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IP Quality of Service
Inner Mongolia University
Objectives
Upon completing this module, you will be able to: Describe the need for IP QoS Describe the Integrated Services model Describe the Differentiated Services model Describe the building blocks of IP QoS mechanisms (classification,
marking, metering, policing, shaping, dropping, forwarding, queuing)
Introduction
Inner Mongolia University
Objectives
Upon completing this lesson, you will be able to: Describe different types of applications and services that have
special resource requirements List the network components that affect the throughput, delay,
and jitter in IP networks List the benefits of deploying QoS mechanisms in IP networks Describe typical enterprise and service provider networks and
their QoS-related requirements
Inner Mongolia University5
Why IP QoS?
Application X is slow. Video broadcast occasionally stalls. Phone calls over IP are no better than over satellite. Phone calls can have very bad voice quality. ATMs (the money-dispensing type) are
nonresponsive.
Inner Mongolia University6
Because ...
Application X is slow! (not enough bandwidth)
Video broadcast occasionally stalls! (delay temporarily increases – jitter)
Phone calls over IP are no better than over satellite! (too much delay)
Phone calls can have very bad voice quality! (too many phone calls – admission control)
ATMs (the money-dispensing type) are nonresponsive! (too many drops)
Inner Mongolia University7
What Causes ...
Lack of bandwidth?: Multiple flows are contesting for a limited amount of bandwidth.
Too much delay?: Packets have to traverse many network devices and links.
Variable delay?: Sometimes there is a lot of other traffic, which results in more delay.
Drops?: Packets have to be dropped when a link is congested.
Inner Mongolia University8
Available Bandwidth
Maximum available bandwidth equals the bandwidth of the weakest link.
Multiple flows are competing for the same bandwidth, resulting in much less bandwidth being available to one single application.
IPIP IPIP IPIP IPIP
10 Mbps10 Mbps
256 kbps256 kbps
512 kbps512 kbps
100 Mbps100 Mbps
BWmax = min(10M, 256k, 512k, 100M)=256 kbpsBWavail = BWmax /Flows
Inner Mongolia University9
End-to-End Delay
End-to-end delay equals a sum of all propagation, processing, and queuing delays in the path.
Propagation delay is fixed; processing and queuing delays are unpredictable in best-effort networks.
IPIP
Propagation Delay (P1)
Propagation Delay (P1)
Processing and Queuing Delay (Q1)
Processing and Queuing Delay (Q1)
IPIP IPIP IPIP
Propagation Delay (P2)
Propagation Delay (P2)
Processing and Queuing Delay (Q2)
Processing and Queuing Delay (Q2)
Propagation Delay (P3)
Propagation Delay (P3)
Processing and Queuing Delay (Q3)
Processing and Queuing Delay (Q3)
Delay = P1 + Q1 + P2 + Q2 + P3 + Q3 + P4 = X ms
Propagation Delay (P4)
Propagation Delay (P4)
Inner Mongolia University10
Processing, Queuing, and Propagation Delay
Processing delay is the time it takes for a router to take the packet from an input interface and put it into the output queue of the output interface.
Queuing delay is the time a packet resides in the output queue of a router. Propagation or serialization delay is the time it takes to transmit a packet.
IPIP IPIPIPIPIPIP
Forwarding
Processing Delay Queuing DelayPropagation Delay
Ba
nd
wid
th
Inner Mongolia University11
Packet Loss
Tail-drops occur when the output queue is full. These are the most common drops which happen when a link is congested.
There are also many other types of drops (input queue drop, ignore, overrun, no buffer, etc), which are not as common and which may require a hardware upgrade. These drops are usually a result of router congestion.
IPIP
Forwarding
IPIPIPIPIPIPIPIP
Tail-dropTail-drop
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How to Increase Available Bandwidth?
Upgrade the link—the best solution but also the most expensive.
FIFO queuingIP TCP Data Fancy Queuing
• Take some bandwidth from less important applications.
