Multicast Scheduling Research Articles

Proportional Fair Scheduling for Multicast Services in Wireless Cellular Networks

Recently, there has been extensive research on resource allocation schemes for multicast services that would satisfy the requirements of multimedia traffic. Although several schemes have been proposed to improve the performance of individual multicast groups, it is not easy to achieve both throughput efficiency and user fairness. In this study, we propose a new multicast scheduling scheme for achieving proportional fair (PF) allocation in wireless cellular systems. The basic idea of PF is to schedule the user whose corresponding instantaneous channel quality is the highest relative to the average channel condition over a given time scale. We first extend the PF metric to the extent that the scheduler can reflect the user's varying channel gain, and fairness, not only in the unicast case, but also in multicast transmissions. A multicast PF scheme maximizes the summation of the logarithmic average rate of all multicasting users. Thus, it improves the fairness to mobile users when compared to max-rate allocation, because the logarithmic rate gives more weight to lower rate users, while achieving high throughput. Moreover, the proposed scheme is less complex than max-rate allocation.

Multicast scheduling with resource fairness constraints

Integration of multicast and unicast data in future radio access networks will be necessary in order to improve the resource efficiency and provide new services. Such integration requires new and efficient resource sharing mechanisms. These mechanisms need to be optimized to provide the best possible trade-off between resource efficiency and fairness. In this article, we consider a case where streaming multicast users are multiplexed together with elastic unicast users on a common time-slotted channel. We derive a system model to study the performance of various resource allocations strategies under proportional and resource fairness constraints. Fairness is directly defined in terms of the users' utilities rather than of the throughputs they are assigned to. We also describe an extension of the well-known unicast proportional fair scheduler to the multicast scenario. Through extensive simulations we demonstrate the performance of this scheduler for various traffic loads and multicast group sizes.

Traffic Share-Based Multicast Scheduling for Broadcast Video Delivery in Shared-WDM-PONs

One of the important issues of convergence service design in access networks is its capability to provide an effective video delivery service for high-quality Internet Protocol television and multicast video on demand. In this paper, the authors research the effects of optical traffic sharing on convergence service design and address how to support multicast video delivery service with multicast scheduling in a shared wavelength division multiplexed- passive optical network (S-WDM-PON) which deploys a shared downstream wavelength and a broadcasting arrayed waveguide grating to a WDM-PON. The proposed dynamic channel scheduling mechanism, which is called maximum share first reservation (MSFR), and multicast management adjust transmission channel types based on the effective multicast cost of broadcast video so that the maximum number of videos can be delivered to homes by optical traffic share, while the packet processing burden and service interference among applications are reduced. The authors also discuss the network design issue regarding the optimal provisioning of shared link bandwidth to guarantee effective convergence services and economical efficiency of the network. The analysis and simulation results validate the effectiveness of the proposed mechanisms.

An interference-aware fair scheduling for multicast in wireless mesh networks

Multicast is a fundamental routing service in wireless mesh networks (WMNs) due to its many potential applications such as video conferencing, online games, and webcast. Recently, researchers proposed using link-quality-based routing metrics for finding high-throughput paths for multicast routing. However, the performance of such link-quality-based multicast routing is still limited by severe unfairness. Two major artifacts that exist in WMNs are fading which leads to low quality links, and interference which leads to unfair channel allocation in the 802.11 MAC protocol. These artifacts cause the multicast application to behave unfairly with respect to the performance achieved by the multicast receivers. In this paper, we design a MAC layer solution to improve the fairness of multicast service in WMNs. Our proposed MAC layer takes into account the interference among multicast forwarding nodes and assigns them transmission time slots while maximizing the spatial reuse for high throughput. Detailed simulations and testbed experiments show that our solution significantly increases fairness as well as throughput compared to the 802.11 protocol.

