1 © 2001, Cisco Systems, Inc. All rights reserved. TAC-TOI-01 Quality of Service (QoS) An Overview

1© 2001, Cisco Systems, Inc. All rights reserved.© 2001, Cisco Systems, Inc. All rights reserved.© 2001, Cisco Systems, Inc. All rights reserved.TAC-TOI-01

Quality of Service (QoS)An Overview

© 2001, Cisco Systems, Inc. All rights reserved. 2© 2001, Cisco Systems, Inc. All rights reserved. 2© 2001, Cisco Systems, Inc. All rights reserved. 2TAC-TOI-01

Consistent, Predictable Performance

Voice - Video - Data

What Is Quality of Service?

The ability of the network to provide better or “special” service

to users/applications.


Traffic Is Grouped into SLAsTraffic Is Grouped into SLAs

Not All Traffic Is Equal

VoiceVoice FTPFTP ERP andMission-Critical

ERP andMission-Critical

BandwidthBandwidth Low toModerateLow to

ModerateModerateto High

Moderateto High LowLow

Random Drop SensitiveRandom Drop Sensitive LowLow HighHigh ModerateTo High

ModerateTo High

Delay SensitiveDelay Sensitive HighHigh LowLow Low toModerateLow to

Moderate

Jitter SensitiveJitter Sensitive HighHigh LowLow ModerateModerate


Step 1: Identify Traffic and its Requirements

• Network auditWhat is running and when?

• Business auditHow important is it for business?

• Application auditWhat are it’s requirements from network?

• Service levels required


Differentiated IP Services

Guaranteed: Latency and Delivery

Best Effort Delivery

Guaranteed Delivery

Voice

E-mail, WebBrowsing

E-Commerce

Application Traffic

Platinum Class Low Latency

Step 2: Divide the Traffic into Classes and Color It

Silver

Bronze

Gold

VoiceVoice

TrafficClassification

TrafficClassification


What Is a Class?

• Single user

MAC address, IP address…

• Department, customer

Sub net, interface…

• Application

Port numbers, URL…


What Is Coloring? IP Precedence & DiffServ

• Use ToS field to signal business QoS policies

• Differentiate network services Differentiate network services across any media or topologyacross any media or topology

Len ID Offset TTL Proto FCS IP-SA IP-DA DataVersion Length

ToS 1 Byte

ToS 1 Byte

IP Packet

Type of Service (ToS)

IP Precedence

IP Differentiated Service

Data, Voice, Video


Coloring at Layer 2 and Layer 3

PREAM.PREAM. SFDSFD DADA SASATAG

4 BytesTAG

4 BytesPTPT DATADATA FCSFCS

Three Bits Used for CoS(User Priority)

VersionLengthVersionLength

ToS1 ByteToS

1 Byte LenLen

Standard IPV4: Bits 0-2 Called IP Precedence (Three MSB)(DiffServ Uses Six ToS bits…: Bits 0-5, with Two Reserved)

IDID offsetoffset TTLTTL ProtoProto FCSFCS IP-SAIP-SA IP-DAIP-DA DataData

Layer 2 802.1Q/p

Layer 3IPv4


Separate “Conform” and “Exceed” Actions

Coloring Engine

Color the Packets

• Color closer to the application

• Set the DSCP (DiffServ Code Point) at the edge of network

• Avoid host application-based coloring

VolPVolP HTTP FTPFTP

Gold ClassBronze Class

Platinum ClassVolPVolPHTTPFTPFTP

VolPVolP HTTPHTTP FTPFTP


!! Detour !!Differentiated Services

(DiffServ)The Formula for Scalable QoS


The IETF DiffServ Model(RFC-2474,2475,2597,2598)

• The idea is VERY simple—Offer service levels for packets: Gold, Silver, Bronze, etc…

• What is a service?

“Some significant characteristics of packet transmission in one direction across a set of one or more paths within a network (e.g.: Bandwidth,Latency,etc..)”...RFC-2475

• Packets of a particular service are referred to as packets of a particular “class”

• Meaningful services constructed usingPer-Hop Behaviors (PHB)


The DiffServ Traffic Conditioner Block (TCB)

• Classifier: Identifies packets for assignment to Classes

• Meter: Checks compliance to traffic parameters (Token Bucket) and passes result to Marker and Shaper/Dropper to trigger particular action for in/out-of-profile packets

• Marker: Writes/rewrites the DSCP value

• Shaper: Delays some packets for them to be compliant with the profile

• Dropper: Drops packets that exceed the profile (Bc or Be)


The DiffServ Recipe for Constructing Services

• At the Ingress Network-Edge: (Traffic Conditioning Block—TCB)

1) Classify the packets into ‘Classes’

2) Mark (Color) the packets for purposesof classification in the core

3) Optionally meter a class

4) If performing (3), police or shape the class (at network ingress and/or egress)

