46229467
Packet-Mode Priority Scheduling for Terabit Core Routers
Existing packet-mode schedulers will result in long waiting time for short control packets in IP networks. To overcome this problem, this paper proposes a packet-mode practical scheduling algorithm called short-packets-first (SPF). With uniform Poisson arrival process and low to medium offered load, we prove that SPF can reduce the average packet waiting time for overall packets by greatly lowering the average packet waiting time for short packets. Moreover, simulations under a real traffic model demonstrate that SPF performs very well compared with other packet-mode and cell-mode scheduling algorithms, especially for short packets under heavy offered load..
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.
3143012
TCAM-based distributed parallel packet classification algorithm with range-matching solution
Packet classification (PC) has been a critical data path function for many emerging networking applications. An interesting approach is the use of TCAM to achieve deterministic, high speed PC However, apart from high cost and power consumption, due to slow growing clock rate for memory technology in general, PC based on the traditional single TCAM solution has difficulty to keep up with fast growing line rates. Moreover, the TCAM storage efficiency is largely affected by the need to support rules with ranges, or range matching. In this paper, a distributed TCAM scheme that exploits chip-level-parallelism is proposed to greatly improve the PC throughput. This scheme seamlessly integrates with a range encoding scheme, which not only solves the range matching problem but also ensures a balanced high throughput performance. Using commercially available TCAM chips, the proposed scheme achieves PC performance of more than 100 million packets per second (Mpps), matching OC768 (40 Gbps) line rate.
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.
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.
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.
62878
Single-hop probing asymptotics in available bandwidth estimation: sample-path analysis
In this paper, we take the sample-path approach in analyzing the asymptotic behavior of single-hop bandwidth estimation under bursty cross-traffic and show that these results are provably different from those observed under fluid models of prior work. This difference, which we call the probing bias, is one of the previously unknown factors that can cause measurement inaccuracies in available bandwidth estimation. We present an analytical formulation of "packet probing," based on which we derive several major properties of the probing bias. We then experimentally observe the <i>probing bias</i> and investigate its quantitative relationship to several deciding factors such as probing packet size, probing train length, and cross-traffic burstiness. Both our analytical and experimental results show that the probing bias vanishes as the packet-train length or packet size increases. The vanishing rate is decided by the burstiness of cross-traffic.
14440312
Fluid Simulation of Large Scale Networks: Issues and Tradeoffs
Traditional discrete-event packet-level approaches to simulating computer networks become computationally infeasible as the number of network nodes or their complexity increases. An alternative approach, in which packet-level traffic sources are replaced by fluid sources, has been proposed to address this challenge. In this paper we compare the amount of computational effort needed to simulate a network using a packet-level approach versus a fluid-based approach. We quantitatively characterize the amount of computational effort needed by each approach using the notion of a simulation’s event rate, and derive expressions for the event rate of a packet and fluid flow at both the input and output sides of a queue. We show that fluid simulation can require less computational effort for simple networks. However, as the network size and complexity grow, the so-called ”ripple effect” can result in fluid simulations becoming more expensive than their packet-level counterparts. This suggests that time-driven (approximate) fluid simulation techniques may be needed to efficiently simulate large scale networks.
10886416
Prediction and indexing of moving objects with unknown motion patterns
Existing methods for peediction spatio-temporal databases assume that objects move according to linear functions. This severely limits their applicability, since in practice movement is more complex, and individual objects may follow drastically diffferent motion patterns. In order to overcome these problems, we first introduce a general framework for monitoring and indexing moving objects, where (i) each boject computes individually the function that accurately captures its movement and (ii) a server indexes the object locations at a coarse level and processes queries using a filter-refinement mechanism. Our second contribution is a novel recursive motion function that supports a broad class of non-linear motion patterns. The function does not presume any a-priori movement but can postulate the particular motion of each object by examining its locations at recent timestamps. Finally. we propse an efficient indexing scheme that faciliates the processing of predicitive queries without false misses.
1873553
Toward better wireload models in the presence of obstacles
Efficient and accurate interconnect estimation is crucial to design convergence. With System-on-Chip design, IP blocks form routing obstacles that cannot be accounted for by existing a priori wirelength estimations. In this paper, we identify two distinct effects of obstacles on interconnection length: (i) changes due to the redistribution of interconnect terminals and (ii) detours that have to be made around the obstacles. Theoretical expressions of both effects for point-to-point nets with a single obstacle are derived and compared to experimental observations. We also experimentally assess these effects for multi-terminal interconnections and in the presence of multiple obstacles. We single out cases where the effects are additive, which suggests the use of lookup tables and equivalent blockage relations. Our results are applicable in chip planning tools, where they enable improved accounting for obstacles in a priori wirelength estimation schemes.
2578283
On the efficiency of fluid simulation of networks
Performance evaluation of computer networks through tratitional packet-level simulation is becoming increasingly difficult as networks grow in size along different dimensions. Due to its higher level of abstraction, fluid simulation is a promising approach for evaluating large-scale network models. In this paper we focus on evaluating and comparing the computaional effort required for fluid-and packet-level simulation. To measure the computaional effort required by a simulation approach, we introduce the concept of "simulation event rate", a measure that is both analytically tractable and adequate. We identify the fundamental factors that contribute to the simulation event rate in fluid- and packet-level simulations and provide an analytical characterization of the simulation event rate for specific network models. Among such factors, we identify the "ripple effect" as a significant contributor to the computational effort required by fluid simulation. We also show that the parameter space of a given network model can be divided into different regions where one simulation technique is more efficient than the other. In particular, we consider a realistic large-scale network and demonstrate how the computational effort depends on simulation parameters. Finally, we show that flow aggregation can effectively reduce the impact of the ripple effect and that the ripple effect has less impact when simulating the WFQ scheduling policy.