The history of the development of subscriber access networks. Methods for organizing subscriber access. Models of transport networks
Subscriber access network - This is a combination of technical means between the terminal subscriber devices installed in the user's premises, and the switching equipment, to the numbering plan (or addressing) of which the terminals are connected to the telecommunications system.
5.1. Subscriber access network models
In the modern telecommunications system, not only the role of the access network is changing. In most cases, the territory is expanded, within the boundaries of which the access network is created. In order to eliminate the differences in the modern publications in the interpretation of the place and the role of the access network, in Fig. 5.1 shows a model of a promising telecommunication system.
Figure 5.1 - Model of the Telecommunication System
The first element of the telecommunications system is a set of terminal and other equipment, which is installed in the subscriber's room (user). In English-language technical literature, this element of the telecommunications system corresponds to the term Customer Premises Equipment (CPE).
The second element of the telecommunications system is actually a network of subscriber access. The role of the subscriber access network is to ensure the interaction between the equipment installed in the subscriber's room and the transit network. Usually, a switching station is installed at the pairing point of the subscriber access network with the transit network. The space covered by the subscriber access network lies between the equipment placed in the room at the subscriber and this switching station.
The subscriber access network is divided into two sections - the lower plane rice. 5.1. Subscriber lines (LOOP NETWORK) can be viewed as individual means of connecting terminal equipment. As a rule, this fragment of the subscriber access network is a combination of al. Transfer Network (Transfer Network) is used to improve the efficiency of subscriber access. This fragment of the access network is implemented on the basis of transmission systems, and a number of cases are used and the load concentration devices are used.
The third element of the telecommunications system is the transit network. Its functions consist in establishing connections between terminals included in various subscriber access networks, or between the terminal and tools for supporting any services. In the model under consideration, the transit network can cover the territory lying both within one city or village and between subscriber access networks of two different countries.
The fourth element of the telecommunications system illustrates access to various telecommunication services. In fig. 5.1, in the last ellipse, the name in the original language (Service Nodes) is indicated, which is translated by three words - nodes supporting services. Examples of such a node can be the workplaces of telephone operators and servers in which any information is stored.
Shown in Fig. 5.1 The structure should be considered as a promising model of the telecommunications system. To solve terminological problems, we turn to the model inherent in subscriber access networks of analog PBX. Such a model is shown in Fig. 5.2. Considering the existing local networks, we, as a rule, will operate in two terms - "Subscriber Network" or "Al" network. The words "Subscriber Access Network" are used in cases where it comes to a promising telecommunications system.
Figure 5.2 - Model of the subscriber network
This model is valid for both GTS and STS. Moreover, for the GTS shown in Fig. 5.2 The model is invariant to the inter-intermission structure. It is identical to:
non-irisoned networks consisting of only one telephone exchange;
regional networks, which consist of several district PBXs (RATS) interconnected by the principle of "each with each";
of the zoned networks built with nodes of an incoming message (UVS) or with nodes of an outgoing message (UIS) and UVS.
For all elements of the subscriber network in brackets are the terms in English. It should be noted that the term "line of intergatal communication" (Link Cable) in domestic terminology is not yet applied, since such routes in the GTS and STS are almost not used.
The model illustrating the main options for building a subscriber network is shown in Fig. 5.3. Some fragments of the previous model are detailed in this figure.
Figure 5.3 - Main Building Options
subscriber network
In fig. 5.3 A number of designations are rarely used in domestic technical literature. The cable crossing device (Cross-Connection Point) is shown as two concentric circles. Such a symbol is often used in ITU documents. Also typical can be considered a Distribution Point (Distribution Point) with a black square.
The model shown in fig. 5.3, can be considered universal with respect to the type of switching station. In principle, it is the same for a handheld telephone exchange, and for the most modern digital information distribution system. Moreover, this model is invariant to the type of interactive network, such as telephone or telegraph.
On the other hand, for a digital switching station, a self-model can be proposed that will make it possible to more accurately reflect the specifics of the subscriber access network. This task is quite complex. The problem is that the process of implementing a digital switching station leads to a change in the structure of the local telephone network. In some cases, this is noticeably reflected in the structure of the subscriber network. A characteristic example of such a situation is the installation of a digital switching station that replaces several old electromechanical stations. Plugging of the digital switching station - with this method of upgrading a local telephone network - actually combines all territories that were serviced by previously dismantled electromechanical PBXs. In addition, when the digital switching station is embedded, specific (permanent or temporary) solutions may occur when some remote subscriber groups are connected through the use of hubs.
Of course, such decisions should be taken into account at the development stage of the general concept of modernizing the local telephone network. When the relevant conceptual decisions are accepted, you can start searching for optimal options for building a subscriber access network. For a hypothetical digital switching station, these options are presented in Fig. 5.4. The last two drawings (5.3 and 5.4) have a number of general points.
Figure 5.4 - Subscriber access network model for digital switching station
Firstly, both structures involve the presence of the so-called "direct nutrition zone" - an enclave, within which the AL is included in the cross directly (without connecting cables in distribution cabinets).
Secondly, the following access area of \u200b\u200bthe access network is located for the "direct diet" area for which it is advisable to use remote subscriber modules (hubs or multiplexers) in a digital station, and for analog PBX or non-relaxed cables, or channels formed by transmission systems.
Thirdly, it should be noted that the structure of the subscriber network is out of any dependence on the type of switching station - corresponds to a column with a tree topology. This is essential from the point of view of reliability of communication: the use of digital switching technology not only does not increase the coefficient of the AL, but, in some cases, reduces it due to the introduction of additional equipment on the site from the PBX cross to the user terminal.
To compile a list of those necessary further, terms and, especially, to establish conformity between the concepts adopted in domestic practice and ITU documents, it is advisable to cite the structure of the AL network, presented on the upper part of Fig. 5.5.
For the structural circuit of the al (upper part of Fig. 5.5), three options for connecting the subscriber terminal to the switching station are presented.
The upper branch of this pattern shows a promising connection option that without the use of intermediate cross-drive equipment. The cable is laid from the cross to the distribution box, where the connection is carried out by subscriber posting.
On the middle branch of the figure shows the option of connecting the on the closet system, when intermediate equipment is located between the cross and a junction box. In our model, the role of such equipment is assigned to a distribution cabinet.
In some cases, Al is organized using air lines (VLP). In fig. 5.5 This option is shown on the bottom branch. In such a situation, a cable box (QW) and introductory-output insulators are installed on the pole. In the location of the junction box, the subscriber protective device (AZU) is mounted, which prevents the possible effect on the hazardous currents and stresses. It should be noted that the organization of the Al or its individual sites due to the construction of the WPC is not recommended; But in some cases, this is the only option for the organization of subscriber access.
Figure 5.5 - Structural diagram and joints of subscriber lines for GTS and STS
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Graduation qualifying work
Subject: Subscriber Access Network
Introduction
One of the most important problems of telecommunication networks continues to remain a problem of subscriber access to network services. The relevance of this problem is determined primarily by the rapid development of the Internet, access to which requires a sharp increase in the bandwidth of subscriber access networks. The main tool of the access network, despite the emergence of the new most modern wireless ways of subscriber access, remain traditional copper subscriber pairs. At the same time, high-speed subscriber networks based on fiber-optic communication technologies are widely developed. The distinctive feature is:
* Lack of harmful electromagnetic radiation;
* The signal is not distorted by electromagnetic and radio frequency interference (optical cable is absolutely immune to the effects of high voltage, electromagnetic filing);
* Fiber optic cable is easier;
* has a much greater bandwidth than ordinary copper, which means that fiber can pass much more information for the same time;
* small attenuation of the light signal;
* Protection against unauthorized access, etc.
The construction and operation of optical lines is much cheaper than copper, therefore, as the volume of optical growth services increases, prices should decrease
The purpose of the graduation project is to develop a draft network of high-speed subscriber access based on fiber-optic communication technologies using automated design tools.
To achieve the goal of the graduation project, the following tasks are delivered:
analyze methodical and theoretical materials on the basics of local and telecommunication networks;
explore the features and structure of local and telecommunication networks of subscriber access;
explore network design stages, as well as funds and methods used to design networks and reasonably choose tools to achieve the goal of the graduation project;
develop a subscriber access network project using the selected design tool.
The practical significance of the graduation project is to develop a subscriber access project to the instruments and methods of design and further implementation of this project in real objects.
The structure of the graduation project is subordinated to the logic of solving the tasks. The first chapter of the graduation project will present theoretical foundations of data networks. The second chapter will provide an overview of network technology. The third chapter is devoted to the design: it will present the main stages of the design, the development of a subscriber access network project according to the task of the graduation project, the choice of tools to develop a project. In the fourth chapter will be presented the organizational and economic part. In the fifth chapter, it will be about the safety of life.
