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Research of features of guaranteeing QoS in multiservice networks by adoption of new servises in GSM standart.

Telecommunication networks which use radio channel as an access point of the end user to network services worry at present a stage of rapid development and wide introduction. The direction of development which was outlined, has got received the name of NGN-technology. It has all signs of unification of methods and means which exist also that are creating, in the common integrated structure. This process cannot be simple and unequivocal as should occur in the conditions of reorganisation of existing networks and technologies which often demand basic changes for integration with NGN-structure. At the same time, reorganization which provides increase of an overall efficiency of a network in the nearest future should not have negative effect on competitiveness of the operator of a network in the present, and, more likely, on the contrary - to assist the expansion of the market of users who already are in the network modernization process.

Converged way of development of telecommunication networks, probably, the only pragmatically proved direction for operators who have developed market of users. Nevertheless it demands the weighed decisions so that getting new possibilities at the expense of transformations, not to do much harm to the existing market.

In a reality, for the mobile operator, the problem of construction and improvement convergent networks becomes complicated in a cause of limit of resources in existing GSM networks, decreasing in reliability of granting services in the conditions of an overload of radio channels, weak fitness of GSM-technology for data transmission. Appearance and development of new technologies, in particular Wi-Fi that can potentially give more quantity of services, with threatens outflow of "traditional" GSM-users to Wi-Fi-operators.

Interest of mobile communication operators to a segment of wireless broadband access appeared a long time ago and has initially been connected more likely with granting of services to access to the Internet on technology Wi-Fi, than with high-grade introduction of concept NGN.

General using of networks NGN possibilities and mobile communication networks, their high-grade convergence, is capable of providing subscribers with a unique set of features and services. If granting convergent services is provided by the operator of a mobile communication "from one hands" it causes a jump of attractiveness of such network to clients, it means, the operator acquires serious competitive advantages. Such decisions appear economically effective.

The urgency of the given topic is readily apparent from the fact that convergence gives the chance of an effective existing resources (channel capacity) utilisation. Cost of Wi-Fi strip is cheaper, than GSM/3G network strips that reduces operator’s cost price of telecommunication services that are offered to the client.

Object of research – mobile communication operator’s telecommunication network.

Subject of research - service quality parameters which are typical for different traffic types.

UMA Technology (fig. 1) gives the chance to use broadband wireless Internet connection (Wi-Fi) for mobile telecommunication [2]. It concerns voice calls, mobile Internet, e-mail, MMS, SMS and any other mobile services for which connection to existing mobile networks is necessary.

Figure 1 – UMA Technology in convergent network

The dual-mode user's terminal itself defines possibility of reception of services through one of networks (GSM/Wi-Fi), thus the priority is given to Wi-Fi [3]. Subscribers who have no dual-mode phones, will be connected to classical GSM networks. Wi-Fi access points are connected to an existing transport IP-network which is used for packages EDGE transportation. This IP-network incorporates UMA Network Controller (UNC) which is in turn included in classical MSC. Locking between MSC and UNC occurs through Wireless Media Gateway (WMG) sluices - for voice bearing UMA support, and Security Gateway (SeGW) - a safety sluice - for UMA protection. On UNC packing and voice coding takes place at Wi-Fi/GSM roaming, both unpacking and decoding by return transfer.

Functioning of such convergent GSM/Wi-Fi networks and aspects of their construction are represented on fig. 2.


Figure 2 – UMA Architecture

Transition of the subscriber from the GSM network coverage to UMA network is represented in fig. 3. As it is possible to see, the mechanism of handover allows connection support during transition from one zone of service to another, which will not bring to the subscriber any difficulties.


Figure 3 - Handover in convergent network.
This figure is animated: frames - 36, cycles - 3, duration - 21 sec.

Except a standard set of features which are offered by mobile operators, it is possible to allocate the following services which will appear in the IP network:

- Voice transfer (VoWi-Fi);

- Video calls;

- Video conference;

- Data transmission;

- Internet surfing;

- Voice transfer (VoIP) for corporate subscribers;

- Expansion of femtocells for corporate subscribers.

The success or failure of the convergence depends on how difficult the realization of the guaranteed degrees of quality of service (QoS) in the IP environment will be.

QoS refers to the ability of a network to provide better service to selected network traffic over various underlying technologies..."

QoS implies solving the following problems:

- Definition of priorities and differencing of the traffic;

- Maintenance of information streams with necessary network resources;

- Increase of transmission reliability;

- Prevention of network overloads;

- Formation of the network traffic in order to smooth the stream and make it more uniform.

Let's allocate the main parameters of quality which are considered basic for services rendering:

- Delay at an information transfer – time required for information transfer from a source to the addressee;

- Delay variation - a difference between an absolute delay of a package and a normalized delay;

- Query response time - for network databases and CAD-systems;

- Percent of lost packages - the relation of lost packages to total transferred;

- Communication channel capacity - real quantity of resources, sufficient to the user for a certain way of data transmission;

- Throughput - the maximum speed of the channel on a site.