Compress the Headers
cTCP Data
• Compress the header of IP packets.
Compress the Payload
Compressed Packet
• Compress the payload of Layer 2 frames.
Priority Queuing (PQ)Custom Queuing (CQ)
Modified Deficit Round Robin (MDRR)Class-Based Weighted Fair Queing (CBWFQ)
Priority Queuing (PQ)Custom Queuing (CQ)
Modified Deficit Round Robin (MDRR)Class-Based Weighted Fair Queing (CBWFQ)
StackerPredictorStacker
Predictor
TCP Header CompressionRTP Header CompressionTCP Header CompressionRTP Header Compression
Inner Mongolia University13
How to Reduce Delay?
Upgrade the link—the best solution but also the most expensive.
FIFO queuingIP UDP Data Fancy Queuing
• Forward the important packets first.
Compress the Headers
cRTP Data
• Compress the header of IP packets.
RTP
Compress the Payload
Compressed Packet
• Compress the payload of Layer-2 frames (it takes time).
Priority Queuing (PQ)Custom Queuing (CQ)Strict Priority MDRRIP RTP Prioritization
Class-Based Low-Latency Queuing (CBLLQ)
Priority Queuing (PQ)Custom Queuing (CQ)Strict Priority MDRRIP RTP Prioritization
Class-Based Low-Latency Queuing (CBLLQ)
StackerPredictorStacker
Predictor
TCP Header CompressionRTP Header CompressionTCP Header CompressionRTP Header Compression
Inner Mongolia University14
How to Prevent Packet Loss?
Upgrade the link—the best solution but also the most expensive.
FIFO queuingIPIP DataData Fancy Queuing
• Guarantee enough bandwidth to sensitive packets.
Dropper
• Prevent congestion by randomly dropping less important packets before congestion occurs.
Custom Queuing (CQ)Modified Deficit Round Robin (MDRR)
Class-Based Weighted Fair Queuing (CBWFQ)
Custom Queuing (CQ)Modified Deficit Round Robin (MDRR)
Class-Based Weighted Fair Queuing (CBWFQ)
Weighted Random Early Detection (WRED)Weighted Random Early Detection (WRED)
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Which Applications Have Which QoS Requirements?
Enterprise networks are typically focused on providing QoS to applications.
Throughput Delay Loss Jitter
Interactive (e.g., Telnet)
Batch (e.g., FTP)
Fragile (e.g,. SNA)
Voice
Low Low
Not Important
Not Important
High
Low
LowNot
Important
None Not Important
Low LowLow Low and Predictable
Low Low
Video Low LowHigh Low and Predictable
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Which Services Can Be Implemented in a Network?
Service provider networks typically offer services based on source and destination addresses.
Throughput Delay Loss Jitter
Gold
Silver
Bronze
Best Effort
Guaranteed Low
No Guarantee
Low
Guaranteed
Low
No Guarantee
No Guarantee
No Guarantee
No Guarantee
No Guarantee
No Guarantee
No Guarantee
No Guarantee
GuaranteedLimited
No Guarantee
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How Can QoS Be Applied?
Best effort—no QoS is applied to packets (default behavior)
Integrated Services model—applications signal to the network that they require special QoS
Differentiated Services model—the network recognizes classes that require special QoS
Inner Mongolia University
Summary
Upon completing this lesson, you should be able to: Describe different types of applications and services that have
special resource requirements List the network components that affect the throughput, delay,
and jitter in IP networks List the benefits of deploying QoS mechanisms in IP networks Describe typical enterprise and service provider networks and
their QoS-related requirements
Inner Mongolia University
Review Questions
1.What are the relevant parameters that define quality of service?
2.What can be done to give more bandwidth to an application?
3.What can be done to reduce delay?
4.What can be done to prevent packet loss?
5.Name the two QoS models.