1. Overview of data transfer networks
1.1 Defining local networks
The methods and means of exchanging information have recently been proposed by many: from the simplest transfer of files using a floppy disk to the worldwide computer network that can combine all computers in the world. What place in this hierarchy is given to local networks?
Most often, the term "local networks" or "Local Computing Networks" (LAN, Local Area Network) understand literally, that is, these are networks that have small, local sizes connect closely located computers. However, it is enough to look at the characteristics of some modern local networks to understand what definition is not accurate. For example, some local networks easily provide communication at a distance of several tens of kilometers. This is no longer a room, not a building, not closely located buildings, but maybe even a whole city. On the other hand, the global network (Wan, Wide Area Network or Gan, Global Area Network) may well contact computers that are on neighboring tables in one room, but for some reason no one calls it a local network. Closely located computers can also be born using a cable connecting the connectors of external interfaces (RS232-C, Centronics) or even without a cable by infrared channel (IRDA). But for some reason this connection is also not called local.
Incorrectly and quite common definition of a local network as a small network that combines a small amount of computers. Indeed, as a rule, the local network binds from two to several dozen computers. But the limit features of modern local networks are much higher: the maximum number of subscribers can reach thousands. Call such a small incorrect network.
Some authors define a local network as a "system to directly connect many computers." It is understood that the information is transmitted from the computer to a computer without any intermediaries and by a single transmission medium. However, it is not necessary to talk about a single transmission environment in a modern local network. For example, within the same network, both electrical cables of various types (twisted steam, coaxial cable) and fiber optic cables can be used. The definition of the transmission of "without intermediaries" is also not correct, because in modern local networks, repeaters, transceivers, hubs, switches, routers, bridges, which sometimes produce a rather complex processing of the transmitted information are used. It is not entirely clear whether it is possible to consider them intermediaries or not, is it possible to consider a similar network to local.
Probably, it would be most accurate to determine as a local such network that allows users to not notice links. You can still say that the local network should provide a transparent connection. In essence, the computers associated with a local network are combined into one virtual computer, the resources of which can be accessible to all users, and this access is no less convenient than resources that are included directly into each individual computer. Under convenience, in this case, the high real access speed is understood, the rate of information sharing between applications, almost imperceptible to the user. With this definition, it becomes clear that neither slow global networks nor slow communication through serial or parallel ports does not fall under the concept of a local network.
From this definition it follows that the transfer rate over the local network must necessarily grow as the speed of the most common computers grows. This is what is observed: if another ten years ago, the exchange rate of 10 Mbps was considered quite acceptable, now the network is already considered a network that has a 100 Mbps bandwidth, is actively developed, and in some places of 1000 Mbps velocity C and even more. Without this, it is already possible, otherwise the connection will be too narrow, it will be overly slowing down the work of the virtual computer united network, reduce the convenience of accessing network resources.
Thus, the main difference between the local network from any other is a high speed of information transmission over the network. But this is not all, other factors are not less important.
In particular, it is fundamentally necessary low level of transmission errors caused by both internal and external factors. After all, even very quickly transmitted information that is distorted by errors, it simply does not make sense, it will have to be transferred again. Therefore, local networks necessarily use specially laid high-quality and well-protected links.
This characteristic of the network is of particular importance, as the ability to work with large loads, that is, with a high intensity of exchange (or, as they say, with great traffic). After all, if the exchange control mechanism used on the network is not too effective, then computers can wait for their turn to the transmission for a long time. And even if this transfer will then be carried out at the highest speed and unmistakably, for the network of the network, such a delay in access to all network resources is unacceptable. He doesn't matter why he has to wait.
The exchange control mechanism can be guaranteed to work successfully only when it knows how many computers (or, as they also say, subscribers, nodes) permissible to connect to the network. Otherwise, you can always include so many subscribers that any control mechanism will be discouraged. Finally, the network can only be called such a data transfer system that allows you to combine up to several dozen computers, but not two, as in the case of communication through standard ports.
Thus, it is possible to formulate the distinctive features of the local network as follows:
high speed transfer rate, large network bandwidth. Acceptable speed now - at least 100 Mbps;
low transmission errors (or, also the same, high-quality communication channels). The permissible probability of data transfer errors should be about 10-8 - 10-12;
effective, high-speed exchange mechanism for network exchange;
a pre-limited number of computers connected to the network.
With this definition, it is clear that global networks differ from local primarily by the fact that they are designed for an unlimited number of subscribers. In addition, they use (or can use) not too high-quality communication channels and a relatively low transmission rate. And the exchange control mechanism in them cannot be guaranteed rapidly. In global networks, the quality of communication is much more important, and the very fact of its existence.
Often allocate another class of computer networks - urban, regional networks (MAN, Metropolitan Area Network), which usually in their characteristics closer to global networks, although sometimes still have some features of local networks, for example, high-quality communication channels and relatively high Transmission speeds. In principle, the urban network may be local with all its advantages.
True, now it is impossible to spend a clear border between local and global networks. Most local networks have a global access. But the nature of the transmitted information, the principles of the organization of exchange, the modes of access to resources inside the local network, as a rule, are very different from those adopted in the global network. And although all the LAN computers in this case are also included in the global network, the specifics of the local network does not cancel. The ability to go to the global network remains only one of the resources divided by the users of the local network.
On the local network, the most different digital information can be transmitted: data, images, telephone conversations, emails, etc. By the way, it is the task of transmitting images, especially full-color dynamic, presented the highest requirements for network speed. Most often, local networks are used to separate (sharing) resources such as disk space, printers and exit to the global network, but this is just a minor part of those capabilities that provide local networks. For example, they allow you to exchange information between computers of different types. Not only computers, but also other devices, such as printers, plotters, scanners may be full subscribers (nodes) of the network. Local networks also give the ability to organize a system of parallel computing on all network computers, which repeatedly accelerates solving complex mathematical problems. With their help, as already mentioned, you can manage the work of a technological system or a research plant from several computers at the same time.
However, networks have quite essential flaws that should always be remembered:
the network requires additional, sometimes significant material costs for the purchase of network equipment, software, on laying connecting cables and personnel training;
the network requires admission to the work of a specialist (network administrator), which will be engaged in controlling the network, its upgrades, access to resources, to eliminate possible malfunctions, information protection and backup (for large networks, a whole team of administrators may need);
the network limits the capabilities of moving computers connected to it, since the connecting cable can be needed;
networks are an excellent environment for distributing computer viruses, so much more attention will have to protect against them than in the case of autonomous use of computers, because it is enough to infect one, and all network computers will be amazed;
the network dramatically improves the risk of unauthorized access to information in order to theft or destruction; Information protection requires a whole complex of technical and organizational events.
Here, it should be mentioned about the most important concepts of network theory, as a subscriber, server, client.
The subscriber (node, host, station) is a device connected to the network and actively participating in the information exchange. Most often, the subscriber (node) of the network is a computer, but a subscriber can also be, for example, a network printer or another peripheral device, which is possible directly to connect to the network. Next, instead of the term "subscriber" for simplicity, the term "computer" will be used.
The server is called the subscriber (node) of the network, which provides its resources to other subscribers, but does not use their resources itself. Thus, it serves the network. Servers on the network may be several, and it is not at all necessary that the server is the most powerful computer. Selected (Dedicated) Server is a server dealing with only network tasks. An undefined server may be other tasks in addition to maintaining the network. Specific type of server is a network printer.
The client is called the network subscriber, which only uses network resources, but does not give up its resources to the network, that is, the network serves it, and he only uses it. The client computer is also often referred to as a workstation. In principle, each computer can be simultaneously both the client and the server.
Under the server and the client often understand not computers themselves, but software applications running on them. In this case, the application that only gives the resource to the network is a server, and the application that only uses network resources is a client.
1.2 Types of communication network lines
The information transfer medium is called those links (or communication channels) for which information is exchanged between computers. In the overwhelming majority of computer networks (especially local), wired or cable communication channels are used, although there are wireless networks that are now more widely used, especially in portable computers.
Information on networks is most often transmitted in a sequential code, that is, bit beyond. Such a gear is slower and more complicated than when using a parallel code. However, it is necessary to take into account that with a faster parallel transmission (for several cables at the same time), the number of connecting cables increases a number of times equal to the number of parallel code discharges (for example, 8 times at 8-bit code). This is not a trifle at all, as it may seem at first glance. With considerable distances between the subscribers of the network, the cable cost is quite comparable to the cost of computers and can even exceed it. In addition, lay one cable (less often two multidirectional) is much simpler than 8, 16 or 32. Significantly cheaper, the search for damage and repair of the cable will also cost.
