Quality

of

Service

By:

Abhishek Wadhwa, BVICAM

So what is it?

• Quality of service is the ability to provide

different priority to different applications,

users, or data flows, or to guarantee a

certain level of performance to a data flow

“ it defines the quality of service

as something a flow seeks to

attain”

Flow Characteristics

• Reliability : Lack of Reliability means

losing a packet or ack.

• Delay : Different applications can tolerate

delay in different degrees.

• Jitter : jitter is the variation in packets

belonging to same flow.

• Bandwidth : different application need

different b/w.

Techniques to improve

the quality of service.

Scheduling

FIFO QUEUING

PRIORITY QUEUING

WEIGHTED FAIR QUEUING

Traffic Shaping

LEAKY BUCKET

TOKEN BUCKET

Resource Réservation

Admission Control

Scheduling

• Packets from different flow arrive at switch

or router for processing

• A good scheduling technique treats the

different flow in a fair and appropriate

manner

• FIFO QUEUING

• Packets wait in a buffer (queue) until the

node is ready to process them.

• If avg. arrival rate>avg. processing rate

=>new packets will be discarded.

• FIFO QUEUING

Priority

Queuing

• Packets are assigned to a priority class

• Each class has its own queue.

• Higher class packets are processed first.

• Problem : Starvation

Priority

Queuing

Weighted Fair

Queuing

• Packets are still assigned to different

classes and admitted to different queues

• The queues are weighted based on the

priority

• Higher priority means higher weight

• If weight are 3,2,1 then 3 packets are

processed from q1,2 from q2,and 1 from

q1 in a round robin fashion

Weighted Fair

Queuing

Traffic Shaping

Is the mechanism to control the amount

and the rate of the traffic sent to the

network

Techniques to improve

the quality of service

Scheduling

FIFO QUEUING

PRIORITY QUEUING

WEIGHTED FAIR QUEUING

Traffic Shaping

LEAKY BUCKET

TOKEN BUCKET

Resource Réservation

Admission Control

Leaky Bucket

http://www.epubbud.com/read.php?g=5HEKFDZU&two=1&tocp=48

The rate at which water leaks from a bucket

does not depend on the rate at which the

water is input to the bucket

The input rate varies but the o/p remains

constant ,similarly ,network can

smooth out bursty traffic

Leaky Bucket

Token Bucket

Token Bucket

Leaky bucket does not taken into a/c idle host , if a

host is not sending for a while , its bucket becomes

empty.

If the host has bursty data ,leaky bucket allows

only avg. rate.

Token bucket takes into a/c the idle time , with

each clock tick the tokens are added to bucket

,when the data needs to be send ,it collects token

from bucket and then send the data packet

consisting of data=no of tokens

Techniques to improve

the quality of service

Scheduling

FIFO QUEUING

PRIORITY QUEUING

WEIGHTED FAIR QUEUING

Traffic Shaping

LEAKY BUCKET

TOKEN BUCKET

Resource Réservation

Admission Control

Resource Reservation

• A flow of data needs resources such as

buffer, bandwidth, CPU time, and so on .

• QoS can be improved if these resources

are reserved beforehand.

Techniques to improve

the quality of service

Scheduling

FIFO QUEUING

PRIORITY QUEUING

WEIGHTED FAIR QUEUING

Traffic Shaping

LEAKY BUCKET

TOKEN BUCKET

Resource Réservation

Admission Control

Admission Control

• Routers or switches puts restrictions on

the admission of packets from host.

• Before a router accepts the flow , it

checks the flow for specifications in

terms of bandwidth , buffer size ,cpu

speed etc.

Models deploying QoS

• Two models have been designed to

provide QoS:

->Integrated Service Model(IntServ)

->Differentiated Service Model(Diffserv)

IntServ

• User needs to create flow, kind of virtual

circuit ,from source to destination and

inform all routers of requirement

RSVP: Resource Reservation

Protocol

• Receiver based reservation : the receiver

not the sender make the reservation(eg :

youtube)

• RSVP messages:

->Path Messages

->Resv Messages

DiffServ

• The router routes the packet based in

the class of service defined in the packet

• It defines several classes such as

,constant bit rate class , the variable bit

rate class etc.

DiffServ*

• ToS: type of service field is used to

define the class of service for each

packet

DiffServ*

• ToS: type of service field is used to

define the class of service for each

packet

Conclusion:

Flow characteristics

Scheduling

FIFO QUEUING

PRIORITY QUEUING

WEIGHTED FAIR QUEUING

Traffic Shaping

LEAKY BUCKET

TOKEN BUCKET

Resource Réservation

Admission Control

Models

Integrated Model (Requirement in advance)

Differentiated Model(Classes)

Any

Questions?

Thank You

References

• cisco.tu-sofia.bg/uploads/Additional/Cisco_QoS.pdf

• www.cs.columbia.edu/~coms6181/slides/13/quality-of-service.ppt

• www.cs.princeton.edu/courses/archive/spr03/cs461/lec12/lec12.ppt

• www.csb.uncw.edu/people/.../Topic%207%20Service%20Quality.p

pt

• http://www.rfc-

editor.org/search/rfc_search_detail.php?rfc=2474&title=quality+of+s

ervice&pubstatus%5B%5D=Any&pub_date_type=any

• http://www.epubbud.com/read.php?g=5HEKFDZU&two=1&tocp=48

• *for further reading ->page 9 of Cisco_QoS.pdf

• http://www.rfc-editor.org/