Lawrence H. Landweber

GENI: A federated testbed for innovative network experiments

GENI, the Global Environment for Networking Innovation, is a distributed virtual laboratory for transformative, at-scale experiments in network science, services, and security. Designed in response to concerns over Internet ossification, GENI is enabling a wide variety of experiments in a range of areas, including clean-slate networking, protocol design and evaluation, distributed service offerings, social network integration, content management, and in-network service deployment. Recently, GENI has been leading an effort to explore the potential of its underlying technologies, SDN and GENI racks, in support of university campus network management and applications. With the concurrent deployment of these technologies on regional and national R&E backbones, this will result in a revolutionary new national-scale distributed architecture, bringing to the entire network the shared, deeply programmable environment that the cloud has brought to the datacenter. This deeply programmable environment will support the GENI research mission and as well as enabling research in a wide variety of application areas.

Complexity of some problems in Petri nets

Abstract We consider the complexity of several standard problems for various classes of Petri nets. In particular, the reachability problem, the liveness problem and the k -boundedness problems are analyzed. Some polynomial time and polynomial space complete problems for Petri nets are given. We then show that the problem of deciding whether a Petri net is persistent is reducible to reachability, partially answering a question of Keller. Reachability and boundedness are proved to be undecidable for the Time Petri net introduced by Merlin. Also presented is the concept of controllability, i.e., the capability of a set of transitions to disable a given transition. We show that the controllability problem requires exponential space, even for 1-bounded nets.

On the structure of sets in NP and other complexity classes

The relationship between resource bounded deterministic and nondeterministic complexity classes has been extensively studied. For polynomial time, the associated question P = NP? is particularly important because of the large number of problems of practical interest that can be solved by nondeterministic polynomial time bounded devices. If P = NP, then these psoblems all have determinisitic polynomial time solutiolns whereas otherwise only exponential time solutions exist. Furthermore, the class NP contains complete problen:s to which all other members of NP can be reduced [S, ?,16] and P = NIP if and only if one of these complete problems is in P. With few exceptions, most intuitively appealk?g members of NP have been shown to be complete. In this paper, we study the structure of sets in NP. We develop a number of simple tools which facilitate the study o.? the relatke complexity 04 sets with res,pect to polynomial time reducibility. The method yields the existence of a minimal pair (with respect to P) of sets A,, S E NP which ;\re not complete. This strengthens earlier results “of Ladner [lo] (minimill pair-ncb upper baound) and Machtey Cl!51 (minimal pair-subexponential but not .qecessarily in NP). In addition, the method can be used to constru@ partial orders of degrees with respect to polynomial time reducibility.

Dynamic Time Windows: packet admission control with feedback

We present a feedback congestion control method, Dynamic Time Windows, for use in high speed wide area networks based on controlling source variance. It is part of the two-level integrated congestion control system introduced in our earlier work[1]. The method consists of a packet admission control system and a feedback system to dynamically control source burstiness. Source throughput is not modulated as with traditional packet windows, allowing system throughput to remain high while avoiding congestion. Furthermore, the admission control bounds congestion times in the network, allowing feedback to be effective in the face of large bandwidth delay products. The basic control mechanisms are analogs to traditional packet windows applied to controlling time windows - a new mechanism which allows switches to modulate source variances. The proposed system is simulated, and the results reported and analyzed. Enhancements to the basic system are also proposed and analyzed. We wish to stress that the system described here is the second level of a two-level congestion control. Previous work[1] concentrated on the switch queueing mechanism, Pulse, while this work is a detailed examination of the feedback system used to adjust time windows to changing network load.

The CSNET name server

Abstract CSNET is a project designed to facilitate electronic data communication among academic computer science departments and other groups doing computer-science research in the United States. CSNET will provide communications facilities for electronic mail and file transfer between users of computers connected to a variety of networks. For the system to be simple and easy to use, users must be able to identify each other to the system in a way that is natural to them and which does not require them to understand the details of network organization or to memorize cryptic names. To this end CSNET is implementing a name server service, composed of programs and data residing on a central Service Host computer and on individual member hosts of CSNET. This paper describes the architecture of the name server and discusses the considerations that lead to its design.

