INTRODUCTION

At the present moment an intensive growth of telecommunication services and new services is taken place, which are more demanding to the characteristics of transport networks, as compared with traditional. At the same time, the role of data services has increased and significantly increased their weight in total amount of transmitted traffic. The increasing number of Internet users, the construction of corporate networks and storage area networks, the introduction of “Video on demand” - requires expansion of the transport bandwidth.

Operators more closely compete with each other, increasing the volume of services offered, this changes their structure, resource and technological bases. Against this background, it is particularly important for the operator to find the optimal migration path of its transportation infrastructure to respond the needs of its clients adequately. Over recent years the rapid development of telecommunications network operators have invested in the construction of transport networks is very significant resources.

Thus, operators are interested in solutions that will allow the expense of small additional investment to develop the existing transport network, extending and increasing it. There are technical aspects - the equipment must be compatible with existing network and provide the possibility to work as used today, and promising applications.

In addition, developing a new transport architecture operators seek to ensure:

- simplicity, which means lower capital and operating costs;

- conformity to user expectations in terms of the band and QoS (Quality of Service);

- architectural flexibility and investment protection.

Whatever selected for the construction of the access network technology and equipment based on it, they should allow continued growth of subscriber bandwidth channels and expanding the list of services offered, as well as increase the capacity of existing networks, access to high-performance transport networks.

Until recently, the technical basis for the construction of the transport network is a telecommunications system transmitting digital hierarchy (SDH - Synchronous Digital Hierarchy). Intensive development of this technology practically came to an end, stopping at a speed of 40 Gb/s, which is explained by the presence of dispersion in standard optical fiber, which built most of the networks. Substantially increase the capacity of technology is designed to multiplex by wavelength (WDM - Wavelength Division Multiplexing), by expanding the bandwidth transmission by increasing the number of channels.

1. A THEME URGENCY

With advent and wide dissemination of advanced telecommunications services to transport networks demands are multi-service and economy. Therefore, the new broadband services require a revision of the capacity of existing transport networks operators create new high-speed backbones.

To date, must be addressed the classical problem of optimization of the transport telecommunication network as a whole and specific parts of it with the main indicators of quality of functioning. The urgency of the work is the need to accelerate the process of designing such networks.

2. COMMUNICATION OF WORK WITH SCIENTIFIC PROGRAMS, PLANS, THEMES

Master’s qualification work is executed during 2009-2010 agrees with a scientific direction of the department “Automation and Telecommunications” of Donetsk National Technical University.

3. THE PURPOSE AND PROBLEMS OF THE INVESTIGATION

For the transport network, which is the basis of providing services to the end user, always demands were made for reliability, manageability, scalability and ability to develop. Therefore, fiber-optic transmission systems based on SDH has long occupied a prominent place in the transport networks of virtually all telecom operators. But with the advent and wide dissemination of advanced telecommunications services to transport networks, new demands multi-service and economy. New broadband services require a revision of the capacity of existing transport network operators.

Therefore, the purpose of work is to investigate of the dynamics transport telecommunication network with difficult topology using technologies WDM (DWDM).

To achieve this purpose should be solved the main problems. In the execution of the master plan to analyze the structures of SDH networks of complex topology, to explore how technology is applied WDM (DWDM), to develop a mathematical model of the network for the study of dynamic processes, simulate and study processes in the network and make a feasibility study investigated the effectiveness of the network. The result of research will be recommendations for improving network performance, enhance its functionality and increased reliability.

The object of research is transport telecommunication network.

The subject of research are technology SDH using Wave Division Multiplexing to increase network capacity and topology for solving complex problems to improve network performance, enhance its functionality.

4. SCIENTIFIC NOVELTY

Scientific novelty of the master's work lies in the fact that the object of study is the transport network in mobile networks. Mobile operators rapidly expand its coverage by increasing the number of base transmitting stations, and therefore the transport network is dynamically changing and complicated.

