A practical scheduling algorithm to achieve 100% throughput in input-queued switches
Adisak Mekkittikul,Nick McKeown +1 more
- 29 Mar 1998
- Vol. 2, pp 792-799
TL;DR: This work introduces a new algorithm called longest port first (LPF), which is designed to overcome the complexity problems of LQF, and can be implemented in hardware at high speed.
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Abstract: Input queueing is becoming increasingly used for high-bandwidth switches and routers. In previous work, it was proved that it is possible to achieve 100% throughput for input-queued switches using a combination of virtual output queueing and a scheduling algorithm called LQF However, this is only a theoretical result: LQF is too complex to implement in hardware. We introduce a new algorithm called longest port first (LPF), which is designed to overcome the complexity problems of LQF, and can be implemented in hardware at high speed. By giving preferential service based on queue lengths, we prove that LPF can achieve 100% throughput.
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Figures
Figure 1: A Simple Model of VOQ Switches. 
Figure 3: Transformation of a request graph into a flow network. (a) A weighted request graph. (b) The corresponding flow network, G, whose all edges are of unity capacity. A source and a target are added. The cost of every edge from and to is set to zero. The cost of all other edges are equal to the negated value of the corresponding weight. s 
Figure 6: An iterative LPF algorithm. First, the algorithm builds a sorted list of all inputs and outputs based on their occupancies. Then, starting from the largest output and input, the algorithm finds a maximal size match. 
Figure 7: A block diagram ofiLPF. Referring to the algorithm in Figure 6, inputs and outputs are pre-sorted by the two sorter networks. Raw requests (requests with weights removed) is given in a matrix form. Request reordering is done by the two crossbars which are configured by the sorting results. The maximal size matching block, which implements the double for-loop, finds a maximal size match that approximates an LPF match. The match needs to be permuted back to its natural order. ![Figure 4: Modified Edmonds-Karp algorithm [2]. is a flow network or graph constructed as described in Figure 3. is the set of all edges in ; or is a vertex in representing an input or output; is an edge from to ; is the total flow through the network; denotes a flow from to .](/figures/figure-4-modified-edmonds-karp-algorithm-2-is-a-flow-network-2q7u31ou.png)
Figure 4: Modified Edmonds-Karp algorithm [2]. is a flow network or graph constructed as described in Figure 3. is the set of all edges in ; or is a vertex in representing an input or output; is an edge from to ; is the total flow through the network; denotes a flow from to . 
Figure 5: A largest-unmatched-port first search (LPFS). First, LPFS builds a tree with as its root. Initially every input and output is colored white — undiscovered, then is grayed when it is discovered, and finally is blackened when it is finished. is the predecessor of . From the tree, an augmenting path from to which must go through an unmatched input can be found by walking the predecessor list which begins at a selected unmatched input.
![Figure 4: Modified Edmonds-Karp algorithm [2]. is a flow network or graph constructed as described in Figure 3. is the set of all edges in ; or is a vertex in representing an input or output; is an edge from to ; is the total flow through the network; denotes a flow from to .](/figures/figure-4-modified-edmonds-karp-algorithm-2-is-a-flow-network-2q7u31ou.webp)
Citations
The iSLIP scheduling algorithm for input-queued switches
TL;DR: This paper presents a scheduling algorithm called iSLIP, an iterative, round-robin algorithm that can achieve 100% throughput for uniform traffic, yet is simple to implement in hardware, and describes the implementation complexity of the algorithm.
Power allocation and routing in multibeam satellites with time-varying channels
TL;DR: A power-allocation policy is developed which stabilizes the system whenever the rate vector lies within the capacity region and provides a performance bound for the Choose-the-K-Largest-Connected-Queues policy.
Patent
Fibre channel over Ethernet
Luca Cafiero,Silvano Gai +1 more
- 17 Oct 2005
TL;DR: In this article, the authors present methods and devices for implementing a Low Latency Ethernet (LLE) solution, referred to herein as a Data Center Ethernet (DCE) solution which simplifies the connectivity of data centers and provides a high bandwidth, low latency network for carrying Ethernet and storage traffic.
260
DRILL: Micro Load Balancing for Low-latency Data Center Networks
Soudeh Ghorbani,Zibin Yang,P. Brighten Godfrey,Yashar Ganjali,Amin Firoozshahian +4 more
- 07 Aug 2017
TL;DR: DRILL is presented, a datacenter fabric for Clos networks which performs micro load balancing to distribute load as evenly as possible on microsecond timescales and addresses the resulting key challenges of packet reordering and topological asymmetry.
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CIXB-1: combined input-one-cell-crosspoint buffered switch
Roberto Rojas-Cessa,Eiji Oki,Zhigang Jing,Hung-Hsiang Jonathan Chao +3 more
- 29 May 2001
TL;DR: This work proposes a novel architecture: a combined input-one-cell-crosspoint buffer crossbar (CIXB-1) with virtual output queues (VOQs) at the inputs and round-robin arbitration that can provide 100% throughput under uniform traffic.
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