Facultatea de Electronica, Telecomunicatii si Tehnologia Informatiei
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Facultatea de Electronica, Telecomunicatii si Tehnologia Informatiei
Mecanisme QoS in retele IP multimedia
Baiculescu Andra SorinaMaster IISC
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Cuprins
Introducere in retelele IP multimedia Serviciile oferite in retelele IP Definirea notiunii de QoS Traffic policing si Traffic shaping Cozi si planificarea acestora Mecanisme de control a congestiei Concluzii
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Introducere in retelele IP multimedia
Subsistemul IP multimedia Componente QoS
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Serviciile oferite in retelele IP
Nivelele de servicii oferite de retelele IP:-Best-effort
-Diferentiate
-Garantate
Parametrii care pot afecta calitatea serviciilor:-Banda
-Intarzierea
-Jitter
-Pierderea de pachete
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Definirea notiunii de QoS
Ce este calitatea serviciilor? Parametrii de care depinde calitatea serviciilor:
-Performanta suportului serviciului
-Performanta operabilitatii serviciului
-Serviabilitatea
-Performanta retelei
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Mecanismele de traffic policing si traffic shaping
1.Clasificarea/Marcarea pachetelor de trafic
Criteriile dupa care se impart pachetele Diffserv si Per-Hop Behavior
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2.Mecanismul de traffic policing
Leaky Bucket Token Bucket
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3.Mecanismul de traffic shaping
Traffic shaping Algoritmi de masurare a ratei de sosire
-Algoritmi generali
-Token Bucket
-Extensii ale Token Bucket
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Cozi si planificarea acestora
Tipuri de cozi -FIFO (First In First Out)
-FQ (Fair Queing)
-WFQ (Weighted Fair Queing)
-PQ (Priority Queing)
Mecanisme de planificare a traficului best-effort Metode de planificare pentru oferirea de servicii
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Mecanisme de control a congestiei
Clasificarea mecanismelor-Mecanisme de tip Router-Centric si Host-Centric
-Mecanisme pe baza de rezervare si pe baza de feedback
-Mecanisme pe baza de fereastra si pe baza de rata
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Mecanisme de control ale fluxului
RED (Random Early Detection) Principiu AlgoritmInitializareavg <- 0count <- -1Pentru fiecare pachet care sosesteDaca coada nu este goalaavg <- (1-ωp) x avg+ ωp x qAltfelm <- f(timp – q_timp)avg <- (1- ωp)m x avgDaca minth ≤ avg≤ maxth
Incrementeaza countpb <-pa <-Cu probabilitatea pa:Marcheaza pachetul care soseste count<- 0Altfel daca maxth < avgMarcheaza pachetul care sosestecount <- 0Altfel count <- -1Atunci cand coada devine goalaq_timp <- timp
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Weighted Random Early Detection
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Alte mecanisme de control a fluxului
Tail drop
RIO (Random Early Detection with In/Out)
ARED (Adaptive Random Early Detection)
FRED (Flow Random Early Detection)
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Concluzii
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Bibliografie
[1]. Tatiana Radulescu, Henri-George Coanda - QoS în Retelele IP Multimedia
[2]. Lefteris Mamatas, Tobias Harks, and Vassilis Tsaoussidis - Approaches to Congestion Control in packet networks
[3]. Shudong Jin, Liang Guo, Ibrahim Matta, Azer Bestavros - A Spectrum of TCP-Friendly Window-Based Congestion Control Algorithm
[4]. www.wikipedia.org
[5]. Baswaraj, D.C.Tomar - Modeling of packet switched network over TCP/Ipto suggest modified routing to reduce congestion
[6]. J. Tao – RED: Algorithm, Modeling and Parameters Configuration