In the execution of master's work will be provided the effective implementation of systems, WDM, an analysis of redundancy schemes and an algorithm for redundancy on the basis of P-loop.

5. PRACTICAL VALUE OF THE RECEIVED RESULTS

The practical value of the work involves the application of more efficient methods for designing new or upgrading existing telecommunications transport networks that would allow more efficient use of network resources and minimize the financial cost of its construction and maintenance.

6. THE REVIEW OF DEVELOPMENTS AND RESEARCHES ON THE THEME

Operators are faced with the need for simultaneous support of several generations and communication technologies. Ensure the transfer of voice traffic 2G and 3G, as well as provide intensive data for new applications and Internet access with the required quality of service [1].

6.1. WDM in a Multiservice Network

Modern multi-service networks as the basic link layer protocol using Ethernet, which provides the necessary increase in capacity of the operator's network, including a new generation of services for businesses and individuals. IP is base of communications services, the new generation. Moreover, this IP/Ethernet infrastructure can be deployed as on top of the “dark fiber”, and over optical transport network based on xWDM (CWDM/DWDM).

Application xWDM network operator primarily dictated by the lack of optical fibers. Growth of the amount of information lead to a rapid reduction of stocks of “free” (dark) fiber. In some cases, particularly in urban areas, many of the existing cable channels are completely filled and the physical capacity expansion of optical fiber is practically impossible. The rapid introduction of new telecommunications services can only be due to the increase of virtual tanks fiber, use of spectral compression systems (CWDM or DWDM) [2].

But besides this, there are other reasons for using a multi-service network based on CWDM or DWDM.

First, is the need of transmission of 10 Gigabit Ethernet over long distances (about 100 km and more), as a range of modern broadband XFP transceivers is limited due to chromatic dispersion.

Secondly, the use of xWDM allows rapid recovery of function at a level optical, rather than batch IP/Ethernet network.

Thirdly, it is possible to implement arbitrary topology multiservice network over xWDM. For example, the organization of a star topology between the Ethernet switches over xWDM ring [2].

Another possibility provided xWDM is file, easy drive and the speed increase network capacity in the future. This is a very important point!

Also do not forget that the inherited services and transport infrastructure inherited (as a rule, TDM transport through SDH) anywhere overnight will not disappear, and will coexist with the growing infrastructure Ethernet/IP for a long time.

In this case, CWDM/DWDM is the basis for the integration of inheritance and new transport infrastructures.

Evaluation xWDM systems when it is selected by the operator - simplicity, flexibility, reliability and price (which is especially relevant now in times of economic hardship).

6.2. DWDM Technology

In the past, the design of telecommunications networks from an economic point of view, mainly dictated by the need for voice transmission. With large-scale deployment of data networks is changed network architecture itself. It therefore required a fundamental change in the principles of design, monitoring and control networks. At the core of a new generation of network technologies are multiwave optical networks based on Dense Wave Division Multiplexing DWDM (dense wavelength-division multiplexing).

Dense Wave Division Multiplexing DWDM (dense wavelength-division multiplexing) is a modern technology to transfer a large number of optical channels over a single fiber, which is the basis of a new generation of network technologies [3].

For the aggregation and reliable, efficient transfer of all types of traffic of various broadband services transport network should provide the necessary bandwidth and scalability of network infrastructure. These requirements are particularly relevant to transport networks scale of the city (Metro-networks).

In urban transport networks widely used technique DWDM. Built on the basis of this technology transportation networks differ by a number of advantages:

- support various network topologies;

- have greater scalability in comparison with solutions based on other technologies (SDH);

- support different types of client interfaces and services;

- allow the use of various redundancy schemes;

- effective use of system bandwidth by aggregating low-speed client signals into a single spectral channel;

- support the functionality of ROADM (Reconfigurable Optical Add/Drop Multiplexer) [3].