Integrated Services
Model
Inner Mongolia University
Objectives
Upon completing this lesson, you will be able to: Describe the IntServ model List the key benefits and drawbacks of the IntServ
model List some implementations that are based on the
IntServ model Describe the need for Common Open Policy Service
(COPS)
Inner Mongolia University22
Integrated Services
The Internet was initially based on a best-effort packet delivery service.
Today's Internet carries many more different applications than 20 years ago.
Some applications have special bandwidth and delay requirements.
The Integrated Services model (RFC1633) was introduced to guarantee predictable network behavior for these applications.
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IntServ Building Blocks
Resource reservation is used to identify an application (flow) and signal if there are enough available resources for it.
Admission control is used to determine if the application (flow) can get the requested resources.
requestrequest requestrequest requestrequest requestrequest
reservereservereservereservereservereservereservereserve
Local Admission
Control
Local Admission
Control
Local Admission
Control
Local Admission
Control
Policy Decision Point (PDP)
Policy Enforcement Point (PEP)
req
ue
st
req
ue
st
rep
lyre
ply
Remote Admission Control
Remote Admission Control
Inner Mongolia University24
Reservation and Admission Protocols
The Resource Reservation Protocol (RSVP) was developed to communicate resource needs between hosts and network devices (RFCs 2205 to 2215).
Common Open Policy Service (COPS) was developed to offload admission control to a central policy server (RFCs 2748 to 2753).
Inner Mongolia University25
RSVP-Enabled Applications
RSVP is typically used by applications carrying voice or video over IP networks (initiated by a host).
RSVP with extensions is also used by MPLS Traffic Engineering to establish MPLS/TE tunnels (initiated by a router).
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IntServ Implementation Options
1) Explicit RSVP on each network node
2) RSVP ‘pass-through’ and CoS transport- map RSVP to CoS at network edge- pass-through RSVP request to egress
RSVP
Class of Serviceor
Best Effort
3) RSVP at network edges and ‘pass-through’ with- best-effort forwarding in the core (if there is
enough bandwidth in the core)
Inner Mongolia University27
Explicit RSVP TransportIntServ End-to-End
All Routers• WFQ applied per flow
based on RSVP requests
RSVP
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RSVP Pass-ThroughIntServ - DiffServ Integration
PrecedenceClassifier
PremiumStandard
Ingress Router• RSVP protocol
Mapped to classesPassed through to
egressBackbone• WRED applied based
on class
Egress Router• RSVP protocol
sent on to destination• WFQ applied to
manage egress flow
RSVP RSVP
WRED
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Benefits and Drawbacks of the IntServ Model
+ RSVP benefits:• Explicit resource admission control (end-to-end)
• Per-request policy admission control (authorization object, policy object)
• Signaling of dynamic port numbers (for example, H.323)
– RSVP drawbacks:• Continuous signaling due to stateless architecture
• Not scalable
Inner Mongolia University30
Common Open Policy Service
Common Open Policy Service (COPS) provides the following benefits when used with RSVP:
• Centralized management of services• Centralized admission control and authorization of RSVP
flows
RSVP-based QoS solutions become more scalable
Inner Mongolia University
Summary
Upon completing this lesson, you should be able to: Describe the IntServ model List the key benefits and drawbacks of the IntServ
model List some implementations that are based on the
IntServ model Describe the need for Common Open Policy Service
(COPS)
Inner Mongolia University
Review Questions
1.What are the two building blocks of the Integrated Services model?
2.Which protocol is used to signal QoS requirements to the network?
3.Which protocol is used to offload admission control to a central policy server?
Differentiated Services
Model
Inner Mongolia University
Objectives
Upon completing this lesson, you will be able to: Describe the DiffServ model List the key benefits of the DiffServ model compared to the
IntServ model Describe the purpose of the DS field in IP headers Describe the interoperability between DSCP-based and IP-
Precedence-based devices in a network Describe the expedited forwarding service Describe the assured forwarding service
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Differentiated Services Model
TheDifferentiated Services model describes services associated with traffic classes.