But that's not all. Transmission over long distances At any type of cable requires a complex transmitting and receiving equipment, since it is necessary to generate a powerful signal on the transmitter end and detect a weak signal at the receiving end. With serial transmission, only one transmitter is required and one receiver. With parallel, the number of required transmitters and receivers increases in proportion to the bit of the parallel code used. In this regard, even if a network of minor length is developed (about a dozen meters), the consistent transmission is most often selected.
In addition, with parallel transmission, it is extremely important that the lengths of individual cables are exactly equal to each other. Otherwise, as a result of passing through cables of different lengths between signals at the receiving end, a temporary shift is formed, which can lead to failures in the work or even to the complete non-working network. For example, at a transmission rate of 100 Mbps and a bit duration of 10 ns, this time shift should not exceed 5--10 ns. Such a shift value gives the difference in cable lengths in 1--2 meters. With a cable length of 1000 meters, this is 0.1--0.2%.
It should be noted that in some high-speed local networks, it is still using parallel transmission of 2--4 cables, which allows at a given transmission rate to use cheaper cables with a lower bandwidth. But the permissible length of cables does not exceed hundreds of meters. An example is a segment of the 100Base-T4 network Fast Ethernet.
The industry produces a huge number of types of cables, for example, only one largest cable company Belden offers more than 2000 their names. But all cables can be divided into three large groups:
electrical (copper) cables based on twisted pairs of wires (twisted pair), which are divided into shielded (shielded pair, STP) and unshielded (unshielded twisted pair, UTP);
electrical (copper) coaxial cables (coaxial Cable);
fiber Optic (Fiber Optic).
Each type of cable has its advantages and disadvantages, so that when choosing, it is necessary to take into account both the features of the problem being solved and the features of a particular network, including the topology used.
The following basic cable parameters can be distinguished, fundamentally important for use in local networks:
a cable bandwidth (frequency range of signals transmitted by cable) and attenuation of the signal in the cable; Two of these parameters are closely related to each other, since the attenuation of the signal increases with increasing signal frequency; It is necessary to choose a cable that at a given signal frequency has acceptable attenuation; Or you need to choose the frequency of the signal on which the attenuation is still acceptable; The attenuation is measured in decibels and in proportion to the length of the cable;
cable interference and ensured by the secrecy of information transfer; These two interconnected parameters show how the cable interacts with the environment, that is, how it reacts to external interference, and how easy it is to listen to the information transmitted by the cable;
the speed of the signal propagation over the cable or, the inverse parameter is the signal delay on the cable length meter; This parameter is of fundamental importance when choosing a network length; Typical values \u200b\u200bof signal propagation speeds - from 0.6 to 0.8 from the speed of propagation of light in vacuo; accordingly the typical values \u200b\u200bof delays - from 4 to 5 ns / m;
for electrical cables, the magnitude of the wave resistance of the cable is very important; Wave resistance is important to take into account when negotiating the cable to prevent the signal reflection from the ends of the cable; Wave resistance depends on the shape and interpordability of the conductors, from the manufacturing technology and the material of the cable dielectric; Typical wave resistance values \u200b\u200b- from 50 to 150 ohms.
Currently there are the following standards for cables:
EIA / TIA 568 (Commercial Building Telecommunications Cabling Standard) - American;
ISO / IEC IS 11801 (Generic Cabling for Customer Premises) - international;
CEENELEC EN 50173 (Generic Cabling Systems) - European.
These standards describe almost the same cable systems, but differ in terminology and norms to parameters. In this course, it is proposed to adhere to the terminology of the EIA / TIA 568 standard.
1.3 The main provisions of the reference model of information exchange of the open system
The network produces many operations that ensure data transfer from the computer to the computer. The user does not interest how this happens, it needs access to an application or a computer resource located in another network computer. In fact, all transmitted information passes many stages of processing.
First of all, it is divided into blocks, each of which is supplied with control information. The obtained blocks are made in the form of network packets, then these packets are encoded, are transmitted using electrical or light signals over the network in accordance with the selected access method, then the data blocks are again restored from received packets, blocks are connected to the data that becomes available. Another application. This is, of course, a simplified description of the processes occurring.
Part of the specified procedures is implemented only by programmatically, the other part is hardware, and some operations can be performed both by programs and equipment.
Sort all procedures performed, divide them on levels and sublevels, interacting with each other, just aware of network models. These models allow you to properly organize interaction both subscribers within a single network and most different networks at various levels. Currently, the so-called reference model exchange model of the OSI open system (OPEN SYSTEM INTERCHANGE) has received the greatest distribution. Under the term "open system" is understood as a non-closed system that has the possibility of interacting with some other systems (unlike the closed system).
The OSI model was proposed by the International Standarts Organization standards in 1984. Since then, it is used (more or less strictly) all network products manufacturers. Like any universal model, OSI is quite cumbersome, redundant, and not too flexible. Therefore, the real networks offered by various firms do not necessarily adhere to the received separation of functions. However, acquaintance with the OSI model allows you to better understand what is happening on the network.
All network functions in the model are divided into 7 levels (Figure 1). At the same time, the higher levels perform more complex, global tasks, for which the lower levels use for their own purposes, and also control them. The goal of the lower level is the provision of services to a higher level, and the details of the implementation of these services are not important to the substain level. The downstream levels perform simpler and specific functions. Ideally, each level interacts only with those that are next to it (above and below it). The top level corresponds to an application task that is currently running an application, the lower - direct transmission of signals via the communication channel.
The OSI model refers not only to local networks, but also to any communication networks between computers or other subscribers. In particular, the Internet features can also be divided into levels in accordance with the OSI model. The fundamental differences between local networks from global, from the point of view of the OSI model, are observed only at the low levels of the model.
Figure 1 - seven OSI levels
Functions included in the following levels shown in Figure 1 are implemented by each subscriber of the network. At the same time, each level on one subscriber works as if it has a direct connection with the corresponding level of another subscriber. There is a virtual (logical) connection between the same names of the network subscribers, for example, between the application levels of the subscribers interacting over the network. Real, physical connection (cable, radio channel) Subscribers of the same network have only at the lowest, first, physical level. In the transmitting subscriber, information passes all levels, starting from the top and ending with the bottom. In the receiving subscriber, the received information makes the return path: from the lower level to the top (Figure 2).
The data you want to transfer over the network on the way from the top (seventh) level to the lower (first) pass the encapsulation process. Each of the following level not only makes the processing of data coming from a higher level, but also supplies them with its heading, as well as service information. Such an overvaluation process continues to the last (physical) level. At the physical level, all this multi-column design is transmitted over the cable receiver. There it makes the reverse procedure of decapsulation, that is, when transmitted to a higher level, one of the shells is removed. The top seventh level reaches the data released from all the shells, that is, from all the service information of the lower levels. At the same time, each level of the receiving subscriber makes data processing obtained from the following level in accordance with the service information retractable.
Figure 2 - The path of information from the subscriber to the subscriber
If some intermediate devices are included on the path between subscribers on the network (for example, transceivers, repeaters, hubs, switches, routers), then they can also perform functions included in the lower levels of the OSI model. The greater the complexity of the intermediate device, the more levels it captures. But any intermediate device must receive and return information on the lower, physical level. All internal data transformations must be made twice and in opposite directions. Intermediate network devices, in contrast to full subscribers (for example, computers), operate only at the lowest levels and also perform two-way transform.
Figure 3 - Enable intermediate devices between network subscribers
1.4 Standard Network Protocols
Protocols are a set of rules and procedures governing communication procedure. Computers participating in the exchange must work according to the same protocols so that, as a result of the transfer, all information was recovered in its original form.
The protocols of the lower levels (physical and channel) relating to the equipment have already been mentioned in the previous sections. In particular, it includes coding and decoding methods, as well as network exchange management. Now it is necessary to stay on the features of protocols of higher levels implemented by software.
The network adapter network adapter communication is carried out by network adapter drivers. It is thanks to the driver that the computer may not know any hardware features of the adapter (its addresses, the exchange rules with it, its characteristics). The driver unifitiates, makes a uniform interaction of high-level software tools with any adapter of this class. Network drivers supplied with network adapters allow network programs to work equally with platforms of different suppliers and even with platforms of different local networks (Ethernet, ArcNet, Token-Ring, etc.). If we talk about the standard OSI model, then drivers, as a rule, perform channel-level functions, although sometimes they are implemented and part of the network-level functions (Figure 4). For example, drivers form the transmitted packet in the adapter buffer memory, read from this memory the packet received over the network, give a command to transmit, inform the computer about receiving the package.
Figure 4 - The functions of the network adapter driver in the OSI model
The quality of writing program of the driver largely determines the efficiency of the network in general. Even with the best characteristics of the network adapter, a poor-quality driver can dramatically worsen over the network.
