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Ryadskaya Julia Faculty: Computer Information Technologies and Automation (CITA) Department: Automation and Telecommunications (AT) Speciality: Telecommunication Systems and Networks (TSN) Theme of master's work: «Research and improvement of methods that provide quality indicators of VoIP-distributed networks» Scientific adviser:Bessarab Vladimir Ivanovich |
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ABSTRACT |
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1. Actuality Quality of service (QoS) plays a key role in the implementation of IP networks today. However, QoS can be one of the most complex aspects of networking. Modern networks need to meet an array of QoS requirements to support distinct applications (such as voice, video, and data) and multiple network services on a single converged, multiservice network. Therefore, QoS has become an integral part of network design, implementation, and operation. 2. Connection of work with the scientific programs, plans, themes Qualifying work of master's degree is executed during 2010-2011 pursuant to scientific direction of department of "Automation and telecommunications" of the Donetsk national technical university. 3. Purpose and tasks of research Procedure for delivery and monitoring of voice traffic in a long time perspective would remain the same, if not for the emergence of next generation networks. Over the past few years a number of new VoIP providers has entered the market, which increased interest in services for voice traffic on IP-networks, but also caused new problems for guaranteed services. Therefore, the purpose of research work is to study and improve the methods of quality of service ensuring in VoIP WAN. To achieve this purpose should be solved the main problems in carrying out the work of master plan: - review existing methods for ensuring quality (QoS); - study control algorithms queues; - improve the method of Weighted Fair Queuing; - simulate and research processes in the network. Consequence of studies will result in recommendations to improve the quality of services in the network to meet customer requirements. Object of study is a distributed telecommunications network of AMSTOR Company. The subject of research is to measure the quality of QoS. 4. Supposed scientific novelty In the course of the work we will identify the main principles of ensuring quality VoIP networks and improved algorithms for queue management. 5. Review of developments and researches on the topic 5.1.Principles of IP-telephony The term “telephony” refers to the technology behind voice communications (typically, telephone networks). Telephony ordinarily involves analog electrical signaling over copper wire. Newer IP telephony technology converts analog voice into digital data packets to support telecommunication over Internet Protocol networks. So-caled "voice over IP" (VoIP) solutions today support IP telephony. IP-telephony is based on two basic operations: two-way conversion of analog speech into digital form within the encoder / decoder (codec) and packaging into packets for transmission over IP-based networks. 5.2. Assessment of quality of service For maintenance of traffic in IP-telephony the following main characteristics that define quality exist. The first - the time delay in signal transmission. This would include grading the numerical values of delay: - Level 1 - 200 ms - excellent quality. For comparison, in the PSTN are allowable delay to 150-200 ms. - Level 2 - up to 400 ms - is considered a good quality connection. But if we compare with the quality of communication networks, PSTN, the difference will be visible. If the delay is constantly kept at the upper level 2 (for 400 ms.), It is not recommended to use this connection for business negotiations. - Level 3 - up to 700 ms - is considered an acceptable quality of communication for conducting non-business negotiations. This quality of communication is also possible to transfer packets over satellite links 5.3. The main methods of ensuring quality of service Quality of Service for Voice over IP discusses various quality of service (QoS) concepts and features that are applicable to voice—in particular, Voice over IP (VoIP). This document also provides high-level examples showing how to deploy these features in different network environments. 5.3.1. Best Effort Best effort delivery describes a network service in which the network does not provide any guarantees that data is delivered or that a user is given a guaranteed quality of service level or a certain priority. In a best effort network all users obtain best effort service, meaning that they obtain unspecified variable bit rate and delivery time, depending on the current traffic load. 5.3.2. Integrated Service ( IntServ) Integrated Services (IntServ), also known as Integrated Services Internet, is an architecture, which specifies the elements to guarantee quality of service (QoS) on networks. IntServ can for example be used to allow video and sound to reach the receiver without interruption. IntServ specifies a fine-grained QoS system, which is often contrasted with DiffServ's coarse-grained control system. The idea of IntServ is that every router in the system implements IntServ, and every application that requires some kind of guarantees has to make an individual reservation. "Flow Specs" describe what the reservation is for, while "RSVP" is the underlying mechanism to signal it across the network. 