Modernization of the site zonal networks Stepnogorsk-Kokshetau based fiber-optic line

(2.8)

When = 0 for each of the solutions of equation (2.6) there is a critical value of the normalized frequency (m = 1, 2, 3, ..., n = 0, 1, 2, 3 ...):

etc.

For HE11 mode critical normalized frequency. This fashion spread at any frequency, and structural parameters of the fiber and is a fundamental step fashion agents. Choosing options OM can be achieved only mode of propagation of this mode, which is subject to:

(2.9)

The minimum wavelength at which propagates in the fundamental mode OM, called Fiber cutoff wavelength. The value is determined from the last expression as:

(2.10)

2.1.5 Single-mode optical fiber

Single-mode fiber are subdivided into staggered single-mode fiber (step index single mode fiber) or standard fiber SF (standard fiber), to fiber dispersion shifted DSF (dispersion-shifted single mode fiber), and fibers with a non-zero dispersion-shifted NZDSF (non-zero dispersion-shifted single mode fiber).

In stepped a single-mode optical fiber (SF) (Figure 2.3) the diameter of the light-carrying core is 8-10 microns and is comparable to the wavelength of light. In such a fiber at a sufficiently high light wavelength л> лCF (лCF - cutoff wavelength) covers only one ray (single mode). The single-mode optical fiber mode is realized in the transparent windows 1310 nm and 1550 nm. Spread only one mode eliminates modal dispersion and provides a very high bandwidth single-mode fiber in these windows transparency. The best mode of propagation viewpoint of dispersion is achieved in the vicinity of wavelength 1310 nm, when the chromatic dispersion becomes zero. From the point of view of the losses is not the best transparency of the window. In this window, the loss is 0.3 - 0.4 dB / km, while the smallest attenuation of 0.20 - 0.25 dB / km is achieved in the 1550 nm window.

Figure 2.3 - Profiles of the refractive index

The single-mode optical fiber, dispersion-shifted (DSF) (Figure 2.3), the wavelength at which the dispersion becomes zero - zero dispersion wavelength л0 - biased transparency window of 1550 nm. This shift is achieved thanks to the special profile of the refractive index of the fiber. Thus, in the dispersion-shifted fiber with the best performance are realized both in minimum dispersion, and the loss at a minimum. Therefore, such a fiber is better suited for the construction of long segments with a distance between repeaters to 100 km or more. Of course, only the working wavelength is taken close to 1550 nm.

A single mode optical fiber having non-zero offset NZDSF dispersion unlike DSF optimized for transmission than a single wavelength and multiple wavelength (multiplex waveform), and most effectively be used in the construction of highways "all-optical networks" - networks to nodes which are not optoelectronic conversion takes place in the propagation of the optical signal.

Optimization of these three types of single-mode OB does not mean that they should always be used exclusively for specific tasks: SF - signal transmission at a wavelength of 1310 nm, the DSF - signal transmission at a wavelength of 1550 nm, NZDSF - multiplex signal transmission in the window 1530-1560 nm. For example, multiplexed signal in 1530-1560 nm window can be transmitted stepwise and standard single mode fiber SF [6]. However, the length of hop without using SF fiber will be less than using NZDSF, or otherwise require a very narrow spectral emission band laser transmitters in order to reduce the resultant chromatic dispersion. The maximum allowable distance is determined by the specification of both the fiber (attenuation, dispersion), and transceiver equipment (power, frequency, spectral broadening of the transmitter radiation, receiver sensitivity).

The most widely used fiber-optic fibers following standards:

- Multimode gradient fiber 50/125;

- Multimode gradient fiber 62.5 / 125;

- Single-mode fiber is a step SF (fiber unbiased variance or standard fiber) 8-10 / 125;

- A single-mode dispersion shifted fiber DSF 8-10 / 125;

- Single-mode fiber with a non-zero dispersion-shifted NZDSF (the profile of the refractive index of the fiber is similar to the previous type of fiber).

2.1.6 Constant distribution and phase velocity

The wave number k can be viewed as a vector whose direction coincides with the direction of light propagation in bulk media. This vector is called the wave vector. In a medium with a refractive index equal to the magnitude of the wave vector. In the case of light propagation inside the waveguide light propagation direction coincides with the direction в of the projection of the wave vector k, on the axis of the waveguide:

(2.11)

Where - the angle complementary to the angle of 90 i (or the angle between the beam and the axis as shown in Figure 2.4); в - it called constant propagation and plays the same role as the waveguide in the wave number k in free space so as , in accordance with the formula 2.11, i and wavelength dependent [16].

Figure 2.4 - The wave vector and the constant spread

The angle of incidence varies between and р / 2. Consequently:

(2.12)

Thus, the magnitude of propagation constant inside the waveguide always lies between the values of wave number plane light waves in the material of the core and cladding. If we consider that it is possible to rewrite this relation in terms of the phase velocity:

(2.13)

The phase velocity of propagation modes concluded between the phase velocity of the waves in the two bulk materials.

The speed of propagation of the light signal or the group velocity - is the speed of propagation of the light pulse envelope. In general, the group velocity u is not equal to the phase velocity. The difference of the phase velocities of modes leads to distortion of the input light beam as it propagates along the fiber.

