Bandwidth sharing: objectives and algorithms

This paper concerns the design of distributed algorithms for sharing network bandwidth resources among contending flows. The classical fairness notion is the so-called max-min fairness. The alternative proportional fairness criterion has recently been introduced by F. Kelly (see Eur. Trans. Telecommun., vol.8, p.33-7, 1997); we introduce a third criterion, which is naturally interpreted in terms of the delays experienced by ongoing transfers. We prove that fixed-size window control can achieve fair bandwidth sharing according to any of these criteria, provided scheduling at each link is performed in an appropriate manner. We then consider a distributed random scheme where each traffic source varies its sending rate randomly, based on binary feedback information from the network. We show how to select the source behavior so as to achieve an equilibrium distribution concentrated around the considered fair rate allocations. This stochastic analysis is then used to assess the asymptotic behavior of deterministic rate adaption procedures     

Bandwidth sharing under the assured forwarding Per-Hop behavior

The DiffServ’s Assured Forwarding (af) Per-Hop Behavior (phb) Group defines a differentiated forwarding of packets in four independent classes, each class having three levels of drop precedence. Specific end-to-end services based on thisphb are still being defined. A particular type of service that could assure a given rate to a traffic aggregate has been outlined elsewhere. In such a service, a fair distribution of bandwidth is one of the main concerns. This paper presents experimental work carried out to evaluate howaf distributes bandwidth among flows under different load conditions and traffic patterns. We focused on the effect that marking mechanisms have on bandwidth sharing among flows within a singleaf class. The traffic types we used includeudp flows, individual and aggregatedtcp flows, mix oftcp andudp, tcp sessions with heterogeneous round-trip times, as well as color-blind and color-aware re-marking at the aggregation point fortcp flows. Tests were performed on real and simulated networks. We have found certain conditions under whichaf distributes bandwidth fairly among nonadaptiveudp flows andtcp aggregates. Finally, we evaluate a basic rule for setting the parameters of the two-rate Three-Color Marker conditioning algorithm (trtcm) in order to achieve a better bandwidth distribution fortcp flows.     

Bandwidth sharing and admission control for elastic traffic

We consider the performance of a network like the Internet handling so‐called elastic traffic where the rate of flows adjusts to fill available bandwidth. Realized throughput depends both on the way bandwidth is shared and on the random nature of traffic. We assume traffic consists of point to point transfers of individual documents of finite size arriving according to a Poisson process. Notable results are that weighted sharing has limited impact on perceived quality of service and that discrimination in favour of short documents leads to considerably better performance than fair sharing. In a linear network, max–min fairness is preferable to proportional fairness under random traffic while the converse is true under the assumption of a static configuration of persistent flows. Admission control is advocated as a necessary means to maintain goodput in case of traffic overload. This revised version was published online in June 2006 with corrections to the Cover Date.     

Bandwidth aggregation for real-time applications in heterogeneous wireless networks

A variety of wireless interfaces are available for today's mobile user to access Internet content. When coverage areas of these different technologies overlap, a terminal equipped with multiple interfaces can use them simultaneously to improve the performance of its applications. In this paper, we motivate the advantages that can be had through simultaneous use of multiple interfaces and present a network layer architecture that enables diverse multiaccess services. In particular, we explore in depth one such service provided by the architecture: Bandwidth Aggregation (BAG) for real-time applications. An important aspect of the architecture when providing BAG services for real-time applications is the scheduling algorithm that partitions the traffic onto different interfaces such that the QoS requirements of the application are met. We propose one such algorithm Earliest Delivery Path First (EDPF), that ensures packets meet their playback deadlines by scheduling packets based on the estimated delivery time of the packets. We show through analysis that EDPF performs close to an idealized Aggregated Single Link (ASL) discipline, where the multiple interfaces are replaced by a single interface with same aggregated bandwidth. A prototype implementation and extensive simulations carried using video and delay traces show the performance improvement BAG with EDPF scheduling offers over using just the Highest Bandwidth Interface (HBI) and other scheduling approaches based on weighted round robin.     

A versatile model for TCP bandwidth sharing in networks with heterogeneous users

Enabled by the emergence of various access technologies (such as ADSL and wireless LAN), the number of users with high-speed access to the Internet is growing rapidly, and their expectation with respect to the quality-of-service of the applications has been increasing accordingly. With TCP being the ubiquitous underlying end-to-end control, this motivates the interest in easy-to-evaluate, yet accurate, performance models for a TCP-based network shared by multiple classes of users. Building on the vast body of existing models, we develop a novel versatile model that explicitly captures user heterogeneity, and takes into consideration dynamics at both the packet level and the flow level. It is described as to how the resulting multiple time-scale model can be numerically evaluated. Validation is done by using NS2 simulations as a benchmark. In extensive numerical experiments, we study the impact of heterogeneity in the round-trip times on user-level characteristics such as throughputs and flow transmission times, thus quantifying the resulting bias. We also investigate to what extent this bias is affected by the networks’ ‘packet-level parameters’, such as buffer sizes. We conclude by extending the single-link model in a straightforward way to a general network setting. Also in this network setting the impact of heterogeneity in round-trip times is numerically assessed.     

