Last mile by means of Wireless Local Loop. Digital subscriber lines isdn Analysis of the technical implementation of IP-telephony

Today, thanks to the significant growth of IT, a simple telephone service no longer satisfies end users - they need technology for simultaneous data transmission and fast access in Internet. However, narrow-band analog systems can no longer cope with these tasks ...

The emergence of new IT technologies and a significant increase in their productivity has led not only to the rapid development of new information systems, but also to the expansion of the functionality and range of services provided by existing communication networks. Previously unknown, but promising technologies are becoming essential attributes of modern telecommunications, but without an appropriate communications infrastructure, they can forever remain only projects.

As you know, the basis of the modern telecommunications infrastructure is formed by fiber-optic and other terrestrial digital transmission and switching systems, as well as satellite systems connections. All modern telecommunication networks are optimized and rebuilt according to a two-level hierarchy: backbone transport networks and access networks.

Such a device is much more economical and convenient for building open systems and delivering integrated services: a common technology and a single flow of information unite both levels. However, do not forget that when building a network, most of the entire cost falls on its lower link, namely, on the local network, that is, on the access network. Moreover, its last segment, the so-called last mile, can be much more expensive than the other hundreds and thousands of miles. Building this key segment of the network can be extremely difficult, and there are a number of technologies on the market today to solve this problem. In addition to traditional wired technologies, in particular, wireless subscriber access systems are used to transmit information.

A few years ago, the organization of subscriber access, as they say, “over the air” could seem like complete nonsense to a network operator, but today, the advantages provided by radio access technology are quite obvious to most of them. For beginners technology wireless access allows in the shortest possible time and at the lowest cost to enter the communication services market, and for traditional operators to increase the number of subscribers and the list of services provided, which, as a rule, has a positive effect on profits.

Taking into account the lag of Russia, and especially its remote regions, from Western countries in terms of the prevalence of network infrastructure, the concept of wireless access was an attractive solution for us and became widespread.

Subscriber access systems

There are two groups of subscriber access technologies designed to solve the problem of the last mile - wired and wireless solutions.

Of the wired ones, we should mention technologies that allow organizing high-speed digital subscriber lines even on the basis of existing copper cable lines. These include HDSL (High-bit-rate Digital Subscriber Line), ADSL (Asymmetrical DSL), and SDSL (Symmetrical DSL). Using these technologies, you can transfer data at speeds from 2 to 8 Mbps over a standard copper cable. Transmission systems on fiber optic or coaxial cable today provide data transmission at speeds up to 1 Gb / s. If the access network is a LAN, conventional wired network technologies can be used.

Recently, wireless technologies for organizing subscriber access (Wireless Local Loop, WLL) have become increasingly popular. For data transmission, infrared and light radiation or a radio signal is used here. In order to organize a distribution network, wireless backbones are most often used based on the use of satellite communication channels, laser or narrowly focused infrared communications, narrowband and broadband radio relay communications.

Operators can use different technologies to solve different kinds of problems: narrow-band systems can be especially effective in suburban areas and rural areas, and for alternative operators - in urban areas; radio access can be highly efficient for providing broadband services.

Narrowband systems

Basically, such systems are designed for speech transmission. These facilities are represented by fixed radio terminals for use in networks cellular communication. Such systems are not suitable for high-speed data transmission due to the speech compression algorithms used and are used for residential subscribers, payphone services, etc.

High quality wireless access systems

These systems are built using standards wireless telephony. Fixed radio access systems have higher voice quality than narrowband systems (using 32 Kbit/s ADPCM coding) and are capable of facsimile and modem communications.

Broadband systems

These systems operate in several frequency bands - from 2.4 to 28 GHz. They provide transmission of high-speed data streams to corporate users, transmit n * E1 digital streams to terminal devices (multiplexers, PBXs, basic radio units cellular networks mobile and fixed communications, etc.).

In wireless radio systems for the access network, channel separation methods such as TDMA (Time Division Multiple Access), E-TDMA (Extended TDMA), FDMA (Frequency Division Multiple Access), CDMA (Code Division Multiple Access), W-CDMA (Wideband) are used ), as well as their modifications.

Benefits of WLL

The ever-increasing demands placed by companies on the capacity and quality of communication systems encourage operators and providers to look for new ways to organize data communication networks in order to expand the range and improve the quality of the services offered. Therefore, wireless WLL systems are becoming increasingly popular: in areas where cabling is difficult, unprofitable or completely impossible (hard-to-reach areas, rural areas, suburban areas), they have significant undeniable advantages.

Since cables tend to wear out quickly, and the quality and range of wired access do not always meet expectations, the problem of organizing a subscriber network (last mile) has long been a headache for many operators. Wireless Local Loop networks are free from many of the above disadvantages and have the following advantages:

low cost of equipment, short payback period of the system (about four years) and several times lower cost of a ten-year life cycle. When using wireless technology, the main costs are for equipment, the prices of which are steadily falling. Already today, in some cases, radio access is a profitable alternative to a wired solution. The cost of a WLL system using radio channels does not depend on the length of the cable, the condition of the soil, the presence of water surfaces and wetlands within the service area. In addition, a subscriber network built on a copper or fiber-optic cable is a rather cumbersome economy, requiring, as a rule, a long-term phased implementation and significant capital costs;
simplicity and flexibility when expanding the network. Possibility of relatively easy transformation into a network mobile communications;
ease and speed of expansion. To connect a new subscriber to the system, it is enough to provide him with a subscriber device. With the growth of the system, it can be easily expanded with additional subscriber modules and base station equipment;
high speed of commissioning and significantly less laborious connection work. WLL allows you to quickly deploy a system of large subscriber capacity, with daily connection of tens and hundreds of subscriber devices. First of all, this is of great importance for telecom operators in the conditions of fierce competition in the telecommunications services market, when it is important to get ahead of possible competitors and get a return on investment as quickly as possible. And secondly, it provides simplicity and convenience (and, consequently, low costs) of installation work;
no restrictions on the terrain. Signal transmission is provided regardless of the terrain due to the possibility of placing the BS at dominant heights and / or the use of repeaters;
flexible investment policy of the created network. Wired infrastructure requires large-scale investments that far outstrip forecasted subscriber line requirements and are not always justified, while wireless technology Allows step-by-step investment in small shares, which allows you to more accurately track forecasted needs. The low percentage of use of each subscriber pair on local networks makes large investments inefficient and unattractive for investors and reduces the payback of cable systems. Any expansion of the network requires very large engineering work on cable routes, and the laying and organization of communication lines becomes a difficult problem, especially in old cities, and requires increased capital costs in rural areas;
high reliability. The number of WLL failures is no more than 6-10% of the number of cable network failures.

Taking into account the fact that 90% of the Russian population lives in areas with an average population density of less than 80 people per square kilometer, the construction and operation of WLL systems can be more cost-effective than using systems with a wired access principle.

Building a radio network

The most difficult step in building a wireless network is building the network infrastructure and designing it. Typically, this task is handled by the equipment supplier or a specialized company. The network configuration depends on the topography, network performance and the price that the buyer is willing to pay, on the restrictions imposed by the environment and various regulatory organizations, on the specific strategy of the operator, etc.

Often, the operator cannot indicate in advance the exact location of each specific subscriber, but only the approximate location of user groups. After creating the project, the operator delivers subscriber devices and installs equipment for each user himself - without the involvement of a designer.

It should be noted that the cellular implementation of wireless systems, especially when cells overlap, needs careful frequency planning, which largely determines the system capacity. DSSS technology uses built-in frequency allocation. When using FHSS technology, dynamic frequency control is necessary to prevent interference of signals from neighboring cells; it should improve the efficiency of the use of the frequency spectrum and the capacity of the system.

Equipment and manufacturers

and today there are three main approaches to building wireless subscriber access systems:

Systems based on technologies and standards of cellular mobile communications. This category of systems is characterized by a rather high cell capacity and a long communication range between base stations and user terminals. The communication range (for a specific BS), depending on many factors (on the terrain, antenna parameters, transmission method, frequency range, etc.), can reach tens of kilometers. Taking into account the fact that these systems operate at the frequencies of NMT-450, AMPS, D-AMPS or GSM mobile communication networks, we can assume that from a commercial point of view they are promising for existing cellular network operators and unpromising for new operators due to competition with aspects of existing operators, frequency deficit, etc.
Systems based on cordless telephony standards. Cordless telephony standards systems (CT-2, DECT) provide relatively small cell radii (0.2-5 km). Compared to cellular mobile systems, their low power and less bulky base stations are easier and cheaper to install. These systems do not require frequency planning, which greatly simplifies their installation. CT-2 and DECT systems provide higher voice quality and higher data rates than cellular based systems. For communication between the base station and the system controller, wired and wireless channels, such as radio relay and space communications, can be used. At the same time, it is possible to move base stations (for example, to suburbs, microdistricts, individual settlements, etc.) to a distance of up to 50 km or more. The choice of the physical medium for information transmission remains with the operator.
Corporate systems. Systems in this category differ so much from each other in their basic radio technologies, parameters and capabilities that it is impossible to give them a general description. For convenience, we divide them into two groups: narrowband and broadband. Narrowband systems are similar to WLL systems based on cellular technologies and standards. They provide a fairly long range of radio communication and a low data rate. Broadband systems have a very high data rate (up to 144 Kbps) and high noise immunity, but their maximum BS service area radii are somewhat smaller than those of narrowband systems. The great advantage of such systems is the ability to operate in a frequency range already occupied by other radio facilities, for example cellular systems connections. One of the most important stages in the design of WLL systems is the determination of the required number of radio channels depending on the number of subscribers served and the characteristics of the communication system in terms of the intensity of the generated load and the probability of failures (losses). Most companies offering their systems focus on the load created by one subscriber, within 0.05-0.1 Erl with a 1% failure probability.

