ISC Quality of Service Concepts
C H A P T E R1-1Cisco IP Solution Center Security Management Suite Quality of Service User Guide, 3.2OL-5534-011ISC Quality of Service ConceptsWhen network congestion occurs, all traffic has an equal chance of being dropped. Quality of service
(QoS) provisioning categorizes network traffic, prioritizes it according to its relative importance, and
provides priority treatment through congestion avoidance techniques. Implementing QoS in your
network makes network performance more predictable and bandwidth utilization more effective.QoS classifies traffic by assigning class of service (CoS) values to frames at supported ingress interfaces.
QoS implements scheduling on egress interfaces with transmit queue drop thresholds and multiple
transmit queues that use CoS values to give preference to higher-priority traffic.QoS manages bandwidth to assure the desired performance for network applications. For example, email
generally does not require high performance from a network, but real-time applications such as IP
telephony or video streaming do. If the network is not consistently providing data flow control for these
applications, the performance suffers.Service provider network architecture contains access routers, distribution routers, core routers and
ATM switches. The access routers terminate customer connections. The Cisco IP Solution Center (ISC)
configures QoS at the access circuit, which involves the access router (called provider edge devices, or
PEs) in the service provider network and the customer premise equipment (CPE) in the customer
network. A QoS policy is applied to the selected set of access circuits using a QoS policy configuration.There are three ways to provision QoS using ISC:•IP QoS—Select the device interfaces, create a QoS policy and apply it to the specified device
interfaces. IP QoS can be implemented independent of VPN services and is the most common
method for QoS provisioning using ISC.IP QoS provisioning is described inChapter 5, “Provisioning Process for IP QoS.”.This chapter describes the basic concepts for Quality of Service (QoS) as it is used in the ISC
application.This chapter contains the following sections:•Introduction to ISC QoS, page 1-1•ISC QoS Components, page 1-2Introduction to ISC QoSQoS provisioning is a method for optimizing the flow of traffic in a network. If you have an enterprise
network with services facilitated across a service provider MPLS infrastructure, QoS provisioning can
guarantee that all applications receive the service levels required to meet expected performance in the
network.1-2Cisco IP Solution Center Security Management Suite Quality of Service User Guide, 3.2OL-5534-01Chapter 1 ISC Quality of Service ConceptsISC QoS ComponentsFor complete QoS implementation you should identify:•Low-latency applications (video and voice-over-IP, or VoIP) and mark them for high-priority
treatment throughout the network•Applications that require bandwidth guarantees should be marked and protected•Applications that use more than their fair share of bandwidth can be identified and controlledQoS is a collection of technologies that allows applications to request and receive predictable service
levels in terms of bandwidth, latency variations, and delay.Table 1-1 shows the typical QoS requirements for a multimedia network.Voice and video applications are less tolerant of loss, delay, and delay variation (jitter) than data, but
their QoS requirements are more obvious. Data applications vary widely in their QoS requirements, and
should be profiled before you determine the appropriate classification and scheduling treatment.ISC QoS ComponentsThere are three primary configuration components to QoS:•Classification—Identifying and marking packets so that varying service levels can be enforced
throughout the network.•Scheduling—Assigning packets to one of multiple queues and associated service types based on
classification for specific service level treatment by the network.•Resource management—Accurately calculating the required bandwidth for all applications plus
overhead.In ISC, the QoS components used to achieve classification, scheduling, and resource management are:•Traffic Classification, page 1-3•Marking, page 1-3•Rate Limiting, page 1-4•Traffic Shaping, page 1-4•Congestion Management, page 1-5•Congestion Avoidance, page 1-5Each of these components is described in the following sections.Table 1-1Typical Multimedia QoS RequirementsTraffic TypeMax. Packet
LossMax. One-way
LatencyMax. JitterGuaranteed Priority Bandwidth
Per SessionVoIP1 percent200 ms30 ms12 to 106 kbps*Video-conferencing1 percent200 ms30 msSize of the session plus
20 percentStreaming Video2 percent5 secondsN/ADepends on encoding format and
video stream rate.DataVariableVariableVariableVariable*Depending on sampling rate, codec, and Layer 2 overhead.1-3Cisco IP Solution Center Security Management Suite Quality of Service User Guide, 3.2OL-5534-01Chapter 1 ISC Quality of Service ConceptsISC QoS ComponentsTraffic ClassificationTraffic classification (also called packet classification) partitions traffic into multiple priority levels, or
classes of service. Traffic classification is the primary component of class-based QoS provisioning.For example, using the three precedence bits in the type of service (ToS) field of the IP packet header,
you can categorize packets into a limited set of up to six traffic classes. After you classify packets, you
can use other QoS components to assign the appropriate traffic handling policies for each traffic class.Packets can also be classified by external sources such as; by a customer, or by a downstream network
provider. You can either allow the network to accept the external classification, or override it and
re-classify the packet according to the QoS policy you specify in ISC.ISC allows you to classify traffic based on source address, source port, destination port, port ranges,
protocol ID, DSCP, and IP Precedence values.IP QoS Traffic ClassificationFor IP QoS, ISC uses traffic classification to associate packets with a specific service level IP QoS
policy. ISC provides five template service classes to use for traffic classification.•VoIP•Routing Protocol•Management•Business-Data-1•Best EffortA typical network uses three service classes in a QoS policy; a VoIP service class, a management service
class (which is often combined with a routing protocol service class), and a data service class.For more information on traffic classification in service classes, seeCreating the Service Level IP QoSPolicy, page 5-8.MarkingMarking is a way to identify packet flows to differentiate them. Packet marking allows you to partition
your network into multiple priority levels or classes of service.ISC supports marking based on the following bits in the IP QoS type of service (ToS) byte for the packet:•IP Precedence value•IP differentiated services code point (DSCP) valueThese markings can be used to identify traffic within the network, and other interfaces can match traffic
based on the IP Precedence or DSCP markings. You can set up to 8 different IP precedence markings (0
through 7) and 64 different IP DSCP markings (0 through 63).IP Precedence and DSCP markings are used in the following QoS concepts:•Congestion Management—Used to determine how packets should be scheduled.•Congestion Avoidance—Used to determine how packets should be treated in Weighted Random
Early Detection (WRED), a packet dropping mechanism used in congestion avoidance.1-4Cisco IP Solution Center Security Management Suite Quality of Service User Guide, 3.2OL-5534-01Chapter 1 ISC Quality of Service ConceptsISC QoS Components•Rate Limiting—Used to set the IP precedence or DSCP values for packets entering the network.
