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.
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.
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.
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.
1516306
Analysis of measured single-hop delay from an operational backbone network
We measure and analyze the single-hop packet delay through operational routers in a backbone IP network. First we present our delay measurements through a single router. Then we identify step-by-step the factors contributing to single-hop delay. In addition to packet processing, transmission, and queueing delays, we identify the presence of very large delays due to non-work-conserving router behavior. We use a simple output queue model to separate those delay components. Our step-by-step methodology used to ohtain the pure queueing delay is easily applicable to any single-hop delay measurements. After obtaining the queueing delay, we analyze the tail of its distribution, and find that it is long tailed and fits a Weihull distrihution with the scale parameter, a = 0.5, and the shape parameter, b = 0.58 to 0.6. The measured average queueing delay is larger than predicted by M/M/l, M/G/l, and FBM models when the link utilization is below 70%, but its absolute value is quite small.
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.
32135793
Split-Path Enhanced Pipeline Scheduling
Software pipelining increases the loop execution throughput by overlapping the execution of successive iterations in a pipelined fashion. For loops with control flows, however, software pipelining is not straightforward because we need to consider the overlap of more than one execution path. Modulo scheduling simply transforms them into straightline loops through if-conversion which, in effect, achieves a fixed, worst-case initiation interval (/spl par/) among all paths. On the other hand, all-path pipelining (APP) and enhanced pipeline scheduling (EPS) can achieve a variable /spl par/ depending on the path that is taken at execution time. Unfortunately, APP concentrates only on the overlap within the same path, entirely losing the overlap between different paths, whereas EPS attempts to overlap all paths together, failing to produce a tight schedule for each individual path, especially when resource constraints are tight. In this paper, we propose a new approach to EPS called split-path EPS (SP-EPS), which first splits each individual path via tail duplication and then performs EPS in a way to guarantee a tight schedule for each path, while producing a competitive cross-path schedule. We also extend SP-EPS to outer loops such that frequent paths that bypass the inner loop are split and then scheduled by SP-EPS. Our experimental results on nontrivial integer benchmarks show that SP-EPS can achieve as much as a geometric mean of 10 percent speedup over EPS when innermost loops are scheduled by SP-EPS, while it can achieve a geometric mean of 11.9 percent speedup when outer loops are also scheduled by SP-EPS.
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.