Juan J. Ramos-Munoz

Analysis and modelling of YouTube traffic

YouTube currently accounts for a significant percentage of the Internets global traffic. Hence, understanding the characteristics of the YouTube traffic generation pattern can provide a significant advantage in predicting user video quality and in enhancing network design. In this paper, we present a characterisation of the traffic generated by YouTube when accessed from a regular PC. On the basis of this characterisation, a YouTube server traffic generation model is proposed, which, for example, can be easily implemented in simulation tools. The derived characterisation and model are based on experimental evaluations of traffic generated by the application layer of YouTube servers. A YouTube server commences the download with an initial burst and later throttles down the generation rate. If the available bandwidth is reduced (e.g. in the presence of network congestion), the server behaves as if the data excess that cannot be transmitted because of the reduced bandwidth were accumulated at a servers buffer, which is later drained if the bandwidth availability is recovered. As we will show, the video clip encoding rate plays a relevant role in determining the traffic generation rate, and therefore, a cumulative density function for the most viewed video clips will be presented. The proposed traffic generation model was implemented in a YouTube emulation server, and the generated synthetic traffic traces were compared with downloads from the original YouTube server. The results show that the relative error between downloads from the emulation server and the original server does not exceed 6% for the 90% of the considered videos. Copyright

QoE oriented cross-layer design of a resource allocation algorithm in beyond 3G systems

The provision of high speed access to Internet and IP-based services is one of the main goals of beyond 3G (B3G) wireless systems. These systems will benefit from cross-layer protocol designs that will introduce interactions between different layers to obtain performance gains. The majority of the research in the field of cross-layer in B3G systems aims at improving quality of service (QoS) system centric metrics such as spectral efficiency, service latency, delay variation (jitter), etc. However, minor attention has been paid to the satisfaction of the subjective quality requirements from human users. With the goal of incorporating the subjective human perception into the cross-layer design of B3G systems, this work carries out an experimental survey of the sensitivity of the user subjective quality to the service response time for the Web browsing application. From the experimental results, a mapping from service response time and user data rate (provided by the wireless link) to mean opinion score (MOS) is derived. The presented results will show that the Web page size plays an important role in the mapping function. The derived mapping function is incorporated into a radio resource allocation algorithm for orthogonal frequency division multiple access (OFDMA) systems. This incorporation is carried out maximizing the aggregate utility over all the users in the cell. Its performance has been compared to that of the multicarrier proportional fair (MPF) under heavy load conditions with a 3G LTE simulator. The results have shown that the proposed methodology can provide an interesting enhancement of the user experienced quality compared to the MPF algorithm.

Characteristics of mobile youtube traffic

In this work we present the characterization of the mobile network traffic generated by one of the most relevant social networking applications: YouTube. Understanding its characteristics is of major importance to evaluate its impact on mobile networks and optimize network or application design. For this purpose, we have performed a set of experiments capturing traffic from Apple iOS and Android terminals connected to 3G mobile networks. Our results show that the video formats are 3GP formats, which use lower encoding rates than in other networks. As in accesses from other networks, YouTube servers transfer the video clip with an initial burst and a throttling phase, but they apply different parameters for clients located in mobile networks. Additionally, the mobile terminal can strongly influence the download. Our results with high-end Android terminals show that the client implements a dual-threshold buffer policy that interrupts and resumes the download depending on its buffer occupancy. Our results with iOS terminals show that the video clip download is not interrupted by the client, and a large amount of data may be accumulated at the player buffer. In mid-range Android terminals the TCP receive window may additionally throttle the download if the player buffer is filled up.

Network Slicing for 5G with SDN/NFV: Concepts, Architectures, and Challenges

The fifth generation of mobile communications is anticipated to open up innovation opportunities for new industries such as vertical markets. However, these verticals originate myriad use cases with diverging requirements that future 5G networks have to efficiently support. Network slicing may be a natural solution to simultaneously accommodate, over a common network infrastructure, the wide range of services that vertical- specific use cases will demand. In this article, we present the network slicing concept, with a particular focus on its application to 5G systems. We start by summarizing the key aspects that enable the realization of so-called network slices. Then we give a brief overview on the SDN architecture proposed by the ONF and show that it provides tools to support slicing. We argue that although such architecture paves the way for network slicing implementation, it lacks some essential capabilities that can be supplied by NFV. Hence, we analyze a proposal from ETSI to incorporate the capabilities of SDN into the NFV architecture. Additionally, we present an example scenario that combines SDN and NFV technologies to address the realization of network slices. Finally, we summarize the open research issues with the purpose of motivating new advances in this field.

A Simple Model for Predicting the Number and Duration of Rebuffering Events for YouTube Flows

In this paper, we propose a simple model for predicting the number of rebuffering events and their duration in progressive downloads from YouTube. These metrics are necessary to predict the quality perceived by YouTube users. The proposed rebuffering model is based on two thresholds of the amount of data stored by the player buffer: the first threshold is extracted from the results of previous studies, and the second is derived from the experimental results presented in this paper. The proposed model can be easily implemented in simulation tools and we present an example of its use in a Long-Term Evolution simulator in which the mentioned quality metrics have been estimated for different users.