5) Queue and/or drop packets toward the core

• In the network core: (implementing the PHB)

6) Queue and/or drop packets


How DiffServ WorksStep 1: Classifying Packets into Classes

• The most popular techniques: Incoming/outgoing interface

All/any IP traffic

Standard or extended access control list

IP RTP ports (real-time traffic)

Source/destination MAC address

DSCP or IP precedence value (If trusted and marked appropriately)

MPLS EXP (experimental bits) (If trusted and marked appropriately)

Network-Based Application Recognition (NBAR)

• E.g.: all VoIP (RTP) packets between UDP ports 16384 and 16484 belong to the “Premium Class”


VersionLengthVersionLength

ToS1 ByteToS

1 ByteLenLen IDID offsetoffset TTLTTL ProtoProto FCSFCS IP-SAIP-SA IP-DAIP-DA DataData

Packets are Marked @ the Edge, for Purposes of Classification in the CorePackets are Marked @ the Edge, for Purposes of Classification in the Core

The IPv4 Header and the Type of Service (ToS) ByteThe IPv4 Header and the Type of Service (ToS) Byte

The Hook for Scalable IPv4 Packet-Marking and Classification


Just Remember “DSCP”Just Remember “DSCP”

IPv4 ToS vs. DS-Field(The ToS Byte Is Re-Defined)


How DiffServ WorksStep 2: Marking Packets of the Defined Classes

• Remember that marking can also be in Layer2!

• The most popular techniques:

IP DSCP—Layer 3

MPLS EXP bits—Layer 2.5

ATM CLP-bit—Layer 2

Frame-relay DE-bit—Layer 2

IEEE 802.1Q/p user-priority bits—Layer 2

• E.g.: The Premium Class (VoIP) packets get marked with IP DSCP—‘101110’


p

Tokens

BOverflow

Tokens

PacketsArriving Conform

Exceed

B—Burst Size

p—Token Arrival Rate

How DiffServ Works Optional Step 3: Metering (The Token Bucket)

• Tokens keep pouring into the bucket at apre-defined average-rate

• If Token available, can transmit a packet• Used by policer and shaper• Explained in detail: Next talk

and Sess#: IPS-230


Tra

ffic

Time

Traffic Rate

Tra

ffic

Time

Traffic Rate

Policing

Tra

ffic

Time

Traffic RateTraffic Rate

Tra

ffic

Time

Shaping

How DiffServ Works Step 4: MeteringPolicing (Dropping)/Shaping


• Policing is used not only to drop out-of-profile packets, but also to re-mark them, and indicate to dropping mechanisms downstream that they should be dropped ahead of the in-profile packets!

Direction of Traffic FlowDirection of Traffic Flow

WebWeb

ERPERP

OtherOther

On Policing…


128 Kbps

Branch Office

Bottleneck

FR/ATM WANT1/E1

CentralSite Shaping!

Direction of Traffic FlowDirection of Traffic Flow

On Shaping…

• Shaping is commonly used where speed-mismatches exist (e.g.: Going from a HQ site with a T1/E1 connection to a Frame-Relay Network, down to a remote site with a 128Kbps connection)

• Shaping involves buffering, and various queuing/scheduling techniques may be used when the shaped rate is reached!


How DiffServ WorksSteps 5&6: PHB by Queuing and/ Dropping

• Queuing refers to: (congestion management)

Buffering packets when interface is congested

Scheduling packets out of the buffer onto the link (Algorithms: FIFO, CBQ, WRR, etc…)

Outbound PacketsOutbound PacketsSchedulerScheduler

Packets inVarious Queues

Packets inVarious Queues


How DiffServ WorksSteps 5&6: PHB by Queuing and/ Dropping…(Cont.)

• Dropping can happen:At the edge when policing

In the edge/core when buffers are exhausted and signalcongestion to the end-nodes for back-off (Tail Drop)

In the edge/core to do congestion avoidance and signalcongestion to the end-nodes that can back-off


The Various PHBs(Using Queuing and Dropping)

• Expedited Forwarding (EF): RFC2598Very low delay, low jitter, assured bandwidth

Compare to express mail, with overnight delivery

• Assured Forwarding (AF): RFC2597Assured amount of bandwidth

IETF has defined four AF classes

Compare to registered mail—very safe, and assured

• Class Selector: Backwards compatible withIP precedence for Forwarding Probability (FP)

FP(Precedence (x+1)) FP(Precedence (x))

Compare to FP(Express Mail) FP(Priority Mail)

• Default: Best effort ~ normal mail


AF Class 1: 001dd0

AF Class 2: 010dd0

AF Class 3: 011dd0

AF Class 4: 100dd0

E.g. AF12 = Class 1, Drop 2,thus “001100”

E.g. AF12 = Class 1, Drop 2,thus “001100”

dd = drop preference

The DiffServ AF PHB(4 Classes, 3 Drop Preferences)

• Four independently forwarded/queued classes

• Within each AF class, 3 levels of drop preference

Used to increase the probability of dropping, especially when traffic exceeds configured rate/CIR (Out-of-Profile)


Cisco IOS DiffServ

• Cisco IOS 12.1(5)T,12.2(1)M and later versions are fully compliant with all the core DiffServ RFCs (RFCs: 2474,2475,2597,2598)

• Compliant platforms*:

C26xx, C36xx, C72xx, C75xx

Other platforms have most of the pieces

Full compliancy in the near future…

ARM your network with DiffServ!


