The Hybrid Network Simulator (HNS) System

Benjamin Melamed*
Rutgers University
Rutgers Business School
Newark and New Brunswick
Department of MSIS
Piscataway, NJ 08854

Friday, January 16, 2004 at 3:00pm at MEC203


The fluid-flow paradigm is an alternative approach to the traditional queueing paradigm, where workload movement in a network is described
in terms of a fluid metaphor rather than the familiar customer metaphor. The difference lies in the way workload is processed and moved.
Specifically, workload parcels (customers in traditional queueing) and their discrete "all-or-nothing" motion are replaced by fluid-like
workload whose continuous flow in the network is governed by (random) rates. Fluid-flow networks hold the promise of two advantages.
First, they can considerably speed up the simulation of complex flow networks such as high-speed packet-base telecommunications networks,
manufacturing systems and bulk material handling (e.g., coal), where traditional queueing-based simulation often gives rise to enormous numbers of events. And second, the fluid-flow paradigm permits fast, nonparametric, and unbiased estimation (unlike traditional queueing) of IPA (Infinitesimal
Perturbation Analysis) gradients. Such gradients are derivatives of performance measures with respect to various parameters, which may be used to make decisions on network design, replenishment or control.

In this talk, we describe the design and implementation of HNS (Hybrid Network Simulator), a software package that admits the hybrid simulation of both packet flows and fluid flows. HNS is based on a simple class of fluid-flow models, called Continuous Flow Models (CFMs).
These can be combined and connected to form hybrid networks supporting multiple priority-based flows that compete at network nodes for shared servers and shared buffer space.

The talk will focus on the fluid processing design scheme in the HNS and on efficiency issues. The current status of HNS
as well as future directions, will also be discussed.



Using Certified Policies to Regulate E-Commerce Transactions

Dr. Victoria Ugureanu

Friday, January 23, 2004 at 11:00am in MEC RM 309


E-commerce regulations are usually embedded in mutually agreed upon contracts. Generally, these contracts enumerate agents
authorized to participate in transactions, and spell out rights and obligations of each partner, and terms and conditions of the trade.
An enterprise may be concurrently bound by a set of different contracts that regulate the trading relations with its various clients and suppliers.
This set is dynamic because new contracts are constantly being established, and previously established contracts end, are annulled or revised.

We argue that existent access control mechanisms cannot adequately support the large number of regulations embedded in disparate, evolving contracts.
To deal with this problem we propose to use certified policies. A certified policy (CP) is obtained by expressing contract terms regarding access and control regulations in a formal, interpretable language, and by having them digitally signed by a proper authority.
In this framework, an agent making a request to a server presents to the server such a CP together with other relevant credentials.
A valid certified policy can then be used as the authorization policy for the request in question.

This talk presents a language for stating contract terms, and describes the implementation and performance of the proposed enforcement mechanism.



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