Scheduling and performance analysis of multicast interconnects

Multicast is an important operation in various emerging computing/networking applications. In particular, many multicast applications require not only multicast capability but also predictable communication performance, such as guaranteed multicast latency and bandwidth, called quality-of-service (QoS). In this paper, we consider scheduling in multicast interconnects, which aims to minimize the multicast latency for a set of multicast requests. Unfortunately, such a problem has been proved to be NP-Complete, which means that it is unlikely to find a fast exact algorithm for the multicast scheduling problem. We then turn to propose a simple, fast greedy multicast scheduling algorithm and derive a lower bound and an upper bound on the performance of the algorithm. As can be seen, while a lower bound is fairly straightforward, the upper bound is much more difficult to obtain. By translating the multicast scheduling problem into a graph theory problem and employing a random graph approach, we are able to obtain a probabilistic upper bound on the performance of the multicast scheduling algorithm. Our analytical and simulation results show that the performance of the proposed multicast scheduling algorithm is quite close to the lower bound and is statistically guaranteed by the probabilistic upper bound.

A novel multicast mechanism for optical local area networks

In this paper, we propose a simple and efficient multicast scheduling algorithm, the Lookback Queue Access (LBQA) protocol for the employment in an asynchronous WDM optical star network. Network nodes use ALOHA based random access schemes to send their reservation packets over a common packet reservation control channel. A central traffic scheduler is allocated to coordinate message transmissions. The central scheduler carries out the LBQA scheme in real time in two phases. The first phase is to search (through input queues) for a candidate multicast message that can be sent, without partition, to all of its intended recipients. If phase 1 fails, the second phase is then activated to efficiently partition a multicast message into multiple transmissions. Performance results conducted via simulations have revealed that networks employing such a scheduling mechanism can exhibit superior network throughput levels and delay performances. To obtain sustainable high performances, we further propose an interconnected dual-star structure employed with the enhanced scheduling mechanism, the DS_LBQA algorithm. By using a simple heuristic approach, the DS_LBQA scheme is able to successfully exploit the inter data channels and properly utilize the wavelength reuse property of the intra data channels. Performance results have demonstrated the merits of deploying the DS_LBQA multicast algorithm in such a dual-star structure.

Multicast Scheduling in Buffered Crossbar Switches with Multiple Input Queues

Multicast Scheduling in Buffered Crossbar Switches with Multiple Input Queues

FIFO-Based Multicast Scheduling Algorithm for Virtual Output Queued Packet Switches

Many networking/computing applications require high speed switching for multicast traffic at the switch/router level to save network bandwidth. However, existing queuing-based packet switches and scheduling algorithms cannot perform well under multicast traffic. While the speedup requirement makes the output queued switch difficult to scale, the single input queued switch suffers from head of line (HOL) blocking, which severely limits the network throughput. An efficient yet simple buffering strategy to remove the HOL blocking is to use the virtual output queued (VOQ) switch structure, which has been shown to perform well under unicast traffic. However, the traditional VOQ switch is impractical for multicast traffic because a VOQ switch for multicast traffic has to maintain an exponential number of queues in each input port (i.e., 2/sup N/-1 queues for a switch with N output ports). In this paper, we give a novel queue structure for the input buffers of a multicast VOQ switch by separately storing the address information and data information of a packet so that an input port only needs to manage a linear number (N) of queues. In conjunction with the multicast VOQ switch, we present a first-in-first-out based multicast scheduling algorithm, FIFO multicast scheduling (FIFOMS), and conduct extensive simulations to compare FIFOMS with other popular scheduling algorithms. Our results fully demonstrate the superiority of FIFOMS in both multicast latency and queue space requirement.

Back Pressure Based Multicast Scheduling for Fair Bandwidth Allocation

We study the fair allocation of bandwidth in multicast networks with multirate capabilities. In multirate transmission, each source encodes its signal in layers. The lowest layer contains the most important information and all receivers of a session should receive it. If a receiver's data path has additional bandwidth, it receives higher layers which leads to a better quality of reception. The bandwidth allocation objective is to distribute the layers fairly. We present a computationally simple, decentralized scheduling policy that attains the maxmin fair rates without using any knowledge of traffic statistics and layer bandwidths. This policy learns the congestion level from the queue lengths at the nodes, and adapts the packet transmissions accordingly. When the network is congested, packets are dropped from the higher layers; therefore, the more important lower layers suffer negligible packet loss. We present analytical and simulation results that guarantee the maxmin fairness of the resulting rate allocation, and upper bound the packet loss rates for different layers.

