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Introduction
Publications
Publications (99)
Common sense suggests that networks are not random mazes of purposeless connections, but that these connections are organized so that networks can perform their functions well. One function common to many networks is targeted transport or navigation. Here, using game theory, we show that minimalistic networks designed to maximize the navigation eff...
Various hypotheses exist about the paths used for communication between the nodes of complex networks. Most studies simply suppose that communication goes via shortest paths, while others have more explicit assumptions about how routing (alternatively navigation or search) works or should work in real networks. However, these assumptions are rarely...
The rich club organization (the presence of highly connected hub core in a network) influences many structural and functional characteristics of networks including topology, the efficiency of paths and distribution of load. Despite its major role, the literature contains only a very limited set of models capable of generating networks with realisti...
This open access book explores the amazing similarity between paths taken by people and many other things in life, and its impact on the way we live, teach and learn.
Offering insights into the new scientific field of paths as part of the science of networks, it entertainingly describes the universal nature of paths in large networked structures. I...
Despite its importance for public transportation, communication within organizations or the general understanding of organized knowledge, our understanding of how human individuals navigate complex networked systems is still limited owing to the lack of datasets recording a sufficient amount of navigation paths of individual humans. Here, we analys...
Models of human navigation have been investigated in many ways on complex networks. These findings suggest that the characteristics of human navigation change during navigation from the start to the destination. Nonetheless, the degree to which navigation is influenced by the human navigator versus the graph and environment remains somewhat unclear...
Models of human navigation have been investigated in many ways on complex networks. These findings suggest that the characteristics of human navigation change during the navigation from the start to the destination. However, it is not fully clear to what extent the navigation is defined by the human navigator or the graph and the environment. Our w...
Greedy navigation/routing plays an important role in geometric routing of networks because of its locality and simplicity. This can operate in geometrically embedded networks in a distributed manner, distances are calculated based on coordinates of network nodes for choosing the next hop in the routing. Based only on node coordinates in any metric...
Although it was not always particularly straightforward, by the end of the last chapter we came up with methods enabling the exact measurement or the estimation of empirical paths in various real-life networks. From now on, we will refer to the paths coming from measurements in real networks as empirical paths, to clearly distinguish them from othe...
Once upon a time, there was a cock and a mouse. One day the mouse said to the cock, “Friend cock, shall we go and eat some nuts on yonder tree?” “As you like.” So they both went under the tree, and the mouse climbed up at once and began to eat. The poor cock began to fly, and flew and flew, but could not come where the mouse was. When it saw that t...
There is something compelling about shortest paths. They are so simple and reasonable. They seem to be the most efficient paths for traveling between nodes in a network. They may take the lowest amount of distance, time or energy. For grasping the idea of shortest paths, let’s consider the network in the first figure of this chapter. In this networ...
On a typical day, before starting an activity, we set an explicit or implicit goal. The path that leads towards that goal is often selected without carefully designing it. It just comes naturally to select the right route to work or the appropriate series of actions to prepare breakfast. It is no wonder that an optimal execution is rarely considere...
In addition to the scientific applications, are there any personal benefits for the reader? Are there any messages which can be kept in mind that would affect our everyday lives? In order to answer this, consider first figure in this chapter. This figure represents an abstract map of a city showing its core at the top and boundaries at the bottom a...
Have you ever wondered how you would be able to navigate yourself through the labyrinthine street network of a town without any central knowledge base like a map or a GPS device? One thing is sure, to wander around would result in an inadmissibly long journey, even in a smaller settlement. How about the letter in the social acquaintance network of...
In general, a path can be thought of as a sequence, timely ordered sequence of consecutive events or choices which can lead us far from the starting point.
Besides the philosophical arguments, one could think of a series of possibilities where all these observations about paths could be used. Have you ever wondered, for example, what happens in your body after you swallow an Aspirin? As incredible as it sounds, this question was answered only 74 years after the development of the medicine. It was 1897...
Our one sentence conclusion about the nature of paths was that they follow an internal logic of the underlying network even if this comes at the price of being slightly longer. Does it imply that our paths will be the same? Does it imply that our behavior will be deterministic and totally constrained by the network? Before contemplating these quest...
To get closer to understand the nature of paths we need two kinds of data about the same networked system like the Internet, or the Bridges of Königsberg. First, we need at least an approximate network connecting its nodes and a large number of paths collected from real traces of packets. Using the words of the Bridges of Königsberg problem, we nee...