The fiber with a parabolic refractive index gradient oblique rays propagate along a curved trajectory which is naturally longer than the propagation path of the axial ray. However, because of the refractive index decreasing with distance from the axis of the fiber, the velocity of propagation of the light signal components when approaching the optical fiber cladding increases, so that the resulting propagation time constituting at RH is approximately the same. Thus, the variance or change in the propagation time of the different modes are minimized, and the width of the fiber bandwidth increases. Exact calculation shows that the difference in group velocities of the various modes in such a fiber is substantially less than in the fiber with a step refractive index profile. Optical fiber that can support the spread of only the lowest-order mode, called single-mode.

Thus, each mode propagating in OM, characterized by constant along the fiber length distribution of intensity in the cross section of the propagation constant в, and v of the phase and group velocities u propagation along the optical axis, which are different for different modes. Due to the difference of phase velocities of the modes of the wave front and the field distribution in the cross-sectional change along the fiber axis. Due to different modes of group velocities of light pulses widen, and a phenomenon called modal dispersion.

The single-mode fiber there exists only one mode of propagation, so such fiber is characterized by a constant field distribution in the cross section, it does not intermode dispersion, and it can transmit radiation with a very broad modulation bandwidth limited only other kinds of dispersion [13].



2.1.7 Calculation of the main characteristics of the fiber optic link

OK Quality checked using conventional measurement methods. If you have a single-mode Sun bends or connections, the mode field diameter size is an important factor influencing the damping characteristics. Thus, increasing the mode field diameter leads to deterioration of light transmittance in the bends, but reduces the loss of detachable and non-detachable joints [17].

Calculation of the numerical aperture of the optical fiber. The most important parameter of the generalized optical fiber is the aperture.

The numerical aperture - the angle between the optical axis and forming a cone of light entering the optical fiber end, wherein the condition of total internal reflection.

We calculate the index of refraction n2 shell. Based on optical characteristics of the cable numerical aperture NA = 0,11.

It is known that:

, (2.14)

where n1 - according to the formula 2.1 core refractive index equal to 1.4681, then

n2=, (2.15)

n2=

The calculation of the normalized frequency. The most important parameter of the generalized optical fiber used for the evaluation of its properties, is the normalized frequency V (Formula 2.8).

In practice, this option is determined by the expression:



V = , (2.16)

where a - core shell radius a = 4.5 m; n1 - the refractive index of the core, n1 = 1,4681; n2 - (according to 2.15), the clad refractive index, n2 = 1,4639, then

V = = 2,3741.

The calculation of the cable parameters, based on the fact that we have a single-mode fiber with a step refractive index profile with a core diameter 2a = 9mkm and critical wavelength = 1250 nm, the mode diameter 20 field at a wavelength of 1310 nm [14]:

20 2a, (2.17)

where - working wavelength, = 1310 nm; с - critical wavelength above which the fiber is sent to only the fundamental mode, с = 1250 nm; Vc - normalized critical frequency for single-mode Vc = 2,405.

20 9 = 10,196 mcm.

This means that it is possible to select OF core with a diameter of 10 microns. Given that the fiber boundary between two media core - shell are transparent glass, perhaps not only a reflection of the optical beam, and its penetration into the skin. To prevent the transition energy to the shell and radiation into the environment must observe the condition of total internal reflection and aperture [16,17].

It is known that the transition from a medium with a higher density in the environment with lower density, that is, when n1> n2, wave at a certain angle of incidence is totally reflected and passes into another medium. The angle of incidence at which all of the energy is reflected from the boundary between two media, while wp =v in, is called the angle of total internal reflection:

, (2.18)

where m and h -, respectively, and the dielectric core magnetic permeability (m1, e1) and shell (m2, e2).

When wp <v in the refracted beam passes along the boundary between "core - shell" and not emitted into the surrounding space.

When wp>v in the energy received by the core is completely reflected and propagates through the optical fiber. The greater the angle of incidence, wp>v in the range of up to 90 degrees in the better propagation conditions and the faster the wave comes to the receiving end. In this case, all energy is concentrated in the fiber core and substantially no emitted into the environment. When the beam angle of incidence smaller than the angle of total reflection, wpv <a, the energy penetrates the membrane, is emitted into the external space through the optical fiber transmission and inefficient.

Total internal reflection mode determines the supply condition of the light on the front end of the optical fiber. Fiber optic transmits only light enclosed within a solid angle v, the value of which is due to the angle of total internal reflection inv. This solid anglev characterized by a numerical aperture.

Between the angles of total internal reflection v in the beam aperture angle v and fall and there is a correlation. The greater the angle v, the smaller the aperture v of a fiber. It seeks to ensure that the angle of incidence on the boundary core - shell wp was greater than the angle v of total internal reflection in and ranged from v to 90 degrees and the angle of the input beam to the end face of the fiber w fit into the aperture anglea (w <a) .