Virtual partitioning for robust resource sharing: computationaltechniques for heterogeneous traffic

We consider virtual partitioning (VP), which is a scheme for sharing a resource among several traffic classes in an efficient, fair, and robust manner. In the preliminary design stage, each traffic class is allocated a nominal capacity, which is based on expected offered traffic and required quality of service. During operations, if the current capacity usage by a class exceeds its nominal allocation, then it is declared to be in “overload,” and a state-dependent trunk reservation mechanism gives it lower priority in the admission of new calls. We develop efficient computational algorithms for the case of heterogeneous traffic, and perform extensive numerical experiments to demonstrate the accuracy of the various approximations. The performance of VP is examined and compared to that of complete sharing and complete partitioning. Particular weight is placed on robustness, meaning that traffic classes with arrival rates conforming to the design continue to receive the required quality of service, despite the presence of misbehaving classes with excessive arrival rates. We adopt a reward-penalty paradigm as a combined measure for efficiency and fairness, and show that not only is the revenue generated by VP extremely close to the maximum achievable value, but that the structural form of the optimal policy also closely resembles that of VP. The numerical results confirm that the scheme is efficient, fair, and very robust     

On multicast flow control for heterogeneous receivers

In this paper, we study the impact of heterogeneous receivers on the throughput of multicast flow control and propose a new multicast flow control algorithm to optimally partition group members into multiple subgroups. Our main contributions are as follows. First, we cast the multicast flow control problem in the Internet as the list partition problem and then prove that the list partition problem is equivalent to the optimal paging problem in cellular networks. The result is not only interesting in itself but also essential to derive the first known analytical bounds for the throughput of multicast flow control. Furthermore, we propose an algorithm to solve not only the list partition problem but also the optimal paging problem and the problem of bulk data transfer using multiple multicast groups. The complexity of our algorithm is one order less than the best known algorithm designed only for the problem of bulk data transfer using multiple multicast groups in the literature. While earlier work uses simulations to justify the usage of multiple subgroups to deliver information to a large amount of receivers in heterogeneous networks, we provide the first analytical support     

带宽可配置的拉曼光纤放大器

设计了一种带宽可配置的拉曼光纤放大器(RFA),泵浦源和驱动电路采用插卡式.根据不同波段的信号光选用不同的带宽进行放大,提高了RFA的放大效率.通过实验验证在1520～1610nm内可灵活调整放大带宽,且最大增益为16.4dB,增益平坦度小于1.3dB.     

具有带宽约束的静态多播路由算法

网络通信中的多播分为单树多播和成组多播。本文研究具有带宽约束的静肪多播路由问题,分别建立了基于带宽约束的单树多播和成组多播的数学并构造了相应的路由算法,利用此算法可使成组多播达到全局最优。     

一种新型的大带宽微带天线研究

本文对一种新颖的具有宽频带特性的微带天线进行了实验研究，给出了这种天线的设计方法和测试结果，同时探讨了各结构参数对天线性能的影响．测试结果表明，这种天线其驻波比小于２（ＶＳＷＲ≤２）的相对带宽可达到３３％。在整个频带内，不同频率点上其Ｈ面方向图的３ｄＢ波瓣宽度在５０°～７０°之间。     

带宽稳定的低压锁相环

基于UMC 0.18/μm混合信号工艺,设计实现了一种具有稳定带宽的低压低功耗电荷泵型锁相环电路,参考频率32.768 kHz,输出频率范围1～50 MHz,主要为音频A/D提供采样时钟.分析了锁相环环路带宽,给出了一种稳定环路带宽的简易方法.采用低电源电压1 V,克服了低压设计的一些难点.仿真结果表明,输出频率24.576 NHz(512倍48 kHz采样)时,压控振荡器(VCO)相位噪声为-109 dBc/Hz@1 MHz补偿,总功耗180μW.初步测试结果显示,系统输出正确的频率范围.     

Dielectric-Lined Circular Waveguide with Increased Usable Bandwidth

This report describes how the useful (single-mode) bandwidth of circular waveguide can be significantly increased by using a smaller diameter with dielectric lining. The increased bandwidth results from an increase in the ratio of the cutoff frequency of the second, or TM-01, mode over that of the dominant, or TE-11 mode. A cavity test is described which permits the measurement of mode separation for any thickness of dielectric lining. A lining with a dielectric constant in the vicinity of 4 appears to be near optimum for maximum single-mode bandwidth. For a dielectric constant of 3.8 (fused silica), the greatest mode separation is obtained if the dielectric cross section has about 0.44 of the area of the entire cross section, in which case the useful bandwidth is about doubled (perhaps increased from 8 to 16 per cent, if the entire band is to clear the TE-11 cutoff frequency by 20 per cent). Over the useful bandwidth of such a waveguide, the guide wavelength may be calculated approximately by the simple waveguide formula in terms of the equivalent dielectric constant, as determined by the cavity measurement. Applications which would benefit from increased dominant-mode bandwidth in circular waveguide include rotary joints carrying circular polarization, rotary attenuators and phase shifters, and array radiators.     