5.3.4. Differentiated Service (DiffServ) The Differentiated Services (DS) architecture QoS model provides a scalable mechanism to classify packets into groups or classes that have similar QoS requirements. Integrated Service Operation over Differentiated Service Networks (Int-DiffServ) In this framework Intserv provides means for end-to-end QoS over different heterogeneous networks and it must be supported in different network elements, thus Diffserv network is just a network element in this end-to-end path. It is primarily intended to support the quantitative (guaranteed) services end-to-end, which has not been deployed yet by RSVP/Intserv, due to the lack of scalability. 5.3.5. MPLS protocol Multiprotocol Label Switching (MPLS) is a mechanism in high-performance telecommunications networks which directs and carries data from one network node to the next with the help of labels. MPLS makes it easy to create "virtual links" between distant nodes. It can encapsulate packets of various network protocols. In the MPLS-based networks labels conveniently implemented transmission with It performs the following : - Specifies mechanisms to manage traffic flows of various granularities, such as flows between different hardware, machines, or even flows between different applications; - Remains independent of the layer-2 and layer-3 protocols; - Provides a means to map IP addresses to simple, fixed-length labels used by different packet-forwarding and packet-switching technologies; - Interfaces to existing routing protocols, such as Resource ReSerVation Protocol (RSVP) and Open Shortest PathFirst (OSPF); - Supports IP, ATM, and Frame Relay layer-2 protocols. 5.4. Software Queueing Mechanism There are the following queuing algorithms: • traditional algorithm FIFO; • Priority Queueing (PQ); • Custom Queueing (CQ) • Weighted Fair Queuing (WFQ). The principle of FIFO algorithm is as follows - Packets arrive and leave the queue in exactly the same order. Benefits: Simple configuration and fast operation. Limitations: No priority servicing or bandwidth guarantees are possible. The principle of Priority Queueing algorithm is as follows - Traffic is classified into high, medium, normal, and low priority queues. The high priority traffic is serviced first, then medium priority traffic, followed by normal and low priority traffic. Benefits: Has been available for a few years and provides priority servicing. Limitations: Higher priority traffic can starve the lower priority queues of and width. No bandwidth guarantees are possible. The principle of Custom Queueing algorithm is as follows - Traffic is classified into multiple queues with configurable queue limits. The queue limits are calculated based on average packet size, maximum transmission unit (MTU), and the percentage of bandwidth to be allocated. Queue limits (in number of bytes) are dequeued for each queue, therefore providing the allocated bandwidth statistically. Benefits: Has been available for a few years and allows approximate bandwidth allocation for different queues. Limitations: No priority servicing is possible. Bandwidth guarantees are approximate, and there are a limited number of queues. Configuration is relatively difficult. The principle of Weighted Fair Queuing algorithm is as follows - A hashing algorithm places flows into separate queues where weights are used to determine how many packets are serviced at a time. You define weights by setting IP Precedence and DSCP values. Benefits: Simple configuration. Default on links less than 2 Mbps. Limitations: No priority servicing or bandwidth guarantees are possible. 6. The description of obtained and planned results of the work The work involved analysis of existing methods to ensure quality and choose the most suitable for further studies. This method consists in the construction of network on a base MPLS It is planned, using the simulation package OpNet, to build a network of technology-based MPLS, to prove its advantages in practice. With regard to processing algorithms models of queues are being developed at this stage to improve the method of weighted fair queuing. Conclusions The most promising technologies of the QoS ensuring are the MPLS and Int-DiffServ due to the fact that they combine the best aspects of both models. But these technologies have limitations to use these methods. MPLS is still poorly distributed, and is an expensive technology for corporate networks, and Int-DiffServ requires certain costs to sell and cannot provide high levels of interoperability. Literature:
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