EXPERIMENTAL STUDY FOR QUALITY OF SERVICE IN VOICE OVER IP

Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 2 (16) ISSN 1843-6188 EXPERIMENTAL STUDY FOR QUALITY OF SERVICE IN VOICE OVER IP Emil DIACONU 1, Gabriel PREDUŞCĂ 2, Denisa CÎRCIUMĂRESCU 3, Sabin BUCUR 4, Lucian NĂSTASE 1 1 PhD. Student, Faculty of Electrical Engineering, Valahia University of Targoviste, 2 Lecturer Faculty of Electrical Engineering, Valahia University of Targoviste, 3 Inspector, National Authority for Management and Regulation in Communications, 4 Master student, Faculty of Electrical Engineering, Valahia University of Targoviste E-mail: emy_diaconu@yahoo.com, gpredusca@valahia.ro, denisa.circiumarescu@gmail.com, sabin_ocnita@yahoo.com Abstract. Quality of Service is the capacity to give priority to different kinds of software applications, to users, to data flows, or guaranteeing a certain level of performance for data flows. QoS is used to manage the special requirements for voice and video communications, providing data with low delay rate (usually less than 250 milliseconds), less interference (usually less than 10 or 20 milliseconds), reducing packet loss (usually less than 0.5 percent of packets). Exceeding these values can cause poor quality of VoIP calls. Keywords: QoS, VoIP, RSVP, Opnet. 1. INTRODUCTION Quality of Service or QoS is to prioritize traffic by protocol. This concept has been defined by ITU-T recommendation E.800, as: the collective effect of service performance which determines the degree of satisfaction of a user of that service or measure of how well a service is presented to a client, which is expressed in the language understood by the client and is manifested by a number of parameters. Providing QoS in the internet requires the implementation of mechanisms to provide call control protocols and guidance packages in accordance with specific requirements of each type of application. It is necessary to use a signalling system to inform network users about application requirements. To ensure QoS, network management is necessary to enable reservations of resources for real-time applications [1]. Figure 1. Graphical representation of the QoS mechanism The term QoS, used extensively in the past decade, has a very broad sense and may refer to any method which can provide an improvement/prioritization to the standard service offered by the internet, namely,,best effort. By default, the term,,best effort can be considered synonymous with the absence of any QoS mechanism. A broad classification of QoS mechanism to identify the following categories: control mechanisms and policies and control queues / congestion avoidance; traffic policing mechanisms and traffic shaping; mechanisms for marking / classification of traffic (ToS, Diffserv, NBAR); mechanisms reservation (RSVP). Figure 2 illustrates the model of a router, the site of action of various QoS mechanisms. Figure 2. Actions QoS mechanisms in a Cisco router, source: Cisco When demand exceeds the available bandwidth it becomes the phenomenon of congestion. For example, there are several input streams into a knot and the sum bands (maximum) of these flows exceed the available bandwidth on the output interface. In this case, the solution is to obstruct (or prevent) congestion, but when this is impossible the solution is to implement control mechanisms of queues that means that even some of the traffic (by priority) can use the output conditions controlled interface. Traffic shaping is also known as packet shaping or ITMPs (traffic management practices in the internet), traffic control sends (upload/upstream) the delay (delay packages) so as not to form the tail or to be controlled in order to optimize or guarantee performance, to improve and/or increase usable bandwidth by delaying packets that meet certain criteria. Traffic shaping provides a means to control the volume of traffic sent over a 58

ISSN 1843-6188 Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 2 (16) network in a given period (bandwidth optimization), or the maximum rate at which traffic is sent (rate limiting). Traffic policing is controlling traffic by the same law, but only to download/downstream. Access or core network capacity which treats well traffic generated by applications that require a high-bandwidth, means providing a quality service. Reliability of a core network capable of providing QoS is the first step required to interconnect access networks and to provide services to end users. More, with quality service, you can configure your own LAN, so if a customer downloads a priority, not to influence the activity of other clients performing simultaneous [2], [4]. 