Showing papers by "Anja Feldmann published in 2001"

Deriving traffic demands for operational IP networks: methodology and experience

Abstract: Engineering a large IP backbone network without an accurate network-wide view of the traffic demands is challenging. Shifts in user behavior, changes in routing policies, and failures of network elements can result in significant (and sudden) fluctuations in load. In this paper, we present a model of traffic demands to support traffic engineering and performance debugging of large Internet Service Provider networks. By defining a traffic demand as a volume of load originating from an ingress link and destined to a set of egress links, we can capture and predict how routing affects the traffic traveling between domains. To infer the traffic demands, we propose a measurement methodology that combines flow-level measurements collected at all ingress links with reachability information about all egress links. We discuss how to cope with situations where practical considerations limit the amount and quality of the necessary data. Specifically, we show how to infer interdomain traffic demands using measurements collected at a smaller number of edge links-the peering links connecting the neighboring providers. We report on our experiences in deriving the traffic demands in the AT&T IP BAckbone, by collecting, validating, and joining very large and diverse sets of usage, configuration, and routing data over extended periods of time. The paper concludes with a preliminary analysis of the observed dynamics of the traffic demands and a discussion of the practical implications for traffic engineering.

IP network configuration for intradomain traffic engineering

Abstract: The smooth operation of the Internet depends on the careful configuration of routers in thousands of autonomous systems throughout the world. Configuring routers is extremely complicated because of the diversity of network equipment, the large number of configuration options, and the interaction of configuration parameters across multiple routers. Network operators have limited tools to aid in configuring large backbone networks. Manual configuration of individual routers can introduce errors and inconsistencies with unforeseen consequences for the operational network. In this article we describe how to identify configuration mistakes by parsing and analyzing configuration data extracted from the various routers. We first present an overview of IP networking from the viewpoint of an Internet service provider and describe the kinds of errors that can appear within and across router configuration files. To narrow the scope of the problem, we then focus our attention on the configuration commands that relate to traffic engineering-tuning the intradomain routing protocol to control the flow of traffic through the ISP network. We present a case study of a prototype tool, developed in collaboration with AT&T IP Services, for checking the configuration of the AT&T IP Backbone and providing input to other systems visualization and traffic engineering.

A non-instrusive, wavelet-based approach to detecting network performance problems

Abstract: The main objective of this paper is to explore how much information about the characteristics of end-to-end network paths can be inferred from relying solely on passive packet-level traces of existing traffic collected from a single tap point in the network. To this end, we show that a number of structural properties of aggregate TCP/IP packet traces reveal themselves and can be compared across different time periods and across paths of the traffic destined to different subnets by exploiting the built-in scale-localization ability of wavelets. In turn, these structural properties and the resulting comparisons suggest the feasibility of new approaches for inferring and detecting qualitative aspects of network performance in a fashion that is similar to relying on active measurements, but without disturbing or biasing the metrics of interest. To showcase the feasibility, we developed WIND, a prototype tool for Wavelet-based INference for Detecting network performance problems and illustrate its capabilities to detect anomalies in underlying network path conditions with two examples of passively measured packet traces from two different networking environments. We address and experiment with ways of validating the output of WIND and end with a discussion of the potential of full-fledged wavelet-based analysis (i.e., the ability to localize a signal in scale and time) for future measurement studies.

Traffic engineering system and method

Abstract: The present invention is directed to a novel system and method for traffic engineering in a packet-switched network, such as an Internet Protocol (“IP”) based backbone network A global view of the network is constructed utilizing a network data model that can be readily constructed from the balkanized network information associated locally with the individual elements in the network The data model, in turn, can be utilized to support useful traffic engineering tools such as routing modeling and visualization

System and method for packet network configuration debugging and database

Abstract: The present invention discloses a method and system of extracting relevant information from a collection of router configuration files and using the information to populate a data model. Each section of the router configuration files is read and parsed in a pre-specified order reflecting the dependencies within a single configuration file. Customized information about the network nodes, not reflected in the router configuration files, can be input as well into the data model. Consistency checks and policy checks can then be performed against the data. The data model provides a network-wide view of the topology and configuration, which is crucial for a variety of network engineering tasks.

TCP/IP traffic dynamics and network performance: a lesson in workload modeling, flow control, and trace-driven simulations

Abstract: The main objective of this paper is to demonstrate in the context of a simple TCP/IP-based network that depending on the underlying assumptions about the inherent nature of the dynamics of network traffic, very different conclusions can be derived for a number of well-studied and apparently well-understood problems in the area of performance evaluation. For example, a traffic workload model can either completely ignore the empirically observed high variability at the TCP connection level (i.e., assume "infinite sources") or explicitly account for it with the help of heavy-tailed distributions for TCP connection sizes or durations. Based on detailed ns-2 simulation results, we illustrate that these two commonly-used traffic workload scenarios can give rise to fundamentally different buffer dynamics in IP routers. Using a second set of ns-2 simulation experiments, we also illustrate a qualitatively very different queueing behavior within IP routers depending on whether the traffic arriving at the router is assumed to be endogenous in nature (i.e., a result of the "closed loop" nature of the feedback-based congestion control algorithm of TCP) or exogenously determined (i.e., given by some conventional traffic model --- a fixed "open loop" description of the traffic as seen by the router).

System and method for deriving traffic demands for a packet-switched network

Abstract: The present invention is directed to a method and system for deriving traffic demands for a packet-switched network. A novel model of defining traffic demands as a volume of load originating from an ingress link and destined to a set of egress links enables support for traffic engineering and performance debugging of large operational packet-switched networks.