RCA SpeedTouch User Manual
SpeedTouch™
(Wireless) Business DSL Router
IPQoS Configuration Guide
Release R5.3.0
SpeedTouch™608WL and
SpeedTouch™620 only
SpeedTouch™
IPQoS Configuration Guide
R5.3.0
Copyright
Copyright ©1999-2005 THOMSON. All rights reserved.
Passing on, and copying of this document, use and communication of its contents is not permitted without written authorization
from THOMSON. The content of this document is furnished for informational use only, may be subject to change without notice,
and should not be construed as a commitment by THOMSON. THOMSON assumes no responsibility or liability for any errors or
inaccuracies that may appear in this document.
Thomson Telecom Belgium
Prins Boudewijnlaan, 47
B-2650 Edegem
Belgium
www.speedtouch.com
Trademarks
The following trademarks are used in this document:
SpeedTouch™ is a trademark of THOMSON.
Microsoft®, MS-DOS®, Windows® and Windows NT® are either registered trademarks or trademarks of Microsoft Corpora-
tion in the United States and/or other countries.
UNIX® is a registered trademark of UNIX System Laboratories, Incorporated.
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rated, registered in the United States and/or other countries.
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Ethernet™ is a trademark of Xerox Corporation.
UPnP™ is a certification mark of the UPnP™ Implementers Corporation.
Wi-Fi® and the Wi-Fi logo are registered trademarks of the Wi-Fi Alliance. "Wi-Fi CERTIFIED", "Wi-Fi ZONE", "Wi-Fi Alli-
ance", their respective logos and "Wi-Fi Protected Access" are trademarks of the Wi-Fi Alliance.
Other products may be trademarks or registered trademarks of their respective manufacturers.
Document Information
Status: v0.5 (March 2005)
Reference: E-NIT-CTC-20041213-0013
Short Title: IPQoS Configuration Guide STBUS R5.3.0
Contents
Contents
About this IPQoS Configuration Guide...................... 7
1 Document scope ........................................................... 9
2 Introduction .................................................................11
2.1 What is Quality of Service? .......................................................... 12
2.2 Relative versus Guaranteed QoS.................................................. 14
3 Basic QoS Concepts.................................................... 15
3.1 Precedence and TOS .................................................................... 16
3.2 Differentiated Services ................................................................ 18
3.3 Classification and conditioning principles................................... 20
3.4 Differentiated Services Code Point (DSCP) ................................. 22
4 IP QoS Framework Overview..................................... 25
4.1 Main Framework Components ..................................................... 26
E-NIT-CTC-20041213-0013 v0.5
4.2 Resource Management ................................................................. 27
5 Packet Classification and Labelling ........................... 29
3
Contents
5.1 Classification ............................................................................... 30
5.1.1 Order of classification rules............................................................................ 31
5.2 Labels ........................................................................................... 33
5.2.1 Label parameters explained............................................................................ 35
5.2.2 Using TOS, DSCP or Precedence .................................................................... 38
5.2.3 Forwarding parameters.................................................................................. 40
5.3 Rules ............................................................................................ 42
5.3.1 Rules parameters explained............................................................................ 43
5.3.2 Rule debug commands .................................................................................. 47
5.4 Chains .......................................................................................... 49
5.4.1 Define a relation between chains .................................................................... 51
5.5 Expressions .................................................................................. 52
5.5.1 Expression parameters .................................................................................. 53
6 Meters, queues and IPQoS......................................... 59
6.1 Meters and queues ....................................................................... 60
6.2 The IPQoS command group ......................................................... 61
6.3 EF timers ...................................................................................... 63
6.4 Meter command group ................................................................. 67
6.4.1 Meter config command ................................................................................. 68
6.4.2 Packet flow ................................................................................................. 74
6.5 Queue command group ................................................................ 75
6.5.1 Queue config parameters explained................................................................. 76
6.6 IPQoS Command group ................................................................ 81
6.6.1 Ipqos config parameters explained.................................................................. 82
7 Scenario 1: Residential user....................................... 85
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E-NIT-CTC-20041213-0013 v0.5
Contents
7.1 Configuring labels and rules for VoIP. ......................................... 86
7.2 Configuring labels and rules for DSCP. ....................................... 90
7.3 Configuring labels and rules for Interactive traffic. .................... 92
7.4 IPQoS configuration..................................................................... 95
8 Scenario 2: Business user with TOS marking. ......... 97
8.1 Labels ........................................................................................... 99
8.2 Rules. ......................................................................................... 103
8.3 IPQoS per PVC ........................................................................... 112
9 Scenario 3: Metering................................................. 115
E-NIT-CTC-20041213-0013 v0.5
5
Contents
About this IPQoS Configuration Guide
About this IPQoS Configuration Guide
In this configuration
guide
Used Symbols
Applicability and
terminology
This routing configuration guide explains how routes can/must be used in
SpeedTouch™ R5.3 products. To explain the use of routes, a distinction is made
between standard IP forwarding and packet-based classification.