We find kritichesry с angle at which the condition of total internal reflection:

с= (2.19)

с=

Knowing the indicators of refraction n2 shell and core n1 calculate the relative refractive index difference :

(2.20)

The calculation of the length of the regeneration area. The calculation of the length of the regeneration area () is an important section of the design. To provide a better quality of information transfer and saving of costs is preferable that a maximum. The amount is determined mainly by two factors: the loss and dispersion in the optical cable. The most promising in this respect are systems with single-mode fiber (AF) and a wavelength of 1.3. . .1,55 That for small losses it possible to obtain a high information capacity. Determination of length FOL regenerator section is based on a predetermined communication quality parameters and line capacity after the selected transmission system and a typical optical cable. The quality of communication in the digital transmission systems in the first approximation, determined by the level of fluctuating noise at the input of the photodetector and inter-symbol interference, that is, pulses overlap with their broadening. With increasing length of the line broadening of the pulses, characterized magnitude, increases, the probability of error increases. Thus, the length of the regeneration area limited either attenuation or pulse broadening in line.

For undistorted receiving PCM signals sufficient to fulfill the requirement:

(2.21)

Where - the duration of the clock period PCM signal; - pulse duration; - the resultant dispersion or:

(2.22)

where - the clock frequency of the signal line.

If the pause is sending duration, then:

(2.23)

i.e. pulse broadening waveguide past one section does not exceed half the length of the clock interval. These conditions determine the first estimated the ratio to determine the permissible length of the regeneration of the area:

- , (2.24)

or:

(2.25)

where - the resultant dispersion, as selected single-mode cable, the mode dispersion not consider. In singlemode optical fibers the resultant value is defined chromatic dispersion of the dispersion:

(2.26)

where () - material dispersion; () - Wave dispersion.

Material dispersion () - the material dependence of the refractive index on the wavelength. With increasing wavelength dispersion coefficient decreases:

(2.27)

where - the width of the spectral line of the radiation source, which is equal to 0,14 laser (for technical data on our equipment = 1,8); M () - specific material dispersion of silica glass is -20.

=

The wave dispersion () - dependence of the propagation coefficient of the wavelength:

(2.28)



where B () - Specific wave dispersion for quartz glass is 10

=

Summarizing the material and waveguide dispersion, chromatic or obtain the resulting dispersion:

(2.29)

This value is close to the technical data of the equipment and cables.

We find the permissible length of the regeneration of the area:

The second calculated ratio can be obtained by considering that the useful signal power at the input of the detector should not be less than the specified minimum permissible power , which provides a necessary reliability of signal transmission:

where - the power level of the radiation generator; ; - loss of detachable connections (used to connect the receiver and the transmitter to the UK); , - losses at the input and output of radiation from fiber; ; - loss of permanent connections; ; - attenuation of the optical fiber; ; - construction length OK.

The value is the name of the power equipment capacity and depends on the type of the selected light source and a photodetector:

(2.31)

The energy potential of taking passport data of the selected equipment. It is equal to = 31 .

The length of the maximum regeneration area defined by lines of weakening can be obtained from the relationship:

(2.32)

where - the average value plus 6;- 0.5; ,- 1,0;

- 0.1; - 0.22; - 4 km ; - (-36) (For the type of photo detector); m- System supply FOTS attenuation in the regeneration area.

System margin takes into account changes in the composition of the optical cable due to the appearance of additional (repair) of inserts, welded joints, as well as changes caused by environmental exposure to optical cable characteristics of the environment and the deterioration of optical connectors, quality for life, and is set in the design FOTS on the basis of its destination operating conditions and service provider, in particular based on statistical damage (breaks) in the cable operator's service area. Recommended range of values ??set by the system reserve of 2 (the most favorable operating conditions) to 6 (worst-case operating conditions). These data are taken from the data sheet for the equipment [25].

Specifies the maximum length of the regeneration section, according to the formula (2.32):

Therefore, for single-mode fiber length depends on the regeneration site attenuation, but the calculation is performed with some margin, so more than in the technical specifications of the equipment manufacturer, which may be because the span calculation. It may not have been taken into account some parameters changed by the manufacturer in the design and manufacturing techniques that may be a trade secret, the use of cable with less attenuation.

Length between OP-1 (Stepnogorsk) and OP-2 (Kokshetau) is 251, which exceeds the maximum = 98.4, therefore, must be installed on the cable line URP (SRP).

Therefore, you must choose a location point of the regeneration that it satisfies the requirements of regeneration, and preferably located in the village, to ensure a constant supply of stationary equipment. In this case, it takes two regeneration points, to fit such requirements pos. Saule and g.Schuchinsk.

2.2 Digital transmission systems

2.2.1 The concept of building a modern transmission systems

The development of science and the acceleration of technological progress is not possible without improving communications, data collection, transmission and processing of information.

Intensive development of new information technologies in recent years has led to the rapid development of microprocessor technology, which stimulated the development of digital transmission techniques.

Ultimately, this led to the creation of new high-speed WAN technologies: PDH, SONET, SDH, ISDN, Frame Relay and ATM.

One of the most advanced technology currently used for the construction of communication networks is the technology SDH synchronous digital hierarchy.

Interest in the SDH due to the fact that this technology has replaced the PCM pulse code modulation (PCM) and plesiochronous digital hierarchy of PDH (PDH).

Began actively implemented as a result of the mass installation of modern foreign digital PBX, allowing to operate with flows of 2 Mbit / s, and the creation of local regional SDH rings.