In the case of organizing a radio link between the access point and subscribers, in the radio visibility zone of the base station, mobile terminal devices of users or subscriber units are located, forming one cell. If it is impossible to cover all subscribers using one base station, then the multi-cell principle is used.

When the access network is implemented in the form of radio links, it usually has a single or dual frequency structure. In the first case, one frequency band is used to transmit packets to and from the base station, but this structure has a number of significant drawbacks that limit its use in networks with big amount subscribers. Another option is a dual-frequency structure: on one of the frequencies, a multiple access channel is implemented, where all subscribers transmit to the base station, and on the other, receive from the base station, from where subscribers receive packets.

The main parameters of WLL systems and companies producing these systems are presented in Table. 2.

Providers and operators

A few years ago, WLL systems occupied only a small niche of the telecommunications market, and, according to analysts, the scale of their use in the installation of new communication lines should have been equal to about 5%. But already today, wireless access systems are used extremely widely, their share is about 20% of newly installed lines and continues to grow. However, in order to attract customers, wireless access providers need to prove their superiority over incumbents, and price is not the only criterion.

Today the trend is towards integration, meaning service providers offer Internet connectivity, long distance communications and other services based on existing operators' existing infrastructure.

Depending on the type of service offered and operational requirements, the general technology requirements of operators can be divided into several categories:

advanced radio technology;
efficient and flexible spectrum use;
simple frequency planning;
ease of installation;
providing high capacity in a variety of scenarios.

Prospects for the development of WLL

In general, forecasts of analysts and specialists regarding the development of systems based on wireless access are positive. For example, Motorola NSS Global Strategy Manager for Subscriber Radio Access Networks, William Webb, is full of optimism: “Forecasts made in the last year look quite realistic. It is predicted that the average number of WLL lines will reach about 50 million by 2004. Our own forecast is very close to this.”

ComputerPress 12"2001

The modern development of local telecommunication networks is focused on providing the most complete range of services, from standard telephony to modern multimedia services. This allows us to consider the elements of networks not only from the point of view of the presence of certain linear structures and various equipment, but also from the point of view of their functional purpose.

The subscriber access network is a set of technical means between the terminal subscriber devices installed in the user's premises and the switching equipment, the numbering plan (or addressing) of which includes terminals connected to the telecommunications system.

Based on this definition, the boundaries of the subscriber access network vary widely depending on the type of information transmitted (analogue telephony, ISDN services, data transmission and the Internet, broadcasting, television) and include various fragments of traditional wired and wireless networks. In some cases, these are just subscriber lines, in some cases they are subscriber lines, subscriber concentrators and trunk lines to core exchanges, in some cases they are a combination of xDSL active equipment and copper or optical communication lines, etc.

Also, fragments of a cable television network, wireless communication equipment can be used as an information transfer medium.

Subscriber access networks operating on the basis of wired technologies can be divided into the following types:

PBX analogue subscriber lines and digital subscriber line multiplexing systems that allow organizing several telephone lines over one pair of copper cable;

Integrated services digital network (ISDN), which involves the organization of digital subscriber lines based on basic interfaces (BRI) and primary access (PRI). Often, in addition to ISDN terminals, these networks include equipment for office and office-industrial automatic telephone exchanges of corporate users of communication services;

C) a network based on ADSL technology (asymmetric digital subscriber line), which allows organizing simultaneously with analog telephony asymmetric data link. The greatest development of this technology is associated with an increase in the need for access to the Internet. The network provides at low cost a dedicated channel for Internet access, operates over existing subscriber lines and is used mainly by individual customers of the telephone network;

Access network based on xDSL technologies (except ADSL), providing various options (speed, type of transmitted information) for access to communication networks. The network is designed to connect corporate and individual users and can operate over copper and optical communication lines;

Wireless subscriber access network WLL (wireless subscriber line), which involves fixed placement or limited mobility of subscriber radio equipment and does not require large costs for the construction of cable structures when deployed. This network can be built on the basis of equipment operating according to the DECT standard.

The technology of wired subscriber access has five main groups according to the criterion of transmission medium and categories of users. On fig. 1 shows their classification.

LAN (Local Area Network) is a group of technologies designed to provide corporate users with access to local area network resources and using structured cabling systems of categories 3, 4 and 5, coaxial cable and fiber optic cable as a transmission medium.

DSL (Digital Subscriber Line) is a group of technologies designed to provide PSTN users with multimedia services and use the existing PSTN infrastructure as a transmission medium.

CATV (cable television) is a group of technologies designed to provide users of CATV networks with multimedia services (due to the organization of a reverse channel) and using fiber optic and coaxial cables as a transmission medium.

OAN (Optical Access Networks) is a group of technologies designed to provide users with broadband services, a line of access to multimedia services and using fiber optic cable as a transmission medium.

SKD (multiple access networks) - a group of hybrid technologies for organizing access networks in apartment buildings; the existing infrastructure of the PSTN, radio broadcasting networks and power supply networks is used as a transmission medium.

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Institution "University "Turan"

APPROVED

at a meeting of the department

Radio engineering, electronics and telecommunications

Name of the institution "University "Turan"

Protocol No. __ dated "___" ______ 2012

Head of department

Verveikina L.S.

LECTURE COMPLEX-CONTENT

(THESES OF LECTURES, ILLUSTRATIVE AND HANDOUT MATERIAL, LIST OF RECOMMENDED LITERATURE)

"Subscriber access systems"

Specialty: 5В071900, Radio engineering, electronics and telecommunications

Teaching technology: credit

Form of education: full-time / part-time

Language department: Russian

Almaty, 2012

Topic 1. Introduction. Basic concepts of subscriber access systems

In a modern telecommunications system, not only the role of the access network is changing. In most cases, the territory within which the access network is being created is also expanding. In order to eliminate the differences in the interpretation of the place and role of the access network that are available in modern publications, Figure 1.1 shows a model of a promising telecommunications system. This model is based on the network structures given in the publications.

1.1 Place of the subscriber access network in the telecommunications system

Figure 1.1

The first element of the telecommunications system is a set of terminal and other equipment that is installed in the premises of the subscriber (user). In the 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, in fact, the subject of this monograph. The role of the subscriber access network is to ensure the interaction between the equipment installed at the subscriber's premises and the backhaul network. Typically, a switching station is installed at the junction point of the subscriber access network with the transit network. The space covered by the subscriber access network lies between the equipment located at the subscriber's premises and this exchange.

In a number of works, for example, in, the subscriber access network is divided into two sections - the lower plane of Figure 1.1. Subscriber lines (Loop Network) can be considered as individual means of connecting terminal equipment. As a rule, this fragment of the subscriber access network is a set of SLs. The Transfer Network serves to increase the efficiency of subscriber access facilities. This fragment of the access network is implemented on the basis of transmission systems, and in some cases load concentration devices are also 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 a terminal and means of supporting any services. In the model under consideration, the transit network can cover the territory both within the same city or village, and between subscriber access networks of two different countries.

The fourth element of the telecommunications system illustrates the means of accessing various telecommunication services. In figure 1.1, in the last ellipse, the name in the original language (Service Nodes) is indicated, which is translated in three words - nodes that support services. Examples of such a node can be the workplaces of telephonists-operators and servers that store any information.

The structure shown in Figure 1.1 should be considered as a promising model of a telecommunications system. To solve terminological problems, let us turn to the model inherent in subscriber access networks of analog exchanges. Such a model is shown in Figure 1.2. Considering the existing local networks, we, as a rule, will operate with two terms - "Subscriber network" or "AL network". The words "Subscriber access network" are used when it comes to a promising telecommunications system.

1.2 Subscriber network model

Figure 1.2

This model is valid for both HTS and STS. Moreover, for GTS, the model shown in Figure 1.2 is invariant to the structure of inter-office communication. It is identical for:

Non-regional networks, consisting, by definition, of only one telephone exchange;

Zoned networks, which consist of several regional exchanges (RATS), interconnected according to the principle "each with each";

Area networks built with nodes incoming message(UHS) or with knots outgoing message(UIS) and UVS.

