XV International PhD Workshop OWD 2013, October Ensuring quality of service in computer networks based on IPv4 and IPv6

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1 XV International PhD Workshop OWD 2013, October 2013 Ensuring quality of service in computer networks based on IPv4 and IPv6 M.Sc. Paweł Onyśków, University of Zielona Góra Faculty of Electrical Engineering, Computer Science and Telecommunications Institute of Control and Computation Engineering Abstract The paper describes issues related with ensuring the Quality of Service (QoS) in computer networks which are based on the IPv4 and IPv6 communication protocols. A review of the QoS methods with a special consideration to congestion avoidance and queuing techniques is provided. The practical part of the paper contains the tests conducted to compare efficiency of queuing methods and congestion avoidance mechanisms in the IPv4 and IPv6 computer networks. A special attention is devoted to the Low Latency Queuing (LLQ) method which offers a high level of QoS in the Voice over Internet Protocol (VoIP) communication. 1. Introduction The Internet constitutes one of dominating methods of communication in contemporary world. Unfortunately, the Internet was not originally designed to transfer data in the real-time. This fact has a huge impact on the quality and efficiency of multimedia transmissions that dominate the Internet. In order to provide reliability of the VoIP [8] and telepresence system [9] there are numerous methods ensuring QoS [10]. The existing methods are characterised by different effectiveness especially when they are used in the IPv6 protocol. A detailed knowledge about such methods is indispensable for proper configuration of contemporary convergent computer network. Weakness of known QoS methods constitutes motivation to search new and more effective approaches supporting a real-time communication in the Internet [14 16]. 2. QoS Models Currently, there are three models of ensuring the QoS in the computer networks. BestEfford (BES) model is responsible for transmission of data of the highest possible bandwidth. In this model no service guarantees are provided. The QoS obtained by a user depends largely on current network load. An example of service usage is a queuing method First In First Out (FIFO). Integrated Services (IntServ) [4] model provides high QoS. IntServ defines processes of signalling software to network. Before the commencement of data transmission the software requires particular type of service. The software transfers a traffic profile and asks for specific traffic parameters that can ensure required bandwidth and level of delay. The software is expected to commence transfer of data streams only after obtaining response from network and in order to check their compatibility with the traffic profile communicated to network. Network conducts controls of its resources, checks if it can provide proper parameters to the new data stream. The usage of IntServ introduces guarantee of delivery of data packages, yet it largely restricts network scalability. Differentiated Services (DiffServ) [4] is a multiple service model that can fulfil various QoS requirements. Unlike integrated services model applications using differentiated methods it does not signalize requirements demanded from network before transmission. The differentiated model attempts to deliver data packages in compliance with priority of each of them. The priority is a value that can be set using: value included in the IP Precedence field belonging to the header of IPv4 protocol. Network uses this specification to classify, mark and shape traffic in network. 30

2 2. QoS Techniques Fig. 1 presents division of QoS intro three basic groups: congestion avoidance, policing and shaping, queuing methods. Each of mechanisms modifies traffic in its particular way thanks to which it is possible to shape it properly according to requirements demanded by users. Data packages sent to network first undergo classification, i.e. traffic grouping. The grouping is conducted with regard to principles entered by an administrator. In the next stage, each traffic group (traffic class) obtains assigned priority value. For this purpose the fields: IP Precedence and Differentiated services code point, DSCP in IPv4 and IPv6 protocols are used. On the basis of these parameters the transmission devices inside the computer network determine how important is a given package without analysis of its content. Such a strategy allows reducing the time necessary to pass routers by packages to reach the destination network. This factor has a main impact on transmission delay constituting one of the most important quality parameters in the network communication. 