Rate Proportional SCFQ Algorithm for High-Speed Packet-Switched Networks

For pt.I see ibid., p.509-18 (1997). The total implementation complexity of cell schedulers which aim at approximating the generalized processor sharing (GPS) policy is the combination of the complexity of their system-potential function and the complexity involved in sorting the timestamps in order to select the cell with minimum timestamp for transmission. Given that several scheduling algorithms which use a system-potential function of O(1) complexity have been introduced (among them, the minimum-delay self-clocked fair queueing (MD-SCFQ) algorithm achieves optimal delay and excellent fairness properties), the major contribution to the total complexity comes from the task of sorting the timestamps every time a cell is transmitted or received, which is common to all GPS-related schedulers. In this paper, we present a technique, called the logarithmic calendar queue (LCQ), that can achieve a dramatic reduction of the implementation complexity of a GPS-related scheduler, at the cost of a very small and controllable degradation of the delay bounds. We then use the LCQ to implement MD-SCFQ with reduced complexity. By applying the general methodology for the delay analysis presented in the first part of this paper (Chiussi et al. 1997), we are able to provide a closed-form expression of the delay bounds as a function of the LCQ design parameters, which can be used to optimize the design. The LCQ is not exclusively related to MD-SCFQ, but can be applied to any GPS-related scheduler to simplify implementation complexity.

Although weighted fair queueing (WFQ) has been regarded as an ideal scheduling algorithm in terms of its combined delay bound and proportional fairness properties, its asymptotic time complexity increases linearly with the number of sessions serviced by the scheduler, thus limiting its use in high-speed networks. An algorithm that combines the delay and fairness bounds of WFQ with O(1) timestamp computations had remained elusive so far. In this paper we present two novel scheduling algorithms that have O(1) complexity for timestamp computations and provide the same bounds on end-to-end delay and buffer requirements as those of WFQ. The first algorithm, frame-based fair queueing (FFQ), uses a framing mechanism to periodically recalibrate a global variable tracking the progress of work in the system, limiting any short-term unfairness to within a frame period. The second algorithm, starting potential based fair queueing (SPFQ), performs the recalibration at packet boundaries, resulting in improved fairness while still maintaining the O(1) timestamp computations. Both algorithms are based on the general framework of rate-proportional servers (RPSs) introduced by Stiliadis and Varma (see ibid., vol.6, no.2, p.164-74, 1998). The algorithms may be used in both general packet networks with variable packet sizes and in asynchronous transfer mode (ATM) networks.

Summary form only given, as follows. High-speed links in emerging communication networks require simple and efficient algorithms for apportioning bandwidth to competing connections. A single link may carry traffic for thousands of connections with different quality-of-service parameters, requiring scalable switch architectures that avoid performing operations for every connection or cell during each transmission slot. Still, effective cell scheduling algorithms should provide delay and bandwidth guarantees for a wide variety of applications, even in the presence of bursty traffic. The author has investigated a collection of self-clocked fair queueing (SCFQ) architectures amenable to efficient hardware implementation in network switches. These event-driven architectures perform a small, bounded amount of work in response to each cell arrival and departure, independent of the number of connections. Exact and approximate implementations of SCFQ efficiently handle a moderate range of connection bandwidth parameters, while hierarchical arbitration schemes scale to a large range of throughput requirements. Simulation experiments demonstrate that these architectures divide link bandwidth fairly on a small time scale, preserving connection bandwidth and burstiness properties.

This paper proposes a dynamic scheduling scheme to provide quality of service (QoS) guarantees in wireless multiple access control (MAC). In order to achieve high bandwidth utilization and QoS guarantee ratio, token models of sources are constructed in the base station (BS) scheduler. A token model weighted fair queuing (WFQ) algorithm is developed to combine loss and delay requirements for uplink scheduling of real-time traffic. Dynamic priorities are implemented in a real-time traffic token model. In addition, an emergency token buffer is used to accommodate the bursty characteristics of rt-VBR (real-time variable bit rate). The backlogged token buffer compensates the backlogged flow suffering from channel error. Simulations are done to demonstrate that our DWFQ scheme can greatly improve both QoS performance and bandwidth allocation efficiency.

