Transcript qos10s01

Introduction
© 2001, Cisco Systems, Inc.
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)
• List the IP QoS mechanisms available in Cisco IOS
• Describe what QoS features are supported by different
IP QoS mechanisms
© 2001, Cisco Systems, Inc.
QoS v1.0—1-2
Introduction to IP
Quality of Service
© 2001, Cisco Systems, Inc.
QOS v1.0—1-3
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
• Name some QoS mechanisms available in
Cisco IOS
• Describe typical enterprise and service provider
networks and their QoS-related requirements
© 2001, Cisco Systems, Inc.
QoS v1.0—1-4
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-5
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)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-6
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-7
Available Bandwidth
IP
IP
IP
IP
512 kbps
256 kbps
10 Mbps
100 Mbps
BWmax = min(10M, 256k, 512k, 100M)=256 kbps
BWavail = BWmax /Flows
• 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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-8
End-to-End Delay
IP
IP
Propagation
Delay (P1)
Processing and
Queuing Delay (Q1)
Propagation
Delay (P2)
Processing and
Queuing Delay (Q2)
IP
IP
Propagation
Delay (P3)
Propagation
Delay (P4)
Processing and
Queuing Delay (Q3)
Delay = P1 + Q1 + P2 + Q2 + P3 + Q3 + P4 = X ms
• 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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-9
Processing, Queuing, and
Propagation Delay
IP
IP
Processing Delay
IP
Bandwidth
Forwarding
IP
Queuing Delay
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-10
Packet Loss
Forwarding
IP
IP
IP
IP
IP
Tail-drop
• 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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-11
How to Increase Available
Bandwidth?
TCP Header Compression
RTP Header Compression
cTCP Data
Compress
the Headers
IP
TCP
Fancy
FIFO queuing
Queuing
Data
Compress
the Payload
Compressed Packet
Stacker
Predictor
Priority Queuing (PQ)
Custom Queuing (CQ)
Modified Deficit Round Robin (MDRR)
Class-Based Weighted Fair Queing (CBWFQ)
• Upgrade the link—the best solution but also the most expensive.
• Take some bandwidth from less important applications.
• Compress the payload of Layer 2 frames.
• Compress the header of IP packets.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-12
How to Reduce Delay?
TCP Header Compression
RTP Header Compression
cRTP Data
Compress
the Headers
IP
UDP RTP
FIFO queuing
Fancy
Queuing
Data
Compress
the Payload
Compressed Packet
Stacker
Predictor
Priority Queuing (PQ)
Custom Queuing (CQ)
Strict Priority MDRR
IP RTP Prioritization
Class-Based Low-Latency Queuing (CBLLQ)
• Upgrade the link—the best solution but also the most expensive.
• Forward the important packets first.
• Compress the payload of Layer-2 frames (it takes time).
• Compress the header of IP packets.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-13
How to Prevent Packet Loss?
Weighted Random Early Detection (WRED)
IP
Data
Dropper
Fancy
FIFO queuing
Queuing
Custom Queuing (CQ)
Modified Deficit Round Robin (MDRR)
Class-Based Weighted Fair Queuing (CBWFQ)
• Upgrade the link—the best solution but also the most expensive.
• Guarantee enough bandwidth to sensitive packets.
• Prevent congestion by randomly dropping less important packets
before congestion occurs.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-14
Which Applications Have Which
QoS Requirements?
Throughput
Delay
Loss
Jitter
Interactive
(e.g., Telnet)
Low
Low
Low
Not
Important
Batch (e.g.,
FTP)
High
Not
Important
Low
Not
Important
Fragile (e.g,.
SNA)
Low
Low
None
Not
Important
Voice
Low
Low and
Predictable
Low
Low
Video
High
Low and
Predictable
Low
Low
• Enterprise networks are typically focused on
providing QoS to applications.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-15
Which Services Can Be
Implemented in a Network?
Throughput
Delay
Loss
Jitter
Gold
Guaranteed
Low
Low
Low
Silver
Guaranteed
No
Guarantee
No
Guarantee
No
Guarantee
Bronze
Guaranteed
Limited
No
Guarantee
No
Guarantee
No
Guarantee
No
Guarantee
No
Guarantee
No
Guarantee
No
Guarantee
Best Effort
• Service provider networks typically offer services
based on source and destination addresses.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-16
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-17
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
• Name some QoS mechanisms available in Cisco IOS
• Describe typical enterprise and service provider
networks and their QoS-related requirements
© 2001, Cisco Systems, Inc.
QoS v1.0—1-18
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-19
Integrated Services
Model
© 2001, Cisco Systems, Inc.