Complex traffic classification and conditioning are performed at network edge, resulting in a per-packet Differentiated Services Code Point (DSCP).
No per-flow/per-application state exists in the core. The core performs only simple “per-hop behaviors” on traffic
aggregates. The goal is scalability.
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Additional DiffServ Requirements
Wide variety of services and provisioning policies Decouple service and application in use No application modification No hop-by-hop signaling Interoperability with non-DS-compliant nodes Incremental deployment
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DiffServ Elements
The service defines QoS requirements and guarantees provided to a traffic aggregate.
The conditioning functions and per-hop behaviors are used to realize services.
The DS field value (DSCP) is used to mark packets to select a per-hop behavior.
Per-hop Behavior (PHB) is implemented using a particular QoS mechanism.
Provisioning is used to allocate resources to traffic classes.
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Why Is Provisioning Important?
QoS does not create bandwidth! QoS manages bandwidth usage among
multiple classes. QoS gives better service to a well-provisioned class
with respect to another class.
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DownstreamDS Domain
Traffic Stream = set of flows
DS Region
UpstreamDS Domain
Behavior Aggregate (flows with the same DSCP)
Topological Terminology
DS Ingress Boundary NodeDS Ingress Boundary Node
DS Interior NodeDS Interior Node
DS Egress Boundary Node
DS Egress Boundary Node
Boundary LinkBoundary Link
Inner Mongolia University40
Traffic Terminology
Flow: a single instance of an application-to-application flow of packets. A flow is identified by source address, source port, destination address, destination port, and protocol ID.
Traffic stream: an administratively significant set of one or more flows that traverse a path segment. A traffic stream may consist of a set of active flows that are selected by a particular classifier.
Traffic profile: a description of the temporal properties of a traffic stream, such as average and peak rate and burst size.
Inner Mongolia University41
Traffic Terminology (cont.)
A behavior aggregate (BA) is a collection of packets with the same DSCP crossing a link in a particular direction.
Per-hop behavior (queuing in a node) is externally observable forwarding behavior applied at a DiffServ-compliant node to a DiffServ behavior aggregate.
A PHB Mechanism is a specific algorithm or operation (e.g., queuing discipline) that is implemented in a node to realize a set of one or more per-hop behaviors.
Inner Mongolia University42
DSCP Field: 6 bits Unused: 2 bits
Former ToS Byte = New DS Field
Packet Header Terminology
DSCP: a specific value of the DSCP portion of the DS field. The DSCP is used to select a PHB (Per-Hop Behavior; forwarding and queuing method)
DS field: the IPv4 header ToS octet or the IPv6 traffic class octet when interpreted in conformance with the definition given in RFC 2474. The bits of the DSCP field encode the DSCP, while the remaining bits are currently unused.
