Vertical WLAN Handover Algorithm and Protocol to Improve the IPTV QoS of the End User Alejandro Cánovas1, Diana Bri2, Sandra Sendra3, Jaime Lloret4 Universitat Politècnica de València, Camino de Vera, s/n. 46022 València. SPAIN
[email protected],
[email protected],
[email protected],
[email protected]
Abstract—The appearance of several IEEE 802.11 variants made possible the availability of many wireless local area network access options for end users in the same location. Network requirements for IPTV service become higher when the quality of the delivered video is higher. Moreover, in wireless networks the network performance is highly degraded when there is high number of users. In this paper, we propose a protocol and algorithm that makes to handover IPTV users to the best available WLAN when the QoS parameters received by the end user reaches a threshold. It guarantees anytime the highest QoS for the user. Real measurements show that the vertical handover performed by the user is performed without noticing it. This algorithm is highly appropriate for mobile users. Keywords-IPTV; handover; QoS; WLAN.
I.
INTRODUCTION
In the recent years, broadband wireless access technologies have evolved spectacularly. They range from different IEEE 802 standards to 3GPP-LTE and 4G systems [1]. All of them have been competing to become the most important wireless technology by improving their features and performance. 4G systems, based completely on IP, assume the combination of several technologies as the best result to provide broadband wireless access for mobile networks. Recent advances suggest that worldwide interoperability for microwave access (WIMAX) and Long Term Evolution (LTE) will be the technological base for the implementation of 4G systems [2]. The evolution of these wireless technologies is focused on increasing their data transfer rate. Their purpose is to support new multimedia services which require higher bandwidths to work correctly and to guarantee the needs of the end users. Nowadays, some of the most demanded multimedia services are Audio/Video On Demand, Voice over IP, IP Television (IPTV), High-definition television or any other Internet multimedia applications [3]. The primary issue in this field is the user’s mobility and the ubiquity requirement provided by the wireless networks. Solutions to enable interoperability between providers and technologies are totally essential to get it. Therefore, roaming and handover models which let interconnect different broadband wireless access technologies are necessary to reach fully mobility and to guarantee ubiquitous networks [4]. In the literature, a handover process generally allows the user to move from one cell to another without loss, or even disruption, of the services that are being used in that moment. The most important handover decision techniques are based on [5]: Received signal strength, available bandwidth, power consumption, monetary cost, service quality, interference,
security, user preferences and imperative handover. Handover operation enables the maintenance of ongoing connections while a user moves across different wireless access networks. In this way, handover procedure requires to re-route the incoming and outgoing traffic of an ongoing connection without causing any interruption from the user's view point. Hence, handover delay is the most important parameter. Some studies, like the one presented in [6], try to decrease this parameter by using positioning techniques. Roaming procedure enables wireless access in areas that are covered by access providers with which the user does not have any prior arrangement. Hence, it does not suppose a continuous re-connection. Roaming thus includes updating the location information of a roaming user, as well as re-routing incoming user traffic to the user's new network placement [7]. There are two kinds of handover: vertical handovers (inter-technologies) and horizontal handovers (intra-technologies). Vertical handover is needed in the field of ubiquitous networks and users’ mobility in order to let a mobile node move between access points of different wireless technologies while interrupting the use of any network service. Bearing in mind this need, Media Independent Handover (MIH) was standardized in 2008 [8]. One way to perform this task is focusing the efforts on the management of the technologies involved in the vertical handover [9]. Moreover, different information can be included to perform decisions depending on the application field (e.g. in [10], for pervasive computing, some authors have used context information regarding user devices, user location, network environment and requested QoS). Other works take into account the power consumption to take handover decisions [11]. It is important to guarantee continuous data reception and QoS to the end user in mobile wireless systems. Thus, we must analyze the QoS at the end user side [12]. In this paper, we propose a handover model based on the QoS of the end user in order to ensure the user’s complete mobility between wireless networks, regardless of the wireless technology. Our algorithm allows the users to roam from one network to another without interrupting the used service. The content of this paper is structured as follows. Research papers related to handover between different wireless technologies are shown in Section 3. Then, in Section 4, we propose an algorithm and protocol to improve the performance of the networks when handover is needed to improve the QoS. Measurements taken from a real system are shown in Section 5. They let us prove the benefits of our handover algorithm. Finally, in Section 6, we summarize our proposal and introduce our future work.