6.3. Planning Principles of Digital Networks

When planning for modern digital networks should distinguish between three network levels: the level of the primary network, the level of secondary networks and the level of systems or telecommunications services. The basis of any real communication network is the level of general purpose (universal), the primary network, which is a set of nodes and connecting transmission lines. Thus, the primary network is a basic network model of the universal channels and network channels, on which are formed the secondary network [4].

Primary network is basic transport or backbone networks, as already noted above, provide the basis for the construction of the diversity of today's multiservice networks.

The main requirement for transport networks, is to implement a network of basic function - to ensure customers to access to all shared network resources. All other requirements - performance (speed transfer), reliability, compatibility, manageability, security, extensibility and scalability - are linked to the quality of service end-users.

Basic information and specifications DTS, which greatly determines its ability to provide guaranteed quality of service network users and network capabilities as a whole, the following:

1. The capacity of highways or base transmission rate determined by the level of transport modules (STM-N, N = 1, 4, 16 ,...).
2. The amount of incoming and outgoing traffic at the network nodes.
3. Total traffic in the channels and the network backbone.
4. Reliability or availability factor network in general [4].

To date DTS and corporate networks makes the following basic requirements, making it possible not only to guarantee quality of service, but also the further development of the network:

1. Necessary bandwidth.
2. Extensibility and scalability of the network.
3. Control network.
4. Integration of different types of traffic.
5. Compatibility of equipment.
6. Reservation of traffic channels and channels.
7. Given the highest reliability and availability [4].

The most rational for the global transmission or transport, networking is a layered architecture type IP/ATM/SDH/DWDM.

The essence of the organization construction planned transport networks is shown in fig. 6.1.

Figure 6.1 - The principle of the transport network construction

This model can serve as a basis for designing communication networks of all sizes.

6.4. Features of Modern Technology WDM

Network operators, using advanced broadband transport technology of digital data in the struggle for dominance in the market of telecommunications services rely on technology for the optical division multiplexing wavelength (WDM), suggesting an increase in the total transmission bandwidth by increasing the number of channels (or carriers), thus promoting an extensive way of development [5].

In WDM technology lacks many of the constraints and technological difficulties inherent in TDM. To increase the capacity of WDM technology increases the number of channels (wavelengths) used in transmission systems.

The growth capacity using WDM technology is carried out without expensive replacement of optical cable. The use of WDM technology allows you to rent, not only fiber optic cables or fiber, but also the individual wavelengths, to implement the concept of “virtual fiber”. For a single fiber at different wavelengths can simultaneously transmit a variety of applications. As a consequence, part of the fiber optic cable can be used to reserve [6].

The use of WDM technology avoids gasket optic cables in the existing network. Even if the future value of the fiber decreases due to the use of new technologies, fiber-optic infrastructure (padded fiber and fixed equipment) will always cost quite expensive. For its effective use, you must have the opportunity for a long time to increase network capacity and change the set of services without replacing the optical cable. WDM technology provides just such an opportunity.

WDM technology is still mainly used in communication lines long, which require much bandwidth. Networks of urban and regional scale, and cable television systems are also potentially large market for technologies WDM. The need for efficient use of wiring led to a significant increase in the number of channels transmitted over a single fiber, and reduce the distance between them [6].

In the technology of WDM channels are completely independent, but because it gives more flexibility than technology TDM. WDM technology allows without any difficulties to pass through the communication set of channels, type of traffic and speed of data transmission in each of which may vary significantly.

6.5. Model of Interaction of Transport Technologies

Multilevel model of interaction between transportation technology signal in the global digital networks - SDH/SONET, ATM and IP (without taking into account the possibility of transfer of IP-traffic through the ATM-backbone) - until the WDM-systems (fig. 6.2.a).

After the appearance of WDM-systems model has become the form shown in fig. 6.2.b. Now it includes three or four levels, not counting the transmission medium. Intermediate WDM, like SDH/SONET, provides a physical interface that allows a physical level to enter the optical transmission medium not only technology SDH/SONET, and ATM and IP [7].

