In the Laboratory for Communications and Telematics (LCT) of the Centre of Informatics and Systems of the University of Coimbra (CISUC), research is ongoing towards a Measurement Based Admission Control (MBAC) framework for DiffServ [1] based networks. Till now, many research in this area was and still is undertaken with an encyclopedic literature about this subject as one achievement. While so...

Stability is one of the important issues for a TCP/AQM (Active Queue Management) system. In this paper, we study the local and global stability of TCP-newReno/RED under many flows regime. The existing results of the local stability are mostly for TCP-Reno, not for newReno. These results are obtained based on a small scale model with a few number of flows and thus cannot be blindly applied to a ...

In this paper, we investigate stability and bifurcation arising in a communication network model with a large number of homogeneous (symmetric) users and a single bottleneck AQM queue. We carry out bifurcation analysis to study the effect of user delay and strength of feedback. It is shown that for any given delay, there exists a critical amount of feedback (due to AQM) at which the equilibrium...

In the context of Active Queue Management, intelligent dropping algorithms have been proposed to achieve a better link utilization with TCP. In this paper we apply this research to the problem of achieving a better utilization of a customer’s contracted throughput when it is sending a TCP traffic aggregate. We propose a scheme, Random Early Marking (REM), that improves the throughput of a TCP a...

Many modern applications require low latency transmission in the Internet which is not explicitly supported today. Most networks are optimized for high throughput and low loss. This increases latency due to high queuing delays. Only very few applications actually need both high thorughput and low latency, therefore the network could offer a new parallel Internet service that provides lower late...

The CoDel algorithm has been a significant advance in the field of AQM. However, it does not provide bounded delay. Rather than allowing bursts of traffic, we argue that a hard limit is necessary especially at the edge of the Internet where a single flow can congest a link. Thus in this paper we proposed an extension of the CoDel algorithm called “hard limit CoDel”, which is fairly simple but e...

Notably absent in the study of congested service facilities is the transition from a non-priority to a priority system. Building on the framework first presented in Mendelson (1985), we study this transition from the perspective of both the system manager and the system user. Using an M/G/1 priority queueing discipline with a fixed traffic assumption, we present three fundamental theorems about...

This paper compares the performance of Tail Drop and three different flavors of the RED (Random Early Detection) queue management mechanism: RED with a standard parameter setting, RED with an optimized parameter setting based on a model of RED with TCP flows, and finally a version of RED with a smoother drop function called “gentle RED”. Performance is evaluated under various load situations fo...

The organic fraction of atmospheric aerosols has proven to be a critical element of air quality and climate issues. However, its composition and the aging processes it undergoes remain insufficiently understood. This work builds on laboratory knowledge to simulate the formation of oligomers from biogenic secondary organic aerosol (BSOA) in the troposphere at the continental scale. We compare th...

This paper presents the LQ-Servo control with observer for TCP/AQM system. In order to estimate the state of TCP window packet size, the control structure is extended with observer based on Kalman filter.