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1Presentation_ID © 1999, Cisco Systems, Inc.

IP QoS Basics

Peter Tomsu

Senior Consultant Cisco Systems EMEA

[email protected]

2Presentation_ID © 1999, Cisco Systems, Inc. 2Presentation_ID © 1999, Cisco Systems, Inc. www.cisco.com

IP QoS

3oebb_update_062k © 1999, Cisco Systems, Inc. www.cisco.com

QoS—Optimizing Throughput

30 Kbps

300 Kbps

Bursty applications contending for bandwidth reduce collective throughputbetter throughput neededWhat can we do to improve things?


Internet

Classification and marking of packets at the edge of the network makes the packets accessible to QoS handling within the network

Network Management

Classifying and Marking


Internet

Optimized queueing and forwarding in the core of the network (PHB – Per Hop Behavior) allows for fast efficient delivery

Optimized Forwarding


Architecture for Differentiated Services

RFC 2475RFC 2475An Architecture for An Architecture for

Differentiated ServicesDifferentiated ServicesDec 98Dec 98

• defines an architecture for implementing scalable service differentiation in the Internet !


DSCP

• DSCP : Differentiated Service Code Point = 6 bits• CU: Currently Unused = 2 bits (lined up for ECN)• DSCP is the field identifying what treatment the

packet should receive

DSCPDSCP CUCU

DS fieldDS field


Diff-Serv Traffic Conditioner

• Classifierselects a pkt in a traffic stream based on the content of some portion of the pkt header

• Meterchecks compliance to traffic parameters (eg Token Bucket) and passes result to marker and shaper/dropper to trigger particular action for in/out-of-profile packets

• MarkerWrites/rewrites DSCP

• Shaperdelay some pkts for them to be compliant with the profile

Pkts Classifier

Meter

Marker Shaper/ Dropper

Shaped

Dropped


Per-Hop Behavior

• Per Hop Behavior (PHB) description of the externally observable forwarding behavior of a DS node applied to a the set of packets with the same DSCP

PHB may be defined in terms of DS nodes resources priority relative to other PHBs

observable traffic characteristics (delay, loss, …)

• PHBs are defined as “black box”does NOT mandate particular implementation mechanisms !

Different boxes implement PHBs in different ways which are optimised for each platform

As long as it complies with “black box” spec, this is perfectly fine


EF PHB Definition

• RFC 2598 Expedited Forwarding PHB, June 99• EF PHB can be used to build a low loss, low latency, low

jitter, assured bandwidth, end-to-end service – targets VoIP, Virtual Leased Lines– Assured traffic sees no (or very small) queues/delay– Constraint: Requires bounding rates such that, at every transit node, the aggregate’s max arrival rate is less than the aggregate min departure rate

• An example of how EF can be implemented is a PQ (with rate limit).

• Recommended DSCP=101110


AF PHB Group Definition

• RFC2597, Assured Forwarding PHB Group, June 99

• Assured Forwarding (AF) PHB Group is meant to offer different levels of forwardindifferent levels of forwardingg assurances for IP packetsassurances for IP packets received from a customer DS domain

• Olympic Service (Gold, Silver, Bronze) gold (C1) >= silver (C2) >= bronze (C3)

• No quantifiable timing requirements! delay or delay variation


AF PHB Group Definition

• Currently definedCurrently defined4 independentlyindependently forwarded AF classes (ie 4 “queues” and 4 virtual networks with independent capacity management) Within each AF class, 3 levels of drop precedenceWithin each AF class, RED-like buffer mgt

• DS node should implement all 4 general AF classes• DS node must allocate a configurable minimum amount of forwarding resources to each

implemented AF class

AF Class 1: 001dd0

AF Class 2: 010dd0

AF Class 3: 011dd0

AF Class 4: 100dd0

dd= drop precedence

Recommended DSCP:


Cisco’s Diff-Serv Implementation

ToS - Pre-Diff-Serv implementation (IP Precedence)not RFC compliant

DS-byte encoding (RFC2474)

Diff-Serv Architecture (RFC 2475)Default ForwardingClass Selectors

Expedited ForwardingAssured Forwarding

Data

IP Precedence

Type of Service (ToS)

Diff-Serv Code Point (DSCP)

Data, Voice, Video


Diff-Serv Functional Blocks

Diff-Serv Functional BlocksClassifier Conditioner Forwarding PHB

MeteringDroppingMarkingShapingAccounting

SchedulingDiscard

ACLQPPB

CARTS

Netflow

CEF CBWFQPQ

WRED

Implementation Features


IP Precedence Setting Techniques

MQC – Modular QoS CLI (12.0(5)T)Policy-Based Routing

Fast-switched since Release 11.3QoS Policy Propagation with BGP (QPPB) Committed Access Rate (CAR)

Inbound / outboundDial peers (Voice over X)


What Is Modular QoS CLI (MQC)?

