7263630
On TCP and self-similar traffic
We re-examine the same TCP trace that was used by Veres et al. [A. Veres, M. Boda, The chaotic nature of TCP congestion control, in: Proceedings of the IEEE INFOCOM, 2000] to claim that TCP creates self-similar traffic. A careful reassessment of their data analysis shows that this claim is not justified and suggests that the TCP trace in question is not consistent with (asymptotic second-order) self-similarity or long-range dependence (LRD). We illustrate the reasons that led to the claim in [A. Veres, M. Boda, The chaotic nature of TCP congestion control, in: Proceedings of the IEEE INFOCOM, 2000] and provide some practical guidelines for assessing a statistical characteristic of trace data such as LRD that is defined in strictly asymptotic terms. Our conclusion is in full agreement with the findings obtained from analyzing a much longer TCP trace (resulting from repeating the same simulation as in [A. Veres, M. Boda, The chaotic nature of TCP congestion control, in: Proceedings of the IEEE INFOCOM, 2000], but running it for a longer period) and with analytical results derived from a detailed Markovian model of TCP. These results show that the traffic generated by a long-lived TCP connection, while exhibiting pronounced correlations over a predictable finite range of time-scales, cannot be (asymptotically second-order) self-similar or exhibit LRD. Our work serves as a reminder of the importance of careful trace analysis and detailed examination (and cross-validation) of alternative explanations when establishing or characterizing the generality of any particular finding about Internet traffic.
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.
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.
800712
On the autocorrelation structure of TCP traffic
The statistical characteristics of network traffic--in particular the observation that it can exhibit long range dependence--have received considerable attention from the research community over the past few years. In addition, the recent claims that the TCP protocol can generate traffic with long range dependent behavior has also received much attention. Contrary to the latter claims, in this paper we show that the TCP protocol can generate traffic with correlation structures that spans only an analytically predictable finite range of time-scales. We identify and analyze separately the two mechanisms within TCP that are responsible for this scaling behavior: timeouts and congestion avoidance. We provide analytical models for both mechanisms that, under the proper loss probabilities, accurately predict the range in time-scales and the strength of the sustained correlation structure of the traffic sending rate of a single TCP source. We also analyze an existing comprehensive model of TCP that accounts for both mechanisms and show that TCP itself exhibits a predictable finite range of time-scales under which traffic presents sustained correlations. Our claims and results are derived from Markovian models that are supported by simulations. We note that traffic generated by TCP can be misinterpreted to have long range dependence, but that long range dependence is not possible due to inherent finite time-scales of the mechanisms of TCP.
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.
2853015
On the capacity of hybrid wireless networks
This paper involves the study of the throughput capacity of hybrid wireless networks. A hybrid network is formed by placing a sparse network of base stations in an ad hoc network. These base stations are assumed to be connected by a high-bandwidth wired network and act as relays for wireless nodes. They are not data sources nor data receivers. Hybrid networks present a tradeoff between traditional cellular networks and pure ad hoc networks in that data may be forwarded in a multihop fashion or through the infrastructure. It has been shown that the capacity of a random ad hoc network does not scale well with the number of nodes in the system. In this work, we consider two different routing strategies and study the scaling behavior of the throughput capacity of a hybrid network. Analytical expressions of the throughput capacity are obtained. For a hybrid network of n nodes and m base stations, the results show that if m grows asymptotically slower than √n, the benefit of adding base stations on capacity is insignificant. However, if m grows faster than √n, the throughput capacity increases linearly with the number of base stations, providing an effective improvement over a pure ad hoc network. Therefore, in order to achieve nonnegligible capacity gain, the investment in the wired infrastructure should be high enough.
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.
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.
8364982
Supporting Complex Multi-Dimensional Queries in P2P Systems
More and more applications require peer-to-peer (P2P) systems to support complex queries over multi-dimensional data. For example, a P2P auction network for real estate frequently needs to answer queries such as "select five available buildings closest to the airport". Such queries are not efficiently supported in current P2P systems. Towards an efficient and scalable P2P system capable of processing complex multi-dimensional queries, the authors first proposed a comprehensive framework for sharing, indexing, and querying multi-dimensional data, where (i) peers with more computational power coordinate indexing and query processing, and (ii) other peers participate in part of the computation in order to achieve scalability and load-balance. Based on this framework, Network-R-tree (NR-tree), a P2P adaptation of the dominant spatial index - R*-tree was proposed. NR-tree, indexing spatial data at clustered peers, is capable of processing complex queries such as range queries and k-nearest neighbor queries. The authors proposed query processing algorithms for range and k-nearest neighbor queries and experimentally prove the effectiveness of proposed techniques with real data
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.
53249400
Non-tree routing for reliability and yield improvement
We propose to introduce redundant interconnects for manufacturing yield and reliability improvement. By introducing redundant interconnects, the potential for open faults is reduced at the cost of increased potential for short faults; overall, manufacturing yield and fault tolerance can be improved. We focus on a post-processing, tree augmentation approach which can be easily integrated in current physical design flows. Experiments on randomly generated and industry testcases show that our greedy augmentation method achieves significant increase in reliability (as measured by the percentage of biconnected tree edges) with very small increase in wirelength. SPICE simulations imply that non-tree routing has smaller delay variation due to process variability.