arquitectura de redes qos 3

8/13/2019 Arquitectura de Redes QoS 3

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MECHANISMS OF QOS

CLASSIFICATION

MARKING

CONGESTION MANAGEMENT

CONGESTION AVOIDANCE

POLICING

SHAPING

LINK FRAGMENTATION

EXAMPLE

Mechanisms of QoS

Classification: Each class-oriented QoS mechanism has to supportsome type of classification.

Marking:Used to mark packets based on classification, metering,or both.

Congestion management:Each interface must have a queuing

mechanism to prioritize transmission of packets.

Congestion avoidance:Used to drop packetsearly to avoidcongestion later in the network.

Policing and shaping:Used to enforce a rate limit based on themetering (excess traffic is either dropped, marked, or delayed).

Link Efficiency:Used to improve bandwidth efficiency through

compression, link fragmentation, and interleaving.

Classification

Classification is the identifying and splitting of traffic into different classes.

Traffic can be classed by various means, including the DSCP.

Modular QoS CLI allows classification to be implemented separately frompolicy.


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Marking

Marking, also known as coloring, marks each packet as a member of a

network class so that the packet class can be quickly recognizedthroughout the rest of the network.

Congestion Management

Congestion management uses the marking on each packet to

determine in which queue to place packets.

Congestion management uses sophisticated queuing technologies,such as WFQ and LLQ, to ensure that time-sensitive packets such as

voice are transmitted first.

Congestion Avoidance

Congestion avoidance may randomly drop packets from selected queueswhen previously defined limits are reached.

By dropping packets early, congestion avoidance helps preventbottlenecks downstream in the network.

Congestion avoidance technologies include random early detection andweighted random early detection.


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Policing

Policing drops or marks packets when a predefined limit isreached.

Shaping

Shaping queuespackets when a predefined limit is reached.

Compression

Header compression can dramatically reduce the overheadassociated with voice transport.


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Link Fragmentation and Interleaving

Without link fragmentation and interleaving, time-sensitive voice traffic canbe delayed behind long, non-time-sensitive data packets.

Link fragmentation breaks long data packets apart and interleaves time-sensitive packets so that the time-sensitive packets are not delayed.

Congestion

Management*

Congestion

Avoidance

(Always)

(High-speed to

low-speed links or

aggregation points)

Mark

Classify(Always)

(As close to the

source as possible)

Policing Policing

Shaping(Going to lower-speed

links or from points of

aggregation)

(Coming from a

higher-speed link oraggregation)

Fragmentation

and Interleaving

Compression

(Low-speed

WAN links)

Output

interface

Input

interface

Mark

Applying QoS to Input and Output Interfaces

EXAMPLE OF MECHANISM OF QoS


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Overview

Life of a High-Priority VoIP Packet

Life of a High-Priority VoIP Packet (Cont.)


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Life of a Low-Priority FTP Packet

Life of a Low-Priority FTP Packet (Cont.)


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arquitectura de redes qos 3

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