Back on Track


Step 3: Define Policies for the Classes

• Set minimum bandwidth guaranteeThis is the minimum guaranteed bandwidth to the class all the time

• Set maximum bandwidth limits This is the maximum amount of bandwidth class will ever get

• Assign priorities to each classClass is treated in a strict priority manner

• Manage congestion


Policy required:

Make sure my platinum class gets a priority treatment and gold class gets

a minimum bandwidth guarantee

Minimum Bandwidth Guarantee/ Priority for a Class

“

”


40%

25%

10%

Gold

Silver

Bronze

Step 1:Define Buffering

Step 2:Define Bandwidth

Guaranteed: Latency, DeliveryGuaranteed: Latency, Delivery

Guaranteed: DeliveryGuaranteed: Delivery

Best EffortBest Effort

Scheduling

• Weights guarantee minimum bandwidth

• Buffering controls latency

• Unused capacity is shared amongst the other classes

• Each queue can be separately configured for QoS

• Benefits:Maximize transport of paying trafficNo loss of service class guaranteesNo wasted bandwidth as with PVCs


WFQWFQ

Interface

33 3333 33

44 33 22 11 11VV

44 4444 44

PQPQWANCircuit

ExhaustiveQueuing

22 22

11 11VVVV

PQ—Voice

WFQ—Data

WFQ—Data

WFQ—Data

Low Latency Queuing


VoiceVoice 1500 Bytes of Data1500 Bytes of Data VoiceVoice

~214 ms Serialization Delay

10 Mbps Ethernet 10 Mbps Ethernet

Voice Packet60 Bytes

Every 20 ms


Every >214 ms


Every >214 ms

Large Packets “Freeze Out” Voice

• Large packets can cause playback buffer underrun, resulting in slight voice degradation

• Jitter or playback buffer can accommodate some delay/delay variation

VoiceVoice 1500 Bytes of Data1500 Bytes of Data VoiceVoice VoiceVoice 1500 Bytes of Data1500 Bytes of Data VoiceVoice

56 Kb WAN


VoiceVoice 1500 Bytes of Data1500 Bytes of Data VoiceVoice

~214 ms Serialization Delay

10 Mbps Ethernet 10 Mbps Ethernet


Every 20 ms


Every >214 ms


Every >214 ms

Large Packets “Freeze Out” Voice

• Large packets can cause playback buffer underrun, resulting in slight voice degradation

• Jitter or playback buffer can accommodate some delay/delay variation

VoiceVoice 1500 Bytes of Data1500 Bytes of Data VoiceVoice VoiceVoice 1500 Bytes of Data1500 Bytes of Data VoiceVoice

56 Kb WAN


10 ms/Time for 1 Byte at BW =

Fragment Size56kbps56kbps 70

Bytes70

Bytes

FragSizeFragSize

64kbps64kbps80

Bytes80

Bytes

128kbps128kbps 160Bytes160

Bytes

256kbps256kbps

512kbps512kbps

768kbps768kbps

1536kbs1536kbs

320Bytes320

Bytes

640Bytes640

Bytes

1000Bytes1000Bytes

2000Bytes2000BytesXX

LinkSpeedLink

Speed

Fragmentation Not Needed ifMax Frame Size Is 1500 Bytes

Fragmentation Recommendations Assuming 10 ms Max Blocking Delay “Rules of Thumb”


Link Fragmentation and Interleaving (LFI)

• Fragment large packets and interleave with voice packets over WAN links

• Reassemble at other end of link

• Reduces voice delay and jitter

FragmentFragment


Policy required:

Make sure my bronze traffic does not get more than x kbps of

bandwidth at any time

Maximum Rate Limiting

“

”


Shaping

Tra

ffic

Time

Traffic Rate

Tra

ffic

Time

Traffic Rate

Policing

Tra

ffic

Time

Tra

ffic

Time

Traffic Rate

Traffic Policing vs. Shaping

Traffic Rate


WebWeb

ERP/SAPERP/SAP

PointcastPointcast

Trash

Policer


128 Kbps

Branch Office

Bottleneck

Internet Service Provider (ISP) Cloud

T1

CentralSiteI Need to Reduce

the Pace at Which I Send Packets

I Need to Reduce the Pace at Which I

Send Packets

Shaper

• Reduces outbound traffic flow to avoid congestion (via buffering)

