Convenio Marco de Cooperación y Asistencia Técnica

..\Presentacion\SLS\barra.jpgFundación Proydesa y la filial Argentina de SLS LATAM Tienen el agrado de comunicar la formalización de un Convenio Marco de Cooperación y Asistencia Técnica con el objeto de investigar, desarrollar y promover la formación en y con tecnología, ingresando decididamente como actores protagónicos en la Educación del Siglo XXI y acompañando en forma coordinada el esfuerzo que diariamente realiza Cisco Systems por cambiar la forma en que nos comunicamos y educamos

Using the Medium

Introducing QoS

Understanding the Need for QoS

QoS Defined

Before Converged Networks

Traditional data traffic characteristics:– Bursty data flow– First-come, first-served access – Mostly not time-sensitive – delays OK – Brief outages are survivable

After Converged Networks

Converged traffic characteristics:– Constant small-packet voice flow competes

with bursty data flow – Critical traffic must get priority – Voice and video are time-sensitive– Brief outages not acceptable

Converged Networks: Quality Issues

– Telephone Call: “I cannot understand you; your voice is breaking up.”

– Teleconferencing: “The picture is very jerky. Voice not synchronized.”

– Brokerage House: “I needed that information two hours ago. Where is it?”

– Call Center: “Please hold while my screen refreshes.”

QoS Traffic Requirements: Data• Different applications have

different traffic characteristics.

• Different versions of the same application can have different traffic characteristics.

• Classify data into relative-priority model with no more than four to five classes:

– Mission-Critical Apps: Locally defined critical applications

– Transactional: Interactive traffic, preferred data service

– Best-Effort: Internet, e-mail, unspecified traffic

– Less-Than-Best-Effort (Scavenger): Napster, Kazaa, peer-to-peer applications

QoS Traffic Requirements: Voice• Latency < 150 ms*

• Jitter < 30 ms*

• Loss < 1%*

• 17-106 kbps guaranteed priority bandwidth per call

• 150 bps (+ Layer 2 overhead) guaranteed bandwidth for voice-control traffic per call

*one-way requirements

–QoS Traffic Requirements: Voice

QoS Requirements: Videoconferencing• Latency ≤ 150 ms*

• Jitter ≤ 30 ms*

• Loss ≤ 1%*

• Minimum priority bandwidth guarantee required is:

– Video stream + 20%

– For example, a 384 kbps stream would require 460 kbps of priority bandwidth

*one-way requirements

Converged Networks:Quality Issues (Cont.)

– Lack of bandwidth: Multiple flows compete for a limited amount of bandwidth.

– End-to-end delay (fixed and variable): Packets have to traverse many network devices and links that add up to the overall delay.

– Variation of delay (jitter): Sometimes there is a lot of other traffic, which results in more delay.

– Packet loss: Packets may have to be dropped when a link is congested.

Video Lacking Proper QoS

– Best-Effort: No QoS is applied to packets. – IntServ: Applications signal to the network that they require

special QoS.– DiffServ: The network recognizes classes that require special

QoS.

Best-Effort Model

It will get there when it gets there.

– Internet initially based on a best-effort packet delivery service

– The default mode for all traffic

– No differentiation between types of traffic

– Like using standard mail

Best-Effort Model (Cont.)

+ Benefits:

• Highly scalable

• No special mechanisms required– Drawbacks:

• No service guarantees

• No service differentiation

IntServ Model– Some applications have

special bandwidth or delay requirements or both

– IntServ introduced to guarantee a predictable behavior of the network for these applications

– Guaranteed delivery: no other traffic can use reserved bandwidth

– Like having your own private courier plane

It will be there by 10:30 a.m.

IntServ Model (Cont.)– Provides multiple service

levels– Requests specific kind of

service from the network before sending data

– Uses RSVP to reserve network resources

– Uses intelligent queuing mechanisms

– End to end

– RSVP QoS services• Guaranteed-rate service• Controlled-load service

– RSVP provides policy to QoS mechanisms

IntServ Model (Cont.)

IntServ Model (Cont.)+ Benefits:

• Explicit resource admission control (end to end)• Per-request policy admission control (authorization object,

policy object)• Signaling of dynamic port numbers (for example, H.323)

– Drawbacks:• Continuous signaling because of stateful architecture• Flow-based approach not scalable to large implementations

such as the public Internet (can be made more scalable when combined with elements of the DiffServ model)

DiffServ Model– Network traffic identified by

class– Network QoS policy enforces

differentiated treatment of traffic classes

– You choose level of service for each traffic class

– Like using a package delivery service

Do you want overnight delivery?