Before purchasing an adapter fee, you need to read the list of compatible equipment (HARDWARE compatibility list, HCl), which publishes all manufacturers of network operating systems. The selection there is quite large (for example, for Microsoft Windows Server, the list includes more than a hundred network adapter drivers). If the HCl list does not include a type adapter, it is better not to buy it.
There are several standard sets (or, as they are also called, stacks) protocols that have now received widespread:
set of ISO / OSI protocols;
IBM SYSTEM NETWORK ARCHITECTURE (SNA);
Apple AppleTalk;
global Internet, TCP / IP protocols.
The global network protocols in this list are quite explained, because, as already noted, the OSI model is used for any open system: on the basis of both local and global network or a combination of local and global networks.
The protocols of the listed sets are divided into three main types:
application protocols (performing functions of the three top levels of the OSI model - applied, representation and session);
transport protocols (implementing the functions of the average levels of the OSI model - transport and session);
network protocols (performing functions of the three lower levels of the OSI model).
Applied protocols provide application interaction and data exchange between them. Most popular:
FTAM (FILE TRANSFER ACCESS AND MANAGEMENT) - File access OSI protocol;
X.400 - CCITT protocol for international email exchange;
X.500 - CCITT protocol files and directories on multiple systems;
SMTP (Simple Mail Transfer Protocol) - Motor Internet for email exchange;
FTP (File Transfer Protocol) - Global Internet Protocol for File Transferring;
SNMP (Simple Network Management Protocol) - Protocol for network monitoring, controlling the operation of network components and management of them;
Telnet is a global Internet protocol for registration on remote servers and data processing on them;
Microsoft SMBS (Server Server Message Blocks, Server Message Blocks) and Client Shells or Microsoft Proofreaders;
NCP (Novell Netware Core Protocol) and Client Shells or Novell Proofreaders.
Transport protocols support communication sessions between computers and guarantee a reliable data exchange between them. The most popular of them are as follows:
TCP (TRANSMISSION CONTOCOL) - part of the TCP / IP protocol set for the guaranteed delivery of data, broken into the sequence of fragments;
SPX is part of the IPX / SPX (InternetWork Packet Exchange / Sequential Packet Exchange) set for guaranteed data delivery, broken into the sequence of fragments proposed by Novell;
NetBeui - (NetBiOS Extended User Interface, Advanced NetBIOS Interface) - Sets communication sessions between computers (NetBIOS) and provides upper levels of transport services (NetBeUI).
Network protocols manage addressing, routing, error checks and retransmission requests. The following of them are widespread:
IP (Internet Protocol) - TCP / IP protocol for non-marginal packet transmission without establishing connections;
IPX (Internetwork Packet Exchange) is a NetWare protocol for non-gears of packet transmission and packet routing;
NWLINK - Microsoft IPX / SPX Protocol;
NetBeUI is a transport protocol providing data transportation services for sessions and NetBIOS applications.
All listed protocols can be delivered in compliance with one or another levels of the OSI reference model. But at the same time it must be borne in mind that protocol developers are not too strictly adhered to these levels. For example, some protocols perform functions relating to several levels of the OSI model, while others are only part of the functions of one of the levels. This leads to the fact that the protocols of different companies often turn out to be incompatible. In addition, the protocols can be successfully used solely as part of their dialing of protocols (protocol stack), which performs a more or less complete group of functions. Just this makes the network operating system "branded", that is, essentially incompatible with the standard model of the OSI open system.
As an example, in Figure 5, Figure 6 and Figure 7 schematically shows the ratio of protocols used by popular proprietary network operating systems, and levels of the standard OSI model. As can be seen from the drawings, practically no one level is not a clear compliance of the real protocol of any level of the ideal model. Lining such relations is quite conditionally, as it is difficult to clearly distinguish between the functions of all parts of the software. In addition, software manufacturers are far from always describe in detail the internal structure of products.
Figure 5 - The ratio of the levels of the OSI model and Internet protocols
Figure 6 - The ratio of the levels of the OSI model and Windows Server operating system protocols
Figure 7 - The ratio of the levels of the OSI model and the NetWare operating system protocols
2. Technology Networks
2.1 Networks based on PDH technology
The first digital stream installed in 1957. Bell System. In the future, the technology was standardized, and is now known as T1. It was done to meet the ever-increasing needs of telecom operators. Local telephony in the homeland of technology, in the United States, at that time was relatively well developed. Changes on the client network consisting of copper pairs, not foreseen (and did not occur still). Therefore, the main efforts of operators focused on building trunk (transport) networks and their effective use for voice transmission. Naturally, the transmission of data in those times did not even go and speech.
The developed systems used the principle of pulse-code modulation and multiplexing (summation) methods with a temporary division of channels (TDM transmission) to transmit multiple voice channels, otherwise called time slots, in one data stream.
In the US, Canada and Japan, a flow T1 was adopted as a basis, which was transferred at a rate of 1.536 Mbit / s, a 24 time slot passed, and in Europe (and a little later in the Soviet Union) - flow E1, having a speed of 2.048Mbps, and allowing Transmit 30 data transmission channels with a speed of 64 kbps, plus alarm channel (16 half-time slot) and synchronization (zero time slot). This seemed to the top of progress without exaggeration.
Further development led to the emergence of a number of standardized streams E2 - E3 - E4 - E5 data transmission speeds, respectively, 8,448 - 34,368 - 139,264 - 564.992 Mbps. They got the name of a PlesiOhron Digital Hierarchy - PDH (Plesiochronous Digital Hierarchy), which is still often used for both telephony and data transmission. More modern technologies have almost completely outset PDH with optical communications, but on obsolete copper cables of its position still unshakable. The PDH network structure is presented in Figure 8.
Figure 8 - PDH network structure
Each device has its own clock generator that works with small differences from others. In a pair of transceivers, the lead node sets its synchronization (SYNC 1-2), and the slave adjusts to it. Unified sync for a large network is absent. Therefore, PlesiOihronnaya in this case means "almost" synchronous. It is convenient for the construction of individual channels, but it raises extra difficulty when creating global networks.
2.2 Networks based on SDH technology
As networks of various communication operators, the problem of global nodes synchronization is sharply. Plus, the complication of the topology caused difficulties in extracting the components of the channels. The technical features of the independent synchronization of different nodes (the presence of leveling bits) were impossible. That is, in order to remove the flow E1 from the E4 stream, it is necessary to demultiplexing E4 by four E3, then one of E3 into four E2, and only after that get the necessary E1.
In this situation, the SONET synchronous optical network developed in the 1980s was a successful solution, and the SDH synchronous digital hierarchy, which are often considered as a single SONET / SDH technology.
The emergence of the standards of a synchronous digital data hierarchy (SDH) in 1988 marked a new stage of development of transport networks. The synchronous transmission systems not only overcame the limitations of PlesiOhron-predecessor systems (PDH), but also reduced overhead of information transmission. A number of unique advantages (access to low-speed channels without complete demultiplexing of the entire flow, high fault tolerance, developed means of monitoring and management, flexible management of permanent subscriber compounds) led to the choice of specialists in favor of the new technology that became the basis of the primary new generation networks. To date, the SDH technology is deservedly considered not only promising, but also enough technology used to create transport networks. SDH technology has a number of important advantages from user, operational and investment points of view. Namely:
Moderate structural complexity, which reduces the cost of installation, operation and development of the network, including connecting new nodes.
A wide range of possible velocities - from 155.520 Mbps (STM-1) to 2.488 Gb / s (STM-16) and above.
The ability to integrate with PDH channels, since the PDH digital channels are input channels for SDH networks.
High reliability of the system due to centralized monitoring and management, as well as the possibility of using backup channels.
High degree of controller system due to fully software management.
The possibility of dynamic service provision - channels for subscribers can be created and configured dynamically without making changes to the system infrastructure.
A high level of technology standardization, which makes it easier to integrate and expand the system, makes it possible to use equipment from various manufacturers.
High degree of standard distribution in world practice.
9. The SDH standard has a sufficient degree of maturity, which makes it reliable for investment. In addition to the listed advantages, it is necessary to note the development of the main telecommunications of Russian SDH-based communication operators, which provides additional opportunities for attractive integration solutions. Conversion and data transfer in this system is quite complex. It should be noted only a few moments. As the minimum "transport" unit, a container is used, the amount of payload of which is 1890 bytes, and the service part is 540 bytes. Simplified, they can be considered as a number of channels T1 / E1, combined (multiplexed) into one SONET / SDH channel. At the same time, any relationship between threads, or their change, is not provided (except for those who appeared later and relatively low-prolonged cross connectors). The SDH network scheme is presented in Figure 9.
