Mobile broadband (MBB) connections are often exposed to varying network conditions under mobility scenarios, which can result in packet loss and higher end-to-end delays. Such performance degradation in turn can adversely impact the user experience. In this paper, we study packet loss characteristics of MBB networks under mobility using six measurement nodes that are placed on regional and inter-city trains in Norway for a period of seven months. Our findings show that packet loss is significantly higher for mobility scenarios compared to the stationary. In order to understand the cause of packet loss, we investigate Radio Access Technology (RAT) changes, temporary loss of service, and changes in cells and location area codes (LAC). We surprisingly find that almost all periods with RAT changes involve packet loss. We also observe that 70% of the overall loss happens in periods with RAT changes or temporary loss of service. Further, one third of RAT changes involve connection termination. Our findings highlight the importance of radio access network (RAN) planning and configuration, and provide guidelines to alleviate packet loss in MBB networks.

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.

Some network applications have requirements that exceed the service levels offered by the best-effort Internet. Several network-layer Quality of Service architectures with ex- tended service levels have been designed, but the massive scale and distributed nature of the Internet have prohibited their wide deployment. It now seems clear that the special needs of demanding applications must be met through other approaches. This paper describes how incrementally- deployed innovative solutions at the network level can con- tribute to an improved service for a particular type of applications, namely high-quality, wide-area video conferencing. We have built a global IP network, aiming to give users a better video conferencing experience primarily through packet loss reduction in transport networks. The key concept in our approach is a well-provisioned network-layer overlay, combined with geography-based “cold potato” BGP routing. Through an extensive set of experiments we show how our design choices impact routing and data plane behavior in the network, and demonstrate that we are able to significantly reduce packet loss compared to wide-area transport through global transit providers.

The scalability limitations of BGP have been a major concern lately. An important aspect of this issue is the rate of routing updates (churn) that BGP routers must process. This paper presents an analysis of the evolution of churn in four networks at the backbone of the Internet over a period of seven years and eight months, using BGP update traces from the RouteViews project. The churn rate varies widely over time and between networks. Instead of descriptive ``black-box'' statistical analysis, we take an exploratory data analysis approach attempting to understand the reasons behind major observed characteristics of the churn time series. We find that duplicate announcements is a major churn contributor, responsible for most large spikes. Remaining spikes are mostly caused by routing incidents that affect a large number of prefixes simultaneously. More long-term intense periods of churn, on the other hand, are caused by misconfigurations or other special events at or close to the monitored AS. After filtering pathologies and effects that are not related to the long-term evolution of churn, we analyze the remaining ``baseline'' churn and find that it is increasing at a rate that is similar to the growth of the number of Autonomous Systems.

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 fall's 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.

This paper develops a new resilient multipath routing technique, referred to as SPT-DAG, that has the following characteristics: (1) provides multipath routing over directed acyclic graphs (DAG); (2) the shortest path tree is guaranteed to be part of the DAG; and (3) provides guaranteed recovery from single link failures. We develop a polynomial time algorithm to compute the SPT-DAG and a routing protocol to forward packets over the SPT-DAG using one overhead bit in the packet. We consider different load-balancing approaches for forwarding a packet when the packet has not encountered a failure. Through extensive flow-based simulations, we show that the SPT-DAG performs significantly better than those approaches that exclusively target load balancing or resiliency.

This paper develops novel mechanisms for recovering from failures in IP networks with proactive backup path calculations and IP tunneling. The primary scheme provides resiliency against up to two link failures in a packet path in the network. The highlight of the developed routing approach is that a node re-routes a packet around the failed link without the knowledge of the second link failure. The proposed technique requires three protection addresses for every node, in addition to the normal address. Associated with every protection address of a node is a protection graph. Each link connected to the node is removed in at least one of the protection graphs and every protection graph is guaranteed to be two-edge connected. The network recovers from the first failure by tunneling the packet to the next-hop node using one of the protection addresses of the next-hop node; and the packet is routed over the protection graph corresponding to that protection address. We prove that it is sufficient to provide up to three protection addresses per node to tolerate any arbitrary two link failures in a three-edge connected graph. An extension to the basic scheme provides recovery from single node failures in the network. It involves identification of the failed node in the packet path and then routing the packet to the destination along an alternate path not containing the failed node. The effectiveness of the proposed techniques were evaluated by simulating the developed algorithms over several network topologies.