Integration of unicast and multicast scheduling in input-queued packet switches

Packet queuing and scheduling, two of the critical components in an input-queued packet switch, have been extensively studied in the context of either pure unicast traffic or pure multicast traffic. Unfortunately, the results from a study in one context are not applicable to the other context. The design of integrated scheduling for both types of traffic remains an open issue. This paper deals with the problem of integrating unicast and multicast scheduling in an N × N input-queued packet switch with first in first out buffers. Instead of using isolated switching fabrics for unicast and multicast traffic respectively, we efficiently utilize one switching fabric for both unicast and multicast traffic by a careful design. In our design, each input port maintains a set of unicast queues based on virtual output queuing technique and a set of multicast queues based on a load-balance policy. By employing the research advances that have already been gained for unicast and multicast scheduling, we propose two practical slot-coupled integration algorithms, lSCIA (a loosely slot-coupled integration algorithm) and fSCIA (a fully slot-coupled integration algorithm). In each time slot, unicast scheduling and multicast scheduling cooperate together and the scheduling priority is allocated to either unicast traffic or multicast traffic according to a certain service ratio. The working interval of service ratio is defined as a set such that the saturation throughput is not less than the output load if the service ratio falls into this set. The upper bound and lower bound for the working interval of service ratio are deduced. A 100% throughput can be achieved with strong theoretical guarantees as long as the service ratio lies in the upper bound of the working interval. Both theoretical analysis and simulation studies suggest that the proposed integrated scheduling algorithms exhibit a promising performance in terms of throughput, delay and packet loss ratio, at different traffic compositions under Bernoulli traffic and bursty traffic.

Multicast Pull Scheduling: When Fairness Is Fine

We investigate server scheduling policies to minimize average user perceived latency in pull-based client-server systems (systems where multiple clients request data from a server) where the server answers requests on a multicast/ broadcast channel. We first show that there is no O(1) -competitive algorithm for this problem. We then give a method to convert any nonclairvoyant unicast scheduling algorithm A to nonclairvoyant multicast scheduling algorithm B . We show that if A works well, when jobs can have parallel and sequential phases, then B works well if it is given twice the resources. More formally, if A is an s -speed c -approximation unicast algorithm, then its counterpart algorithm B is a 2s -speed c -approximation multicast algorithm. It is already known [5] that Equi-partition, which devotes an equal amount of processing power to each job, is a (2 + e) -speed O(1 + 1/e) -approximation algorithm for unicast scheduling of such jobs. Hence, it follows that the algorithm {BEQUI}, which broadcasts all requested files at a rate proportional to the number of outstanding requests for that file, is a (4 + e) -speed O(1 + 1/e) -approximation algorithm. We give another algorithm BEQUI-EDF and show that BEQUI-EDF is also a (4 + e) -speed O(1 + 1/e) -approximation algorithm. However, BEQUI-EDF has the advantage that the maximum number of preemptions is linear in the number of requests, and the advantage that no preemptions occur if the data items have unit size.

Multicast traffic in input-queued switches: Optimal scheduling and maximum throughput

The paper studies input-queued packet switches loaded with both unicast and multicast traffic. The packet switch architecture is assumed to comprise a switching fabric with multicast (and broadcast) capabilities, operating in a synchronous slotted fashion. Fixed-size data units, called cells, are transferred from each switch input to any set of outputs in one time slot, according to the decisions of the switch scheduler, that identifies at each time slot a set of nonconflicting cells, i.e., cells neither coming from the same input, nor directed to the same output. First, multicast traffic admissibility conditions are discussed, and a simple counterexample is presented, showing intrinsic performance losses of input-queued with respect to output-queued switch architectures. Second, the optimal scheduling discipline to transfer multicast packets from inputs to outputs is defined. This discipline is rather complex, requires a queuing architecture that probably is not implementable, and does not guarantee in-sequence delivery of data. However, from the definition of the optimal multicast scheduling discipline, the formal characterization of the sustainable multicast traffic region naturally follows. Then, several theorems showing intrinsic performance losses of input-queued with respect to output-queued switch architectures are proved. In particular, we prove that, when using per multicast flow FIFO queueing architectures, the internal speedup that guarantees 100% throughput under admissible traffic grows with the number of switch ports.