Routing in large-scale computer networks today is built on hop-by-hop routing: packet headers specify the destination address and routers use internal forwarding tables to map addresses to next-hop ports. In this paper we take a new look at the scalability of this paradigm. We define a new model that reduces forwarding tables to sequential strings,...
Designing, implementing, and maintaining network policies that protect from internal and external threats is a highly non-trivial task. Often, troubleshooting networks consisting of diverse entities realizing complex policies is even harder. Software-defined networking (SDN) enables networks to adapt to changing scenarios, which significantly lesse...
Despite their importance for public transportation, communication within organizations or the general understanding of organized knowledge, our understanding of how human individuals navigate in complex networked systems is still limited owing to the lack of datasets recording sufficient amount of navigation paths of individual humans. Here, we ana...
Humans are involved in various real-life networked systems. The most obvious examples are social and collaboration networks but the language and the related mental lexicon they use, or the physical map of their territory can also be interpreted as networks. How do they find paths between endpoints in these networks? How do they obtain information a...
Route diversity in networks is elemental for establishing reliable,
high-capacity connections with appropriate security between endpoints. As for
the Internet, route diversity has already been studied at both Autonomous
System- and router-level topologies by means of graph theoretical disjoint
paths. In this paper we complement these approaches by...
An ideal network troubleshooting system would be an almost fully automated system, monitoring the whole network at once, feeding the results to a knowledge-based decision making system that suggests actions to the operator or corrects the failure automatically. Reality is quite the contrary: operators separated in their offices try to track down co...
Various hypotheses exist about the paths used for communication between the nodes of complex networks. Most studies simply suppose that communication goes via shortest paths, while others have more explicit assumptions about how routing (alternatively navigation or search) works or should work in real networks. However, these assumptions are rarely...
The rich club organization (the presence of highly connected hub core in a network) influences many structural and functional characteristics of networks including topology, the efficiency of paths and distribution of load. Despite its major role, the literature contains only a very limited set of models capable of generating networks with realisti...
Network Coding (NC) shows great potential in various communication scenarios through changing the packet forwarding principles of current networks. It can improve not only throughput, latency, reliability and security but also alleviates the need of coordination in many cases. However, it is still controversial due to widespread misunderstandings o...
Our current understanding about the AS level topology of the Internet is based on measurements and inductive-type models which set up rules describing the behavior (node and edge dynamics) of the individual ASes and generalize the consequences of these individual actions for the complete AS ecosystem using induction. In this paper we suggest a thir...
This report provides an understanding of how the UNIFY Service Provider
(SP)-DevOps concept can be applied and integrated with a combined cloud and
transport network NFV architecture. Specifically, the report contains technical
descriptions of a set of novel SP-DevOps tools and support functions that
facilitate observability, troubleshooting, verif...
This report presents a first sketch of the Service Provider DevOps concept
including four major management processes to support the roles of both service
and VNF developers as well as the operator in a more agile manner. The sketch
is based on lessons learned from a study of management and operational
practices in the industry and recent related wo...
Many networking visioners agree that 5G will be much more than the incremental improvement, in terms of data rate, of 4G. Besides the mobile networks, 5G will fundamentally influence the core infrastructure as well. In our vision the realization of the challenging promises of 5G (e.g. extremely fast, low-overhead, low-delay access of mostly cloudif...
SDN opens a new chapter in network troubleshooting as besides misconfigurations and firmware/hardware errors, software bugs can occur all over the SDN stack. As an answer to this challenge the networking community developed a wealth of piecemeal SDN troubleshooting tools aiming to track down misconfigurations or bugs of a specific nature (e.g. in a...
Due to the heterogeneous and distributed nature of computer networks, the detection of misconfigurations and software/hardware failures is frequently reported to be notoriously non-trivial. The advent of SDN complicates the situation even more, since besides troubleshooting, the problem of finding software bugs in controller/switch/VNF implementati...
5G communication networks enable the steering and control of Internet of Things and, therefore, require extremely low latency communications referred to as the tactile Internet. In this paper, we show that the massive use of network coding throughout the network significantly improves latency and reduces the frequency of packet re-transmission. Thu...
