Team MAESTRO

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Section: New Results

Congestion control and IP traffic characterization

Participants : Sara Alouf, Konstantin Avrachenkov, Alberto Blanc, Abdulhalim Dandoush, Alain Jean-Marie, Philippe Nain.

Estimating the round-trip time of long-lived TCP sessions

The Round-Trip Time (RTT) of a TCP connection represents an important characteristic whose knowledge is useful when controlling a long-lived flow at a router. In [43] , K. Avrachenkov, S. Alouf, and P. Nain, in collaboration with D. Carra (Univ. Verona) and G. Post (Alcatel-Lucent Bell Labs ), propose a passive, online RTT estimation methodology based on the traffic observed in one direction. The method uses spectral analysis along with a pattern-matching technique for the extraction of the fundamental frequency. Since the proposed solution estimates in real-time the RTT using one-way traffic, it represents a candidate for a possible implementation in routers.

This research is carried out within ADR “Semantic Networking” (see Section  7.1.1 ).

Flow-aware traffic management

The congestion control mechanism of TCP, while simple and scalable, has several well-known limitations: 1) often different flows experience synchronized losses leading to lower link utilization, and 2) when flows with different Round-Trip Times (RTT) share the same bottleneck link, flows with a smaller RTT receive a larger share of the capacity.

A. Blanc, K. Avrachenkov, and S. Alouf, in collaboration with G. Post (Alcatel-Lucent Bell Labs), propose a new flow-aware traffic management mechanism that aims at addressing the two aforementioned limitations, while being self-configuring and supporting different fairness criteria. The core idea of the proposed mechanism can be described as a two step process: 1) decide a target rate for each flow; 2) control each TCP flow in order to minimize the oscillations around the chosen target rate. We have proposed two mechanisms to control TCP flows individually. These two mechanisms, Monitor Rate and Binary Search are filed as patents [77] , [76] .

This research is carried out within ADR “Semantic Networking” (see Section  7.1.1 ).

Interaction between TCP and bottleneck buffer

K. Avrachenkov, A. Piunovskiy and Z. Yi (Univ. Liverpool) and U. Ayesta (BCAM, Spain) have studied the interaction between the AIMD (Additive Increase Multiplicative Decrease) [24] and MIMD (Multiplicative Increase Multiplicative Decrease) [31] congestion control and a bottleneck router with Drop Tail buffer. The problem is analyzed in the framework of deterministic hybrid models. The authors study conditions under which the system trajectories converge to limiting cycles with a single jump. Following that, they consider the problem of the optimal buffer sizing in the framework of multi-criteria optimization in which the Lagrange function corresponds to a linear combination of the average throughput and the average delay in the queue. Thus, a set of rules for optimal buffer sizing is established.

This research is carried out within ADR “Semantic Networking” (see Section  7.1.1 ).

Flow-level simulation of parallel downloads

Parallelism in the download process of large files is an efficient mechanism for distributed systems. In such systems, peers (clients) exploit the power of parallelism to download blocks of data stored in a distributed way over some other peers (servers). In [44] , A. Dandoush and A. Jean-Marie investigate parallel downloading with capacity constraints. The basic problem is to predict the instantaneous bandwidth sharing that each client/server devotes to each data transfer flow. The authors propose and analyse a simple algorithm that works at the flow-level and uses the concept of “water-filling” (or min-max fairness). The response times of parallel downloading is analyzed (both distributions and averages) using the algorithm by flow level simulations. The results are compared to those of packet-level simulations after implementing the same process in the Network Simulator (ns-2).


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