise and interference immunity;

5) The total cost of the project, including the purchase of equipment, installation and subsequent operation.

The main data transmission medium of the LKS is unshielded twisted pair, coaxial cable, multimode fiber. At approximately the same cost of single-mode and multimode fiber, terminal equipment for single-mode fiber is much more expensive, although it provides long distances... Therefore, LCS uses mainly multimode optics.

Basic LKS technologies: Ethernet, ATM. FDDI technology (2 rings), which was previously used for core networks and has good characteristics in terms of distance, speed and fault tolerance, is now little used, mainly due to its high cost, as, indeed, is the Token Ring technology, although both of them are up to are still supported at a high level by all leading vendors, and in some cases (for example, the use of FDDI for a city-wide backbone, where high resiliency and guaranteed packet delivery are required), the use of these technologies can still be justified.

Types of LCS

Ethernet is originally a collision technology based on a common bus, to which computers connect and "fight" among themselves for the right to transmit a packet. The main protocol is CSMA / CD (Carrier Sensitivity Multiple Access and Collision Detection). The fact is that if two stations simultaneously start transmitting, then a collision situation arises, and the network “waits” for some time until the transient processes “settle down” and “silence” occurs again. There is another access method - CSMA / CA (Collision Avoidance) - the same, but with the exception of collisions. This method is used in the wireless technology Radio Ethernet or Apple Local Talk - before sending any packet on the network, an announcement that a transmission will take place is run through, and the stations no longer try to initiate it.

Ethernet is half-duplex (Half Duplex), over all transmission media: the source and the receiver "speak in turn" (classic collision technology) and full-duplex (Full Duplex), when two pairs of transmitter and receiver on devices speak at the same time. This mechanism works only on twisted pair (one pair for transmitting, one pair for receiving) and optical fiber (one pair for transmitting, one pair for receiving).

Ethernet differs in speeds and encoding methods for different physical media, as well as packet types (Ethernet II, 802.3, RAW, 802.2 (LLC), SNAP).

Ethernet varies in speed: 10 Mbps, 100 Mbps, 1000 Mbps (Gigabit). Since the recently ratified Gigabit Ethernet standard for twisted pair Category 5, it can be said that twisted pair, single mode (SMF) or multimode (MMF) fiber can be used for any Ethernet network. Depending on this, there are different specifications:

· 10 Mbit / s Ethernet: 10BaseT, 10BaseFL, (10Base2 and 10Base5 exist for coaxial cable and are no longer used);

100 Mbps Ethernet: 100BaseTX, 100BaseFX, 100BaseT4, 100BaseT2;

Gigabit Ethernet: 1000BaseLX, 1000BaseSX (fiber) and 1000BaseTX (twisted pair)

There are two options for implementing Ethernet on coax called thin and thick Ethernet (Ethernet on 0.2 "thin cable and Ethernet on 0.4" thick cable).

Thin Ethernet Uses RG-58A / V type cable (0.2 "diameter). For a small network, a 50 ohm cable is used. A coaxial cable runs from computer to computer. Each computer is left with a small amount of cable in case it can be moved. The segment length is 185 m, the number of computers connected to the bus is up to 30.

After attaching all lengths of cable with BNC-connectors (Bayonel-Neill-Concelnan) to the T-connectors (the name is due to the shape of the connector, similar to the letter "T"), you will get a single cable segment. Terminators ("plugs") are installed at both ends. The terminator is constructively a BNC-connector (it is also put on the T-connector) with a soldered resistance. The value of this resistance must correspond to the value of the characteristic impedance of the cable, i.e. for Ethernet, 50 ohm terminators are required.

Thick Ethernet- a network on a thick coaxial cable with a diameter of 0.4 inches and a characteristic impedance of 50 ohms. The maximum length of the cable segment is 500 m.

The routing of the cable itself is almost the same for all types of coaxial cable.

To connect a computer to a thick cable, an additional device called a transceiver is used. The transceiver is connected directly to the network cable. From him to goes to the computer special transceiver cable with a maximum length of 50 m. Both ends have 15-pin DIX connectors (Digital, Intel and Xerox). One connector connects to the transceiver, the other connects to the computer's network card.

Transceivers eliminate the need to run a cable to each computer. The distance from the computer to the network cable is determined by the length of the transceiver cable.

Networking with a transceiver is very convenient. It can literally "skip" the cable anywhere. This simple procedure takes little time and the resulting connection is very reliable.

The cable is not cut into pieces, it can be laid without worrying about the exact location of the computers, and then the transceivers can be installed in the right places. Transceivers are mounted, as a rule, on the walls, which is provided for by their design.

If it is necessary to cover an area with a local network larger than the considered cable systems allow, additional devices are used - repeaters (repeaters). The repeater has a 2-port design, i.e. it can connect 2 segments of 185 m. The segment is connected to a repeater via a T-connector. A segment is connected to one end of the T-connector, and a terminator is placed on the other.

There can be no more than four repeaters in the network. This allows you to get a network with a maximum length of 925 m.

There are 4-port repeaters. 4 segments can be connected to one such repeater at once.

The segment length for Ethernet on a thick cable is 500 m, up to 100 stations can be connected to one segment. With transceiver cables up to 50 m long, thick Ethernet can cover a much larger area in one segment than thin Ethernet. These repeaters have DIX connectors and can be connected by transceivers either to the end of a segment or anywhere else.

Combined repeaters are very convenient, i.e. suitable for both thin and thick cables. Each port has a pair of connectors: DIX and BNC, but they cannot be used at the same time. If it is necessary to combine segments on a different cable, then the thin segment is connected to the BNC connector of one repeater port, and the thick one - to the DIX connector of the other port.

Repeaters are very useful, but they should not be overused as they slow down your network performance.

Twisted pair Ethernet.

A twisted pair is two insulated wires twisted together. For Ethernet, an 8-core cable, consisting of four twisted pairs, is used. For environmental protection, the cable has an outer insulating coating.

The main node on a twisted pair is a hub (in translation it is called a drive, a hub, or simply a hub). Each computer must be connected to it using its own cable segment. The length of each segment should not exceed 100 m. RJ-45 connectors are installed at the ends of the cable segments. One connector connects the cable to the hub, the other to the network card. RJ-45 connectors are very compact, with a plastic housing and eight miniature pads.

A hub is a central device in a twisted-pair network; its performance depends on it. It should be located in an easily accessible place so that you can easily connect the cable and follow the port indication.

Hubs are available for a different number of ports - 8, 12, 16 or 24. Accordingly, you can connect the same number of computers to it.

The main purpose of connecting computers to a network was the separation of resources: users of computers connected to the network, or applications running on these computers, gain access to the resources of computers on the network, such as:

peripheral devices such as disks, printers, plotters, scanners, etc .;

data stored in random access memory or on external storage devices;

computing power.

Network interfaces

For communication between devices, they, first of all, must be provided with external interfaces.

An interface is - in a broad sense - a formally defined logical and / or physical boundary between interacting independent objects. The interface defines the parameters, procedures and characteristics of the interaction of objects.

Separate physical and logical interfaces

Physical interface (also called a port) - defined by a set of electrical connections and signal characteristics. Usually it is a connector with a set of pins, each of which has a specific purpose.

A logical interface (also called a protocol) is a set of information messages of a certain format that are exchanged between two devices or two programs, as well as a set of rules that define the logic of these messages exchange.

Rice. 2.2. Sharing the Printer on a Computer Network

A computer-to-computer interface allows two computers to exchange information. On each side, it is implemented by a pair:

a hardware module called a network adapter or network interface card;

the driver of the network interface card - a special program that controls the operation of the network interface card.

