Ahmed Elmokashfi

Measuring the deployment of IPv6: topology, routing and performance

We use historical BGP data and recent active measurements to analyze trends in the growth, structure, dynamics and performance of the evolving IPv6 Internet, and compare them to the evolution of IPv4. We find that the IPv6 network is maturing, albeit slowly. While most core Internet transit providers have deployed IPv6, edge networks are lagging. Early IPv6 network deployment was stronger in Europe and the Asia-Pacific region, than in North America. Current IPv6 network deployment still shows the same pattern. The IPv6 topology is characterized by a single dominant player -- Hurricane Electric -- which appears in a large fraction of IPv6 AS paths, and is more dominant in IPv6 than the most dominant player in IPv4. Routing dynamics in the IPv6 topology are largely similar to those in IPv4, and churn in both networks grows at the same rate as the underlying topologies. Our measurements suggest that performance over IPv6 paths is comparable to that over IPv4 paths if the AS-level paths are the same, but can be much worse than IPv4 if the AS-level paths differ.

The Nornet Edge platform for mobile broadband measurements

We present Nornet Edge (NNE), a dedicated infrastructure for measurements and experimentation in mobile broadband networks. NNE is unprecedented in size, consisting of more than 400 measurement nodes geographically distributed all over Norway. Each measurement node is a Linux-based embedded computer, and is connected to multiple mobile broadband providers. In addition, NNE includes an extensive backend system for deploying and managing experiments and collecting data. NNE makes it possible to run long-term measurement experiments to assess and compare quality and performance across different network operators on a national scale. Particular focus is put on allowing experiments to run in parallel on multiple network connections, and on collecting rich context information related to the experiments. In this paper we give a detailed presentation of NNE, and describe three different measurement experiments that illustrate how the infrastructure can be used. We also provide a roadmap for further development of NNE.

Social Computing for Mobile Big Data

Mobile big data contains vast statistical features in various dimensions, including spatial, temporal, and the underlying social domain. Understanding and exploiting the features of mobile data from a social network perspective will be extremely beneficial to wireless networks, from planning, operation, and maintenance to optimization and marketing.

Characterizing delays in norwegian 3g networks

This paper presents a first look at long-term delay measurements from data connections in 3 Norwegian 3G Networks. We have performed active measurements for more than 6 months from 90 voting locations used in a trial with electronic voting during this falls regional elections. Our monitors are geographically spread across all of Norway, and give an unprecedented view of the performance and stability of the total 3G infrastructure of a country. In this paper, we focus on delay characteristics. We find large differences in delay between different monitors. More interestingly, we observe that the delay characteristics of the different operators are very different, pointing to operator-specific network design and configurations as the most important factor for delays.

Revisiting BGP churn growth

In the mid 2000s there was some concern in the research and operational communities over the scalability of BGP, the Internets interdomain routing protocol. The focus was on update churn (the number of routing protocol messages that are exchanged when the network undergoes routing changes) and whether churn was growing too fast for routers to handle. Recent work somewhat allayed those fears, showing that update churn grows slowly in IPv4, but the question of routing scalability has re-emerged with IPv6. In this work, we develop a model that expresses BGP churn in terms of four measurable properties of the routing system. We show why the number of updates normalized by the size of the topology is constant, and why routing dynamics are qualitatively similar in IPv4 and IPv6. We also show that the exponential growth of IPv6 churn is entirely expected, as the underlying IPv6 topology is also growing exponentially.

