QoS Requirements of Multimedia Applications

QoS Requirements QoS Requirements of Multimedia of Multimedia Applications Applications

Brett BerlinerBrett BerlinerBrian ClarkBrian Clark

Albert Hartono Albert Hartono

IntroductionIntroduction What does QoS mean?What does QoS mean?

Quality of ServiceQuality of Service probability of the network/protocol meeting a probability of the network/protocol meeting a

given traffic contract.given traffic contract. Who negotiates this contract?Who negotiates this contract?

SLA (Service Level Agreement)SLA (Service Level Agreement) Usually done by prioritizing trafficUsually done by prioritizing traffic Sender and receiverSender and receiver

Mutual agreementMutual agreement Improves reliability of contract by having both ends Improves reliability of contract by having both ends

agreeagree Like with any contract negotiation is the keyLike with any contract negotiation is the key

Introduction Con’tIntroduction Con’t Generally not used for most traffic in Generally not used for most traffic in

internetinternet Usually things are not dependant on time domainUsually things are not dependant on time domain Web browsing, e-mail, ftp, etc.Web browsing, e-mail, ftp, etc.

TCP takes care of this for usTCP takes care of this for us Mainly used for multimedia applicationsMainly used for multimedia applications

Time is of the essenceTime is of the essence Video, voice, games, etc.Video, voice, games, etc.

Always a trade-offAlways a trade-off Higher QoS (higher quality) -> More resourcesHigher QoS (higher quality) -> More resources Users of SLA must be fair and honestUsers of SLA must be fair and honest

Five basic parametersFive basic parameters

Dropped PacketsDropped Packets A router must drop an incoming packet A router must drop an incoming packet

because buffer is fullbecause buffer is full No perfect solution to this problemNo perfect solution to this problem Some, none, or all might get droppedSome, none, or all might get dropped

Impossible to determine in advanceImpossible to determine in advance How to recover?How to recover?

Receiver must request packets to be sent Receiver must request packets to be sent againagain

Causes severe delayCauses severe delay Sometimes not worth it to request packet againSometimes not worth it to request packet again

DelayDelay QueuingQueuing

Time spent waiting in a queue at a routerTime spent waiting in a queue at a router Depends on congestion in the networkDepends on congestion in the network Usually in millisecondsUsually in milliseconds

Processing Delay (usually caused by software)Processing Delay (usually caused by software) At different layers, data must be processedAt different layers, data must be processed Usually in microsecondsUsually in microseconds

Propagation DelayPropagation Delay Time for data to travel from A->BTime for data to travel from A->B Depends on distance, usually in millisecondsDepends on distance, usually in milliseconds

Transmission DelayTransmission Delay Depends on bandwidth and length of message, usually in Depends on bandwidth and length of message, usually in

microsecondsmicroseconds

JitterJitter A lack of synchronizationA lack of synchronization Caused by different delays in packetsCaused by different delays in packets

Result of packets taking different routesResult of packets taking different routes Directly related to congestionDirectly related to congestion

Extreme jitter can lead to out-of-order Extreme jitter can lead to out-of-order deliverydelivery Packets need to be re-ordered at receiverPackets need to be re-ordered at receiver

Sometimes this is impossible due to time Sometimes this is impossible due to time constraintsconstraints

ErrorError Packets do not always arrive in the Packets do not always arrive in the

exact state they were sent out inexact state they were sent out in Can be misdirected (sent to wrong Can be misdirected (sent to wrong

destination)destination) Can get combined together by accidentCan get combined together by accident Can have bit(s) flipped.Can have bit(s) flipped.

Receiver must request information to Receiver must request information to be sent againbe sent again

Many times this is not practical for Many times this is not practical for multimedia applicationsmultimedia applications

BandwidthBandwidth Amount of data that can be sent over a Amount of data that can be sent over a

connection in a given amount of timeconnection in a given amount of time Commonly measured in bits/secondCommonly measured in bits/second

kbps or mbps insteadkbps or mbps instead Sometimes a given connection is simply Sometimes a given connection is simply

physically unable to fulfill a SLAphysically unable to fulfill a SLA Imagine trying to stream HDTV quality Imagine trying to stream HDTV quality

video over a 14.4 kbps modemvideo over a 14.4 kbps modem

What Happens When What Happens When QoS Fails?QoS Fails?