Synchronous Digital Hierarchy (SDH) has significant advantages over previous generations of systems, it allows you to fully realize the potential of fiber-optic transmission lines and create flexible, easy to operate and control the network, ensuring high-quality communications.

Thus, SDH concept allows optimally combine processes high-quality digital data transmission with automated management processes, control and network services in a single system.

SDH systems provide transmission speeds of 155 Mbit / s and above, and can be transported as digital signals of existing systems (eg, common on city network of PCM-30), as well as promising new services, including broadband.

SDH equipment is software-controlled and integrates the means of conversion, transmission, operational switching, control, control.

With the advent of modern fiber-optic cables (FOC) made possible a high transmission rate in linear tract (RT) digital transmission systems with a simultaneous lengthening of the regeneration sections up to 100 km or more.

Performance of LT exceeds the performance of digital paths in the cables with metal vapors 100 times or more that dramatically increases their cost-effectiveness.

Most repeaters it is possible to combine with the terminal or transit stations. From this it follows that the SDH - is not just a new transmission system, this fundamental change in network architecture management. The introduction of SDH is a qualitatively new stage in the development of digital communication network.

Therefore, the program of development of Kazakhstan in the long term the introduction of new information technologies belongs to one of the priority seats. Construction of fiber optic links in this area - the next logical step in the comprehensive modernization of communication of Kazakhstan, which will result in the creation of a powerful modern information network.

Advantages of fiber optic to copper lines are clear: high reliability and noise immunity, large data transmission speed, large bandwidth. FOTS raises means of telecommunications to a new, much higher level of development.

This reliable telephone service, Internet access and other global projects, the implementation of which is currently virtually impossible at this site. Introduction FOTS raise to a higher level and a secondary communication network, with a significant extension of new services which require broadband connections (e.g., network communication technology - video, video conferencing, industrial television, computer networks, operating in real time).

The planned fiber-optic route is intended primarily to provide customers high-quality communications. Advantages of fiber optic to copper lines are clear: high reliability and noise immunity, large data transmission speed, large bandwidth. FOTS raises means of telecommunications to a new, much higher level of development.

This reliable telephone service, Internet access and other global projects, the implementation of which is currently virtually impossible at this site. Introduction FOTS raise to a higher level and a secondary communication network, with a significant extension of new services which require broadband connections (e.g., network communication technology - video, video conferencing, industrial television, computer networks, operating in real time).

The planned fiber-optic route is intended primarily to provide customers high-quality communications.

2.2.2 Transmission systems of PDH, characteristic features

In modern networks are operated as a plesiochronous system and synchronous digital hierarchy systems.

Standard PDH - plesiochronous digital hierarchy. Hierarchy recommended for digital transmission systems, something like a calendar hierarchy. For this purpose it was necessary to select a certain unit of measure "e" bit rate common to all countries and companies that produce equipment of transmission systems and allows you to measure the speed of the total digital streams. This "unit" rate worldwide is digital speech transmission rate of 64 kbit / c. Channel on which are transmitted at 64,000 bits / s, is called the primary digital channel. Possibilities any digital transmission system estimates the number of organized with the help of just such standard channels.

Combining flows leveling speed has been called plesiochronous (nearly synchronous), and the existing hierarchy of speeds transmission of digital streams, and hence the type of PCM transmission systems (PCM) - plesiochronous digital hierarchy (in the English writing Plesiohronous Digital Hierarhi, PDH).

Plesiochronous digital hierarchy was developed in the early 80s. In the hierarchy of great hopes, but it was not very flexible in order to enter into the digital stream "rushing" at a high speed or low-speed output from it flows must be fully "embroider", and then "sew" high flow. This requires installation of a large number of multiplexers and de multiplexers. It is clear that to do this operation is often quite expensive.

The system uses the principle of PDH plesiochronous multiplexing, according to which for multiplexing, for example, the 4-E1 (2048 kbit / s) into one stream E2 (8448 kbit / s) alignment procedure is performed such frequency signals occurring by stuffing. As a result, when multiplexing is necessary to make a step by step process of restoration of the original channels. For example, in the secondary digital telephone networks the most common use of E1. When sending this stream for PDH networks tract E3 must first perform incremental multiplexing E1-E2-E3-step demultiplexing and then E2-E3-E1 at each point E1 channel allocation. This is a major drawback PDH equipment - due to the increase in the number of necessary equipment for the separation of one or two streams. E1 primary digital channel DSO combines 32 channels, of which one DSO used for frame synchronization, another - for signaling. Still this stream consists of 32 time slots of 8 bits each. Frame repetition frequency 8 kHz, which gives the flow rate of 32 * 8 * 8 = 2048 kbit / s.

The essence of the main drawbacks RDN is that the addition of equalizing bit makes it impossible to identify and output, for example, stream 64 Mbit / sec or 2 Mbit / s "hardwired" into the stream of 140 Mbit / s without complete demultiplexing or "embroidered" of this stream and removing leveling bit. One thing to "drive" the flow of long-distance or international calls from one call center to another "mixing" and "bark" them quite rare.