Figure 6.2 - Model of the main transport technology: a - before the introduction of technology WDM, b - after the introduction of WDM

Naturally, ATM-and IP-based traffic can be transmitted and technologies SDH/SONET, SDH/SONET-traffic - using WDM, which preserves the continuity of traditional patterns of transportation and increased flexibility WDM-SDH/SONET systems in general. WDM technology provides the technologies ATM, Ethernet and IP physical interface for accessing the physical layer and then into an optical transmission medium.

6.6. Multiservice Networks: the Infrastructure for Future

Today telecommunications market, in particular its infrastructural component, is experiencing a period of dynamic and symbolic change.

DWDM - is the physical network layer, which operates independently of the type of information transmitted by or on its format. This flexibility, combined with huge bandwidth DWDM makes perfect technology for supporting infrastructure of next generation networks, which are multi-service networks.

However, to DWDM could satisfy the needs of future communication networks, all parties interested in their development, must address the issue in a broader context, including interactions with systems of third generation mobile communication, as well as next generation network (NGN) [8].

As soon as the system of third-generation mobile communication will be commissioned and will be widely available to users, they require high-bandwidth digital paths and broad band channels. In these circumstances, DWDM, SDH, and various technologies will provide new systems of effective solutions to their transportation problems.

7. THE DESCRIPTION OF THE RECEIVED AND PLANNED RESULTS OF THE WORK

With increasing complexity of communications probability of failure of any of its components increases. Modern communication systems use a large number of elements, which makes it necessary to use backup and circuitous routes to improve the readiness factor of the communication system as a whole. Consider the basic ways of increasing the rate of network availability.

Type redundancy scheme 1+1 usually used extensively in ring architectures. In the basic configuration of the ring architecture of the traffic from the source simultaneously transmitted in both directions and the decision to switch between primary and backup lines adopted in the place of destination. In this situation, only the loss of signal (LOS) is required to initiate the transition to the reserve, and does not require any information or control commands to switch between the two states.

This helps to minimize failures of general type. By virtue of simplicity approach, it provides the most rapid recovery of the system with minimum requirements for the implementation of sophisticated monitoring and special equipment. However, it is expensive and less effective, in terms of equipment than the use of backup type N+1. This is inefficient, because backup equipment remains unused for almost all the time, not bringing profit.

More efficient use of backup equipment can be obtained using the method of transmission line protection scheme N+1. N+1 protection makes use of the equipment more efficient economically, but requires more complex management and can not offer the same level of accessibility, as with the protection scheme 1+1. It is also difficult to hold the division of routes for workers and back.

Another option for improving network resiliency is a redundancy of terminal equipment to the schemes of 1:1 or N:1 or N:m. In this case, the recovery efficiency at the expense reserve at the level tribune interfaces. Redundancy scheme, denoted in general as N:m, m using stand on N working interface cards that allow varying degrees of reservation: from 1:1 (100%) to N:m, where m=1 is minimal, when the N key tribune interface cards using one reserve.

The basic structure of transport networks are: linear (simply connected), ring (doubly-connected) and cellular (multiply). Given the doubly connected ring topologies, they are allowed considerably less than the reliability of individual elements of the network compared with a linear structure, which led to a proliferation of transport networks, urban structures of self-healing rings. However, multiply (cellular) networks are much more tenacious.

Practice shows that the development of SDH networks in European countries the most optimal in terms of cost optimization in the network in general and the most reliable and flexible architecture is cellular. Expanding the network for the accumulation of new units and laying of parallel lines, even the network, consisting of a single SDH ring, then it turns out that on the basis of this segment was built some cells. A similar process is repeated for other segments, forming as a result of the classical cellular network with different threads in its various segments dictated by consumer traffic. Similarly, we can build a cellular network based on a network of several rings of SDH, combining some nodes rings links to give the network greater flexibility and reliability.