The common sense suggests that networks are not random mazes of purposeless
connections, but that these connections are organised so that networks can
perform their functions. One common function that many networks perform is
targeted transport or navigation. Here with the help of game theory we show
that minimalistic networks designed to maximise...
Many of our computer networks, not the least of which the Internet, are built upon hop-by-hop routing. At the moment, it is not clear whether we will be able to scale these networks into the future economically. In this paper, we propose a new information-theoretic model to study routing scalability, we present preliminary analysis suggesting that...
Mininet is a great prototyping tool which combines existing SDN-related software components (e.g., Open vSwitch, OpenFlow controllers, network namespaces, cgroups) into a framework, which can automatically set up and configure customized OpenFlow testbeds scaling up to hundreds of nodes. Standing on the shoulders of Mininet, we implement a similar...
In this demo, we show a novel method to multi-layer serviceorchestration in a multi-domain network. This method is a basic implementation of the three layered concept with multi-layer orchestration designed by the UNIFY project. A global orchestrator is capable of instantiating service elements, i.e., virtual network functions (VNFs), in separate d...
The rise of cloud services poses considerable challenges on the control of both cloud and carrier network infrastructures. While traditional telecom network services rely on rather static processes (often involving manual steps), the wide adoption of mobile devices including tablets, smartphones and wearables introduce previously unseen dynamics in...
With the advent of new network architectures, like Software Defined Networks, the rules governing the way traffic is routed through the network are becoming increasingly complex. In this paper, we revisit the theoretic underpinnings of policy routing in the light of the new requirements. We show that certain simple but plausible algebraic propertie...
Today's ever-growing networks call for routing schemes with sound theoretical scalability guarantees. In this context, a routing scheme is scalable if the amount of memory needed to implement it grows significantly slower than the network size. Unfortunately, theoretical scalability characterizations only exist for shortest path routing, but for ge...
Mininet is a great prototyping tool which combines existing SDN-related software components (e.g., Open vSwitch, OpenFlow controllers, network namespaces, cgroups) into a framework, which can automatically set up and configure customized OpenFlow testbeds scaling up to hundreds of nodes. Standing on the shoulders of Mininet, we implement a similar...
Large-scale information dissemination in multicast communications has been increasingly attracting attention, be it through uptake in new services or through recent research efforts. In these, the core issues are supporting increased forwarding speed, avoiding state in the forwarding elements, and scaling in terms of the multicast tree size. This p...
Multipath TCP is an experimental transport protocol with remarkable recent past and non-negligible future potential. It has been standardized recently, however the evaluation studies focus only on a limited set of isolated use-cases and a comprehensive analysis or a feasible path of Internet-wide adoption is still missing. This is mostly because in...
We show that cabling complexity in large flattened butterfly networks can be reduced by an order of magnitude, without increasing capital costs or control plane complexity, by employing DWDM transceivers and arrayed waveguide grating routers.
On the Internet AS level topology, BGP policy routing is in charge of dictating the characteristics of routes which can be used for packet transmission. Furthermore the peculiarities of the BGP policies clearly affect the peering strategies of the ISP-s, hereby influencing the emerging topology. This paper takes a first step towards identifying the...
Multipath TCP is an experimental transport protocol with
remarkable recent past and non-negligible future potential.
However, the lack of available large-scale testbeds and pub-
licly accessible multiple paths grossly prohibits the adoption
of the technology. Here, we demonstrate a large-scale multi-
path playground deployed on PlanetLab Europe, wh...
Multipath TCP is an experimental transport protocol with remarkable recent past and non-negligible future potential. However the lack of available large-scale testbeds and publicly accessible multiple paths grossly prohibits the adoption of the technology. Here, we demonstrate a large-scale multipath playground deployed on PlanetLab Europe, which c...
The increasing popularity of both small and large private clouds and expanding public clouds poses new requirements to data center (DC) architectures. First, DC architectures should be incrementally scalable allowing the creation of DCs of arbitrary size with consistent performance characteristics. Second, initial DC deployments should be increment...
Current trends in cloud computing suggest that both large, public clouds and small, private clouds will proliferate in the near future. Operational requirements, such as high bandwidth, dependability and smooth manageability, are similar for both types of clouds and their underlying data center architecture. Such requirements can be satisfied with...
