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191
The iSLIP Scheduling Algorithm for Input-Queued Switches
, 1999
"... An increasing number of high performance internetworking protocol routers, LAN and asynchronous transfer mode (ATM) switches use a switched backplane based on a crossbar switch. Most often, these systems use input queues to hold packets waiting to traverse the switching fabric. It is well known th ..."
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Cited by 425 (8 self)
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An increasing number of high performance internetworking protocol routers, LAN and asynchronous transfer mode (ATM) switches use a switched backplane based on a crossbar switch. Most often, these systems use input queues to hold packets waiting to traverse the switching fabric. It is well known that if simple first in first out (FIFO) input queues are used to hold packets then, even under benign conditions, head-of-line (HOL) blocking limits the achievable bandwidth to approximately 58.6 % of the maximum. HOL blocking can be overcome by the use of virtual output queueing, which is described in this paper. A scheduling algorithm is used to configure the crossbar switch, deciding the order in which packets will be served. Recent results have shown that with a suitable scheduling algorithm, 100 % throughput can be achieved. In this paper, we present a scheduling algorithm called iSLIP. An iterative, round-robin algorithm, iSLIP can achieve 100% throughput for uniform traffic, yet is simple to implement in hardware. Iterative and noniterative versions of the algorithms are presented, along with modified versions for prioritized traffic. Simulation results are presented to indicate the performance of iSLIP under benign and bursty traffic conditions. Prototype and commercial implementations of iSLIP exist in systems with aggregate bandwidths ranging from 50 to 500 Gb/s. When the traffic is nonuniform, iSLIP quickly adapts to a fair scheduling policy that is guaranteed never to starve an input queue. Finally, we describe the implementation complexity of iSLIP. Based on a two-dimensional (2-D) array of priority encoders, single-chip schedulers have been built supporting up to 32 ports, and making approximately 100 million scheduling decisions per second.
Load Balanced Birkhoff-von Neumann Switches, Part II: Multi-stage Buffering
, 2001
"... The main objective of this sequel is to solve the out-of-sequence problem that occurs in the load balanced Birkhoff-von Neumann switch with one-stage buffering. We do this by adding a load-balancing buffer in front of the first stage and a resequencing-and-output buffer after the second stage. Moreo ..."
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Cited by 141 (16 self)
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The main objective of this sequel is to solve the out-of-sequence problem that occurs in the load balanced Birkhoff-von Neumann switch with one-stage buffering. We do this by adding a load-balancing buffer in front of the first stage and a resequencing-and-output buffer after the second stage. Moreover, packets are distributed at the first stage according to their flows, instead of their arrival times in Part I. In this paper, we consider multicasting ows with two types of scheduling policies: the First Come First Served (FCFS) policy and the Earliest Deadline First (EDF) policy. The FCFS policy requires a jitter control mechanism in front of the second stage to ensure proper ordering of the traffic entering the second stage. For the EDF scheme, there is no need for jitter control. It uses the departure times of the corresponding FCFS output-buffered switch as deadlines and schedules packets according to their deadlines. For both policies, we show that the end-to-end delay through our multistage switch is bounded above by the sum of the delay from the corresponding FCFS output-buffered switch and a constant that only depends on the size of the switch and the number of multicasting flows supported by the switch.
On the speedup required for work-conserving crossbar switches
, 1999
"... This paper describes the architecture for a work-conserving server using a combined I/O-buffered crossbar switch. The switch employs a novel algorithm based on output occupancy, the lowest occupancy output first algorithm (LOOFA), and a speedup of only two. A work-conserving switch provides the same ..."
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Cited by 98 (1 self)
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This paper describes the architecture for a work-conserving server using a combined I/O-buffered crossbar switch. The switch employs a novel algorithm based on output occupancy, the lowest occupancy output first algorithm (LOOFA), and a speedup of only two. A work-conserving switch provides the same throughput performance as an output-buffered switch. The work-conserving property of the switch is independent of the switch size and input traffic pattern. We also present a suite of algorithms that can be used in combination with LOOFA. These algorithms determine the fairness and delay properties of the switch. We also describe a mechanism to provide delay bounds for real-time traffic using LOOFA. These delay bounds are achievable without requiring output-buffered switch emulation.