VoIP Example:VoIP Example: DelaysDelays followed by effect followed by effect

< 100 – 150 ms: < 100 – 150 ms: Delay is not detectable by humansDelay is not detectable by humans 150 – 250 ms: 150 – 250 ms: Acceptable quality, but delay and Acceptable quality, but delay and

hesitation is noticeablehesitation is noticeable > 250 – 300 ms: > 250 – 300 ms: Unacceptable. Normal conversation is Unacceptable. Normal conversation is

impossibleimpossible Jitter Jitter followed by effectfollowed by effect

< 40 ms: < 40 ms: Jitter is not detectableJitter is not detectable 40-75 ms: 40-75 ms: Good quality, but occasional jumble is Good quality, but occasional jumble is

noticeablenoticeable > 75 ms: > 75 ms: Unacceptable. Too much jumble to carry a Unacceptable. Too much jumble to carry a

conversationconversation

What Happens When What Happens When QoS Fails?QoS Fails?

Video ExampleVideo Example Out of sync image Out of sync image

is a result of motion is a result of motion prediction. Result prediction. Result of loss of a P or B of loss of a P or B frameframe

Missing image Missing image parts result of a parts result of a missing I framemissing I frame

Summary of QoS Requirements For Specific Summary of QoS Requirements For Specific ApplicationsApplications

Application Dropped Packets Delay Jitter Bandwidth

VoIP < 3% packet loss ratio

150 – 200 ms < 30 ms 21 – 320 kbps

High Quality Audio & Video

< 1 % packet loss ratio

150 ms < 30 ms 768 kbps + 20% overhead = 921 kbps

Remote Visualization

None none 700 Mbps

Internet Gaming none 150 ms none 56 kbps

Web Browsing none 2 sec is preferred, 4 sec is acceptable

none 10 kbps

Streaming Video < 5% 4-5 seconds n/a Varies with encoding format

Uncompressed HDTV

1.5 Gbps

Who’s Responsibility Is Who’s Responsibility Is It? It?

Routers don’t know typically know what Routers don’t know typically know what the data isthe data is Thus, it requires a lot of overhead to allow Thus, it requires a lot of overhead to allow

the routers to interpret the datathe routers to interpret the data The encoding and decoding of the data The encoding and decoding of the data

in the sender and the receiver(s) makes in the sender and the receiver(s) makes them a prime targetthem a prime target This is where most of the focus of ensuring This is where most of the focus of ensuring

that QoS requirements are met liesthat QoS requirements are met lies

Basic Types of QoS Basic Types of QoS TechnologiesTechnologies

Congestion/Traffic ControlCongestion/Traffic Control Examples: RED, FRED, DroptailExamples: RED, FRED, Droptail

Resource ManagementResource Management Examples: IntServ, DiffServExamples: IntServ, DiffServ

Queuing/BufferingQueuing/Buffering Priority Queuing, FRTSPriority Queuing, FRTS

Congestion Control Congestion Control MethodsMethods

RED/FREDRED/FRED DroptailDroptail BucketingBucketing QoS/BGPQoS/BGP

Congestion Control Congestion Control Methods (cont.)Methods (cont.)

RED, FRED and Droptail MethodsRED, FRED and Droptail Methods Already discussed extensively in classAlready discussed extensively in class Methods to improve congestion, but like Methods to improve congestion, but like

all methods, have their own drawbacks all methods, have their own drawbacks and benefitsand benefits

Important to note that these methods only Important to note that these methods only help improve QoS on a very high level. help improve QoS on a very high level. They improve congestion and traffic, They improve congestion and traffic, which helps the entire internet, not just which helps the entire internet, not just QoS issues.QoS issues.

Congestion Control Congestion Control Methods (cont.)Methods (cont.)

QoS / BGP (QoS Policy Propagation via QoS / BGP (QoS Policy Propagation via Border Gateway Protocol)Border Gateway Protocol) BGP is the core routing protocol of the BGP is the core routing protocol of the

internetinternet Instead of using BGP solely to determine Instead of using BGP solely to determine

where to send the packets, build on top of where to send the packets, build on top of BGP to classify the type of packets being sentBGP to classify the type of packets being sent

Allows other methods, like queuing or Allows other methods, like queuing or scheduling, to be used in conjunction to scheduling, to be used in conjunction to ensure QoS requirements are met ensure QoS requirements are met

Resource Management Resource Management MethodsMethods

IntServ (Integrated Services)IntServ (Integrated Services) A fine grained QoS systemA fine grained QoS system Individual applications must make indvidual Individual applications must make indvidual

reservations of resourcesreservations of resources By making reservations, the application is By making reservations, the application is

guaranteed a certain level of service – from guaranteed a certain level of service – from “best effort” to “100% guarantee”, and “best effort” to “100% guarantee”, and everything in betweeneverything in between

Uses RSVP (Resource ReSerVation Protocol) to Uses RSVP (Resource ReSerVation Protocol) to help determine what resources to allocate help determine what resources to allocate where.where.

Resource Management Resource Management Methods (cont.)Methods (cont.)