For all elements of the subscriber network, the terms in parentheses are given in English language, given in . It should be noted that the term "intercabinet communication line" (Link cable) is not yet used in domestic terminology, since such routes are almost never used in GTS and STS.

A model illustrating the main options for building a subscriber network is shown in Figure 1.3. This figure details some fragments of the previous model.

1.3 Basic options for building a subscriber network

Figure 1.3

Figure 1.3 uses a number of symbols that are rarely found in domestic technical literature. The Cross-connection point is shown as two concentric circles. This symbol is often used in ITU documents. Also typical can be considered the designation of the distribution box (Distribution point) with a black square. We will return to the new abbreviations introduced in Figure 1.3 in the next paragraph.

The model shown in Figure 1.3 can be considered universal in relation to the type of exchange. In principle, it is the same for a manual telephone exchange, as well as for the most modern digital information distribution system. Moreover, this model invariant to the type of interactive network, such as telephone or telegraph.

On the other hand, for a digital switching station, its own model can be proposed, which will more accurately reflect the specifics of the subscriber access network. This task is quite difficult. The problem is that the process of introducing 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 typical example of such a situation is the installation of a digital switching station, replacing several old electromechanical stations. The near-station section of the digital switching station - with this method of upgrading the local telephone network - actually unites all the territories served by the previously dismantled electromechanical exchanges. In addition, when implementing a digital switching exchange, specific (permanent or temporary) solutions may arise when certain groups of remote subscribers are connected through the use of concentrators.

Of course, such decisions must be taken into account at the stage of developing a general concept for the modernization of the local telephone network. When the appropriate conceptual decisions are made, you can start looking for the best options for building a subscriber access network. For a hypothetical digital exchange, these options are shown in Figure 1.4. The last two figures (1.3 and 1.4) have a number of common points.

1.4 Model of a subscriber access network for a digital exchange

Figure 1.4

Firstly, both structures imply the presence of the so-called "direct power zone" - an enclave within which the ALs are directly connected to the cross-connect (without connecting cables in distribution cabinets).

Secondly, behind the "direct power zone" is the next area of the access network, for which it is advisable to use remote subscriber modules (concentrators or multiplexers) in a digital exchange, and either unsealed cables or channels formed by transmission systems for an analog exchange.

Thirdly, it should be noted that the structure of the subscriber network - regardless of the type of switching station - corresponds to a graph with a tree topology. This is significant from the point of view of communication reliability: the use of digital switching technology not only does not increase the AL availability factor, but, in some cases, reduces it due to the introduction of additional equipment in the section from the ATS to the user terminal.

To compile a list of the terms required further and, especially, to establish correspondence between the concepts adopted in domestic practice and ITU documents, it is advisable to give the structure of the AL network used in. This structure is shown in the upper part of Figure 1.5, and in its lower plane a similar model is shown in .

1.5 Structural diagram and joints of equipment of subscriber lines for UTN and STS

Figure 1.5

For the block diagram of the AL (upper part of Figure 1.5), there are three options for connecting a subscriber terminal to a switching station.

The upper branch of this figure shows a promising option for connecting the SLT without the use of intermediate cross-connect equipment. The cable is laid from the cross to the junction box, where the TA is connected by means of subscriber wiring.

The middle branch of the figure shows a variant of connecting the TA via a cabinet system, when intermediate equipment is placed between the cross-counter and the junction box. In our model, the role of such equipment is assigned to the switch cabinet.

In some cases, AL is organized using overhead communication lines (VLAN). Figure 1.5 shows this option on the bottom branch. In such a situation, a cable box (KJ) and input-output insulators are installed on the pole. At the location of the junction box, a subscriber station is mounted protective device(AZU), which prevents the possible impact on the TA of dangerous currents and voltages. It should be noted that the organization of the AL or its individual sections through the construction of an overhead line is not recommended; but in some cases - this is the only option for organizing subscriber access.

1.6 List of key terms

The figures above and the corresponding brief comments make it possible to compile the following list of terms related to the subscriber access network:

1. Local station (MS) to which subscriber lines are connected. For GTS, this is RATS. In STS, subscribers are included in terminal (OS), nodal (CS) and central (CS) stations. In the English-language technical literature, both for the STS and for the GTS, the general term "local exchange" - Local exchange (LE) is used. Another term is sometimes used - Central Office (CO), which is also used for CTA and CTC. From a purely technical point of view, it is convenient in domestic practice to use a single term - MS.

2. AL - a line of the local telephone network connecting the terminal subscriber telephone device with the AK of the terminal station, concentrator or other remote module. In the English-language technical literature, the term Subscriber line or simply Line is used. In the definition, before the word “device”, there is the adjective “telephone”, which emphasizes the main purpose of the AL as an element of the PSTN. At present, the words "Terminal telephone device" are often replaced by a more general term, invariant to the type of switched (secondary) network - "Terminal".

3. Station section AL - a section of the subscriber line from the AK of a local station, concentrator or other remote module to the station side of the cross. In foreign technical literature, this AL section is not considered as an independent element of the subscriber access network.

4. Linear section AL - a section of the subscriber line from the linear side of the cross or input-switching device of the terminal station, concentrator or other remote module to the socket (or other similar element) of the terminal subscriber device of the telephone network. In foreign technical literature, this section of the AL is also not considered as an independent element of the subscriber access network.

5. Trunk section AL - a section of the subscriber line from the linear side of the cross-country or the input-switching device of the local station, concentrator or other remote module to the distribution cabinet, including intercabinet communication sections. The main section of the AL corresponds to the term "Main cable". The main section is also considered the direct power zone, within which distribution cabinets are not used to build a subscriber network. The direct power zone occupies the territory adjacent to the telephone exchange within a radius of approximately 500 meters. In the English-language technical literature, the words "Direct service area" are used to designate this section of the subscriber network.

6. Distribution section AL - section of the subscriber line from the distribution cable cabinet to the subscriber station. This section of the AL - depending on the structure of the access network - corresponds to the terms "Primary distribution cable" and "Secondary distribution cable". And the part of the area occupied by the distribution area is usually called the "Cross-connection area".

7. Subscriber wiring - a section of the subscriber line from the junction box to the socket for switching on the terminal subscriber telephone device. Two terms are used in the English-language technical literature:

- "Subscriber"s lead-in" - the section from the junction box to the subscriber's premises;

- "Subscriber" s service line "- the section from the junction box to the telephone.

8. Cross, VKU - equipment for the junction of station and linear sections of subscriber and connecting lines of urban, rural and combined telephone networks. This element of the access network in the English-language technical literature is called "Main distribution frame"; the abbreviation MDF is often used.

9. Cable distribution cabinet (ShR) - a terminal cable device designed for installation of cable boxes (with plinths, without electrical protection elements) in which trunk and distribution cables of subscriber lines of local telephone networks are connected. The term "Cross-connection point" corresponds to the cable distribution cabinet. If the AL passes through two SRs, then in the English technical literature - for the second cabinet - the adjective "secondary" is added. In addition, if the SR is located in a specially equipped room, then it is referred to as the "Cabinet". In the case when the SR is located against the wall of a building or other similar place, it is called "Sub-cabinet" or "Pillar". These designations are usually indicated in brackets after the functional purpose - "Cross-connection point". In the technical literature, several more terms are used that more or less correspond to SR. The most common word is "Curb".

10. Subscriber junction box (RK) - a terminal cable device designed to connect cable pairs included in the junction box plinth with single-pair wires of subscriber wiring. Distribution point (DP) - an analogue of the term "Subscriber distribution box".

11. Cable duct - a set of underground pipelines and wells (viewing devices) intended for laying, installation and maintenance of communication cables. The term "Cable duct" in the English technical literature is used in two versions: "Duct" or "Cable duct".

12. Well (viewing device) of cable duct - a device designed for laying cables in cable duct pipelines, cable installation, placement of related equipment and maintenance of communication cables. Two terms are equivalent to the words "Cable well" in English: "Jointing chamber" or "Jointing manhole".

13. Cable shaft - a cable duct structure located in the basement of a telephone exchange, through which cables are introduced into the station building and in which, as a rule, multi-pair line cables are soldered into station cables with a capacity of 100 pairs. This term in English is denoted by the words "Exchange manhole".

14. Station site - the territory within which all subscriber lines are connected to this MS. In the English-language technical literature, the term "Local exchange area" is used.

15. Digital cross node (CCU) - equipment for selection and combination digital channels and tracts. The CCU contains a control device capable of autonomously or under the influence of commands from the technical operation center (CTE) to reconfigure the structure of the transport (primary) network. This element of the transport network corresponds to the term "Digital Cross Connect", which has several abbreviations, of which DSC and DXC are most often used.