II.
RELATED WORKS
The need of roaming between different wireless technologies is relatively recent. It came with the appearance of multiple wireless local and metropolitan area networks. IEEE 802.21 standard was published in November 2008 [8]. Its objective is to provide the mechanisms needed to optimize handovers between heterogeneous IEEE 802 networks, and between IEEE 802 networks and non IEEE 802 networks (such as cellular networks). Its purpose is to improve the user’s experience by facilitating handover between networks of different media types, including both wired and wireless. In order to achieve it, this standard provides link-layer intelligence and other network information for upper layers. The media types included in this standard are specified by the Third Generation Partnership Project (3GPP), 3G Partnership Project 2 (3GPP2), and both wired and wireless media in the IEEE 802 standards. Besides, this standard supports link adaptation, which is a fundamental issue for this scenario. In this way, when a user needs an application that requires higher data rate, it may handover in order to have higher data rate. Z. Daia et al. presented in [13] an efficient user-driven vertical handover mechanism to be applied between WiMax and WiFi networks. Their proposal does not imply any change on the network or protocol architecture. They propose two independent triggers: the wireless connectivity trigger, based on SINR (Signal to Interference plus Noise Ratio) indication to determine whether a connection is going to be lost, and the performance trigger, that takes into account the data rate and the network load. But this proposal does not guarantee QoS. Some proposals take into account other parameters in the handover decision algorithm (e.g. the power consumption in [11]). But especially this proposal cannot be used for our purpose because authors do not take care of the number of lost packets, which is very important in multimedia delivery. However, before publishing this standard, several works studied this topic from other points of view. In [7], U. Meyer studied the security challenges imposed on wireless access networks by roaming and handover procedures between different network providers. He proposed new secure solutions for inter-provider and inter-system handover. In [14], M. I. Shi et al. propose a secure architecture which offers wireless LAN seamless roaming in wireless LAN/Cellular Mobile Networks. This work presents a set of signaling mechanisms and an application for layer authentication. Finally, a key negotiation scheme is developed in order to keep a secure air transmission when roaming. Li Ma et al. presented a new method based on the stream control transmission protocol (SCTP) to perform seamless vertical handover between different wide-area cellular data networks [15]. This work shows how to interconnect UMTS and WLAN networks by using a new handover system based on that protocol. K. Taniuchi et al. analyzed the IEEE 802.21 standard in detail [16]. On the one hand, the paper shows the IEEE 802.21 standard framework. Authors state that its operation is focused on guaranteeing a seamless mobility for multi-interface devices. On the other hand, they show the design considerations to deploy this standard on several implementations. Finally, the paper indicates how the standard can optimize the handover performance.
In IEEE 802.11 networks, QoS can be guaranteed by using prediction algorithms. In [17], authors proposed the use of an adaptive user mobility prediction algorithm which can be used for advanced resource reservation and service preconfiguration at minimum cost. But, this paper only presents a proposal, providing some simulations, without analyzing the real performance of their system. The main contribution compared with other published works is that we present a real system and its performance, while many others are only simulations or analytical proposals. III.