DiffServ (Differentiated Services)DiffServ (Differentiated Services) Much more coarse QoS systemMuch more coarse QoS system Reservations are done in bulk, usually Reservations are done in bulk, usually

from a single source (such as a university from a single source (such as a university or a single ISP)or a single ISP)

Policing of data is done completely at Policing of data is done completely at DiffServ clouds (individual systems of DiffServ clouds (individual systems of routers)routers)

Data with highest priority is given highest Data with highest priority is given highest priority, within clouds onlypriority, within clouds only

Resource Management Resource Management Methods (cont.)Methods (cont.)

Weaknesses of these methods:Weaknesses of these methods: IntServIntServ

Similar to FRED, lots of data must be stored. Similar to FRED, lots of data must be stored. Thus, hard to scale for the entire internetThus, hard to scale for the entire internet

DiffServDiffServ Not a good system for most links. Not a good system for most links. Since the traffic comes in very large chunks Since the traffic comes in very large chunks

(e.g., all traffic from OSU as well as all from (e.g., all traffic from OSU as well as all from Otterbein), there is likely to be relatively steady Otterbein), there is likely to be relatively steady traffic. traffic.

If packets need to be dropped, more bandwidth If packets need to be dropped, more bandwidth is needed to fix the problem in most cases.is needed to fix the problem in most cases.

Queuing/Buffering Queuing/Buffering MethodsMethods

FRTS (Frame Relay Traffic Shaping)FRTS (Frame Relay Traffic Shaping) Excess traffic is delayed using a buffer or a Excess traffic is delayed using a buffer or a

queuequeue Idea is to shape the flow’s traffic, usually Idea is to shape the flow’s traffic, usually

when the data rate of the source is higher when the data rate of the source is higher than expected.than expected.

Works very well with a large queue or a small Works very well with a large queue or a small scale. If the queue is too small, or FRTS is scale. If the queue is too small, or FRTS is run on a large scale (e.g., the whole internet), run on a large scale (e.g., the whole internet), a queue management algorithm would be a queue management algorithm would be necessary.necessary.

Queuing/Buffering Methods Queuing/Buffering Methods (cont.)(cont.)

CSFQ (Core Stateless Fair CSFQ (Core Stateless Fair Queuing)Queuing) First step – edge nodes First step – edge nodes

estimate the incoming rate of estimate the incoming rate of packets being sent, then uses packets being sent, then uses that as a label for each of that that as a label for each of that flow’s packetflow’s packet

Next – all nodes (including Next – all nodes (including edge) repeatedly estimate the edge) repeatedly estimate the fair rate from the outgoing fair rate from the outgoing link. Upon arrival, the link. Upon arrival, the probability the packet will be probability the packet will be forwarded is calculated, based forwarded is calculated, based on the previously calculated on the previously calculated probability, as well as the probability, as well as the previous label.previous label.

When that packet is When that packet is forwarded, it is sent with that forwarded, it is sent with that probability, and the label is probability, and the label is replaced with the smaller replaced with the smaller value between its previous value between its previous value and the fair rate.value and the fair rate.


Advantages of CSFQAdvantages of CSFQ Per flow management is performed, Per flow management is performed,

allowing each flow to get a fair rateallowing each flow to get a fair rate Stateless (less information stored, the Stateless (less information stored, the

better)better) Disadvantages of CSFQDisadvantages of CSFQ

Not a lot of room for allowing prioritizationNot a lot of room for allowing prioritization Fair amount of calculation is necessary, Fair amount of calculation is necessary,

and may be futile calculationand may be futile calculation


Priority QueuingPriority Queuing Multiple queues in implementation, Multiple queues in implementation,

each representing a level of priority each representing a level of priority (high, low, and a differing number in (high, low, and a differing number in between)between)

Each queue gets only packets matching Each queue gets only packets matching its priority levelits priority level

Can change calculation equation on the Can change calculation equation on the flyfly


Advantages of Priority QueuingAdvantages of Priority Queuing Simple implementationSimple implementation Very flexibleVery flexible

Disadvantages of Priority QueuingDisadvantages of Priority Queuing Starvation is still possibleStarvation is still possible If equation remains stagnant, traffic If equation remains stagnant, traffic

could be lost in the queuescould be lost in the queues


Weighted Fair QueuingWeighted Fair Queuing An implementation of Priority QueuingAn implementation of Priority Queuing Classifies all traffic through a series of Classifies all traffic through a series of

qualifications to get the traffic in the qualifications to get the traffic in the best possible queuesbest possible queues

Examples – interactive traffic goes Examples – interactive traffic goes before non-interactive, low bandwidth before non-interactive, low bandwidth sessions go before high bandwidth sessions go before high bandwidth sessionssessions

Combing technologiesCombing technologies Right now, to ensure QoS, there are no Right now, to ensure QoS, there are no