• Eliminates bottlenecks in topologies with data rate mismatch

• Provides mechanism to partition interfaces to match far-end requirements


Policy required:

Make sure my bronze or silver traffic gets dropped when there is

congestion and not gold traffic

Congestion Avoidance

“

”


GoldHigh

PrecedenceGuarantee Mission-Critical Apps, e.g.,

ERP, Customer Care, Unified Messaging

SilverMedium

PrecedenceE-Mail, Interactive

Video, Web

BronzeLow

PrecedenceE-Fax, FTP

Weighted Random Early Detection


• Packets are:• Colored (DSCP set) at ingress• Classified and potentially discarded by WRED (congestion management)

• Assigned to the appropriate outgoing queue

• Scheduled for transmission by CBWFQ

IP TrafficPolicer/Marker

DSCP Written

QueuesW-REDCBWFQ or WFQ

Scheduler

LLQ IF

Putting it All Together

VolPVolP HTTP FTPFTPVolP HTTP FTP


PATH

RESV

Policy Server Response:“Admit the Call and Use the

DiffServ Code Point X for Data Flow”

Packet Classified toCode Point X on Client

or Router/Switch

PATH

RESV

PATH

RESV

Directory Policy Server

Policy

RSVP (Quantative) Is Used for the Control Path Flow; Data Path Uses an Aggregate as Identified by the DSCP;

RSVP Is Used to Signal the Data Path Aggregate

RSVP (Quantative) Is Used for the Control Path Flow; Data Path Uses an Aggregate as Identified by the DSCP;

RSVP Is Used to Signal the Data Path Aggregate


XMLXML

XMLXML

XMLXML

Complete QoS Management

CONFIGURECONFIGURE TRENDINGTRENDING MONITORINGMONITORING

De

vic

eD

ev

ice

Ne

two

rk W

ide

Ne

two

rk W

ide

QPM

SLAM

IPM

QDM QDM


Cisco IOS IP Network Services Quality of Service

Platforms

Cisco IP Fabric

Qo

S

Se

cu

rity

Vo

ice

Vid

eo

Mu

ltica

st

VP

N

SN

A E

vo

lutio

n

Lo

ad

Ba

lan

cin

g

Ca

ch

ing

Ad

dre

ss

Mg

mt

…

Internet Application Technologies Man

agem

ent

Po

licyD

irectory

Quality of Service•Class-based Marking•Class-based Shaping•QoS for 1750 Platform•RSVP Support for LLQ•Express Compressed Resource Transport Protocol and TCP Header Compression (CRTP)•Common Open Policy Service for Resource Reservation Protocol (COPS for RSVP)•DOCSIS 1.0+ Quality of Service Enhancements•DOCSIS 1.0+ features for uBR924

•Introduced in Release 12.1T•Introduced in Release 12.1

• IP QoS to ATM CoS integration • CEF-Switched Compressed RTP• Class-Based Weighted Fair Queuing (CBWFQ)• Low Latency Priority Queue with CBWFQ• IP RTP Priority for MLPPP• Frame Relay Fragmentation (FRF.12)


For More Information

http://www.cisco.com/warp/public/732/http://www.cisco.com/warp/public/732/Tech/

http://www.cisco.com/warp/public/732/Tech/quality.shtml

Overview: Network-Based Application Recognition

http://wwwin.cisco.com/cmc/cc/so/neso/ienesv/cxne/nbar_ov.htm


Direction of Data-FlowDirection of Data-Flow

100Mbps100Mbps

WANWAN2Mbps2Mbps

Why QoS??Congestion Scenario #1—Speed Mismatch

• The #1 Reason for Congestion!

• Possibly Persistent when going from LAN to WAN

• Usually Transient when going from LAN to LAN!

1000Mbps1000Mbps 100Mbps100Mbps


Direction of Data-FlowDirection of Data-Flow

Choke Point

Choke Points

Why QoS??Congestion Scenario #2—Aggregation

• Transient Congestion fairly typical!

HQ Hubi

Remotej

2Mbps2Mbps 512Kbps512Kbps

N*56KbpsN*56Kbps

FR/ATMFR/ATM

1000Mbps1000Mbps1000Mbps1000Mbps

S1 S2


STM-64/OC-192cSTM-64/OC-192c

Core1Core1 Core2Core2

STM-16/OC-48cSTM-16/OC-48c

Net-1Net-1

Net-2Net-2

Net-nNet-n

Why QoS?? Congestion Scenario #3—Confluence

• Always need mechanisms to provide guarantees!

• Transient Congestion occurs!

Documents

1 © 2001, Cisco Systems, Inc. All rights reserved. TAC-TOI-01 Quality of Service (QoS) An Overview