ONT10S03 QoS Overview

7/27/2019 ONT10S03 QoS Overview

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Introduction to IP QoS

Introducing QoS



Converged NetworksQuality Issues



Converged Network Quality Issues

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 are not acceptable.



Converged Network Quality Issues (Cont.)

• Lack of bandwidth: Multiple flows compete for a limitedamount of bandwidth.

• End-to-end delay (fixed and variable): Packets have totraverse 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 increased delay.

• Packet loss: Packets may have to be dropped when a link iscongested.



Available Bandwidth



Lack of Bandwidth

• Maximum available bandwidth equals the bandwidth of the slowest link.

• Multiple flows are competing for the same bandwidth, resulting in much lessbandwidth being available to one single application.

• A lack in bandwidth can have performance impacts on network applications.



Bandwidth Availability

• Upgrade the link (the best but also the most expensive solution).

• Forward the important packets first.

• Compress the payload of Layer 2 frames (it takes time).

• Compress IP packet headers.



Efficient Use of Available Bandwidth

Using advanced queuing and header compression mechanisms,the available bandwidth can be used in a much more efficientway:

• Voice: LLQ and RTP header compression

• Interactive traffic: CBWFQ and TCP header compression



End-to-End Delay



Types of Delay

• Processing delay: The time it takes for a router to take the packet from an inputinterface, examine it, and put it into the output queue of the output interface.

• Queuing delay: The time a packet resides in the output queue of a router.

• Serialization delay: The time it takes to place the “bits on the wire.”

• Propagation delay: The time it takes for the packet to cross the link from one end to the

other.



The Impact of Delay on Quality

• End-to-end delay equals the sum of all propagation, processing,serialization, and queuing delays in the path.

• Jitter defines the variation in the delay.

• In best-effort networks, propagation and serialization delays are fixed,while processing and queuing delays are unpredictable.



Ways to Reduce Delay

• Upgrade the link (the best solution but also the most expensive).

• Forward the important packets first.

• Enable reprioritization of important packets.

• Compress the payload of Layer 2 frames (it takes time).

• Compress IP packet headers.



Efficient Use of Ways to Reduce Delay

• Customer routers perform:

– TCP/RTP header compression

– LLQ

– Prioritization

• ISP routers perform:

– Reprioritization according to the QoS policy



Packet Loss



Impact of Packet Loss

• Telephone call: “I cannot understand you. Your voice is breaking up.”

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

• Publishing company: “This file is corrupted.”

• Call center: “Please hold while my screen refreshes.”



Impact of Packet Loss (Cont.)

• Tail drops occur when the output queue is full. Tail drops are commonand happen when a link is congested.

• Many other types of drops occur, usually the result of router congestion, that are uncommon and may require a hardware upgrade(such as, input drop, ignore, overrun, frame errors).



Ways to Prevent Packet Loss

• Upgrade the link (the best solution but also the most expensive).

• Guarantee enough bandwidth to sensitive packets.

• Prevent congestion by randomly dropping less important packetsbefore congestion occurs.



Packet Loss Solution

•Problem: Interface congestion causes TCP and voice packetdrops, resulting in slowing FTP traffic and jerky speechquality.

• Conclusion: Congestion avoidance and queuing can help.

• Solution: Use WRED and LLQ.



QoS Defined



QoS Defined



Implementing QoS



Implementing QoS

1. Identify traffic and itsrequirements.

2. Divide traffic intoclasses.

3. Define QoS policies for each class.



QoS Traffic Classes—

The Requirements of Different Traffic Types



Identify Traffic and Its Requirements

• Network audit: Identify traffic on the network.

• Business audit: Determine how important each type of trafficis for business.

• Service levels required: Determine required response time.



The Requirements of Different Traffic Types



QoS Policy



QoS Policy

• A networkwide definition of the specific levels of QoSassigned to differentclasses of network traffic



Summary

• Converged networks that support voice, video, and datacreate new requirements for managing network traffic. QoSmeets those requirements.

• Converged networks suffer from different quality issues,including lack of adequate bandwidth, end-to-end andvariable delay, and lost packets.

• Packet loss can adversely affect QoS in a network.

• QoS is a way to improve the performance of convergednetworks.



Summary (Cont.)

• Lack of recourses causes networks to experience differenttypes of delay, including processing delay, queuing delay,serialization delay, and propagation delay.