• Modular QoS CLI (MQC):Is how you configure QoS policySeparates the definition of classes from the application of QoS mechanisms

• MQC is template-based:Reduces configurationConfigure policy, not “raw” per-interface commands


QoS Policy Propagation via BGP

Service Provider or Large Enterprise

Network

Advertises route, community attribute=X

Advertises route, community attribute=Y

Community attributeused to set

precedence/DSCPfor return traffic


Committed Access Rate (CAR)

• Two functions

Packet Classification Packet Classification — sort a subset of traffic matching some complex criteria

Traffic Conditioning Traffic Conditioning rate measurement, rate limiting, packet marking (IP Precedence rewrite)


Drop

Drop

Per Application CARPer Application CAR

MultimediaMultimedia

Mission-CriticalMission-Critical

Recolor

Recolor

CAR—Policy Examples


Car Overview

TrafficTrafficMatchingMatching

SpecificationSpecification

NextPolicy

ActionActionPolicyPolicy

TrafficTrafficMeasurementMeasurement

InstrumentationInstrumentation


CAR—Traffic Matching Specification

• Identify packets of interest for packet classification or rate limiting or both

• Matching specification1)1) All traffic

2)2) IP precedence

3)3) MAC address

4)4) QoS group

5)5) IP access list—Standard and extended (slower)


Token Bucket

pp

Tokens

BBOverflowTokens

PacketsArriving Conform

Exceed

BB—Burst Sizepp—Token Arrival Rate


Extended Burst

Exceed %

100

BucketDepth

ExtendedBurst

NormalBurst


CAR

Ingress RouterIngress RouterPacket ClassificationRate Limiting Committed Rate Burst RED-like Managed Drop

Egress RouterEgress RouterPacket Classification(Reset Precedence Bits)Rate Limiting Committed Rate Burst RED-like Managed Drop

L3 CAR L3 CAR

[email protected]’98 25© 1998, Cisco Systems, Inc.


Standard Premium

Weighted Random Early Detection

• Upon congestion, packets from lower precedence are selectively discarded first

• Minimize the congestion impact on higher precedence services

anim


Weighted RED

Pack

et D

rop

Prob

abili

ty

Queue Length

“Slope” is adjustable

Queue Max

Pack

et D

rop

Prob

abili

ty

Queue Length Queue Max

Pack

et D

rop

Prob

abili

ty

Queue Length

Standard Service

Queue Max

WithoutRED

WithRED

WithWRED

Premium Service

Std. Min. Prem. Min.


Weighted Fair Queuing

• Discriminates between CoS• Aggregate guaranteed bandwidth

allocated to each CoS• Excess bandwidth shared

by all CoS’s (based on weight)• High scalability/performance

COS 1 COS 2 COS 3 COS 4

Gold

Gets at least 40% of

bandwidth

Standard

Gets at least10% of

bandwidth

Silver

Gets at least30% of

bandwidth

Bronze

Gets at least20% of

bandwidth


Class-Based WFQ—QoS Guarantees and Bandwidth Efficiency

•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

40%

25%

10%

Gold

Silver

BronzeStep 1:Define Buffering

Step 2:Define Bandwidth

Guaranteed: Latency, DeliveryGuaranteed: DeliveryBest Effort


PQ-WFQ (IP RTP Priority)

WFQ

Interface

3 33 3

2 24 3 2 1 1

VV

4 44 4

PQWAN

Circuit

ExhaustiveQueuing

WFQ

DLCI

3 33 3

2 L

PQ - voice

WFQ - Data

4 44 4

PQ WAN Circuit

WFQ - Data

WFQ - Data

InterfaceHigh

Low

LMI 1 1VV

4 3 2 4 3 L 1V

1V

L

1 1VV

2

1 1VV

PQ - voice

WFQ - Data

WFQ - Data

WFQ - Data

Leas

ed L

ines

Fram

e R

elay


Low Latency Queuing (LLQ)

CBWFQ does not effectively handle real-time traffic well on its ownLLQ adds a priority queue to CBWFQ specifically for priority traffic only Supports VoIP on serial and ATM PVCs onlyVoIP over Frame Relay is not supported

VoIPoFR as of 12.1(2)T


Difference Between IP RTP Priority and LLQ?