All examples start from a clean SpeedTouch™ configuration.
A note provides additional information about a topic.
A tip provides an alternative method or short-cut to perform an action.
A caution warns you about potential problems or specific precautions that
!
need to be taken.
This IPQoS Configuration Guide is applicable to:
SpeedTouch™ 516/536/546/576 Multi-user ADSL gateways.
SpeedTouch™ 585 Residential DSL router.
SpeedTouch™ 620 Business DSL router.
SpeedTouch™ 605 Business Multi-user ADSL gateway.
SpeedTouch™ 608 Business DSL router.
Generally, all these SpeedTouch™620 products will be referred to as SpeedTouch™ in
this IPQoS Configuration Guide, unless a specific device is mentioned.
On some products the expert web pages are not available, almost the same
functionality is offered through CLI configuration.
Typographical
Conventions
Documentation and
software updates
E-NIT-CTC-20041213-0013 v0.5
When we display interactive input and output we’ll show our typed input in a bold
font and the computer output
Comments are added in italics.
Example:
=>language list
CODE LANGUAGE VERSION FILENAME
en* english 4.2.0.1 <system>
Bold is also used in the output to emphasize a specific section.
THOMSON continuously develops new solutions, but is also committed to improve
its existing products.
For more information on THOMSON's latest technological innovations, documents
and software releases, visit us at:
like this.
Only one language is available
www.speedtouch.com
7
About this IPQoS Configuration Guide
8
E-NIT-CTC-20041213-0013 v0.5
Document scope
1 Document scope
Introduction The SpeedTouch™ Release 5.3.0 has a strong Quality of Service (QoS) base that
allows classification and forwarding of data to a single or multiple ATM VPI/VCIs
with each a set of ATMQoS parameters. IP Quality of Service is an extension to this
QoS framework. This configuration guide presents:
An introduction on IPQoS
An overview of the IPQoS framework
An overview of the labels, rules and expressions
An overview of the queue, meters and IPQoS commands
Some IPQoS application examples and how to configure them
A “Residential Scenario” using a single LAN segment with different
services.
A “Business Scenario” using multiple LAN segment with different services
and priorities.
A “Rate Limiting Scenario” using interface based rate limiting.
Chapter 1
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9
Chapter 1
Document scope
2Introduction
Introduction This chapter gives a general description and use of Quality of Service.
In this chapter
Topi c Pag e
2.1 What is Quality of Service? 12
2.2 Relative versus Guaranteed QoS 14
Chapter 2
Introduction
E-NIT-CTC-20041213-0013 v0.5
11
Chapter 2
Introduction
2.1 What is Quality of Service?
Definition Quality of Service is the ability for an application to obtain the network service it
requires for successful operation.
Nowadays the total amount of data traffic increases, while new types of data
emerge, like: voice data, video data, audio data. These new types of data pose new
requirements for data transport, e.g. low latency, low data loss… To meet these
requirements, the entire network must ensure them via a connection service
guarantee. Such a connection service guarantee can both be applied to connectionoriented networks (connection based) and to packet-oriented networks (data-stream
or data type based).