• QoS traffic classes need to be defined to implement a QoSpolicy.

• Implementing QoS requires three steps: identifyrequirements, classify network traffic, and definenetworkwide policies for quality.

• A QoS policy is a networkwide definition of the specific

levels of QoS assigned to classes of network traffic.




Identifying Models for Implementing QoS



QoS Models



QoS Models

Model Characteristics

Best effort No QoS is applied to packets.

IntServ Applications signal to the network that theyrequire certain QoS parameters.

DiffServ The network recognizes classes that require

QoS.



Best Effort Model



Best-Effort Model

• Internet was initially based on a best-effort packet deliveryservice.

• Best-effort is the default mode for all traffic.

• There is no differentiation among types of traffic.

• Best-effort model is similar to using standard mail—It will getthere when it gets there.

B fit d D b k



Benefits and Drawbacksof the Best-Effort Model

• Benefits:

– Highly scalable

– No special mechanisms required

• Drawbacks:

– No service guarantees

– No service differentiation



IntServ Model



IntServ Model

• Introduction of IntServ model (RFC 1633) was driven byreal-time applications, such as remote video andconferencing.

• IntServ end-to-end model ensures guaranteed delivery andpredictable behavior of the network for applications.

• Resource Reservation Protocol (RSVP) is used as a signalingprotocol.

• The requested QoS parameters are then linked to a packetstream.

•End-to-end streams are not established if the required QoSparameters are not available.



IntServ Model (Cont.)

• Provides multiple service levels

• Requests specific kind of service from the network beforesending data

•

Uses RSVP to reserve resourcesfor specified QoS parameters

• Intelligent queuing mechanismsrequired to provide resourcereservation in terms of:

–Guaranteed rate

– Controlled load (low delay,high throughput)



IntServ Functions

IntServ requires several functions on routers andswitches along the path:

• Admission control

• Classification

• Policing

• Queuing

• Scheduling

Benefits and Dra backs of the IntSer



Benefits and Drawbacks of the IntServModel

• 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 mademore scalable when combined with elements of theDiffServ model)



RSVP and the IntServQoS Model



Resource Reservation Protocol

• Is carried in IP—protocol ID 46

• Can use both TCP and UDP port 3455

• Is a signaling protocol and works in conjunction with existingrouting protocols

• Requests QoS parameters from all devices that are betweenthe source and the destination

• Is intended to provide divergent performance requirementsfor multimedia applications:

– Rate-sensitive traffic

– Delay-sensitive traffic



RSVP Operation



RSVP in Action

• RSVP sets up a path through the network with the requested QoS.

• RSVP is used for CAC in Cisco Unified CallManager 5.0.



DiffServ Model



DiffServ Model

• DiffServ (RFC 2474 and RFC 2475) was designed toovercome the limitations of both the best-effort and IntServmodels.

• Network traffic is identified by classes.

•

Network QoS policy enforces differentiated treatment of traffic classes.

• You choose level of service for each traffic class.

Benefits and Drawbacks of the DiffServ



Benefits and Drawbacks of the DiffServModel

• Benefits:

– Highly scalable

– Many levels of quality possible

• Drawbacks:

– No absolute service guarantee

– Complex mechanisms



Summary

• There are three models for providing QoS: best effort,IntServ, and DiffServ.

• Although the best-effort model is highly scalable, it has noprovision for differentiating among types of network trafficand, as a result, does not provide QoS.

• The IntServ model offers absolute QoS guarantees byexplicitly reserving bandwidth by using RSVP. Scalability isachieved in conjunction with elements of the DiffServ model.

• RSVP is not a routing protocol; thus, implementing RSVP inan existing network does not require migration to a newrouting protocol.

• The DiffServ model provides the ability to classify networktraffic and offer many levels of QoS while being highlyscalable.




Identifying Methods for Implementing QoS



Methods for

Implementing QoSPolicy



Methods for Implementing QoS Policy

Method Description

Legacy CLI • CLI

• Configures QoS on interface level

• Time-consuming

MQC • CLI

• Makes configurations modular

• Best way for QoS fine tuning

Cisco AutoQoS • Applies a possible QoS configuration to

the interfaces

• Fastest way to implement QoS

Cisco SDM QoS wizard • Application for simple QoS configurations



Legacy CLI



Legacy CLI

• Uses the CLI via console and Telnet

• Traditional method

• Nonmodular

• Cannot separate traffic classification from policy definitions

• Time-consuming and potentially error-prone task

• Used to augment, fine-tune newer Cisco AutoQoS method



Legacy CLI Usage Guidelines

• Build a traffic policy:

– Identify the traffic pattern.