WDM 방송망에서 수신기의 상태 정보를 이용한 멀티캐스트 스케줄링 알고리즘의 설계 및 성능평가

본 논문에서는 WDM 단일홉 Broadcast-and-select망에서 멀티캐스트 서비스를 지원하기 위한 스케줄링 알고리즘을 제안하였다. 기존의 멀티캐스트 스케줄링 알고리즘들은 고정된 송신기와 튜닝이 가능한 수신기에 대하여 멀티캐스트 서비스의 지연시간을 줄이기 위해 멀티캐스트 그룹을 어떻게 적절한 서브그룹으로 나눌 것인가에 대한 것이었다. 이러한 알고리즘들은 송신측의 파장으로 튜닝되어 바로 수신할 준비가 되어 있는 노드들에 대하여 이루어졌기 때문에 수신측의 상태정보를 이용할 수 없었으며, 모든 수신노드의 튜닝지연으로 인해 전체적인 지연시간이 길어지게 되었다. 따라서 본 논문에서는 튜닝이 가능한 송신기와 수신기의 상태정보, 그리고 메시지 전송시간과 튜닝지연시간을 이용하여 서브그룹을 나누는 H_EAR과 PGM 두 알고리즘을 제안하고, 컴퓨터 시뮬레이션을 통해 제안된 알고리즘의 성능이 기존의 멀티캐스트 스케줄링 알고리즘에 비하여 지연시간과 서브 그룹수의 측면에서 우수함을 보였다. In this paper, new multicast scheduling algorithms are proposed for the WDM single-hop broadcast-and-select networks. The existing multicast scheduling algorithms are focused on the partitioning a multicast group into several subgroups to reduce the delay time of each receiver. These partitioning algorithms are grouping method of the receivers already tuned to the transmitter's wavelength. However, these algorithms ignore the state of receivers, which leads to increase the number of subgroups and the delay time. Therefore, 1 propose two new multicast scheduling algorithms called H_EAR and PGM that partition a multicast group to subgroups using the tunable transmitter, state information of receivers, and pseudo group concept. The performance of proposed algorithms are evaluated through the computer simulation. They show the better performance comparing with the existing multicast scheduling algorithm.

A survey of multicasting protocols for broadcast-and-select single-hop networks

Multicast communication in single-hop broadcast-and-select wavelength-division multiplexing networks has received considerable attention from researchers. This article presents a comprehensive survey of the multicast scheduling techniques in this environment. It considers different challenges that are faced in the design of the multicasting techniques and presents a classification of such schemes. A survey of specific techniques is then presented and a comparison is drawn between such techniques.

Scheduling time-constrained multicast messages in circuit-switched tree networks

In this paper, we consider a kind of multicast scheduling problem in a tree network. Each multicast message is transmitted through a directed subtree within the tree network. The transmission time of each multicast message is assumed to be one unit. Two messages can be transmitted at the same time if their subtrees are edge-disjoint. Each message is constrained by a ready time and a deadline, and has a weight we can gain if it is scheduled within its deadline. The optimality criterion is the total weight we gain. We assume that the degree of each subtree is bounded by a constant d and present an approximation algorithm of which the approximation ratio is at most 4 d+15.

Minimizing the Number of Multicast Transmissions in Single-Hop WDM Networks

The problem of minimizing the number of transmissions for a multicast transmission under the condition that the packet delay is minimum in single-hop wavelength division multiplexing (WDM) networks is studied in this paper. This problem is proved to be NP-complete. A heuristic multicast scheduling algorithm is proposed for this problem. Extensive simulations are performed to compare the performance of the proposed heuristic algorithm with two other multicast scheduling algorithms, namely, the greedy and no-partition scheduling algorithms. The greedy algorithm schedules as many destination nodes as possible in the earliest data slot. The no-partition algorithm schedules the destination nodes of a multicast packet to receive the packet in the same data slot without partitioning the multicast transmission into multiple unicast or multicast transmissions. Our simulation results show that (i) an algorithm which partitions a multicast transmission into multiple unicast or multicast transmissions may not always produce lower mean packet delay than the no-partition algorithm when the number of data channels in the system is limited and (ii) the proposed heuristic algorithm always produces lower mean packet delay than the greedy and the no-partition algorithms because this algorithm not only partitions a multicast transmission into multiple unicast or multicast transmissions to keep the packet delay low but also reduces the number of transmissions to conserve resources.