16. Multiplexer with channel allocation (MVK) - equipment similar in functionality to the CCU, but without a control system. In the English technical literature, the term "Add-Drop Multiplexer" (ADM) is used.

17. Telephone density - a value that determines the number of telephones per 100 inhabitants, the number of families, etc. or per unit area. In the latter case, a clarifying adjective is introduced - "Surface telephone density". Telephone density in English texts is denoted by the terms Telephone density, Line density, Telephone penetration.

The reader has probably drawn attention to the following fact: having defined a number of terms, the author has missed a fundamental - if one is to believe the title of the monograph - definition. This, of course, is about the phrase “Subscriber access network”. The problem is that a precise definition of “Subscriber Access Network” has not yet been developed. Moreover, some interpretations of this term contain significant contradictions. It seems to me that it is expedient to introduce two definitions for the “subscriber access network”: in terms of the functions performed and in terms of the topology of the telecommunications system.

The first definition, in turn, requires clarification of the term “access”. This word is often found in telecommunications and a number of related disciplines. When applied only to telecommunications, the word “access” is used in several aspects (accessibility of the switching system, access to additional services, etc.). In the monograph, the term “access” will be interpreted as it is defined in: “Access (Access) is the process of a subscriber accessing some resources of a system, network”. In this context, the “Subscriber Access Network” can be considered as a fragment of a telecommunications system that provides the subscriber with access to some network-wide resources.

Such a definition gives practically no idea about the boundaries of the subscriber access network. In order to fill this gap, it is advisable to consider a hypothetical model of the subscriber access network shown in Figure 1.6. The structure of the proposed model contains two MS (N1 and N2) and one packet switching center (PSC).

Topic 2. Basic concepts of a multiservice subscriber access network. Digital subscriber line transmission systems

Now it is impossible to say that little attention is paid to the issues of multiservice access. Rather, on the contrary, access networks have become one of the areas most actively developed by telecom operators, and we can safely say that the future of an operator largely depends on what solutions are chosen for its access network. Most of the legacy access networks operated by operators to date have been costly and inefficient. Even with the beginning of the convergence of communication networks in the process of transition to NGN, all new solutions were mainly related to the transport network, methods of creating services and control devices. Faced with the need to provide the subscriber with a full range of infocommunication services, operators have come to the concept of multiservice access considered here.

The general requirement for modern multiservice access technologies is easy to formulate: any type of traffic must be transmitted in one channel. Today it is more beautifully called "triple-plays": video, speech and data, and the transition to NGN requires a broader interpretation of these concepts. Voice transmission is also a local telephone communication, and access to intercity and international communication(according to the new rules, access to an alternative operator should be implemented), and IP-telephony. Similarly, the concepts of video and data services are expanding.

Of course, new infocommunication services will initially be in demand by a relatively small group of subscribers, but this will be the most highly profitable category of users in the operator's subscriber base. The stratification of subscribers by the level of demand for new types of services will continue in the future, thus differentiating the income generated. As a matter of fact, today the operator's task is to find reasonable solutions when building an access network, taking into account the emerging differentiation in the level of demand for services among individual groups of subscribers.

2.2 Modern networks access

2.2.1 Features of access networks in Kazakhstan

One of the advantages of domestic access networks is that shorter subscriber lines than in most countries make it relatively easy to use xDSL equipment and other modern technical means. For Russia, DSL technologies are of particular interest, since multi-pair communication cables with copper conductors predominate in Russian access networks.

However, in practice, the operating conditions of most subscriber cables do not allow the widespread introduction of modern communication services. In almost every application of transmission system equipment (including xDSL type equipment), it is necessary to measure subscriber cables.

2.2.2 Multiservice access

When reviewing approaches to building an access network, operators pursue several main goals: to keep operating costs within reasonable limits, to avoid building specialized networks for each type of traffic and ensure the quality of service that satisfies subscribers. Thus, the concept of a multiservice access network appears, the main purpose of which is to provide fast, economical and high-quality access for any user to all services of the telecom operator's network.

The equipment of a multiservice access network primarily includes multiservice subscriber concentrators, access gateways, IP telephony gateways (media gateways), multiservice access switches, etc., as well as various integrated subscriber access devices (IAD), which largely affect the principles building an access network.

It is important to note some aspects of the operation of modern access equipment. The main transport technology of a multiservice network is IP. Therefore, access must be based on the IP protocol. However, most of the multiservice access solutions on the market today are based on ATM technology. In addition, access is becoming broadband: the access level should no longer be a bottleneck in the operator's network.

Equipment manufacturers tend to use the term "access equipment" without trying to tie their product to any classification. Much more important is the set of supported technologies that will allow the operator to provide subscribers with the required set of services. The second key point is the efficiency and ease of implementation of equipment in the access network.

2.3 Access technologies

So, what technologies should be used when implementing a multi-service access network? Currently, the operator has access to a variety of technologies for upgrading access networks. Before starting the analysis, let's try to separate all technologies by the transmission medium used: optical cable, wireless access and metal lines.

2.3.1 Optical access

The essence of PON (Passive Optical Network) technology is that a completely passive optical network is created between the central node and remote subscriber nodes, which has a "tree" topology. Optics is by no means the most demanded solution for Russian access networks today, but its prospects look quite promising so that one can be sure of the need for an optical interface in access equipment.

2.3.2 Wireless access

Subscribers' radio access to telephony and data transmission services is organized using WLL technologies. One of the first WLL technologies to be widely used on the market is the DECT standard. In addition, technologies of the WPAN (Wireless Personal Area Network), WLAN and WMAN classes are used to organize wireless subscriber access.

Among the WPAN standards that provide direct connection of subscriber terminals to access devices, the most widely used are wireless optical IrDA (IR-channel communication) and Bluetooth. Their main difference is the limited range (1-10 m) and the absence of problems with the frequency range.

IEEE 802.11a/b/g is by far the best known WLAN standard on the market today. wifi technology). The European (ETSI) counterpart of the standard is called HiperLAN2. Various versions of the standard are focused on operation in the ranges from 2.4 to 5.8 GHz and provide data transfer rates from 1 to 54 Mbps.

A new fashionable word in the sector of wireless urban (Wireless MAN) networks - WiMAX. It is the commercial name for a group of IEEE 802.16 standards maintained by an industry group that includes a number of well-known development companies. This protocol is designed to provide wireless access at the metropolitan level and is designed to solve the "last mile" problem for the most demanding providers, as well as reduce financial costs and time spent on deploying new connections due to the unification of the solution. The declared high speeds (up to 70 Mbps) and communication range (up to 50 km) should provide WiMAX technologies with a great future.

2.3.3 Wired access

Among wired access technologies, ISDN still occupies the first place. ISDN Basic Access (ISDN BRI) may be considered a legacy technology, but for many operators and subscribers it is still a very efficient and convenient solution. ISDN is a completely digital (up to the subscriber terminal in countries where the development of ISDN was most intensive), but still a public telephone network; the main application of ISDN - dial-up access to Internet resources - at best will allow you to get a bandwidth of 128 kbit / s. If the connection is established on only one channel B, then the total bandwidth is comparable to what a modern modem can provide. Massive deployment of ISDN services requires costly PSTN upgrades, so ISDN will only be popular in countries where such upgrades are government funded (eg, Germany). Videoconferencing could be a key ISDN application, but since the inception of ISDN, videoconferencing technology has evolved based on IP rather than ISDN circuit switching.

The supported set of protocols of the xDSL family is probably the most important characteristic of access equipment, since the use of DSL technologies, as already mentioned, is most relevant in Kazakhstan.

Asymmetric DSL solutions are convenient for organizing high-speed Internet access at home, for example, ADSL technology, which has become the most common in the segment of individual users. Today, it provides access at speeds of only about 64-128 kbps due to bandwidth limitations in the backbone channels of existing Internet providers.

Symmetric access, such as SHDSL (Rec. G.991.2), is becoming increasingly popular and in demand, especially among corporate users. The standard describes the technology for data transmission at the same speed in the forward and reverse directions - up to 2.3 and 4.6 Mbps over one and two pairs of wires, respectively. SHDSL technology allows the use of repeaters, which allows organizing communication channels up to 18.5 km long.

2.4 Network interfaces

Until recently, interfaces between remote subscriber hubs and modules for connecting to PBX equipment were not subject to international standardization. Practically in all installed before today Digital exchanges for these interfaces use digital paths of 2048 kbps and their own "in-house" protocols. An obvious disadvantage of this approach is the limited freedom of choice for operators when installing additional subscriber equipment. Only in the case of building an operator's network based on the equipment of one manufacturer, this internal interface ceases to be a problem.

