Resource allocation for statistical quality of service provision in buffered crossbar switches

The buffered crossbar switch is a promising switching architecture that plays a crucial role for providing quality of service (QoS) in computer networks. Sufficient amount of resources—bandwidth and buffer space—must be allocated in buffered crossbar switches for QoS provision. Resource allocation based on deterministic QoS objectives might be too conservative in practical network operations. To improve resource utilization in buffered crossbar switches, we study the problem of resource allocation for statistical QoS provision in this paper. First, we develop a model and techniques for analyzing the probabilistic delay performance of buffered crossbar switches, which is described by the delay upper bound with a prescribed violation probability. Then, we determine the required amounts of bandwidth and buffer space to achieve the probabilistic delay objectives for different traffic classes in buffered crossbar switches. In our analysis, we apply the effective arrival envelope to specify traffic load in a statistical manner and characterize switch service capacity by using the service curve technique. Instead of just focusing on one specific type of scheduler, the model and techniques developed in this paper are very flexible and can be used for analyzing buffered crossbar switches with a wide variety of scheduling algorithms. Copyright © 2007 John Wiley & Sons, Ltd.     

Efficient network QoS provisioning based on per node trafficshaping

This paper addresses the problem of providing per-connection end-to-end delay guarantees in a high-speed network. We consider a network comprised of store-and-forward packet switches, in which a packet scheduler is available at each output link. We assume that the network is connection oriented and enforces some admission control which ensures that the source traffic conforms to specified traffic characteristics. We concentrate on the class of rate-controlled service (RCS) disciplines, in which traffic from each connection is reshaped at every hop, and develop end-to-end delay bounds for the general case where different reshapers are used at each hop. In addition, we establish that these bounds can also be achieved when the shapers at each hop have the same “minimal” envelope. The main disadvantage of this class of service discipline is that the end-to-end delay guarantees are obtained as the sum of the worst-case delays at each node, but we show that this problem can be alleviated through “proper” reshaping of the traffic. We illustrate the impact of this reshaping by demonstrating its use in designing RCS disciplines that outperform service disciplines that are based on generalized processor sharing (GPS). Furthermore, we show that we can restrict the space of “good” shapers to a family which is characterized by only one parameter. We also describe extensions to the service discipline that make it work conserving and as a result reduce the average end-to-end delays     

Multi-path content delivery: Efficiency analysis and optimization algorithms

The paper studies the benefits of multi-path content delivery from a rate-distortion efficiency perspective. We develop an optimization framework for computing transmission schedules for streaming media packets over multiple network paths that maximize the end-to-end video quality, for the given bandwidth resources. We comprehensively address the two prospective scenarios of content delivery with packet path diversity. In the context of sender-driven systems, our framework enables the sender to compute at every transmission instance the mapping of packets to network paths that meets a rate constraint while minimizing the end-to-end distortion. In receiver-driven multi-path streaming, our framework enables the client to dynamically decide which packets, if any, to request for transmission and from which media servers, such that the end-to-end distortion is minimized for a given transmission rate constraint. Via simulation experiments, we carefully examine the performance of the scheduling framework in both multi-path delivery scenarios. We demonstrate that the optimization framework closely approaches the performance of an ideal streaming system working at channel capacity with an infinite play-out delay. We also show that the optimization leads to substantial gains in rate-distortion performance over a conventional content-agnostic scheduler. Through the concept of error-cost performance for streaming a single packet, we provide another useful insight into the operation of the optimization framework and the conventional scheduling system.     

Delay Analysis of All-Optical Packet-Switching Ring and Bus Communications Networks

We study the delay performance of all-optical packet communication networks configured as ring and bus topologies employing cross-connect switches (or wavelength routers). Under a cross-connect network implementation, a packet experiences no (or minimal) internal queueing delays. Thus, the network can be implemented by high speed all-optical components. We further assume a packet-switched network operation, such as that using a slotted ring or bus access methods. In this case, a packet's delay is known before it is fed into the network. This can be used to determine if a packet must be dropped (when its end-to-end delay requirement is not met) at the time it accesses the network. It also leads to better utilization of network capacity resources. We also derive the delay performance for networks under a store-and-forward network operation. We show these implementations to yield very close average end-to-end packet queueing delay performance. We note that a cross-connect network operation can yield a somewhat higher queueing delay variance levels. However, the mean queueing delay for all traffic flows are the same for a cross-connect network operation (under equal nodal traffic loading), while that in a store-and-forward network increases as the path length increases. For a ring network loaded by a uniform traffic matrix, the queueing delay incurred by 90% of the packets in a cross-connect network may be lower than that experienced in a store-and-forward network. We also study a store-and-forward network operation under a nodal round robin (fair queueing) scheduling policy. We show the variance performance of the packet queueing delay for such a network to be close to that exhibited by a cross-connect (all-optical) network.     

