Click is a new software architecture for building flexible and configurable routers. A Click router is assembled from packet processing modules called elements. Individual elements implement simple router functions like packet classification, queueing, scheduling, and interfacing with network devices. A router configuration is a directed graph with elements at the vertices; packets flow along the edges of the graph. Configurations are written in a declarative language that supports user-defined abstractions. This language is both readable by humans and easily manipulated by tools. We present language tools that optimize router configurations and ensure they satisfy simple invariants. Due to Click’s architecture and language, Click router configurations are modular and easy to extend. A standards-compliant Click IP router has sixteen elements on its forwarding path. We present extensions to this router that support dropping policies, fairness among flows, quality-of-service, and

In order to stem the increasing packet loss rates caused by an exponential increase in network traffic, the IETF is considering the deployment of active queue management techniques such as RED [13]. While active queue management can potentially reduce packet loss rates in the Internet, this paper shows that current techniques are ineffective in preventing high loss rates. The inherent problem with these queue management algorithms is that they all use queue lengths as the indicator of the severity of congestion.

The congestion control mechanisms used in TCP have been the focus of numerous studies and have undergone a number of enhancements. However, even with these enhancements, TCP connections still experience alarmingly high loss rates, especially during times of congestion. The IETF has addressed this problem by advocating the deployment of active queue management mechanisms, such as RED, in the network. While RED can potentially improve packet loss rates, we show that its effectiveness is highly dependent upon its operating parameters. In fact, in cases where these parameters do not match the requirements of the network load, the performance of the RED gateway can approach that of a traditional drop-tail gateway. To alleviate this problem, we propose and experiment with a self-configuring active queue management mechanism which can significantly reduce loss rates across congested links. When used in the network, this mechanism can effectively reduce packet loss while maintaining high link utilizations under the most difficult scenarios. Keywords: Congestion control, Internet, TCP, RED, queue management 1

Network researchers face a significant problem when deploying software in routers, either for experimentation or for pilot deployment. Router platforms are generally not open systems, in either the open-source or the open-API sense. In this paper we discuss the problems this poses, and present an eXtensible Open Router Platform (XORP) that we are developing to address these issues. Key goals are extensibility, performance and robustness. We show that different parts of a router need to prioritize these differently, and examine techniques by which we can satisfy these often conflicting goals. We aim for XORP to be both a research tool and a stable deployment platform, thus easing the transition of new ideas from the lab to the real world. 1 VALIDATING INTERNET RESEARCH A yawning gap exists between research and practice concerning

The Assured Forwarding (AF) service of the IETF DiffServ architecture provides a qualitative service differentiation between classes of traffic, in the sense that a low-priority class experiences higher loss rates and higher delays than a high-priority class. However, the AF service does not quantify the difference in the service given to classes. In an effort to strengthen the service guarantees of the AF service, we propose a Quantitative Assured Forwarding service with absolute and proportional differentiation of loss, service rates, and packet delays. We present a feedback-based algorithm which enforces the desired class-level differentiation on a per-hop basis, without the need for admission control or signaling. Measurement results from a testbed of FreeBSD PC-routers on a 100 Mbps Ethernet network show the effectiveness of the proposed service, and indicate that our implementation is suitable for networks with high data rates.

In order to stem the increasing packet loss rates caused by an exponential increase in network traffic, the IETF has been considering the deployment of active queue management techniques such as RED [14]. While active queue management can potentially reduce packet loss rates in the Internet, we show that current techniques are ineffective in preventing high loss rates. The inherent problem with these queue management algorithms is that they use queue lengths as the indicator of the severity of congestion. In light of this observation, a fundamentally different active queue management algorithm, called BLUE, is proposed, implemented and evaluated. BLUE uses packet loss and link idle events to manage congestion. Using both simulation and controlled experiments, BLUE is shown to perform significantly better than RED both in terms of packet loss rates and buffer size requirements in the network. As an extension to BLUE, a novel technique based on Bloom filters [2] is described for enforcing fairness among a large number of flows. In particular, we propose and evaluate Stochastic Fair BLUE (SFB), a queue management algorithm which can identify and rate-limit non-responsive flows using a very small amount of state information. I.

Network monitoring is a vital part of modern network infrastructure management. Existing techniques either present a restricted view of network behavior and state, or do not efficiently scale to higher network speeds and heavier monitoring workloads. Considering these shortcomings we present a novel architecture for programmable packet-level network monitoring. Our approach allows users to customize the monitoring function at the lowest possible level of abstraction to suit a wide range of monitoring needs: we use operating system mechanisms that result in a programming environment providing a high degree of flexibility, retaining fine-grained control over security, and minimizing the associated performance overheads. We present the implementation of this architecture as well as a set of experimental applications.

Present day routers typically employ monolithic operating systems which are not easily upgradable and extensible. With the rapid rate of protocol development it is becoming increasingly important to dynamically upgrade router software in an incremental fashion. We have designed and implemented a high performance, modular, extended integrated services router software architecture in the NetBSD operating system kernel. This architecture allows code modules, called plugins, to be dynamically added and configured at run time. One of the novel features of our design is the ability to bind different plugins to individual flows; this allows for distinct plugin implementations to seamlessly coexist in the same runtime environment. High performance is achieved through a carefully designed modular architecture; an innovative packet classification algorithm that is both powerful and highly efficient; and by caching that exploits the flow-like characteristics of Internet traffic. Compared to a mon...

The Internet research community is promoting active queue management in routers as a proactive means of addressing congestion in the Internet. Active queue management mechanisms such as Random Early Detection (RED) work well for TCP flows but can fail in the presence of unresponsive UDP flows. Recent proposals extend RED to strongly favor TCP and TCP-like flows and to actively penalize "misbehaving" flows. This is problematic for multimedia flows that, although potentially well-behaved, do not, or can not, satisfy the definition of a TCP-like flow. In this paper we investigate an extension to RED active queue management called Class-Based Thresholds (CBT). The goal of CBT is to reduce congestion in routers and to protect TCP from all UDP flows while also ensuring acceptable throughput and latency for well-behaved UDP flows. CBT attempts to realize a "better than best effort" service for well-behaved multimedia flows that is comparable to that achieved by a packet or link scheduling dis...

Abstract—This article describes an approach for providing dynamic quality of service (QoS) support in a variable bandwidth network, which may include wireless links and mobile nodes. The dynamic QoS approach centers on the notion of providing QoS support at some point within a range requested by applications. To utilize dynamic QoS, applications must be capable of adapting to the level of QoS provided by the network, which may vary during the course of a connection. To demonstrate and evaluate the dynamic QoS concept, we have implemented a new protocol called dynamic resource reservation protocol (dRSVP) and a new QoS application program interface (API). The paper describes this new protocol and API and also briefly discusses our experience with adaptive streaming video and audio applications that work with the new protocol in a testbed network, including wireless local area network connectivity and wireless link connectivity emulated over wired ethernet. Qualitative and quantitative assessments of the dynamic RSVP protocol are provided. Index Terms—Adaptive applications, Internet protocol, quality of service (QOS), resource allocation, resource reservation setup