2.4.1 V5 interface

Recently, in connection with the expansion of the range of subscriber access network facilities, and in particular with the spread of WLL equipment, the need for a "universal" interface has increased, which would allow combining equipment from different manufacturers in one network that implements various types of access (via analog lines, ISDN BRI and PRI). The V5 interface created for this purpose caused, in fact, revolutionary changes in the organization of interaction between access network equipment and switching nodes.

The V5 interface does not require any particular access technology or transmission medium, although its development was largely driven by the deployment of optical and wireless access media.

National features in the V5 interface specification are defined on a country by country basis. Russian specifications were approved in 1997 by the RF Ministry of Information and Communications (then - Goskomsvyazi).

The V5.1 interface allows you to connect the access network equipment to the PBX via a digital path of 2048 kbps. This provides connection (without load concentration) up to 30 analog subscriber lines or 15 ISDN BRI subscribers. The signaling information is transmitted over the KI16 channel.

The V5.2 interface is oriented to a group of 1 to 16 2048 kbps paths and supports load concentration. Each path has several signaling channels (KI16, KI15, KI31). Thus, one V5.2 interface can support (depending on concentration factor) up to 2000 PSTN ports or up to 1000 ISDN BRI ports.

In both cases, the PSTN and ISDN ports can use the same V5 interface path. The V5.1 interface allows to provide services for network clients in the on-demand mode, as well as in the semi-permanent line mode (Semi-permanent). V5.2, which provides for the possibility of concentration of subscriber load, includes a protocol for placing bearer channels for ports that are in the active state.

2.4.2 ISDN interface

Sometimes it is more convenient for the operator to use the ISDN already implemented in the network as an interface between the access equipment and the network. This type of access is commonly used to include PBXs, hubs and other remote modules in digital exchanges. Of course, in such cases, there is no universality inherent in V5, the possibility of providing additional services (VAS) of the telephone exchange disappears, however, not all PBXs to which access equipment is connected support V5. In this case, it is necessary to replace the version more often, which leads to additional costs.

2.5 Design

The design of access equipment is more standard than the technology used. As a rule, this is a 19-inch rack, which allows you to "pick up" boards for the implementation of the services necessary for the operator. In some cases, the boards are replaceable, that is, it is possible to connect ISDN subscribers instead of some analog subscribers (POTS). The most convenient for operators is the modular equipment architecture with the possibility of expansion.

The placement of access equipment can vary both physically and architecturally. With physical placement, everything is quite familiar - access equipment can be located on the territory of the reference station and work as a subscriber extension or a block for providing new services, such as VoIP (especially in the media gateway version).

The architectural component is more interesting. The equipment can be an integral part of the network concept and, when assembled, represent a new network node. A multi-service hub can be part of an NGN (Softswitch Class 5) node, and a media gateway can be part of a distributed IP PBX.

Topic 3. Digital transmission systems for subscriber lines. Subscriber access networks - ISDN

One of the most important problems of telecommunication networks continues to be the problem of subscriber access to network services. The urgency 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 means of the access network, despite the emergence of new most modern wireless methods of subscriber access, are traditional copper subscriber pairs. The reason for this is the natural desire of network operators to protect the investments made. Therefore, at present and in the foreseeable future, the technology of asymmetric digital subscriber line ADSL will remain a strategic direction for increasing the capacity of subscriber access networks, using a traditional copper subscriber pair as a transmission medium and at the same time preserving already provided services in the form of an analog telephone or basic access to ISDN. The implementation of this strategic direction in the evolution of subscriber access networks depends on the specific conditions of the existing subscriber access network of each country and is determined by each telecom operator, taking into account these specific conditions. It is clear that the diversity of local conditions determines a large number possible ways migration of the existing subscriber access network to ADSL technology.

Telecommunication technologies are constantly improving, quickly adapting to new requirements and conditions. Until quite recently, the main and only means of subscriber access to network services - and, first of all, to Internet services, was an analog modem. However, the most advanced analog modems are the ITU-T V.34 compliant modem with a potential transmission rate of up to 33.6 Kbps, and the next generation ITU-T V.90 recommendation compliant modem with a potential transmission rate 56 kbit/s practically cannot provide effective user experience on the Internet.

Thus, a sharp increase in the speed of access to network services, and primarily to Internet services, is critically important. One of the methods for solving this problem is the use of the xDSL high-speed subscriber line technology family. These technologies provide a high throughput of the subscriber access network, the main element of which is a twisted copper pair of the local subscriber telephone network. Although each of the xDSL technologies occupies its own niche in the telecommunications network, it is nevertheless undeniable that the ADSL asymmetric digital high-speed subscriber line and VDSL ultra-high-speed digital subscriber line technologies are of the greatest interest to telecommunications service providers, equipment manufacturers, and users. And this is not accidental - ADSL technology appeared as a way to provide the user with a wide range of telecommunication services, including, first of all, high-speed access to the Internet. In turn, VDSL technology is able to provide the user with a wide bandwidth, which allows him to access almost any broadband network service both in the near and distant future, but not in a pure copper, but in a mixed, copper-optical access network . Thus, both of these technologies will provide an evolutionary path for the introduction of optical fiber into the subscriber access network, protecting the past investments of local network operators in the most effective way. Thus, ADSL can be seen as the most promising member of the xDSL family of technologies, which will be succeeded by VDSL technology.

Although the key idea of migrating network service delivery methods using xDSL technologies is to move from the analogue public telephone network first to ADSL, and then, as necessary, to VDSL, this does not exclude the use of other intermediate steps for the same purpose. types of xDSL technologies. For example, IDSL and HDSL technologies can be used to increase subscriber line capacity.

3.1 From analog modem to ADSL

The most common migration scenario for accessing Internet services is by far the transition from a source access network using analog PSTN modems to a target access network using ADSL modems.

ADSL (Asymmetric Digital Subscriber Line - asymmetric digital subscriber line). This technology is asymmetric. This asymmetry, combined with the "always connected" state (where there is no need to dial a phone number each time and wait for a connection to be established), makes ADSL technology ideal for providing access to the Internet, access to local area networks (LANs), etc. When organizing such connections, users usually receive much more information than they transmit. ADSL technology provides downstream data rates ranging from 1.5 Mbps to 8 Mbps and upstream data rates from 640 Kbps to 1.5 Mbps. ADSL technology makes it possible to maintain the traditional service without significant costs and provide additional services, including:

Preservation of traditional telephone service,

High-speed data transmission at a speed of up to 8 Mbps to the user of the service and up to 1.5 Mbps from him,

high speed internet access,

Transfer one TV channel high quality, video-on-demand,

Distance learning.

Compared to alternative cable modems and fiber optic lines, the main advantage of ADSL is that it uses existing telephone cable. At the ends of the existing telephone line, frequency separators are installed (some use tracing paper from the English splitter), one for the PBX and one for the subscriber. An ordinary analog telephone and an ADSL modem are connected to the subscriber splitter, which, depending on the version, can act as a router or a bridge between local network subscriber and the provider's border router. At the same time, the operation of the modem absolutely does not interfere with the use of conventional telephone communication, which exists regardless of whether the ADSL line is functioning or not.

Currently, there are two versions of ADSL technology: the so-called full-blown ADSL, which is simply called ADSL, and the so-called "light" version of ADSL, which is called "ADSL G. Lite". Both versions of ADSL are currently governed by ITU-T G.992.1 and G.992.2, respectively.

The concept of full scale ADSL was originally born as an attempt at a competitive response from local telephone network operators to cable television broadcasting (CATV) operators. Almost 7 years have passed since the appearance of ADSL technology, but so far it has not received mass practical application. Already in the process of developing a full-scale ADSL and the first experience of its implementation, a number of factors emerged that required correction of the original concept.

The main of these factors are the following:

1) Change in the main targeted use of ADSL: at present, the main type of broadband subscriber access is no longer the provision of cable TV services, but the organization of broadband access to the Internet. To meet this new challenge, 20% of the maximum throughput of full-blown ADSL is sufficient, which corresponds to a downstream (network-to-subscriber) rate of 8.192 Mbps and an upstream (subscriber-to-network) rate of 768 Kbps.

2) Unavailability of the Internet to provide full-scale ADSL services. The fact is that the ADSL system itself is only part of a network of broadband access to network services. Already the first experiences of introducing ADSL into real access networks have shown that today's Internet infrastructure cannot support transmission rates above 300 - 400 Kbps. Although the backbone of the Internet access network is usually carried out on an optical cable, however, it is not this network, but other elements of the Internet access network - such as routers, servers and PCs, including the characteristics of Internet traffic, that determine the real throughput of this network. Therefore, the use of full-scale ADSL on the existing network practically does not solve the problem of broadband subscriber access, but simply moves it from the subscriber section of the network to the backbone network, exacerbating the problems of the network infrastructure. Therefore, the introduction of full-scale ADSL will require a significant increase in the bandwidth of the backbone section of the Internet, and, consequently, significant additional costs.