Optimal and suboptimal packet scheduling over correlated time varying flat fading channels

We address the issue of optimal packet scheduling over correlated fading channels which trades off between minimization of three goals: average transmission power, average delay and average packet dropping probability. We show that the problem forms a weakly communicating Markov decision process and formulate the problem as both unconstrained and constrained problem. Relative value iteration (RVI) algorithm is used to find optimal deterministic policy for unconstrained problem, while optimal randomized policy for constrained problem is obtained using linear programming (LP) technique. Whereas with RVI only a finite number of scheduling policies can be obtained over the feasible delay region, LP can produce policies for all feasible delays with a fixed dropping probability and is computationally faster than the RVI. We show the structure of optimal deterministic policy in terms of the channel and buffer state and form a simple log functional suboptimal scheduler that approximately follows the optimal structure. Performance results are given for both constant and bursty Poisson arrivals, and the proposed suboptimal scheduler is compared with the optimal and channel threshold scheduler. Our suboptimal scheduler performs close to the optimal scheduler for every feasible delay and is robust to different channel parameters, number of actions and incoming traffic distributions.     

Rate-proportional servers: a design methodology for fair queueingalgorithms

Generalized processor sharing (GPS) has been considered as an ideal scheduling discipline based on its end-to-end delay bounds and fairness properties. Until recently, emulation of GPS in a packet server has been regarded as the ideal means of designing a packet-level scheduling algorithm to obtain low delay bounds and bounded unfairness. Strict emulation of GPS, as required in the weighted fair queueing (WFQ) scheduler, however, incurs a time-complexity of O(N) where N is the number of sessions sharing the link. Efforts in the past to simplify the implementation of WFQ, such as self-clocked fair queueing (SCFQ), have resulted in degrading its isolation properties, thus affecting the delay bound. We present a methodology for the design of scheduling algorithms that provide the same end-to-end delay bound as that of WFQ and bounded unfairness without the complexity of GPS emulation. The resulting class of algorithms, called rate-proportional servers (RPSs), are based on isolating scheduler properties that give rise to ideal delay and fairness behavior. Network designers can use this methodology to construct efficient fair-queueing algorithms, balancing their fairness with implementation complexity     

A distributed scheduling architecture for scalable packet switches

The continuous growth in the demand for diversified quality-of-service (QoS) guarantees in broadband networks introduces new challenges in the design of packet switches that scale to large switching capacities. Packet scheduling is the most critical function involved in the provision of individual bandwidth and delay guarantees to the switched flows. Most of the scheduling techniques proposed so far assume the presence in the switch of a single contention point, residing in front of the outgoing links. Such an assumption is not consistent with the highly distributed nature of many popular architectures for scalable switches, which typically have multiple contention points, located in both ingress and egress port cards, as well as in the switching fabric. We define a distributed multilayered scheduler (DMS) to provide differentiated QoS guarantees to individual end-to-end flows in packet switches with multiple contention points. Our scheduling architecture is simple to implement, since it keeps per-flow scheduling confined within the port cards, and is suitable to support guaranteed and best-effort traffic in a wide range of QoS frameworks in both IP and ATM networks     

Generalized quality-of-service routing with resource allocation

We present a general framework for the problem of quality-of-service (QoS) routing with resource allocation for data networks. The framework represents the QoS parameters as functions rather than static metrics. The formulation incorporates the hardware/software implementation and its relation to the allocated resources into a single framework. The proposed formulation allows intelligent adaptation of QoS parameters and allocated resources during a path search, rather than decoupling the path search process from resource allocation. We present a dynamic programming algorithm that, under certain conditions, finds an optimal path between a source and destination node and computes the amount of resources needed at each node so that the end-to-end QoS requirements are satisfied. We present jitter and data droppage analyzes of various rate-based service disciplines and use the dynamic programming algorithm to solve the problem of QoS routing with resource allocation for networks that employ these service disciplines.     