It can be seen that such a scheme was created strictly for the needs of telephony. Indeed, multiplexers (MUX) are usually installed on a PBX, where E1 streams (collected from other multiplexers) are transferred to copper analog lines. Optimization of network bandwidth (in other words, inter-interstant compounds) is achieved by the selection of the ratio of the number of subscriber lines and the streams used.
The listed advantages make solutions based on SDH technology, rational in terms of investment. Currently, it can be considered basic to build modern transport networks, both for corporate networks of various scale and for public communication networks. SDH is becoming more and more applied to build modern digital primary networks.
Frame Relay, ISDN (Integrated Service Digital Network), ATM (ASYNCHRONOUS Transfer Mode) were also developed. But the broad use of these technology has not found. WWELENGTH DIVISION MULTIPLEXING -SPRED Channel Sealing), Technology
Figure 9- The structure of the SONET / SDH transport network and the scheme of possible options for passing the flow of E1
dense Wave Division Multiplexing (DWDM Dense Division Multiplexing - DWDM), multi-protocol switching MPLS labels. These technology data received in the USA, where the fiber-optic system is well developed. They are used on network networks of other regions of the world, especially in Europe, Asia and Latin America.
2.3 Network topology
Under the network topology, it is customary to understand the method of describing the configuration of the network, the location scheme and connecting network devices. There are many ways to connect network devices from which eight basic topologies can be distinguished: tire, ring, star, double ring, cellular topology, grille, wood, fat tree. The remaining methods are combinations of basic. In this case, such topologies are called mixed or hybrid.
Consider some types of network topologies. The topology is widespread - "total tire" (Figure 10).
Figure 10 - Topology "Total Tire"
Topology The total bus involves using one cable to which all network computers are connected. The message sent by the workstation applies to all network computers. Each car checks - to whom the message is addressed and if it processes it. Special measures are taken to ensure that computers do not interfere with each other to transmit and receive data when working. In order to eliminate the simultaneous data parcel, either the "carrier" signal is applied, or one of the computers is the main and "gives the word" marker "by the remaining stations. Typical tire topology has a simple structure of the cable system with short cable cuts. Therefore, in comparison with other topologies, the cost of its implementation is small. However, the low cost of implementation is compensated by a high management cost. In fact, the biggest disadvantage of the tire topology is that error diagnoses and the isolated network problems can be quite complicated, since there are several concentration points here. Since the data environment does not pass through the nodes connected to the network, the loss of performance of one of the devices does not affect other devices. Although the use of only one cable can be considered as the advantage of tire topology, but it is compensated by the fact that the cable used in this type of topology can become a critical point of failure. In other words, if the bus is broken, then none of the devices connected to it can transmit signals.
Consider the "Ring" topology (Figure 11).
Figure 11- Topology "Ring"
The ring is a topology in which each computer is connected by link lines only with two others: it only receives information from one, and only transmits the other. On each link, as in the case of a star, only one transmitter and one receiver works. This allows you to abandon the use of external terminators. The work in the ring network is that each computer relays (renews) a signal, that is, acts as a repeater, because the attenuation of the signal across the ring does not matter, it is important only attenuation between adjacent ring computers. There is no clearly dedicated center in this case, all computers may be the same. However, quite often in the ring allocated a special subscriber who manages the exchange or controls the exchange. It is clear that the presence of such a manager of the subscriber reduces the reliability of the network, because its output immediately paralyzes the entire exchange.
Computers in the ring are not completely equal (in contrast, for example, from tire topology). Some of them necessarily receive information from the computer, which leads to the transmission at this point, before, and others later. It is on this particular topology that the methods of network exchange management on a network specifically designed for the "ring" are built. In these methods, the right to the next transmission (or, as elsewhere, to capture the network) passes sequentially to the next computer in a circle. Connecting new subscribers in the "ring" is usually completely painless, although it requires a mandatory stop of the operation of the entire network during connection time. As in the case of the topology "tire", the maximum number of subscribers in the ring can be quite large (up to thousands and more). The ring topology is usually the most resistant to overload, it provides confident work with the largest flows transmitted over the network information, because in it, as a rule, there are no conflicts (unlike the tire), and there is also no central subscriber (unlike the star) .
In the ring, unlike other topologies (star, tire), the competitive method of data sending is not used, the computer in the network receives data from the previously previously in the list of addressees and redirects them further if they are not addressed to it. The list of addressees is generated by a computer that is a marker generator. The network module generates a marker signal (usually about 2-10 bytes to avoid attenuation) and transmits it with the following system (sometimes ascending MAC address). The next system, accepting the signal, does not analyze it, but simply transmits further. This is the so-called zero cycle.
The subsequent work algorithm is such - the GRE data packet passed by the sender addressee begins to follow the path laid by the marker. The package is transmitted until it gets to the recipient.
The following type of topology is "Star" (Figure 12).
Star - the basic topology of the computer network, in which all network computers are attached to the central node (usually a network hub), forming a physical segment of the network. Such a network segment can function both separately and as part of a complex network topology (as a rule "tree"). The whole exchange of information is exclusively through the central computer, which in such a way there is a very large load, therefore, it cannot be engaged in any other way. As a rule, it is
Figure 12 - Topology "Star"
the central computer is the most powerful, and it is on it that all the functions for the exchange management are imposed. No conflicts on the network with a topology star are in principle are impossible, because the management is fully centrally. The workstation with which it is necessary to transmit the data, refers them to the hub, and the one defines the addressee and gives it information. At a certain point in time, only one machine on the network can send data if two packages come to the hub at the same time, both parcels are not accepted and senders will need to wait a random period of time to resume data transmission. This disadvantage is absent on a higher-level network device - switch, which, unlike a hub that feeds the package to all ports, gives only a certain port to the recipient. At the same time, several packets can be transmitted. How much - depends on the switch.
Along with the known topologies of computing networks, the ring, star and tire, in practice it is also used and combined, for example, a tree structure (Figure. 13). It is formed mainly in the form of combinations of the above-mentioned topologies of computing networks. The base of the piece of the computer network is located at the point (root) in which communication lines (tree branches) are collected.
Computing networks with a tree structure are used where it is impossible to directly apply basic network structures in its pure form. To connect a large number of workstations, network amplifiers and / or switches are used according to adapter fees. The switch with an amplifier simultaneously is called an active concentrator.
Figure 13 - Topology "Tree"
In practice, two types of their varieties are used, ensuring the connection, respectively, eight or sixteen lines.
The device to which you can attach a maximum of three stations are called a passive hub. Passive hub is usually used as a splitter. It does not need an amplifier. The prerequisite for connecting the passive hub is that the maximum possible distance to the workstation should not exceed several tens of meters.
The network topology determines not only the physical location of the computers, but that much more important, the nature of the links between them, the characteristics of the distribution of signals over the network. It is the nature of the links that determines the degree of refusallessness of the network, the necessary complexity of the network equipment, the most appropriate exchange method of the exchange is possible, the types of transmission (communication channels) are possible, the permissible network size (length of communication lines and number of subscribers), the need for electrical approval, and a lot of other things.
3. Subscriber access network development
3.1 Original data for development
The subscriber access network is developed according to the task on the graduation project for the territory shown in Figure 14 in order to provide broadband Internet access and information exchange between network users. The network is developed using Ethernet technology using fiber optic communication lines and copper cable and assumes the presence of several servers. The estimated speed of subscriber access taking into account the bandwidth of the urban network is 100 Mbps. Previously, the subscriber access speed was 10 Mbps, but due to the use of improved equipment, it was possible to provide users with a greater speed. To connect to the network, the following requirements are put forward to computers:
Availability in a network adapter computer with an Ethernet 10 / 100BaseTX interface;
The presence of an operating system supporting TCP / IP protocol.
3.2 Main Network Solutions
For the convenience of network segmentation, we use a quarterly separation by the type "Star". Segments to increase network manageability Delim on the subnet. The territory is divided into segments, each of which embrace several houses (from 4 to 10). Each segment is associated with quarterly equipment through an optical converter according to 1000baselx standard using a fiber-optic cable in order to increase the distance of the cable segment and high speed transmission rate. Each quarterly equipment is connected to the central communication center via the optical converter according to the Gigabit Ethernet 1000Baselx standard to increase the throughput on the network highway.
Figure 14 - Design Territory
Central Communication Node (located on the PBX in terms of agreed by the Parties): Select the SDH access technology due to the high bandwidth of paths, flexibility, the ability to dynamically increase the network capacity without interrupting traffic. On the central node there will be a main switch and a router to access the SDH network of the main provider and the servers that are responsible for the traffic count, for network monitoring, will also be installed DNS server.dns server - specialized software for DNS maintenance (Domain Name System - domain name system ), as well as a computer on which this software is performed. The DNS server may be responsible for some zones or can redirect requests to higher servers.