QOS v1.0—1-20
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)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-21
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-22
IntServ Building Blocks
Local
Admission
Control
request
Policy Enforcement
Point (PEP)
request
request
reserve
reserve
Local
Admission
Control
request
reserve
reply
request
reserve
Remote Admission
Control
Policy Decision
Point (PDP)
• 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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-23
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).
© 2001, Cisco Systems, Inc.
QoS v1.0—1-24
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).
© 2001, Cisco Systems, Inc.
QoS v1.0—1-25
IntServ Implementation Options
RSVP
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
Class of Service
or
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)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-26
Explicit RSVP Transport
IntServ End-to-End
RSVP
All Routers
• WFQ applied per flow
based on RSVP requests
© 2001, Cisco Systems, Inc.
QoS v1.0—1-27
RSVP Pass-Through
IntServ - DiffServ Integration
RSVP
RSVP
Precedence
Classifier
Premium
Standard
WRED
• RSVP protocol
sent on to destination
• WFQ applied to
manage egress flow
Ingress Router
• RSVP protocol
Mapped to classes
Passed through to egress
Egress Router
Backbone
• WRED applied based
on class
© 2001, Cisco Systems, Inc.
QoS v1.0—1-28
IntServ 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 passthrough RSVP
• RSVP-to-DSCP (DiffServ code point) mapping
(RSVP proxy) in 12.1T
© 2001, Cisco Systems, Inc.
QoS v1.0—1-29
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-30
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-31
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)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-32
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?
© 2001, Cisco Systems, Inc.
QoS v1.0—1-33
Differentiated Services
Model
© 2001, Cisco Systems, Inc.
QOS v1.0—1-34
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-35
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-36
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-37
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-38
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-39
Topological Terminology
DS Interior Node
DS Egress
Boundary Node
DS Ingress Boundary Node
Boundary Link
Upstream
DS Domain
Downstream
DS Domain
DS Region
Traffic Stream = set of flows
Behavior Aggregate (flows with the same DSCP)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-40
Traffic Terminology
• Flow: a single instance of an application-toapplication 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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-41
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-42
Packet Header Terminology
DSCP Field: 6 bits
Unused: 2 bits
Former ToS Byte = New DS Field
• 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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-43
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-44
DSCP Usage
DSCP selects per-hop behavior (PHB)
throughout the network:
• Default PHB
• Class selector (IP Precedence) PHB
• Expedited forwarding PHB
• Assured forwarding PHB
© 2001, Cisco Systems, Inc.
QoS v1.0—1-45
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)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-46
Class Selector Code Point
• Compatibility with current IP Precedence
usage (RFC 1812)
• “xxx000” DSCPs
• Differentiates PTF
– PTF(xyz000) >= PTF(abc000) ifxyz > abc
© 2001, Cisco Systems, Inc.
QoS v1.0—1-47
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-48
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-49
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-50
Assured Forwarding Encoding
Class
AF1
AF2
AF3
AF4
Value
001dd0
010dd0
011dd0
100dd0
Drop
Value
Probability
(dd)
Low
01
Medium
10
High
11
• 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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-51
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-52
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)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-53
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-54
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-55
Building Blocks of IP
QoS Mechanisms
© 2001, Cisco Systems, Inc.
QOS v1.0—1-56
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
• List the forwarding mechanisms available in Cisco IOS
• List the queuing mechanisms available in Cisco IOS
© 2001, Cisco Systems, Inc.
QoS v1.0—1-57
Router Functions
Defragmentation
Decompression (payload, header)
Source-based QoS-label/precedence setting
Destination-based QoS-label/precedence
setting
Rate limiting
Class-based marking
Policy-based routing
...
Input I/O
Input
Processing
Rate limiting
Random dropping
Shaping
Compression (payload, header)
Fragmentation
Queuing and scheduling
...
Forwarding
Output
Processing
Output I/O
Process switching
Fast/optimum switching
Netflow switching
CEF switching
• 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)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-58
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).
© 2001, Cisco Systems, Inc.
QoS v1.0—1-59
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.).
© 2001, Cisco Systems, Inc.
QoS v1.0—1-60
DiffServ Mechanisms in IOS
Meter
Inbound
traffic
stream
Classifier
Marker
Conditioner
Queuing
Shaping
Dropping
Scheduling
Dropping
• 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)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-61
DiffServ Mechanisms in IOS
(cont.)
Meter
Inbound
traffic
stream
Classifier
Marker
Conditioner
Queuing
Shaping
Dropping
Scheduling
Dropping
• 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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-62
DiffServ Mechanisms in IOS
(cont.)
Meter
Inbound
traffic
stream
Classifier
Marker
• 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
© 2001, Cisco Systems, Inc.