Quality of Service allows specifying a connection service guarantee via a set of
connection parameters. Throughout the network, this set of connection parameters
will be used to handle the connection data in a way to achieve the connection
service guarantee. This handling includes reserving bandwidth, priority based
queuing, scheduling, modifying data characteristics, …
Examples of connection parameters include the maximum amount of bandwidth that
may be used, the guaranteed amount of bandwidth that will always be available, the
maximum delay the data can experience throughout the network, a priority
indication,…
Misunderstandings A common misunderstanding about QoS is that QoS is about gaining a superior level
of network service for particular individuals.
The example below illustrates this.
The best illustration of why it is pointless to give enhanced network service to
particular individuals is shown by video-conferencing. Imagine John: he sees a
horrible quality image of the other video conference participant; but the other
participant sees John’s face perfectly. This is obviously not the desired result.
For John to also see a high-quality image, all participants in the video conference
need appropriate network service, not only John.
IP QoS provides such service. With IP QoS voice and/or video traffic can get a higher
priority then data traffic. This way good voice and video quality is guaranteed.
Note that QoS is no solution for overloaded networks, it only helps to shape
!
bursty peaks on the network. (See Bandwidth versus QoS )
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E-NIT-CTC-20041213-0013 v0.5
Bandwidth versus QoS Quality of Service is really best noticed when the Best Effort service encounters
congestion. So a common question is "why not provide more bandwidth, use Best
Effort, and get rid of complicated QoS architectures?"
There are four answers:
First of all, it is less economic to use more bandwidth than to use QoS. Many
congestion problems can be resolved by using QoS.
The second reason is, Denial of Service (DoS) attacks can always fill links. Even
a 10Gbps link can be flooded by ten compromised gigabit ethernet hosts. QoS
allows Voice traffic to work perfectly even at the peak of a DoS incident.
The third reason is, a scavenger service (also known as a "worst effort" or "less
than best effort" service) gives Best Effort traffic such as web browsing priority
over traffic such as large downloads.
Last but not least, we can use quality of service to ameliorate the effect of TCP
unfriendly traffic, such as unauthenticated video (UDP). This amelioration can
prevent congestion collapse of Best Effort traffic due to excessive video load.
Using QoS for this function is in no way as satisfactory as modifying video
stream and video multicast protocols to become TCP friendly. But using QoS
does ameliorate the worst effect of these TCP unfriendly protocols.
Chapter 2
Introduction
Bandwidth does improve the latency for data, but may still require QoS for
congestion management and “guaranteed QoS”.
E-NIT-CTC-20041213-0013 v0.5
13
Chapter 2
Introduction
2.2 Relative versus Guaranteed QoS
Typ es of QoS There are two different approaches to achieve QoS:
Guaranteed QoS:
Measurable connection parameters are specified for certain data or for a
connection, for example a guaranteed amount of bandwidth or delay across the
network. This allows for an exact specification and measurement of the Quality
of Service of data or a connection.
Examples of “guaranteed QoS” are Integrated Services (IntServ) and ATM QoS
like VBR and CBR connections.
Relative QoS (also referred to as differentiated QoS):
A priority indication is given as connection parameter to certain data or to a
connection, so that this data or connection will be handled with precedence
over data or connections with less priority. Obviously this approach guarantees
no specified bandwidth or latency, but it is the easiest approach to achieve
some level of QoS for high priority data.
Examples of “relative QoS” are Differentiated Services (DiffServ, DS) and
Ethernet VLAN user priority indication.
The guaranteed QoS approach is slightly more complicated than Relative
QoS because the connection parameters have to be specified and may be
verified throughout the entire network.
In case of relative QoS, data is often specified to belong to a certain Class of
Service (CoS) instead of QoS. Treatment and priority of data throughout the
network is configured for each supported CoS.
14
E-NIT-CTC-20041213-0013 v0.5
3 Basic QoS Concepts
Introduction This chapter provides a brief explanation about:
Basic concepts of Quality of Service in general.
Precedence and TOS in general
The Differentiated Services architecture in detail
In this chapter
Topi c Pag e
3.1 Precedence and TOS 16
3.2 Differentiated Services 18
3.3 Classification and conditioning principles 20
Chapter 3
Basic QoS Concepts
3.4 Differentiated Services Code Point (DSCP) 22
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15
Chapter 3
Basic QoS Concepts
3.1 Precedence and TOS
Introduction There are two generations of quality of service architectures in the Internet Protocol.