An Adaptive Resource Management Architecture for Active Networks

This paper presents a framework for resource management in highly dynamic active networks. The goal is to allocate and manage node resources in an efficient way while ensuring effective utilization of network and supporting load balancing. The framework supports co-existence of active and non-active nodes and proposes a novel Directory Service (DS) architecture that can be used to discover the suitable active nodes in the Internet and for selecting the best network path (end-to-end) and reserving the resources along the selected path. Intranode and internode resource management are facilitated through the DS, while within an active node the framework implements a composite scheduling scheme to schedule both the CPU and bandwidth resources to resolve the combined resource scheduling problems. In addition, a flexible active node database system and a simple adaptive prediction technique have been introduced in order to resolve the challenging problem of determining the CPU requirements of the incoming packets.     

Contention-free distributed dynamic reservation MAC protocol withdeterministic scheduling (C-FD3R MAC) for wireless ATMnetworks

This paper proposes a novel MAC protocol for wireless ATM networks, which is characterized by a contention-free mechanism of the reservation request and a deterministic nature of mobile-assisted (distributed) uplink scheduling under a framework of the dynamic reservation TDMA, as discussed in the current standardization activities of ETSI Project BRAN (broadband radio access network) and the wireless ATM working group in the ATM Forum. The design objective of the proposed MAC protocol is to guarantee the real-time constraint of the real-time VBR (rt-VBR) traffic class while maximizing the multiplexing gain among all ATM traffic classes, especially with a fixed length frame. The proposed deterministic scheduling scheme for the rt-VBR traffic class lends itself to implementing the minimal configuration of control data units for reservation request as desired under the limited wireless resources. Simulation experiments using statistically multiplexed MPEG-2 video streams are performed for a 25 Mbits/s wireless ATM access link scenario. It has been shown that the proposed framework guarantees the delay constraint of rt-VBR sessions along with its cell loss rate significantly reduced, while improving the average delay performance of the nrt-VBR in the range of 10%-30% without compromising the channel utilization as compared to the DSA++ system     

Performance analysis of IP QoS provision model

The Performance of a heterogeneous IP QoS provision service model was analyzed. This model utilized RSVP technique to set up dynamic resource reservation interface between the user and the network, meanwhile, DiffServ technique was utilized to transmit class-based packets in different per hop behaviors. Furthermore, accordingly queue management and packets scheduling mechanisms were presented for end-to-end QoS guarantees and appropriate cooperation of network elements.     

Dynamic congestion-based pricing of bandwidth and buffer

We consider pricing of network resources in a reservation-based quality-of-service architecture. The pricing policy implements a distributed resource allocation to provide guaranteed bounds on packet loss and end-to-end delay for real-time applications. Distributed pricing roles are assigned to each user, each network node, and an arbitrager in between the user and the network. When delay constraints are not binding, we investigate two dynamic pricing algorithms using gradient projection and Newton's method to update prices, and prove their convergence. We analyze the performance of the dynamic pricing policies and show that the gradient algorithm using Newton's method converges more quickly and displays only a few small fluctuations. When delay constraints are binding, we investigate subgradient methods which can provide convergence to some range of the optimal allocation.     

一种基于OBGP协议的光网络域间路由的新型机制

本文提出一种采用光边界网关协议(OBGP)实现WDM光格状网的域间路由的新型机制;该机制基于最小跳选择策略建立最优化路径的思想,同时引进"迂回路由"策略和"并行信令"方式,实现了动态、分布式的光通道确立过程.在OPNet平台上针对两种网络拓扑进行仿真实验,结果表明:该机制能够在网络繁忙时期降低阻塞率,提高网络性能;同时发现:网络规模、单信道波长数以及网络负载等网络参数对于网络性能具有一定的影响.     

Downlink scheduling in a cellular network for quality-of-service assurance

We consider the problem of scheduling data in the downlink of a cellular network over parallel time-varying channels, while providing quality-of-service (QoS) guarantees to multiple users in the network. We design simple and efficient admission control, resource allocation, and scheduling algorithms for guaranteeing requested QoS. In our design, a joint Knopp and Humblet (K&H)/round robin (RR) scheduler, composed of K&H scheduling and RR scheduling, utilizes both multiuser and frequency diversity to achieve capacity gain when delay constraints are loose or moderate. However, for tight delay constraints, an additional reference channel scheduler is required to obtain additional frequency diversity gain. The key advantage of our formulation is that the desired QoS constraints can be explicitly enforced by utilizing the concept of effective capacity.     