Inner Mongolia University43
DSCP Encoding
Three pools:• “xxxxx0” Standard Action
• “xxxx11” Experimental/Local Use
• “xxxx01” EXP/LU (possible std action) Default DSCP: “000000” Default PHB: FIFO, tail-drop
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DSCP Usage
DSCP selects per-hop behavior (PHB) throughout the network: Default PHB Class selector (IP Precedence) PHB Expedited forwarding PHB Assured forwarding PHB
Inner Mongolia University45
Backward Compatibility Using the Class Selector
Non-DS-compliant node: node that does not interpret the DSCP correctly or that does not support all the standardized PHBs
Legacy node: a non-DS-compliant node that interprets IPv4 ToS as defined by RFC 791 and RFC 1812
DSCP: backward compatible with IP Precedence (class selector code point, RFC 1812) but not with the ToS byte definition from RFC 791 (“DTR” bits)
Inner Mongolia University46
Class Selector Code Point
Compatibility with current IP Precedence usage (RFC 1812)
“xxx000” DSCPs Differentiates Probability of Timely Forwarding (PTF)
• PTF(xyz000) >= PTF(abc000) ifxyz > abc
Inner Mongolia University47
Expedited Forwarding
Expedited forwarding PHB:• Ensures a minimum departure rate• Guarantees bandwidth—the class is guaranteed an
amount of bandwidth with prioritized forwarding• Polices bandwidth—the class is not allowed to exceed the
guaranteed amount (excess traffic is dropped) DSCP value: “101110”; looks like IP Precedence 5 to non-
DS-compliant devices
Inner Mongolia University48
IOS Expedited Forwarding PHB Implementations
Priority queuing IP RTP Prioritization Class-based low-latency queuing (CBLLQ) Strict priority queuing within modified deficit round
robin (MDRR) on GSRs
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Assured Forwarding
Assured forwarding PHB:• Guarantees bandwidth
• Allows access to extra bandwidth if available Four standard classes (af1, af2, af3, and af4) DSCP value range: “aaadd0” where “aaa” is a binary
value of the class and “dd” is the drop probability
Inner Mongolia University50
Assured Forwarding Encoding
Each Assured Forwarding class uses three DSCP values Each Assured Forwarding class is independently forwarded with
its guaranteed bandwidth Differentiated RED is used within each class to prevent
congestion within the class
Class Value
AF1 001dd0
AF2 010dd0
AF3 011dd0
AF4 100dd0
DropProbability
(dd)
Value
Low 01
Medium 10
High 11
Inner Mongolia University51
Assured Forwarding PHB Definition
A DS node must allocate a configurable, minimum amount of forwarding resources (buffer space and bandwidth) per assured forwarding class.
Excess resources may be allocated between non-idle classes. The manner must be specified.
Reordering of IP packets of the same flow is not allowed if they belong to the same assured forwarding class.
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Assured Forwarding PHB Implementation
CBWFQ (four classes) with WRED within each class (M)DRR with WRED within each class Optional custom queuing
(does not support differentiated dropping)
Inner Mongolia University
Summary
Upon completing this lesson, you should be able to: Describe the DiffServ model List the key benefits of the DiffServ model compared to the
IntServ model Describe the purpose of the DS field in IP headers Describe the interoperability between DSCP-based and IP-
Precedence-based devices in a network Describe the expedited forwarding service Describe the assured forwarding service
Inner Mongolia University
Review Questions
1.What are the benefits of the DiffServ model compared to the IntServ model?
2.What is a DiffServ code point?
3.Name the standard PHBs.
4.How was backward compatibility with IP Precedence achieved?
5.Describe the PHB of assured forwarding.
6.Describe the PHB of expedited forwarding.
Building Blocks of IP
QoS Mechanisms
Inner Mongolia University
Objectives
Upon completing this lesson, you will be able to: Describe different classification options in IP networks Describe different marking options in IP networks List the mechanisms that are capable of measuring the rate of traffic List the mechanisms that are used for traffic conditioning, shaping,
and avoiding congestion
Inner Mongolia University57
Router Functions
Depending on the configuration, a router may perform a number of actions prior to forwarding a packet (input processing)
Depending on the configuration, a router may perform a number of actions prior to enqueuing a packet in the hardware queue (output processing)
InputProcessing
InputProcessing ForwardingForwarding Output
ProcessingOutput
ProcessingInput I/O Output I/O
DefragmentationDecompression (payload, header)Source-based QoS-label/precedence settingDestination-based QoS-label/precedence settingRate limitingClass-based markingPolicy-based routing. . .
DefragmentationDecompression (payload, header)Source-based QoS-label/precedence settingDestination-based QoS-label/precedence settingRate limitingClass-based markingPolicy-based routing. . .
Rate limitingRandom dropping ShapingCompression (payload, header)FragmentationQueuing and scheduling. . .
Rate limitingRandom dropping ShapingCompression (payload, header)FragmentationQueuing and scheduling. . .