The interpretation of the Type of Service Octet in the Internet Protocol header varies
between these two generations.
The figure below shows the Internet Protocol header.
The Type of Service Octet is the second 8-bit octet of the Internet Protocol header.
04
Version Header
Length
Identification DM
Time to Live Protocol Header Chuckles
Type of Service Total Length
Source Address
Destination Address
First generation Precedence and Type of Service bits.
The initial definition of the Type of Service Octet looked like this:
01234567
Precedence D T R C
Most Precedence descriptions are obscure: they relate to message handling priorities
of US military communications in the 1960s. The essence is that higher values of
Precedence lead to higher levels of network service.
To prevent high link utilisation causing routing traffic to be lost, it is traditional to use
Precedence = 7 for interior routing protocols, such as OSPF and RIP and to use
Precedence = 6 for exterior routing protocols such as BGP.
The D type of service bit can be a value of 0 to request normal delay, a value of 1 to
request a low delay service.
The T type of service bit can be a value of 0 to request normal throughput, a value of
1 to request a high throughput service.
The R type of service bit can be a value of 0 to request normal reliability, a value of 1
to request a high reliability service.
The C type of service bit can be a value of 0 to request normal costs, a value of 1 to
request a low cost service.
The D,T,R and C type of service bit is defined in RFC791 (Internet Protocol)
81631
OFF
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E-NIT-CTC-20041213-0013 v0.5
Precedence values The table below gives the precedence values:
Precedence Purpose
0Routine
1Priority
2 Immediate
3Flash
4Flash Override
5CRITIC/ECP
6 Internetwork Control
7 Network Control
Chapter 3
Basic QoS Concepts
Note that IP Precedence is obsolete and is only implemented to provide
backwards compatibility.
Second generation The Differentiated Service Code Point is a selector for router's per-hop behaviours.
01234567
Differentiated Service Code Point ECT CE
The fields ECT and CE are spare bits in the IP header used by Explicit Congestion
Notification (RFC3168).
As can be seen, the DSCP field supersedes the old Precedence field. So the values of
DSCP provide limited backwards compatibility with Precedence.
This leads to notions of "class", each class being the group of DSCPs with the same
Precedence value. Values within a class would offer similar network services but
with slight differences (used to create different levels of service such as "gold",
"silver" and "bronze").
E-NIT-CTC-20041213-0013 v0.5
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Chapter 3
Basic QoS Concepts
3.2 Differentiated Services
Introduction Differentiated Services (DiffServ) is an architecture which allows service providers to
offer different kinds of services to different customers and their traffic streams.
Differentiated Services is a framework for scalable service discrimination and allows
an approach to modular IPQoS objectives for the needs of various types of
applications.
The premise to DiffServ networks is that routers within the core of the network are
capable to forward the packets of different traffic streams in different Per-Hop
Behaviours (PHB). The PHB for the packets is indicated by a Differentiated Services
Codepoint (DSCP) in the IP header. The DiffServ architecture does not use any
signalling between the routers but all the forwarding behaviour is defined by using
the DSCP.
Terminology Before we continue we will explain the abbreviations used in this section.
Behaviour Aggregate (BA):
Is a collection of packets with the same Differentiated Services codepoint, thus
receiving the same PHB, crossing a DiffServ node in a particular direction.
Differentiated Services CodePoint (DSCP):
Is the value in the IP header in the DS field, used to select the PHB.
Per-Hop Behaviour (PHB):
Is the forwarding behaviour for the packet applied at DiffServ compliant nodes
to a DiffServ BA.
Service Level Specification (SLS):
Is a set of parameters and their values which together define the service offered
to a traffic stream by a DiffServ domain.
Traffic Conditioning Specification (TCS):
Is a set of parameters and their values which together specify a set of classifier
rules.
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Chapter 3
e
Basic QoS Concepts
Differentiated Services
domain
A DiffServ domain consists of a set of DiffServ nodes which can provide the
common service and which have a set of PHBs implemented on each node. The
DiffServ domain has two types of nodes:
boundary nodes at the edges of the domain
interior nodes inside of the domain.
