Future Network Services Research Articles

Delivering relative differentiated services in future high-speed networks using hierarchical dynamic deficit round robin

With the increasing deployment of real-time audio/video services over the Internet, provision of quality of service (QoS) has attracted much attention. When the line rate of future networks upgrades to multi-terabits per second, if routers/switches intend to deliver differentiated services through packet scheduling, the reduction of computational overhead and elimination of bottleneck resulting from memory latency will both become important factors. In addition, the decrease of average queueing delay and provision of small delays for short packets are two further critical factors influencing the delivery of better QoS for real-time applications. The advanced waiting time priority (AWTP) is a timestamp-based packet scheduler which is enhanced from the well-known WTP. Although AWTP considers the effect of packet size, the latency resulting from timestamp access and a great quantity of computational overhead may result in bottlenecks for AWTP being deployed over high-speed links. Many existing schedulers have the same problems. We propose a multi-level hierarchical dynamic deficit round-robin (MLHDDRR) scheduling scheme which is enhanced from the existing dynamic deficit round-robin scheduler. The new scheme can resolve these issues and efficiently provide relative differentiated services under a variety of load conditions. Besides, MLHDDRR can also protect the highest priority traffic from significant performance degradation due to bursts of low-priority traffic. We compare the performance of AWTP with the proposed scheme. Extensive simulation results and complexity analysis are presented to illustrate the effectiveness and efficiency of MLHDDRR.

Effective capacity channel model for frequency-selective fading channels

To efficiently support quality of service (QoS) in future wireless networks, it is important to model a wireless channel in terms of connection-level QoS metrics such as data rate, delay and delay-violation probability. To achieve this, in [7], we proposed and developed a link-layer channel model termed effective capacity (EC) for flat fading channels. In this paper, we apply the effective capacity technique to modeling frequency selective fading channels. Specifically, we utilize the duality between the distribution of a queue with superposition of N i.i.d. sources, and the distribution of a queue with a frequency-selective fading channel that consists of N i.i.d. sub-channels, to model a frequency selective fading channel. In the proposed model, a frequency selective fading channel is modeled by three EC functions; we also propose a simple and efficient algorithm to estimate these EC functions. Simulation results show that the actual QoS metric is closely approximated by the QoS metric predicted by the proposed EC channel model. The accuracy of the prediction using our model can translate into efficiency in admission control and resource reservation.

Enabling Technologies for Next-Generation Optical Packet-Switching Networks

The optical packet-switching network is considered to be one of the most promising solutions for end-to-end delivery of high-bitrate data, video, and voice signals across optical networks of the future. Optical label switching (OLS) technology incurs simpler extraction and processing of the labels so that the optical packets can be routed with low latency to the destinations. We have developed several key enabling technologies for integrated optical networks, including optical label generation, label swapping, optical buffering, clock recovery, and wavelength conversion. We have designed and experimentally demonstrated these enabling techniques that can provide efficient broadband services in future optical networks.

Movement-based mobility management and trade off analysis for wireless mobile networks

Mobility management plays a central role in providing ubiquitous communications services in future wireless mobile networks. In mobility management, there are two key operations, location update and paging, commonly used in tracking mobile users on the move. Location update is to inform the network about a mobile user's current location, while paging is used for the network to locate a mobile user. Both operations will incur signaling traffic in the resource limited wireless networks. The more frequent the location updates, the less paging in locating a mobile user; thus, there is a trade off in terms of signaling cost. Most trade off analysis in the literature is carried out under the assumption that some time variables are exponentially distributed. However, such assumptions will not be valid, particularly for the wireless Internet. In this paper, we present some general analytical results without these assumptions, which are essential for the general trade off analysis. Specifically, we analytically derive the average number of location updates during the interservice time for a movement-based location update scheme under fairly realistic assumptions, which are crucial for all trade off analysis. Our general analytical results make thorough numerical analysis for finding the optimal mobility management under various network operation scenarios possible.

An adaptive path routing scheme for satellite IP networks

AbstractMobile satellites can be considered as the promising solution to the global IP network. In order to provide quality of service (QoS) in future networks, mobile satellite can be integrated with the asynchronous transfer mode (ATM) to switch IP datagrams in the space. For such a network, new and sophisticated routing and handoff algorithms are essential. In this paper, a new scheme called adaptive path routing scheme (APRS) is proposed. It is shown that the APRS can provide superior performance for routing and handoff in mobile satellite networks compared with conventional schemes. Copyright © 2003 John Wiley & Sons, Ltd.

