74834
Estimation and removal of clock skew from network delay measurements
Packet delay and loss traces are frequently used by network engineers, as well as network applications, to analyze network performance. The clocks on the end-systems used to measure the delays, however, are not always synchronized, and this lack of synchronization reduces the accuracy of these measurements. Therefore, estimating and removing relative skews and offsets from delay measurements between sender and receiver clocks are critical to the accurate assessment and analysis of network performance. We introduce a linear programming-based algorithm to estimate the clock skew in network delay measurements and compare it with three other algorithms. We show that our algorithm has a time complexity of O(N), leaves the delay after the skew removal positive, and is robust in the sense that the error margin of the skew estimate is independent of the magnitude of the skew. We use traces of real Internet delay measurements to assess the algorithm, and compare its performance to that of three other algorithms. Furthermore, we show through simulation that our algorithm is unbiased, and that the sample variance of the skew estimate is better (smaller) than existing algorithms.
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.
37970940
Prefix-preserving IP address anonymization: measurement-based security evaluation and a new cryptography-based scheme
Real-world traffic traces are crucial for Internet research, but only a very small percentage of traces collected are made public. One major reason why traffic trace owners hesitate to make the traces publicly available is the concern that confidential and private information may be inferred from the trace. We focus on the problem of anonymizing IP addresses in a trace. More specifically, we are interested in prefix-preserving anonymization in which the prefix relationship among IP addresses is preserved in the anonymized trace, making such a trace usable in situations where prefix relationships are important. The goal of our work is two fold. First, we develop a cryptography-based, prefix-preserving anonymization technique that is provably as secure as the existing well-known TCPdpriv scheme, and unlike TCPdpriv, provides consistent prefix-preservation in large scale distributed setting. Second, we evaluate the security properties inherent in all prefix-preserving IP address anonymization schemes (including TCPdpriv). Through the analysis of Internet backbone traffic traces, we investigate the effect of some types of attacks on the security of any prefix-preserving anonymization algorithm. We also derive results for the optimum manner in which an attack should proceed, which provides a bound on the effectiveness of attacks in general.
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.
11481277
On the correlation between route dynamics and routing loops
Routing loops are caused by inconsistencies in the routing state of the network. Although undesirable from this aspect, they can provide insight into the routing dynamics that caused them. In this work we present a methodology that utilizes a priori knowledge of loops to study the correlation between routing loops and routing events that could have caused them. We apply our technique to associate route changes with packet loops detected in actual traffic traces collected from the Sprint Backbone. Our study shows that a strong correlation exists between loops and changes in the BGP routing state while the link state protocols ISIS is seldom responsible for such events. Our analysis also identifies factors that influence the distribution of loop path lengths as well as the effectiveness of our detection techniques.
12382521
On the design and performance of prefix-preserving IP traffic trace anonymization
Even though real-world Internet traffic traces are crucial for network research, only a tiny percentage of traffic traces collected are made public. One major reason why traffic trace owners hesitate to make the traces publicly available is the concern that the confidential and private information may be inferred from the trace. In this paper we focus on the problem of anonymizing IP addresses in a trace. More specifically, we are interested in prefixpreserving anonymization in which the prefix relationship among IP addresses is preserved in the anonymized trace, making such a trace usable in situations where such prefix relationships are important. The goal of our work is two fold. First, we are interested in analyzing the security properties inherent in prefix-preserving IP address anonymization. Through the analysis of IP traffic traces, we investigate the effect of some types of attacks on the security of the prefix-preserving anonymization process. We also derive results for the optimum manner in which an attack should proceed which provides a bound on the performance of attacks in general. Second, we observe that an existing scheme used for prefix-preserving anonymization, TCPdpriv, has some drawbacks that limit its use in a large-scale, distributed setting. We develop an alternative cryptography-based, prefixpreserving anonymization technique to address these drawbacks while maintaining the same level of anonymity as TCPdpriv.
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.
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.