The large amount of peer-to-peer (P2P) traffic in today's Internet represents a great challenge for most Internet Service providers (ISPs). P2P traffic does not conform to traditional ISP traffic policies, and it makes it harder to perform traffic engineering in the network. It is especially the peer-selection mechanism of the P2P application that influences the traffic patterns and creates an imbalance for the ISP business. Some ISPs benefit from the P2P traffic, while others suffer. There are research efforts proposing cross-layer solutions where the P2P application uses the underlying routing information for the peer selection. These works put a lot of focus on improving the application performance, but take to a little extent into account how the ISPs are affected. In this paper we propose a framework to measure the effects of the peer-selection mechanism, not only on the P2P application performance, but also on the economy of different types of ISPs. We categorize all ISPs into three groups; core, transit and stub, depending on their position in the global Internet hierarchy. Using our proposed framework, we analyze the performance of different peer-selection algorithms.

As the Internet takes an increasingly central role in our communications infrastructure, the slow convergence of routing protocols after a network failure becomes a growing problem. To assure fast recovery from link and node failures in IP networks, we present a new recovery scheme called Multiple Routing Configurations (MRC). Our proposed scheme guarantees recovery in all single failure scenarios, using a single mechanism to handle both link and node failures, and without knowing the root cause of the failure. MRC is strictly connectionless, and assumes only destination based hop-by-hop forwarding. MRC is based on keeping additional routing information in the routers, and allows packet forwarding to continue on an alternative output link immediately after the detection of a failure. It can be implemented with only minor changes to existing solutions. In this paper we present MRC, and analyze its performance with respect to scalability, backup path lengths, and load distribution after a failure. We also show how an estimate of the traffic demands in the network can be used to improve the distribution of the recovered traffic, and thus reduce the chances of congestion when MRC is used.

The scalability of BGP routing is a major concern for the Internet community. Scalability is an issue in two different aspects: increasing routing table size, and increasing rate of BGP updates. In this paper, we focus on the latter. Our objective is to characterize the churn increase experienced by ASes in different levels of the Internet hierarchy as the network grows. We look at several ``what-if'' growth scenarios that are either plausible directions in the evolution of the Internet or educational corner cases, and investigate their scalability implications. In addition, we examine the effect of the BGP update rate-limiting timer (MRAI), considering both major variations with which it has been deployed. Our findings explain the dramatically different impact of multihoming and peering on BGP scalability, identify which topological growth scenarios will lead to faster churn increase, and emphasize the importance of not rate-limiting explicit withdrawals (despite what RFC-4271 recently required).

The concept of Multi-Topology routing allows each router in a network to maintain several valid routes to each destination. This increases the possibilities to spread traffic towards a destination over multiple paths with connectionless routing protocols like OSPF or IS-IS. In this paper, we report early ideas on how this can be utilized as a Traffic Engineering tool. We look at both offline and online approaches, and argue that a Multi-Topology based solution has advantages over previous solutions in both paradigms.

Fast proactive recovery has for years been a very import- ant research field due to increased reliability in the Internet for business critical and real-time communications. Resilient Routing Layers (RRL) and Multiple Routing Configurations (MRC) has been proposed as a new approach providing local and proactive recovery. RRL and MRC also provides a network manager with a simple set of sub-topologies as abstractions for the recovery routing. This paper will compare different methods for generating such layers and configurations along two para- meters, scalability and effects on routing of the recovered traffic.

Resilient Packet Ring (RPR) is a new standard, designated IEEE standard number 802.17, for MAN and WAN dual ring topologies. RPR uses the buffer insertion principle as a basis for its medium access control protocol. In this paper, we analyze parts of the aggressive mode of the RPR fairness protocol. We look at a congested node, and utilize control systems theory to analyze the stability of the associated fairness algorithm. In particular, we discuss how the settings of the two important parameters ageCoef and lpCoef influence the stability of an RPR-network. At the end of the paper we present simulated scenarios in order to illustrate our results.

Resilient Packet Ring (RPR, IEEE 802.17) is designed with a protection mechanism aiming at restoring traffic on the ring within 50 ms in case of a link or station failure. In this article, we evaluate RPR protection with respect to service disruption, packet reordering and packet loss. Different error scenarios are simulated, with both steering and wrapping protection. Unfortunately, the 50 ms restoration time guarantee can not always be met if in order delivery of packets is required, since RPR uses a quite long (default 40 ms) topology stabilisation period to avoid packet reordering. We suggest a novel protection mechanism, that does not have to wait for the new topology to be stable, and that gives sub 50 ms restoration for all traffic. We also show that for in order delivery of packets, our new mechanisms discards a very low number of packets compared to the mechanism of the RPR standard.