As to parameters of delays, percent of loss of the packages resulted in table 1 it is reversible to recommendations ITU-T Y.1540 [4].

Table 1. Parameters of IP QoS classes.

Mentioned above package is correlated to a certain traffic class. According to ITU-T Y.1541 [4] recommendations it is necessary to allocate 6 classes of traffic which are resulted in table 2, for QoS mechanisms maintenance.

The 802.11e standard, and also Wi-Fi Multimedia specification are developed by the Wi-Fi alliance, somewhat regulates questions of QoS in wireless IP networks.

WMM emphasizes on the following traffic classes of a wireless network:

- Voice communication, IP-telephony (highest);

- Video;

- Usual;

- Background (lowest).

Experimental researches and the analysis of numerous measurements of information streams at package level specifies in the specific nature of processes in telecommunication networks which does not keep within traditional frameworks of known random models. [8].

Self-similarity properties or scaled statistical characteristic invariance proved to be characteristic for the description of processes of data transmission by the package traffic. These properties are linked with a special physical processes class, fractal processes, in modern scientific literature.

Traffic generation is a stationery process because traffic itself is generated randomly. Intervals between the points of this graph are independent random values that possess equal density of distribution.

Let us consider «ON/OFF» mode traffic modeling [9,10]. ON – time interval when data transmission is carried out, OFF – absence of similar transfer. Duration of intervals is random, and the termination of the ON state is itself the beginning of the OFF state. It is necessary to pay special attention during the analysis of the given mode operation to the "heavy" distribution characterising the fact that probabilities of ON/OFF intervals of order Т (long series of data transmission and interserial intervals) can be considerable: Dispersions of these intervals appear considerable.

Results

Use of UMA technology will release a part of radio channel resources in places where overloads are observed.

Transition to a packet transmission of data will allow introduction of the new users’ services with minimum expenses.

The following kinds of traffic for convergent WiFi/GSM networks are defined: voice transfer (VoWi-Fi), video calls, video conference, data transmission, Internet surfing, voice transfer (VoIP) for corporate subscribers, expansion of femtocells for corporate subscribers, also is defined 6 classes of priority of the traffic.

Hybrid Coordination Function (HCF) mode is the most comprehensible from the point of view of access granting by environment of the priority traffic, thus providing QoS for various services.

The probability of successful beacon transfer falls slowly to certain number of devices in a network, as probability of a beacon collision is small. At the fixed number of devices in a network the probability of a beacons collision depends on number virtual slots, that grows with ATIM-window increase.

Forecasting with application fractal properties will be more accurate and possible as the majority of parameters of system, such as correlation function, dispersion will be static, and only a part - dynamic - time, quantity delivered data.

Literature

1. Alex Shneyderman, Alessio Casati. Fixed Mobile Convergence. – McGraw-Hill Osborne Media.-2008.–272 p.
2. The Role of UMA in Mobile Networks Evolution.–Kineto Wireless inc.–2007. (http://www.kineto.com/products/downloads/kineto_wp_UMA_MNE_2007.pdf)
3. Praphul Chandra, David Lide. Wi-Fi Telephony: Challenges and Solutions for Voice over WLANs. – Newnes. – 2006. – 286 p.
4. ITU-T Recommendation Y.1540/Y.1541. Network perfomance objectives for IP-based services. Geneva: International Telecommunication Union. – 2006. (http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-Y.1541-200602-I!!PDF-E&type=items)
5. IEEE 802.11e: Medium Access Control (MAC) Quality of Service Enhancements, NY – 2005.
6. Соловьёв М.С. Механізми забезпечення якості в конвергентних Wi-Fi/ GSM мережах. Проблемы Телекоммуникаций – 2009 / Материалы III международной научно-технической конференции. – Киев, КПИ – 2009, с.57.
7. ITU-T Recommendation G.1010 Quality of Service and perfomance. Geneva: International Telecommunication Union. – 2006.
8. Соловьёв М.С., Воропаева В.Я. Прогноз трафика GSM сетей с учётом свойств фрактальности. Проблемы Телекоммуникаций – 2008 / Материалы II международной научно-технической конференции. – Киев, КПИ – 2008, с.99-101.
9. В.Вишневский, Д.Лаконцев, А.Сафонов, С.Шпилев: QoS в сетях Wi-Fi, Связь и телекоммуникации – 2008.
10. А.Я. Городецкий, В.С. Заборовский Фрактальные процессы в компьютерных сетях. СПб: 2000.
11. Paxson V. and Floud S. Wide Area traffic: The failure of Poisson Modeling v.3 – N3 1995.
12. Lucantioni O.D., Neuts M.F. and Reibman A.R. Methods for Perfomance Evaluation of VBR Video Traffic Models v.2 – N2, 1994.