Bench-style network research in an Internet Instance Laboratory

Network researchers employ a variety of experimental methods and tools including analytic modeling techniques, simulators, and widely depolyed measurement infrastructures. It is natural to assume that the overall scope of network research may be limited by the type and capability of the tools and test systems that are available. In this paper we describe a new, bench-style approach for conducting network research that we argue is essential for effectively investigating different classes of important problems. We describe the architecture for the workbench environment that enables this approach-what we call the Internet Instance Laboratory (IIL). The conceptual model for an IIL is a highly configurable laboratory environment containing commercial networking equipment typical of any end-to-end path in the Internet. An IIL would also have the capability to create accurately a broad range of conditions across all networking layers. The two most important advantages of an IIL are the ability to instrument entire end-to-end paths and the ability to install new equipment or protocols in any location in the environment. Clearly, neither of these opporutnities is available in the live Internet. while an IIL offers significant challenges. We describe these challenges and approaches for addressing them. Finnlay, we discuss different classes of research questions that would become tractable if an IIL were available.

Architecture of the CSNET name server

An important function of CSNET is to simplify communication by electronic mail. To this end, a Name Server facility is being implemented, which will free users from having to understand the complexities of inter-network mail addressing. The Name Server includes a database and accessing software on a central Service Host machine, as well as programs and data structures on CSNET member hosts. We describe the architecture of the Name Server and discuss considerations that lead to its design.

Dynamic time windows and generalized virtual clock: combined closed-loop/open-loop congestion control

The authors present mechanisms for congestion control of data traffic in high-speed wide area networks. The network model assumes reservation of resources based on average requirements. The key ideas involve separation of different sources of network congestion, short-term bursts and medium-term load, and using separate mechanisms to address them. Thus, dynamic time window (DTW) admission control is proposed as a mechanism to limit traffic burstiness from sources as a function of the medium-term load on the system, while a new fairness criterion for short-term congestion (Pulse) is proposed as a mechanism for dealing with fair scheduling by switches of short-term bursts. The model of the network is presented. The DTW and Pulse mechanisms are discussed. A detailed analytical and simulation study is presented for static time-windows and various scheduling algorithms. Preliminary results on DTW are discussed.<<ETX>>

A grammar-based methodology for protocol specification and implementation

A new methodology for specifying and implementing communication protocols is presented. This methodology is based on a formalism called “Real-Time Asynchronous Grammars” (RTAG), which uses a syntax similar to that of attribute grammars to specify allowable message sequences. In addition RTAG provides mechanisms for specifying data-dependent protocol activities, real-time constraints, and concurrent activities within a protocol entity. RTAG encourages a top-down approach to protocol design that can be of significant benefit in expressing and reasoning about highly complex protocols. As an example, an RTAG specification is given for part of the Class 4 ISO Transport Protocol (TP-4). Because RTAG allows protocols to be specified at a highly detailed level, major parts of an implementation can be automatically generated from a specification. An RTAG parser can be written which, when combined with an RTAG specification of a protocol and a set of interface and utility routines, constitutes an implementation of the protocol. To demonstrate the viability of RTAG for implementation generation, an RTAG parser has been integrated into the kernel of the 4.2 BSD UNIX operating system, and has been used in conjunction with the RTAG TP-4 specification to obtain an RTAG-based TP-4 implementation in the DoD Internet domain.

Bench-style network research in an Internet instance laboratory

Network researchers employ a variety of experimental methods and tools including analytic modeling techniques, simulators, and widely deployed measurement infrastructures. It is natural to assume that the overall scope of network research may be limited by the type and capability of the tools and test systems that are available. In this paper we describe a new, bench--style approach for conducting network research that we argue is essential for effectively investigating different classes of important problems. We describe the architecture for the workbench environment which enables this approach - what we call the Internet Instance Laboratory (IIL). The conceptual model for an IIL is a highly configurable laboratory environment containing commercial networking equipment typical of any end--to--end path in the Internet. An IIL would also have the capability to create accurately a broad range of conditions across all networking layers. The two most important advantages of an IIL are the ability to instrument entire end--to--end paths and the ability to install new equipment or protocols in any location in the environment. Clearly, neither of these opportunities is available in the live Internet. While an IIL offers significant capabilities, developing such a testbed is not without significant challenges. We describe these challenges and approaches for addressing them. Finally, we discuss different classes of research questions which would become tractable if an IIL were available.