The computer-peripheral device interface (in this case, the computer-printer interface) allows the computer to control the operation of the peripheral device (CP), This interface is implemented:

from the computer side - by an interface card and a CP (printer) driver, similar to a network interface card and its driver;

from the PU side - by the PU (printer) controller, usually a hardware device that receives from the computer both data, for example bytes of information that needs to be printed on paper, and commands that it executes by controlling the electromechanical parts of a peripheral device, for example, pushing out a sheet from the printer or by moving the magnetic head of the disc.

1. Communication problems between multiple computers

Physical link topology

When connecting several (more than two) computers into a network, it is necessary to decide how to connect them to each other, otherwise, choose a configuration of physical connections, or topology.

The network topology is understood as the configuration of the graph, the vertices of which correspond to the end nodes of the network (for example, computers) and communication equipment (for example, routers), and the edges correspond to physical or informational connections between the vertices.

You can connect each computer to each or link them in series, assuming that they will communicate, passing messages to each other "in transit". Both a universal computer and a specialized device can act as a transit node.

The network characteristics significantly depend on the choice of the link topology:

the presence of several paths between nodes increases the reliability of the network and makes it possible to distribute the load between individual channels.

the ease of attaching new nodes, inherent in some topologies, makes the network easily expandable.

economic considerations often lead to the choice of topologies, which are characterized by the minimum total length of the communication lines.

Among the many possible configurations, a distinction is made between fully connected and not fully connected.

A fully connected topology corresponds to a network in which each computer is directly connected to all others. This option turns out to be cumbersome and ineffective. In this case, each computer on the network must have a large number of communication ports. Fully connected topologies are rarely used in large networks. More often this type of topology is used in multi-machine complexes or in networks involving a small number of computers.

Rice. 2.10. Typical network topologies

All other options are based on loosely coupled topologies, when data transfer between two computers may require transit data transmission through other network nodes.

Ring topology. Data is transferred in a loop from one computer to another. The main advantage of the ring is that by its nature it provides redundancy for connections. The data in the ring, having made a full turn, returns to the source node. Therefore, the source can control the process of delivering data to the addressee. This property is used to test network connectivity and find a node that is malfunctioning. At the same time, in networks with a ring topology, it is necessary to take special measures so that in the event of a failure or disconnection of a computer, the communication channel between the rest of the ring nodes is not interrupted.

A star topology is formed when each computer is connected directly to a common central device called a hub. The function of the hub is to direct the information transmitted by the computer to one or all of the other computers on the network. The hub can be either a universal computer or a specialized device. Disadvantages of a star topology: higher cost of network equipment due to the need to purchase a specialized central device; the possibilities for increasing the number of nodes in the network are limited by the number of ports on the hub.

Sometimes it makes sense to build a network using several hubs, hierarchically interconnected by star-shaped links. The resulting structure is called a hierarchical star, or tree. Currently, the tree is the most common communication topology, both in local and wide area networks.

The common bus is a special special case of the star. Here, a passive cable acts as a central element (many networks using wireless communication have the same topology - the common radio environment plays the role of a common bus here). The transmitted information is distributed over the cable and is available simultaneously to all computers connected to this cable. Advantages: cheapness and simplicity of connecting new nodes to the network, and disadvantages - low reliability (any cable defect completely paralyzes the entire network) and low performance (at a time, only one computer can transmit data over the network, so the bandwidth is divided here between all nodes network).

Rice. 2.11. Mixed topology

Small networks have a typical topology - a star, a ring or a common bus; large networks are characterized by the presence of arbitrary connections between computers. In such networks, it is possible to distinguish individual arbitrarily connected fragments (subnets) with a typical topology, therefore they are called networks with a mixed topology.

Host addressing

One of the problems that must be taken into account when combining three or more computers is the problem of addressing, namely the addressing of their network interfaces. One computer can have multiple network interfaces. For example, to create a fully connected structure of N computers, each of them must have N - 1 interface.

By the number of addressable interfaces, addresses can be classified as follows:

a unique address (unicast) is used to identify individual interfaces;

the multicast address identifies several interfaces at once, so the data marked with the multicast address is delivered to each of the nodes in the group;

data sent to the broadcast address must be delivered to all nodes on the network;

the anycast address defined in the new version of IPv6, just like a multicast address, defines a group of addresses, however, data sent to this address should not be delivered to all addresses in this group, but to any of them.

Addresses can be numeric (for example, 129.26.255.255 or 81. la. ff. ff) and symbolic (site.domen.ru).

Symbolic addresses (names) are human-readable and therefore usually carry semantic meaning.

The set of all addresses that are valid within a certain addressing scheme is called an address space.

The address space can have a flat (linear) organization or a hierarchical organization.

In a flat organization, many addresses are not structured in any way. An example of a flat numeric address is a MAC address designed to uniquely identify network interfaces on local networks. This address is usually used only by hardware and is written as a binary or hexadecimal number, for example 0081005e24a8. MAC addresses are built into the hardware by the manufacturer and are therefore also referred to as hardware addresses.

In a hierarchical organization, the address space is structured in the form of nested subgroups, which, by successively narrowing the addressable area, ultimately define a separate network interface.

Typical representatives of hierarchical numeric addresses are network IP and IPX addresses. They support a two-level hierarchy, the address is divided into the upper part - the network number and the lower part - the node number. This division allows messages to be transmitted between networks only based on the network number, and the node number is required after the message is delivered to the desired network. In practice, several addressing schemes are usually used at once, so that a computer's network interface can simultaneously have several address-names. Each address is used in the situation when the corresponding type of addressing is most convenient. And to convert addresses from one type to another, special auxiliary protocols are used, which are called address resolution protocols.

Commutation

Let the computers be physically interconnected according to some topology. Then you need to decide how to transfer data between end nodes?

The connection of end nodes through a network of transit nodes is called switching. A sequence of nodes along the path from sender to receiver forms a route.

For example, in the network shown in Fig. 2.14, nodes 2 and 4, not directly connected to each other, are forced to transmit data through transit nodes, which can be, for example, nodes 1 and 5. Node 1 must transfer data between its interfaces A and B, and node 5 - between interfaces F and B. In this case, the route is the sequence: 2-1-5-4, where 2 is the sending node, 1 and 5 are transit nodes, 4 is the receiving node.

Rice. 2-14. Subscriber switching through a network of transit nodes

Generalized switching problem

In general, the switching task can be represented in the form of the following interrelated particular tasks.

Determination of information flows for which routes are required.

Stream routing.

Stream forwarding, that is, recognition of streams and their local switching at each transit node.

Stream multiplexing and demultiplexing.

Routing

The routing task, in turn, includes two subtasks:

determination of the route;

notifying the network about the selected route.

Define a route means to select a sequence of transit nodes and their interfaces through which data must be transmitted in order to deliver it to the addressee. Determining a route is difficult, especially when the network configuration is such that there are many paths between a pair of interacting network interfaces. Most often, the choice is stopped on one route that is optimal according to some criterion. The criteria for optimality can be, for example, the nominal throughput and the load of communication channels; channel delays; number of transit hubs; reliability of channels and transit nodes.

The route can be determined empirically (“manually”) by the network administrator, but this approach to determining routes is not very suitable for a large network with complex topology. In this case, automatic routing methods are used. For this end nodes and other devices of the network are equipped with special software that organizes the mutual exchange of service messages, allowing each node to form its own "idea" of the network. Then, based on the collected data, rational routes are determined programmatically.

