Self-clocked Fair Queueing Research Articles

Equivalence of SCFQ and CBFQ Schemes in Packet Scheduling

Self-Clocked Fair Queueing (SCFQ) and Credit-Based Fair Queueing (CBFQ) are well-known fair scheduling schemes for packet-switched network. In this paper, it is shown that SCFQ and CBFQ are equivalent in selecting packets to transmit. For this, we modified the per-packet service tag based SCFQ algorithm to an equivalent per-session service tag based algorithm, SCFQ+, and showed that the service tags for SCFQ+ and CBFQ evolve identically.

Interframe-Space (IFS)-Based Distributed Fair Queuing for Proportional Fairness in IEEE 802.11 WLANs

In this paper, we propose an interframe-space (IFS)-based distributed-fair-queuing (IDFQ) mechanism to provide proportional fairness service for IEEE 802.11 wireless local-area networks (WLANs). IDFQ is designed to emulate self-clocked fair queuing in a distributed manner. It eliminates the backoff process as implemented in existing work and introduces a new mechanism to assign the IFS value to each station. IDFQ is immune from the implementation problem suffered by existing IFS-based mechanisms and is adaptive to the collision state in the system. Moreover, it can be used to eliminate the performance-anomaly problem of 802.11 medium-access control. The performance of IDFQ is validated by ns-2 simulations. The simulation results show that IDFQ supports fairness service for flows in proportion to their weights and outperforms existing mechanisms in terms of fairness and stability, rendering IDFQ an excellent candidate to provide weighted fairness in IEEE 802.11 WLANs

Design of MAC protocols with fast collision resolution for wireless local area networks

Development of efficient medium access control (MAC) protocols providing both high throughput performance for data traffic and good quality of service (QoS) support for real-time traffic is the current major focus in distributed contention-based MAC protocol research. In this paper, we propose an efficient contention resolution algorithm for wireless local area networks, namely, the fast collision resolution (FCR) algorithm. The MAC protocol with this new algorithm attempts to provide significantly higher throughput performance for data services than the IEEE 802.11 MAC algorithm and more advanced dynamic tuning backoff (DTB) algorithm. We demonstrate that this algorithm indeed resolves collisions faster and reduces the idle slots more effectively. To provide good fairness performance and to support good QoS for real-time traffic, we incorporate the self-clocked fair queueing algorithm and a priority scheme into the FCR algorithm and come up with the real-time FCR (RT-FCR) algorithm, and show that RT-FCR can simultaneously achieve high throughput and good fairness performance for nonreal-time traffic while maintaining satisfactory QoS support for real-time traffic.

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

Self-Clocked Fair Queueing (SCFQ) algorithm has been considered as an attractive packet scheduling algorithm because of its implementation simplicity, but it has unbounded delay property in some input traffic conditions. In this paper, we propose a Rate Proportional SCFQ (RP-SCFQ) algorithm which is a rate proportional version of SCFQ. If any fair queueing algorithm can be categorized into the rate proportional class and input is constrained by a leaky bucket, its delay is bounded and the same as that of Weighted Fair Queueing (WFQ) which is known as an optimal fair queueing algorithm. RP-SCFQ calculates the timestamps of packets arriving during the transmission of a packet using the current value of system potential updated at every packet departing instant and uses a starting potential when it updates the system potential. By doing so, RP-SCFQ can have the rate proportional property. RP-SCFQ is appropriate for high-speed packet-switched networks since its implementation complexity is low while it guarantees the bounded delay even in the worst-case input traffic conditions.

Fair queueing algorithm with rate independent delayfor ATM networks

A new scheduling algorithm based on self-clocked fair queueing is proposed. The algorithm employs an array of sorting bins for managing the virtual finishing time of connections and uses token buckets as a behaviour-indicator. It remedies the drawbacks of existing fair queueing algorithms and is able to reserve bandwidth to connections while guaranteeing a class-dependent and rate-independent delay for behaving connections.

Rate-proportional servers: a design methodology for fair queueing algorithms

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.

Latency-rate servers: a general model for analysis of traffic scheduling algorithms

We develop a general model, called latency-rate servers (/spl Lscr//spl Rscr/ servers), for the analysis of traffic scheduling algorithms in broadband packet networks. The behavior of an /spl Lscr//spl Rscr/ server is determined by two parameters-the latency and the allocated rate. Several well-known scheduling algorithms, such as weighted fair queueing, virtualclock, self-clocked fair queueing, weighted round robin, and deficit round robin, belong to the class of /spl Lscr//spl Rscr/ servers. We derive tight upper bounds on the end-to-end delay, internal burstiness, and buffer requirements of individual sessions in an arbitrary network of /spl Lscr//spl Rscr/ servers in terms of the latencies of the individual schedulers in the network, when the session traffic is shaped by a token bucket. The theory of /spl Lscr//spl Rscr/ servers enables computation of tight upper bounds on end-to-end delay and buffer requirements in a heterogeneous network, where individual servers may support different scheduling architectures and under different traffic models.

