CS 447 Network & Data Communication

QoS (Quality of Service) & DiffServIntroduction

Department of Computer ScienceSouthern Illinois University Edwardsville

Fall, 2013

Dr. Hiroshi FujinokiE-mail: hfujino@siue.edu

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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

• 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

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

• 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

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

• 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

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

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-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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