– Classify the traffic.

– Prioritize the traffic.

– Select a proper QoS mechanism:

• Queuing

• Compression

• Apply the traffic policy to the interface.



Legacy CLI Example

For interactive traffic, CQ and TCP header compression can be used.

interface multilinkip address 10.1.61.1 255.255.255.0

load-interval 30custom-queue-list 1 ppp multilink ppp multilink fragment-delay 10 ppp multilink interleave multilink-group 1ip tcp header-compression iphc-format!queue-list 1 protocol ip 2 tcp 23



Modular QoS CLI



Modular QoS CLI

• A command syntax for configuring QoS policy

• Reduces configuration steps and time

• Configures 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



Modular QoS CLI Components









Class Maps

• “What traffic do we care about?”

• Each class is identified using a class map.

• A traffic class contains three major elements:

– A case-sensitive name

– A series of match commands

– An instruction on how to evaluate the match commands if more than one match command exists in the traffic class

• Class maps can operate in two modes:

–Match all: All conditions have to succeed.

– Match any: At least one condition must succeed.

• The default mode is match all.



Configuring Class Maps

• Enters class-map configuration mode.

• Specifies the matching strategy.

class-map [match-all | match-any] class-map-name

router(config)#

match any

router(config-cmap)#

description description


• Use at least one condition to match packets.

• You should use descriptions in large and complex configurations.

• The description has no operational meaning.

match not match-criteria



ACLs for Traffic Classification

• Standard ACL

access-list access-list-number {permit | deny | remark}

source [ mask ]

router(config)#

access-list access-list-number {permit | deny} protocol

source source-wildcard [operator port] destination

destination-wildcard [operator port] [established] [log]

router(config)#

match access-group access-list-number


•

Extended ACL

• Uses an ACL as a match criterion.



Policy Maps

• “What will be done to this traffic?”

• Defines a traffic policy, which configures the QoS featuresassociated with a traffic class previously identified using aclass map.

• A traffic policy contains three major elements:

– A case-sensitive name

– A traffic class

– The QoS policy associated with that traffic class

• Up to 256 traffic classes can be associated with a singletraffic policy.

• Multiple policy maps can be nested to influence thesequence of QoS actions.



Configuring Policy Maps

• Enters policy-map configuration mode.

• Policy maps are identified by a case-sensitive name.

policy-map policy-map-name

router(config)#

class {class-name | class-default}router(config-pmap)#

class class-name conditionrouter(config-pmap)#

• Enters the per-class policy configuration mode by using the name of apreviously configured class map.

• Use the class-default name to configure the policy for the default class.

• Optionally, you can define a new class map by entering the condition after the name of the new class map.

• Uses the match any strategy.



Service Policy

• “Where will this policy be implemented?”

• Attaches a traffic policy configured with a policy map to aninterface.

• Service policies can be applied to an interface for inbound or outbound packets.



Attaching Service Policies to Interfaces

• Attaches the specified service policy map to the input or output interface

service-policy {input | output} policy-map-name

router(config-if)#

class-map HTTP match protocol http! policy-map PM class HTTP bandwidth 2000class class-default bandwidth 6000

!interface Serial0/0service-policy output PM



MQC Example

• Voice traffic needs priority, low delay, and constantbandwidth.

• Interactive traffic needs bandwidth and low delay.



MQC Example (Cont.)

hostname Office!class-map VoIP match access-group 100class-map Application match access-group 101! policy-map QoS-Policy

class VoIP priority 100class Application bandwidth 25class class-defaultfair-queue

!interface Serial0/0

service-policy output QoS-Policy!access-list 100 permit ip any any precedence 5access-list 100 permit ip any any dscp efaccess-list 101 permit tcp any host 10.1.10.20access-list 101 permit tcp any host 10.1.10.40

Classification

QoS Policy

QoS Policy on Interface

Classification



Basic Verification Commands

• Displays the class maps

show class-map

router#

show policy-maprouter#

show policy-map interface type number router#

• Displays the policy maps

• Displays the applied policy map on the interface



AutoQoS



Cisco AutoQoS

• Automatically discovers applications and providesappropriate QoS treatment

• Automatically generates initial and ongoing QoS policies

• Provides high-level business knobs and multidevice anddomain automation for QoS