Leveraging the IPv4/IPv6 identity duality by using multi-path transport

With the 20th anniversary of IPv6 nearing quickly, a growing number of Internet service providers (ISPs) now offer their customers both IPv6 and IPv4 connectivity. This makes multi-homing with IPv4 and IPv6 increasingly common even with just a single ISP connection. Furthermore, the growing popularity of multi-path transport, especially Multi-Path TCP (MPTCP) that is the extension of the well-known Transmission Control Protocol (TCP), leads to the question of whether this identity duality can be utilized for improving application performance in addition to providing resilience. In this paper, we first investigate the AS-level congruency of IPv4 and IPv6 paths in the Internet. We find that more than 60% of the current IPv4 and IPv6 AS-paths are non-congruent at the AS-level, which motivates us to explore how MPTCP can utilize the IPv4/IPv6 identity duality to improve data transfer performance. Our results show that MPTCP, even with a single dual-stack Internet connection, can significantly improve the end-to-end performance when the underlying paths are non-congruent. The extent of the improvement can reach up to the aggregate of the IPv4 and IPv6 bandwidths.

Characterizing IPv6 control and data plane stability

End-to-end IPv6 performance is a factor that can influence IPv6 adoption. The stability of IPv6 - both in the control and data plane - is an important determinant of end-to-end performance, as it influences packet loss, network latency, and hence application performance. In this paper we compare stability and performance measurements from the control and data plane in IPv6 and IPv4. To study control plane stability, we use BGP feeds from five dual-stacked vantage points to measure routing dynamics towards IPv4 and IPv6 destinations. To study data plane stability, we probe dual-stacked webservers in 629 target ASes to determine the availability, RTT performance and RTT stability of paths toward these targets. In both control and data plane experiments IPv6 exhibited less stability than IPv4. In the control plane, most routing dynamics were generated by a small fraction of pathological unstable prefixes. In the data-plane, episodes of unavailability were longer on IPv6 than on IPv4. We found evidence of correlated performance degradation over IPv4 and IPv6 caused by shared infrastructure.

A first look at IPv4 transfer markets

In February 2011 the Internet Assigned Numbers Authority (IANA) exhausted its free pool of IPv4 addresses, and the regional registries (RIRs) have started to run out of IPv4 addresses as well. As RIRs have started rationing allocations, IPv4 transfer markets have emerged as a new mechanism to acquire IPv4 addresses. Barring a few high-profile exceptions, IPv4 transfers have largely flown under the radar. In this work, we use the lists of transfers published by three RIRs to characterise the transfer market - the types of players involved, the sizes and characteristics of transferred address blocks, and the visibility of transferred address blocks in the routing table before and after the transfer. Next, we take first steps toward detecting address transfers using BGP data from the Routeviews and RIPE repositories from 2004-2013. We identify reasons why legitimate changes in prefix origin could be mistakenly inferred to be transfers, and implement a series of 10 filters that remove 86% of candidate transfers. Our results indicate that BGP-based detection of transfers is prone to false positives due to significant noise in BGP data, while some transfers remain undetectable as they involve non-BGP speakers. We describe some additional data sources and analysis techniques that may help reveal an opaque market for IPv4 address block transfers.

Dissecting packet loss in mobile broadband networks from the edge

This paper demonstrates that end-to-end active measurements can give invaluable insights into the nature and characteristics of packet loss in cellular networks. We conduct a large-scale measurement study of packet loss in four UMTS networks. The study is based on active measurements from hundreds of measurement nodes over a period of one year. We find that a significant fraction of loss occurs during pathological and normal Radio Resource Control (RRC) state transitions. The remaining loss exhibits pronounced diurnal patterns and shows a relatively strong correlation between geographically diverse measurement nodes. Our results indicate that the causes of a significant part of the remaining loss lie beyond the radio access network.

Investigating Excessive Delays in Mobile Broadband Networks

Systematic monitoring of performance characteristics of mobile broadband networks can help users, operators, and regulators understand this increasingly critical infrastructure. We report the results of a measurement study of round trip delays in two mobile networks in Norway using over 200 geographically distributed subscriptions for a period of one month. In general, we find high variation in delay within the same radio access type and RRC state. Across both networks we study, we observe connections with round trip delays of several seconds, often multiple times per hour, that are more frequent when nodes are moving. Correlating these extreme delay events with available metadata, we find they are related to handovers, radio state transitions, and retransmissions at the link and physical layers.