• IP RTP PriorityDoes not need CBWFQ, but can be combined with itConfigured on interfaceWhen using voice ports, gives priority to even ports (actual call) within specified range only

• LLQConfigured as part of CBWFQ priority mapsWhen using voice ports, gives priority to both odd (RTCP control) and even (actual call) ports

• Note: the initial call control is TCP traffic


Transmit Queue

Output Line

Traffic Destined

for Interface

Classification by:Extended Access List Functionality

“Leaky Bucket” Shaping

Configured Queuing (WFQ, PQ, and so on)

Match

No Match

Classify

(Generic) Traffic Shaping


Link Fragmentation and Interleaving (LFI)

LFI fragments large datagrams and interleaves them with low-delay traffic packets

Transmit Queue

Output Line

Traffic Destined

for Interface

Large Packet Fragmentation:

Fragment Size Basedon Required Delay

WFQ

Multlink PPPwith LFI on

Jumbogram

IP Voice


Compressed Real-Time Transport Protocol (cRTP)

Configured Queuing

Traffic Destined for Interface

Identify RTPTraffic

Compression

RTP Traffic (Video, Audio, and so on)

Classify

RTP Compressor

Non-RTP

Transmit Queue

Output Line

VoIPSQL

FTP

20 Byte256 Byte

1,500 Byte

EfficienciesPayload

Packet Size Reduction*

*Also ~5 ms Reduction in serialization delay at 64 Kbps

~ 240%~ 13%

~ 2.3%

RTP12

UDP8

IPH20

5

IP Data

IP Data


IntServ Over DiffServ

• Framework describing how to achieve end-to-end Int-Serv in the presence of Diff-Serv clouds

• Key to scaling RSVP both in Enterprise and SP

• Mapping of RSVP flows onto PHBs

• Multiple Alternatives for Admission Control over DS Cloud

No Admission ControlAdmission Control AT EDGE ONLYAdmission Control at every hop in DS cloudAdmission Control at every hop in DS cloud BUT via Aggregated Resevations

Handset

PBX

Server

Server

IntServ e2e

DiffServ


QoS AdminConsole

PolicyServer

Policy Servers

Policies

ApplicationServers

RSVP: Vehicle for Policy Based Networking

LDAP

Directory

COPS

DNS/DHCP

COPS

RSVP RSVPRSVP

name, passwordsecret

You can do thisor you can’t

COPS= Common Open PolicyService protocol

RAP WG = Resource AllocationProtocol


Typical Use for ERP/Mission Critical

• 1: Application signals “identity” and no bandwidth (“Null Service”)

• 2: Router relays identity to Policy Server via COPS

• 3: PS returns DSCP to be used for this application

• 4: Network edge Device programmed to allow this DSCP on this port

• 5: Host notified of which DSCP to use via DCLASS in Resv

handset

PBX

server

Server

Diff-Serv

(*) concept formerly introduced as “RSVP+”

Path

Resv

1PolicyServer 2

3

5

4


Diff-Serv Acceptance

Time

Enthusiasm

today

Diff-Serv will solvesome of the world’s QoS

Diff-Serv Engineering?Diff-Serv SLA ?Internet e2e SLA?

•Diff-Serv Routers•Diff-Serv Design & Deploymentintra Domain (eg VPN QoS)

Realvalue

Inter-SP Diff-Serv and end-to-endInternet QoS need furtherstandardisation and commercialarrangements


Int-Serv/RSVP Acceptance

Time

Enthusiasm

TodayIntra-ISP

Int-Serv/RSVP will solvethe world’s QoS

ISP mapping RSVPover ATM

Realvalue

TodayEnterprise

for VoIP in Enterprise

for Mission Critical andMultimedia in Enterprise(Int-Serv over Diff-Serv)

for MPLS TE in ISP

Cool thing to say:“RSVP does not scale”


What Are 802.1P and ISL?

•QoS for a Layer 2 Ethernet switched world!802.1P QoS is:

An IEEE specificationFocuses on support for QoS over LANs and 802.1Q

trunksSupports 8 classes of service

ISL QoS is:Cisco specificationFocuses on support for QoS over ISL trunksSupports 8 classes of service


Differences Between 802.1P and ISL

ISL Header26 Bytes Encapsulated Frame 1 to 24.5 KBytes FCS

4 Bytes

PT DATA FCSPREAM. SFD DA SA

Layer 2 802.1Q/p

TAG4 Bytes

3 bits used for CoS(user priority)

Layer 2 ISL

3 bits used for CoS


How 802.1p QoS Functions

Edge QoS based on 802.1P CoS:Mark 802.1p Priority bits on

untagged packets on per port basisDo you trust the device on the port to set the bits correctly?

Upstream Layer 3 device performs TOS mapping to map 802.1P to IP Precedence or DSCP

47Presentation_ID © 1999, Cisco Systems, Inc. www.cisco.com

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