The boundary nodes are the access routers and edge routers that directly peer with
customers (either individual users or other ISPs).
SpeedTouch™
as boundary nod
Router at ISP as
interior node
Interior nodes only connect to other interior nodes or boundary nodes within the
same DiffServ domain.
Both DiffServ node types must be able to apply the appropriate PHB to packets,
according to the DSCP. The boundary nodes are required to perform traffic
conditioning functionality when the functionality of the interior nodes may be limited.
Boundary nodes act both as DiffServ ingress and DiffServ egress node, depending on
the direction of the traffic.
In practice this means that the boundary node makes sure that the TOS/DSCP byte is
set correctly.
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19
Chapter 3
Basic QoS Concepts
Traffic classification A packet is classified as belonging to a "class of service". This classification is done
3.3 Classification and conditioning principles
Introduction Packets go through a number of phases as they transit the network: classification,
marking, shaping, policing and queuing. These phases can occur a number of times
at each QoS-aware router in the path of the packet.
For example, a host might mark outgoing traffic as "best effort", "scavenger",
"discard at edge" or "discard at paid link". The hosts router might then police the
host's traffic to ensure that these are the only markings applied to traffic, and remark
invalidly marked packets as "best effort".
The traffic conditioners are usually located in DiffServ boundary nodes, so interior
nodes do not need to perform any traffic conditioning.
by the boundary nodes.
The BA classifier classifies the packets by the DSCP. Classification is based on the
value of combination of one or more IP header fields, such as source and destination
addresses, source and destination ports, protocol ID and other information like
incoming interface.
For example, we might classify data from a VoIP gateway as being "voice" traffic.
Traffic conditioning Traffic conditioning includes metering, policing, shaping and possibly re-marking to
ensure that the traffic stream entering the DiffServ domain conforms to the rules
specified in the SLS. The traffic conditioning policies are negotiated between the
networks and vary from simple re-marking to complex policing and shaping
operations.
The traffic conditioner includes meter, marker, shaper and dropper. The packets are
directed from the traffic classifier to the logical instance of traffic conditioner.
meter
packet
stream
The figure above shows that the packets travel from the classifier either to the meter
or to the marker.
The meter measures the rate at which packets of one BA pass the meter. It is used
to measure the traffic stream against the traffic profile.
The marker adds the packet to the appropriate BA according to the DSCP. The DSCP
may be changed by the marker, i.e. re-marked.
Shapers shape the packet stream to fit in the used traffic profile. The shaper may
also act as a dropper by dropping packets to fit the stream into the profile.
classifier
marker
shaper/dropper
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E-NIT-CTC-20041213-0013 v0.5
Basic QoS Concepts
Marking Once classified, a packet is marked to avoid repeated re-classifications. The marking
is made to the Differentiated Services Code Point (DSCP). The DSCP is trusted by
later routers, so that the high cost of classifying traffic occurs only once.
Shaping At the outgoing network edge, traffic is shaped to meet the traffic contract.
Metering At the outgoing network edge, traffic is metered to meet the traffic profile. This
means that the bandwidth can be limited for certain traffic.
Policing At the incoming network edge traffic is measured and traffic in excess of the traffic
contract is either re-marked to "best effort" or discarded.
Chapter 3
E-NIT-CTC-20041213-0013 v0.5
21
Chapter 3
Basic QoS Concepts
3.4 Differentiated Services Code Point (DSCP)
Introduction A small bit-pattern, called the DS field, in each IP packet is used to mark the packets
that should receive a particular forwarding treatment. The DS field uses the space of
the former ToS byte in the IPv4 IP header and the traffic class byte in the IPv6
header. All network traffic inside of a domain receives a service that depends on the
traffic class that is specified in the DS field.
The structure of the DS field is shown below:
7 6 5 4 3 2 1 0
DSCP ECN
A six-bit field, known as the Differentiated Services Code Point (DSCP), in the DS
field specifies the PHB for a given flow of packets. The DSCP is composed of the six
most significant bits of the DS field. The two least significant bits of the DS field are
used for Explicit Congestion Notification (ECN) by DiffServ-capable nodes that
support ECN. The ECN field contains 2 bits, the ECT bit and the CE bit.
