Quality of Service

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Quality of Service

Ib Hansen

ibhansen@cisco.com

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TECRST-2500_c2

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Why Enable QoS?

QoS:

Enables UC and other collaborative applications

Drives productivity by enhancing service levels to mission-critical applications

Cuts costs by bandwidth optimization

Helps maintain network availability in the event of DoS/worm attacks Quality of

Service

High Availability

Security

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Enabling QoS in the Network

Traffic Profiles and Requirements

Latency ≤ 150 ms Jitter ≤ 30 ms Loss ≤ 1%

One-Way Requirements Smooth

Benign

Drop sensitive Delay sensitive UDP priority

Voice

Bandwidth per Call Depends on Codec, Sampling-Rate, and Layer 2 Media

Bursty Greedy

Drop sensitive Delay sensitive UDP priority

Video

Latency ≤ 150–300ms Jitter ≤ 10 ms–50ms Loss ≤ .05%

One-Way Requirements Network requirements for video traffic can vary greatly, based on the type of application being used, as well as whether the media flows are standard or high definition.

Smooth/bursty Benign/greedy Drop insensitive Delay insensitive TCP retransmits

Data

Data Classes:

Mission-Critical Apps

Transactional/Interactive Apps Bulk Data Apps

Best Effort Apps (Default)

Traffic patterns for

Data Vary Among

Applications

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TECRST-2500_c2

4 Typical Voice and Video QoS Requirements

Elements that Affect Latency and Jitter

Campus Branch Office

IP WAN PSTN

End-to-End Delay (Must Be ≤≤≤≤ 150 ms)

20–50 ms Jitter Buffer

Fixed (6.3 µs/Km) + Network Delay

(Variable) Propagation and Network

Variable Serialization Variable

Queuing G.729A: 25 ms

CODEC

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What Is Quality of Service?

To the End User

User’s perception that their applications are performing properly

Voice—No drop calls, no static Video—High quality, smooth video Data—Rapid response time

To the Network Manager

Maximize network bandwidth utilization while meeting performance expectations

Control Delay—The finite amount of time it takes a packet to reach the receiving endpoint

Jitter—The difference in the end-to-end delay between packets

Packet Loss—Relative measure of the number

of packets that were not received compared to

the total number of packets transmitted

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How Is QoS Optimally Deployed?

1. Strategically define the business objectives to be achieved via QoS

2. Analyze the service-level requirements of the various traffic classes to be provisioned for

3. Design and test the QoS policies prior to production- network rollout

4. Roll-out the tested QoS designs to the production-network in phases, during scheduled downtime

5. Monitor service levels to ensure

that the QoS objectives are being met

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Business Objectives

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New Business Requirements

Why Video?

1

Kandola, Pearn “The Psychology of Effective Business Communications in Geographically Dispersed Teams”, Cisco Systems, September 2006

2

Vision Group Research, FMRIB, University of Oxford, UK

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New Application Requirements

The Impact of HD on the Network

User demand for HD video has a major impact on the network

(H.264) 720p HD video requires twice as much bandwidth as (H.323) DVD

(H.264) 1080p HD video requires twice as much bandwidth as (H.264) 720p

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How does QOS work ?

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Quality of Service Operations

How Does It Work and Essential Elements

CLASSIFICATION

AND MARKING QUEUEING AND

DROPPING POST-QUEUING OPERATIONS

Classification and Marking:

The first element to a QoS policy is to classify/identify the traffic that is to be treated differently; following classification, marking tools can set an attribute of a frame or packet to a specific value

Policing:

Determine whether packets are conforming to administratively-defined traffic rates and take action accordingly; such action could include marking, remarking or dropping a packet

Scheduling (including Queuing and Dropping):

Scheduling tools determine how a frame/packet exits a device; queuing algorithms are activated only when a device is experiencing congestion and are deactivated when the congestion clears

Link Specific Mechanisms (Shaping, Fragmentation, Compression, Tx Ring)

Offers network administrators tools to optimize link utilization

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Classification

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Catalyst 2960/3560/3750 + 3560-E and 3750-E