Another thing - to connect several banks and / or their separation via PDH network. In the latter case often have to either output stream 64 kbit / s and 2 Mbit / s from the flow of 140 Mbit / s to make it, for example, a bank branch, or vice versa to output a stream of 64 kbit / s and 2 Mbit / s from the bank for putting it back into the flow of 140 Mbps, the implementation of such a step input \ conclusion have to spend quite a complex operation the three-level demultiplexing ( "bark") PDH signal removing \ adding leveling bit (all three levels) and his subsequent three-level multiplexing ( "stitching") adding new leveling bits. the alarm. However, these tools are too weak.

If you have many users that require input \ output source (of 2 Mbit \ s) for the instrumental implementation of network flows require an excessively large number of multiplexers, as a result of operation of the network becomes economically advantageous.

Another bottleneck technology PDH - weak capacity in the organization of channels for purposes of control and flow control in the network and the almost complete absence of routing funds grassroots multiplexed streams, which is essential for use in data networks. Typically, for the purposes of identification and subsequent signaling flow is divided into groups of time slots or frames, which are then assembled in groups of several frames or multiframe. The latter, allowing the identification of the receiving side of the individual frames are supplied with additional bits of cyclic error-correcting codes and used PDH frames and multiframes increases (with an increase in the number of multiplexing and switching streams for routing), the possibility of error in tracking the "history" of current switching, and hence increases and the possibility of "losing" information not only about the current switching, but also about his "history" in general, which leads to disruption of routing all traffic scheme. So it would seem essential advantage of the method - a small "congestion headings" (Recommendation G.704 does not provide for the necessary for normal routing headers) - in fact, turns into another serious shortcoming as soon as there is a need for advanced routing, network PDH caused by the use of data .

And so, a number of shortcomings PDH:

-hard input / output digital streams at intermediate points;

-no funds network of automatic monitoring and control;

-multistage restore the presence of three different hierarchies.

2.2.3 SDH Standard

These shortcomings RDN and a number of other factors led to the development in the United States is still one of the hierarchy - the hierarchy of SONET synchronous optical network, and in Europe Analytical SDH synchronous digital hierarchy, proposed for use in the fiber optic link. But due to unfortunate selected baud rate for STS-1, the decision was made - to abandon the creation of the SONET, and to create an it-based SONET / SDH at a rate of 51.84 Mbit / s of the first level of the SDH OC1. As a result, the NEO SONET / SDH STM-1 corresponds to the SDH hierarchy. Transmission speed SDH hierarchy presented in Table 3.1.



Table 3.1 - SDH hierarchy bit rates

SDH level	Transmission speed Mb / s
STМ-1	155,520
STМ-4	622,080
STМ-16	2487,320

SDH - Synchronous Digital Hierarchy. SDH - is a set of digital structures, standardized for the purpose of transporting it necessary to adapt the load on the physical network. SDH - calculated as a transport signal existing PDH, with the speed specified in recommendation G.703 as the signals of new broadband services. At the same time significantly increase the reliability and survivability of networks, their flexibility, quality of communication, Linear SDH signals are arranged in a so-called synchronous transport modules STM. The first of these STM - 1 corresponds to the speed of 155 Mbit / s. Each subsequent rate is four times greater than the previous one and formed by a synchronous byte multiplexing. Already standardized STM - 4 (622 Mbit / s) and STM - 16 (2.5 Gbit / s).

In the SDH network using the principle of container traffic to be pre-arranged transportation of signals in standard containers C. All operations are performed with the containers, regardless of their content. This ensures the transparency of the SDH network, it is possible to transport a variety of SDH signals, streams of ATM cells, or any new signals. There are four levels of containers. All of them, together with SDH signals placed in them are listed in Table 3.

Table 3.2- SDH containers four levels

Level	Container	SDH signal Mbit / s
1 2 3 4	С-11, С-12 С-2 С-3 С-4	1,5; 2 6 34 and 45 140



An important feature of SDH network is to divide it into three functional layers, which are subdivided into sublayers (Table 3.3). Each layer maintains the overlying layer and has a certain access point. Layers have their own control and management tools, simplifies operation on liquidation of consequences of failures and reduce their impact on the overlying layer. The independence of the layers enables you to implement, upgrade or replace them without affecting other layers.

Table 3.3 - SDH division into functional layers

Layer	Sublayer
Channels Paths	Lower order
	Higher-order
Transfer funds	Multiplex Section Regeneration
	Physical Environment: Fiber optic, radio relay link, copper cable

The most important for the following discussion are network layers: channels, paths and sections, a network of canals - a layer that serves the user's own. These terminals are connected to the sets of SDH terminal equipment trunks. channel network connects different sets SDH terminal equipment through the switching station.

Channel groups are combined in different orders group paths, forming a network of paths. There are two paths of network layers (from top to bottom over SDH hierarchy) of the lower and higher order. The layer paths provide software and remote monitoring and control connections. All the paths end at operational switching equipment, part of the SDH multiplexers.

Group paths are organized in line, the construction of which depends on the transmission medium (OM, RRL). This network transmission layer. It is divided into two parts: a layer sections (upper) layer and a physical medium. The network layer is divided into two sections. The top layer is a multiplex section (MS). MS - provides transfer of information between the points where terminate or switch paths. The bottom layer of regeneration section (RS) - provides the transfer of information between the regenerators and the end points or switching paths. New digital hierarchy was conceived as a high-speed.