Selective packet dropping for VoIP and TCP flows

The adoption of the IP protocol for serving diverse applications arises the need for mechanisms to prevent network congestion in scenarios with different traffic types (responsive and unresponsive) sharing limited network resources. To deal with this issue, a number of algorithms for active queue management (AQM) have been proposed. However, most of them do not observe the traffic type and usually disregard this knowledge. In this way, the provided service could not comply with the distinctive requirements of the different type of traffic, such as VoIP services, which demand bounded packet latency and loss rate.This paper proposes a new approach to be applied for preventing network congestion in AQM routers. Our scheme includes a procedure for selecting the packet to be dropped that improves the fairness among different classes of flows. We evaluate the use of this approach on distinct AQM schemes in scenarios with different degrees of UDP and TCP traffic mix. Objective and subjective performance measurements are reported. The experimental evaluation indicates that our approach improves the fairness among different traffic classes without using any packet scheduler. In fact, it also improves the VoIP traffic performance in terms of packet dropping probability, MOS (Mean Opinion Score) and intelligibility. We also show that our approach has no negative impact on the packet delay. Moreover, it is not achieved at the expense of TCP responsive traffic.

Latency evaluation of a virtualized MME

Network Virtualization is one of the key technologies for developing the future mobile networks. In this paper we propose an LTE virtualized Mobility Management Entity queue model to evaluate its service time for a given signaling workload. Additionally, we provide a compound data traffic model for the future mobile applications, and we predict theoretically the control workload that it will generate. Finally, we evaluate the virtualized Mobility Management Entity overall mean delay by simulation, providing insights for selecting the number of processing instances for a given number of users.

Serial experiments online

Current network protocols must comply with rigid interfaces and rules of behavior to fit into well defined, vertical protocol stacks. It is difficult for network designers to offer a wide spectrum of alternative protocols suitable for diverse situations, and to make the stack evolve to match new needs. The tendency is to design protocols that can adapt to the widest possible spread of use. However, even the best adaptive protocols cannot possibly cope with all situations. When their adaptivity limits are reached, the ability to switch to other protocols becomes a clear advantage Our aim in this paper is to present Lightweight Autonomous resIlient Networks (LAIN), a framework that exploits the multiplicity of alternative protocol, and exposes the spectrum of choice to the advantage of the applications. The system runs continuous experiments with alternative protocols online, in parallel as well as serially, in order to select automatically those that best match the applications needs under the current network conditions. We report first results on the feasibility of the approach and point out the need for such a system in network and protocol evolution

Optimized LTE data transmission procedures for IoT: Device side energy consumption analysis

The efficient deployment of Internet of Things (IoT) over cellular networks, such as Long Term Evolution (LTE) or the next generation 5G, entails several challenges. For massive IoT, reducing the energy consumption on the device side becomes essential. One of the main characteristics of massive IoT is small data transmissions. To improve the support of them, the 3GPP has included two novel optimizations in LTE: one of them based on the Control Plane (CP), and the other on the User Plane (UP). In this paper, we analyze the average energy consumption per data packet using these two optimizations compared to conventional LTE Service Request procedure. We propose an analytical model to calculate the energy consumption for each procedure based on a Markov chain. In the considered scenario, for large and small Inter-Arrival Times (IATs), the results of the three procedures are similar. While for medium IATs CP reduces the energy consumption per packet up to 87% due to its connection release optimization.

Removing redundant TCP functionalities in wired-cum-wireless networks with IEEE 802.11e HCCA support

The TCP was originally designed for wired networks, assuming transmission errors were negligible. Actually, any acknowledgment time-out unconditionally triggers the congestion control mechanism, even in wireless networks in which this assumption is not valid. Consequently, in wireless networks, TCP performance significantly degrades. To avoid this degradation, this paper proposes the so-called split TCP and UDP. In this approach, the access point splits the TCP connection and uses a customized and lighter transport protocol for the wireless segment. It takes advantage of the IEEE 802.11e Hybrid Coordination Function Controlled Channel Access HCCA mechanisms to remove redundant TCP functionalities. Specifically, the HCCA scheduler allows disabling of the congestion control in the wireless link. Similarly, the IEEE 802.11e error control service makes possible to eliminate TCP acknowledgments, therefore reducing the TCP protocol overhead. Finally, the usage of an HCCA scheduler permits providing fairness among the different data flows. The proposed split scheme is evaluated via extensive simulations. Results show that split TCP and User Datagram Protocol outperforms the analyzed TCP flavors-specifically designed for wireless environments-and the split TCP solution, achieving up to 95% of end-user throughput gain. Furthermore, the proposed solution is TCP friendly because TCP flows are not degraded by the presence of flows by using this approach. Copyright