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70
The impact of imperfect scheduling on crosslayer congestion control in wireless networks
, 2005
"... In this paper, we study crosslayer design for congestion control in multihop wireless networks. In previous work, we have developed an optimal crosslayer congestion control scheme that jointly computes both the rate allocation and the stabilizing schedule that controls the resources at the under ..."
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Cited by 349 (32 self)
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In this paper, we study crosslayer design for congestion control in multihop wireless networks. In previous work, we have developed an optimal crosslayer congestion control scheme that jointly computes both the rate allocation and the stabilizing schedule that controls the resources at the underlying layers. However, the scheduling component in this optimal crosslayer congestion control scheme has to solve a complex global optimization problem at each time, and is hence too computationally expensive for online implementation. In this paper, we study how the performance of crosslayer congestion control will be impacted if the network can only use an imperfect (and potentially distributed) scheduling component that is easier to implement. We study both the case when the number of users in the system is fixed and the case with dynamic arrivals and departures of the users, and we establish performance bounds of crosslayer congestion control with imperfect scheduling. Compared with a layered approach that does not design congestion control and scheduling together, our crosslayer approach has provably better performance bounds, and substantially outperforms the layered approach. The insights drawn from our analyses also enable us to design a fully distributed crosslayer congestion control and scheduling algorithm for a restrictive interference model.
A tutorial on crosslayer optimization in wireless networks
 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS
, 2006
"... This tutorial paper overviews recent developments in optimization based approaches for resource allocation problems in wireless systems. We begin by overviewing important results in the area of opportunistic (channelaware) scheduling for cellular (singlehop) networks, where easily implementable my ..."
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Cited by 248 (29 self)
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This tutorial paper overviews recent developments in optimization based approaches for resource allocation problems in wireless systems. We begin by overviewing important results in the area of opportunistic (channelaware) scheduling for cellular (singlehop) networks, where easily implementable myopic policies are shown to optimize system performance. We then describe key lessons learned and the main obstacles in extending the work to general resource allocation problems for multihop wireless networks. Towards this end, we show that a cleanslate optimization based approach to the multihop resource allocation problem naturally results in a “loosely coupled” crosslayer solution. That is, the algorithms obtained map to different layers (transport, network, and MAC/PHY) of the protocol stack are coupled through a limited amount of information being passed back and forth. It turns out that the optimal scheduling component at the MAC layer is very complex and thus needs simpler (potentially imperfect) distributed solutions. We demonstrate how to use imperfect scheduling in the crosslayer framework and describe recently developed distributed algorithms along these lines. We conclude by describing a set of open research problems.
Understanding the capacity region of the greedy maximal scheduling algorithm in multihop wireless networks
 Proc. of IEEE INFOCOM
, 2008
"... Abstract—In this paper, we characterize the performance of an important class of scheduling schemes, called Greedy Maximal Scheduling (GMS), for multihop wireless networks. While a lower bound on the throughput performance of GMS is relatively wellknown in the simple nodeexclusive interference mo ..."
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Cited by 125 (9 self)
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Abstract—In this paper, we characterize the performance of an important class of scheduling schemes, called Greedy Maximal Scheduling (GMS), for multihop wireless networks. While a lower bound on the throughput performance of GMS is relatively wellknown in the simple nodeexclusive interference model, it has not been thoroughly explored in the more general Khop interference model. Moreover, empirical observations suggest that the known bounds are quite loose, and that the performance of GMS is often close to optimal. In this paper, we provide a number of new analytic results characterizing the performance limits of GMS. We first provide an equivalent characterization of the efficiency ratio of GMS through a topological property called the localpooling factor of the network graph. We then develop an iterative procedure to estimate the localpooling factor under a large class of network topologies and interference models. We use these results to study the worstcase efficiency ratio of GMS on two classes of network topologies. First, we show how these results can be applied to tree networks to prove that GMS achieves the full capacity region in tree networks under theKhop interference model. Second, we show that the worstcase efficiency ratio of GMS in geometric network graphs is between 1 6
A Distributed Joint ChannelAssignment, Scheduling and Routing Algorithm for MultiChannel Ad Hoc Wireless Networks
 In Proceedings of IEEE INFOCOM
, 2007
"... Abstract — The capacity of ad hoc wireless networks can be substantially increased by equipping each network node with multiple radio interfaces that can operate on multiple nonoverlapping channels. However, new scheduling, channelassignment, and routing algorithms are required to fully utilize the ..."
