© 2001, Cisco Systems, Inc. Introduction. © 2001, Cisco Systems, Inc. QoS v1.0—1-2 Objectives Upon completing this module, you will be able to: Describe

© 2001, Cisco Systems, Inc.

Introduction

© 2001, Cisco Systems, Inc. QoS v1.0—1-2

ObjectivesObjectives

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)

• List the IP QoS mechanisms available in Cisco IOS

• Describe what QoS features are supported by different IP QoS mechanisms

Introduction to IP Quality of ServiceIntroduction to IP Quality of Service

QOS v1.0—1-3© 2001, Cisco Systems, Inc.



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

• Name some QoS mechanisms available in Cisco IOS

• Describe typical enterprise and service provider networks and their QoS-related requirements


Why IP QoS?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.


Because ...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)


What Causes ...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.


Available BandwidthAvailable 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


End-to-End DelayEnd-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)


Processing and Queuing Delay (Q1)


IPIP IPIP IPIP









Delay = P1 + Q1 + P2 + Q2 + P3 + Q3 + P4 = X ms




Processing, Queuing, and Propagation Delay

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


Packet LossPacket 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


How to Increase Available Bandwidth?

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


How to Reduce Delay? How to Reduce Delay?


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


How to Prevent Packet Loss?How to Prevent Packet Loss?


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)


Which Applications Have Which QoS Requirements?

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


Which Services Can Be Implemented in a Network?

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


How Can QoS Be Applied?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


SummarySummary

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

• Name some QoS mechanisms available in Cisco IOS

• Describe typical enterprise and service provider networks and their QoS-related requirements


Review QuestionsReview 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

Integrated Services Model




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)


Integrated ServicesIntegrated 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.


IntServ Building BlocksIntServ 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


Reservation and Admission Protocols

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).


RSVP-Enabled ApplicationsRSVP-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).


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)


Explicit RSVP TransportIntServ End-to-End

All Routers• WFQ applied per flow

based on RSVP requests

RSVP


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


IntServ Support in IOSIntServ Support in IOS

• RSVP and Weighted Fair Queuing supported since ’95

• RSVP signaling for VoIP calls supported on all VoIP platforms

• Cisco IOS supports hop-by-hop and pass-through RSVP

• RSVP-to-DSCP (DiffServ code point) mapping (RSVP proxy) in 12.1T


Benefits and Drawbacks of the IntServ Model

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


Common Open Policy ServiceCommon 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


SummarySummary

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)



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

Differentiated Services Model





• 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


Differentiated Services Model 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.


Additional DiffServ RequirementsAdditional 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


DiffServ ElementsDiffServ 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.


Why Is Provisioning Important?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.


DownstreamDS Domain

Traffic Stream = set of flows

DS Region

UpstreamDS Domain

Behavior Aggregate (flows with the same DSCP)

Topological TerminologyTopological Terminology

DS Ingress Boundary NodeDS Ingress Boundary Node

DS Interior NodeDS Interior Node

DS Egress Boundary Node

DS Egress Boundary Node

Boundary LinkBoundary Link


Traffic TerminologyTraffic 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.


Traffic Terminology (cont.)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.


DSCP Field: 6 bits Unused: 2 bits

Former ToS Byte = New DS Field

Packet Header TerminologyPacket 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.


DSCP EncodingDSCP Encoding

• Three pools:

– “xxxxx0” Standard Action

– “xxxx11” Experimental/Local Use

– “xxxx01” EXP/LU (possible std action)

• Default DSCP: “000000”

• Default PHB: FIFO, tail-drop


DSCP UsageDSCP Usage

DSCP selects per-hop behavior (PHB) throughout the network:• Default PHB

• Class selector (IP Precedence) PHB

• Expedited forwarding PHB

• Assured forwarding PHB


Backward Compatibility Using the Class Selector

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-DS0-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)


Class Selector Code PointClass Selector Code Point

• Compatibility with current IP Precedence usage (RFC 1812)

• “xxx000” DSCPs

• Differentiates PTF

– PTF(xyz000) >= PTF(abc000) ifxyz > abc


Expedited ForwardingExpedited 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


IOS Expedited Forwarding PHB Implementations

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


Assured Forwarding 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


Assured Forwarding EncodingAssured 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

Drop

Probability (dd)

Value

Low 01

Medium 10

High 11


Assured Forwarding PHB Definition

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.


Assured Forwarding PHB Implementation

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)


SummarySummary

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



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

Building Blocks of IP QoS Mechanisms





• 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

• List the forwarding mechanisms available in Cisco IOS

• List the queuing mechanisms available in Cisco IOS


Router FunctionsRouter 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


IP QoS ActionsIP 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).


IP QoS Actions (cont.)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.).


DiffServ Mechanisms in IOSDiffServ 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


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



Meter

Queuing

SchedulingDropping

ShapingDropping




• 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



Meter

Queuing

SchedulingDropping

ShapingDropping

• Marking mechanisms:

– Comitted access rate (CAR)

– QoS Policy Propagation on BGP (QPPB)

– Policy-based routing (PBR)

– Class-based marking


Comparison of MarkersComparison 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)




• Shaping mechanisms:–Generic traffic shaping (GTS)

– Frame Relay traffic shaping (FRTS)

–Class-based shaping

–Hardware shaping on ATM VC



Meter

Queuing

SchedulingDropping

ShapingDropping






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.




• Cisco Express Forwarding (CEF) is recommended from IOS 12.0.

• Some QoS features work only in combination with CEF.



Meter

Forwarding Queuing

SchedulingDropping

ShapingDropping




• 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



Meter

Forwarding Queuing

SchedulingDropping

ShapingDropping




• Tail drop is used for most queue congestion.

• WFQ has an improved tail-drop scheme.

• WRED randomly drops packets when nearing congestion.



Meter

Forwarding Queuing

SchedulingDropping

ShapingDropping


SummarySummary

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

• List the forwarding mechanisms available in Cisco IOS

• List the queuing mechanisms available in Cisco IOS



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. Which forwarding mechanisms exist in Cisco IOS ?

8. Which queuing mechanisms exist in Cisco IOS ?

9. How, when, and where do routers drop packets?

Enterprise Network Case Study

Enterprise Network Case Study




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


X.25 (ancient), Frame Relay (old), ATM (newer)




TraditionalEnterprise Networks

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)


MPLS/VPN (new)MPLS/VPN (new)

ModernEnterprise Networks

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)


QoS in Enterprise NetworksQoS 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.


Case StudyCase 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


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




• 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)


SummarySummary

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



1. What is the typical enterprise network topology?

2. How is resilience achieved?

3. Based on what information do typical enterprise networks apply QoS?

Service Provider Case Study

Service Provider Case Study




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


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

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


QoS in Service Provider NetworksQoS 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.


Case StudyCase 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


Case StudyImplementation

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


SummarySummary

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



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?


Module SummaryModule 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

© 2001, Cisco Systems, Inc. IP QoS Introduction-91

Documents

© 2001, Cisco Systems, Inc. Introduction. © 2001, Cisco Systems, Inc. QoS v1.0—1-2 Objectives Upon completing this module, you will be able to: Describe