Multicasting in WDM networks

Wavelength-division multiplexing (WDM) networks are believed to be a promising candidate to meet the explosive increase of bandwidth demand in the Internet. In this article, we survey the problems of and approaches to multicasting in WDM networks. In particular, we address the issues in the context of three types of WDM networks: broadcast-and-select, wavelength-routed, and optical burst-switched (OBS) WDM networks. Broadcast-and-select WDM networks are typically for WDM LANs?MANs, and can be either single-hop or multihop. Various multicast scheduling algorithms (MSAs) are discussed for single-hop networks. For multihop networks, we discuss how channel sharing can be employed to effectively support multicast. In a wavelength-routed WDM network, supporting multicast leads to the multicast routing and wavelength assignment (MC-RWA) problem, which has been discussed for different scenarios, including sparse-splitting networks. We also discuss the problem of efficiently supporting multicast in optical burst-switched (OBS) networks, where the overheads due to control packets and guard bands need to considered.

In single-hop WDM networks, a data packet can be transmitted from one node to another only when one of the transmitters of the source node and one of the receivers of the destination node are tuned to the same wavelength, i.e., a data packet is transmitted from one node to another without going through intermediate nodes. A hybrid multicast scheduling

This paper shows that, for single-hop wavelength division multiplexing (WDM) networks, a multicast scheduling algorithm which always tries to partition a multicast transmission into multiple unicast or multicast transmissions may not always produce lower mean packet delay than a multicast scheduling algorithm that does not partition multicast transmissions. The performance of a multicast scheduling algorithm may depend on the traffic conditions and the availability of the channel resource in the network. A hybrid multicast scheduling algorithm that can be used in single-hop WDM networks.

Source-limited inclusive routing: A new paradigm for multicast communication

In this paper, we study a combination of the multicast communication problem and the maximum disjoint paths problem. Specifically, we are given a directed tree T rooted at r, and we want to send a message from r to a subset of nodes in T. We accomplish this via a multicast schedule which consists of a number of time steps in which informed nodes deliver the message to uninformed nodes until all destinations have received the message. In each time step, any informed node s may forward the message to one of its uninformed descendant nodes d via the unique directed path, or dipath, p from s to d in ditree T. A multicast schedule is called edge-disjoint if the dipaths used in any time step do not share any edges. We call a multicast schedule a node-disjoint schedule if the dipaths used in any time step are node-disjoint. We show that directed trees can be used to represent source-limited inclusive routing, a realistic class of routing schemes used in popular direct network systems. We then show that node-disjoint multicast schedules in directed trees can be used to closely approximate optimal edge-disjoint multicast schedules. In addition, we show that node-disjoint multicast in directed trees can be reduced to an equivalent broadcast problem in directed trees. We describe an O(n2) greedy algorithm (GA) for performing node-disjoint broadcast in directed trees. The greatest advantages of the GA algorithm are its simplicity and its optimal performance in popular topologies such as meshes, tori, and hypercubes. We also describe an O(n3) algorithm that always produces minimum-length node-disjoint broadcast schedules for directed tree topologies, which can be easily transformed into an algorithm that produces edge-disjoint multicast schedules that are no more than twice the length of an optimal edge-disjoint multicast schedule for an arbitrary topology. © 2000 John Wiley & Sons, Inc.

Probability distribution of the receiver busy time in a multicasting local lightwave network

Wavelength-division multiplexing (WDM) has the ability to utilize the enormous bandwidth offered by optical networks using today's electronics. A reservation-based multicasting protocol for local lightwave networks was examined in Borella and Mukherjee, 1995. If implemented properly, multicasting allows the use of scarce network resources more efficiently than unicasting. On the other hand, a multicasting protocol is usually more complex than a unicasting protocol. An analytical model of a multicasting protocol can enable its comparison with a simpler but less efficient unicasting protocol. We present an approximate analytical solution for the average packet delay in a local lightwave network, which employs the Multicast Scheduling Algorithm (Borella and Mukherjee, 1995) as its medium-access control (MAC) protocol. First, we develop an approximate analytical solution for the probability distribution of the receiver busy time. We demonstrate and explain some interesting and unobvious behavior of this distribution. Then, using the receiver busy time distribution, we calculate the maximum receiver throughput and the average packet delay. Results from the analytical solution match very well with those obtained from simulation.