Kenneth L. Calvert

Modeling Internet topology

The topology of a network, or a group of networks such as the Internet, has a strong bearing on many management and performance issues. Good models of the topological structure of a network are essential for developing and analyzing internetworking technology. This article discusses how graph-based models can be used to represent the topology of large networks, particularly aspects of locality and hierarchy present in the Internet. Two implementations that generate networks whose topology resembles that of typical internetworks are described, together with publicly available source code.

An architecture for active networking

Active networking offers a change in the usual network paradigm: from passive carrier of bits to a more general computation engine. The implementation of such a change is likely to enable radical new applications that cannot be foreseen today. Large-scale deployment, however, involves significant challenges in interoperability, security, and scalability. In this paper we define an active networking architecture in which users control the invocation of pre-defined, network-based functions through control information in packet headers.

Formal methods for protocol conversion

Consideration is given to ways of overcoming a protocol mismatch using protocol conversion. Three different methods for finding a protocol converter are described. Two of these are bottom up in nature, and involve relating the conversion system to existing protocols. The third approach, which is new, is top down: the desired global properties of the conversion system are used in deriving the converter. An example is used to illustrate each method. The authors discuss more general forms of the abstract problem in the context of layered network architectures. >

Bowman: a node OS for active networks

Bowman is an extensible platform for active networking: it layers active networking functionality in user space software over variants of the System V UNIX operating system. The packet processing path implemented in Bowman incorporates an efficient and flexible packet classification algorithm, supports multi-threaded per-flow processing, and utilizes real time processor scheduling to achieve deterministic performance in the user-space. In this paper we describe the design and implementation of Bowman; discuss the support that Bowman provides for implementing execution environments for active networking; discuss the network-level architecture of Bowman that can be used to implement virtual networks; and present performance data showing that Bowman is able to sustain 100 Mbps throughput while forwarding IP packets over fast Ethernets.

Lightweight network support for scalable end-to-end services

Some end-to-end network services benefit greatly from network support in terms of utility and scalability. However, when such support is provided through service-specific mechanisms, the proliferation of one-off solutions tend to decrease the robustness of the network over time. Programmable routers, on the other hand, offer generic support for a variety of end-to-end services, but face a different set of challenges with respect to performance, scalability, security, and robustness. Ideally, router-based support for end-to-end services should exhibit the kind of generality, simplicity, scalability, and performance that made the Internet Protocol (IP) so successful. In this paper we present a router-based building block called ephemeral state processing (ESP), which is designed to have IP-like characteristics. ESP allows packets to create and manipulate small amounts of temporary state at routers via short, predefined computations. We discuss the issues involved in the design of such a service and describe three broad classes of problems for which ESP enables robust solutions. We also present performance measurements from a network-processor-based implementation.

Instrumenting home networks

In managing and troubleshooting home networks, one of the challenges is in knowing what is actually happening. Availability of a record of events that occurred on the home network before trouble appeared would go a long way toward addressing that challenge. In this position/work-in-progress paper, we consider requirements for a general-purpose logging facility for home networks. Such a facility, if properly designed, would potentially have other uses. We describe several such uses and discuss requirements to be considered in the design of a logging platform that would be widely supported and accepted. We also report on our initial experience deploying such a facility.

Choice as a principle in network architecture

There has been a great interest in defining a new network architecture that can meet the needs of a future Internet. One of the main challenges in this context is how to realize the many different technical solutions that have developed in recent years in a single coherent architecture. In addition, it is necessary to consider how to ensure economic viability of architecture solutions. In this work, we discuss how to design a network architecture where choices at different layers of the protocol stack are explicitly exposed to users. This approach ensures that innovative technical solutions can be used and rewarded, which is essential to encourage wide deployment of this architecture.

Deriving a protocol converter: a top-down method

A protocol converter mediates the communication between implementations of different protocols, enabling them to achieve some form of useful interaction. The problem of deriving a protocol converter from specifications of the protocols and a desired service can be viewed as the problem of finding the “quotient” of two specifications. We define a class of finite-state specifications and present an algorithm for solving “quotient” problems for the class. The algorithm is applied to an example conversion problem. We also discuss its application in the context of layered network architectures.

Building multicast services from unicast forwarding and ephemeral state

We present an approach to building multicast services at the network layer using unicast forwarding and two additional building blocks: ephemeral state probes, i.e. extremely lightweight distributed computations based on a time-bounded associative memory; and the ability to inject or enable packet processing functions that modify router behavior in a very limited way. In our approach, senders and receivers use ephemeral state probes to determine where to inject functionality. A special function that duplicates packets matching a particular pattern and forwards them to a specific destination is then instantiated at the desired network location. Our approach eliminates the need for sophisticated multicast routing protocols and gives the end-systems control over the multicast service, allowing the application to tailor the service to its needs. At the same time, our approach creates efficient forwarding paths by using ephemeral state probes to determine (only) the relevant aspects of the network and group topology. We present two multicast implementations: one builds a multicast tree with centralized control, another provides the traditional IP multicast abstraction. Both implementations can be done in a simple and scalable manner with minimal added functionality in the routers beyond unicast forwarding.

Concast: design and implementation of a new network service

This paper introduces concast, a new network service. Concast is the inverse of multicast: multiple sources send messages toward the same destination, which results in a single message being delivered to the destination. The received message appears to come from the concast group rather than any particular receiver. Different forms of concast service can be defined by varying the mapping from the set of sent messages to the received message. The service is useful for preventing implosion and reducing bandwidth consumption in cases where many senders transmit to the same receiver-for example in aggregating (or suppressing) positive (or negative) acknowledgements. We define the semantics of a simple concast service that is the inverse of multicast, as well as a more general custom concast, which allows users to define certain aspects of the services semantics. We describe how to implement the service so that it scales approximately as well as IP multicast. We also present results from a simulation study showing that concast provides significant benefits in a layered-video application.