The ongoing evolution towards the generalization of wireless access to multi-service networks stresses on the need for optimizing the control of radio resources and in particular, for designing efficient scheduling approaches. The scheduling mechanisms proposed for wireline links do not carry over to wireless interfaces due to the variability of radio links capacity. Efficient schedulers for the radio channel have to take into account information relative to the channel state when allocating resources to the various connected equipments. For the case of delay tolerant traffic, the scheduler may take advantage of terminals diversity. We propose in this paper a modified version of the weighted fair queueing (WFQ) algorithm, termed OWFQ (opportunistic WFQ), that notably increases the average system performance through opportunistic scheduling while fulfilling users' QoS needs in terms of minimum realized throughput.

Fairness is an important criterion in the design and evaluation of scheduling algorithms of data packets in networks. Ensuring fairness, however, limits the randomness in scheduling policies thus reducing the privacy of network activity from an eavesdropper. In this work, the design of max-min fair scheduling protocols is investigated from the perspective of achieving a desired degree of user anonymity. Specifically, the Fair Queueing algorithm, which is known to be max-min fair, is considered and a metric is proposed to compute the anonymity of this scheduling algorithm. It is found that the Fair Queueing algorithm does not achieve maximum anonymity even with unlimited buffer capacity. Consequently, a relaxation of the Fair Queueing algorithm is proposed, where the window of minimum fairness computation is expanded. It is shown that with sufficient relaxation, the modified fair queuing algorithm can achieve any desired degree of anonymity thus demonstrating the trade off between fairness and anonymity.

Fair queuing (FQ) algorithms, which have been proposed for QoS wireline-wireless networking, rely on the fundamental idea that the service rate allocated to user m is proportional to a positive weight /spl phi//sub m/. Targeting wireless data networks with a multicode CDMA-based physical layer, we develop FQ with time-varying weight assignments in order to minimize the queuing delays of mobile users. Applying dynamic programming, we design a computationally efficient algorithm which produces the optimal service rates while obeying (i) constraints imposed by the underlying physical layer, and (ii) QoS requirements. Simulations illustrate the merits of our designs.

Packet scheduling constitutes the core problem in efficient fair allocation of bandwidth to competing flows. To date, numerous algorithms for packet scheduling have been suggested and tested. However, only a few of them are currently deployed. One of the key reasons for rarity of applied packet scheduling methods lies in the complexity of their implementation. This paper describes a family of randomized algorithms for packet scheduling. These algorithms are simple to implement and require small amounts of computation time. Specifically we present an O(1) probabilistic weighted fair queuing algorithm that emits packets from flows with an improved delay jitter. Experimental results of the proposed randomized algorithms suggest that the randomized approach is a viable alternative to the currently deployed deterministic fair queuing algorithms.

Scarcity of bandwidth for fixed allocation of frequency and also current growth trends in wireless communications shows that Cognitive Radio Networks (CRNs) are followed strictly. Fluctuating nature of the radio spectrum with a variety of quality services which needs causes some challenges in CRNs, such as spectrum sharing. In many previous works, the problem of performance loss is seen due to the sudden presence of primary user. In such a situation, secondary user has to vacate bandwidth at the moment. This often leads to long wait for secondary user on access the channel. However, Spectrum Pooling concept is used with the ability of secondary utility for licensed frequency band, without reducing quality of service and without requiring new hardware. In this paper, a fair queuing algorithm with weighting and prioritization between different users is recommended. This type of queuing model with weighted fair queuing policy is efficient to share the bandwidth among systems with different priority levels. The proposed algorithm offers shared use of spectrum to invest a fair sharing of bandwidth between cognitive users. The proposed model involves a different service rates for unlicensed users and can be used as an acceptable model in heterogeneous networks. By the use of analytical and simulation results, we can achieve a desirable level of performance and an improvement in fairness.

