Traffic engineering is an important concept that allows Internet Service Providers (ISPs) to utilize their existing routing hardware more efficiently. One technology that can be used is Segment Routing (SR). In this paper, we address the use of SR to increase the resilience against failure scenarios. In addition, we develop solutions that are manageable and, thus, deployable in a tier 1 ISP network. We propose a post-convergence aware SR based optimization model. With it, we can proactively find a single SR configuration that is beneficial in all predefined failure scenarios, including single link failures, shared risk link group failures, and node failures. In addition to this use-case, we also extend the optimization model to include other important practical requirements such as keeping the number of SR tunnels to a minimum, avoiding arbitrary traffic splitting, or meeting latency bounds. We evaluate our approaches with recently measured data from a tier 1 ISP and show that we can improve over state of the art routing approaches.

Traffic engineering is an important concept that allows Internet Service Providers (ISPs) to utilize their existing routing hardware more efficiently. One technology that can be used in this field is Segment Routing (SR). While transferring SR approaches from theory towards an actual deployment, it quickly becomes apparent that there are many requirements and constraints that have to be satisfied. One of the most important requirement for a traffic engineering approach is the resilience against failure scenarios. In this paper, we propose a post-convergence aware 2-SR based optimization model. With it, we are able to proactively find a single SR configuration that is beneficial in all predefined failure scenarios, including single link failures, shared risk link group failures, and node failures. We evaluate our model with recently measured data from a tier 1 ISP and show that we can improve over state of the art routing approaches.

Segment Routing (SR) based traffic engineering can be used to avoid network congestion effectively. Most research about SR considers the routing metric as a given constant. The metric defines shortest paths. As shortest paths are essential building blocks of SR paths, the metrics heavily influence SR. In this paper, we evaluate this influence thoroughly using data from a tier one Internet Service Provider (ISP) backbone, as well as other, publicly available topologies. We conclude that metrics do in fact play a role in SR optimization. Simple metrics, however, already push SR close to the optimum with respect to the most common traffic engineering objective of minimizing maximum utilization.

Segment Routing (SR) can be used as a traffic engineering strategy to counteract increasing loads on networks like Internet Service Provider (ISP) backbones. Many SR approaches, however, optimize traffic flows that were measured in the past. This paper introduces a new tunnel training architecture. It aims to show that the results of these strategies can still be beneficial for routing new traffic flows using the tunnel training architecture. We evaluate the selection of different matrices for training, as well as the choice of different tunnel selection heuristics. The results show that optimization results tend to be beneficial even for traffic matrices that were not known during the optimization. Classifying the quality of SR tunnels, though, proves to be difficult and trace dependent.

Today, spreading global routing information within an Autonomous System (AS) is usually implemented by means of internal BGP (iBGP), a particular operational mode of the Border Gateway Protocol (BGP). Considering the research activities around BGP, anomalies turned out to be one major issue of iBGP: But even if the trouble iBGP anomalies induce in practice is well known for nearly a decade, new iBGP extensions still define highly problematic protocol modifications. Apparently, protocol designers are either not aware of the conceptual defects that induce anomalies or validating correctness appears to be too complex. In this paper, we provide a basis to solve both problems. Focussing the basic correctness properties of routing protocols, we will show that iBGP anomalies are caused by five root causes. These causes provide protocol designers with a tool set to reveal problematic properties of a concept and verify correctness. Based on exemplary studies for two common iBGP architectures, we will provide detailed guidance for practical usage.

Especially for large Network Operators (NOs), eliminating routing anomalies is an important aspect for the internal BGP design. To avoid such unwanted effects, classical architectures have need of certain restrictions kept in both, the network design and the iBGP peering. However, these restrictions are in conflict with the optimized network designs NOs seek. In this study we develop an inherently anomaly-free iBGP architecture that takes the demands of NOs into account. It is based on a central server that guarantees consistent local views in the entire system. This is done by exchanging additional routing information with the Border Routers of the Autonomous System. The architecture implements the results of iBGP analyses made in. Despite not being that as flexible as classical information reduction techniques, our design scales equal or better in practice. All required protocol extensions are supported by IETF Internet Drafts from persons affiliated with important router vendors.

Scalability is an important aspect when spreading externally learned routing information via the Border Gateway Protocol within Autonomous Systems. However, research showed that common iBGP scalability techniques like Route Reflection and AS Confederations are involved with anomalies in general. These unwanted effects can be inherently avoided by providing routers with individual sets of routing information. Implementing a modified iBGP routing information exchange in productive systems requires a scalability which is comparable to conventional techniques. Our studies show that providing routers with suitable individual information should not cause any serious decline at this point: While the most crucial parameters proved to be not problematic, only the number of paths managed by routers turn out to be hard to predict. Hence, we examine this parameter for the productive system of a large Service Provider, showing only irrelevant increases. Our results indicate that this approach could be an alternative for future iBGP routing architectures.

In this paper we consider the problem of determining traffic matrices for end-to-end demands in an IP/MPLS network that supports multiple quality of service (QoS) classes. More precisely, we want to determine the set of traffic matrices Ti for each QoS class i separately. Ti contains average bandwidth levels for QoS class i for every pair of routers within the network. We propose a new method for obtaining QoS class specific traffic matrices that combines estimation and measurement methods: We take advantage of the fact that the total traffic matrix can be measured precisely in MPLS networks using either the LDP or RSVP-TE protocol. These measurements can then be used in a mathematical model to improve estimation methods - known as network tomography - that estimate QoS class specific traffic matrices from QoS class specific link utilizations. In addition to the mathematical model, we present results of the proposed method from its application in Deutsche Telekom's global IP/MPLS backbone network and we show that the estimation accuracy (mean relative error) is improved by a factor of 2.5 compared to results from network tomogravity. We investigate the structure of the estimated traffic matrices for the different QoS classes and motivate in this paper why QoS class specific traffic matrices will be essential for efficient network planning and network engineering in the future.

The article investigates the usage of adaptive directed antennas for the Mobile Broadband System (MBS). The advantages and problems are considered. Solutions for the problems are proposed and evaluated with respect to cost, feasibility and efficiency. The MBS is a wireless cellular network operating at 60 GHz. It has been developed in the European collaborative RACE II project R2057, addressing techniques and technology (especially GaAs MMIC, i.e. millimetre-wave monolithic integrated circuits) as well as system concepts. A major feature of MBS is to transparently transport ATM cells over the air interface at bit rates of 34 Mbit/s per carrier.