3063801
Iteration-Shared Scheduling Algorithms Abolishing the Departure-Time-Compatible Graph in Switch-Memory-Switch Switches
Switch-Memory-Switch (SMS) architecture exhibits an excellent performance due to its emulating the Output Queueing structure. However, in order to achieve the maximal matching, the first stage scheduling operates at a huge computational complexity, which blocks the SMS from practical implementation. In order to put SMS into more effective industrial applications, especially in super-large size switches/routers with multi-services environment, two parallel iterative scheduling algorithms, named IS-RRM and AIS-RRM respectively, are proposed in this paper. The algorithms abolish totally the traditional departure-time-compatible (DTC) graph, and by using iteration-sharing technology, greatly reduce the required iteration number in each time slot. Using a discrete-time Markov chain to model the AIS-RRM algorithm, we obtain its upper bound of cell loss rate. Meanwhile, experimental and theoretical results show that so long as the number of shared memories is twice the switch size, AIS-RRM algorithm can achieve a cell loss rate of 10 when the input buffer size is 15 and the iteration number of each time slot is 6, despite the arrival traffic pattern and the switch size. Furthermore, the iteration number required in each time slot can be further decreased by increasing the input buffer size.
1001399
DS-PPS: A Practical Framework to Guarantee Differentiated QoS in Terabit Routers with Parallel Packet Switch
Parallel Packet Switch (PPS) is used intensively in today's terabit router to construct the switching fabric. Basic PPS equally deals with all of the traffic in order to achieve uniform load-balancing and high throughput, but it fails to support differentiated QoS. With the recent blooming of delay- sensitive Internet traffic, such as the peer-to-peer live streaming and IPTV, differentiated QoS is becoming an urgent demand. In this paper, we propose a novel and practical framework, the Differentiated Service Parallel Packet Switch (DS-PPS), which supports three fundamental QoS features: guaranteed-delay (GD), guaranteed-bandwidth (GB) and best-effort (BE). By adaptively adjusting the number of switching planes offered to each QoS class, DS-PPS precisely controls the delay bounds of GD traffic and the drop precedence of GB traffic. We evaluate DS-PPS by extensive theoretical analyses and comprehensive simulations. Experimental results on a prototype implementation of the framework show that DS-PPS outperforms the basic PPS in three main aspects. First, the average delay of TCP short packet under full load is reduced by more than 94%. Second, the average delay of real-time traffic under full load is reduced by more than 82%. And third, the GB traffic of low drop precedence is guaranteed of nearly three times the throughput of high drop precedence at the hotspots. Significantly, our proposed DS-PPS framework is universal and scalable to support various kinds of emerging QoS-sensitive applications in multi-service terabit routers without any extra overhead.
13323849
On the Extreme Parallelism Inside Next-Generation Network Processors
Next-generation high-end network processors (NP) must address demands from both diversified applications and ever-increasing traffic pressure. One major challenge is to design an extraordinary scalable architecture. In this paper, it is argued that such an objective can only be sufficed by introducing highly paralleled structure, namely the paralleled processing-engine cluster (PPC). We demonstrate this point from the trade-off among aspects such as performance, programmability and flexibility. However, PPC natively suffers from several critical issues on load-balancing, intra-flow packet ordering and memory contention. After investigating several existing approaches, we present novel solutions for each issue according to the balance between performance and coast. Through intensive analysis and comprehensive simulations, it is shown that the shortest queue first scheduling with class-based prediction (SQF-C) performs nearly optimally, while the hardware based per-flow ordering mechanism resolves packet out-of-order independently with the load-balancing issue, inducting little throughput degradation. Implementing the unified solution, it is capable to design a PPC supporting up to OC-768c line rate. Real implementation is also carried out in our THNPU-1 prototype to verify the conclusions.
5712150
Preemptive Packet-Mode Scheduling to Improve TCP Performance
Recent Internet traffic measurements show that 60% of the total packets are short packets, which include TCP acknowledgment and control segments. These short packets make a great impact on the performance of TCP. Unfortunately, short packets suffer from large delay due to serving long data packets in switches running in the packet mode, i.e. a packet is switched in its entirety. To optimize TCP performance, we apply a cross-layer approach to the design of switching architectures and scheduling algorithms. Specifically, we propose a preemptive packet-mode scheduling architecture and an algorithm called preemptive short packets first (P-SPF). Analysis and simulation results demonstrate that compared to existing packet-mode schedulers, P-SPF significantly reduces the waiting time for short packets while achieving a high overall throughput when the traffic load is heavy. Moreover, with a relatively low speedup, P-SPF performs better than existing packet-mode schedulers under any traffic load.
7704531
A TCAM-based distributed parallel IP lookup scheme and performance analysis
Using ternary content addressable memory (TCAM) for high-speed IP address lookup has been gaining popularity due to its deterministic high performance. However, restricted by the slow improvement of memory accessing speed, the route lookup engines for next-generation terabit routers demand exploiting parallelism among multiple TCAM chips. Traditional parallel methods always incur excessive redundancy and high power consumption. We propose in this paper an original TCAM-based IP lookup scheme that achieves both ultra-high lookup throughput and optimal utilization of the memory while being power-efficient. In our multi-chip scheme, we devise a load-balanced TCAM table construction algorithm together with an adaptive load balancing mechanism. The power efficiency is well controlled by decreasing the number of TCAM entries triggered in each lookup operation. Using four 133 MHz TCAM chips and given 25% more TCAM entries than the original route table, the proposed scheme achieves a lookup throughput of up to 533 MPPS while remains simple for ASIC implementation
17725194
SPF: to improve the performance of packet-mode scheduling
Recent researches present that packet-mode scheduling may provide overall performance advantages over cell-mode scheduling in input queueing switches. But one significant drawback of existing packet-mode schedulers is that they tend to result in longer waiting time of short packets, whose delay is critical to the performance of IP networks. To mitigate the problem, this paper proposes a simple but effective packet-mode scheduling algorithm called Short Packets First (SPF), studies the corresponding buffering architecture, and evaluates the performance on throughput and packet delay. SPF achieves 100% throughput under an accurate Internet traffic model. Theoretical analysis proves that SPF can reduce the average packet waiting time of short packets as well as overall packets, under the condition of uniform Poisson arrival process and low to medium offered load. Furthermore, extended simulation studies show that SPF is superior to general packet-mode and cell-mode scheduling, especially under heavy offered load.