Do you want two-day air delivery?

Do you want three- to seven-day ground delivery?

Overview

R1 R2

QoS for Converged Networks

Step 1: Identify Traffic and Its Requirements

– Network audit

• Identify traffic on the network

– Business audit

• Determine how each type of traffic is important for business

– Service levels required

• Determine required response time

Step 2: Divide Traffic into Classes

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 from policy.

Marking

– Marking, also known as coloring, marks each packet as a member of a network class so that the packet class can be quickly recognized throughout the rest of the network.

Differentiated Services Model– The Differentiated Services model describes services associated

with traffic classes.– Complex traffic classification and conditioning is performed at

the network edge, resulting in a per-packet DSCP.– No per-flow state in the core.– The core only performs simple “per-hop behaviors” on traffic

aggregates.– The goal is scalability.

DSCP Encoding

– DiffServ field: The IP version 4 header ToS octet or the IPv6 traffic class octet, when interpreted in conformance with the definition given in RFC 2474

– DSCP: The first six bits of the DiffServ field, used to select a PHB (forwarding and queuing method)

DiffServ Model (Cont.)

+ Benefits:

• Highly scalable

• Many levels of quality possible– Drawbacks:

• No absolute service guarantee

• Complex mechanisms

Break - 10 mins

QoS for Converged Networks

QoS Mechanisms

– Classification: Each class-oriented QoS mechanism has to support some 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 packets early to avoid congestion later in the network.

– Policing and shaping: Used to enforce a rate limit based on the metering (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 from

policy.

Marking

– Marking, also known as coloring, marks each packet as a member of a network class so that the packet class can be quickly recognized throughout 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 queues when previously defined limits are reached.

– By dropping packets early, congestion avoidance helps prevent bottlenecks downstream in the network.

– Congestion avoidance technologies include random early detection and weighted random early detection.

Policing

– Policing drops or marks packets when a predefined limit is reached.

Shaping

– Shaping queues packets when a predefined limit is reached.

Compression

– Header compression can dramatically reduce the overhead associated with voice transport.

Link Fragmentation and Interleaving

– Without link fragmentation and interleaving, time-sensitive voice traffic can be 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.

Applying QoS to Input andOutput Interfaces

Methods for Implementing QoS Policy

– CLI– MQC– AutoQoS VoIP (voice QoS)– AutoQoS Enterprise (voice, video, and data QoS) – QPM

Implementing QoS with CLI

interface Multilink1

ip address 10.1.61.1 255.255.255.0

ip tcp header-compression iphc-format

load-interval 30

custom-queue-list 1

ppp multilink

ppp multilink fragment-delay 10

ppp multilink interleave

multilink-group 1

ip rtp header-compression iphc-format

!

– Traditional method

– Nonmodular

– Cannot separate traffic classification from policy definitions

– Used to augment, fine-tune newer AutoQoS method

Implementing QoS with MQC

• A command syntax for configuring QoS policy

• Reduces configuration steps and time

• Configure policy, not “raw” per-interface commands

• Uniform CLI across major Cisco IOS platforms

• Uniform CLI structure for all QoS features

• Separates classification engine from the policy

class-map VoIP-RTP

match access-group 100

class-map VoIP-Control

match access-group 101

!

policy-map QoS-Policy

class VoIP-RTP

priority 100

class VoIP-Control

bandwidth 8

class class-default

fair-queue

!

interface serial 0/0

service-policy output QoS-Policy

!

access-list 100 permit ip any any precedence 5

access-list 100 permit ip any any dscp ef

access-list 101 permit tcp any host 10.1.10.20 range 2000 2002

access-list 101 permit tcp any host 10.1.10.20 range 11000 11999

Implementing QoS with AutoQoS

[trust] option is used to trust DSCP marking

– AutoQoS VoIP supported both in the LAN and WAN environments

– AutoQoS Enterprise supported on WAN interfaces

– Routers can deploy Enterprise QoS policy treatment for voice, video, and data traffic

– Switches can deploy QoS policy treatments for voice by a single command

Comparing Methods for Implementing QoS