Application of SDH-technology:

- Transportation of data streams in the ATM networks. This SDH equipment transmits the signal over long distances, carries ATM Cross Connect - streams and allows you to organize the ATM network with complex topology, even for a linear arrangement of ATM switches;

- The transfer of a large number of E1. Primary E1 digital circuit 32 combines the channel DCO (main digital channel), one of which is used to DCO frame synchronization, another - for signaling. This stream frame consists of 32 time slots of 8 bits each. Frame repetition frequency 8 kHz, which gives the flow rate of 32 x 8 x 8 = 2048 kbit / s.

- Creation of fail-safe transport networks with a fast recovery time performance (on this indicator SDH significantly superior to other technologies).

With the spread of SDH - technology, when combined networks of various operators sharply there is a problem of global synchronization of nodes, and this point should not be underestimated.

The trend of recent years - the replacement of currently existing PDH SDH networking systems, as well as the use of not only the operators of technology, but also for the construction of highways corporate information systems.



3. Working documents

3.1 Proposals for the selection of equipment for communication

3.1.1 The main function module SDH networks

The main function module is a multiplexer SDH networks. The term itself is used as a multiplexer for the multiplexers that are used to build (multiplexing) a high speed flow of the low-speed and disassembly (demultiplexing) the high-flow in order to separate low-speed streams.

SDH multiplexers in contrast to conventional multiplexers are used, for example, in the PDH network, as a function properly operate the multiplexer and the terminal access function devices, allowing low-speed channels PDH connect directly to their input ports. They are more versatile and flexible devices that perform tasks other than multiplexing and switching problems still, concentration and regeneration. Accepted, however, to distinguish two main types of multiplexer: terminal multiplexer and the multiplexer input - output.

Terminal Multiplexer (TM) is a multiplexer and terminal SDH network with the access channels, the appropriate tribes PDH and SDH. TM can be administered or channels, that is, switch them with tribnogo interface input to line input or output channels, that is, switch them with a linear input to output tribnogo interface. Typically, this is limited to switching tribes 1,5 and 2 Mbit / s.

Another important feature of the multiplexer is the presence of two optical line outputs (reception / transmission channels), called aggregate outputs and used to create one hundred percent redundancy mode, or the protection of 1 + 1 in order to increase reliability.

The multiplexer input / output (ADM) has the same inlet tribo set as a terminal multiplexer. It allows you to enter and display the corresponding channels. In addition to switching capabilities provided by TM, the ADM allows a through switching output streams in both directions, as well as to the closure of the channel on the receiving channel on both sides in the case of failure of one of the directions. Finally, it allows (in case of accidental failure of the multiplexer) to skip the main optical flow by themselves in the bypass mode.

Consider options for the acquisition of synchronous multiplexers: SDM-1 (ECI Telecom, Israel), SMA-1 R2 (Siemens, Germany) and FOX-1640 (Alcatel, Germany). The comparison results are summarized in Table 1 [PV].

Currently, due to the high saturation of the market of telecommunications, equipment selection problem ceases to be purely technical and economic challenge and becomes a component of policy makers in relation to suppliers.

In this thesis project we propose to use the SDM-1 equipment company ECI Telecom (Israel), because this site is part of a single zone network route Stepnogorsk-Kokshetau.

Multiplexer SDM-1 consists of the following sections (Table 3.1):

Table 3.1-SDM-1 multiplexer Sections

Name of section	Design
TR #1 - TR #8	board component interfaces
ATR	two transmitter / receiver aggregate fee including: optical charge - ATRO and electrical charge - ATRE;
SPU	two SDH processing unit
MCP4	the control Multiplexer processor (with integrated non-volatile memory NVM);
COM	connection fee
AMU1	block signaling and notification service

Each SDM-1 is a unit located on the same shelf, which may contain from 21 to 63 component interfaces with a transmission speed of 2 Mbit / s, three - 34 Mbit / s, three - 45 Mbit / s, one - 140 Mbit / s or one - 155 Mbit / s (STM-1), and certain combinations of these interfaces. Since STM-1 standard allows a maximum of 155 Mbit / s aggregate line, the number of supported component interfaces (with protection) in a given moment of time is more limited: either 63 to 2 Mbit / s, three 34 Mbit / s, three 45 Mbit / with one 140 Mbit / s, a completely filled 155 Mbit / s, four partially filled with 155 Mbit / s, or some combination of these interfaces, in an amount not exceeding the STM-1 rate.

Using two modular line in an unprotected mode, you can increase the total number of supported component interfaces. In addition, SDM-1 provided more bandwidth can serve the purpose of dynamic allocation in response to changing traffic requirements.

Aggregate interfaces provide access to the lines connecting the mounting location of various SDM-1. The interface works with SDH data rate STM-1 (155.52 Mbit / s). When combined with a fiber-optic cables 1 from one another SDM SDM system 1 located in a remote location using optical aggregate interfaces. At shorter distances in this connection, instead you can use the optical electric aggregation channel.

