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TECRST-2500_c2 © 2009 Cisco Systems, Inc. All rights reserved. Cisco Public 1
Quality of ServiceIb [email protected]
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© 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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 3
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 4
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 5
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 6
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 7
Business Objectives
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 8
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
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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
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How does QOS work ?
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 11
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
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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 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
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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
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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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 16
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
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Scheduling
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 18
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 19
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
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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
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Link specific tools
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 22
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 23
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
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QOS Requirements
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 25
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 26
Networks that supports end to end QOS� Leased Lines� MPLS
� MPLS best price / perfomance
CE Router MPLS VPNPE Router
P Routers
CE RouterPE Router
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 27
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?
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 28
Voice 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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 29
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 30
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 31
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 32
Campus Branch Office
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
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© 2009 Cisco Systems, Inc. All rights reserved. Cisco PublicTECRST-2500_c2 33
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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