3) High cost of equipment and services: for a wide deployment of technology, it is necessary that the cost of an ADSL subscriber line be no more than $500; existing prices are significantly higher than this value. Therefore, other xDSL products are actually used and, first of all, HDSL modifications (such as multi-rate MSDSL) with a bandwidth of 2 Mbps over a single copper pair.

4) The need to modernize the infrastructure of the existing access network: the concept of a full-scale ADSL requires the use of special crossover filters - the so-called splitters (splitter "s), separating the low-frequency signals of an analog phone or BRI ISDN main access and high-frequency broadband access signals both in the PBX premises and at the user's premises.This operation is labor-intensive, especially in a branch exchange where thousands of subscriber lines terminate.

5) The problem of electromagnetic compatibility, which consists in the insufficient study of the effect of full-scale ADSL on other high-speed digital transmission systems (including the xDSL type) operating in parallel in the same cable.

6) Large power consumption and footprint: Existing ADSL modems, in addition to high cost, require a lot of space and consume significant power (up to 8 W per active ADSL modem). In order for ADSL technology to be acceptable for deployment in a switching office, it is necessary to reduce power consumption and increase port density.

Asymmetric mode of operation of full-scale ADSL: with a constant bandwidth of the ADSL line, it is an obstacle for some applications that require symmetrical mode of transmission, such as video conferencing, as well as for organizing the work of some users who have their own Internet servers. Therefore, an adaptive ADSL capable of operating in both asymmetric and symmetrical modes is needed.

User premises hardware and software have also been tested to be the bottleneck of ADSL systems. Testing has shown, for example, that popular programs -- web browsers and platforms hardware PCs can limit PC bandwidth to 600 Kbps. So for full use high-speed ADSL connections require improvements in client hardware and software user.

These problems of full-scale ADSL initiated the emergence of its "light" version, which is the already mentioned ADSL G.Lite. Here are the most significant features of this technology.

Ability to work in both asymmetric and symmetric modes: in asymmetric mode at a transmission rate of up to 1536 Kbps in the downstream direction (from the network to the subscriber) and up to 512 Kbps in the upstream direction (from the subscriber to the network); in symmetrical mode - up to 256 Kbps in each direction of transmission. In both modes, the use of the DMT code provides automatic adjustment of the transmission rate in steps of 32 Kbps depending on the length of the line and the interference power.

Simplification of the process of installing and configuring ADSL GLite modems by eliminating the use of crossover filters (splitters) at the user's premises, which allows the user to perform these procedures himself. It does not require replacement of internal wiring in the user's premises. However, as the test results show, this can not always be done. An effective measure to protect a broadband data transmission channel from pulse dialing signals and ringing signals is to install special microfilters directly in the telephone socket.

Realizable lengths of ADSL GLite lines make it possible to provide the vast majority of home sector users with high-speed Internet access. It should be noted that many ADSL equipment manufacturers have chosen the concept of ADSL equipment that supports both full speed ADSL mode and ADSL G.Lite mode. It is assumed that the emergence of ADSL G.Lite equipment will sharply activate the market for broadband Internet access devices. It is highly likely that it will occupy the niche of broadband access to network services for home users.

The advent of the ADSL intermediate stage in the form of ADSL G.Lite creates the possibility of a seamless transition from existing analog modems to broadband access - first to the Internet using G.Lite, and then to multimedia services using full-blown ADSL.

Migration from an analog modem to any of the ADSL modifications is beneficial to the service provider, since calls of increased duration, such as user calls to the Internet, are routed bypassing the public switched telephone network. If the service provider is a traditional local network operator, then this scenario gives him another additional (but no less important) advantage, since there is no need for a costly upgrade of the existing telephone network switch to an ISDN switch, which would be needed to increase the speed of access to Internet services with option of migration from public telephone network services to ISDN network services. The significant additional investment in migrating from analog PSTN to ISDN is because the latter is a networking concept with its own very powerful layered protocol stack. Therefore, this upgrade requires significant changes in the hardware and software of the PSTN digital switching station. At the same time, an ADSL modem is simply a high-speed modem that uses standard data network protocols based on ATM packet or cell transmission. This significantly reduces the difficulty of accessing the Internet and hence the investment required.

Also, from the point of view of Internet users, network operators, and Internet service providers, it makes more sense to move directly from a PSTN modem not to an ISDN modem, but directly to ADSL modem. With a maximum narrowband ISDN throughput of 128 Kbps (which corresponds to the combination of two B-channels of the main ISDN access), the transition to ISDN gives an increase in access speed compared to the PSTN network by a potentially slightly more than 4 times and requires in addition significant investment. Therefore, the intermediate stage of transition from the PSTN to ISDN as an effective means of accessing the Internet is practically meaningless. Of course, this does not apply to those regions where there is already widespread adoption of ISDN. Here, of course, the determining factor is the protection of the investments made.

Thus, the main incentives for the considered method of access network migration are:

A huge increase in the speed of access to Internet services.

Preservation of an analog telephone or basic access to ISDN (BRI ISDN).

Moving Internet traffic from the PSTN network to an IP or ATM network.

No need to upgrade the PSTN switch to an ISDN switch.

If the main incentive for migrating from an analog modem to an ADSL modem is high-speed Internet access, then the most appropriate way to implement this service should be considered to be the implementation of an ADSL remote terminal, called ATU-R, in the form of a card. personal computer(PC). This reduces the overall complexity of the modem and eliminates internal wiring problems (from modem to PC) at the user's premises. However, telephone network operators are generally reluctant to rent an ADSL modem if it is an internal PC card, as they do not want to be held responsible for possible damage to the PC. Therefore, remote ATU-R terminals have become more widespread so far in the form of a separate unit, called an external ADSL modem. An external ADSL modem is connected to a LAN port (10BaseT) or a serial port (universal serial port). USB bus) computer. This design is more complex as it requires additional space and a separate power supply. But such an ADSL modem can be purchased by a subscriber of the local telephone network and put into operation by a PC user on his own. In addition, an external modem can be connected not to a PC, but to a LAN hub or router in cases where the user has several computers.

And this situation is typical for organizations, business centers and residential complexes.

3.2 Migration to ADSL in the presence of DSLAN access in the network

The previous migration scenario requires a continuous physical copper pair between the local PBX premises and the customer premises. This situation is more typical for developing countries with a relatively underdeveloped telecommunications network, which include Kazakhstan. In countries with a developed telecommunications network on the subscriber telephone network, digital subscriber transmission systems (DSLTS) are widely used to increase the overlapped distances, mainly using the equipment of primary digital systems transmission of plesiochronous hierarchies (E1). For example, in the United States in the early 90s, approximately 15% of all subscriber lines were serviced using DSLSL (in the United States they are called Digital Local Carrier - DLC), in the future it is expected to increase their total capacity to 45% of the total number of subscriber lines. Currently, very reliable subscriber access networks are being built that use a combined copper-optical transmission medium and secure ring structures using SDH synchronous digital hierarchy equipment.

5.1. Subscriber Access Network Models

In a modern telecommunications system, not only the role of the access network is changing. In most cases, the territory within which the access network is being created is also expanding. In order to eliminate the differences in the interpretation of the place and role of the access network that are available in modern publications, in Fig. 5.1 shows a model of a promising telecommunications system.

Figure 5.1 - Telecommunication system model

The second element of the telecommunications system is, in fact, the subscriber access network. The role of the subscriber access network is to ensure the interaction between the equipment installed at the subscriber's premises and the backhaul network. Typically, a switching station is installed at the junction point of the subscriber access network with the transit network. The space covered by the subscriber access network lies between the equipment located at the subscriber's premises and this exchange.

The subscriber access network is divided into two sections - the lower plane of Fig. 5.1. Subscriber lines (Loop Network) can be considered as individual means of connecting terminal equipment. As a rule, this fragment of the subscriber access network is a set of SLs. The Transfer Network serves to increase the efficiency of subscriber access facilities. This fragment of the access network is implemented on the basis of transmission systems, and in some cases load concentration devices are also used.

The fourth element of the telecommunications system illustrates the means of accessing various telecommunication services. On fig. 5.1, in the last ellipse, the name in the original language (Service Nodes) is indicated, which is translated in three words - nodes that support services. Examples of such a node can be the workplaces of telephonists-operators and servers that store any information.

Shown in Fig. 5.1 structure should be considered as a perspective model of a telecommunication system. To solve terminological problems, let us turn to the model inherent in subscriber access networks of analog exchanges. Such a model is shown in Fig. 5.2. Considering the existing local networks, we, as a rule, will operate with two terms - "Subscriber network" or "AL network". The words "Subscriber access network" are used when it comes to a promising telecommunications system.

Figure 5.2 - Subscriber network model

This model is valid for both HTS and STS. Moreover, for the HTS shown in Fig. 5.2 the model is invariant to the structure of interoffice communication. It is identical for:

non-regional networks, consisting of only one telephone exchange;

zoned networks, which consist of several regional exchanges (RATS), interconnected according to the principle "each with each";

regionalized networks built with incoming message nodes (UCN) or with outgoing message nodes (UIN) and UCS.