1727263
A study of networks simulation efficiency: fluid simulation vs. packet-level simulation
Network performance evaluation through traditional packet-level simulation is becoming increasingly difficult as today's networks grow in scale along many dimensions. As a consequence, fluid simulation has been proposed to cope with the size and complexity of such systems. This study focuses on analyzing and comparing the relative efficiencies of fluid simulation and packet-level simulation for several network scenarios. We use the "simulation event" rate to measure the computational effort of the simulators and show that this measure is both adequate and accurate. For some scenarios, we derive analytical results for the simulation event rate and identify the major factors that contribute to the simulation event rate. Among these factors, the "ripple effect" is very important since it can significantly increase the fluid simulation event rate. For a tandem queueing system, we identify the boundary condition to establish regions where one simulation paradigm is more efficient than the other. Flow aggregation is considered as a technique to reduce the impact of the "ripple effect" in fluid simulation. We also show that WFQ scheduling discipline can limit the "ripple effect", making fluid simulation particularly well suited for WFQ models. Our results show that tradeoffs between parameters of a network model determines the most efficient simulation approach.
1259464
Using Temporal Semantics for Live Media Stream Queries
Querying live media streams is a challenging problem that becomes an essential requirement in a growing number of applications. We address the problem of evaluating continuous queries on media streams produced by media sources such as webcams and microphones. The temporal attributes and the order of stream tuples play essential roles in live stream generation and query execution. Furthermore, the temporal constraints and query semantics of related streams provide additional query optimization opportunities. We investigate the modeling issues and introduce the query processing techniques of a live media stream management system (MedSMan), including media capturing, automatic feature generating, declaration and query languages, temporal stream operators and querying algorithms. A prototype is implemented and we present experimental results to show the performance of our prototype using various real-time media experiments.
8584874
Throughput Optimization and Fair Bandwidth Allocation in Multi-Hop Wireless LANs
There is an inherent well-known conflict between fairness and throughput that arises in many networking scenarios. A number of researchers have studied this problem in the context of (single-hop) wireless local area networks (WLANs), where clients directly exchange traffic with access points (APs). More recently, researchers have proposed multi-hop extensions to WLANs where client traffic is forwarded via a series of client-client links. In this paper, we show that the objective of improving throughput without sacrificing fairness can be much better met in multi-hop WLANs. We decouple this objective into two separate but related problems. First, we need an algorithm to organize clients into a multi-hop structure such that fair bandwidth allocation within this structure leads to improved throughput. Second, we need algorithms for performing fair bandwidth allocation within the determined multi-hop structure. In this paper, we first design optimal fair bandwidth allocation algorithms for both max-min throughput fairness and max-min time fairness in multi-hop WLANs. Subsequently, we design an efficient algorithm to find desirable multi-hop structures. With slight modifications, our results in this paper can be generalized to other multi-hop wireless networks as well. Our proposed solutions seamlessly integrate with legacy devices and hence are incrementally deployable. Simulation results demonstrate that our solutions can effectively improve throughput (by up to 114% or more) as well as network coverage while preserving fairness.
1437746
On the skew-bounded minimum-buffer routing tree problem
Bounding the load capacitance at gate outputs is a standard element in today's electrical correctness methodologies for high-speed digital very large scale integration design. Bounds on load caps improve coupling-noise immunity, reduce degradation of signal transition edges, and reduce delay uncertainty due to coupling noise (Kahng et al. 1998). For clock and test distribution, an additional design requirement is bounding the buffer skew, i.e., the difference between the maximum and the minimum number of buffers over all of the source-to-sink paths in the routing tree, since buffer skew is one of the main factors affecting delay skew (Tellez and Sarrafzadeh 1997). In this paper, we consider algorithms for buffering a given tree with the minimum number of buffers under given load cap and buffer skew constraints. We show that the greedy algorithm proposed by Tellez and Sarrafzadeh is suboptimal for nonzero buffer-skew bounds and give examples showing that no bottom-up greedy algorithm can achieve optimality. The main contribution of the paper is an optimal dynamic programming algorithm for the problem. Experiments on test cases extracted from recent industrial designs show that the dynamic programming algorithm has practical running time and saves up to 37.5% of the buffers inserted by Tellez and Sarrafzadeh's algorithm.
40457509
Temporal segmentation of video using frame and histogram space
Two algorithms are presented for the detection of gradual transitions in video sequences. The first is a dissolve detection algorithm utilizing certain properties of a dissolve's trajectory in image-space. It is implemented both as a simple threshold-based detector, and as a parametric detector by modeling the error properties of the extracted statistics. The second is an algorithm to detect a wide variety of wipes based on image histogram characteristics during such transitions. Both algorithms operate in the compressed domain, requiring only partial decoding of the compressed video stream. Experiments show the algorithms perform as well as-and in some cases, better than-full-frame methods, on a wide variety of gradual transitions, and can operate significantly faster than real-time.