quality of service - medcommedcom.dk/media/2610/ib-hansen.pdf · ip precedence and diffservcode...

TECRST-2500_c2 © 2009 Cisco Systems, Inc. All rights reserved. Cisco Public 1

Quality of ServiceIb [email protected]

© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 2

Why Enable QoS?

QoS:� Enables UC and

other collaborative applications

� Drives productivity by enhancing servicelevels to mission-critical applications

� Cuts costs by bandwidth optimization

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

Quality ofService

High Availability

Security


Enabling QoS in the NetworkTraffic 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 CallDepends 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 AppsTransactional/Interactive AppsBulk Data AppsBest Effort Apps (Default)

Traffic patterns for Data Vary Among Applications


Typical Voice and Video QoS RequirementsElements that Affect Latency and Jitter

Campus Branch Office

IP WAN

PSTN

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

20–50 ms

Jitter BufferFixed

(6.3 µs/Km) +Network Delay(Variable)

Propagationand Network

Variable

Serialization

Variable

Queuing

G.729A: 25 ms

CODEC


What Is Quality of Service? � To the End User

User’s perception that their applications are performing properly

Voice—No drop calls, no staticVideo—High quality, smooth videoData—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 packetsPacket Loss—Relative measure of the number of packets that were not received compared to the total number of packets transmitted

5


How Is QoS Optimally Deployed?1. Strategically define the business objectives to

be achieved via QoS2. Analyze the service-level requirements of the various

traffic classes to be provisioned for3. Design and test the QoS policies prior to production-

network rollout4. 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


Business Objectives


New Business RequirementsWhy Video?

1Kandola, Pearn “The Psychology of Effective Business Communications in Geographically Dispersed Teams”, Cisco Systems, September 20062Vision Group Research, FMRIB, University of Oxford, UK


New Application RequirementsThe 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


How does QOS work ?


Quality of Service OperationsHow Does It Work and Essential ElementsCLASSIFICATION 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


Classification


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 dropout-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

PolicerPolicer

Marker

PolicerPolicer

Marker

MarkerMarker

SRR SRRClassifyTraffic

Stack Ring

Egress QueuesIngress

Queues

QoS Model


Classification Tools—Layer 2Ethernet 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

TAG4 Bytes

Three Bits Used for CoS(802.1p User Priority)

Data FCSPTSADASFDPream. Type

802.1Q/pHeaderPRI VLAN IDCFI

Ethernet Frame

1234567

0 Best Effort DataBulk DataCritical DataCall Signaling

VideoVoiceRoutingReserved

CoS Application


Classification Tools—Layer 3IP 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 DiffServCode 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 DataLenVersion Length

ToSByte

DiffServ Code Point (DSCP) IP ECN

IPv4 Packet

IP Precedence Unused Standard IPv4DiffServ Extensions


Classification ToolsMPLS 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 30 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 HeaderLabel HeaderLabel Header

Label Stack


Scheduling


Scheduling ToolsQueuing Algorithms

� Congestion can occur at any point in the network where there arespeed mismatches

� Routers use Cisco IOS®-based software queuingLow-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

VoiceVideo

Data 33

2 2

1 1


Police

Scheduling ToolsLLQ/CBWFQ Subsystems

CBWFQ Fragment

Interleave

FQ

Link Fragmentationand Interleave

Low Latency Queueing

PacketsOutPackets

In

VoIPIP/VC PQ

Layer 3 Queueing Subsystem Layer 2 Queueing Subsystem

SignalingCriticalBulkMgmtDefault

TXRing


312302021201

TAIL DROP

3

3

3

WRED

01

0

1

0

3

Queue

Scheduling ToolsCongestion 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 markingsWRED works best with TCP-based applications, like data


Link specific tools


Link-Specific ToolsLink-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 DataDataDataData

DataSerializationCan Cause

Excessive Delay

With Fragmentation and Interleaving Serialization Delay Is Minimized


Link-Specific ToolsIP RTP Header Compression

cRTP Reduces L3 VoIP BW by:~ 20% for G.711~ 60% for G.729

2–5 Bytes

RTP Header12 Bytes

VoicePayload

IP Header20 Bytes

UDP Header8 Bytes


QOS Requirements


QoS and IPSECQOS when using the Internet as transport

IPSec Tunnel

= IPsec tunnelsRate: 8Mbps / 768 Kbps ADSL

Rate: 100 MbpsLeased line

QOS � End – End QOS not possible� QOS possible at each end of tunnel� Internet service provider routers typically not QOS enabled

Internet


Networks that supports end to end QOS� Leased Lines� MPLS

� MPLS best price / perfomance

CE Router MPLS VPNPE Router

P Routers

CE RouterPE Router


Voice QoS RequirementsEnd-to-End Latency

Delay Target

Avoid the “Human Ethernet”

Time (msec)0 100 200 300 400

CB ZoneSatellite Quality

Fax Relay, BroadcastHigh Quality

500 600 700 800

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

Hello? Hello?


Voice QoS RequirementsElements that Affect Latency and Jitter


IP WAN

PSTN

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

20–50 ms

Jitter BufferFixed

(6.3 µs/Km) +Network Delay(Variable)

Propagationand Network

Variable

Serialization

Variable

Queuing

G.729A: 25 ms

CODEC


Voice QoS RequirementsPacket 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

Voice1

Voice2

Voice3

Voice4

Voice1

Voice2

Voice3

Voice4

Voice3

Voice3

Voice3

Voice3 Reconstructed Voice Sample


Voice QoS RequirementsProvisioning 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

VoiceOne-WayRequirements


Video QoS RequirementsProvisioning 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

VideoOne-WayRequirements



SRSTrouter

IP WAN

PSTN

• LLQ• CBWFQ • WRED• LFI/FRF.12• cRTP• FRTS, dTS• H-Shaping

WAN Aggregator

• Inline Power• Multiple Queues• 802.1Q/p

Branch Switch

BandwidthBandwidthProvisioningProvisioning

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 linkconvergence

Campus Access

• Multiple Queues• 802.1Q/p• DSCP

Campus Distribution


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

quality of service - medcommedcom.dk/media/2610/ib-hansen.pdf · ip precedence and diffservcode...

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