1 © 2001, cisco systems, inc. all rights reserved. tac-toi-01 quality of service (qos) an overview
TRANSCRIPT
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.
© 2001, Cisco Systems, Inc. All rights reserved. 3© 2001, Cisco Systems, Inc. All rights reserved. 3© 2001, Cisco Systems, Inc. All rights reserved. 3TAC-TOI-01
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
© 2001, Cisco Systems, Inc. All rights reserved. 4© 2001, Cisco Systems, Inc. All rights reserved. 4© 2001, Cisco Systems, Inc. All rights reserved. 4TAC-TOI-01
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
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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
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What Is a Class?
• Single user
MAC address, IP address…
• Department, customer
Sub net, interface…
• Application
Port numbers, URL…
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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
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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
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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
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!! Detour !!Differentiated Services
(DiffServ)The Formula for Scalable QoS
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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)
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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)
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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
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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”
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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
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Just Remember “DSCP”Just Remember “DSCP”
IPv4 ToS vs. DS-Field(The ToS Byte Is Re-Defined)
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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’
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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
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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
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• 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…
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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!
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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
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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
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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
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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)
© 2001, Cisco Systems, Inc. All rights reserved. 26© 2001, Cisco Systems, Inc. All rights reserved. 26© 2001, Cisco Systems, Inc. All rights reserved. 26TAC-TOI-01
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!
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Back on Track
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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
© 2001, Cisco Systems, Inc. All rights reserved. 29© 2001, Cisco Systems, Inc. All rights reserved. 29© 2001, Cisco Systems, Inc. All rights reserved. 29TAC-TOI-01
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
“
”
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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
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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
© 2001, Cisco Systems, Inc. All rights reserved. 32© 2001, Cisco Systems, Inc. All rights reserved. 32© 2001, Cisco Systems, Inc. All rights reserved. 32TAC-TOI-01
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
Voice Packet60 Bytes
Every >214 ms
Voice Packet60 Bytes
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
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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
Voice Packet60 Bytes
Every >214 ms
Voice Packet60 Bytes
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
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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”
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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
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Policy required:
Make sure my bronze traffic does not get more than x kbps of
bandwidth at any time
Maximum Rate Limiting
“
”
© 2001, Cisco Systems, Inc. All rights reserved. 37© 2001, Cisco Systems, Inc. All rights reserved. 37© 2001, Cisco Systems, Inc. All rights reserved. 37TAC-TOI-01
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
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WebWeb
ERP/SAPERP/SAP
PointcastPointcast
Trash
Policer
© 2001, Cisco Systems, Inc. All rights reserved. 39© 2001, Cisco Systems, Inc. All rights reserved. 39© 2001, Cisco Systems, Inc. All rights reserved. 39TAC-TOI-01
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
© 2001, Cisco Systems, Inc. All rights reserved. 40© 2001, Cisco Systems, Inc. All rights reserved. 40© 2001, Cisco Systems, Inc. All rights reserved. 40TAC-TOI-01
Policy required:
Make sure my bronze or silver traffic gets dropped when there is
congestion and not gold traffic
Congestion Avoidance
“
”
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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
© 2001, Cisco Systems, Inc. All rights reserved. 42© 2001, Cisco Systems, Inc. All rights reserved. 42© 2001, Cisco Systems, Inc. All rights reserved. 42TAC-TOI-01
• 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
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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
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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
© 2001, Cisco Systems, Inc. All rights reserved. 45© 2001, Cisco Systems, Inc. All rights reserved. 45© 2001, Cisco Systems, Inc. All rights reserved. 45TAC-TOI-01
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)
© 2001, Cisco Systems, Inc. All rights reserved. 46© 2001, Cisco Systems, Inc. All rights reserved. 46© 2001, Cisco Systems, Inc. All rights reserved. 46TAC-TOI-01
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
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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
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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
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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!