2.1 Policing and Shaping The Policing and Shaping are two main approaches, which allow managing the excessive number of packages in the computer network. After obtaining the overflow traffic by the routers the Shaping method causes rejection of excessive data packets whereas in the Policing method the packets are stored in the queues for the later transmission. In this way an increased delay for packages appears, but the number of rejected packages decreases. Both, mechanisms are presented in Fig Queuing methods Fig.2. Policing and Shaping First In, First Out (FIFO) [11] is a method of queuing consisting in buffering and sending packets in the order of their arrival. This means that a packet that reached the queue as the first one will be served by it ahead of packets that will enter it after it. Each data packet is sent in its entirety (served until the end) - while using this method no preemption occurs. Priority Queuing (PQ) [11] is a modification of FIFO queuing method. Its operation is based on four queues. Each of these is a separate FIFO queue. Before entering these queues traffic is analysed and on the basis of the network principles defined by an administrator it is appropriately assigned to particular queues. Each of the four available queues has arbitrarily assigned priority. At a given time only one queue has an access to the connection. The order of queue service determines its priority. Each queue is served until sending all the packets or alternatively connection preemption can occur. This happens due to occurrence of traffic qualified to a queue of higher priority than currently served Fig.1. QoS Techniques 31

3 Configuring Custom (CQ) [6] is composed of seventeen outgoing queues but only sixteen of them can be managed. Each queue has an access time assigned to a connection bandwidth. If after certain time determined in a queue packets the algorithm closes the stream and proceeds to next queue. If there is a queue declared in network, but traffic assigned to it doesn't occur, then the connection is left unused during the time assigned to this queue. Weighted Fair Queuing (WFQ) [6] is a dynamic planning method that assures an equal division of bandwidth for each type of traffic present in network. This mechanism is analysed by IP header of in incoming packet. It reads package value then it allocates bandwidth value to data transmission. Transmissions with higher priority receive an increased share of the bandwidth in comparison to the ones with lower priority. The WFQ algorithm is a flow one as if there is an empty queue (there are no packages in it), then the time belonging to connection bandwidth is not used, but dynamically distributed among other queues in which at a particular moment there are data packages waiting to be sent Class-Based Weighted Fair Queuing (CBWFQ) [6] is an extension of functionality of the WFQ method by the provision of the support for the traffic classes defined by a user. Low Latency Queuing (LLQ) [6] consists of best features of the CBWFQ and PQ methods. Like in the case of the CBWFQ the operation of the LLQ mechanism is based on differentiation of traffic classes. Such a method is better scaled as it does not require recognition of each data stream and reservation of bandwidth for it. Packages holding crucial data requiring provision of high QoS, are placed in one privileged queue of strict priority type. The packages included in it are served prior to other packages. The packages, that do not end up in privileged queue, are treated according to principles binding in the CBWFQ mechanism. 2.3 Preventing congestion methods The overload of the queue results in the traffic congestions. In this situation the mechanisms ensuring low probability of loss of VoIP data should be introduced to the computer network. In order to solve such a problem one of the two methods of congestion prevention can be used: Tail Drop (TD) [13] is an algorithm whose operation is based on the principle of rejecting all incoming packages that cannot be stored in an already filled-up queue. The method causes dramatic changes in speed of data transmission. It also has a negative effect on transmission of data using Transmission Control Protocol (TCP). For the TD method it does not matter what traffic class is assigned to rejected packages, if they carry traffic of VoIP type or for example packages carrying data to Internet browsers as it removes all those packages leveling congestions. TD method does not provide high QoS in computer networks because whole data streams belonging to crucial