The ECT bit is set to 1 to advertise to the network that the node is an ECN capable
node.
The CE bit is set to 1 incase the node experiences congestion.
Refer to RFC2474 for more information on the definition of the DS field.
Per Hop Behaviour Routers look at the DSCP to select a per-hop behaviour, such as a queueing
algorithm and its parameters.
A PHB defines a DiffServ router’s externally observable forwarding behaviour (in
terms of buffer/bandwidth resource allocation) related to a BA. This is essentially
defined by the queuing/scheduling/buffer management in the forwarding path.
PHBs are implemented in DiffServ nodes by means of some buffer management and
packet scheduling mechanism. The PHB definition is not depending on the
mechanism that offers the service but in terms of behaviour characteristics relevant
to service provisioning policy.
For example, "voice" traffic might select a "strict" queuing algorithm with a
parameter of "place in top priority queue".
Refer to RFC2475 for more information.
Standardized PHBs The following specific PHBs and recommended DSCPs for each PHB have been
standardized by the IETF:
Default PHB.
Expedited Forwarding PHB.
Class Selector (CS) PHB.
Assured Forwarding PHB.
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Chapter 3
Basic QoS Concepts
E-NIT-CTC-20041213-0013 v0.5
23
Chapter 3
Basic QoS Concepts
Assured Forwarding
(AF) PHB Group:
The Assured Forwarding (AF) PHB group allows a provider to offer different levels of
forwarding assurances for IP packets. The delivery of IP packets is provided in four
independently forwarded AF classes (AF1x through AF4x). Each AF class is allocated
a certain amount of forwarding resources (buffer space and bandwidth) in a DS node.
Within each AF class, there are three drop probabilities: Low, Medium and High drop
precedence (the higher the precedence, the higher the probability the packet will be
dropped in case of congestion).
Packets can be selected for a PHB based on required throughput, delay, jitter, loss, or
according to priority of access to network services.
The table below illustrates the recommended DSCP coding for specifying the AF
class with the drop probability. The AF value, the decimal value and the binary value
are shown for each DSCP.
Drop Precedence Class 1
AF1
Low Gold
AF11
10
(001010)
Medium Silver
AF12
12
(001100)
Class 2
AF2
Gold
AF21
18
(010010)
Silver
AF22
20
(010100)
Class 3
AF3
Gold
AF31
26
(011010)
Silver
AF32
28
(011100)
Class 4
AF4
Gold
AF41
34
(100010)
Silver
AF42
36
(100100)
High Bronze
AF13
14
(001110)
For more information on the AF PHB, refer to RFC2597.
Bronze
AF23
22
(010110)
Bronze
AF33
30
(011110)
Bronze
AF43
38
(100110)
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IP QoS Framework Overview
4 IP QoS Framework Overview
Introduction This chapter presents an overview of the main components of the IP QoS framework
within the SpeedTouch™.
In this chapter
Topi c Pag e
4.1 Main Framework Components 26
4.2 Resource Management 27
Chapter 4
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25
Chapter 4
W
IP QoS Framework Overview
Graphical overview The figure below shows a graphical overview of the main components in the
4.1 Main Framework Components
upstream datapath.Notice that there are two main blocks, the input and output.
In between these two blocks the IP packets go through a series of processes like
firewall, nat etc.
INPUT OUTPUT
MANAGEMENT
ETH
ireless
LAN
USB
RESOURCE
Classification
IP forwarding
destination
or
label-based
QoS Components The main QoS components are:
Resource Management: The main purpose of this module is to assure that
arriving low priority data cannot consume all the internal memory resources. In
case of congestion and resource starvation, this module will deny low priority
data from consuming memory resources. The Resource Management module
also maps the Layer 2 VLAN user priority to an internal Class.