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Total telecommunication network architecture
Access networks
8.3.2. Technical Access Networks
Transport networks.
Structure and technology of transport networks
Models of transport networks
Principles of building transport networks
General trends in the development of transport networks
Channel Switching Networks
General provisions
Principles for building telephone networks
Batch communication networks
Analysis of the technical implementation of IP telephony
Types of connections in IP telephony network
Network H.323.
MPLS technology
Overall NGN Network Characteristics
NGN appointment and capabilities
Basic NGN Concept
Section 8 considers the overall structure of the telecommunications network. Marked
that at this stage of development, the telecommunication network acquires new properties, developing gradually into the infocommunication network. The advantages of digital networks are indicated, which allows you to move from a multi-level principle for building networks to a more specific two-level principle that includes an access network and a transport network. The classification of telecommunication networks given in the section allows you to determine the location and role of each network in ESE. The principles of construction and technology used on access networks and transport networks are considered. The role of the network of each level in the unified telecommunication network is noted. There is a re-stroke on transport networks to IP information transfer technologies. The principles of constructing switched networks are considered. An important place in the section occupy the issues of building a basic telephone network - as the dominant network of ESE. Attention is paid to the principles of building batch networks using IP technology. The foundations of building a new generation NGN network are considered, the elements of which are being introduced on the ESE and which is the prototype of the ESE in the near future. The section provides control questions, a list of recommended literature and glossary.
8.1 Total telecommunication network architecture
The modern telecommunications network is one of the most complex systems that have ever created a person. This network combines millions of various sources and consumers of information that can be the simplest signaling devices, individuals, computer networks, enterprises, as well as objects scattered in large areas and even in space. The main purpose of the telecommunications network is to transmit information between users and ensure access to the information you need. The architecture of the telecommunications network is presented in Fig. 8.1
Figure 8.1 Telecommunication network architecture
Elements of telecommunication network are:
· terminal points;
· communication nodes;
· channels of connection;
· network management system.
Terminal points (OP) (including subscriber), contain equipment input and output information, and sometimes for its storage and processing, which is intended:
· To receive information from the user and convert it to the message required for communication over the communication network;
· To receive a message from the network and its conversion in the view user-friendly.
Communication nodes (mustache) Designed to distribute information. Communication nodes, in turn, are divided into switching (CC switching Channels, messages or packages), designed to distribute messages, and networks intended for the distribution of channels, canal beams and group tracts.
Communication channels (COP)provide the transmission of electromagnetic signals limited by power in a specific frequency domain, or at a certain speed. Channels are combined in line between items and network nodes and serve to transfer information in space.
Communication lineconnecting the subscriber point from the Criminal Code called the subscriber line. Communication lines are equipped with channel-forming equipment, with which separate communication channels (COP) are highlighted in the LAN. Channels, together with the transfer and reception equipment, form a message transmission path (TPS). The two transmission path of messages and more, with switched together with the help of the Criminal Procedure, form a messaging transmission path.
Introduction of HC and DB, intelligent platforms On the telecommunications network allows us to provide users with almost any information services and the network acquires new properties, turning into infocommunication net.
Communication network management system (SUSS) provides:
· normal operation of individual devices and channels;
· delivery of messages to the address;
· Normal network functioning, including the organization of repair and recovery, redistribution of channels and tracts, redistribution and limiting reports;
· distribution of tasks and queries on the HF and the optimal use of their capacities;
· managing the calculation for services and network services;
· the functioning of the network as a whole as the industry of the national economy and its development.
Modern communication networks are primarily characterized by:
· the use of digital switching and transmission systems and computing;
· Integration of various types of transmitted information (speech, image, data, facsimile and other messages).
On the basis of such networks, various kinds of private (evident) and corporate networks are created.
Digital delivery technique and information distribution has a number of advantages:
FirstlyThe process of improvement in the production technology of large integrated circuits decreases the cost of digital equipment and its dimensions, an order of magnitude reduces the intensity of the failures of its elements. Currently, digital diagrams are reliably working with hundreds of thousands of elements with a total idle time a few hours for 20 years of operation. Modern technology allows you to form on a crystal, an area of \u200b\u200bseveral square millimeters, up to 10 thousand elements and more with a very small consumption of materials and electricity.
Secondly, Digital signal transmission methods allow you to increase the bandwidth of communication channels. Currently, such broadband transmissions are developed as optical cables. However, for the full implementation of the optical cable bandwidth, noise immunity is required inherent in digital technology. Low efficiency of the use of subscriber lines can be increased by their digital seal. Data with different transmission rates can be transferred much more efficiently using digital transmission technology than the analog item. Digital methods in a single stream We spend speech, data and signals of images, as well as control signals and control the processes of establishing connections on the network.
Thirdly, Digital methods provide the possibility of complex signal processing. The encoding of analog signals makes it possible to realize their digital processing and significantly reduce redundancy, and the use of inexpensive microprocessors and micro-computer provides the possibility of more complex processing. Digital information can be quickly accumulated without distortion in digital memory, which is now becoming more and more cheap and allows you to more efficiently use network equipment and provide such advantages as signal regeneration and change the transmission rate.
Finally, Digital methods provide the best interaction conditions with computer and user terminals.
Principles used to build a communication network as a whole, depends on many factors. These include:
· capacity of the national network;
· the area of \u200b\u200bthe territory that the communication network covers;
· administrative division of the country's territory;
· structure and organization of technical operation of means and communication networks;
· technical means and technologies that are used to build a network and implement services;
· the need for communication services.
In connection with the above, two general principles of building a communication network can be distinguished:
· multi-level;
· two-level.
The multi-level principle was designed for analog communication networks.
The two-level principle is characteristic of the complete digitalization of the network and the introduction of modern switching systems (asynchronous using packet switching technologies - atm, IP), as well as powerful transmission systems using SDH, WDM, Ethernet technology based on optical cables, high-speed satellite transmission systems.
In accordance with the multi-level principle of construction in relation to the telephone network, the entire territory of the country is divided into numbering zones. TO numbering zones The following requirements are imposed:
· The zone size should be such that for a long time (50 years) did not have to change the numbering system within the zone;
· Within the numbering zone, a significant part of the exchange arising on the network should be closed;
· The container of the numbering zone should not exceed 8 million rooms.
Given the foregoing, the boundaries of the zone, as a rule, coincide with the administrative boundaries of areas, edges, republics. It is allowed, if necessary, the formation of several zones in the region, the region, the republic.
Currently, in the territory of Russia, 81 zones of numbering are formed. Most of them are created within the borders of the region or republics. But in some areas two zones are created and even three. For example, four zones were created on the territory of the Moscow region - 495, 496, 497,499.
Within the number of numbering zone, local telephone networks (GTS, STS, TC) are created and the intra-zone telephone network (PSOT), which is designed to communicate various local telephone networks within the numbering zone and user output of local networks on a long-distance telephone network (MGTS). Local networks and intrazon networks Numbering zones form a zone telephone network (CTS). Zonal telephone networks of various zones are associated with a long-distance telephone network (MGTS). Zone and long-distance telephone networks form a national telephone network of Russia. National networks of various states are associated with each other with the help of an international telephone network (MNTS).
The development of information technologies allows, taking into account the needs of users in a wide range of telecommunication services, already currently create completely digital broadband communications networks. As the calculations show, for the efficient use of communication tools, solving the quality of the provision of services, the multi-level principle of building broadband networks is inappropriate.
Therefore, to build broadband communications networks, called multiservice networks, a two-level construction principle was proposed. The two-level principle involves creating within the national network, as well as the world, access networks and transport network.
Access network - A communication network that connects the terminal devices (multifunctional) to the terminal node of the communication network.
Transport network Communication is a network that transfers the transfer of different types of information using various transmission protocols.
8.2 Telecommunication Network Classification
Classification of telecommunication networks According to essential features, it allows to determine the place of each network in the telecommunication system of the Russian Federation, to identify the properties of networks from different points of view on the basis of a systematic approach, assess the role and significance of each network in the process of informatization of society and the country's economy. This will make it possible to compare the networks among themselves, develop requirements for networks and create networks with specified characteristics. Networks included in ESE can classify According to the following features:
· types of transmitted information;
· territorial sign;
· accessories;
· channel organizations;
· scope of application for the provision of services;
· method of delivering messages;
· the level of integration of services;
· the type of transmitted signal;
· method of distribution of messages;
· functional sign;
· subscriber mobility;
· numbering codes;
· type of distribution environment;
· volume of services provided;
· network structure.
According to the transmitted information Networks are divided into telephone, telegraph, data transmission, computer networks, signal networks, etc.