Process switchingFast/optimum switchingNetflow switchingCEF switching
Process switchingFast/optimum switchingNetflow switchingCEF switching
Inner Mongolia University58
IP QoS Actions
Classification—Each class-oriented QoS mechanism has to support some type of classification (access lists, route maps, class maps, etc.).
Metering—Some mechanisms measure the rate of traffic to enforce a certain policy (e.g., rate limiting, shaping, scheduling, etc.).
Dropping—Some mechanisms are used to drop packets (e.g., random early detection).
Policing—Some mechanisms are used to enforce a rate limit based on the metering (excess traffic is dropped).
Shaping—Some mechanisms are used to enforce a rate limit based on the metering (excess traffic is delayed).
Inner Mongolia University59
IP QoS Actions (cont.)
Marking—Some mechanisms have the capability to mark packets based on classification or metering (e.g., CAR, class-based marking, etc.).
Queuing—Each interface has to have a queuing mechanism.
Forwarding—There are several supported forwarding mechanisms (process switching, fast switching, CEF switching, etc.).
Inner Mongolia University60
DiffServ Mechanisms in IOS
Most traditional QoS mechanisms include extensive built-in classifiers• Committed access rate (CAR)• QoS Policy Propagation on BGP (QPPB)• Route maps• Queuing mechanisms
Modular QoS CLI (first implemented in 12.0(5)T) separates classifiers from other actions
• Includes all traditional classifiers and network-based application recognition (NBAR)
Inboundtrafficstream
Classifier Marker Conditioner
Meter
Queuing
SchedulingDropping
ShapingDropping
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DiffServ Mechanisms in IOS (cont.)
Token bucket model is used for metering:• Committed access rate (CAR)• Generic traffic shaping (GTS)• Frame Relay traffic shaping (FRTS)• Class-based weighted fair queuing (CBWFQ)• Class-based low latency queuing (CBLLQ)• Class-based policing• Class-based shaping• IP RTP Prioritization
Inboundtrafficstream
Classifier Marker Conditioner
Meter
Queuing
SchedulingDropping
ShapingDropping
Inner Mongolia University62
DiffServ Mechanisms in IOS (cont.)
Marker is used to set:• IP Precedence• DSCP• QoS group• MPLS experimental bits• Frame Relay DE bit• ATM CLP bit• IEEE 802.1Q or ISL CoS
Inboundtrafficstream
Classifier Marker Conditioner
Meter
Queuing
SchedulingDropping
ShapingDropping
• Marking mechanisms:
– Comitted access rate (CAR)
– QoS Policy Propagation on BGP (QPPB)
– Policy-based routing (PBR)
– Class-based marking
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Comparison of Markers
Marker Preservation
IP Precedence Throughout a network 8 values, 2 reserved(0 to 7)
Value Range
DSCP Throughout a network 64 values, 32 are standard(0 to 63)
QoS group Local to a router 100 values(0 to 99)
MPLS experimental bits Throughout an MPLS network(optionally throughout an entire IP network)
8 values
Frame Relay DE bit Throughout a Frame Relay network
2 values(0 or 1)
ATM CLP bit Throughout an ATM network
2 values(0 or 1)
IEEE 802.1Q or ISL CoS Throughout a LAN switched network
8 values(0 to 7)
Inner Mongolia University64
DiffServ Mechanisms in IOS (cont.)
Shaping mechanisms:• Generic traffic shaping (GTS)• Frame Relay traffic shaping (FRTS)• Class-based shaping• Hardware shaping on ATM VC
Inboundtrafficstream
Classifier Marker Conditioner
Meter
Queuing
SchedulingDropping
ShapingDropping
Inner Mongolia University65
DiffServ Mechanisms in IOS (cont.)
Inboundtrafficstream
Classifier Marker Conditioner
Meter
Queuing
SchedulingDropping
ShapingDropping
Dropping mechanisms:• Committed access rate (CAR) and class-based policing can drop
packets that exceed the contractual rate.
• Weighted random early detection (WRED) can randomly drop packets when an interface is nearing congestion.
