14680075
Design and Deployment of a Passive Monitoring Infrastructure
This paper presents the architecture of a passive monitoring system installed within the Sprint IP backbone network. This system differs from other packet monitoring systems in that it collects packet-level traces from multiple links within the network and provides the capability to correlate the data using highly accurate GPS timestamps. After a thorough description of the monitoring systems, we demonstrate the system's capabilities and the diversity of the results that can be obtained from the collected data. These results include workload characterization, packet size analysis, and packet delay incurred through a single backbone router. We conclude with lessons learned from the development of the monitoring infrastructure and present future research goals.
13506842
Small-time scaling behavior of Internet backbone traffic
We perform an extensive wavelet analysis of Internet backbone traffic traces to observe and understand the causes of small-time scaling phenomena present in them. We observe that for a majority of the traces, the second-order scaling exponents at small time scales (1-100ms) are fairly close to 0.5, indicating that traffic fluctuations at these time scales are nearly uncorrelated. Some traces, however, do exhibit moderately large scaling exponents (~0.7) at small time scales. In addition, the traces manifest mostly monofractal behaviors at small time scales. To identify the network causes of the observed scaling behavior, we analyze the flow composition of the traffic along two dimensions-flow byte contribution and flow density. Our study points to the dense flows (i.e., flows with densely clustered packets) as the correlation-causing factor in small time scales, and reveals that the traffic composition in terms of proportions of dense vs. sparse flows plays a major role in influencing the small-time scalings of aggregate traffic. Since queuing inside routers is influenced by traffic fluctuations at small time-scales, our observations and results have important implications for networking modeling, service provisioning and traffic engineering.
687466
Placing Relay Nodes for Intra-Domain Path Diversity
Meeyoung Cha and Sue Moon are supported by Korea 
Science and Engineering Foundation through Advanced Information 
Technology Research Center (AITrc). Chong-Dae Park 
is supported by Brain Korea 21 Project through the school 
of information technology in KAIST. Part of this work was 
done while Meeyoung Cha was visiting DIMACS (Center for 
Discrete Mathematics and Theoretical Computer Science). We 
thank Joel Gottlieb for help with ISP data, and Lun Li for 
providing the HOT topology used in our simulation. We thank 
Jennifer Rexford and anonymous reviewers for providing us 
valuable comments.
8164368
Detection and analysis of routing loops in packet traces
Routing loops are caused by inconsistencies in routing state among a set of routers. They occur in perfectly engineered networks, and have a detrimental effect on performance. They impact end-to-end performance through increased packet loss and delay for packets caught in the loop, and through increased link utilization and corresponding delay and jitter for packets that traverse the link but are not caught in the loop.Using packet traces from a tier-1 ISP backbone, we first explain how routing loops manifest in packet traces. We characterize routing loops in terms of the packet types caught in the loop, the loop sizes, and the loop durations. Finally, we analyze the impact of routing loops on network performance in terms of loss and delay.
5965700
Analysis of topological characteristics of huge online social networking services
Social networking services are a fast-growing business in the Internet. However, it is unknown if online relationships and their growth patterns are the same as in real-life social networks. In this paper, we compare the structures of three online social networking services: Cyworld, MySpace, and orkut, each with more than 10 million users, respectively. We have access to complete data of Cyworld's ilchon (friend) relationships and analyze its degree distribution, clustering property, degree correlation, and evolution over time. We also use Cyworld data to evaluate the validity of snowball sampling method, which we use to crawl and obtain partial network topologies of MySpace and orkut. Cyworld, the oldest of the three, demonstrates a changing scaling behavior over time in degree distribution. The latest Cyworld data's degree distribution exhibits a multi-scaling behavior, while those of MySpace and orkut have simple scaling behaviors with different exponents. Very interestingly, each of the two e ponents corresponds to the different segments in Cyworld's degree distribution. Certain online social networking services encourage online activities that cannot be easily copied in real life; we show that they deviate from close-knit online social networks which show a similar degree correlation pattern to real-life social networks.
10959051
Path Protection Routing with SRLG Constraints to Support IPTV in WDM Mesh Networks
The distribution of broadcast TV across large provider networks has become a highly topical subject as satellite distribution capacity exhausts and competitive pressures increase. In a typical IPTV architecture, broadcast TV is distributed from two sources (for redundancy) to multiple destinations. The aim of this paper is to examine how IPTV can be reliably and cost effectively supported in wavelength division multiplexed (WDM) networks. WDM networks have evolved to mesh topologies and recently to support multicast, which is particularly valuable in reducing the network cost in broadcast TV applications. Our goal is to find two trees with a minimal total cost such that we have two physically (or Shared Risk Link Group (SRLG)) diverse paths to each of the destinations - one from each of the sources. Any two links that belong to a common SRLG are subject to a single point of failure, be it a channel or wavelength failure, a fiber cut, or a complete conduit cut. We first show that our path protection routing problem is NP-complete. We then propose an Integer Programming (IP) formulation for this problem. Using real network topology data, we show that the real networks are amenable to the IP problem formulation and yield optimal solutions.
15969885
Optimistic register coalescing
Graph-coloring register allocators eliminate copies by coalescing the source and target nodes of a copy if they do not interfere in the interference graph. Coalescing, however, can be harmful to the colorability of the graph because it tends to yield a graph with nodes of higher degrees. Unlike aggressive coalescing, which coalesces any pair of noninterfering copy-related nodes, conservative coalescing or iterated coalescing perform safe coalescing that preserves the colorability. Unfortunately, these heuristics give up coalescing too early, losing many opportunities for coalescing that would turn out to be safe. Moreover, they ignore the fact that coalescing may even improve the colorability of the graph by reducing the degree of neighbor nodes that are interfering with both the source and target nodes being coalesced. This article proposes a new heuristic called optimistic coalescing which optimistically performs aggressive coalescing, thus exploiting the positive impact of coalescing aggressively, but when a coalesced node is to be spilled, it is split back into separate nodes. Since there is a better chance of coloring one of those splits, we can reduce the overall spill amount.
2527806
Knowledge representation for product design using Techspecs Concept Ontology
Sharing and reusing product design information can help reduce cost and time when developing new products and facilitate good product family design. An appropriate representation scheme for components and products is important to share and reuse this information effectively. The objective in this research is to develop a method for representing components and products using an ontology based on the Techspecs Concept Ontology (TCO), which consists of functionality, assembly, and product technical specifications. We use a device ontology for representing the behavior, functionality, and relationships of products and their components. This concept enables better understanding of the representation of the products and components and improves the process of searching for components satisfying customer needs and functional requirements. We demonstrate TCO development using a case study involving a family of power tools. Future work involving the use of TCO to capture semantics associated with components and products to represent knowledge for use with agents is also discussed.
1748996
Reducing sweep time for a nearly empty heap
Mark and sweep garbage collectors are known for using time proportional to the heap size when sweeping memory, since all objects in the heap, regardless of whether they are live or not, must be visited in order to reclaim the memory occupied by dead objects. This paper introduces a sweeping method which traverses only the live objects, so that sweeping can be done in time dependent only on the number of live objects in the heap.
This allows each collection to use time independent of the size of the heap, which can result in a large reduction of overall garbage collection time in empty heaps. Unfortunately, the algorithm used may slow down overall garbage collection if the heap is not so empty. So a way to select the sweeping algorithm depending on the heap occupancy is introduced, which can avoid any significant slowdown.