The unified telecommunication network of the Russian Federation consists of telecommunication networks located on the territory of the Russian Federation following categories:
· general use network;
· technological communication networks;
· allocated communication networks;
· special Advanced Communications Networks.
General Communication Network (SSP) Designed for compensated for the provision of telecommunication services to any user in the territory of the Russian Federation. It includes telephone telecommunication telephone networks determined by geographically within the service area and numbering resource and non-geographically determined within the territory of the Russian Federation and the numbering resource, as well as networks intended for the provision of other communication services to the population.
The public communication network is a complex of telecommunication networks, including communication networks for the distribution of broadcasting programs, television broadcasting and multiservice networks.
The network of the SSP has accession to the network communication networks of foreign states.
Dedicated communication networks (ALC). There are communication networks intended for the provision of electrical communication services limited circle of users or groups of such users. ARUs can interact with each other. ARUs, as a rule, do not have accession to the public communication network, as well as to the SSP of foreign countries. Technologies and communication means of allocated communication networks, as well as the principles of their construction are set by owners or other owners of these networks.
The NCC network can be attached to a transition to the public communication category, if the ACC complies with the requirements established for the SSP. At the same time, the selected numbering resource is made and the numbering resource from the SSP numbering resource is selected. The provision of communication services by operators of allocated communication networks is carried out on the basis of relevant licenses within the territories specified in them.
Technological communication networks (TCC) Designed to ensure the production activities of organizations, management of technological processes in production. Technologies and communications used to create technological communication networks, as well as the principles of their construction are set by the owners or other owners of these networks. In the presence of free resources of the technological network of communication, some of this network can be attached to the SSP network with a translation into the SSP category to provide paid communication services to any user based on the relevant license. Such joining is allowed if:
- A part of the technological network intended for joining the SSP can be technically, or programmatically, or is physically separated by the owner from the technological network.
- The part of the technological communication network complies with the requirements of the SSP function.
Parts of the TCC attached to the SSP, there is a numbering resource from the SSP numbering resource. National TCC networks can be attached to the networks of the TCC of foreign states to ensure a single technological cycle.
Special Advanced Communications Networks (SSSN)designed for the needs of state administration, country defense, state security and law enforcement. These networks cannot be used for the paid provision of communication services, unless otherwise provided by the legislation of the Russian Federation.
Dedicated, technological and special-purpose networks are combined into network category limited use (OGP).
By territorial sign Networks are divided into local, intraosone, long-distance, international, regional, interregional, mainstural. The specified feature is used for primary networks, secondary networks, for networks of individual operators and operators of interregional companies.
Sign of belonging Defines the owner of the network. They may be a state, private person, joint-stock company, organizations and individual enterprises.
On the organization of channels distinguish primary and secondary networks.
On the scope of application To provide services, you can allocate telecommunication and infocommunication networks. Telecommunication network It consists of lines and communication channels, nodes and terminal stations and is intended to provide electrical communications of users. Infocommunication Network Designed to provide users with electrical communications and access to the information you need.
By method of delivering messages The networks with switching channels and networks with accumulation (network switched network and packet switching) are distinguished.
In terms of integration of services Networks are divided into several classes: monoservice, low-level networks, middle-level integration and multiservice networks that provide unlimited services. The monoservice network includes a telegraph network. Networks with low integration can be attributed an analog telephone network. Networks with an average level of integration of services include N - ISDN network, 2G mobile network. Multiservice network is a new generation NGN network.
In the form of transmitted signals We share networks on analog, analog-digital and digital.
By the method of distribution of messages Networks are divided: switched, non-commutable, circular communication.
By functional sign There are access networks and transport networks.
Mobility subscribers You can select a fixed and mobile network. Fixed communication subscribers have stationary terminals, in contrast to mobile network subscribers.
By numbering codes Networks are divided into geographic networks (ABC codes) and non-geographic (DEF codes) zones. The use of these codes is associated with the creation of dedicated, including mobile networks, on the ECE network of the Russian Federation.
By type of distribution environment Networks are divided: on wired, radio networks and mixed. In turn, the radio network is divided into ground and satellite networks.
In terms of services provided You can select the networks that occupy a significant position (more than 25% of traffic are missing and have more than 25% of the mounted switching capacitance from the total network capacity). Such a network owns dominant communication operator.
An important classification feature is an network Structure Communication. Fig. 8.3 presents typical network structures that differ from each other by the number of communication lines, the nature of the interaction of nodes, connectivity of nodes, etc.
Complete network (fig. 8.3A) - "Each with each". In such a network, the number of communication lines is N (N - 1) / 2, where N is the number of nodes on the network. Connectivity H \u003d N-1.
Tree network (Fig. 8.3b). In such a network between any two nodes, there can be only one way, that is, the single-connected network H \u003d 1. The number of communication lines in such a network is N - 1. Private cases of the tree network are: a radial node network (Fig. 8.2V) , Star-shaped network (Fig. 8.3g) and a linear network (Fig. 8.3d).
Loop (loop, ring) Network (Fig. 8.3e). In it, the number of communication lines is N, and there are two ways between each two nodes (H \u003d 2).
Grid - Sea-shaped network (Fig. 8.3 f - M). In such a network, each node is adjusted only with a small number of other nodes. The choice of one or another network structure is determined primarily by economic indicators and requirements for reliability and the survivability of the network.
Figure 8.3 Network structure of various types
8.3 Access Networks
Currently, the division of communication network into two parts is becoming increasingly recognized: a transport network and access network. The transport network is represented by long-distance and intra-monomial communication networks. The access network is represented by local networks and is designed to connect a variety of subscriber terminals to the communication network.
Figure 8.4 shows a model of a promising telecommunications system and a subscriber access network.
The first element of the telecommunications system is a combination of terminal and other equipment, which is installed in the subscriber's room.
Figure 8.4 Telecommunication System Structure
Second element subscriber access network. Usually, a switching station is installed at the pairing point of the subscriber access network with the transit network. The space covered by the subscriber access network lies between the equipment placed in the subscriber's room and this switching station.
In a number of work subscriber access network divided into two plots:
· subscriber lines (al) are considered as individual means of connecting terminal equipment;
· transport networkserving to improve the effectiveness of subscriber access funds.
Third element telecommunications system - transport network. Its functions are in establishing connections between terminals included in various subscriber access networks, or between terminal and support means of any services.
Fourth element of the telecommunications system - access tools for serviceswhich provide user access to various telecommunication services.
Development of subscriber access
Significant qualitative changes inherent in the modern telecommunications system were touched by one of the most conservative elements of the telecommunication network - a subscriber line (al). The peculiarity of the modern telecommunications system is that the role of the AL and the principles of its creation varies very significantly. The concept of "subscriber line" no longer reflects the essence of the telecommunication network element between the user terminal and the switching station. The technical literature appeared a new, adopted in international standards and recommendations, the term "Access Network" - "Access Network". The subscriber access network consists of two main elements. The first element of the DTPE network is a combination of al, and the second is the network of transfer. Most often al are associated with an individual two-wire chain, providing the exchange of information in the bandwidth of the tone frequency (PM). The transfer network is intended to reduce capital expenditures on line-cable facilities within the subscriber access system. This access network fragment is implemented on the basis of transmission systems and, in some cases, the device concentration devices. In a particular case, the transfer network may be absent. Then, the concepts of the AL network and the access network (SD) become identical.
The subscriber access network can be considered as a totality of the primary network and several secondary networks. It should be emphasized that in the process of the development of telecommunications, differences between the primary network and secondary networks are becoming less visible.
Organization of subscriber access network
Subscriber access network - a set of technical means to transfer messages on the site from the subscriber device to the local telephone terminal station;
Subscriber Access Organization
In today's world of telecommunications, a factor in the coexistence of standard and new technologies is becoming increasingly important. This situation is the basis for the next-generation NGN networks. Custom and signaling information are always transmitted via interfaces and on predetermined protocols.
Triple Play technology provides simultaneous transmission of speech, video, Internet operation, data transmission. Technology is implemented using optical fiber in the subscriber line.
Interface divorous devices. Interfaces always implement any protocols.
The concept of the interface includes:
Hardware connecting various devices with each other or user (communication lines, conjugation devices, physical characteristics of the communication channel)
Software tools for the connection of various devices with each other or user (programs that provide information between different users; data types; list of available areas of memory; Set of permissible procedures and operations and parameters)
Rules and algorithms based on software and hardware function. (for example, ways to convert signals and data)
Protocol - This is software and hardware intended for conjugation. homogeneous devices. The protocol provides interaction between the elements located at one hierarchical level, but in different network nodes.