When choosing a route, they are often limited only to information about the network topology. This approach is illustrated in Fig. 2.15. To transfer traffic between end nodes A and C there are two alternative routes: A-1-2-3-C and A-1-3-C. If we take into account only the topology, then the choice is obvious - the route A-1-3-C, which has fewer transit nodes.

Rice. 2.15. Route selection

Data promotion

So, let the routes be defined, records about them are made in the tables of all transit nodes, everything is ready for data transfer between subscribers (subscriber switching).

First of all, the sender must set the data on the interface from which the found route begins, and all transit nodes must accordingly “transfer” data from one of their interfaces to another, in other words, perform commutationinterfaces. A device whose functional purpose is switching is called switch. In fig. 2.16 shows a switch that switches traffic between its four interfaces.

Rice. 2.16. Switch

A switch can be either a specialized device or a universal computer with a built-in software switching mechanism, in this case the switch is called a software switch.

Multiplexing and demultiplexing

To determine which interface the incoming data should be sent to, the switch must figure out which stream it belongs to. This problem should be solved regardless of whether only one "pure" stream or a "mixed" stream arrives at the switch input.

Demultiplexing is the division of the total aggregated stream into several constituent streams.

Multiplexing is the formation of a common aggregated stream from several separate streams, which is transmitted over one physical communication channel,

In other words, multiplexing is a method of dividing one available physical channel between several concurrent communication sessions between network subscribers.

Figure 2.18 . Operations of multiplexing and demultiplexing streams during switching

One of the main ways to multiplex streams is time divisionneither. With this method, each stream from time to time (with a fixed or random period) receives a physical channel at its complete disposal and transmits its data through it. Also distributed frequency division channel, when each stream transmits data in the frequency range allocated to it.

Rice. 2.19. Multiplexer and demultiplexer

Switching types

Among the many possible approaches to solving the problem of switching, subscribers in networks are distinguished two fundamental ones, which include circuit switching and packet switching.

INTRODUCTION .. 5

1. GENERAL PRINCIPLES OF CONSTRUCTION OF NETWORKS .. 7

1.1. Functionality of networks. 7

1.2. Structural organization computer network. ten

1.2.1. Networks of different scale. 10

1.2.2. Data transmission media. ten

1.2.3. Data transfer modes. eleven

1.2.4. Switching methods. 12

1.2.5. Virtual channels .. 13

2. ANALOGUE DATA TRANSMISSION CHANNELS .. 14

2.1. Analog modulation. fourteen

2.2. Modems .. 15

2.3. Protocols supported by modems. 16

2.4. Transfer modes. 17

2.5. Asynchronous, synchronous, isochronous and plesiochronous transmission. 17

3. DIGITAL DATA TRANSMISSION CHANNELS .. 19

3.1. Frequency and time division of channels. 19

3.2. Wire communication lines and their characteristics. twenty

3.2.1. Twisted pair. twenty

3.2.2. Coaxial cable. 22

3.2.3. Fiber optic cable. 24

3.3. Wireless transmission media. 25

3.3.1. Infrared waves .. 25

3.3.2. Radio waves, narrowband signals ... 25

3.3.3. Radio waves, broadband signals ... 26

3.3.4. Satellite connection. 27

3.3.5. Cellular. 28

4. TRANSFER OF DATA AND CODING OF INFORMATION .. 30

4.1. The amount of information and entropy. thirty

4.2. Entropy properties. 31

4.3. Units of the amount of information. 32

4.4. Information coding. 32

4.5. Logical coding. 35

4.6. Self-Synchronizing Codes. 37

5. CONTROL OF INFORMATION TRANSMISSION AND DATA COMPRESSION .. 38

5.1. Self-healing codes .. 38

5.2. Systematic codes .. 39

5.3. Data compression algorithms. 39

5.3.1. RLE algorithm. 40

5.3.2. Lempel-Ziv algorithm. 40

5.3.3. Shannon-Fano coding. 41

5.3.4. Huffman algorithm. 41

6. NETWORK SOFTWARE .. 43

6.1. Architecture of open source software .. 43

6.2. Basic Principles of Open Systems Interconnection. 44

7. MODEL OF OPEN SYSTEMS INTERACTION ... 45

7.1. OSI model structure. 45

7.2. Protocols and interfaces .. 47

7.3. OSI model layers. 48

7.3.1. Physical layer. 48

7.3.2. Link layer. 50

7.3.3. Network layer. 52

7.3.4. Transport layer. 54

7.3.5. Session level. 54

7.3.6. Presentation layer. 55

7.3.7. Application level. 55

7.4. Layer assignment of the OSI model. 55

8. MAIN CHARACTERISTICS OF LOCAL NETWORKS .. 58

8.1. Network topologies. 58

8.1.1. Tire. 58

8.1.2. Wood. 59

8.1.3. A star with a passive center. 59

8.1.4. A star with an intellectual center. 60

8.1.5. Ring. 60

8.1.6. Chain. 60

8.1.7. Fully connected topology. 61

8.1.8. Arbitrary (mesh) topology. 61

8.2. Access methods and their classification. 62

8.2.1. Carrier sense access method with collision detection. 63

8.2.2. Marker accessor methods. 63

9. BASIC TYPES OF NETWORK DEVICES .. 65

9.1. Network adapters .. 65

9.2. Hubs .. 66

9.3. Bridges .. 68

9.4. Switches .. 71

9.5. Firewalls .. 73

10. TOKEN RING AND FDDI NETWORKS. 76

10.1. Token technology Ring .. 76

10.1.1. Token accessor method. 76

10.1.2. Priority access system. 80

10.1.3. Token Ring hardware. 81

10.2. FDDI technology. 82

11. ETHERNET TECHNOLOGY .. 84

11.1. The emergence and essence of Ethernet technology. 84

11.2. Formats Ethernet frames. 87

11.3. High-speed technologies of local area networks. 91

11.3.1. Fast Ethernet 100Mbps technology. 91

11.3.2. Gigabit Ethernet 1000 Mbps technology. 93

11.3.3. 100VG-AnyLAN technology .. 94

12. NETWORK REQUIREMENTS ... 96

12.1. Performance. 96

12.2. Reliability and safety. 99

12.3. Extensibility and scalability. 100

12.4. Transparency. 101

12.5. Support different types traffic. 102

12.6. Controllability. 103

12.7. Compatibility. 104

12.8. Quality of service. 104

REFERENCES ... 108

INTRODUCTION

The last decade of the 20th century can be called the decade of computer networks with great reason. In commercial firms and government agencies, educational institutions, and even at home, computers that are in no way connected with others are less and less common. If for enterprises and organizations the deployment of local networks turned out to be the most important, then home users are increasingly attracted global networks- Internet, sometimes FIDO.

Two or three decades ago, only a large organization could afford to buy at least one computer, because it cost hundreds of thousands of dollars, required a lot of space, and needed qualified, and therefore highly paid, service personnel. As a rule, computers then worked in batch mode, the user (usually a programmer) might never even see the computer performing his tasks. The programs were recorded on special forms, according to which the operators prepared punched cards, finally, the program in the form of a deck of punched cards had to be given system administrator, which put the task in the queue and, after its completion, gave a printout with the results.

Such a mode cannot be called convenient (although it is in this mode that the efficiency of the computer is maximum), and ten years later terminals appeared - devices that included a display and a keyboard. The terminal was connected to the central computer with a cable. The first terminals were of little intelligence, they were even called "dumb" (dumb): all they could do was tell the central computer which key was pressed and, having received a control command from it, display the symbol on the display. (At first we used telex communication devices as terminals - teletypes, hence the limited set of their capabilities.) A little later we realized that if the terminal was equipped with its own simple processor and RAM, then the central computer itself would have to do less unproductive work.