services can be rejected in the case of filling a queue. Weighted Random Early Detection (WRED) [13] is a modification of Random Early Detection (RED) [12] mechanism and bases on the rejection of selected packages before overloading a queue. Decision about removed number of packets and type of queue is taken on the basis of packets priority in a queue. For example, the number of rejected packages of Hyper Text Transfer Protocol (HTTP) will be much bigger than in the case of VoIP type. 4. Implementing QoS mechanisms The purpose of experiments is a comparison of the selected QoS methods according to delays in data transmission. The experiments were conducted in laboratory computer network using Cisco devices. The topology of the examined network is presented in Fig. 3. It consists of three routers, three switches and six hosts. Four of the hosts (SIP, HTTP, SMTP, FTP) are used to generate traffic and transfer it in the direction of the hosts OD1 and OD2 with implemented software for analysis of network traffic. The generated packets belong to the following protocols: Session Initiation Protocol (SIP), HTTP, Simple Mail Transfer Protocol (SMTP), File Transfer Protocol (FTP). They represent the most commonly used services in the computer networks. Real-time services are represented by SIP protocol. The computer network was configured for IPv4 and IPv6 communication protocols.. Thanks to the usage of network constructed in the laboratory it is possible to provide the same conditions for each examined method. The examination used an author software 'Generator' and application 'Wireshark' [7]. Packages marking and classification occur using interfaces F0/0 and F0/1 belonging to router A. Queuing and preventing congestion methods are implement on outgoing port S0/0/1 of the router A. 32

4 Furthermore, the delay level also obtained very good level. On the basis of the conducted tests it may be concluded that the LLQ queuing method works best with handling traffic generated by real-time software in terms of delays and level of packages rejection. Fig.3. Diagram of the computer network Fig. 4-6 present traffic inside network using different methods of queuing. The schemes present traffic in network based on communication protocol IPv6. Table 1 presents parameters of transmission obtained through particular types of traffic in the network with various queuing methods. Exemplary results were presented in Fig. 4 that show effect of queuing method WFQ. Each type of traffic obtained different value of bandwidth connection. The greater the share, the higher the priority assigned to a package. Thanks to this all the network services possess access to the connection. It is convenient in networks where proper quality for selected services is not important. Such policy leads to the growth of packages rejections. Because of that it is not suited to handle VoIP traffic which is especially vulnerable to this transmission parameter. The CBWFQ method presented in Fig. 5 exhibited greater level of matching bandwidth value to traffic priority. Allocation in the line is done on the basis of declared value of traffic priority. The mechanism caused differentiated allocation of bandwidth. The SIP traffic, representing real-time services, obtained the highest value. However, analysis of the results in Tab. 1. shows that the method did not improve transmission parameters considerably. On the contrary, it caused increase in delays in relation to the WFQ mechanism. The CBWFQ facilitates network management, introduces possibility of managing traffic class as opposed to individual streams, which happens in the case of the WFQ. Fig.6 presents packages flow in a computer network using the LLQ queuing method. Irrespective of number of various packages in the network the mechanism allocates constant bandwidth value to a defined traffic. If there are new traffic streams in a network, then also bandwidth value for the most important traffic is decreased. The analysis of the results in Table 1 shows that the level of rejection of packages for the SIP traffic in the LLQ method obtained the lowest value among the examined queuing mechanisms. Fig.4. Results of the WFQ queuing application Fig.5. Results of the CBWFQ queuing application Fig.6. Results of the LLQ queuing application 33