The protocol is a set of rules for the interaction of UU inside CSK and on the network defining:
Algorithm for the interaction of devices, programs, data processing systems, processes or users.
Rules for addressing network equipment.
Codes used to submit data.
Information transmission rate.
Information transfer methods.
Message formats.
Rules for forming message packages.
Methods for detecting and correcting errors.
Methods of electrical connections.
Select the message transfer route.
Digital subscriber lines ISDN
ISDN - (Integrated Services Digital Network) - digital network integral services. ISDN technology allows one Physical line to organize some temporary channels
ITU-T identified the following ISDN subscriber device groups:
Te1 - ISDN terminal. Terminals of this type are fully compatible with ISDN standards and are connected to the network through a 4-wire line in which 3 time intervals (WE) are organized: B, B, D.
Te2 - Terminal incompatible with ISDN standard. As such a terminal, the telephone apparatus of TA, facsimile, telecast, video music, PEVM devices are considered.
The terminal adapter for connecting terminals incompatible with ISDN. It converts other standards signals to the ISDN standard.
NT - network ending, providing the following functions:
power supply to the subscriber installation,
provision of maintenance of lines,
performance control, synchronization,
multiplexing, switching and concentration,
resolution of access conflicts.
The network end may be a single physical equipment NT, and may be divided into network end of two categories: NT1 and NT2, taking into account categories of served subscribers.
(NT1 - network end of level 1. (These are the levels of the reference model of interaction of open systems). The NT1 function includes power supply to the subscriber installation, maintenance of lines, performance monitoring, synchronization, multiplexing, resolution of access conflicts.
NT2 - network termination of 2.3 levels. Performs levels of processing protocols 2 and 3, multiplexing, switching and concentration, maintenance of lines, control of performance, resolution of access conflicts. As a functional block, NT2 can act, for example, optes, LAN.)
LT - the linear end of the CSK to which the ISDN line is connected. LT is an integral agreement linear kit.
ET - stationary end of the CSK, which is a subscriber module for connecting ISDN subscribers. (For example, in S-12 is an ISM module).
Interfaces at the reference points:
Interface at R
Ties incompatible with ISDN equipment Te2 with a terminal adapter that.
Interface at point t Binds the equipment of the user with a network end of NT or two types of NT1 and NT2 network end.
Interface at the point U It is an interface between NT equipment and PBX TFP equipment and provides:
linear coding of information for transmission over pairs of copper wires;
bilateral exchange of information on any existing physical pairs of wires;
connecting ISDN subscribers over a two-wire diagram via NT.
Interface at point sprovides the ISDN subscribers using a 4-wire circuit without NT.
Interface at point V
(V5.1 and V5.2) provides the possibility of sharing equipment from different manufacturers with various subscriber access systems, including wireless communication lines, optical fiber lines and copper cables
Subscriber access terminal
(Terminal I / O devices of telecommunication systems and Peripheral devices PEVM)
Introduction
The task of this module is student learning terminal (peripherals ) Output input devices (UVV) telecommunication systems (data transmission systems, PEVM or PC). At the same time, the focus will be paid to the study of the principles of UVF operation, their hardware and software, as well as interface equipment through which access to telecommunication systems for transmitting information is provided.
Since the PC is currently acting as a telecommunications system with a hardware and software implementation method, then, when studying this module, attention will be paid to the study of the principles of the functioning of a personal computer (PC), hardware and software and maintenance, as well as UVV PC.
In addition, attention will be paid:
signal conversion devices (UPS) and their interaction protocols. Modems for various communication systems (telephone, cable and radio) can be played in OPS;
Study of the principles of construction facsimile transmission systems And their interaction protocols.
By definition of the SPD, this is a combination of technical means - UVV, ADF, and transmission media, including physical communication lines and channel-forming equipment.
ADF, physical communication lines and channel-forming equipment you have studied earlier, and you will study in this module
Subscriber access
A-priory, subscriber access - This is the user's access to any information telecommunications transmission system (analog or digital type) by means of the terminal devices for entering output and communication lines (channel) or interface equipment.
The successful implementation of many of the most important plans and events in various sectors of the national economy depends on the reliability of the garden.
We will call a network of subscriber access (garden) - a set of technical means, between terminal subscriber devices and telecommunication systems (data transmission systems, PCs).
At the same time, various terminals for entering output of any type of information will be used as the terminal input entry devices.
Classification of subscriber access systems
Today there are many technologies for building an access network. All of them can be divided into two large groups: wired and wireless Subscriber access technologies. As an access network and distribution network can be built on the basis of wired and wireless technologies.
In foreign literature you can also meet the abbreviation LL (Local Loop), i.e. subscriber access system.
Among wired Technologies To create a distribution network most often use transmission systems built on copper, fiber optic or coaxial cable.
Wireless Radio systems Local Loop (LL) have an abbreviation WLL (Wireless Local Loop), i.e., a system of wireless subscriber access. Sometimes WLL is called yet Rll(Radio Local Loop), i.e., the system of the subscriber radio accessibility.
Among the wired, it is necessary to mention the already developed and accessible technologies that allow you to organize high-speed digital subscriber lines based on the existing copper cable lines.
It - HDSL. (High-Bit-Rate Digital Subscriber Loop) ADSL ASYMMETRICAL DIGITAL Subscriber Loop) and SDSL Symmetrical Digital Subscriber Loop).
With their help, you can transmit data on the usual telephone copper Cable at a speed of 2 to 10 Mbps.
Transmission Systems fiber optic or coaxial Cable provide data transmission at a speed of up to 1 Gb / s.
Three main class of such systems can be distinguished:
Subscriber access systems to data networks;
Systems for connecting subscribers to public telephone network;
Integral type systems.
In turn, subscriber access systems to data networks can be divided into the following subclasses:
a) systems focused on serving subscribers with a small individual intensity of short transactions (monitoring systems for various purposes, payment systems of non-cash calculation, etc.);
b) Systems focused on ensuring access to network information resources (Internet, ISDN services and remote access to local computer networks, etc.). Integral type systems combine the first two types in themselves and are more versatile. The range of services provided by the systems of this class is extremely wide.
Radio system To connect subscribers to the telephone network, sometimes called "telephone radio". As a rule, the main purpose of such systems is to ensure the connection of telephone subscribers to the general use telecommunications networks. Often wireless "telephone extensifiers" also provide data services through modem and fax messages.
Subscriber wireless access systems, as a means of connecting subscribers to communication networks now acquire wide popularity worldwide. This is mainly due to low-cost, brief deadlines for the implementation and level of services, comparable to the level of services of wired communication technologies. Wll systems are considered an optimal solution for countries with a weak or outdated communication network infrastructure. Therefore, such networks are actively unfolding around the world. The problem of connecting subscribers to PBX or data networks is now very relevant.
Wll systems are designed by many firms, including Alvarion, Motorola, Alcatel, Philips, Ericsson, Qualcomm, Siemens.
The standard structure of the subscriber access system, as a rule, includes access network (Access Network) and distribution network (Distribution Network).
Term " access network"Used to describe the part of the network between subscriber equipment and access point to the primary network resource.
Term " distribution network"It implies part of the network between access point and distribution point.
The distribution network may be absent if the access network begins directly from the distribution point of the primary network resource. At the access point, the access network protocols must be implemented when interacting with subscriber blocks, public network protocols when working with switching node, as well as mutual conversion of these protocols and managing the data stream in the subscriber access system.
In practice, these functions perform the following devices: routers (in data transmission networks), hubs and base stations (in cellular networks and wireless subscriber systems), switches and mini-PBXs (in wired telephone networks) and others.
As for the access network, various technologies can be used for the distribution network. You can deploy hybrid networks like "Cable Radio" or "Radio Cable". A variety of network configurations are permissible, which depend on the throughput, the cost of the planned network, topology, restrictions administered by various regulatory organizations, and so on.
In the event of a radio organization between the access point and subscribers in the baseband zone of the base station, mobile terminal devices of users or subscriber blocks forming one cell are located. If you cover all subscribers using a single base station, it is impossible to use a multiple principle.
Mobile terminal - Compact portable device, with which the subscriber has direct access to the communication network.
The subscriber unit is a stationary receiving-transmitting radio device of small sizes with an internal or external antenna.
The terminal user equipment (PC, or the telephone) is connected directly to the subscriber block and through the radio channel has access to the communication network.
When the access network is implemented as radio, it usually has a single or two-frequency structure. In the first case, a single frequency band is used to transfer packets to the base station and from it. This structure has a number of significant disadvantages that limit its use in networks with a large number of subscribers.
Another option is a two-frequency structure. At one of the frequencies, the multiple access channel is implemented, where all subscribers carry out the transmission to the base station, and on the other - reception from the base station, from where the subscribers receive packages.
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