It also turned out to be convenient if the terminal is on the desk of the person who uses it, even if this desk is not in the same building as the central computer. This is how modems appeared, which provided terminals with the ability to communicate with their central computers via telephone networks.

Until now, news and financial agencies (for example, Reiter and Bloomberg) provide access to their information using terminals. It was from solving the problems of connecting terminals with central computers that the entire industry of data transmission networks grew.

It should be understood that in the West the problem of "inherited" systems is still very acute: many large organizations still use mainframes and terminals in their work, and a critical mass of their data is located there. At the same time, mass computerization in Russia began in the late 1980s and relied almost entirely on IBM PC-compatible personal computers. Only in rare large organizations did the need for voluminous computing and / or increased reliability requirements lead to the use of "big" computers, such as the IBM AS / 400, various Sun servers and workstations, and the like. Computers of the class IBM System / 360 (ES computers), so widespread in the West that Microsoft included a communication server with such computers (SNA Server) in its BackOffice server applications package, practically ceased to exist in Russia.

The usual road to networks for our organizations and businesses looked like this: there are several IBM PC-compatible computers. Texts are entered on them, tables are built, calculations are performed. Text files, spreadsheet files, drawings, data and calculation results must be constantly transferred from computer to computer. To do this, use floppy disks. While the amount of data is small, and you can process this data one by one, special problems does not arise. However, the desire soon arises, for example, to collect all the sales data into a database, and make it so that several sellers can simultaneously issue invoices and record payments for the goods so that others can immediately see these new invoices and payment records. Running with a floppy disk after each bill is unrealistic. And then it turns out that you can buy inexpensive network cards for each of the computers, connect them with a cable, install special network software, and the problem can be solved. This is the way "from convenience".

Another path to networks lies "from savings". Why spend money on several full-fledged computers for typists when you can buy one more powerful computer with a large volume disk memory, several machines without hard drives at all, and connect them to a network. Then weaker computers will be able to use the disk space of a more powerful computer. That's the savings - the cost of multiple hard drives is significantly higher than the cost of the required network equipment. Finally, the path "from fashion". When all acquaintances, neighbors and competitors have already set up local networks for themselves, then, probably, this makes some sense. And although there is no urgent need yet, it is worth keeping in line with technological progress. As a rule, in this case too, it turns out that the network helps to simplify life and is beneficial.

GENERAL NETWORKING PRINCIPLES

© 2015-2019 site
All rights belong to their authors. This site does not claim authorship, but provides free use.
Date the page was created: 2016-02-16

While creating computer networks their developers had to solve mhoi problems. In this section, we will consider only the most important of them, and in the sequence in which they naturally arose in the process of development and improvement of network technologies.

The mechanisms of interaction between computers in a network have borrowed a lot from the scheme of interaction of a computer with peripheral devices, so we will begin to consider the principles of network operation from this "pre-network" case.

Communication of the computer with peripheral devices.

For data exchange between a computer and a peripheral device (CP), an external interface(Fig. 1.6), that is, a set of wires connecting a computer and a peripheral device, as well as a set of rules for the exchange of information along these wires (sometimes instead of the term interface the term is used protocol - We will talk about these important terms in more detail.) Examples of interfaces used in computers are the Centronics parallel interface, usually intended for connecting printers, and the RS-232C serial interface, through which a mouse, modem and many other devices are connected. The interface is implemented from the computer side by a combination of hardware and software: the PU controller and a special program that controls this controller, which is often called driver the corresponding peripheral.

On the PC side, the interface is most often implemented by a hardware control device, although software-controlled peripheral devices are also encountered.

The program executed by the processor can exchange data using I / O commands with any modules connected to the internal bus of the computer, including the controllers of the CP.

Peripheral devices can receive from the computer both data, for example bytes of information that needs to be printed on paper, and control commands, in response to which the PU can perform special actions, for example, move the disk head to the required track or push a sheet of paper out of the printer. The peripheral device uses the external interface of the computer not only to receive information, but also to transmit information to the computer, that is, the exchange of data via the external interface is usually bi-directional. For example, even a printer, which by its nature is an output device, returns its status data to the computer.

PU controllers receive commands and data from the processor into their internal buffer, which is often called a register or port, then execute! the necessary transformations of these data and commands in accordance with the formats understood by the control panel, and issue them to the external interface.

The distribution of responsibilities between the controller and the CP driver could be different, but usually the controller executes a set of simple commands to control the CP, and the driver uses these commands to force the device to perform more complex actions according to some algorithm. For example, the printer controller can support such elementary commands as "Print a character", "Line feed", "Carriage return", etc. The printer driver uses these commands to organize the printing of character strings, dividing the document into pages and other higher-level operations. For the same controller, you can develop various drivers, which will manage the given PU in different ways - some are better, while others are worse - depending on the experience and abilities of the programmers who developed them.

Rice. 1.6. Communication of a computer with a peripheral device.

Consider the scheme of transferring one byte of information from an application program to a peripheral device. The program that needed to exchange data with the control panel accesses the driver of this device, telling it as a parameter the address of the memory byte that needs to be transferred. The driver loads the value of this byte into the CP controller buffer, which starts sequentially transmitting bits to the communication line, representing each bit with a corresponding electrical signal. In order for the control device CP to understand that the transmission of a byte begins, before the transmission of the first bit of information, the controller forms a start signal of a specific form, and after the transmission of the last information bit, a table signal. These signals synchronize transfer of a byte. In addition to information bits, the controller can transmit a parity bit to increase the reliability of the exchange. The control unit, having detected a start bit on the corresponding line, performs preparatory actions and begins to receive information bits, forming a byte from them in its receive buffer. If the transmission is accompanied by a parity bit, then the correctness of the transmission is checked: when the transmission is performed correctly, the sign of the completion of information reception is set in the corresponding register of the control device.

Usually, the driver is responsible for the most complex protocol functions (for example, calculating the checksum of a sequence of transmitted bytes, analyzing the state of a peripheral device, checking the correctness of the command execution). But even the most primitive controller driver must support at least two operations: "Take data from the controller to RAM" and "Transfer data from RAM to the controller".

They exist as highly specialized interfaces suitable for connecting a narrow class of devices (for example, graphic monitors high resolution Vista), and general-purpose interfaces, which are standard and allow you to connect various peripheral devices. An example of such an interface is the RS-232C interface, which is supported by many terminals, printers, plotters, mice, and many other devices.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

Ministry of Education and Science of the Russian Federation

Federal State Autonomous educational institution higher professional education "Russian State Vocational Pedagogical University"

Institute of Informatics

Department of Information Technology

CONTROLWORK

ondiscipline

"WORLDINFORMATIONRESOURCES"

abstractonsubject:"Generalprinciplesconstructingnetworks.Local,corporate "

Completed by Student gr. Kp-514 IE

Karpov G.R.

Yekaterinburg 2012

1. General principles networking

1.1 Network functionality

1.2 Communication media

1.3 Data transfer modes

1.4 Ways of commutation

1.5 Organization of virtual channels

2. Local networks

2.1 Local area networks in the enterprise

3. Corporate networks

3.1 Principles of building corporate data transmission networks Using the Internet

3.2 Virtual networks

3.3 X.25 networks

3.4 Frame Relay networks

3.5 Corporate network structure

Terms and basic concepts of telecommunications

List of sources

1. General principles of networking

1.1 Functionalpossibilitiesnetworks

The benefits of using networks can fall into different categories.

First, direct communication between people (communication). In this case, the network is used as a medium that transmits from one person to another a text typed on the keyboard, a voice entered from a microphone, an image received from a video camera, or both. This includes email, various systems for conversations (chat systems), systems such as ICQ, Internet Phone, video conferencing, and much more. Naturally, software is used for this, but it plays a purely technical role of a transceiver, like a telephone when talking on the phone.