MANAGEMENT ALGORITHM
One of the main issues of IPTV delivery is the quality of service (QoS) of the network. This problem worsens in wireless networks due to their limited bandwidth and the roaming when a device changes from one wireless network to another. We propose a network management algorithm and protocol for wireless networks in order to ensure the best available IPTV QoS to the end user. Initially, after the device has joined the wireless network, it analyzes the wireless network QoS parameters. If these values exceed a threshold, the system looks for another wireless network in order to guarantee the IPTV QoS of the end user. When this wireless network is found, the device roams to it. If it is not found after a certain time limit, the system returns to its initial state and repeats the process. In the following subsections we describe the proposed algorithm. It can be observed in Fig. 1. This algorithm can be divided in three main phases: QoS analysis phase, wireless network search phase and wireless network roaming phase. A. QoS analysis phase In the analysis phase, after the device joins the wireless network, it tests the network in order to analyze the QoS parameters. These parameters are: jitter, delay and packet loss. Next, these values are stored in memory. According to studies previously made by us in [18] and [19], there is a jitter, delay and packet loss threshold values in which below these values the QoS of the network guarantees a good video quality at the end user. These values are ±20 ms for jitter, 80 ms for delay and 0.1% for packet lost. Then, the system compares these values with the network QoS parameter values performed in the last analysis. If any of these values exceeds the threshold, the system will change to the wireless network search phase. If the system does not exceed the threshold of any parameter for a time slot, the system continues analyzing the network QoS parameters. B.
Wireless network search phase Once the threshold is exceeded, the system changes to the phase of wireless network search. In this phase, the system searches the available wireless networks. This search phase has a time limit in order to prevent the system to remain searching for a long time. Moreover, the overload of the system resources, such as the processing unit and memory, should be avoided. To perform this, we set a timer at the beginning of this phase. The system analyzes existing WLANs and evaluates each network based on the QoS parameters. Once the system has found the network with best QoS parameters, it reads the QoS parameters stored in the memory and compares them.
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Figure 1. Managment algorithm of Wi-Fi networks Access Point (C) IEEE 802.11a
IPTV Multicast Server
239.125.125.55
1. Steps to Association: Client sends probe (A&B).
Access Point (A) IEEE 802.11g
Access Point (B) IEEE 802.11n
APs send Probe Response (A&B). 2. Client evaluates AP response selects best AP: Client sends authentication request to select AP (A). AP (A) confirms authentication. Clients sends association request to select AP (A).
Initial Connection to an Access Point
AP (A) confirms association and registers client in the database server. 3. Multicast connection:
Client 239.125.125.55
Client connect to IPTV multicast server by AP(A)
Figure 2. Managment algorithm of Wi-Fi networks
After comparing QoS parameters, if the QoS parameters of the new wireless network improve the ones of the existing network, then the system starts the roaming process in order to join the new wireless network. Thus, it starts the wireless network roaming phase. If no wireless network has better QoS parameters than the ones obtained in the initial wireless network, the system will keep inside the wireless network and go to the wireless network search phase. This process is repeated until it exceeds the initialized search time. If the system does not detect any available wireless network, it will continue searching until it exceeds the search time limit. C. Wireless network roaming phase The last step is the roaming phase. This starts a roaming process between both networks. First, the device is disconnected from the current wireless network and connects to the new wireless network. Fig. 2 shows the messages sent
between the client and two APs in order to perform a fast roaming procedure (including the authentication phase) in order to continue receiving IPTV streams from the server. Once this phase ends, the systems returns to the first phase, where the device analyzes QoS parameter values. We can see in the algorithm that the most critical part is when the device roams between wireless networks. Roaming can be critical in IPTV delivery, therefore a fundamental issue of this study is to analyze more deeply this moment and see how handover affects to the QoS. IV.
SCENARIO AND MEASUREMENTS RESULTS
This section shows the network topology used to perform the measurements. In addition, we show the handover performed between different technologies with the aim of testing the network performance. Finally, we see the results of the measurements.
TABLE I. WLAN IEEE 802.11n IPTV content distribution network IPTV Server
WLAN IEEE 802.11a
WLAN IEEE 802.11g
IEEE 802.11n Wireless Card
IEEE 802.11a Wireless Card
IEEE 802.11g Wireless Card
Origin Technology IEEE 802.11a IEEE 802.11a IEEE 802.11n IEEE 802.11n IEEE 802.11g IEEE 802.11g
HANDOVER BETWEEN TECHNOLOGIES
Working Frequency 5 GHz. 5 GHz. 2,4 GHz. 2,4 GHz. 2,4 GHz. 2,4 GHz.
Destination Technology IEEE 802.11g IEEE 802.11n IEEE 802.11a IEEE 802.11g IEEE 802.11a IEEE 802.11n
Working Frequency 2,4 GHz. 2,4 GHz. 5 GHz. 2,4 GHz. 5 GHz. 2,4 GHz.