Classification

• Inspect incoming packets

• Based on ACLs or configuration, determine

classification label

Policing

• Ensure

conformance to a specified rate

• On an aggregate or individual flow basis

• Up to 256 policers per Port ASIC

• Support for rate and burst

Marking

• Act on policer decision

• Reclass or drop out-of-profile

Egress Queue/

Schedule Congestion

Control

• Four SRR queues/port shared or shaped servicing

• One queue is configurable for strict priority servicing

• WTD for congestion control (three thresholds per queue)

• Egress queue shaping

• Egress port rate limiting Ingress Queue/

Schedule Congestion

Control

• Two queues/port ASIC shared servicing

• One queue is

configurable for strict priority servicing

• WTD for congestion control (three

thresholds per queue)

• SRR is performed

Ingress Egress

Policer Policer

Marker

Policer Policer

Marker

Marker Marker

SRR SRR

Classify Traffic

Stack Ring

Egress Queues Ingress

Queues

QoS Model

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Classification Tools—Layer 2

Ethernet 802.1Q Class of Service

802.1p user priority field also called Class of Service (CoS) Different types of traffic are

assigned different CoS values CoS 6 and 7 are reserved for

network use

4 Bytes TAG

Three Bits Used for CoS (802.1p User Priority)

Data FCS

PT SA

DA SFD

Pream. Type

802.1Q/p Header PRI CFI VLAN ID

Ethernet Frame

1 2 3 4 5 6 7

0 Best Effort Data Bulk Data Critical Data Call Signaling

Video Voice Routing Reserved

CoS Application

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Classification Tools—Layer 3

IP Precedence and DiffServ Code Points

IPv4: Three most significant bits of ToS byte are called IP Precedence (IPP)—other bits unused

DiffServ: Six most significant bits of ToS byte are called DiffServ Code Point (DSCP)—remaining two bits used for flow control DSCP is backward-compatible with IP precedence

7 6 5 4 3 2 1 0

ID Offset TTL Proto FCS IP SA IP DA Data Version Len

Length ToS Byte

DiffServ Code Point (DSCP) IP ECN

IPv4 Packet

IP Precedence Unused Standard IPv4

DiffServ Extensions

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Classification Tools

MPLS EXP Bits

Packet Class and drop precedence inferred from EXP (three-bit) field

RFC3270 does not recommend specific EXP values for DiffServ PHB (EF/AF/DF)

Used for frame-based MPLS

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

Label EXP S TTL

MPLS Shim Header

EXP

Payload

Frame Encapsulation

3 2 1 0

MPLS EXP ^S

Layer-2 Header Label Header Label Header Label

Stack

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Scheduling

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Scheduling Tools

Queuing Algorithms

Congestion can occur at any point in the network where there are speed mismatches

Routers use Cisco IOS ^® -based software queuing

Low-Latency Queuing (LLQ) used for highest-priority traffic (voice/video)

Class-Based Weighted-Fair Queuing (CBWFQ) used for guaranteeing bandwidth to data applications

Cisco Catalyst ^® switches use hardware queuing

Voice Video

Data ³ ³

2 2

1 1

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Police

Scheduling Tools

LLQ/CBWFQ Subsystems

CBWFQ Fragment

Interleave

FQ

Link Fragmentation and Interleave Low Latency Queueing

Packets Packets Out

In

VoIP

IP/VC PQ

Layer 3 Queueing Subsystem Layer 2 Queueing Subsystem

Signaling Critical

Bulk Mgmt Default

Ring TX

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20 3 1

2 3

0 2

0 2 1

2 0

1 TAIL DROP

3 3 3

WRED

0 1

0 3

Queue

Scheduling Tools

Congestion Avoidance Algorithms

Queueing algorithms manage the front of the queue

which packets get transmitted first

Congestion avoidance algorithms manage the tail of the queue

which packets get dropped first when queuing buffers fill

Weighted Random Early Detection (WRED)

WRED can operate in a DiffServ-compliant mode Drops packets according to their DSCP markings

WRED works best with TCP-based applications, like data

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Link specific tools

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Link-Specific Tools

Link-Fragmentation and Interleaving

Serialization delay is the finite amount of time required to put frames on a wire