• Generates intelligent, automatic alerts and summary reports

• Enables automatic, seamless interoperability among all QoSfeatures and parameters across a network topology—LAN,MAN, and WAN



The Features of Cisco AutoQoS

DiffServFunction

Cisco IOS and CatalystSoftware QoS Feature

Behavior

Classification NBAR DSCP, port Classifies VoIP based on packetattributes or port trust

Marking Class-based marking Sets Layer 2 and Layer 3 attributes

to categorize packets into a class

Congestionmanagement

Percentage-based LLQ,WRR

Provides Expedited Forwardingtreatment to voice and best-efforttreatment to data

Shaping Class-based shaping or FRTS

Shapes to CIR to prevent burst andsmooth traffic to configured rate

Link efficiencymechanism

Header compression Reduces the VoIP bandwidthrequirement

Link efficiencymechanism

Link Fragmentation andInterleaving

Reduces jitter experienced by voicepackets



Cisco AutoQoS Usage Guidelines

• Make sure that:

– CEF is enabled.

– NBAR is enabled.

– Correct bandwidth statement is configured on the

interface.• Finally, enable Cisco AutoQoS on the interface.



Cisco AutoQoS Example

Enable Cisco AutoQoS on relevant devices (such as LAN switches and WANrouters) that need to perform QoS.



Cisco AutoQoS Example (Cont.)

interface Serial1/3ip cef bandwidth 1540ip address 10.10.100.1 255.255.255.0auto qos voip

IP CEF and Bandwidth

AutoQoS for VoIP Traffic Recognized by NBAR



SDM QoS Wizard



Cisco SDM QoS Wizard

• Cisco SDM is an intuitive, web-based device managementtool for easy and reliable deployment and management of Cisco IOS routers.

• Cisco SDM provides wizards for:

– Firewall and NAT

– Intrusion prevention

– IPsec VPNs

– QoS

– Routing

Q S



QoS Features

• Cisco SDM QoS wizard provides:

– QoS policing

– NBAR

– Traffic monitoring

• Supported and preinstalled on Cisco 850, 870, 1800, 2800,and 3800 Cisco Integrated Services Routers

• Supported on devices 830, 1700, 2600 XM, 2800, 3700, 7200VXR, and 7301

G tti St t d ith Ci SDM



Getting Started with Cisco SDM

C t Q S P li



Create QoS Policy

1.

2.

3.

4.

Q S Wi d



QoS Wizard

I t f S l ti



Interface Selection

Q S P li G ti



QoS Policy Generation

S



Summary

S (C t )



Summary (Cont.)

S (C t )



Summary (Cont.)

Summary (Cont )



Summary (Cont.)

Summary (Cont )



Summary (Cont.)

Command Delivery Status



Command Delivery Status

QoS Status



QoS Status

1.

2.

A

B



QoS Implementation

Methods Compared



Summary



Summary

• There are four methods for implementing QoS: legacy CLI,MQC, Cisco AutoQoS, and Cisco SDM QoS wizard.

• CLI QoS configuration can be complex and in many casesrequires learning different syntax for different QoSmechanisms.

• MQC separates the classification of network traffic from thedefinition of the QoS policy.

• Cisco AutoQoS is used to automatically implement a set of QoS policies on a router or a switch.

• Cisco SDM QoS wizard provides a GUI to ease QoSconfiguration.

• MQC is the recommended manual approach to configureQoS. MQC reduces configuration steps and time compared tothe legacy approach.

Module Summary



Module Summary

• The problems that can lead to poor QoS for applications

running on a converged network include lack of bandwidth,excessive delay, jitter, and packet loss.

• To implement QoS on a converged network, follow thisprocess:

– Identify the traffic types and their requirements.

–

Classify the traffic. – Define and implement QoS policies for each traffic class.

• The three QoS models are best effort, IntServ, and DiffServ.

• In the best effort model, no special QoS mechanisms areapplied.

• With IntServ, applications signal their QoS requirements.

• With DiffServ, network devices recognize the traffic classesand provide different QoS levels.

• The four techniques to implement QoS are the legacy CLImethod, MQC, Cisco AutoQoS, and Cisco SDM QoS wizard.



Documents

ONT10S03 QoS Overview