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DiffServ Mechanisms in IOS (cont.)
Cisco Express Forwarding (CEF) is recommended from IOS 12.0.
Some QoS features work only in combination with CEF.
Inboundtrafficstream
Classifier Marker Conditioner
Meter
Forwarding Queuing
SchedulingDropping
ShapingDropping
Inner Mongolia University67
DiffServ Mechanisms in IOS (cont.)
Traditional queuing mechanisms• FIFO, priority queuing (PQ), custom queuing (CQ)
Weighted fair queuing (WFQ) family• WFQ, DWFQ, CoS-based DWFQ, QoS-group DWFQ
Advanced queuing mechanisms• Class-based WFQ, Class-based LLQ
Inboundtrafficstream
Classifier Marker Conditioner
Meter
Forwarding Queuing
SchedulingDropping
ShapingDropping
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DiffServ Mechanisms in IOS (cont.)
Tail drop is used for most queue congestion. WFQ has an improved tail-drop scheme. WRED randomly drops packets when nearing
congestion.
Inboundtrafficstream
Classifier Marker Conditioner
Meter
Forwarding Queuing
SchedulingDropping
ShapingDropping
Inner Mongolia University
Summary
Upon completing this lesson, you should be able to: Describe different classification options in IP networks Describe different marking options in IP networks List the mechanisms that are capable of measuring the rate of
traffic List the mechanisms that are used for traffic conditioning,
shaping, and avoiding congestion
Inner Mongolia University
Review Questions
1.Name the QoS building blocks.2.What is the purpose of classification?3.What is the purpose of marking?4.Which parameters can be used to mark packets? 5.Which mechanisms can classify and mark packets?6.Which mechanisms have the ability to measure the rate of traffic?
7.How, when, and where do routers drop packets?
Enterprise Network
Case Study
Inner Mongolia University
Objectives
Upon completing this lesson, you will be able to: Describe the typical structure of an enterprise network Describe the need for QoS in enterprise networks List typical QoS requirements in enterprise networks List the QoS mechanisms that are typically used in enterprise
networks
Inner Mongolia University73
X.25 (ancient), Frame Relay (old), ATM (newer)
X.25 (ancient), Frame Relay (old), ATM (newer)
X.25 (ancient), Frame Relay (old), ATM (newer)
X.25 (ancient), Frame Relay (old), ATM (newer)
TraditionalEnterprise Networks
Traditional enterprise networks use a hub-and-spoke topology. Redundant connections are used to improve resilience. A partial mesh can be used between the core sites and the distribution sites.
Core(central sites
and data centers)
Distribution(regional centers)
Access(branch offices)
Inner Mongolia University74
MPLS/VPN (new)MPLS/VPN (new)
ModernEnterprise Networks
Modern enterprise networks use a full mesh topology provided by an MPLS/VPN backbone. Redundant connections to the backbone can be used to improve resilience The MPLS/VPN backbone uses redundant connections and a partial mesh to improve
resilience.
Core(central sites
and data centers)
Access(branch offices)
Inner Mongolia University75
QoS in Enterprise Networks
Typical enterprise networks have a large number of different applications.
Some applications are business-critical and require some guarantees (bandwidth, delay).
The network should provide enough resources to these business-critical applications.
Applications are usually identified based on TCP or UDP port numbers.