Classification: The classification module classifies incoming data. Data that
matches the classification criteria will be labelled. A label is only of internal
significance and can be used in forwarding and QoS definition. Each label can
have an internal QoS class associated with it. Data will experience treatment
(queuing and scheduling) according to its QoS class. The SpeedTouch™
Business DSL Router support 16 internal classes which are linked to the 6
queues. The 6 queues are:
The Real Time queue (EF)
The Weight Fair queue 4 (WFQ4)
The Weight Fair queue 3 (WFQ3)
The Weight Fair queue 2 (WFQ2)
The Weight Fair queue 1 (WFQ1)
The Best Effort queue (BE)
There are 6 queues defined per ATM interface. So each ATM interface
can have different QoS settings.
Packect
handeling
MANAGEMENT
RESOURCE
IP QoS
queueing
+
scheduling
+
rate limiting
ATM
QoS
DSL
IP Forwarding: IP forwarding supports the use of labels to forward classified
data to any IP interface. This allows, for example, to forward data based upon
port(-ranges), IP addresses, protocol, source interface, Differentiated Services
Code Point (DSCP), … (see the “Routing Configuration Guide” for more details
on routing and forwarding)
IP QoS Queuing, Scheduling and Rate Limiting: This module implements the
internal IP QoS queues and scheduling and maps the internal class (set during
classification or set by the Resource management module) to one of these
queues. Rate-limiting can be configured for the fixed priority real-time queue.
This queue has fixed priority over other queues. This ensures a low latency but
could lead to starvation of lower priority queues. By configuring a percentage of
the total available interface bandwidth, data from this queue will be limited to
this bandwidth in case of congestion.
ATM QoS: The ATM Quality of Service module holds the extensive ATM QoS
features, starting with per ATM VP/VC queuing and shaping, per ATM QoS
class queuing and scheduling, performing connection admission control.
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Chapter 4
IP QoS Framework Overview
4.2 Resource Management
Introduction The RM module reserves memory for four independent traffic classes. Resources are
reserved for each RM-class, both in the upstream and in the downstream direction (8
reservations in total). The figure below shows the Resource Management
reservations.
Dynamic Memory Pool
resource
reservation
For incoming data towards the IP host, this module copies the VLAN user priority
field into the packet internal class indication. The module also sets (or raises) the
internal class indication based upon the ATM VP/VC QoS category for reassembled
frames.
As a result, incoming low priority UBR (Unspecified Bit Rate) traffic will not be able to
consume all resources because resources are reserved for VBR (Variable Bit Rate)
and CBR (Constant Bit Rate) data. Similarly, low priority VLAN frames won't be able
to consume all resources because resources are reserved for high priority (based
upon the VLAN user priority field) VLAN frames.
0 1 2 3
UPSTREAM
0 1 2 3
DOWNSTREAM
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Chapter 4
IP QoS Framework Overview
Mapping to internal
class
The RM module maps packets to the an internal class depending on ATM QoS, VLAN
priority or DSCP settings. The table below shows the relation between these
settings. Once the mapping to the internal classes has been completed the packet
goes through a number of processes like firewall, nat etc. Finally once the packet is
ready for output it will be put in one of the 6 queues based upon its internal class.
INPUT
ATM QoS
Category
CBR 7 CS6,CS7
VBR-rt 6
VBR-nrt
(low CDVT)
GFR
(low CDVT)
VBR-nrt
(high CDVT)
GFR
(high CDVT)
VLAN User
Priority
-
-
-
5
DiffServ
DSCP
EF
CS5
AF41
CS4
AF42,AF4
3
AF31
CS3
AF32,AF3
3
Mapping OUTPUT
Internal
Class
15
14
13
12
11
10
Queue Label
5
4WFQ4
3WFQ3
Real
Time
--
-4
UBR BCS 7 -
ABR /UBR
BCS 6
UBR-mdcr /
UBR BCS 5
UBR / UBR
BCS 4
UBR BCS 3 - - 3
UBR BCS 2 2 - 2
UBR BCS 1 - - 1
UBR BCS 0 1 - 0
3
--
0
AF21
CS2
AF22,AF2
3
AF11
CS1
AF12,AF1
3
CS0
Best Effort
9
2WFQ2
8
7
1WFQ1
6
5
4
0
Best
Effort
28
E-NIT-CTC-20041213-0013 v0.5
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