Conditioner
Queuing
Shaping
Dropping
Scheduling
Dropping
• Marking mechanisms:
– Comitted access rate (CAR)
– QoS Policy Propagation on
BGP (QPPB)
– Policy-based routing (PBR)
– Class-based marking
QoS v1.0—1-63
Comparison of Markers
Marker
Preservation
Value Range
IP Precedence
Throughout a network
8 values, 2 reserved
(0 to 7)
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)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-64
DiffServ Mechanisms in IOS
(cont.)
Meter
Inbound
traffic
stream
Classifier
Marker
Conditioner
Queuing
Shaping
Dropping
Scheduling
Dropping
• Shaping mechanisms:
– Generic traffic shaping (GTS)
– Frame Relay traffic shaping (FRTS)
– Class-based shaping
– Hardware shaping on ATM VC
© 2001, Cisco Systems, Inc.
QoS v1.0—1-65
DiffServ Mechanisms in IOS
(cont.)
Meter
Inbound
traffic
stream
Classifier
Marker
Conditioner
Queuing
Shaping
Dropping
Scheduling
Dropping
• 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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-66
DiffServ Mechanisms in IOS
(cont.)
Meter
Inbound
traffic
stream
Classifier
Marker
Conditioner
Forwarding
Shaping
Dropping
Queuing
Scheduling
Dropping
• Cisco Express Forwarding (CEF) is
recommended from IOS 12.0.
• Some QoS features work only in combination
with CEF.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-67
DiffServ Mechanisms in IOS
(cont.)
Meter
Inbound
traffic
stream
Classifier
Marker
Conditioner
Forwarding
Shaping
Dropping
Queuing
Scheduling
Dropping
• 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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-68
DiffServ Mechanisms in IOS
(cont.)
Meter
Inbound
traffic
stream
Classifier
Marker
Conditioner
Forwarding
Shaping
Dropping
Queuing
Scheduling
Dropping
• Tail drop is used for most queue congestion.
• WFQ has an improved tail-drop scheme.
• WRED randomly drops packets when nearing
congestion.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-69
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
• List the forwarding mechanisms available in Cisco
IOS
• List the queuing mechanisms available in Cisco IOS
© 2001, Cisco Systems, Inc.
QoS v1.0—1-70
Review Questions
1.
2.
3.
4.
5.
6.
7.
8.
9.
Name the QoS building blocks.
What is the purpose of classification?
What is the purpose of marking?
Which parameters can be used to mark packets?
Which mechanisms can classify and mark
packets?
Which mechanisms have the ability to measure the
rate of traffic?
Which forwarding mechanisms exist in Cisco IOS ?
Which queuing mechanisms exist in Cisco IOS ?
How, when, and where do routers drop packets?
© 2001, Cisco Systems, Inc.
QoS v1.0—1-71
Enterprise Network
Case Study
© 2001, Cisco Systems, Inc.
QOS v1.0—1-72
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-73
Traditional
Enterprise Networks
Core
(central sites
and
data centers)
X.25 (ancient), Frame Relay (old),
ATM (newer)
Distribution
(regional centers)
X.25 (ancient), Frame Relay (old),
ATM (newer)
Access
(branch offices)
• 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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-74
Modern
Enterprise Networks
Core
(central sites
and
data centers)
MPLS/VPN (new)
Access
(branch offices)
• 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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-75
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-76
Case Study
• Typical line speeds:
– Core to Distribution
– Distribution to Branch
< 2 Mbps
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-77
Case Study
Implementation #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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-78
Case Study
Implementation #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)
© 2001, Cisco Systems, Inc.
QoS v1.0—1-79
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-80
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?
© 2001, Cisco Systems, Inc.
QoS v1.0—1-81
Service Provider Case
Study
© 2001, Cisco Systems, Inc.
QOS v1.0—1-82
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-83
Typical
Service Provider Networks
Core
ATM, SONET/SDH, DPT, GE, ...
Partial mesh
Rings
ATM, SONET/SDH, DPT, GE, ...
Redundant connections
Rings
Distribution
(regional POPs)
Frame Relay, ATM, leased line (analog, TDM),
dial-up (PSTN, ISDN, GSM), xDSL, (fast) Ethernet, ...
Single connections
Optional redundant connections
Dial backup
Access
(customers)
•
•
•
•
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).
© 2001, Cisco Systems, Inc.
QoS v1.0—1-84
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.
© 2001, Cisco Systems, Inc.
QoS v1.0—1-85
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-86
Case Study
Implementation
• 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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-87
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-88
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?
© 2001, Cisco Systems, Inc.
QoS v1.0—1-89
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
© 2001, Cisco Systems, Inc.
QoS v1.0—1-90
© 2001, Cisco Systems, Inc.
IP QoS Introduction-91