Admission control in Flow-Aware Networking (FAN) architectures under GridFTP traffic

Deficit round-robin is a packet scheduling algorithm devised to provide fair queueing in the presence of variable length packets (see Shreedhar, M. and Varghese, G., IEEE Trans. on Networking, vol.4, p.375-85, 1996). DRR can be implemented at O(1) complexity provided that each flow is allowed to transmit at least one maximum size packet on each round; however, under this constraint, DRR may exhibit high latency and poor fairness. We first generalize previous results known for DRR, related to its latency and fairness. We then introduce a novel DRR implementation technique, called active lists queue method (Aliquem), which allows the above constraint to be relaxed while preserving O(1) complexity, thus achieving better latency and fairness that are comparable to those of more complex algorithms, such as self-clocked fair queueing.

A work conserving O(1) per-VC queueing algorithm named QLWFQ (Queue Length based Weighted Fair Queueing) for high-speed ATM networks is proposed. The basic process in QLWFQ is the comparison of the current queue length with the weight when a cell arrival or departure occurs. QLWFQ has upward compatibility with fair queueing and FIFO, and can be considered to be a simplified version of weighted round robin. A delay bound and a fairness index are derived analytically for the QLWFQ algorithm. The simulation results for heavily and lightly loaded conditions are also presented. The analytical and simulation results show that QLWFQ achieves a better balance between traffic isolation and traffic sharing than timestamp based algorithms.

We present Start-time Fair Queuing (SFQ) algorithm that is computationally efficient, achieves fairness regardless of variation in a server capacity, and has the smallest fairness measure among all known fair scheduling algorithms. We analyze its throughput, single server delay, and end-to-end delay guarantee for variable rate Fluctuation Constrained (FC) and Exponentially Bounded Fluctuation (EBF) servers. We show that SFQ is better suited than Weighted Fair Queuing for integrated services networks and it is strictly better than Self Clocked Fair Queuing. To support heterogeneous services and multiple protocol families in integrated services networks, we present a hierarchical SFQ scheduler and derive its performance bounds. Our analysis demonstrates that SFQ is suitable for integrated services networks since it: (1) achieves low average as well as maximum delay for low-throughput applications (e.g., interactive audio, telnet, etc.); (2) provides fairness which is desirable for VBR video; (3) provides fairness, regardless of variation in a server capacity, for throughput-intensive, flow-controlled data applications; (4) enables hierarchical link sharing which is desirable for managing heterogeneity; and (5) is computationally efficient.

We describe an efficient fair queuing scheme, leap forward virtual clock, that provides end-to-end delay bounds similar to weighted fair queuing (WFQ), along with throughput fairness. Our scheme can be implemented with a worst-case time O(loglogN) per packet (inclusive of sorting costs), which improves upon all previously known schemes that guarantee delay and throughput fairness similar to WFQ. Interestingly, both the classical virtual clock and the self-clocked fair queuing schemes can be thought of as special cases of our scheme, by setting the leap forward parameter appropriately.

The Internet is facing two problems simultaneously: there is a need for a faster switching/routing infrastructure and a need to introduce guaranteed qualities-of-service (QoS). Each problem can be solved independently: high performance routers can be made faster by using input-queued crossbars instead of shared memory systems; QoS can be provided using packet fair queueing (PFQ) algorithms. Until now, however, the two solutions have been mutually exclusive-all of the work on PFQ algorithms has required that routers use output-queueing or centralized shared memory. In this paper, we design and implement a packet scheduling algorithm, DF/sup 2/Q (distributed feedback fair queueing), on the basis of CIOQ (combined input output queueing) architecture. The most important feature of this scheduling algorithm is the introduction of a feedback mechanism. We analyze and discuss the performance of DF/sup 2/Q, and the experimental results show that it can avoid internal congestion effectively and improve the efficiency of resource utilization.