2. VOIP. CRITERIA FOR ASSESSING THE QoS. VoIP is based on processes that many times are made in,,gateway sites for the prevention of quality problems. To use the most efficient bandwidth, VoIP uses a function called the elimination of terms that do not speak or voice detection. This function is performed by an element which is,,gateway sites or terminals and remove the appropriate packages moments when not speaking. They operate on the output of a,,gateway and can adapt to different noise levels [3]. VoIP is experiencing quite a few technical problems as existing IP networks were not designed to serve realtime application, an application that has limits imposed on response time. The requirements for voice are difficult: for a real-time communication and good quality, it is necessary to return the maximum delay of 200-300 ms and in the end should not exceed 100-150 ms. To compensate the jitter a buffer is used for reception, the length of this buffer influences the return delay. Therefore, jitter must be small so that the sound playback remains smooth at reception. Quality of Service (QoS) is the collective effect of service performance, which determines the degree of satisfaction, in terms of user for service. Network performance (NP) is the network capacity or a portion of a network to perform functions related to communication between users: access to the requested service, establishing communication, ensuring quality communication. QoS provided by network provider, is the quality that can be made available to the user/customer by the service provider. Quality level is expressed by attribute values QoS parameters. Each service should have its own set of QoS parameters. There are two conceptually different ways to implement the service QoS: IntServ and DiffServ. Each of the two methods has their advantages and disadvantages. DiffServ, for instance, has superior scaling possibilities, but suffer from real-time applications area, while IntServ has exactly complementary. IntServ is better used in a framework between areas, while DiffServ provides satisfactory results in between fields. This led to implementation of joint solutions IntServ-DiffServ. 3. MECHANISMS FOR IMPLEMENTING THE QOS 3.1 Integrated services QoS properties enable efficient management of traffic over a network infrastructure. Mechanisms developed in recent years IntServ (Integrated Services) and DiffServ (Differentiated Services) are using a new concept such as new models for Internet network services and protocols for providing resources. Working Group,,Integrated Services appointed by the IETF (Internet Engineering Task Force) in the mid 1990s, proposed two new models of services that a user can use Guaranteed Service and Controlled Load Service. The Guaranteed Service GS offers a fixed maximum delay margin, the deterministic path through strict admission control and scheduling queues. It provides a guaranteed bandwidth, constant packet transmission delay and no loss of packets of data flow for all datagram s belonging to the traffic profile agreed by SLA. Controlled Load Service CL provides a less firm guarantee, a service that is near a network of,,besteffort a little loaded, but not guaranteed QoS in all conditions. CL services provides the following performance: a large percentage of packets successfully transmitted will be delivered to the receiving terminal nodes; the percentage of undelivered packets is determined mainly by the error rate of transmission of packets into the environment, transit time; a very large percentage of packages will not exceed the minimum transmission delay for packets transmitted successfully. Routers that use this service must verify that data flows originally made that booking. Any deviation of such a flow should not affect the QoS granted to affect the traffic flows or other best effort. 3.2 RSVP: Guaranteeing QoS s RSVP (Resource Reservation Protocol) is described in RFC 2205 and RFC 2750 and is a part of the IETF Integrated Service architecture described in RFC 1633, which allows different devices to communicate QoS requests. IntServ produced a protocol for signalling QoS demands of applications and incorporate specifications to describe service requests, and is directed to support real-time data traffic (video/voice). RSVP was designed to signal QoS requests for internet connections, is a protocol based on IP protocol, hop-byhop to inform the equipment of a certain way to a stream of data applications for quality of service. Basic obligation of the protocol is to reserve sources so that application can receive the desired amount of bandwidth. RSVP treats the data stream from source to destination independently, from a logical standpoint, the data flow from destination to source. Accordingly, a reservation data from a source to a destination is independent of a 59

Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 2 (16) ISSN 1843-6188 reservation data from destination to the source. Booking of traffic can be made for any direction or both directions. RSVP is a QoS signalling protocol, node by node. This means that RSVP messages are transmitted from one node to another through all the nodes along the path of data. distribution). FTP application always has the download operations (GET). Each client downloaded objects with a length of 1MB (exponential distribution), with an average of 10 seconds between downloads (exponential distribution). The proposed schemes for the simulation are shown in the figure below. Figure 4 shows IntServ over DiffServ network configuration, for voice and data traffic. The following is described, depending on the scenarios used and implemented in the projects, the objectives to highlight the need for QoS mechanisms both IntServ technology as well as DiffServ, the degree of loading network links and traffic generated by application type (data and voice). Figure 3. RSVP reservation process RSVP is a signalling protocol that provides a resource reservation request from the network, the Path message, in accordance with the requirements imposed on quality of service provided by an application. Network answer explicit, by admitting reservation resources required (the message Resv) or rejecting the reservation request by Resvtear message. 4. EXPERIMENTAL STUDY FOR QUALITY OF SERVICE IN VOICE OVER IP The main objective of this paper is to analyze a combined model of integrated services over differentiated services that offer service guarantees QoS, end-to-end, for realtime voice applications and proposed access to service providers the internet-related indicators of quality parameters, to provide internet access service, the parameters on which electronic communications service providers will be obliged to include in contracts with the end user and the general conditions of service. In achieving this objective, to assess the QoS, we chose a simulation tool Opnet Guru Academic. We will focus particularly on the interoperability between the IntServ and DiffServ, as a solution that offers greater scalability and efficiency, in terms of QoS. There is a growing availability of the internet, services such as large file transfer, audio and video distribution, video or audio conferences, IP telephony, or interactive of real-time applications. The script used in simulation assumes that RSVP and IntServ, are employed in access networks and DiffServbasic network. Customers have the option to use one or more applications: FTP (Low Load), HTTP (Image Browsing), Email (Low Load) and Voice. HTTP application is characterized by a sequence of HTTP 1.1 connections each connection is a page load. The average page load time is 10 seconds, varying exponentially. Each object contained in a single page has a length between 500 and 20000 bytes. Each page has an average of seven items (exponential Figure 4. IntServ over DiffServ network configuration for voice and data traffic To simulate data traffic (HTTP Image Browsing, FTP - Low Load, Email Low Load), and voice traffic: voice traffic BE without using QoS mechanisms (encoding scheme used is G711, is not using booking resources) and QoS for voice traffic (encoding scheme used is familiar with all the G711, using the RSVP resource reservation). Thus, application Telefon_1 and Telefon_3 supports Voce_BE profile for the BE scenario and profile Voce_QoS and PC1 support applications data (HTTP, FTP, email). They are clients connected to a switch Ethernet16 type, connected in turn to a router Cisco_1750. The central part consists of two routers NEC_CX5210 model with three slots and four Ethernet ports. The link that connects the central part is the PPP, with a capacity of 256 kbps. The receiver consists of a router CISCO_1750 also connected to an Ethernet16 switch. Telefon_2 and telefon_4 it as well supports Voce_BE profile for BE scenario and profile Voce_QoS for the scenarios WFQ, PQ, CQ, DWRR and FIFO. There has been a charge for the access link (256kbps for both data traffic and voice traffic) in order to observe the disciplines of planning efficiency in case of congestion. In figure 5 and 6 we observe the usage of the 256kbps link between Access Router1 Core Router1 compared to the scenarios WFQ, PQ, CQ, DWRR and FIFO: 60

