Devre bağlaşmalı telefon şebekesi için yönlendirme yazılımı tasarımı
Software design of routing for circuit switched telephone network
- Tez No: 22080
- Danışmanlar: YRD. DOÇ. DR. ÜMİT AYGÖLÜ
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 121
Özet
ÖZET Yönlendirme (routing) fonksiyonu, iletişim sistemlerinde, hizmet kalitesi, kalımlılık, güvenirlik ve maliyet gibi önemli sistem karakteristiklerini etkiler. Bu çalışmada geliştirilen yönlendirme yazılımı, trafiğin iyi bir şekilde kestirilebildiği ve durağan olduğu durumlarda uyarlamalı stratejilerden daha iyi bir sonuç veren deterministik bir algoritma kullanır. Olası yolların önceden belirlenen sırada kullanıldığı ardışıl yönlendirme metodu kullanılmıştır. Her çağrının 5 alternatif yolu vardır. Ardışıl yollar sırayla denenir. Seçilen yolda serbest trank bulunamadığında bir sonraki ardışıl yol seçilir. Burada şebeke meşguliyeti, yolun seçiminde dolaylı olarak etkili olarak etkili olduğundan, yönlendirme şeması statik olarak isimlendirilir. Bu model, ilişki olarak adlandırılan veri tabanı tablolarının uygun olarak doldurulması ile zamana, maliyete ve kaliteye bağımlı yapılabilir. Ayrıca yol seçiminin adım-adım gerçekleştirileceği düşünülmüştür.
Özet (Çeviri)
SOFTWARE DESIGN OF ROUTING FOR CIRCUIT SWITCHED TELEPHONE NETWORK SUMMARY The routing function is one of the function in a communication system with most influence on important system characteristic like : Grade of service, survivability, reliability and cost. The objective of the routing is to establish a successfull connection between any two exchanges or in other words nodes in the network. The function of traffic routing is the selection of a particular circuit group, for a given call attempt, at an exchange in the network. The choice of a circuit group may be affected by information on the availability of failure or overload conditions of the network. So failure or overload conditions may require temporary changes to routing patterns. The signalling function in a communication network is used to interchange information between exchange in the network. New signalling systems for fault and overload detection are developed. This signalling systems help routing algorithms by utilize the possibilities for a global overview of the network when doing routing decisions. Consequently modern communication networks will have reliable routing systems with high capacity signalling channels. A network comprises a number of nodes (switching centers or exchanges) interconnected by circuit groups. There may be several direct circuit groups between a pair of nodes. These may be unidirectional or bothway. A direct route consists of one or more circuit groups connecting adjacent nodes. An indirect route is a series of circuit groups connecting two nodes providing an end-to-end connection via other nodes. Within national networks, it is often appropriate to prepare a hierarchy of switching units, e.g. local, area, trunk, regional trunk, international. Each level of the hierarchy is performing different functions. There is no recommended hierarchy for VIinternational switching centers (ISCs) in the international network. Thus, ISCs are free to determine the most suitable utilization of their individual ISCs. It is important to note that the concept of hierarchical routing need not be directly related to the concept of a hierarchy of switching centers as described above. At a specific node if, all calls offered to a given route overflow to the same set of routes, this routing structure is hierarchical. A routing structure is non-hierarchical if it violates the definition mentioned above. The requirements met a good routing system are highly dependent on type of network. Trafic handling capacity, grade of service, sensitivity to overload, reliability and adaptability to changing traffic and topolojies are said as the most important requirements. The routing scheme defines how a set of routes is made available for calls between a pair of nodes. If the set of routes in the routing pattern is always the same, this routing scheme is called fixed, if the set of routes in the routing pattern varies, this is called dynamic. Routing pattern in the networks may be fixed, if a permanent changes require and these changes are arranged by manually. Routing schemes may also incorporate automatic variations. Such changes may be time and/or state dependent. The updating of routing patterns may take place periodically or aperiodically, predetermined or depending on the state of the network. Routing patterns will be altered at fixed times during the day (week or any period) to allow changing traffic demands. It is important to note that these changes are pre-planned and will be implemented over a long time period. Routing patterns will vary automatically according to the state of the network. Such routing schemes are said to be adaptive. In order to support this type of routing scheme, it is necessary to collect information about the status of the network. For example, each exchange may compile records of successful calls or outgoing trunk group occupancies. This v!iinformation may be distributed through the network to other exchanges or passed to a centralized database. Based on this network status information, routing decisions will be made either in each exchange or at a central processor serving all exchanges. If the routes in a set are always tested in sequence and the first available route is chosen, this route selection is sequential. This strategy is also defined deterministic. Route selection is non-sequential, if the routes in a set are tested in non spesific order. The decision to select a route can be based on the state of the outgoing circuit group or the states