Eight slots provided for component boards. Additional fees may give the opportunity to save on administrative costs because the network provider can place these or other additional fees in the system and enter them into operation as the demands from the traffic.

SDM-1 is monitored and controlled by the CPU, which communicates with the various parts of the system and the outside world. The system software is stored on the memory card that allows you to frequently and easily update the software by downloading from a remote source. Software communication management software is based on a seven-element model of OSI, working in a UNIX environment.

In normal operation, the system synchronizes to choose the source of synchronization. With this source connected a voltage controlled crystal oscillator, which generates an internal clock signal to SDM-1, and the time for SDH transmission line. This source can be an external timer signal, a component signal or SDH line signal. If synchronization sources are unavailable, SDM-1 is able to maintain standby mode with the stability of 4,6 ppm (parts per million).

SDM-1 is powered -48 or -60 VDC from the external battery system. The system's power structure implemented the principle of distributed architecture, ie, each card has its own built-in power supply. This achieves low cost and low power consumption in a partially filled SDM-1 configurations.

An important property of sequentially implemented in the system is its modularity. As already mentioned, all the component boards are completely interchangeable, and therefore can be installed in the same slots, regardless of the exchange rate supported by them.

SDM-1 architecture is similar to the architecture of the SDM-4 company ECI Telecom, which provides a family of products that are compatible with each other, and cost-effective in terms of maintenance and spare parts. Most boards are interchangeable with boards SDM-4, which makes it easy to modify the system.

Proposals on Timing of SDH network sources listed at the end of the explanatory note [PG].

3.1.2 Proposal for the selection of the radiation source and photodetector

There are two types of semiconductor light sources, light emitting diodes and lasers. For the fiber optic portion of Stepnogorsk Kokshetau, you need to select as a radiation source laser.

The laser has a high speed and a narrow spectrum width. From the family of semiconductor lasers is best to choose lasers with distributed feedback. These lasers operate in single-frequency mode, the emission spectrum width is less than 0.5 km. Temperature instability wavelength lasers with distributed feedback amounts to about OD km / k. The level of the output radiation, lasers powerful version highly varies within 3 to 6 dB m.

As the photodetectors in optical fiber communication systems using semiconductor p-i-n photodiodes and avalanche photodiodes. These devices are small and fairly well joined to optical fibers. The p-i-n photodiodes each absorbed photon creates a pair of "electron-hole". In avalanche photodiodes internal amplification of the signal occurs, since they are designed so that they formed a region with a strong electric field E (3 x 106 V / cm). In this field, the electrons generated by the light, are accelerated to energies sufficient to impact ionization of atoms of the crystal lattice. The resulting ionization of the free carriers is also accelerated and give birth to a new pair. This avalanche process leads to the fact that the absorption of a photon generates more than one electron-hole pair, and the tens and hundreds. Thus, by using a highly sensitive avalanche photodiodes as photodetectors version designed for fiber optic link, you can change the input level from - 39 to -17 dBm.

Using lasers with distributed feedback and avalanche photodiodes can get quite large regeneration areas that allow IUU fishing to place in the settlements. In Kazakhstan, the distance between the settlements can be up to 250 km. In this case, the power transmission system margin may be insufficient for covering this distance. In such cases it is possible to use optical amplifiers and preamplifiers.

The main equipment optical amplifying element is an optical waveguide fiber doped with erbium. Figure 1 shows a functional block diagram of an optical amplifier [PD].

Figure 2 is a functional diagram of an optical preamplifier. The input optical signal in a location with the pumping laser beam enters the optical fiber doped with erbium, wherein the light energy is redistributed between radiations [PD].

Further, through the optical isolator radiation enters the optical bandpass filter tuned to the operating wavelength, wherein the removal of parasitic modes occurs.

The input level varies from -45 dB to -15 m. In the case of using an optical preamplifier is used as a photodetector APD power standard. The output level changes from +12 to +15 dBm.

An optical preamplifier used in conjunction with an optical amplifier, while the optical amplifier can be used separately.

3.2 Welding questions, and measurement of the optical fiber connection

We have said that optical cables are manufactured certain dli¬ny called construction. Usually it does not exceed 4 ... 5 km (for transoceanic fiber optic - 50 km). optic line length in the overwhelming number of cases exceeds the building many times. Therefore optic cables laid in the sewer, the ground or hung on poles, you must so¬edinyat, t. E. To splice together. For this optical fiber end is freed from QA module length and 0.5 ... 1.0 m and interconnected "to¬rets-end" by means of welding or gluing.

Above it was said that optical cables are made of a certain length, which is called building. Usually it does not exceed 4 ... 5 km (for transoceanic fiber optic - 50 km). optic line length in the overwhelming number of cases exceeds the building many times. Therefore optic cables laid in the sewer, the ground or hung on poles, must be connected, ie. E. To splice together. For this optical fiber end is freed from OC module length and 0.5 ... 1.0 m and interconnected "butt-end" by means of welding or gluing.

To carry out welding or bonding, optical fiber length of about 1 mm from the end of the release of the containment, and then using a special tool - the cleaver produce shearing fibers. The purpose of this operation - to get a flat end perpendicular to the axis of 0V. Removing the shell 0V, release it from the module OK, cleaning of a hydrophobic gel and other necessary operations are performed using a set of tools placed in a special suitcase - case.