Second, the transfer of data between programs and people. In this case, on one side of the information flow there is a software process, for example, a Database Management System (DBMS), and on the other - human user... A person, of course, uses programs to access the DBMS, but these programs, as in the first case, play a purely technical role. However, the DBMS is already acting as a full-fledged participant in data transfer. Another example is a network file system that provides access to files on another computer. Such programs that perform some actions on their own initiative, and not on a direct command from the user, will be called active programs or software agents.

Third, the transfer of data between active programs. In this case, the person is clearly not involved in the data transfer process. For example, the system for mirroring the content of Internet sites can be performed automatically at specified intervals or in accordance with other criteria. It must be understood that, in the end, the results of the functioning of such programs will still be used by a person, and only for this they were created and launched.

The human-program relationship is functionally asymmetric: a person is either a provider of data or a user of it. Programs, on the other hand, either simply store or transform the stored information.

The relationship between the network and the computer is also asymmetric. If a computer can work without a network, autonomously, then a network without computers is unthinkable.

Let's define what a computer network is. It is customary to understand a computer network as a set of computers connecting them with communication channels and additional equipment designed for data exchange.

Then the diagram in Figure 1.1. converts slightly:

Let us consider in order what properties should have computer system to be called a network.

First, the network requires computers - at least two. We will call these computers - network nodes, or simply knots... You can also find the terms " stationdata", "terminalsystem". There are no fundamental upper limits on the number of computers in the network (however, for any specific network technology there are always such restrictions - either the total number of computers is limited, or the number of network segments and computers in them). It is customary to classify networks not so much by size (number of nodes), but by scale (covered territory) - local, regional, etc.

Second, computers must be connected channelstransmissiondata(Efficiency). The data link consists of the linestransmissiondata(LPD) and apparatusendingschanneldata(AOKD). The last term hides devices such as a modem or Network Card... To designate AOKD we will use the modern term " networkinterface". Often, to ensure the functioning of the network, it is necessary to use optional equipment- repeaters, bridges, switches, routers, etc. The set of data transmission channels and additional network equipment is called networktransmissiondata(SPD).

Thirdly, computers must be equipped with network software (NSS) - as a rule, a network operating system (SOS) or a network add-on over a conventional operating system. The open source software installed on different computers may be different, but necessarily compatible with each other - that is, implement one set of data transfer protocols.

Fourthly, at least one computer must provide a part of its resources for public use - disk space, printer, programs, etc. Such a computer is called server... In addition, all other network nodes (clients) must be able to use the resources of the servers. The resources provided for the general use by the server will be called sharedresources.

The fourth property is not always obvious (for example, in the case of a network used only for exchanging e-mail, it is difficult to allocate shared resources), but it is necessarily present (for example, with e-mail, such resources can be a mail server program, disk space allocated for storing messages, processor time spent on mail processing).

In most cases, the name of the shared resource is indicated in the name of the server: file server (resource - disk files), print server (resource - printers), application server (resource - application programs), database server (resource - databases), etc.

Note that the listed properties reflect different aspects of the essence of a computer network. The first two properties can be called structural - they determine what elements the network consists of and how these elements are related to each other. The third property is software, indicating the need for special programs, without which the elements of the network will remain disconnected, even being physically connected. Finally, the fourth property is pragmatic, it contains an indication that the purpose of creating a network is not in itself, but in the benefits that the network can bring.

1.2 Wednesdaytransmissiondata

Data transmission can occur via cable (in this case, they speak of limited or cable transmission medium) and with the help of electromagnetic waves of one nature or another - infrared, microwaves, radio waves - propagating in space (unlimited transmission medium, wireless networks).

In most cases, cabled environments are more convenient, more reliable, and more profitable than unlimited. As a rule, cable and related networking equipment is much cheaper than wireless equipment, and the data transfer rate over the cable is higher. Nevertheless, in some cases, cable laying is either technically difficult (for example, water barriers), or economically unjustified (the cost of laying a cable is high, and a high transmission speed is not required), or faces organizational or other problems (for example, it is necessary to lay a trench through a busy highway in the city center, which is very difficult to obtain the consent of the city authorities). In addition, there may be a need to connect to the network of users who, by their occupation, often change their location (for example, storekeepers in a large warehouse). In all these (and many other) cases, wireless networks can be used.

According to the material used, cable media are divided into "copper" (in fact, the conductive cores of such cables can contain not only copper, but also other metals and their alloys) and optical (fiber-optic, the conductive core is made of optically transparent materials - quartz or polymers) ... Copper cables are symmetrical (all conductors are the same, for example, a twisted pair of conductors) and asymmetric (for example, a coaxial cable consisting of a central core and braid isolated from each other). Optical cables differ in the ratio between the conductor thickness and the carrier frequency of the data transmission. Thin conductors, the cross-sectional diameter of which is comparable to the wavelength of the carrier frequency, form single-mode cables (typical thickness 8-10 microns), and thicker ones - multimode cables (up to 50-60 microns).

When building wireless networks, as a rule, one of three technologies is used: transmission in the infrared range, data transmission using narrowband radio signals, and data transmission using spread spectrum radio signals.

1.3 Modestransmissiondata

Networks are divided into two classes, which differ in the way they use the data transmission channel: networks with data selection and data routing.

In networks with breedingdata there is a common transmission channel to which all nodes are connected. At a time, only one node owns the channel, which sends data to the channel. Any block of data issued to the channel is received (in the form of copies) by all network nodes. Each node checks the destination address transmitted with the data block and compares it with own address, in case of a match, processes the received data, and in case of a mismatch, it discards it (destroys its copy).

Networks with routingdata consist of many separate channels connecting pairs of network nodes. A pair of nodes that have a common channel can transmit data to each other independently of the rest of the network nodes. To transfer data between nodes that do not have a common channel, it is necessary to use one or more other nodes that would carry out routing of the transmitted information.

1.4 The wayscommutation

Switching is a necessary element of communication between nodes, allowing to reduce the number of required communication lines and increase the load of communication channels. It is practically impossible to provide each pair of nodes with a dedicated communication line, therefore, networks always use one or another method of switching subscribers, using existing communication lines to transfer data from different nodes.

Switchednetwork is called a network in which communication between nodes is established only on demand.

Subscribers are connected to switches with dedicated (individual) communication lines. The communication lines connecting the switches are shared by the subscribers.

Switching can be carried out in two modes: dynamically and statically. In the first case, switching is performed for the duration of the communication session (usually from seconds to hours) at the initiative of one of the nodes, and at the end of the session the communication is broken. In the second case, the switching is performed by the network service personnel for a much longer period of time (several months or years) and cannot be changed at the initiative of users. Such channels are called highlighted(dedicated) or rented(leased).

Two groups of switching methods: commutationchannels(circuit switching) and commutationwithintermediatestorage(store-and-forward). The second group consists of two ways: commutationmessages(message switching) and commutationpackages(packet switching).

When switching channels between nodes that need to establish communication with each other, the organization of a continuous composite channel is provided, consisting of sequentially connected individual channels between the nodes. Separate channels are interconnected by switching equipment (switches). Before transmitting data, you must complete the connection establishment procedure, during which a concatenated channel is created.

Message switching is understood as the transfer of a single data block between network nodes with temporary buffering of this block by each of the transit nodes. The message can be text file, file with graphic image, email- the message has an arbitrary size, determined solely by its content, and not by one or another technological considerations.

