Tài liệu Introduction to Quality of Service pdf

www.cisco.com Econ_0385_02_010.pptKeep All Graphics Inside This Box Class-Based Weighted Fair • Finer granularity and scalability is easier to use Class-Based Weighted Fair Queuing CBWF

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Introduction to Quality of Service

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Keep All Graphics Inside This Box

Objectives

Upon completion of this module, you will be able to perform the following tasks:

• Explain the significance of Quality of Service (QoS)

• Describe new Quality of Service (QoS) features in Cisco IOS 12.1

• Explain which problems QoS solves

The purpose of this module is to quickly survey the new Quality of Service (QoS) features in Cisco IOS 12.1 and to describe the problems they solve

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Topics

QoS overview

New QoS features Quick look at Diff Serv framework

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Why Is QoS So Important?

– Certain business applications

– Voice, SNA traffic

• Can prioritize different groups of users , such as finance, sales, or suppliers

The Cisco IOS QoS features enable networks to control and predictably service a variety of networked applications and traffic types Implementing Cisco IOS QoS

in your network promotes the following:

• Control over resources—You control which resources (bandwidth, equipment, wide-area facilities, and so on) are being used For example, you can limit

bandwidth consumed over a backbone link by File Transfer Protocol (FTP) transfers or give priority to an important database access

• Tailored services—If you are an Internet Service Provider (ISP), the control and visibility provided by QoS enables you to offer carefully tailored grades of service differentiation to your customers

• Coexistence of mission-critical applications

Cisco QoS features make certain of the following:

• That your WAN is used efficiently by mission-critical applications that are

most important to your business.

• That bandwidth and minimum delays required by time-sensitive multimedia and voice applications are available.

• That other applications using the link get their fair service without interfering with mission-critical traffic.

Moreover, in implementing QoS features in your network, you put in place the

foundation for a future fully integrated network

http://cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/qos_c/qcdintro.htm

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Where Do We Use QoS?

Low bandwidth links Managing bandwidth Application service levels

The slide lists some of the places where QoS is being applied today

QoS is important to those using low bandwidth links, to protect voice or

mission-critical traffic on those links, especially in the event of congestion Control and protection of voice and mission-critical traffic can also be important to the

customer over higher speed links

Sometimes QoS is desired because IP networking is replacing ATM, and QoS is something valuable that ATM has to offer, and the customer wishes to also have comparable capabilities with IP networking

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on the same infrastructure

• Is not a magic solution to every problem

QoS refers to the ability of a network to provide better service to selected network traffic over various underlying technologies including Frame Relay, ATM,

Ethernet and 802.1 networks, Synchronous Optical Network (SONET), and

IP-routed networks In particular, QoS features provide better and more predictable network service by:

• Supporting dedicated bandwidth

• Reducing loss

• Avoiding and managing network congestion

• Shaping network traffic

• Setting traffic priorities across the network

The slide also reminds us that QoS is not necessarily a solution to every problem With low bandwidth links, there comes a point where you just simply need more bandwidth, and nothing else will really work If your network is poorly designed, it may have high latency, many hops, or be unstable — and QoS is not going to fix that or work in spite of that Think of QoS as taking a well-tuned network and

making it work even better, not as a quick fix to all sorts of problems

Applications can sometimes be changed to vastly improve performance On the other hand, commercial applications generally cannot be changed, in which case

we do what we can to improve things on the network side Some performance

issues are server sizing or tuning issues QoS cannot do much in such

circumstances.

http://cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/qos_c/qcdintro.htm

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Applying QoS

Mobile User Home User

Hunt Group

Network Management

FR, xDSL

Small Office

Customer Premises Equipment

• Queuing / Scheduling

• Congestion Avoidance

The slide shows a large network, with access, distribution, and core layers This could be a view of a large Enterprise network or a view of a Service Provider

network.

This graphic introduces some of the basic terminology and concepts of QoS in the next slides.