On the Stability of Input-Queued Switches with Speed-Up
- IEEE/ACM TRANSACTIONS ON NETWORKING
, 2001
"... We consider cell-based switch and router architectures whose internal switching matrix does not provide enough speed to avoid input buffering. These architectures require a scheduling algorithm to select at each slot a subset of input buffered cells which can be transferred toward output ports. In t ..."
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Cited by 70 (6 self)
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We consider cell-based switch and router architectures whose internal switching matrix does not provide enough speed to avoid input buffering. These architectures require a scheduling algorithm to select at each slot a subset of input buffered cells which can be transferred toward output ports. In this paper, we propose several classes of scheduling algorithms whose stability properties are studied using analytical techniques mainly based upon Lyapunov functions. Original stability conditions are also derived for scheduling algorithms that are being used today in highperformance switch and router architectures.
Exact emulation of an output queueing switch by a combined input output.
- In International Workshop on Quality of Service,
, 1998
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Throughput and fairness guarantees through maximal scheduling in wireless networks
- IEEE Transactions on Information Theory
, 2008
"... We address the question of providing throughput guarantees through distributed scheduling, which has remained an open problem for some time. We consider a simple distributed scheduling strategy, maximal scheduling, and prove that it attains a guaranteed fraction of the maximum throughput region in a ..."
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Cited by 56 (2 self)
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We address the question of providing throughput guarantees through distributed scheduling, which has remained an open problem for some time. We consider a simple distributed scheduling strategy, maximal scheduling, and prove that it attains a guaranteed fraction of the maximum throughput region in arbitrary wireless networks. The guaranteed fraction depends on the “interference degree ” of the network, which is the maximum number of transmitter-receiver pairs that interfere with any given transmitter-receiver pair in the network and do not interfere with each other. Depending on the nature of communication, the transmission powers and the propagation models, the guaranteed fraction can be lower bounded by the maximum link degrees in the underlying topology, or even by constants that are independent of the topology. We prove that the guarantees are tight in that they can not be improved any further with maximal scheduling. Our results can also be generalized to end-to-end multi-hop sessions. Finally, we enhance maximal scheduling to guarantee fairness of rate allocation among different sessions. I.
Stateless Core: A scalable approach for Quality of Service
- in the Internet, Ph.D. Dissertation
, 2000
"... Today’s Internet provides one simple service: best effort datagram delivery. This minimalist service allows the Internet to be stateless, that is, routers do not need to maintain any fine grained information about traffic. As a result of this stateless architecture, the Internet is both highly scala ..."
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Cited by 51 (3 self)
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Today’s Internet provides one simple service: best effort datagram delivery. This minimalist service allows the Internet to be stateless, that is, routers do not need to maintain any fine grained information about traffic. As a result of this stateless architecture, the Internet is both highly scalable and robust. However, as the Internet evolves into a global commercial infrastructure that is expected to support a plethora of new applications such as IP telephony, interactive TV, and e-commerce, the existing best effort service will no longer be sufficient. In consequence, there is an urgent need to provide more powerful services such as guaranteed services, differentiated services, and flow protection. Over the past decade, there has been intense research toward achieving this goal. Two classes of solutions have been proposed: those maintaining the stateless property of the original Internet (e.g., Differentiated Services), and those requiring a new stateful architecture (e.g., Integrated Services). While stateful solutions can provide more powerful and flexible services such as per flow bandwidth and delay guarantees, they are less scalable than stateless solutions. In particular, stateful solutions require each router to maintain and manage per flow state on the control path, and to perform per flow classification, scheduling, and buffer management on the data path. Since today’s routers can
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 long-haul 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 real-time 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...