Secret sharing with public reconstruction

All known constructions of information theoretic t-out-of-n secret-sharing schemes require secure, private communication channels among the parties for the reconstruction of the secret. We investigate the cost of performing the reconstruction over public communication channels. A naive implementation of this task distributes 2n-2 one times pads to each party. This results in shares whose size is 2n-1 times the secret size. We present three implementations of such schemes that are substantially more efficient. A scheme enabling multiple reconstructions of the secret by different subsets of parties, with factor O(n/t) increase in the shares' size. A one-time scheme, enabling a single reconstruction of the secret, with O(log(n/t)) increase in the shares' size. A one-time scheme, enabling a single reconstruction by a set of size exactly t, with factor O(1) increase in the shares' size. We prove that the first implementation is optimal (up to constant factors) by showing a tight Ω(n/t) lower bound for the increase in the shares' size     

Fundamental Limits for Radio Signals with Large Bandwidth

Radio services have traditionally used narrow frequency bands individually assigned. More recently, the concept of sharing very wide frequency bands by several users has been advanced, and this opens the door for the use of much larger bandwidths than in the past. This paper investigates the limits imposed by nature on the bandwidth of line-of-sight radio services operating in the earth's atmosphere. Furthermore, it investigates the limits for time resolution of radio signals, as well as the related limit of the angular resolution of a line array of sensors that receive signals with large bandwidth, and compares it with the classical resolution angle that holds for sinusoidal signals with vanishing bandwidth. Finally, an example is given where the concept of a practically finite bandwidth of a signal reaches its limit, and a more rigorous specification of the signal is required.     

Bandwidth as currency

Provisioning bandwidth in an actuarially consistent manner has many far-reaching implications reminiscent of the commercial rationalization of railways in the 1870s - in that period's path to profitability. Mapping packet flow to willingness to pay, as rail cargo content was matched to the cost of carry, will better utilize bandwidth, enhancing network value consistent with the information being exchanged. The author discusses the notion of a packet watermark which can enable bandwidth as currency. Payment facilities are generally treated as separate, independent data flows from the actual data being transacted. Packet watermarks map payment facilities to the fidelity, discreteness, or functionality of the data demanded, representing a consistent means of determining a willingness to pay. This mapping acts as a receipt for data commerce.     

Bandwidth of reflectarrays

It is shown that the dominant factor controlling reflectarray bandwidth is the bandwidth of the radiating element, and that the effect of non-constant path delays over the surface of the flat reflector has little significance unless the aperture is electrically very large and the f/D ratio is small. An example of a polarisation-twist reflectarray using aperture coupled elements with time delay lines is used to demonstrate this conclusion.     

Bandwidth extension in CMOS with optimized on-chip inductors

We present a technique for enhancing the bandwidth of gigahertz broad-band circuitry by using optimized on-chip spiral inductors as shunt-peaking elements. The series resistance of the on-chip inductor is incorporated as part of the load resistance to permit a large inductance to be realized with minimum area and capacitance. Simple, accurate inductance expressions are used in a lumped circuit inductor model to allow the passive and active components in the circuit to be simultaneously optimized. A quick and efficient global optimization method, based on geometric programming, is discussed. The bandwidth extension technique is applied in the implementation of a 2.125-Gbaud preamplifier that employs a common-gate input stage followed by a cascoded common-source stage. On-chip shunt peaking is introduced at the dominant pole to improve the overall system performance, including a 40% increase in the transimpedance. This implementation achieves a 1.6-kΩ transimpedance and a 0.6-μA input-referred current noise, while operating with a photodiode capacitance of 0.6 pF. A fully differential topology ensures good substrate and supply noise immunity. The amplifier, implemented in a triple-metal, single-poly, 14-GHz f_Tmax, 0.5-μm CMOS process, dissipates 225 mW, of which 110 mW is consumed by the 50-Ω output driver stage. The optimized on-chip inductors consume only 15% of the total area of 0.6 mm²      

一种快速捕获、带宽可调的锁相环电路

设计实现了一个快速捕获,带宽可调的电荷泵型锁相环电路。采用了一种利用状态机拓展鉴频鉴相器检测范围的方法,加快了环路的锁定;通过SPI总线实现电荷泵电流配置和调整VCO延时单元的延迟时间,优化了电路性能。芯片采用中芯国际0.18μmCMOS工艺,测试结果表明,锁相环锁定在100MHz时的抖动均方值为24ps,偏离中心频率1MHz处的相位噪声为-98.62dBc/Hz。