When switching packets, all data transmitted by the user is divided by the transmitting node into small (up to several kilobytes) parts - packages(packet). Each packet is supplied with a header that indicates, at a minimum, the destination node address and the packet number. Packets are transmitted over the network independently of each other. The switches of such a network have an internal buffer memory for temporary storage of packets, which makes it possible to smooth out traffic ripples on communication lines between switches. Packages are sometimes called datagrams( datagram ) , and the mode of individual packet switching is datagram mode.

A packet-switched network slows down the interaction of each particular pair of nodes, because their packets can wait in the switches while other packets are transmitted. However, the overall efficiency (the amount of data transmitted per unit time) with packet switching will be higher than with circuit switching. This is due to the fact that the traffic of each individual subscriber is pulsating, and the pulsations different subscribers, in accordance with the law of large numbers, are distributed over time, increasing the uniformity of the network load.

1.4 Organizationvirtualchannels

In contrast to the datagram transmission mode, which assumes independent routing of each packet, the mode virtualchannel(virtual circuit or virtual channel) establishes a single route for all packets within one connection. Before starting the transmission, the transmitting node issues a special packet to the network - a request to establish a connection.

This packet, passing through the switches, “builds” a virtual channel - the switches remember the route for this connection, and subsequent packets will be sent along it.

At the same time, the time spent on establishing a virtual channel is compensated by more than fast transmission packet flow due to the fact that the switches do not fully route each packet, but quickly determine its route by the virtual channel number.

2. Localthe network

local corporate network switching

Today, local area networks (LANs) allow computers located in a limited space to be combined into unified system allowing you to exchange data with each other.

To build a high-performance LAN with high reliability, flexibility and versatility, you need to observe the following principles of building local area networks.

The LAN must be an open system, that is, it must be combined with modern technologies and equipment for further expansion.

· Must have high reliability and resistance to failures of communication channels and equipment, software failures.

· The LAN must implement the means of protecting valuable information.

· The construction and operation of a LAN should be in accordance with generally accepted models and standards.

· When the structure of the enterprise changes, the LAN should easily change its logical structure.

The local network must be able to connect to wide-area networks to integrate into single network(for example, VLAN technology).

· Equipment, both active and passive, must be from the same manufacturer to avoid unforeseen conflicts.

Localcomputingthe networkLAN are cable systems, divided into various structural subsystems. LANs are either wired or wireless. For normal network operation, active equipment is used - routers and switches.

Today local area networks (LAN) are a necessary and indispensable part of a modern enterprise or office.

By building a local network, you can use a variety of equipment - scanners, faxes, printers. A LAN can significantly save time and increase productivity.

Local area networks LAN are:

1. Data protection from unauthorized access;

2. High-speed access to any information on the network;

3. Reliable means for storing information;

4. Possibility of joint use of network resources.

For the reliability of the LAN, it must be laid and debugged correctly. Therefore, the design, installation and adjustment of local networks should be carried out by qualified craftsmen. In this case, only high-quality equipment from good and well-known foreign manufacturers should be used.

2.1 Localthe networkonenterprise

LAN enterprises - it is a transport infrastructure for transferring data streams. Nowadays it is no longer possible to imagine a modern enterprise without a local network. The local area network significantly increases labor productivity and saves time. Enterprise LAN saves employees from running around their offices. Using a local network, you can easily contact any employee, transmit or receive important information. A modern LAN has the following essential characteristics:

· Manageability;

· Fault tolerance;

· Scalability;

· Compatibility with equipment of other subsystems;

· Good performance;

· Support for the required communication standards.

LANenterprises usually quite voluminous. Accordingly, it must be very reliable and, moreover, safe, since in the event of any abnormal situation, the enterprise will suffer losses. Therefore, only qualified craftsmen should be engaged in the development and installation of a local network. In this case, only high-quality high-precision equipment should be used.

An enterprise LAN is a transport infrastructure designed to transfer information. Now almost all enterprises already have modern local area networks, which significantly save employees' time and increase productivity. After all, with the help of a modern LAN, you do not need to constantly run around the offices, you can instantly contact an employee and transmit (receive) information.

The latest generation enterprise LAN has many essential characteristics such as excellent manageability, future scalability, powerful fault tolerance, high performance and full compatibility with other equipment.

Typically, an enterprise LAN is very voluminous. It is known that, as the scale of the local network increases, it becomes much more difficult to ensure its excellent reliability and complete safety... Indeed, if a LAN breaks down in a large enterprise, it will suffer colossal losses associated with downtime. Therefore, experts strongly advise against installing large LANs on their own, but entrusting its installation to qualified craftsmen.

3. Corporatethe network

TOcorporatenetwork- means a system that ensures the transfer of information between the various applications used in the system of the corporation.

At the same time, it is believed that the network should be as versatile as possible, that is, allow the integration of existing and future applications with the lowest possible costs and restrictions.

A corporate network, as a rule, is geographically distributed, i.e. uniting offices, divisions and other structures located at a considerable distance from each other. Often, corporate network nodes are located in different cities and sometimes countries. The principles by which such a network is built are quite different from those used to create a local network, even covering several buildings. The main difference is that geographically distributed networks use rather slow (today - tens and hundreds of kilobits per second, sometimes up to 2 Mbit / s) leased communication lines. If, when creating a local network, the main costs fall on the purchase of equipment and laying of cables, then in wide-area networks the most significant cost element is the rent for the use of channels, which grows rapidly with an increase in the quality and speed of data transmission. This limitation is fundamental, and when designing a corporate network, all measures should be taken to minimize the amount of data transferred. For the rest, the corporate network should not impose restrictions on which applications and how they process the information carried over it.

Applications here are system software - databases, mail systems, computing resources, file service, and so on - as well as the tools with which the end user works. The main tasks of a corporate network are the interaction of system applications located in various nodes, and access to them by remote users.

3.1 Principlesconstructingcorporatenetworkstransmissiondata

The first problem that has to be solved when creating a corporate network is the organization of communication channels. If within the same city it is possible to count on leasing dedicated lines, including high-speed ones, then when moving to geographically distant nodes the cost of leasing channels becomes simply astronomical, and their quality and reliability often turn out to be very low.

A natural solution to this problem is to use existing global networks. In this case, it is sufficient to provide channels from offices to the nearest network nodes. In this case, the global network will take over the task of delivering information between nodes. Even when creating a small network within one city, one should keep in mind the possibility of further expansion and use technologies that are compatible with existing global networks. Often the first, if not the only, such network that comes to mind is the Internet.

3.2 ANDuseInternet

At using the Internet as the basis for a corporate data network, it turns out to be very interesting thing... It turns out that the Network is not a network. This is precisely the Internet - the interconnection. If we look inside the Internet, we will see that information passes through many completely independent and mostly non-profit nodes, connected through the most diverse channels and data networks. The rapid growth of services provided on the Internet leads to overloading of nodes and communication channels, which sharply reduces the speed and reliability of information transmission. At the same time, Internet service providers do not bear any responsibility for the functioning of the network as a whole, and communication channels are developing extremely unevenly and mainly where the state considers it necessary to invest in this. In addition, the Internet binds users to a single protocol - IP. This is good when we use standard applications that work with this protocol. The use of any other systems with the Internet is not easy and expensive. If we need to provide access mobile users to our private network - the Internet is also not the best the best solution... It would seem that, big problems It shouldn't be here - ISPs are almost everywhere, get a laptop with a modem, call and go. However, a supplier, say, in Yekaterinburg, has no obligation to you if you are connected to the Internet in Moscow. He does not receive money for services from you and, of course, will not provide access to the network. Another Internet issue widely discussed in recent times, - security. If we are talking about a private network, it seems quite natural to protect transmitted information from someone else's gaze. The unpredictability of information paths between many independent Internet sites not only increases the risk that some overly curious network operator might put your data on disk (technically not that difficult), but also makes it impossible to determine the location of the information leak. Another aspect of the security problem is again related to the decentralization of the Internet - there is no one who can restrict access to the resources of your private network. Since this is an open system where everyone can see everyone, anyone can try to get into your office network and gain access to data or programs.