ISSN 1843-6188 Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 2 (16) Figure 5. The degree of use of the link Access Router Core Router 1 (256 kps) Figure 8. Throughput (bits/second) for link Access Router Core Router (256 kps) Figure 6. The degree of use of the link Access Router Core Router 1 (256 kps) Figure 9. Delay in the queue for link Access Router Core Router (256 kps) Moreover, for the same link with a 256kbps upload between Access Router Core Router 1 is presented the point to point throughput (bit/sec) and the delay in the queue for voice and data traffic. Figure 10. Delay in the queue for link Access Router Core Router (256 kps) Figure 7. Throughput (bits/second) for link Access Router Core Router (256 kps) According to the graph presented, we can see that the choice of link capacity Access Router Core Router for 256kbps, QoS mechanisms demonstrate the efficiency in case of congestion. PPP link carrying both data traffic and voice traffic, with capacity exceeding 256kbps. The delay in the queue is very small, for the scenarios dealing with QoS implementation mechanisms, and large for BE the scenario. Chosen bandwidth is sufficient for Ethernet links (100Mbps) and insufficient for PPP links (note the phenomenon of congestion). In figure 11 and figure 12 it can be seen Telefon_1 voice traffic generated, using G.711 encoding scheme in packets/second, and the fact that the scenarios that implement QoS mechanisms, to use reservation of resources. 61

Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 2 (16) ISSN 1843-6188 Packet loss also has a negative effect on voice quality received. A relatively small percentage (5-10%) of the lost packet will cause a decrease in voice quality. If the percentage of packet loss amounts to 10%, quality will become unacceptable. We analyzed also the voice traffic generated by Telefon_1, Telefon_2, Telefon_3 and Telefon_4 (measured in bits/second). When voice traffic is presented and generated traffic for data applications, compared by type of script, HTTP and email (figure 15 and figure 16). Figure 11. Telefon_1: Generated traffic (packets/sec) Reservation of resources: RSVP Figure 15. Server HTTP: Generated traffic - Email (bytes/sec) Figure 12. Telefon_1: Traffic receiver (packets/sec) Reservation of resources: RSVP Figure 16. Server HTTP: generated traffic - HTTP (bytes/sec) Figura 13. Telefon_1: Number of requests solved successfully. Reservation of resources: RSVP Figure 14. Telefon_1: Number of applications rejected. Reservation of resources: RSVP 5. CONCLUSIONS After analyzing the graphs presented it was found the following: - the FIFO discipline voice traffic is treated in the same way as data traffic. The obtained delays for voice traffic, leads to a high degree of utilization of network links; - the planners analyzed WFQ, PQ, CQ, DWRR ensured priority voice traffic, in comparison with data traffic. Voice packet delay and reduce network overload situations. However, it increases the response time for data packets; - PQ scheduler ensures prioritization of voice packets, data packets that can disadvantage, because it is considered a schedule of all classes balanced QoS. 62

ISSN 1843-6188 Scientific Bulletin of the Electrical Engineering Faculty Year 11 No. 2 (16) QoS guarantee is also a source of direct profit for providers of electronic communications as soon as they will extend the duration and volume charge, the taxation of QoS levels required by their customers and guaranteed. A proposed service, end-user communication network is the ability to configure, by choosing a less efficient service, but cheaper or more efficient service, but more expensive in the context of assisted decision depending on the application of resources used available. This means greater flexibility given to the user, along with a more efficient use of resources of the operator. VoIP applications can determine the required values for bit rate, delay/jitter and error rate of the voice signal codec s. Acknowledgements This work was supported by POSDRU, PREDEX ID 7749/2010 and by UEFISCDI, Grant ID 2200/2008. 6. REFERENCES [1] R. Dobrescu, D. Cîrciumărescu, Interoperability of integrated services and differentiated services architectures, U. P. B. Sci. Bull., Series C, Vol. 71, Iss. 1, 2009, p.21-32, ISSN 1454-234x. [2] G. Armitage, Quality of Service in IP Networks, New Riders, 2000. [3] Tomi Yletyinen, The Quality of voice over IP, published on the internet at, http://keskus.hut.fi/tutkimus/ipana/paperit/tomidt.pdf. [4] CCITT "Recommendation E.410 - Telephone Network and ISDN - Quality of Service, Network Management and Traffic Engineering - International Network Management - General Information". 63