At the initial stage of modernization of the network connection, the most rational and cost-effective is the combined use of existing SDH equipment and implement WDM. Thus, WDM systems will be used to transfer large data streams (eg, transfer of internet-traffic). SDH systems will be used to transfer and allocation of low-speed traffic. Construction of such a combined system will provide these additional features:

1. More efficient use of network capacity, due to the optimal distribution of low-speed and high-speed data streams.
2. Increase the reliability of the network, due to different redundancy schemes for WDM and SDH levels.
3. Increase the speed backbone connections and allow to expand the existing network.

Later, when translating the network entirely in WDM systems will be obtained a number of advantages, such as:

1. Ability to keep existing schemes to ensure reliability.
2. Release employed optical fibers, through the optimal use of other fibers.
3. No need to install new fiber cable.
4. The possibility of operating the network scalability and ease of further increasing capacity.
5. Ensuring the independence of data of any type over a single fiber at different wavelengths.

In systems WDM, implementing the transfer of traffic SDH, there are both specific methods of protection of traffic, such as switching to a backup wavelength in case of failure the initial carrier, as well as traditional, in principle, but not always possible under the traditional system of SDH, for example, dynamic routing - redirection of the optical carrier by a new route for the cable breakage or degradation of the signal at the previous route.

The transport system of modern telecommunications networks consists of backbone networks and access networks.

As a result of work on the topic of master's work transport network of Donetsk city and Donetsk region were designed. The total traffic was calculated and the findings on the network load were made. For organize the network technology of synchronous digital hierarchy SDH with WDM has been selected. Based on information technology block diagram of the network is built and shown on the fig. 7.1. All the necessary types of equipment used in the network were chosen.

Figure 7.1 - The block diagram of a complex transport network topology for the Donetsk city

(Animation: volume - 84 KB; size - 756х575; number of shots - 10; delay between shots - 250 мс; delay between the last and first shots - 250 мс; number of repetition cycles - infinity)

CONCLUSIONS

To create an efficient system backup and recovery of the transport network is necessary to investigate methods of improving the reliability of the application of redundancy schemes using the advantages of signal transmission at several wavelengths, as well as to solve the following problem:

1. Identify major sources of failures and ways to improve the reliability of communication networks.
2. Review the existing methods of backup and redundancy of equipment SDH systems with varying topology.
3. To analyze the main benefits of the system spectral compression in order to improve reliability.

In the modern development of telecommunication networks task design, modeling and optimization of transportation networks, is quite interesting and relevant.

The obvious advantages of SDH equipment in the areas of access and backbone transport network operator are:

1. High reliability and speed recovery services.
2. The ability of centrally management and monitor of the network.
3. Transfer of all types of traffic without loss of quality.
4. Very wide range of hierarchy speeds, providing network scalability within a single technology.
5. High quality of services for all types of traffic and in any combination.
6. Flexibility of interfaces, through which you can connect to the highway almost any modern equipment of the access network.
7. Simple in operation and low operating costs.

For even greater reliability possible docking rings are not one, but two network nodes. Thus, the ring topology is complemented by redundant lines, cross ties, other topological solution for greater reliability and efficient use of network bandwidth. The result is a mesh topology.

Structure of transport networks is dynamic, i.e., the network gradually expands and reconfigures. The main topological solution, used in trunk networks - is a complex mesh topology, which provides a good backup and easy network expansion.

In the study of the dynamics of the network it is necessary to solve the problem: when the load on the transport network to estimate the change and a number of assessments to competent technical solution of network reconfiguration.

The main methods of research is modeling, analysis of the results.

At this stage of research the models of networks is developing to get the dynamic characteristics of load-specific sections of the network and on their basis to formulate general recommendations for reconfiguring networks SDH.

BIBLIOGRAPHY

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NOTE

When writing this abstract the master’s qualification work is not completed. Date of final completion of work: December, 1, 2010. Full text of the work and materials on a work theme can be received from the author or his scientific supervisor after that date.

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