3.3 Virtualthe network

The ideal option for a private network would be to create communication channels only in those areas where it is necessary, and transfer over them any network protocols that are required by running applications. At first glance, this is a return to leased communication lines, however, there are technologies for building data transmission networks that allow organizing channels inside them that arise only at the right time and in the right place. Such channels are called virtual. A system that combines remote resources using virtual channels can naturally be called a virtual network. Today there are two main technologies of virtual networks - circuit-switched networks and packet-switched networks. The former include the conventional telephone network, ISDN and a number of other, more exotic technologies. Packet-switched networks are represented by X.25 technologies, Frame Relay and, more recently, ATM. Other types of virtual (in various combinations) networks are widely used in the construction of corporate information systems.

Circuit-switched networks provide the subscriber with several communication channels with a fixed bandwidth per connection. The well-known telephone network provides one communication channel between subscribers. If you need to increase the number of simultaneously available resources, you have to install additional phone numbers, which is very expensive. Even if we forget about the low quality of communication, then the limitation on the number of channels and big time Connectivity does not allow telephony to be used as the backbone of a corporate network. For connecting individual remote users, this is quite convenient and often the only one. available method... It should only be borne in mind that access to ISDN in our country is the exception rather than the rule.

An alternative to circuit-switched networks is packet-switched networks. When using packet switching, one communication channel is used in a time-sharing mode by many users - much the same as on the Internet. However, unlike networks such as the Internet, where each packet is routed separately, packet-switched networks require establishing a connection between end resources before transmitting information. After establishing a connection, the network "remembers" the route (virtual channel) through which information should be transmitted between subscribers and remembers it until it receives a signal that the connection is broken. For applications operating in a packet switching network, virtual circuits look like ordinary communication lines - with the only difference that their bandwidth and introduced delays vary depending on the network congestion.

3.4 NetworksX.25

The classic packet switching technology is the X.25 protocol. The X.25 protocol includes powerful tools error correction, ensuring reliable delivery of information even on bad lines and is widely used where there are no high-quality communication channels. In our country, they are not almost everywhere. Naturally, reliability comes at a price — in this case, the speed of the network equipment and the relatively large — but predictable — delays in the dissemination of information. At the same time, X.25 is a universal protocol that allows you to transfer almost any type of data.

Other standard feature X.25 networks - communication via ordinary asynchronous COM ports. Figuratively speaking, an X.25 network lengthens the cable connected to a serial port, bringing its connector to remote resources. Thus, virtually any application that can be accessed through a COM port can be easily integrated into an X.25 network. Examples of such applications include not only terminal access to remote host computers, but also cc: Mail, MS Mail, etc.

Today, there are dozens of public X.25 global networks in the world, their nodes are located in almost all major business, industrial and administrative centers. In Russia, X.25 services are offered by Sprint Network, Infotel, Rospak, Rosnet, Sovam Teleport and a number of other providers. In addition to connecting remote sites, X.25 networks always provide means of access for end users. In order to connect to any resource on the X.25 network, the user only needs to have a computer with an asynchronous serial port and a modem. At the same time, there are no problems with access authorization in geographically remote sites. Thus, if your resource is connected to an X.25 network, you can access it both from your vendor's nodes and through nodes on other networks - that is, from virtually anywhere in the world.

From a security perspective, X.25 networks offer some very attractive capabilities. First of all, due to the very structure of the network, the cost of intercepting information on an X.25 network turns out to be high enough to already serve as a good defense. The problem of unauthorized access can also be solved quite effectively by means of the network itself.

The disadvantage of X.25 technology is that there are a number of fundamental speed limits. The first of them is associated precisely with the developed capabilities of correction and recovery. These tools cause delays in the transmission of information and require a lot of processing power and performance from the X.25 hardware, as a result of which it simply "cannot keep up" with fast communication lines. Although there is equipment that has two megabit ports, the actual speed provided by it does not exceed 250 - 300 Kbps per port. On the other hand, for modern high-speed communication lines, X.25 correction means are redundant and when they are used, the equipment power is often idle.

The second feature that makes X.25 networks look slow is the encapsulation of the LAN protocols (primarily IP and IPX). All other things being equal, the connection of local networks over X.25 is, depending on the parameters of the network, 15-40 percent slower than when using HDLC over a dedicated line. Moreover, the worse the communication line, the higher the loss of productivity. Again we are dealing with an obvious redundancy: LAN protocols have own funds correction and recovery (TCP, SPX), however, when using X.25 networks, you have to do it again, losing speed. It is on these grounds that X.25 networks are declared slow and obsolete. But before talking about the fact that any technology is outdated, it should be indicated for what applications and in what conditions. On low quality links, X.25 networks are quite efficient and offer significant cost and performance gains over leased lines. On the other hand, even if you count on rapid improvement quality of communication - a prerequisite for the obsolescence of X.25 - then even then the investment in X.25 equipment will not be lost, since modern equipment includes the ability to migrate to Frame Relay technology.

3.5 NetworksFrameRelay

Frame Relay technology emerged as a means to realize the benefits of packet switching on high-speed lines. The main difference between Frame Relay and X.25 networks is that they exclude error correction between network nodes. The tasks of restoring the information flow are assigned to the terminal equipment and user software. Naturally, this requires the use of sufficiently high-quality communication channels.

The second difference between Frame Relay networks is that today almost all of them implement only a mechanism (PVC). This means that when connecting to a Frame Relay port, you must determine in advance which remote resources you will have access to. The principle of packet switching - many independent virtual connections in one communication channel - remains here, but you cannot choose the address of any subscriber of the network. All resources available to you are determined when you configure the port. Thus, on the basis of Frame Relay technology, it is convenient to build closed virtual networks used to transfer other protocols by means of which routing is carried out. "Closure" virtual network means that it is completely inaccessible to other users working in the same Frame networks Relay. For example, in the United States, Frame Relay networks are widely used as the backbone for the Internet. However, your private network can use Frame Relay VCs on the same lines as Inernet traffic - and be completely isolated from it.

The lack of error correction and complex packet switching mechanisms typical for X.25 allows information to be transmitted over Frame Relay with minimal delays. Additionally, it is possible to enable a prioritization mechanism that allows the user to have a guaranteed minimum information transfer rate for a virtual channel. This capability allows Frame Relay to be used to carry delay-critical information such as real-time voice and video. This relatively new feature is gaining popularity and is often the main reason for choosing Frame Relay as the backbone of the corporate network.

There are also private Frame Relay networks that operate within the same city or use long-distance - usually satellite - leased lines. Building private networks based on Frame Relay allows you to reduce the number of leased lines and integrate voice and data transmission.

3.6 Structurecorporatethe network

When building a geographically distributed network, all the technologies described above can be used. To connect remote users the easiest and affordable option is the use of telephone communications. ISDN networks can be used where possible. To connect the nodes of the network, in most cases, global data transmission networks are used. Even where it is possible to lay dedicated lines (for example, within the same city), the use of packet switching technologies allows to reduce the number of necessary communication channels and - which is important - to ensure the compatibility of the system with existing global networks.