‘magic bullets’‘magic bullets’ Each technology type has many methods Each technology type has many methods

for a reasonfor a reason The way to effectively ensure QoS The way to effectively ensure QoS

requirements best is to combine methods requirements best is to combine methods effectivelyeffectively

As a result, we see certain technologies As a result, we see certain technologies that we cannot implement fully because of that we cannot implement fully because of the inability to meet the necessary QoS the inability to meet the necessary QoS requirementsrequirements

TelesurgeryTelesurgery Robotic and computer-aided surgery Robotic and computer-aided surgery

across a distant location across a distant location Time-critical (delay-oriented) Time-critical (delay-oriented)

applicationapplication Data to send: Data to send:

surgical movementssurgical movements real-time medical images real-time medical images voice and video signalvoice and video signal

Telesurgery (cont.)Telesurgery (cont.) QoS requirements: QoS requirements:

reliability of the network linereliability of the network line low end-to-end delaylow end-to-end delay low data error ratelow data error rate data transfer from sources with various data transfer from sources with various

data ratesdata rates The acceptable limit of delay The acceptable limit of delay

requirement: 330 msrequirement: 330 ms

Telesurgery (cont.)Telesurgery (cont.) The use of the Internet for The use of the Internet for

telesurgery is not possibletelesurgery is not possible

ATM and SDH/SONET (optical ATM and SDH/SONET (optical network) meet the network network) meet the network requirements of telesurgery.requirements of telesurgery.

Telesurgery (cont.)Telesurgery (cont.) On September 7th, 2002, the first On September 7th, 2002, the first

human transoceanic (New York - human transoceanic (New York - Strasbourg, France) operation was Strasbourg, France) operation was successfully performedsuccessfully performed

Telesurgery (cont.)Telesurgery (cont.) High-speed optical-fiber networkHigh-speed optical-fiber network Dedicated connection-oriented ATM Dedicated connection-oriented ATM

transporttransport Reserved bandwidth of 10 MbpsReserved bandwidth of 10 Mbps Measured mean-time of delays: 155 msMeasured mean-time of delays: 155 ms

ATM round trip delay: 78-80 msATM round trip delay: 78-80 ms Video coding and decoding: 70 msVideo coding and decoding: 70 ms Rate adaptation and Ethernet-to-ATM packet Rate adaptation and Ethernet-to-ATM packet

conversion: ~ 5 msconversion: ~ 5 ms No packet loss was detectedNo packet loss was detected

Remote VisualizationRemote Visualization Interactive viewing of 3-D Interactive viewing of 3-D

scientific data sets over scientific data sets over networksnetworks

Gigabyte size range of Gigabyte size range of data setsdata sets

Interactivity → tight delay Interactivity → tight delay requirementrequirement

Remote Visualization Remote Visualization (cont.)(cont.)

QoS requirements:QoS requirements: very high network bandwidthvery high network bandwidth low latencylow latency constant jitterconstant jitter

The use of Internet for remote The use of Internet for remote visualization is not feasiblevisualization is not feasible


RealityGrid implements tools for RealityGrid implements tools for computational steering in the Open computational steering in the Open Grid Services Architecture (OGSA) Grid Services Architecture (OGSA)


High bandwidth links → at least 700 High bandwidth links → at least 700 MbpsMbps

Compressed video sent to remote Compressed video sent to remote observers → 100 - 200 Mbps (with low observers → 100 - 200 Mbps (with low latency and constant jitter)latency and constant jitter)

These QoS requirements These QoS requirements increase linearly with #remote observers increase linearly with #remote observers doubled again if remote stereoscopic doubled again if remote stereoscopic

rendering is employedrendering is employed

Tele-ImmersionTele-Immersion Enable individuals in different Enable individuals in different

locations to interact with each other locations to interact with each other in a shared, computer-generated in a shared, computer-generated environment as if they were in the environment as if they were in the same physical room → Virtual Realitysame physical room → Virtual Reality

The same QoS requirements as The same QoS requirements as those of remote visualizationthose of remote visualization

ConclusionsConclusions Some benefits of QoS:Some benefits of QoS:

Control over which resources are being usedControl over which resources are being used Ensure time-critical and mission-critical applications Ensure time-critical and mission-critical applications

have their required resourceshave their required resources More efficient use of existing network resources, More efficient use of existing network resources,

rather than the need for expansion or upgradesrather than the need for expansion or upgrades Foundation for a fully-integrated multimedia network Foundation for a fully-integrated multimedia network

needed in the near futureneeded in the near future QoS of scientific-computation creates technical QoS of scientific-computation creates technical

challenges for designing the next generation of challenges for designing the next generation of networknetwork

The challenge of insuring QoS requirements is The challenge of insuring QoS requirements is a large part of what drives today’s interneta large part of what drives today’s internet

Documents

QoS Requirements of Multimedia Applications