Design of a generalized priority queue manager for ATM switches

Meeting quality of service (QoS) requirements for various services in ATM networks has been very challenging to network designers. Various control techniques at either the call or cell level have been proposed. In this paper, we deal with cell transmission scheduling and discarding at the output buffers of an ATM switch. We propose a generalized priority queue manager (GPQM) that uses per-virtual-connection queueing to support multiple QoS requirements and achieve fairness in both cell transmission and discarding. It achieves the ultimate goal of guaranteeing the QoS requirement for each connection. The GPQM adopts the earliest due date (EDD) and self-clocked fair queueing (SCFQ) schemes for scheduling cell transmission and a new self-calibrating pushout (SCP) scheme for discarding cells. The GPQM's performance in cell loss rate and delay is presented. An implementation architecture for the GPQM is also proposed, which is facilitated by a new VLSI chip called the priority content-addressable memory (PCAM) chip.

Determining end-to-end delay bounds in heterogeneous networks

We define a class of Guaranteed Rate (GR) scheduling algorithms. The GR class includes Virtual Clock, Packet-by-Packet Generalized Processor Sharing and Self-Clocked Fair Queuing. For networks that employ scheduling algorithms belonging to GR, we present a method for determining an upper bound on end-to-end delay. The method facilitates determination of end-to-end delay bounds for a Variety of sources. We illustrate the method by determining end-to-end delay bounds for sources conforming to Leaky Bucket and exponentially bounded burstiness.

Generalized guaranteed rate scheduling algorithms: a framework

In this paper, we define a class of generalized guaranteed rate (GR) scheduling algorithms that includes algorithms which allocate a variable rate to the packets of a flow. We define work-conserving generalized virtual clock, packet-by-packet generalized processor sharing, and self-clocked fair queueing scheduling algorithms that can allocate a variable rate to the packets of a flow. We also define scheduling algorithms suitable for servers where packet fragmentation may occur. We demonstrate that if a class of rate controllers is employed for a flow in conjunction with any scheduling algorithm in GR, then the resulting non-work-conserving algorithm also belongs to GR. This leads to the definition of several non-work-conserving algorithms. We then present a method for deriving the delay guarantee of a network of servers when: (1) different rates are allocated to packets of a flow at different servers along the path and the bottleneck server for each packet may be different, and (2) packet fragmentation and/or reassembly may occur. This delay guarantee enables a network to provide various service guarantees to flows conforming to any specification. We illustrate this by utilizing delay guarantee to derive delay bounds for flows conforming to leaky bucket, exponentially bounded burstiness, and flow specification. Our method for determining these bounds is valid in internetworks and leads to tighter results.

Bandwidth scheduling for wide-area ATM networks using virtual finishing times

The paper is concerned with the design of a class of bandwidth scheduling policies that are suitable for public, wide-area asynchronous transfer mode (ATM) networks. The authors specify design goals for such strategies including ease of implementation and the ability to guarantee minimum bandwidths to individual buffers. Packetized generalized processor sharing is briefly discussed and a minimum bandwidth result for self-clocked fair queueing is given. The authors revisit an approach originally proposed by Zhang (1991) and prove that it is appropriate for ATM. Some novel, related approaches are described and analyzed.

Network delay analysis of a class of fair queueing algorithms

A self-clocked fair queueing (SCFQ) scheme has been proposed by Golestani (see Proc. IEEE INFOCOM, p. 636-636, 1994) as an easily implementable version of fair queueing. In this paper, the worst case network delay performance of a class of fair queueing algorithms, including the SCFQ scheme, is studied. We build upon and generalize the methodology developed by Parekh and Gallager (see ACM/IEEE Trans. Networking, vol.1, no.3, p.344-357, 1993, and vol.2, no.2, p.137-150, 1994) to study this class of algorithms based on the leaky-bucket characterization of traffic. Under modest resource allocation conditions, the end-to-end session delays and backlogs corresponding to this class of algorithms are shown to be bounded. For the SCFQ scheme, these bounds are larger, but practically as good as the corresponding bounds for the PGPS scheme. It is shown that the SCFQ scheme can provide adequate performance guarantees for the delay-sensitive traffic in ATM.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>