Diffusive capture processes are known to be an effective method for information search on complex networks. The biased NN lions–lamb model provides quick search time by attracting random walkers to high degree nodes, where most capture events take place. The price of the efficiency is extreme traffic concentration on top hubs. We propose traffic lo...
Federated testbeds for future Internet experimentation have been de-ployed worldwide to enable large scale and diverse experiments with future In-ternet technologies ranging from components to complete systems. They serve the purpose of validating new solutions to identified problems and to compare them with current or other evolving solutions. The...
Large-scale information distribution has been increasingly attracting attention, be it through uptake in new services or through recent research efforts in fields like information-centric networking. The core issue to be addressed is the more efficient distribution of information to a large set of receivers. Avoiding state in the forwarding element...
Greedy navigability is a central issue in the theory of networks. However, the exogenous nature of network models do not allow for describing how greedy routable-networks emerge in reality. In turn, network formation games focus on the very emergence proess, but the applied shortest-path based cost functions exclude navigational aspects. This paper...
The limited capabilities of the switches renders the implementation of unorthodox routing and forwarding mechanisms as a hard task in OpenFlow. Our high level goal is therefore to inspect the possibilities of slightly smartening up the OpenFlow switches. As a first step in this direction we demonstrate (with Bloom filters, greedy routing and networ...
Due to its simplicity, transparency and performance, Flow Visor takes it all in today's virtualization tools for OpenFlow networks. We argue that this effectiveness comes at the price of intolerance towards diverse OpenFlow versions used simultaneously and also limited switch functionality. What is more Flow Visor based management frameworks cannot...
OpenFlow is the most promising architecture for future Software Defined Networks (SDNs). However, from the aspects of large-scale or carrier-grade networks, it still lacks some key components. For example, QoS (Quality of Service) provisioning is an indispensable part of such production networks. During the evolution of the OpenFlow standard, some...
The limited capabilities of the switches renders the implementation of unorthodox routing and forwarding mechanisms as a hard task in OpenFlow. Our high level goal is therefore to inspect the possibilities of slightly smartening up the OpenFlow switches. As a first step in this direction we demonstrate (with Bloom filters, greedy routing and networ...
Two new algorithms are given for randomized consensus in a shared-memory model with an oblivious adversary. Each is based on a new construction of a conciliator, an object that guarantees termination and validity, but that only guarantees agreement with ...
Current trends in cloud computing suggest that both large, public clouds and small, private clouds will proliferate in the near future. Operational requirements, such as high bandwidth, dependability and smooth manageability, are similar for both types of clouds and their underlying data center architecture. Such requirements can be satisfied with...
Power management is a critical issue for mobile devices, where a significant portion of the total system energy can be often consumed by heavy wireless network activity. In this paper we present a framework that reduces the energy consumption of wireless mobile devices during streaming video content over Wireless LAN networks by utilizing the power...
This paper takes a first step towards generalizing compact routing to arbitrary routing policies that favor a broader set of path attributes beyond path length. Using the formalism of routing algebras we identify the algebraic requirements for a routing policy to be realizable with sublinear size routing tables and we show that a wealth of practica...
In-packet Bloom filters are recently proposed as a possible building block of future Internet architectures replacing IP or MPLS addressing that solves efficient multicast routing, security and other functions in a stateless manner. In such frameworks a bloom filter is placed in the header which stores the addresses of the destination nodes or the...
The wireless community networking paradigm shows great promise in achieving a global status. However, in creating a “global wireless village”, both user participation and support from traditional Internet Service Providers (ISPs) are key ingredients; for this end a viable incentive system is essential. In this paper we investigate the economic inte...
Research works concerning AS (Autonomous Systems) level Internet topology measurements typically aim at obtaining near-complete maps of the AS structure. In this paper, we take a fundamentally different approach by inspecting several concurrently visible local views of the AS graph stored at individual BGP route servers. We find that each of these...
Recently some stochastic (probabilistic) extensions of the deterministic network calculus have been developed, mainly for exploiting the statistical multiplexing of flows aggregated in packet based communication networks. This exploitation could result "better" stochastic performance bounds than those bounds provided by the inherently worst case an...
Network calculus is the result of recent developments in the area of network analysis, providing considerable insight into the behavior of (packet-based) communication networks. The classical approach uses deterministic bounds to describe systems having stochastic properties in nature, offering simple formulation to a set of¿otherwise analytically...