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Topics

QoS overview New QoS features

• New features covered in this section’s modules

• Other related new features

Quick look at Diff Serv framework

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Class-Based Weighted Fair

• Finer granularity and scalability

is easier to use

Class-Based Weighted Fair Queuing (CBWFQ) allows the user to define traffic classes based on customer-defined match criteria such as access control lists (ACLs), input interfaces, protocol, and QoS label For example, a class might consist of a team working on a certain project or a class can

be created for the important mission-critical applications, for example, enterprise resources

planning (ERP) When the traffic classes have been defined, they can be assigned a bandwidth, queue limit, or drop policy such as Weighted Random Early Detection (WRED)

• Bandwidth allocation —CBWFQ allows you to specify the exact amount of bandwidth to be allocated for a specific class of traffic Accounting for available bandwidth on the interface, you can configure up to 64 classes

• Finer granularity and scalability—CBWFQ allows you total flexibility to define a class based

on ACLs and protocols or input interfaces, thereby providing finer granularity

• Support in the modular command-line interface (CLI) framework—CBWFQ is supported in the new modular CLI framework, which is a new, template-based CLI This new modular CLI

eases the configuration of CBWFQ by introducing the class -map, service-map and policy-map approach This “virtual template” eases the constant configuration of policies per interface, and reduces the configuration by allowing the service maps to be assigned to each interface –

without reconfiguring the match criteria/ACLs and policies

• WRED supported as a drop policy—CBWFQ supports WRED as a drop policy per class, thus allowing you to provide differentiated service within a class

This feature is supported on all platforms that WFQ is supported on, in other words, the Cisco 7200,

4700, 4500, 3600, and 2600 series, and so on

First appearance in a Cisco IOS software T release: 12.0(5)T

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/ 120newft/120t/120t5/cbwfq.htm

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IP Real-Time Transport Protocol (RTP) Priority

(WFQ), or Class-Based Weighted Fair Queuing (CBWFQ), on the same outgoing

interface When used in conjunction with CBWFQ, the “ip rtp prio rity” command provides strict priority to Voice Additionally, CBWFQ can also be used to set up

classes (for example, gold/silver/bronze) for other types of traffic (for example, SNA

or PeopleSoft) that require dedicated bandwidth and better servicing than

“best-effort”, but not as strict as Priority Queuing CBWFQ can also support flow-based WFQ within the “Default CBWFQ Class”, if so configured.

IP RTP Priority extends, and will obsolete, the functionality offered by the feature IP RTP Reserve By specifying a range of UDP RTP ports, the user ensures that voice traffic is guaranteed strict priority service over any other queues or classes using the same output interface Strict priority means that if packets exist in the priority queue, they are de-queued and sent first—before packets in other queues are dequeued.

Because voice packets are small in size and the interface may have larger data packets requiring servicing simultaneously, the Link Fragmentation and Interleaving (LFI) feature, also known as Multi- link PPP Fragmentation, is recommended to be

configured for lower-speed interfaces LFI will fragment the larger data packets (for example, FTP at 1500 bytes) so the smaller voice packets can be interleaved among the data fragments, thus ensuring that voice traffic is serviced with minimal delay.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t5/iprtp.htm

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IP Real-Time Transport Protocol (RTP) Priority

• Higher quality Voice—reduced latency for VoIP traffic: The strict priority

queuing scheme allows delay-sensitive data such as voice to be de-queued and transmitted first – before packets in other queues are de-queued Delay-

sensitive data is given preferential treatment over other traffic

• Scalable QoS for voice admission control—IP RTP Priority closely polices use

of bandwidth for the priority queue, ensuring the allocated amount is not

exceeded In fact, IP RTP Priority polices the flow every second IP RTP

Priority prohibits the transmission of additional packets once the allocated

bandwidth is consumed If it discovers that the configured amount of

bandwidth is exceeded, IP RTP Priority drops packets

• Higher quality voice over slow speed links—IP RTP Priority is the only

recommended solution for VoIP at low speeds links (for example, 56/64 Kbps)

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Low Latency Queuing (LLQ)

Capabilities:

Queuing (CBWFQ)

to PQ-WFQ), now called LLQBenefits:

ATM Virtual Circuits (VCs)

Capability:

The Low Latency Queuing (LLQ) feature brings strict priority queuing to Class-Based Weighted Fair Queuing (CBWFQ) Strict priority queuing allows delay-sensitive data such as voice to be de-queued and sent first, before packets in other queues are de-queued, giving delay-sensitive data preferential treatment over other traffic

Without LLQ, CBWFQ provides weighted fair queuing (WFQ) based on defined classes with no strict priority queue available for real-time traffic CBWFQ allows you to define traffic classes and then assign characteristics to that class For example, you can desig nate the minimum bandwidth delivered

to the class during congestion

Benefits:

• Provides strict priority service on ATM VCs and serial interfaces—The strict priority queuing scheme allows delay-sensitive data such as voice to be de-queued and sent first – that is, before packets in other queues are de-queued Delay-sensitive data is given preferential treatment over other traffic This feature provides strict priority queuing on ATM Virtual Circuits (VCs); the IP RTP Priority feature only allows priority queuing on interfaces

• Not limited to UDP port numbers—Because you can configure the priority status for a class withinCBWFQ, you are no longer limited to UDP port numbers to stipulate priority flows Instead, all of the valid match criteria used to specify traffic for a class now apply to priority traffic

• Admission control—By configuring the maximum amount of bandwidth allocated for packets belonging to a class, you can avoid starving non-priority traffic

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/ 120newft/120t/120t7/pqcbwfq.htm

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Flow Weighted Random Early

flow exceeds share of output interface buffer

Benefits:

monopolize all the buffer resources

• Adaptive flows get fair share of resources

This feature provides a mechanism to penalize the flows that do not respond to Weighted Random Early Detection (WRED) drops This feature is provided as an extension to the existing WRED functionality and can be turned on after WRED is turned on

Flow-WRED ensures that no single flow can monopolize all the buffer resources at the output interface queue (With just WRED, this can occur in the presence of

traffic sources that do not back off during congestion.) Flow-WRED maintains

minimal information about the buffer occupancy per flow Whenever a flow

exceeds its share of the output interface buffer resource, the packets of the flow are penalized because the probability of their drop (by WRED) is increased

With FRED, adaptive flows get a fair share of the resources.

Post-implementation experience suggests that FRED can be a bit strict with adaptive flows, especially voice The current suggestion is to use RED with

non-CBWFQ

This feature is supported on all platforms that WRED is supported on, that is, the Cisco 7200, 4700, 4500, 2600 series, and so on It is not supported on the VIP-

based platforms or on platforms that have distributed queuing functionality

First appearance in a Cisco IOS software T release: 12.0(3)T.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t3/flowwred.htm

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Topics

QoS overview New QoS features

• New features covered in this section’s modules

• Other related new features

Quick look at Diff Serv framework

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Response Time Reporter

• User Datagram Protocol (UDP) response time operation

• TCP connect time operation

• Type-of-service support for the Internet Control Message Protocol (ICMP) operations

• Loose source routing (LSR) in the ICMP path operation

The Service Assurance Agent (SAA) is both an enhancement to and a new name for the Response Time Reporter (RTR) feature that was introduced in Cisco IOS Release 11.2 The feature allows you to monitor network performance by measuring key Service Level Agreement (SLA) metrics such as response time, network resources, availability, jitter, connect time, packet loss, and application performance

With Cisco IOS Release 12.0(5)T, the SA Agent provides new capabilities that enable you to:

• Monitor the Domain Name Server, DHCP Server, and DLSw peer stack and tunnel performance

• Specify thresholds that can be used to trigger additional collection of time delay statistics

• Monitor network one-way delay variance (jitter) and packet loss

• Monitor web server response time

Platforms/Considerations: These features are available on all platforms running Cisco IOS 12.0(3)T First

Tiêu đề	Introduction to Quality of Service
Trường học	Cisco Systems, Inc.
Chuyên ngành	Quality of Service
Thể loại	Module
Năm xuất bản	2000
Thành phố	San Jose

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