On the time scales in video traffic characterization for queueing behavior

To guarantee quality of service (QoS) in future integrated service networks, traffic sources must be characterized to capture the traffic characteristics relevant to network performance. Recent studies reveal that multimedia traffic shows burstiness over multiple time scales and long range dependence (LRD). While researchers agree on the importance of traffic correlation, there is no agreement on how much correlation should be incorporated into a traffic model for performance estimation and dimensioning of networks. In this article, we present an approach for defining a relevant time scale for the characterization of VBR video traffic in the sense of queueing delay. We first consider the Reich formula and characterize traffic by the Piecewise Linear Arrival Envelope Function (PLAEF). We then define the cutoff interval above which the correlation does not affect the queue buildup. The cutoff interval is the upper bound of the time scale which is required for the estimation of queue size and thus the characterization of VBR video traffic. We also give a procedure to approximate the empirical PLAEF with a concave function; this significantly simplifies the calculation in the estimation of the cutoff interval and delay bound with little estimation loss. We quantify the relationship between the time scale in the correlation of video traffic and the queue buildup using a set of experiments with traces of MPEG/JPEG-compressed video. We show that the critical interval, i.e. the range for the correlation relevant to the queueing delay, depends on the traffic load: as the traffic load increases, the range of the time scale required for estimation for queueing delay also increases. These results offer further insights into the implication of LRD in VBR video traffic.

Optical services in future broadband networks

Optical transmission technology is progressing to the point where it can deliver data at rates that can strain conventional electronic broadband networks. We discuss how optical networks may play a role in relieving this strain. Different optical network architectures are discussed according to the services they provide, the technologies used to implement those services, and the geographical size of the network. We first discuss broadband network architectures and where optics might play a role in the protocol stack. We then discuss in detail the services optical networks can provide, the technologies used to implement those services, and some of the major technological limitations. Finally, we use this knowledge base to analyze the potential role of optics in WANs, MANs, and then local area networks (LANs).

An adaptive congestion control scheme for real time packet video transport

We show that modulating the source rate of a video encoder based on congestion signals from the network has two major benefits: the quality of the video transmission degrades gracefully when the network is congested and the transmission capacity is used efficiently. Source rate modulation techniques have been used in the past in designing fixed rate video encoders used over telephone networks. In such constant bit rate encoders, the source rate modulation is done using feedback information about the occupancy of a local buffer. Thus, the feedback information is available instantaneously to the encoder. In the scheme proposed, the feedback may be delayed by several frames because it comes from an intermediate switching node of a packet switched network. The paper shows the proposed scheme performs quite well despite this delay in feedback. We believe the use of such schemes will simplify the architecture used for supporting real time video services in future nationwide gigabit networks.

Analysis of quality factors in synthetic speech produced by rules

This paper investigates how various factors affect the quality of synthetic speech produced by rules. Using rules to synthesize speech will be an important technique for providing various telecommunication services in future intelligent networks. The quality of synthetic speech is generally measured by subjectively evaluating the speech from the viewpoint of intelligibility, or by comparing it with the quality of other types of synthetic speech. However, the development of a practical speech synthesis method for use in telecommunication networks requires an overall quality evaluation, including intelligibility and naturalness. The quality should be compared with that of natural telephone speech. To establish an overall quality evaluation method, the effects of several factors on the overall quality (expressed by MOS) of speech synthesized by several Japanese text-to-speech systems are quantitatively compared with the effects of using additive speech-correlated white noise as a natural speech material. Experimental results show that such factors as subject, listening experience, average pitch frequency, and text affect synthetic speech more than natural speech. Quality evaluation characteristics due to these factors are discussed and an overall quality evaluation method for synthetic speech is proposed.

An adaptive congestion control scheme for real-time packet video transport

In this paper we show that modulating the source rate of a video encoder based on feedback information from the network results in graceful degradation in picture quality during periods of congestion. Such source rate modulation techniques have been used in the past in designing video encoders used to generate data at a fixed rate. In such constant bit rate encoders, the source rate modulation is done using feedback information about the occupancy of a local buffer. Since the buffer is local, the feedback information is available instantaneously to the encoder. In the proposed scheme, the feedback information is delayed because it comes from within a packet-switching network. The feedback provides information about the traffic at switches along the path of the video connection. We show that the proposed scheme performs well, even though the information is delayed for relatively large intervals of time. We believe that the use of such schemes will simplify the architecture used for supporting real-time services in future nationwide gigabit networks.

Managing SONET equipment

The initial deployment of SONET products in the network has raised the issue of how to manage bandwidth allocations and use network management features to support existing and future network services. The requirements for managing the new transport with the features available, using management systems in existence today, are addressed. It is concluded that SONET will require new solutions in managing tomorrow's, networks, and that operations systems must develop a graceful migration plan in managing the existing and new networks.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fast Packet Technology for Future Switches

New network services other than the traditional voice communications between people will be increasingly bursty in bandwidth needs and will require distributed processing and control. The new fast packet technology for transmission and switching is ideally matched to these future network service needs. In this paper, we give a high-level sketch of the evolution of fast packet switch technology starting with the first packet switches and ending with some architectures that offer promise as potential switching vehicles for Broadband ISDN. We shall be using examples of AT&T experimental switch architectures to illustrate the evolution and technical capabilities.