CS 447 Network & Data Communication QoS (Quality of Service) & DiffServ Introduction Department of Computer Science Southern Illinois University Edwardsville.

CS 447 Network & Data Communication

QoS (Quality of Service) & DiffServIntroduction

Department of Computer ScienceSouthern Illinois University Edwardsville

Fall, 2013

Dr. Hiroshi FujinokiE-mail: [email protected]

QOS_PART1/001


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What are QoS & DiffServ?

QoS = Quality of Service

Techniques and standards developed for controlling ways networktraffic (= “packets”) is handled in a network.

DiffServ = Differentiated Service

A standard that implements QoS in the Internet


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Background

• Before the concept of QoS was introduced to the Internet, all what the Internet could provide was “best-effort service”.

What is “best-effort service”?

Sender Receiver

The Internet

No guarantee for transmitted packets to reach the destination

No guarantee for available transmission bandwidth

- They could be dropped at anytime anywhere

- Tx bandwidth dynamically changes


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No guarantee for successful transmissions nor Tx bandwidth

Time

Tx-

Rat

e (i

n b

ps)

Time

Tx-

Rat

e (i

n b

ps)

packetis lost

No guaranteed Tx rate (observed at the receiver)

No guarantee for successful Tx (observed at the receiver)

Sharp dropin Tx rate

UnpredictableTx-rate


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Background



Sender Receiver

The Internet

End-to-end delay dynamically fluctuates

- This is a result of in the previous slide


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Sender Receiver

Dynamically fluctuating E2E delay

R1 RN

Physical Distance

Sender transmitsa packet Router

Delay

E2EDelay• Router delay dynamically fluctuates

• The longer the physical distance, the longer E2E delay

• The larger the E2E hop-count, the longer E2E delay


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Background



Sender Receiver

The Internet

Unpredictable (no control for) delay jitter

- Delay jitter = variance in E2E delay for arriving packets


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Sender Receiver

R1 RN

Sender transmitsa packet Router

Delay

E2EDelay

Time Time

Tim

e

packet

Unpredictable (no control for) delay jitter


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Background



Sender Receiver

The Internet

Unpredictable (no control for) packet-loss rate

- Packet-loss rate = (number of lost packets)/(number of packets sent)

- Because router resources (memory buffers) are shared


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Sender Receiver

R1 RN

Unpredictable (no control for) packet-loss rate

• A large # of senders might be transmitting packets through a router(Router buffers’ are shared resource in the Internet)

• We can not predict which senders transmit how much and when(Senders do not reserve resources in advance in the Internet)


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QoS parameters and various network applications

• So far, we defined “best-effort service” as lack of controls for Tx-rate, E2E delay, delay jitter and packet-loss rate.

Question Which network applications need a good control for whichparameters?

Applications Control required for

HTTP (web)

FTP

E-mail(No MIME)

Telnet

VoIP


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QoS parameters and various network applications

• So far, we defined “best-effort service” as lack of controls for Tx-rate, E2E delay, delay jitter and packet-loss rate.

Question Which network applications need a good control for whichparameters?

Applications Control required for

Online chatting

On-line game (Real-Time)

Problem

The best-effort Internet service can not handle for network applicationswith various QoS requirements


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Existing QoS controlling components

Admission Control

Traffic Classifier

Traffic Policing and Shaper

Packet Scheduler


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Admission Control

Network

Router Router Router Router

Request forreserve resources

PositiveACKAdmitted

“signaling”

Reserveresources

Reserveresources

Reserveresources

Reserveresources


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Admission Control

Network

Router Router Router Router

Request forreserve resources

Reserveresources

I don’t haveenough resource

Rejected

Reserveresources

NegativeACK

On rejection, the requesting host:

Give up now and try again later

Reduce the requested resources and try again


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Admission Control

• Admission control is a mechanism that prevents overloading a network

• Each host must reserve network resources before it starts transmission(This is exactly what “virtual-circuit” networks do)

• Router resources are reserved by signaling messages

• On success, a positive ACK from the destination

• On fail, a negative ACK from a rejecting router

• The Internet does not perform admission control

(The Internet is a datagram packet-switching network)


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Traffic Classifier

Sender Receiver

R1 RN

ReceivingNIC

Routing Classifier Policing SchedulerTransmitting

NIC

Decide which transmittingNIC each packet is directed

Detect the type of packetso that a different policing

and scheduling can be applied for each different type


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Classifier

TrafficType-A

TrafficType-B

TrafficType-X

ShaperPolicing

ShaperPolicing

ShaperPolicing

Queues

Routing

Traffic Classifier

The classifier “classifies” incoming packets to groups, eachof which holds packets that have the same “requirements (demands)”


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-a Traffic Policing

• If some hosts (or a group of network applications) are transmitting more network traffic than they are supposed to, drop the traffic.

-b Traffic Shaping

• Reduce delay jitter

• Control on transmission rate (in bps)

• Reduce transmission burst


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-a Traffic Policing

Tra

ffic

Loa

d (

in b

ps)

Time

Upper Threshold


QOS_PART1/020

-a Traffic Policing

Tra

ffic

Loa

d (

in b

ps)

Time

Upper Threshold


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-b Traffic Shaper

packet

Tra

ffic

Loa

d (

in b

ps)

TransmissionBurst

TransmissionBurst

TransmissionBurst

Time

(i) Jitter Reduction (micro-shaping)

(Zero jitter) (High jitter) (Low jitter)

(ii) Flattening transmission burst (macro-shaping)


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= an implementation of traffic policing/shaping

Token Bucket

Leaky Bucket

Bursty Traffic (Average Traffic Rate = R1 bps)

Drain (Output Rate = R2 bps)

Incoming Link

Bucket Capacity = B bits

Must be: R2 R1

(memory buffer in a router)

(network traffic with a high jitter)

(outgoing drain with a constant rate)


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Packet Scheduler

Classifier

TrafficType-A

TrafficType-B

TrafficType-X

ShaperPolicing

ShaperPolicing

ShaperPolicing

Queues

TransmittingNIC

Scheduler

• Decide from which queue packets will be forwarded to the transmitting NIC

Routing


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CS 447 Network & Data Communication QoS (Quality of Service) & DiffServ Introduction Department of Computer Science Southern Illinois University Edwardsville.

Documents

network data communicationqos

network resources

besteffort internet

besteffort service

internet unpredictable

internet endtoend delay

delay jitter delay jitter

admission controlthe