Figure 3. Network topology
A. Scenario In order to perform these measures, we have set up a mixed network formed by a wired side, consisting of an IPTV server and a wireless side, responsible for delivering IPTV service over IEEE 802.11a/g/n technologies to the wireless devices. In order to avoid any dependence with the manufacturer, we used an access point that was able to offer all measured wireless technologies. Fig. 3 shows the network used to gather measurements. This topology is ideal to perform our study because, although it is very simple, it provides all possible cases used in our handover performance test. Moreover, it allows us to analyze different environment conditions in the video streaming process. Table 1 summarizes the scheduled handovers between technologies. B. Measurements Initially, the device belonging to the original technology is receiving video streams from the IPTV server ensuring that the connectivity between the server and the device is correct. After some time, we forced the device to change to another wireless technology with different network parameters in order to show how change the QoS parameters. Next graphs show the performance of our proposal in terms of jitter, delay, and lost packets per sample and packets per second when the device roams between technologies. We took 100 samples before and 100 samples after the roaming process in order to see how the behavior network evolves before and after the moments of the roaming. Fig. 4 shows the number of packets received per second gathered during the roaming between the studied technologies. We have taken 20 seconds before and 20 seconds after the roaming. We observe that the minimum value of received packets is between 95 and 128 packets/sec for all cases. However, when we analyze the average value of the packets/sec received, it is easy to see that the roaming from IEEE 802.11n to IEEE802.11a, and from IEEE802.11n to IEEE 802.11g provides much higher values than in the rest of cases (around 750 packets/sec). In fact, if we compare this value with the roaming from IEEE 802.11a to IEEE802.11n, this value is reduced to almost a third (around 270 packets/sec). The remaining cases present an average value around 305 packets/sec.
Fig. 5 shows the number of lost packets per sample in the roaming process between technologies. On the one hand, we observe that all cases have a packet loss peak around the 100th sample (the point where the roaming between technologies is performed). The cases that present higher number of lost packets are from IEEE 802.11a to IEEE 802.11g, and from IEEE 802.11g to IEEE802.11a, which present the highest values. These values have around 18% lost packets per sample. All other cases have values between 8% and 13% lost packets per sample. Fig. 6 shows the jitter, in ms, gathered during the roaming between technologies. In this case, it is easy to see that the roaming with worst performance is from IEEE 802.11a to IEEE802.11n, with a peak of 2.73 ms. It had an average value of 0.53 ms. Remaining cases present a mean value between 0.25 ms and 0.30 ms, with the exception of the roaming from IEEE 802.11a to IEEE802.11g and from IEEE 802.11g to IEEE802.11a, which present the lowest average values (0.139 ms and 0.074 ms. respectively). Fig. 7 shows the delay, in ms, gathered during the roaming between technologies. If we analyze in detail each measure, we can see that those transitions which origin technology is IEEE 802.11a present delay values much higher than the rest. This value is between 5 ms and 6 ms, showing peaks higher than 20 ms. Other roaming cases have an average value between 2 ms and 4 ms., with maximum values lower than 10 ms in all cases. V.
CONCLUSIONS
In this paper we proposed an algorithm and protocol that takes into account the QoS parameters when the end user is receiving IPTV. We described the proposed algorithm and explained the protocol for its proper operation. The measurements performed in our test bench demonstrates its feasibility because although there are more lost packets, and higher delay and jitter, during the roaming process, they have happened without implying high impact on the quality of the video received by the end user (no video quality degradation was appreciated by the user). We have observed that the worst cases happen when IEEE 802.11a technology is involved. In future works we are going to add to our algorithm a cognitive system in order to learn from the environment and chose the most appropriate wireless network for IPTV delivery based on the knowledge obtained by our previous tests. This cognitive system will use the information gathered from the network and transport layers.
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ACKNOWLEDGEMENTS This work is supported by the Polytechnic University of Valencia, though the PAID-15-10 multidisciplinary projects. REFERENCES
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