For all elements of the subscriber network, terms in English are given in brackets. It should be noted that the term "intercabinet communication line" (Link cable) is not yet used in domestic terminology, since such routes are almost never used in GTS and STS.

The model illustrating the main options for building a subscriber network is shown in fig. 5.3. This figure details some fragments of the previous model.

Figure 5.3 - Basic construction options

subscriber network

On fig. 5.3 uses a number of designations that are rarely found in domestic technical literature. The Cross-connection point is shown as two concentric circles. This symbol is often used in ITU documents. Also typical can be considered the designation of the distribution box (Distribution point) with a black square.

The model shown in fig. 5.3 can be considered universal in relation to the type of exchange. In principle, it is the same for a manual telephone exchange, as well as for the most modern digital information distribution system. Moreover, this model is invariant to the type of interactive network, such as telephone or telegraph.

Of course, such decisions must be taken into account at the stage of developing a general concept for the modernization of the local telephone network. When the appropriate conceptual decisions are made, you can start looking for the best options for building a subscriber access network. For a hypothetical digital exchange, these options are shown in fig. 5.4. The last two figures (5.3 and 5.4) have a number of things in common.

Figure 5.4 - Model of a subscriber access network for a digital switching station

Thirdly, it should be noted that the structure of the subscriber network - regardless of the type of exchange - corresponds to a graph with a tree topology. This is significant from the point of view of communication reliability: the use of digital switching technology not only does not increase the AL availability factor, but, in some cases, reduces it due to the introduction of additional equipment in the section from the ATS to the user terminal.

In order to compile a list of the terms required further and, especially, to establish correspondence between the concepts adopted in domestic practice and ITU documents, it is advisable to present the structure of the AL network presented in the upper part of Fig. 5.5.

For the block diagram of the AL (upper part of Fig. 5.5), three options for connecting a subscriber terminal to a switching station are presented.

In some cases, AL is organized using overhead communication lines (VLAN). On fig. 5.5 this option is shown on the lower branch. In such a situation, a cable box (KJ) and input-output insulators are installed on the pole. At the location of the junction box, a subscriber protective device (AZU) is mounted, which prevents the possible impact on the TA of dangerous currents and voltages. It should be noted that the organization of the AL or its individual sections through the construction of an overhead line is not recommended; but in some cases this is the only option for organizing subscriber access.

Figure 5.5 - Structural diagram and joints of subscriber line equipment for UTN and STS

General architecture of a telecommunications network

Access networks

8.3.2. Technical means of the access network

Transport networks.

Structure and technologies of transport networks

Transport network models

Principles of building transport networks

General trends development of transport networks

Circuit Switched Networks

General provisions

Principles of building telephone networks

Packet communication networks

Analysis of the technical implementation of IP telephony

Types of connections in the IP-telephony network

H.323 networks

MPLS technology

general characteristics NGN networks

Purpose and capabilities of the NGN network

Basic provisions of the NGN concept

Section 8 discusses the general structure of a telecommunications network. Noted

What's on this stage development, the telecommunication network acquires new properties, gradually turning into an infocommunication network. The advantages of digital networks are indicated, which makes it possible to move from a multi-level principle of building networks to a more efficient two-level principle, including an access network and a transport network. The classification of telecommunication networks given in the section makes it possible to determine the place and role of each network in the ESE. The construction principles and technologies used in 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 transition on transport networks to IP technologies for information transfer. The principles of construction of switched networks are considered. An important place in the section is occupied by the issues of building the Basic Telephone Network - as the dominant network of the ESE. Attention is paid to the principles of building packet networks using IP technologies. The basics of building a new generation network NGN, the elements of which are being implemented on the ESE and which is the prototype of the ESE in the near future, are considered. The section contains Control questions, a list of recommended reading and a glossary.

8.1 General architecture of a telecommunications network

The modern telecommunications network is one of the most complex systems ever created by man. This network unites millions of different sources and consumers of information, which can be the simplest signaling devices, individuals, computer networks, enterprises, as well as objects scattered over a large area and even located in space. The main purpose of a telecommunications network is to transfer information between users and provide access to the information they need. The architecture of the telecommunications network is shown in fig. 8.1

Figure 8.1 Telecommunication network architecture

Telecommunication network elements are:

· end points;

· communication nodes;

· channels of connection;

· network management system.

Endpoints(OP) (including subscriber ones), contain equipment for input and output of information, and sometimes for its storage and processing, which is intended:

· to receive information from the user and convert it into a message necessary for transmission over the communication network;

· to receive a message from the network and convert it into a form convenient for issuing to the user.

Communication nodes (US) are intended to distribute information. Communication nodes, in turn, are divided into switching nodes (MC with circuit, message or packet switching), designed to distribute messages, and network nodes, designed to distribute channels, channel bundles and group paths.

Communication channels (CS) provide the transmission of electromagnetic signals limited in power in a certain frequency range, or at a certain speed. Channels are combined into communication lines between points and nodes of the network and serve to transfer (transmit) information in space.

Communication line, connecting the subscriber station with the UK, is called the subscriber line. Communication lines are equipped with channel-forming equipment, with the help of which separate communication channels (CS) are allocated in the LAN. Communication channels, together with the equipment for transmitting and receiving a message, form a message transmission path (TPS). Two message transmission paths and more, switched between each other with the help of the AC, form a connecting message transmission path.

Implementation of CC and DB, intelligent platforms on a telecommunications network makes it possible to provide network users with virtually 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 functioning of the network, including the organization of repair and restoration, redistribution of channels and paths, redistribution and restriction of message flows;

· distribution of tasks and requests for computer centers and the optimal use of their capacities;

· managing billing for services and network services;

· the functioning of the network as a whole as a branch of the national economy and its development.

Modern communication networks are primarily characterized by:

· the use of digital switching and transmission systems and computing facilities;

integration of various types of transmitted information (speech, image, data, facsimile and other messages).

On the basis of such networks, various kinds of private (institutional) and corporate networks are created.
Digital technology for the delivery and distribution of information has a number of advantages:
Firstly, the process of improvement in the technology of production of large integrated circuits reduces the cost of digital equipment and its dimensions, reduces the failure rate of its elements by an order of magnitude. Currently working reliably digital circuits with hundreds of thousands of elements with a total downtime of several hours over 20 years of operation. Modern technology makes it possible to form up to 10,000 elements or more on a chip with an area of several square millimeters at a very low consumption of materials and electricity.
Secondly, digital methods of signal transmission can increase the bandwidth of communication channels. At present, broadband transmission media such as optical cables have been developed. However, to fully realize the bandwidth of an optical cable, noise immunity is required, which is inherent only in digital technology. The low efficiency of the use of subscriber lines can be improved by their digital multiplexing. Data with different bit rates can be transmitted much more efficiently using digital technology transmission than analog. digital methods in one stream voice, data and image signals can be transmitted, as well as control and monitoring signals for establishing connections in the network.
Third, digital techniques enable complex signal processing. The coding of analog signals makes it possible to implement their digital processing and significantly reduce redundancy, and the use of inexpensive microprocessors and microcomputers provides the possibility of more complex processing. Digital information can be stored quickly without distortion in digital memory, which is now becoming cheaper and allows more efficient use of network equipment and provides benefits such as signal regeneration and transmission rate changes.

Finally, digital methods provide the best conditions for interaction with computers and user terminals.
Principles used to build a communication network as a whole, depends on many factors. These include:

· national network capacity;

· the area of the territory covered by the communication network;

· administrative division of the country;

· structure and organization of technical operation of communication facilities and networks;

· technical means and technologies that are used to build a network and provide services;

· the need for communication services.

With this in mind, there are two general principles building a communication network:

· multilevel;

· two-level.

The multilayer principle was developed for analog communication networks.
The two-level principle is typical for 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 apply:

· the size of the zone should be such that for a long time (50 years) it is not necessary to change the numbering system within the zone;

· within the numbering zone, a significant part of the exchange that occurs on the network should be closed;

· The capacity of the numbering zone should not exceed 8 million numbers.