Inner Mongolia University76
Case Study
Typical line speeds:• Core to Distribution < 2 Mbps• Distribution to Branch 64 kbps - 256 kbps
Typical protocols:• SNA, NetBIOS, desktop protocols (IPX), some TCP/IP,
voice, multimedia Typical QoS requirements:
• SNA and voice are high priority• Guaranteed bandwidth for some applications• Rest of the traffic is best-effort
Inner Mongolia University77
Case StudyImplementation #1
Core to Distribution:• Custom queuing
Distribution to Branch:• Priority queuing or • Custom queuing with a priority queue
Options:• Traffic shaping• Adaptation to Frame Relay congestion notification
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Case StudyImplementation #2
Core to Distribution:• Class-based weighted fair queuing (CBWFQ)• Class-based low-latency queuing (CBLLQ)
Distribution to Branch:• Class-based weighted fair queuing (CBWFQ)• Class-based low-latency queuing (CBLLQ)
Options:• Class-based shaping• Adaptation to Frame Relay congestion notification • Class-based policing• Weighted random early detection (WRED)
Inner Mongolia University
Summary
Upon completing this lesson, you should be able to: Describe the typical structure of an enterprise network Describe the need for QoS in enterprise networks List typical QoS requirements in enterprise networks List the QoS mechanisms that are typically used in
enterprise networks
Inner Mongolia University
Review Questions
1.What is the typical enterprise network topology?
2.How is resilience achieved?
3.Based on what information do typical enterprise networks apply QoS?
Services Provider
Case Study
Inner Mongolia University
Objectives
Upon completing this lesson, you will be able to: Describe the typical structure of a service provider
network Describe the need for QoS in service provider
networks List typical QoS requirements in service provider
networks List the QoS mechanisms that can be used in service
provider networks
Inner Mongolia University83
ATM, SONET/SDH, DPT, GE, ...ATM, SONET/SDH, DPT, GE, ...
Frame Relay, ATM, leased line (analog, TDM), dial-up (PSTN, ISDN, GSM), xDSL, (fast) Ethernet, ...
Frame Relay, ATM, leased line (analog, TDM), dial-up (PSTN, ISDN, GSM), xDSL, (fast) Ethernet, ...
ATM, SONET/SDH, DPT, GE, ...ATM, SONET/SDH, DPT, GE, ...
TypicalService Provider Networks
Typical service provider networks use a high-speed partially meshed core (backbone). Regional POPs use two or more connections to the core. There may be another layer of smaller POPs connected to distribution-layer POPs. Customers are usually connected to the service provider via a single point-to-point link (a secondary
link or a dial line can be used to improve resilience).
Core
Distribution(regional POPs)
Access(customers)
Redundant connectionsRings
Partial meshRings
Single connectionsOptional redundant connectionsDial backup
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QoS in Service Provider Networks
Service providers extend their service offerings by introducing quality.
Customers can get bandwidth guarantees (like CIR in Frame Relay).
Customers can get delay guarantees (like CBR in ATM).
Customers can get preferential treatment in case of congestion (Olympic service).
QoS mechanisms have to be deployed where congestion is likely (usually at the network edge).
The customer traffic is identified based on source or destination IP addresses.
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Case Study
A service provider wants to offer bronze, silver, gold and premium services: Bronze gets 10% of available bandwidth Silver gets 20% of available bandwidth Gold gets 30% of available bandwidth Premium gets 40% of available bandwidth with a low-
delay guarantee
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Case StudyImplementation
Class-based weighted fair queuing (CBWFQ) on slow to moderate-speed links
Class-based low latency queuing (CBLLQ) on slow to moderate-speed links
Weighted random early detection (WRED) on fast links
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Summary
Upon completing this lesson, you should be able to: Describe the typical structure of a service provider
network Describe the need for QoS in service provider
networks List typical QoS requirements in service provider
networks List the QoS mechanisms that can be used in service
provider networks
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Review Questions
1.What is the typical topology of service provider networks?
2.How is resilience achieved?
3.Based on what information do typical service provider networks apply QoS?
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Module Summary
Upon completing this module, you should be able to: Describe the need for IP QoS Describe the Integrated Services model Describe the Differentiated Services model Describe the building blocks of IP QoS mechanisms
(classification, marking, metering, policing, shaping, dropping, forwarding, queuing)
List the IP QoS mechanisms available in Cisco IOS Describe what QoS features are supported by different IP QoS
mechanisms
Thank Youand
Good-bye !!
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Cisco’s Certification Track