of the series of circuit groups in the route, if the choice of the route involves a probabilistic distribution, route selection can be classified as stochastic or probabilistic. A particular type of progressive routing is automatic alternative routing (AAR). When an exchange has the option of using more than one route to the next exchange, an alternative routing scheme can be employed. Two main types are available: -when there is a choice of direct circuit groups between the two exchanges; -when there is a choice of direct and indirect routes between the two exchanges. Alternative routing takes place when all appropriate circuits in a group are busy. Several circuit groups may be tested sequentially. The testing order will be fixed or time-dependent. Automatic rerouting (ARR) takes place upon receipt of a signal at A from a downstream exchange B, indicating that a call once routed to B encountered an“all circuits busy”state on circuit groups out of that exchange. This application is also referred to as crank-back. The objective of service protection methods is to control the grade of service for certain streams of traffic by restricting the access to circuit groups. The common feature of available methods is that they may reject certain call attempts when the considered circuit group has little spare capacity. Service protection is generally used in alternative routing networks to restrict overflow traffic, but can also be used to give priority service to one class of traffic over another. VÎÎÎIn connection with adaptive routing, the service protection concept can be used not only to block overflow calls but also in the selection of a good alternative route (generally this will be a route on which all circuit groups have at least a requested number of free circuits). All routing schemes result in the sharing of traffic load between network elements. Routing schemes can however be developed to ensure that call attempts are offered to route choices according to a preplanned distribution. This application called load sharing works by distributing the call attempts to a particular destination in a fixed ratio between the specified outgoing routing patterns. In our study, for circuit switched telephone network, a routing software is designed, developed and implemented in Pascal programming language. In this study, SDL (Specification and Description Language) diagrams were also utilized for program flow and finite state machine mode with two states was implemented. These diagrams give a better understanding of the routing software and lead to a structured programming. Specification and Description language (SDL) is a CCITT reccommended language suggested to the designers for a clear and precise representation of the telecommunication protocols. In our software, a deterministic algorithm, better than an adaptive procedure when the traffic requirement can be reasonably well estimated and is stationary, is used. As mentioned above, our software is developed for telephone network. A routing strategy can be classified as sthochastic or probabilistic if the choice of the route involves a probabilistic distribution. A strategy which is not probabilistic will be defined as deterministic. Our strategy can be transformed probabilistic routing strategy by simple verifications, like assigning the probabilistic weights to five alternatives, generate a random number and according to this number selecting a route from five alternative. The often used 'sequential routing' where possible routes are hunted in a prescribed order is used I Xin our strategy. Every call have five alternative routes. In selected route if there is no free channel, another alternative is selected. In our strategy, routing decisions arenit directly based on the network occupancy. Because of this, this method is classified as static. A routing strategy is defined as dynamic only when the information concerning network occupancy is used in the process of choosing a route, and not indirectly as in a 'sequential routing' strategy. This method can be developed as dependent on time, cost and quality, by filling the database table which is called relations.“Step-by-step”routing strategy is selected as mode of route selection. A“step-by-step”routing strategy will distribute the routing decisions to those exchanges which are involved in a call setup. In the present study, in first section, generally routing concept is mentioned. The objective and function of the routing, relations between routing and signalling function is given briefly. Network hierarchy and concept of hierarchical routing and difference between these concept are mentioned. The requirements met a good routing system, routing schemes like fixed, time and/or state dependent, sequential, stochastic or probabilistic are given briefly. In addition to these concepts automatic alternative routing is another subject mentioned briefly in first section. A relatively detailed discussion around the routing aspects is carried out in chapter 2. This sections name is main issues and principles in routing. In 2.1, we give routing and signalling system. In 2.2, requirements to a routing system are mentioned. These requirements are traffic handling capacity, grade of service, sensitivity to overload, reliability and adaptability to changing traffic and topolojies. Next sections name is classification of routing systems. In 2.4 we give an examples of the routing algorithms. Packet switched and circuit switched network routing algorithm examples are both given. In chapter 3, developed software is main subject. SDL and database relations are given detailed. In addition, software results are served.
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