The recently developed H.264/AVC video codec with Scalable Video Coding (SVC) extension, compresses non-scalable (single-layer) and scalable video significantly more efficiently than MPEG–4 Part 2. Since the traffic characteristics of encoded video have a significant impact on its network transport, we examine the bit rate-distortion and bit rate variability-distortion performance of single-layer video traffic of the H.264/AVC codec and SVC extension using long CIF resolution videos. We also compare the traffic characteristics of the hierarchical B frames (SVC) versus classical B frames. In addition, we examine the impact of frame size smoothing on the video traffic to mitigate the effect of bit rate variabilities. We find that compared to MPEG–4 Part 2, the H.264/AVC codec and SVC extension achieve lower average bit rates at the expense of significantly increased traffic variabilities that remain at a high level even with smoothing. Through simulations we investigate the implications of this increase in rate variability on (i) frame losses when transmitting a single video, and (ii) on the number of supported video streams in a bufferless statistical multiplexing scenario with restricted link capacity and information loss. We find increased frame losses, and rate-distortion/rate-variability/encoding complexity tradeoffs. We conclude that solely assessing bit rate-distortion improvements of video encoder technologies is not sufficient to predict the performance in specific networked application scenarios. Index Terms Frame loss ratio, H.264/AVC, hierarchical B frames, rate-distortion (RD), rate variability-distortion (VD), single-layer video, statistical multiplexing, SVC, video traffic. I.

The focus of this paper is on developing and evaluating a practical methodology for determining if and when different types of traffic can be safely multiplexed within the same service class. The use of class rather than individual service guarantees offers many advantages in terms of scalability, but raises the concern that not all users within a class see the same performance. Understanding when and why a user will experience performance that differs significantly from that of other users in its class is, therefore, of importance. Our approach relies on an analytical model developed under a number of simplifying assumptions, which we test using several real traffic traces corresponding to different types of users. This testing is carried out primarily by means of simulation, to allow a comprehensive coverage of different configurations. Our findings establish that although the simplistic model does not accurately predict the absolute performance that individual users experience, it is quite successful and robust when it comes to identifying situations that can give rise to substantial performance deviations within a service class. As a result, it provides a simple and practical tool for rapidly characterizing real traffic profiles that can be safely multiplexed.

Class-based traffic treatment frameworks such as Differentiated Service (DiffServ) have been proposed to resolve the poor scalability problem in the flow-based approach. Although the performance is differentiated in a class-based basis, the performance seen by individual flows in the same class may differ from that seen by the class and has not been well understood. We investigate this issue by simulation in a single node under FIFO, static priority, waiting time priority, and weighted fair queueing scheduling schemes. Our results indicate that such performance discrepancy occurs especially when flows joining the same class are heterogeneous, which is not uncommon considering that the same type of applications can generate traffic having very different statistical behaviors such as video traffic with different activity levels, or voice traffic with different compression schemes. We found that per-flow delay statistics, including the average and the percentile delay, can be very different from the corresponding class delay statistics, depending on flow burstiness, overall traffic load, as well as the queue discipline. We also propose a solution to reduce the mean delay variance experienced by flows in the same class.

Abstract — Service Level Agreements (SLAs) are contracts signed between a provider and a customer to govern the amount of traffic that will be serviced. The Metro-Ethernet access network, the Differentiated Services (DiffServ) architecture and the ATM reference model are three architectural models where edge routers perform traffic metering and coloring of aggregated flows according to the SLA. In this paper we examine an important problem faced by the Internet service provider (ISP) which is how to provide service differentiation for aggregates of multiple TCP connections that have different data volumes and packet sizes to transfer, as it is in the real Internet traffic mix. Finer color marking was suggested to improve differentiation quality. We observe that increasing the number of colors indeed provides a good differentiation between the aggregates according to the committed and the excess rates. We also show that the token bucket coloring policies, which are widely used for this purpose, prefer short packets and mark them with higher priority colors. We also show that the differentiation process is more difficult for the short TCP connections that remain in the slow start phase, than for the long connections that are usually in the congestion avoidance phase. I.

Abstract: To support multimedia applications, it is desirable that an ad hoc network has a provision of Quality of Service (QoS). However, the provision of QoS in a mobile ad hoc network is a challenging task. In this paper, we present a review of the current research related to the provision of QoS in an ad hoc environment. We examine issues and challenges involved in providing QoS in an ad hoc network. We discuss methods of QoS provisioning at different levels including those at the levels of routing, Medium Access Control (MAC), and cross layer. Also, we discuss schemes for admission control and scheduling that are proposed in the literature for the provision of QoS. We compare salient features of various solutions and approaches and point out directions for future work.

Abstract — The integration of third generation (3G) cellular networks and IEEE 802.16e networks is an important interworking case within the forthcoming fourth generation (4G) heterogeneous wireless networks. In this paper, we extend the virtual partitioning with preemption technique for admission control in cellular/802.16e interworking and evaluate its performance. First, we describe the mobility scenario between 3G cellular networks and IEEE 802.16e networks in terms of the horizontal (intra-system) and vertical (inter-system) handoffs that can occur and derive the corresponding handoff rate equations. We then propose admission control algorithms for connection requests that consider the class of service (i.e., real-time or non-real-time) and the type of user (i.e., new or handoff). For the handoff requests, different priority is assigned to each type of handoff. A joint connection and packet-level optimization approach is used for quality of service (QoS) provisioning. The accuracy of the analytical model is validated via simulations. Numerical results show significant performance improvement. The blocking probabilities for new connection requests can be reduced by 70% when the joint QoS optimization approach is used. Index Terms — Cellular/802.16e interworking, handoff management, admission control, heterogeneous wireless networks.