Carry-over round robin: a simple cell scheduling mechanism for ATMnetworks

We propose a simple mechanism named carry-over round robin (CORR) for scheduling cells in asynchronous transfer mode networks. We quantify the operational complexity of CORR scheduling and show that it is comparable to that of a simple round-robin scheduler. We then show that, albeit its simplicity, CORR is very competitive with much more sophisticated and significantly more complex scheduling disciplines in terms of performance. We evaluate the performance of CORR using both analysis and simulation, We derive analytical bounds on the worst case end-to-end delay achieved by a CORR scheduler for different traffic arrival patterns. Using traffic traces from MPEG video streams, we compare the delay performance of CORR with that of packet-by-packet generalized processor sharing (PGPS) and stop-and-go (SG). Our results show that, in terms of delay performance, CORR compares favorably with both PGPS and SG. We also analyze the fairness properties of CORR and show that it achieves near perfect fairness     

Edge-Reconfigurable Optical Networks (ERONs): Rationale, Network Design, and Evaluation

To bridge the gap between the current practice of setting up expensive, dedicated, lightpath connections (i.e., static topologies), and the distant future vision of inexpensive access to dynamically switched end-to-end lightpaths, we propose a medium term solution in the form of edge-reconfigurable optical networks (ERONs). An ERON is an overlay-control network created by installing readily available MEMS optical switches, and implementing a GMPLS control plane at sites interconnected by static lightpaths. The switches and control software are deployed at the edge of the network and operated by the organization-user (i.e., outside the network provider's control), hence the term ldquoedge-reconfigurablerdquo. By providing dynamic, automated control of end-to-end lightpaths, ERONs enable the sharing of expensive network resources among multiple users and applications that require sporadic access to these resources. We develop an algorithm for creating an ERON from an existing topology of static lightpaths. We also present simulation results that quantify the benefits of ERONs, in terms of the number of lightpaths that are needed when compared to a static configuration of independent and dedicated circuits.     

WDM疏导网络中的基于连接的动态恢复

针对WDM网络中单链路出错的生存性流量疏导问题,提出了一种基于连接的动态恢复机制(DRAC).DRAC不预留任何资源,当链路出错时,通过在网络中动态的发现资源来对错误进行恢复,将一个出错连接转发到一条新的多跳路径.仿真结果显示,提出的这种动态恢复机制拥有很高的恢复概率.     

A dynamic regulation and scheduling scheme for real-time trafficmanagement

Typical rate-based traffic management schemes for real-time applications attempt to allocate resources by controlling the packet delivery to the resource arbitrator (scheduler). This control is typically based only on the characteristics of the particular (tagged) traffic stream and would fail to optimally adjust to non-nominal network conditions such as overload. In this paper, a dynamic regulation and scheduling (dynamic-R&S) scheme is proposed whose regulation function is modulated by both the tagged stream's characteristics and information capturing the state of the coexisting applications as provided by the scheduler. The performance of the proposed scheme-versus an equivalent static one-is investigated under both underload and overload traffic conditions. The substantially better throughput/jitter characteristics of the dynamic-R&S scheme are established     

Hybrid switching and p-routing for optical burst switching networks

One promising switching technology for wavelength-division multiplexing optical networks is optical burst switching (OBS). However, there are major deficiencies of OBS. (1) The delay offset between a control message and its corresponding data burst is based on the diameter of a network. This affects network efficiency, quality-of-service, and network scalability.( 2) OBS adopts one-way resource reservation scheme, which causes frequent burst collision and, thus, burst loss. We address the above two important issues in OBS. In particular, we study how to improve the performance of delay and loss in OBS. To reduce the end-to-end delay, we propose a hybrid switching scheme. The hybrid switching is a combination of lightpath switching and OBS switching. A virtual topology design algorithm based on simulated annealing to minimize the longest shortest path through the virtual topology is presented. To minimize burst collision and loss, we propose a new routing algorithm, namely, p-routing, for OBS network. The p-routing is based on the wavelength available probability. A path that has higher available probability is less likely to drop bursts due to collision. The probability-based p-routing can reduce the volatility, randomness, and uncertainty of one-way resource reservation. Our studies show that hybrid switching and p-routing are complementary and both can dramatically improve the performance of OBS networks.