Given the above, the boundaries of the zone, as a rule, coincide with the administrative boundaries of regions, territories, and republics. It is allowed, if necessary, the formation of several zones on the territory of the region, territory, republic.
Currently, 81 numbering zones have been formed on the territory of Russia. Most of them were created within the borders of the region or republics. But in some areas two zones and even three have been created. For example, four zones have been created on the territory of the Moscow Region - 495, 496, 497.499.
Within the numbering zone, local telephone networks (GTS, STS, TS) and an intrazonal telephone network (VzTS) are created, which is designed to connect various local telephone networks within the numbering zone and access the user of local networks to the long-distance telephone network (MGTS). Local networks and intrazonal networks of the numbering zone form a zone telephone network (ZTN). Zonal telephone networks of different zones are interconnected using the long-distance telephone network (MGTS). Zonal and long-distance telephone networks form the National Telephone Network of Russia. The national networks of different states are interconnected using the international telephone network (ISTN).
The development of information technology makes it possible, taking into account the needs of users in a wide range of telecommunication services, already at the present time to create fully digital broadband communication networks. As calculations show, for effective use means of communication, solving problems of the quality of service provision, the multi-level principle of building broadband networks is inappropriate.
Therefore, to build broadband communication networks, called multiservice networks, a two-level construction principle was proposed. The two-tier principle involves the creation within the national network, as well as the world, access networks and transport network.
Access network- a communication network that provides connection of terminal devices (multifunctional) to the terminal node of the transport communication network.
transport network communication is a network that provides the transfer of different types of information using various transmission protocols.

8.2 Classification of telecommunication networks

Classification of telecommunication networks by 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 based on a systematic approach, to evaluate the role and importance of each network in the process of informatization of society and the country's economy. This will make it possible to compare networks with each other, develop requirements for networks and create networks with specified characteristics. Networks included in the ESE can be classify on the following grounds:

· types of transmitted information;

· territorial basis;

· accessories;

· channel organization;

· scope for the provision of services;

· message delivery method;

· the level of service integration;

· type of transmitted signal;

· the way messages are distributed;

· functional feature;

· subscriber mobility;

· numbering codes;

· type of distribution medium;

· scope of services provided;

· network structure.

By type of information transmitted networks are divided into telephone, telegraph, data transmission, computer networks, signal networks, etc.

The unified telecommunication network of the Russian Federation consists of Russian Federation telecommunication networks of the following categories:

· public communication network;

· technological communication networks;

· dedicated communication networks;

· special purpose communication networks.

Public Communications Network (PSTN) is intended for the provision of paid telecommunication services to any user on the territory of the Russian Federation. It includes telecommunication telephone networks that are geographically defined within the service area and numbering resource and not geographically defined within the territory of the Russian Federation and the numbering resource, as well as networks designed to provide other communication services to the population.
The public communication network is a complex of interacting telecommunication networks, including communication networks for the distribution of radio broadcasting programs, television broadcasting and multiservice networks.
The SSOP network is connected to public communication networks of foreign states.

Dedicated communication networks (VSN). They are communication networks designed to provide telecommunication services to a limited circle of users or groups of such users. VSS can interact with each other. VSS, as a rule, do not have access to the public communication network, as well as to the SSOP of foreign states. Technologies and means of communication of dedicated communication networks, as well as the principles of their construction, are established by the owners or other owners of these networks.
The VSN network can be connected to the SSTN with transfer to the category of a public communication network if the VSS meets the requirements established for the SSTN. In this case, the allocated numbering resource is withdrawn and the numbering resource is provided from the SSOP numbering resource. The provision of communication services by operators of dedicated communication networks is carried out on the basis of appropriate licenses within the territories specified in them.

Technological communication networks (TCN) designed to ensure the production activities of organizations, management of technological processes in production. The technologies and means of communication used to create technological communication networks, as well as the principles for their construction, are established by the owners or other owners of these networks. If there are free resources of the technological communication network, a part of this network can be connected to the SSNS network with transfer to the SSNS category to provide paid services communication to any user on the basis of the appropriate license. Such connection is allowed if:
- Part of the technological network intended for connection to the SSOP can be technically, or programmatically, or physically separated by the owner from the technological network.
- The part of the technological communication network connected to the SSTN meets the requirements for the functioning of the SSNS.
The part of the TSS attached to the SSDN is allocated a numbering resource from the SSNS numbering resource. National TSS networks can be connected to TSS networks of foreign states to ensure a single technological cycle.

Special Purpose Communication Networks (SSSN) designed for the needs of public administration, national 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 a category of networks limited use (OGP).

On a territorial basis networks are divided into local, intrazonal, intercity, international, regional, interregional, backbone. The specified sign is used for primary networks, secondary networks, for networks of individual operators and operators of interregional companies.

Ownership sign determines the owner of the network. It can be the state, an individual, a joint-stock company, organizations and individual enterprises.

Channel organization distinguish between primary and secondary networks.

By scope for the provision of services, telecommunication and infocommunication networks can be distinguished. telecommunications network consists of communication lines and channels, nodes and terminal stations and is designed to provide users with electrical communication. Infocommunication network designed to provide users with electrical communications and access to the information they need.

Message delivery method a distinction is made between circuit-switched networks and accumulation networks (message-switched and packet-switched networks).

By level of service integration networks are divided into several classes: monoservice networks, networks with a low level of integration, an average level of integration, and multiservice networks that provide an unlimited amount of services. The monoservice network includes the telegraph network. The networks with a low level of integration include the analog telephone network. Networks with a medium level of service integration include the N - ISDN network, a 2G mobile communication network. The multiservice network is a new generation NGN network.

According to the form of transmitted signals networks are divided into analog, analog-digital and digital.

By way of message distribution Networks are divided into: switched, non-switched, circular communication.

On a functional basis Distinguish between access networks and transport networks.

By mobility of subscribers fixed and mobile networks can be distinguished. Fixed-line subscribers have fixed terminals, unlike mobile network subscribers.

by numbering codes networks are divided into geographic (ABC codes) and non-geographic (DEF codes) area networks. The use of these codes is associated with the creation of dedicated, including mobile networks, on the network of the Unified Energy System of the Russian Federation.

By type of distribution medium used networks are divided into wired, radio networks and mixed. In turn, radio networks are divided into terrestrial and satellite networks.

By the volume of services provided it is possible to single out networks that occupy a significant position (pass more than 25% of traffic and have more than 25% of the installed switching capacity of the total network capacity). Such a network owns dominant telecom operator.

An important classification feature is network structure connections. Figure 8.3 shows typical network structures that differ from each other in the number of communication lines, the nature of the interaction of nodes, the connectivity of nodes, etc.

Fully connected network ( rice. 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 = N-1.

tree network(Fig. 8.3b). In such a network, there can be only one path between any two nodes, i.e., a single-connected network h \u003d 1. The number of communication lines in such a network is N - 1. Particular cases of a tree network are: radial node network (Fig. 8.2c) , a star network (Fig. 8.3d) and a linear network (Fig. 8.3e).

Loop (stub, ring) network (Fig. 8.3e). In it, the number of communication lines is N, and between each two nodes there are two paths (h = 2).

Mesh - network-like network(Fig. 8.3 g - m). In such a network, each node is adjacent to only a small number of other nodes. The choice of one or another network structure is determined, first of all, by economic indicators and requirements for the reliability and survivability of the network.

Figure 8.3 Structure of different types of networks

8.3 Access networks

At present, the division of the communication network into two parts is gaining recognition: the transport network and the access network. The transport network is represented by intercity and intrazonal communication networks. The access network is represented by local networks and is designed to connect a variety of subscriber terminals to the transport communication network.
Figure 8.4 shows a model of a promising telecommunications system and the location of a subscriber access network.
The first element of the telecommunications system is a set of terminal and other equipment that is installed in the subscriber's premises.

Figure 8.4 Telecommunication system structure

Second element subscriber access network. Typically, a switching station is installed at the junction point of the subscriber access network with the transit network. The space covered by the subscriber access network lies between the equipment located at the subscriber's premises and this exchange.

In a number of works subscriber access network is divided into two sections:

· subscriber lines (AL) are considered as individual means of connecting terminal equipment;

· transfer network, which serves to improve the efficiency of subscriber access.

Third element telecommunication system - transport network. Its functions consist in establishing connections between terminals included in various subscriber access networks, or between a terminal and means of supporting any services.
The fourth element of the telecommunications system is means of access to services which provide users with access to various telecommunication services.

Development of subscriber access

Significant qualitative changes inherent in the modern telecommunications system have affected one of the most conservative elements of the telecommunications network - the subscriber line (SL). A feature of the modern telecommunications system is that the role of AL and the principles of its creation are changing 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. In the technical literature, a new term, already adopted in international standards and recommendations, has appeared - "Access Network" - "access network". The subscriber access network consists of two main elements. The first element of the access network is a collection of ALs, and the second element is a transfer network. Most often, ALs are associated with an individual two-wire circuit that provides information exchange in the voice frequency (TF) bandwidth. The transfer network is designed to reduce capital costs for line-cable facilities within the subscriber access system. This fragment of the access network is implemented on the basis of transmission systems and, in some cases, load concentration devices. In a particular case, the transfer network may be absent. Then, the concepts of AL network and access network (AN) become identical.
The subscriber access network can be considered as a combination of a primary network and several secondary networks. It should be emphasized that in the process of development of telecommunications, the differences between the primary network and secondary networks are becoming less noticeable.