CCNA Quality of Services (QoS)

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8- QUALITY OF SERVICE

8.1 Basics Of QoS

8.2 QoS Mechanisms


8.1 Basics Of QoS


QoS OVERVIEW

• Quality Of Service

• Industry-wide set of standards and

mechanisms for ensuring high-quality

performance for critical applications

• Ability to provide different priority to

different applications, users, or data

flows, or to guarantee a certain level

of performance to a data flow


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PRIORITIZATION OF NETWORK TRAFFIC

• Some traffic flows are more important

for the companies

• If the bandwidth demand exceeds the

available amount, traffic congestion

occurs

• Result = Loss / Delay of the critical

data


NETWORK CHARACHTERIST. MANAGED BY QOS

• Bandwidth : The rate at which traffic

is carried by the network

• Latency : The delay in data

transmission from source to

destination

• Jitter : The variation in latency.

• Reliability : The percentage of packets

discarded by a router


VOICE TRAFFIC

• Sensitive for delays / drops

• No retransmission if the packet is lost

(UDP Based)

• Smooth (Flows at even rate, doesn’t burst)

• Benign (Not greedy for lots of BW fairly

low per call)


VIDEO TRAFFIC

• Sensitive for delays / drops

• No retransmission if the packet is lost

(UDP Based)

• Bursty (Part of picture moves rest is

static on screen cause of keyframes)

• Greedy (More BW you define, better

the picture quality is)


DATA TRAFFIC

• Insensitive for delays / drops

• Smooth/Bursty

• Benign/Greedy

• TCP-based retransmits.


QUEUING ALGORITHMS

• Instead of dropping traffic, routers

and switches queue packets into an

output queue and all new packets go

through the queuing system

1. FIFO

2. WFQ

3. CBWFQ

4. LLQ


FIFO (FIRST IN FIRST OUT)

• Traffic departs from the interface as it

arrived

• No traffic priority

FIFO


WFQ (WEIGHTED FAIR QUEUING)

• Flow-based queuing algorithm

• Schedules interactive traffic to the

front of the queue to reduce response

time

• Fairly shares the remaining bandwidth

between high bandwidth flows.


CBWFQ(CLASS BASED WEIGHTED FAIR QUEUIN)

• Extends the standard WFQ

functionality to provide support for

user-defined traffic classes

• A queue is reserved for each class, and

traffic belonging to a class is directed

to the queue for that class


LLQ (LOW LATENCY QUEUING)

• Brings strict priority queuing to class-

based weighted fair queuing

(CBWFQ)

• Allows delay-sensitive data (such as

voice) to be given preferential

treatment over other traffic by letting

the data to be dequeued and sent first


8.2 QoS Mechanisms


QoS TECHNOLOGIES

• Used to provide improved network

"service" to the applications at the

edges of the network

1. Best Effort

2. Integrated Services

3. Differentiated Services


BEST EFFORT

• Network does not provide any

guarantees that data is delivered

Users obtain unspecified variable bit

rate and delivery time, depending

on the current traffic load


INTEGRATED SERVICES

• Provides a way to deliver the QoS that

real-time applications require by

explicitly managing network resources

to provide QoS to specific user packet

streams

• Uses "resource reservation" and

"admission control" mechanisms


INTEGRATED SERVICES (cont…)

• Use the Resource Reservation Protocol

(RSVP) to signal the QoS needs of an

application’s traffic along devices in the

end-to-end path through the network


DIFFERENTIATED SERVICES

• Architecture that specifies a simple,

scalable and coarse-grained mechanism

for classifying and managing network

traffic and providing QoS

• Packet's "class" can be marked directly

in the packet (No need for RSVP)

• Achieves better QoS scalability, while

IntServ provides a tighter QoS

mechanism for real-time traffic


DIFFERENTIATED SERVICES (cont…)

• Architecture that specifies a simple,

scalable and coarse-grained mechanism

for classifying and managing network

traffic and providing QoS

• Packet's "class" can be marked directly

in the packet

• Achieves better QoS scalability, while

IntServ provides a tighter QoS

mechanism for real-time traffic


QoS TOOLS

• QoS technologies refer to the set of

tools and techniques to manage

network resources

• QoS Tools :

1. Classification & Marking Tools

2. Congestion Avoidence Tools

3. Congestion Management Tools


CLASSIFICATION AND MARKING

• Traffic is analyzed to discover that

which class it belongs to and packets

are marked after discovery process

• Classification of the traffic is made via

ACLs or Class-Maps

• Marking network traffic allows to set or

modify the attributes for a specific class

of traffic ( Layer -2 or Layer-3 )


LAYER-2 MARKING

• Implemented via 3 bit priority code

point field (which identifies class of

service markings) in TCI field of

Ethernet header

• Ethernet frames are marked with 8

levels of priority

VALUE DESCRIPTION

7 Reserved

6 Reserved

5 Voice

4 Video Conference

3 Call Signal

2 High Priority Data

1 Medium Priority Data

0 Best Effort Data


LAYER-3 MARKING

• Implemented via 8 bit Type Of Service

Field (IPv4) or Traffic Class Field

(IPv6) in IP header

• In Diffserv model packet is marked

using DiffServ Code Point (DSCP) bits

(6 bits)

VALUE DESCRIPTION

7 Network

6 Internet

5 Critical

4 Flash-Override

3 Flash

2 Immediate

1 Priority

0 Routine


TRAFFIC SHAPING & POLICING

• Traffic Policing: When the traffic rate

reaches the configured maximum rate,

excess traffic is dropped (or remarked)

• Traffic Shaping : Retains excess packets

in a queue and then schedules the

excess for later transmission over

increments of time


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CCNA Quality of Services (QoS)

Technology

Transcript of CCNA Quality of Services (QoS)