Describing And Manipulating Experiment Topologies in DETER

This page describes the model, specification and implementation of DETER's topology description. A topology is the layout of an experment's physcial or logical environment including the topologies of its control and data networks.

Because DETER experiments are intended to be large - thousands or millions of entities - DETER's topology system must support large scale

• Specification
• Operations - realize, initialize, etc.
• Visualization

We describe a model that suports these, an API that describes how to use the model and an initial implementation in the Descartes interface.

Model

A DETER topology is a collection of experimental elements that can communicate with one another. The topology model consists of elements that represent those experimental entities and substrates which indicate the valid commuincations scopes. An element may be specialized depending on the capabilities supplied or required. A substrate includes limits on how the communication rate and delay when communicating through it.

The topology is represented as a bipartite graph where vertices are either substrates or elements. Edges are interfaces. Each interface connects an element to a substrate, indicating that the element can communicate on the substrate. An element may have additional communication constraints encoded in it as well.

We stress that these are logical descriptions. Within DETERlab a substrate is usually realized as a virtual LAN (VLAN), but a substrate in general may capture a VLAN, a shared WDM frequency, a microwave line-of-sight or an open window across an alley. Similarly, an interface may represent a single card in a computer or a specific radio configuration. The mapping of interfaces or substrates to physical items is not always one-to-one. Similarly elements are logical communicating entities. They are specialized by the basic role they play in the experiment. Currently the most commonly encountered element is a computer, which may be a physical machine, a virtual machine instance, or even a process.

Element specialization is a fairly heavyweight extensbility mechanism. A simpler one is the ability to attach attributes to elements, substrates, interfaces, and the various sub components of specialized elements. Attributes are named strings where the names are scoped by the thing they are attached to. This allows tools that construct or manipulate topologies to annotate the topologies even if the core testbed does not use the information.