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Cited by 81 (0 self)
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Abstract — The capacity of ad hoc wireless networks can be substantially increased by equipping each network node with multiple radio interfaces that can operate on multiple nonoverlapping channels. However, new scheduling, channelassignment, and routing algorithms are required to fully utilize the increased bandwidth in multichannel multiradio ad hoc networks. In this paper, we develop a fully distributed algorithm that jointly solves the channelassignment, scheduling and routing problem. Our algorithm is an online algorithm, i.e., it does not require prior information on the offered load to the network, and can adapt automatically to the changes in the network topology and offered load. We show that our algorithm is provably efficient. That is, even compared with the optimal centralized and offline algorithm, our proposed distributed algorithm can achieve a provable fraction of the maximum system capacity. Further, the achievable fraction that we can guarantee is larger than that of some other comparable algorithms in the literature. I.
Constanttime distributed scheduling policies for ad hoc wireless networks
 in Proceedings of IEEE Conference on Decision and Control
, 2006
"... Abstract — We propose two new distributed scheduling policies for ad hoc wireless networks that can achieve provable capacity regions. Known scheduling policies that guarantee comparable capacity regions are either centralized or need computation time that increases with the size of the network. In ..."
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Cited by 79 (7 self)
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Abstract — We propose two new distributed scheduling policies for ad hoc wireless networks that can achieve provable capacity regions. Known scheduling policies that guarantee comparable capacity regions are either centralized or need computation time that increases with the size of the network. In contrast, the unique feature of the proposed distributed scheduling policies is that they are constanttime policies, i.e., the time needed for computing a schedule is independent of the network size. Hence, they can be easily deployed in large networks. I.
Performance of Random Access Scheduling Schemes in Multihop Wireless Networks
"... The scheduling problem in multihop wireless networks has been extensively investigated. Although throughput optimal scheduling solutions have been developed in the literature, they are unsuitable for multihop wireless systems because they are usually centralized and have very high complexity. In ..."
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Cited by 74 (7 self)
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The scheduling problem in multihop wireless networks has been extensively investigated. Although throughput optimal scheduling solutions have been developed in the literature, they are unsuitable for multihop wireless systems because they are usually centralized and have very high complexity. In this paper, we develop a randomaccess based scheduling scheme that utilizes local information. The important features of this scheme include constanttime complexity, distributed operations, and a provable performance guarantee. Analytical results show that it guarantees a larger fraction of the optimal throughput performance than the stateoftheart. Through simulations with both singlehop and multihop traffics, we observe that the scheme provides high throughput, close to that of a wellknown highlyefficient centralized greedy solution called the Greedy Maximal Scheduler.
Maintaining Packet Order in TwoStage Switches
, 2002
"... High performance packet switches frequently use a centralized scheduler (also known as an arbiter) to determine the configuration of a nonblocking crossbar. The scheduler often limits the scalability of the system because of the frequency and complexity of its decisions. A recent paper by C.S. Cha ..."
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Cited by 50 (6 self)
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High performance packet switches frequently use a centralized scheduler (also known as an arbiter) to determine the configuration of a nonblocking crossbar. The scheduler often limits the scalability of the system because of the frequency and complexity of its decisions. A recent paper by C.S. Chang et al. introduces an interesting twostage switch, in which each stage uses a trivial deterministic sequence of configurations. The switch is simple to implement at high speed and has been proved to provide 100% throughput for a broad class of traffic. Furthermore, there is a bound between the average delay of the twostage switch and that of an ideal outputqueued switch. However, in its simplest form, the switch missequences packets by an arbitrary amount. In this paper, building on the twostage switch, we present an algorithm called Full Frames First (FFF), that prevents missequencing while maintaining the performance benefits (in terms of throughput and delay) of the basic twostage switch. FFF comes at some additional cost, which we evaluate in this paper.