For links ≤ 768 kbps serialization delay is a major factor affecting latency and jitter

For such slow links, large data packets need to be fragmented and interleaved with smaller, more urgent voice packets

Voice

Voice Data Data

Data Data

Serialization Data

Can Cause Excessive Delay

With Fragmentation and Interleaving Serialization Delay Is Minimized

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Link-Specific Tools

IP RTP Header Compression

cRTP Reduces L3 VoIP BW by:

~ 20% for G.711

~ 60% for G.729

2–5 Bytes RTP Header

12 Bytes

Voice Payload

IP Header

20 Bytes UDP Header

8 Bytes

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QOS Requirements

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QoS and IPSEC

QOS when using the Internet as transport

IPSec Tunnel

= IPsec tunnels

Rate: 8Mbps / 768 Kbps ADSL

Rate: 100 Mbps Leased line

QOS

End – End QOS not possible

QOS possible at each end of tunnel Internet service provider routers

typically not QOS enabled

Internet

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Networks that supports end to end QOS

Leased Lines

MPLS

MPLS best price / perfomance

CE Router _{PE Router} MPLS VPN

P Routers

CE Router

PE Router

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Voice QoS Requirements

End-to-End Latency

Delay Target

Avoid the

“Human Ethernet”

Time (msec)

0 100 200 300 400

CB Zone Satellite Quality

Fax Relay, Broadcast High Quality

500 600 700 800

ITU’s G.114 Recommendation: ≤≤≤≤ 150msec One-Way Delay

Hello? Hello?

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Voice QoS Requirements

Elements that Affect Latency and Jitter

Campus Branch Office

IP WAN PSTN

End-to-End Delay (Must Be ≤≤≤≤ 150 ms)

20–50 ms Jitter Buffer

Fixed (6.3 µs/Km) + Network Delay

(Variable) Propagation and Network

Variable Serialization Variable

Queuing G.729A: 25 ms

CODEC

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Voice QoS Requirements

Packet Loss Limitations

Cisco DSP codecs can use predictor algorithms to compensate for a single lost packet in a row

Two lost packets in a row will cause an audible clip in the conversation

Voice 1 Voice

2 Voice

3 Voice

4 Voice

1 Voice

2 Voice

3 Voice

4 Voice 3 Voice

3 Voice

3 Reconstructed Voice Sample

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Voice QoS Requirements

Provisioning for 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 CAC must be enabled

Smooth Benign

Drop sensitive Delay sensitive UDP priority

Voice

One-Way

Requirements

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Video QoS Requirements

Provisioning for Interactive Video

Latency ≤ 150 – 300ms Jitter ≤ 10 – 50ms

Loss ≤ .05%

Minimum priority bandwidth guarantee required is:

Video-stream + 10–20%

e.g., a 384 kbps stream could require up to 460 kbps of priority bandwidth

CAC must be enabled

Bursty

Drop sensitive Delay sensitive UDP priority

Video

One-Way

Requirements

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32 Campus Branch Office

SRST router

IP WAN

PSTN

• LLQ

• CBWFQ

• WRED

• LFI/FRF.12

• cRTP

• FRTS, dTS

• H-Shaping

Aggregator WAN

• Inline Power

• Multiple Queues

• 802.1Q/p

Branch Switch

Bandwidth Bandwidth Provisioning Provisioning

QoS Tools Mapped

to Design Requirements

• LLQ

• CBWFQ

• WRED

• LFI/FRF.12

• cRTP

• FRTS

• NBAR

• H-Shaping

Branch Router

• Inline Power

• Multiple Queues

• 802.1Q/p

• DSCP

• Fast link convergence

Campus Access

• Multiple Queues

• 802.1Q/p

• DSCP

Campus

Distribution

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What Is the Challenge?

Baseline Challenge: Know how much traffic is flowing, what and where

Deployment Challenge:

QoS policies are difficult to configure and scale in a

consistent end-to-end manner Operations Challenge:

The lack of QoS operational visibility to evaluate the

effectiveness and

validate results

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