Catálogo de publicaciones - libros

IEEE 802.3 Ethernet networks, a standard LAN environment, provide a way to auto-negotiate the settings of capacity (10, 100, or 1000 Mb/s) and duplex (full- or half-). Under certain conditions described below, the auto-negotiation protocol fails to work properly. The resultant configuration problem, , appears to be common; when this problem occurs, the connectivity is impaired, but not completely removed. This can result in performance problems that are hard to locate.

This paper describes a work in progress aimed at (i) studying the condition of duplex mismatch in IEEE 802.3 Ethernet networks, (ii) producing an analytical model of duplex mismatch, (iii) validating the model, (iv) studying the effects of duplex mismatch on TCP throughput, (v) designing an algorithm for duplex mismatch detection using data from active testing, and (vi) incorporating the detection algorithm into an existing open-source network troubleshooting tool (NDT).

Topology discovery systems are starting to be introduced in the form of easily and widely deployed software. However, little consideration has been given as to how to perform large-scale topology discovery efficiently and in a network-friendly manner. In prior work, we have described how large numbers of traceroute monitors can coordinate their efforts to map the network while reducing their impact on routers and end-systems. The key is for them to share information regarding the paths they have explored. However, such sharing introduces considerable communication overhead. Here, we show how to improve the communication scaling properties through the use of Bloom filters to encode a probing stop set. Also, any system in which every monitor traces routes towards every destination has inherent scaling problems. We propose capping the number of monitors per destination, and dividing the monitors into clusters, each cluster focusing on a different destination list.

At present, link layer topology discovery methodologies rely on protocols that are not universally available, such as SNMP. Such methodologies can only be applied to a subset of all possible networks. Our goal is to work towards a generic link layer topology discovery method that does not rely on SNMP. In this paper, we will present a new link layer topology discovery methodology based on variable packet size capacity estimation. We will also discuss the problems that arose from preliminary testing where different brands of network cards affected the capacity estimates used to detect serializations. As a result, topologically equivalent links fail to be classified as such by the capacity estimation tool. To circumvent this issue, non-VPS methods of capacity estimation that utilise back to back packet pairs have been investigated as a calibration technique.

The development of veracious models of the Internet topology has received a lot of attention in the last few years. Many proposed models are based on topologies derived from RouteViews [1] BGP table dumps (BTDs). However, BTDs do not capture all AS–links of the Internet topology and most importantly the number of the hidden AS–links is unknown, resulting in AS–graphs of questionable quality. As a first step to address this problem, we introduce a new AS–topology discovery methodology that results in more complete and accurate graphs. Moreover, we use data available from existing measurement facilities, circumventing the burden of additional measurement infrastructure. We deploy our methodology and construct an AS–topology that has at least 61.5% more AS–links than BTD–derived AS–topologies we examined. Finally, we analyze the temporal and topological properties of the augmented graph and pinpoint the differences from BTD–derived AS–topologies.

The growth of wireless LANs has brought the expectation for high-bitrate streaming video to wireless PCs. However, it remains unknown how to best adapt video to wireless channel characteristics as they degrade. This paper presents results from experiments that stream commercial video over a wireless campus network and analyze performance across application, network and wireless link layers. Some of the key findings include: 1) Wireless LANs make it difficult for streaming video to gracefully degrade as network performance decreases; 2) Video streams with multiple encoding levels can more readily adapt to degraded wireless network conditions than can clips with a single encoding level; 3) Under degraded wireless network conditions, TCP streaming can provide higher video frame rates than can UDP streaming, but TCP streaming will often result in significantly longer playout durations than will UDP streaming; 4) Current techniques used by streaming media systems to determine effective capacity over wireless LAN are inadequate, resulting in streaming target bitrates significantly higher than can be effectively supported by the wireless network.

This paper studies the problems related to mobile connectivity on a wireless environment with Mobile IPv6, specially the handover, which is the most critical part. The main goal of this paper is to develop a structured methodology for analyzing 802.11/IPv6/MIPv6 handovers and their impact on application’s level. This is accomplished by capturing traffic on a testbed and analyzing it with two applications developed for this purpose. The analysis covers passive and active measurements. This methodology is applicable for measuring improvements on handover (such as Fast Handovers for Mobile IPv6, Hierarchical Mobile IPv6 or 802.11 handover).

In this paper we describe a distributed passive measurement infrastructure. Its goals are to reduce the cost and configuration effort per measurement. The infrastructure is scalable with regards to link speeds and measurement locations. A prototype is currently deployed at our university and a demo is online at http://inga.its.bth.se/projects/dpmi. The infrastructure differentiates between measurements and the analysis of measurements, this way the actual measurement equipment can focus on the practical issues of packet measurements. By using a modular approach the infrastructure can handle many different capturing devices. The infrastructure can also deal with the security and privacy aspects that might arise during measurements.

This paper presents lambdaMON – a novel approach to passive monitoring of very high performance optical networks based on dense wavelength division multiplexing (DWDM). The approach offers very attractive cost/benefit scaling properties, which are further refined by introducing state-of-the-art transparent fiber switching equipment. The rapid pace at which we intend to implement lambdaMONs opens new opportunities to apply passive monitoring facilities for debugging, troubleshooting and performance analysis of novel protocols and applications. To the best of our knowledge, this is the first attempt at designing a passive monitoring facility for optical networks. We report detailed architectural parameters, measurements and experience from laboratory tests and initial field deployment.

Round trip times (RTTs) play an important role in Internet measurements. In this paper, we explore some of the ways in which routing policies impact RTTs. In particular, we investigate how routing policies for both intra- and inter-domain routing can naturally give rise to violations of the triangle inequality with respect to RTTs. Triangle Inequality Violations (TIVs) might be exploited by overlay routing if an end-to-end forwarding path can be stitched together with paths routed at layer 3. However, TIVs pose a problem for Internet Coordinate Systems that attempt to associate Internet hosts with points in Euclidean space so that RTTs between hosts are accurately captured by distances between their associated points. Three points having RTTs that violate the triangle inequality cannot be embedded into Euclidean space without some level of inaccuracy. We argue that TIVs should not be treated as measurement artifacts, but rather as natural features of the Internet’s structure. In addition to explaining routing policies that give rise to TIVs, we present illustrating examples from the current Internet.

A represents the load from each ingress point to each egress point in an IP network. Although networks are engineered to tolerate some variation in the traffic matrix, large changes can lead to congested links and poor performance. The variations in the traffic matrix are caused by statistical fluctuations in the traffic the network and shifts in where the traffic the network. For an accurate view of how the traffic matrix evolves over time, we combine fine-grained traffic measurements with a continuous view of routing, including changes in the egress points. Our approach is in sharp contrast to previous work that either inferred the traffic matrix from link-load statistics or computed it using periodic snapshots of routing tables. Analyzing seven months of data from eight vantage points in a large Internet Service Provider (ISP) network, we show that routing changes are responsible for the majority of the large traffic variations. In addition, we identify the shifts caused by routing changes and show that these events are responsible for the largest traffic shifts. We discuss the implications of our findings on the accuracy of previous work on traffic matrix estimation and analysis.