Practical Algorithms for Performance Guarantees in Buffered Crossbars
, 2005
"... Network operators would like high capacity routers that give guaranteed throughput, rate and delay guarantees. Because they want high capacity, the trend has been towards input queued or combined input and output queued (CIOQ) routers using crossbar switching fabrics. But these routers require impra ..."
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Cited by 50 (2 self)
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Network operators would like high capacity routers that give guaranteed throughput, rate and delay guarantees. Because they want high capacity, the trend has been towards input queued or combined input and output queued (CIOQ) routers using crossbar switching fabrics. But these routers require impractically complex scheduling algorithms to provide the desired guarantees. In this paper, we explore how a buffered crossbar  a crossbar switch with a packet buffer at each crosspoint  can provide guaranteed performance (throughput, rate, and delay), with less complex, practical scheduling algorithms. We describe scheduling algorithms that operate in parallel on each input and output port, and hence are scalable. With these algorithms, buffered crossbars with a speedup of two can provide 100% throughput, rate, and delay guarantees. Index Terms system design, combinatorics, packet switching, buffered crossbar, scheduling algorithm, performance guarantees, throughput, mimic, quality of service. I. BACKGROUND Network operators would like high capacity routers that give guaranteed performance. First, they prefer routers that guarantee throughput so they can maximize the utilization of their expensive longhaul links. Second, they want routers that can allocate to each flow a guaranteed rate. Third, they want the capability to control the delay for packets of individual flows for realtime applications. Because they want high capacity, the trend has been towards input queued or combined input and output queued (CIOQ) routers. Most of these routers use a crossbar switching fabric with a centralized scheduler. While it is theoretically possible to build crossbar schedulers that give 100% throughput [1] or rate and delay guarantees [2][3] they are considered too complex to b...
Multicast Traffic in InputQueued Switches: Optimal Scheduling and Maximum Throughput
 IEEE/ACM Trans. Networking
, 2003
"... Abstract—This paper studies inputqueued 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. Fixedsize data units, called cel ..."
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Cited by 43 (5 self)
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Abstract—This paper studies inputqueued 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. Fixedsize 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 showing intrinsic performance losses of inputqueued with respect to outputqueued switch architectures is presented. Second, the optimal scheduling discipline to transfer multicast packets from inputs to outputs is defined. This discipline is rather complex, requires a queuing architecture
Strong performance guarantees for asynchronous crossbar schedulers
 In IEEE INFOCOM
, 2006
"... Crossbarbased switches are commonly used to implement routers with throughputs up to about 1 Tb/s. The advent of crossbar scheduling algorithms that provide strong performance guarantees now makes it possible to engineer systems that perform well, even under extreme traffic conditions. Until recent ..."
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Cited by 29 (3 self)
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Crossbarbased switches are commonly used to implement routers with throughputs up to about 1 Tb/s. The advent of crossbar scheduling algorithms that provide strong performance guarantees now makes it possible to engineer systems that perform well, even under extreme traffic conditions. Until recently, such performance guarantees have only been developed for crossbars that switch cells rather than variable length packets. Cellbased crossbars incur a worstcase bandwidth penalty of up to a factor of two, since they must fragment variable length packets into fixed length cells. In addition, schedulers for cellbased crossbars may fail to deliver the expected performance guarantees when used in routers that forward packets. We show how to obtain performance guarantees for asynchronous crossbars that are directly comparable to those previously developed for synchronous, cellbased crossbars. In particular we define derivatives of the Group by Virtual Output Queue (GVOQ) scheduler of Chuang et al. and the Least Occupied Output First Scheduler of Krishna et al. and show that both can provide strong performance guarantees in systems with speedup 2. Specifically, we show that these schedulers are workconserving and that they can emulate an outputqueued switch using any queueing discipline in the class of restricted PushIn, FirstOut queueing disciplines. We also show that there are schedulers for segmentbased crossbars, (introduced recently by Katevenis and Passas) that can deliver strong performance guarantees with small buffer requirements and no bandwidth fragmentation. 1