Fiber-to-end welding is carried out in a special welding machine. Modern welding machines for welding OB automatically perform the optimum mutual alignment RH choose the optimal welding parameters and monitor losses in spot welding. The welding process can be monitored visually in two coordinates on the liquid crystal display. These operations are carried out, for example, welding machine manufactured by FUJIKURA presented in Figure 3.1

Figure 3.1 - The welding machine manufactured by FUJIKURA

Place splicing spetsialnom fixed in the device, which is a heat-shrinkable tubing with a metal reinforcing rod, or in a special clip - metal V-shaped bracket.

United thus the optical fibers are placed in special trays, and they in turn in a special container, which is also fixed to those ends OK sections where it is not removed the protective outer shell. Such a container is called the optical coupling. There are various designs optical coupling. Figure 3.2 shows the optical coupling FUJIKURA production, in Figure 3.3 - the KRONE optical coupler.

Figure 3.2- The optical coupler connecting production FUJIKURA

Figure 3.3 - Optical coupling KRONE firms

Measurement of loss in optical fibers and cables are currently engaged in one of two ways.

The first - a two-point measurement method, which is divided into three types - the breaking of the method, and the method calibrated hitless dispersion.

Of these, the most widely used as a hitless nondestructive measurement method. When measuring the attenuation or OB OK RH input end of the test cut in the optical connector. This connector is connected with the reference emitter stabilized optical power and wavelength. To the output end OM, as the split in the OR, connect a calibrated optical power meter. Since the reference value of the power of the radiation source is known - Rae, is counting losses in OB negligible, we can assume that Pr = Pin. The measured output power value - Pout. Attenuation OF or OC is determined from the relationship:

dB

Devices that produce such measurements are part of an optical tester. Optical testers are available in two versions:

- Option 1 - a reference transmitter and optical power meter is placed in a single package (eg, AQ215, company ANDO, Japan);

- Option 2 - a reference transmitter and optical power meter available in different housings, as two separate device (model K2702, K2503, K2505 and SIEMENS devices DIAMOND series, the company LONIIR, Russia and FOD, Russia).

Gauges of the power in these kits have two calibration - in power units of milliwatts and dBm (dBm - power level in dB relative to the magnitude Popt = 1 mW).

In practice it is more convenient to use the 2nd calibration. At the same time measure the power level of the transmitter output in dBm, then - the power level at the output of OB or OK. Subtracting the second reading of the first, to give the desired result.

The described method of measurement accuracy differs. Its main drawback - the need for access to both ends of the OK, it is often inconvenient for linear measurements.

Currently, the most widely used method of attenuation reflectometry measurements based on the measurement of that part of the Rayleigh scattering in the OB, which is circulated in the opposite direction (reverse). For this purpose, the fiber is introduced periodic sequence of optical pulses of duration and repetition period T. At the same time to the input end OM will return pulses at each time point. These pulses time lag from the input (reference pulse), reflected from the input end planes for a period of time equal to the double pulse to travel - in forward and backward directions. If the x-axis represents time (starting from t = 0 to the reference pulse), and the vertical axis - the average values ??of the amplitudes of these pulses for each value of the time, you get the so-called trace.

If the attenuation coefficient and backscatter coefficient at a given A for the fiber under test is constant along its length, the curve (trace) decreases from the beginning of OB exponentially. Scattering - statistical process. Therefore, the value of the pulse amplitude (ordinate) for the same time axis values ??(distances) will have some dispersion in each count (with periodic repetition of the probing pulses). Due to the statistical averaging of a large number of samples can be obtained pure line (exponential) dependence of the damping of the length of OB. However, an exponential curve to use awkward and difficult. So after averaging each sample is subjected to the logarithm operation, resulting in exponential (decaying) becomes the slope of the line. Thus counts on the ordinate calibrated in decibels. In the case where the reverse attenuation and Rayleigh scattering coefficients have sharp local change that indicates the presence of local inhomogeneities in OF, they appear on the trace in the form of steps or pulses. Figure 3.4 shows an example of the trace mode optical fiber length of 18.84 km.

Figure 3.4- Trace optical fibers 18,84 km

One of the advantages of the OTDR measurement method is that it is enough to have access to one end IA. Furthermore, using the OTDR can determine the distance to the local inhomogeneities, route length, length distribution inhomogeneities OF.

Modern OTDRs made a number of leading world companies:. ANDO (Japan), HEWLETT PACKARD, WAVETEK WANDEL & JGOLTERMANN, IIT, Minsk, Belarus, etc. Figure 3.5 shows a general view ANDO OTDR production.

Figure 3.5-OTDR company Anritsu (ANDO)

Measurement of chromatic dispersion. For modern trunk (zonal) PLAYBACK main factor limiting the length of the regeneration area is not fading, and introduced optic chromatic dispersion. The energy loss of an optical signal propagating in the CC compensated by use of intermediate optical amplifiers. In the process of propagation of optical pulses as a result they increase the duration of the chromatic dispersion. If the duration of the optical pulses becomes greater than the duration of a clock interval digital signals begin to cause errors in information transmission.