Global scheduler properties derived from local restrictions

Abstract

The VoDka server is a video-on-demand system for a Spanish cable company. We look at the distributed scheduler of this system. This scheduler enables that whenever a user agent is asking for a certain movie, this request is transferred through the system and a set of possible play-back qualities is returned to the agent. In case of a non-empty set, the agent selects one and the movie is streamed to the user.The storage subsystem of the server is composed by a hierarchy of different storage systems, i.e. disks, CD players or tapes. These devices all have restrictions of which the process controlling the device is aware of. A second layer of processes controls a set of devices in one machine and has restrictions, for example, the bandwidth of its connection. A third layer may be further out in the network and serve as a cache to store more popular movies.Every process in the scheduler of the system has a function determining local restrictions, given the configuration and present state of the system. We have built a tool to construct complete models of several configurations. With techniques from the area of formal methods (in particular model checking) these models are used to determine global properties of the system, such as the maximum number of a certain class of movies that can be served in parallel.

Erlang/Otp Framework for Complex Management Applications Development

“…concepts to the functional environment is a key factor for success. Another advantage of using Erlang/OTP as the underlying platform for the system development (in addition to those common in declarative languages), is that techniques coming from the formal methods area can be applied in order to improve the system design and performance (Arts and Benac Earle, 2002), and to ensure (at least partially) the system correctness (Arts and Sánchez Penas, 2002). These techniques can be used more naturally with high level declarative languages, and their results are specially appreciated in complex management software.…”

Extending the VoDKA architecture to improve resource modelling

“…In the near future, work in the project should be made in the following topics: End the prototype implementation that is now under development; integration of the prototype with the real working system; and apply formal methods tools [2,1] in order to know more about the system and to do small redesigns in the architecture to solve possible errors.…”

Translating Erlang to μCRL

“…About eighty percent of the communicating processes implements a server that uses the generic server pattern. This server restricts communication in a way that eases the transformation for us 3 . In the next section the server pattern and its translation to CRL are explained in more detail.…”

“…In the next section the server pattern and its translation to CRL are explained in more detail. The 3 The restriction in the communication imposed by the design pattern allows a better understanding of complex systems. The same restriction that makes the system easier to understand for the engineers is making supervision tree pattern is another frequently used pattern and is described in Sect.…”

“…In this paper we describe the tool that we developed to verify two industrial case-studies: a resource manager application in the AXD 301 switch [2] and the scheduler of a video-on-demand server [3,16]. By our focus on these case-studies we ensured that the translation is useful for a rather general class of verification problems.…”