Networking devices within the network can then use the adjusted IP Precedence values to determine
how the traffic should be treated based on the transmission rate.Rate LimitingRate limiting allows you to control the maximum rate of traffic sent or received on an interface. Rate
limiting is configured on the CPE device interfaces at the edge of the network and limits traffic into or
out of the network. Traffic that falls within the rate parameters is sent, while traffic that exceeds the
parameters is dropped or sent with a different priority.ISC supports class-based rate limiting and interface-based aggregated rate limiting.•Class-based rate limiting applies rate limiting parameters to an ISC service class.•Interface-based aggregated rate limiting matches all packets, or a subset of packets, on an interface
or subinterface and allows you to control the maximum rate of traffic sent or received. You can also
specify traffic handling policies for traffic that either conforms to or exceeds the specified rate
limits.Rate limiting parameters in ISC include:•Mean or peak rate•Burst sizes•Conform, exceed, and violate actionsFor more information on configuring rate limiting QoS parameters in ISC, seeInterface-BasedAggregated Rate Limiters, page 6-27.Traffic ShapingTraffic shaping allows you to control the traffic exiting an interface to match its flow to the speed of the
remote target interface and to ensure that traffic conforms to the policies assigned to it.ISC supports class-based traffic shaping and aggregated traffic shaping.•Class-based traffic shaping applies traffic shaping to an ISC service class.•Aggregated traffic shaping applies these parameters to an interface instead of to a class of traffic.Specifying traffic shaping allows you to make better use of available bandwidth. Traffic shaping
parameters in ISC include:•Average rate or peak rate for class-based traffic shaping•Cell rates for ATM traffic shaping•Rate factors for ATM traffic shapingTipThe difference between a rate limiter parameter and a traffic shaping parameter is that the a rate limiter
drops traffic in the presence of congestion, while a traffic shaper delays excess traffic using a buffer, or
queueing mechanism.For more information on configuring traffic shaping parameters in ISC, seeAggregated Traffic Shapers,page 6-16.1-5Cisco IP Solution Center Security Management Suite Quality of Service User Guide, 3.2OL-5534-01Chapter 1 ISC Quality of Service ConceptsISC QoS ComponentsCongestion ManagementCongestion management controls congestion by determining the order in which packets are sent out an
interface based on priorities assigned to those packets.Congestion management involves:•Creating queues•Assigning packets to those queues based on packet classification•Scheduling packets in a queue for transmissionWith congestion management, packets are scheduled for transmission according to their assigned
priority and the queueing mechanism configured for the interface. The router determines the order of
packet transmission by controlling which packets are placed in which queue and how queues are serviced
with respect to each other.The congestion management component of QoS offers different types of queueing techniques, each of
which allows you to specify creation of a different number of queues, with greater or lesser degrees of
differentiation of traffic, and to specify the order in which that traffic is sent.Congestion management parameters in ISC include:•Bandwidth•Queue limitsCongestion management parameters are configured at the service class level in ISC. For more
information, seeService Level IP QoS Parameters, page 6-1.Congestion AvoidanceCongestion avoidance monitors network traffic loads in an effort to anticipate and avoid congestion at
common network bottlenecks. Congestion management parameters provide preferential treatment for
priority class traffic under congestion situations, while concurrently maximizing network throughput
and capacity utilization and minimizing packet loss and delay.ISC implements congestion avoidance parameters through packet dropping methods, such as WRED.
WRED is used in combination with DSCP and IP Precedence and provides buffer management. WRED
is frequently used to slow down TCP flows.Congestion avoidance techniques monitor network traffic loads in an effort to anticipate and avoid
congestion at common network and internetwork bottlenecks before it becomes a problem.Congestion avoidance parameters are configured at the service class level in ISC. For more information,
seeService Level IP QoS Parameters, page 6-1.1-6Cisco IP Solution Center Security Management Suite Quality of Service User Guide, 3.2OL-5534-01Chapter 1 ISC Quality of Service ConceptsISC QoS Components
refer page:-------http://www.officesoon.com/doc/147655-isc-quality-of-service-concepts
Click Here To Download...