5 FTP HTTP SIP Traffic Tab. 1. IPv6 - Comparison of queuing methods Parameter WFQ CBWFQ LLQ delay [ms] 2,06 4,5 2,2 packets dropped [%] delay [ms] 3 8,5 3,9 packets dropped [%] delay [ms] 2,6 12 8,7 packets dropped [%] As presented in Tab. 2. the differences in network efficiency using those two communication protocols are substantial. Network based on the IPv6 obtained better transmission parameters than the one based on the IPv4. The difference in the results is caused by difference in construction of the IPv4 and IPv6 protocol headers. The header in IPv6 does not have certain fields available in the IPv4. Additionally, the IPv6 possesses constant length of its header. The IPv6 is much simpler than the header of the previous version of the protocol thanks to which it is much simpler to process by network devices. It has an obvious effect on time needed to handle data packages. Next tests were devoted to operation of mechanisms preventing congestion (Figs. 7-8). SMTP delay [ms] 2,2 10,1 10,4 packets dropped [%] In the examined network it is possible to communicate using two communication protocols IPv4 and IPv6. The older and most popular is the IPv4. The results of the measurements presented so far were obtained in a network having a newer version of the IPv6 protocol. Table 2 presents comparison of transmission parameters obtained by using the LLQ queuing mechanism. Tab. 2. Comparison of queuing method LLQ in the IPv4 and IPv6 protocols Fig.7. Results of TD mechanism application Traffic Parameter LLQ - IPv4 SMTP FTP HTTP SIP LLQ - IPv6 delay [ms] 8,37 2,2 packets dropped [%] 7 2 delay [ms] 12,5 3,9 packets dropped [%] delay [ms] 50,9 8,7 packets dropped [%] delay [ms] 460,9 10,4 packets dropped [%] Fig.8. Results of the WRED application The TD method begins its action after filling up queuing methods. This causes rejection of all packages incoming to a node and not accepted by the queuing buffer. Its function is depicted in Fig. 7. First data string presents operation of a network 34

6 without restrictions, the other one was restricted by traffic. Fig. 8 presents operation of the WRED method that is activated when queues are filled up and not when they are empty. It rejects intelligently individual packages, not whole data strings which is reflected in better quality of data transmission. It is worth noting that the obtained results for the examined jam prevention mechanisms do not depend on the type of applied IP protocol. 5. Summary This article includes a review of basic methods used to provide the QoS. However, network is a variable environment in which setting the highest allocation of bandwidth doesn't guarantee its optimal management. In order to provide the best management of bandwidth it is possible to analyse flow of packages in computer network in real time. The results of traffic analysis can be used for dynamic adjustment of network depending on type of packages included in it currently. Further works attempt to create a system which would optimize connection bandwidth management. 6. Bibliography 1. J. Ellis, C. Ursell, J. Rahman: Voice, Video, and Data Network Convergence, Academic Press, San Diego, T. Braun, M. Diaz, J. Enríquez-Gabeiras, T. Staub: End-to-End Quality of Service Over Heterogeneous Networks, Springer-Verlag, Berlin, Z. Wang: Internet QoS, Morgan Kaufmann Publishers, San Francisco, R. Hunt: A review of quality of service mechanisms in IP-based networks integrated and differentiated services, multi-layer switching, MPLS and traffic engineering, Computer Communications Volume 25, Issue 1, 1 January 2002, Pages D. Sierociuk, A. Dzieliński: Fractional Kalman filter algorithm for the states, parameters and order of fractional system estimation, International Journal of Applied Mathematics and Computer Science Vol. 16., No ns_docs/qos_solutions/qosvoip/qosvoip.pdf W. Flangan: Understanding VoIP and Unified Communications, John Wiley & Sons, New Jersey K. Roebuck: Video Telepresence, Emereo Pty Ltd M. Barreiros, P. Lundqvist: QOS-Enabled Networks: Tools and Foundations, John Wiley & Sons, New Jersey P. Wróblewski: Algorytmy,struktury danych i techniki programowania, Helion, Gliwice, A. Chydziński, Ł. Chróst: Analysis of AQM queues with queue size based packet dropping, International Journal of Applied Mathematics and Computer Science Vol. 21., No /qos/configuration/guide/qcfconav.pdf 14. A. Abouzeid, S. Roy: Modeling random early detection in a differentiated services network, Computer Networks 40 (2002) A. Francini: Periodic early detection for improved TCP performance and energy efficiency, Computer Networks 56 (2012) K. Kim, C. Choi: Queue delay estimation and its application to TCP Vegas, Computer Networks 43 (2003) Authors: M.Sc. Paweł Onyśków University of Zielona Góra Faculty of Electrical Engineering, Computer Science and Telecommunications Institute of Control and Computation Engineering ul. Profesora Szafrana Zielona Góra paonyskow@gmail.com The work was done under Ph.D. Marcin Mrugalski s supervision. 35