Connecting a corporate network to the Internet is justified if you need access to the appropriate services. It is worth using the Internet as a data transmission medium only when other methods are unavailable and financial considerations outweigh the requirements of reliability and security. If you only want to use the Internet as a source of information, dial-on-demand is a better choice. This dramatically reduces the risk of unauthorized intrusion into the network from the outside. The simplest way to provide such a connection - use dial-up to the Internet site via a telephone line or, if possible, via ISDN. Another, more reliable way provide a connection on demand - use a leased line and X.25 protocol, or - which is much preferable - Frame Relay. In this case, the router must be configured to disconnect the virtual connection if there is no data for a certain amount of time and re-establish it only when data appears. If you need to provide your information on the Internet - for example, to set up a WWW or FTP server, the on-demand connection turns out to be inapplicable. In this case, you should not only use access restriction using Firewall, but also isolate the Internet server from other resources as much as possible. A good solution is to use a single Internet connection point for the entire wide area network, the nodes of which are connected to each other using X.25 or Frame Relay virtual circuits. In this case, access from the Internet is possible to a single site, while users at other sites can access the Internet using a connection on demand.

For data transmission within the corporate network, it is also worth using virtual circuits of packet-switched networks. The main advantages of this approach - versatility, flexibility, security - were discussed in detail above. Today, the cost of using Frame Relay for long distance communication turn out to be several times higher than for X.25 networks. On the other hand, higher data rates and the ability to simultaneously transmit data and voice can be decisive arguments in favor of Frame Relay. To connect remote users to the corporate network, access nodes of X.25 networks can be used, as well as their own communication nodes. In the latter case, the allocation of the required amount is required phone numbers(or ISDN lines), which can be too expensive. If you need to provide a connection a large number users at the same time, it may be cheaper to use X.25 network access nodes, even within the same city.

Termsandthe mainconceptstelecommunications

ISDN

Digital networks of complex services, originally intended for the transmission of voice, and now actively used for the transmission of both voice and data. Provide the subscriber with several (at least two) transparent digital channels at a speed of 64 kbps. Channels can be used independently (for example, for two simultaneous telephone conversations or one for conversation, the other for data transmission) or combine to increase bandwidth. Both channel switching between ISDN network subscribers and their "fixing" between two points are possible. A special feature of ISDN is the presence of a separate signaling channel, which allows transferring control information for the network not only at the stage of establishing a connection, but also at any time during a conversation or data transfer.

B-channel

"Transparent" information transfer channel at a speed of 64 kbps, provided by the ISDN network between subscribers. The subscriber is provided with several (at least two) B-channels, each of which can be switched independently. The B-channel can carry both voice and data.

D-channel

An additional channel used to transfer signals between the subscriber and the ISDN network. Constantly connects the subscriber to the PBX. Signals are transmitted in the form of information packets containing commands and responses to them. The D-channel can also transmit information in an X.25 network. This capability must be supported not only by your equipment, but also by your ISDN network operator. It is important to be aware that there are several incompatible command formats ("D-channel protocols") adopted in different countries. Currently, Europe uses a single Euro-ISDN (ETSI) standard, which is also adopted in Russia. When purchasing ISDN equipment, you should pay attention to the compatibility of the D-channel protocol with your ISDN operator.

BRI

Basic Rate Interface is the basic type of ISDN subscriber connection. Provides two 64 kbps B-channels and one 16 kbps D-channel. If more B-channels are required, multiple ISDN BRI or ISDN PRI can be used (see below).

ATM

Asynchronous Transfer Mode is an advanced packet switching technology that enables high-speed transmission of fixed-length packets (53 bytes) over broadband and narrowband LANs or corporate networks. ATM is capable of delivering: speech, data, faxes, real-time video, CD quality audio, multi-megabit data streams with very high speed(66 Mbps to 622 Mbps and even higher)

Currently, ATM components are produced by a narrow range of suppliers. All equipment on the ATM network must be ATM-compatible. Therefore, the implementation of ATM under existing conditions requires a massive replacement of equipment, which is the reason for the slow spread of ATM.

LAN

Local area network - computers connected to a network located in a limited area (for example, in a room, building, a group of nearby buildings).

TCP / IP

Transmission Control Protocol / Internet Protocol - Industrial standard set protocols that ensure communication in a heterogeneous environment, that is, ensures compatibility between computers of different types. Interoperability is one of the benefits of TCP / IP, which is why most networks support it. It also provides Internet access and a routable protocol for enterprise-wide networks, but has two major drawbacks: size and lack of speed.

IPX / SPX

Internetwork Packet Exchange / Sequenced Packet Exchange is a protocol stack used in Novell networks. A relatively small and fast protocol that supports routing.

HDLC

High-level Data Link Control is a widely used international data link control protocol. Developed by the International Standards Organization (ISO). HDLC is a bit-oriented synchronous protocol that runs on data link level OSI model (Open Systems Interconnection Reference Model. This protocol transfers data in blocks of arbitrary length, but in a standard format.

PVC

The Permanent Virtual Circuit is similar to a leased line, that is, it is a permanent and actually existing channel. However, unlike line rental, the fee is paid only for the time during which it is used. Importance of this type communication services are increasing as PVCs are used by frame relay in ATM.

WWW

The World Wide Web is a hypertext multimedia service on the Internet. Contains information in the form of addressable pages written in HTML.

FTP

File Transfer Protocol is a process for transferring files between a local and a remote computer. Supports several commands that implement bidirectional transfer of binary and ASCII files between computers.

Listsources

http://compseti.ru

Posted on Allbest.ru

...

Similar documents

The architecture of computer networks, their classification, topology and principles of construction. Transmission of data on the network, collisions and methods of their resolution. TCP-IP protocols. OSI, DNS, NetBios. Hardware for data transmission. Domain Name System DNS.

abstract, added 11/03/2010


Characteristic state of the art digital broadband data transmission networks, peculiarities of their application for the transmission of telemetric information from special objects. Principles of building and calculating networks using Wi-Fi and WiMax technologies.

thesis, added 06/01/2010


Consideration of switched (SVC) and permanent (PVC) channels of virtual connections. Characteristics of the structure and size of packets, transmission protocols and routing algorithms for X.25 networks, Frame RELAY, ATM and determination of their benefits.

abstract, added 03/17/2010


The main advantages obtained by networking personal computers in the form of an intra-industrial computer network. Methods for evaluating the effectiveness of local area networks. Types of building networks by methods of transferring information.

abstract, added 10/19/2014


The structure of telegraph and facsimile communication networks, data transmission. Components of discrete message transmission networks, methods of switching in them. Building a correcting code. SDH network design. Calculation of the load on the track segments, the choice of multiplexers.

term paper, added 01/06/2013


Classification of networks and methods of switching. Types of communication and modes of operation of message transmission networks. Unification and standardization of protocols. Reference Model for Open Systems Interconnection. Feature of data preparation. Interaction of information systems.

abstract, added 09/15/2014


The role and general principles of building computer networks. Topologies: busbar, mesh, combined. The main systems for building "Token Ring" networks on personal computers... Information transfer protocols. Software, network installation technology.

term paper added on 10/11/2013


Types of data transmission networks. Types of geographic distribution, functional interaction, and network topology. Principles of using network equipment. Switching channels, packets, messages and cells. Switched and non-switched networks.

term paper added 07/30/2015


The role of computer networks, principles of construction. Protocols for transferring information in the ArcNet network, used topologies and communication means. Software, scanning technology. OS computer networks. Safety instructions.

term paper added on 10/11/2013


The process of building multiservice communication networks, its stages. Analysis of technologies of data transmission networks, their advantages and disadvantages. Designing a multiservice communication network using telecommunication equipment from different manufacturers.