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Multimedia

Multimedia

on the

Internet

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Is the Internet Real-Time (MM)?

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Internet/Multimedia Assumptions

• Internet – Point-to-Point (unicast)– Best-Effort Delivery– Elastic Applications– FIFO Packet Scheduling– Provides average Packet

Delay– End-to-End Reliability– Statistical Multiplexing

Gain

• Multimedia– Multipoint

– Soft RT Constraints

– Inelastic Applications

– Need Control over Delay and Jitter

– Various Traffic Classes

– Need QoS Guarantees

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Application Taxonomy (1)

Elastic Inelastic

Applications

Elastic Applications:

Can tolerate relatively large delay variance – essentially the traditional data application.

Inelastic Applications:

Comparatively intolerant to delay, delay variance, throughput variance and errors.

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Examples of Elastic Applications

• Email:– asynchronous

– message is not real-time

– delivery in several minutes is acceptable

• File transfer:– interactive service

– require “quick” transfer

– “slow” transfer acceptable

• Network file service:– interactive service– similar to file transfer– fast response required– (usually over LAN)

• WWW:– interactive– file access mechanism– fast response required– QoS sensitive content on

WWW pages

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Examples of Inelastic Applications

• Streaming voice:– not interactive– end-to-end delay

not important– end-to-end jitter not

important– data rate and loss

very important

• Real-time voice:– person-to-person– interactive– important to control:

• end-to-end data rate• end-to-end delay• end-to-end jitter• end-to-end loss

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Application Taxonomy (2)

Elastic Inelastic

Applications

Tolerant

Loose Delay Bounds

Firm Delay Bounds

IntolerantInteractiveBurst

Best EffortLevel 1

InteractiveBulk

Best EffortLevel 2

AsynchronousBulk

Best EffortLevel 3

TelnetX

NFS Web

FTP E-MailMM-Mail

Fax

Streaming VOD

Medical ImagingCAD Schemes

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QoS Types of Service

Best-effort Serviceno/partial guarantees/bounds

Predictive Serviceestimation based on past network behavior

Guaranteed Servicedeterministicstatistical

Current service in most

protocols

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Soft RT QoS Guarantees

• DeterministicProvide Bounds on Performance of all

Packets in a Session.

• StatisticalNo more than a Specified Fraction of

Packets will see Performance Below a Certain Specified Value.

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Deterministic RT QoS Guarantee

• Delay: no packets delayed more than D time units on E2E basis (T<=D).

• Loss: no packet loss occurs.

• Transit Window: bound transit window(Tmax-Tmin<=E).

• Queuing: the delay of every packet from session i is less than x at queue j.

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Statistical RT QoS Guarantee

• Delay: no more than x% of packets have a delay larger than D (PR[T>D]<epsilon)

• Loss: no more than x% of packets in a session are lost PR[Packet-loss]<epsilon

• Queuing: the probability that a packet from session i has a delay greater than x is guaranteed to be less than y at queue j.

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Application Taxonomy (3)

Elastic InelasticApplications

Tolerant

Loose Delay Bounds

Firm Delay Bounds

IntolerantInteractiveBurst

Best EffortLevel 1

InteractiveBulk

Best EffortLevel 2

AsynchronousBulk

Best EffortLevel 3

TelnetX

NFS Web

FTP E-MailMM-Mail

Fax

Streaming VOD

Medical ImagingCAD Schemes

Best-effort Service Predictive GuaranteedGrab BandwidthNo Certain Arrival TimeUses Data ImmediatelyNo Admission Control

The Opposite

Care About Average Packet Delay Quantitative Maximum Delay

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Example: Playback Applications

• Audio/Video Services

• Soft Real-Time Tolerant Constraints

sender receiver

bufferNetwork

Varying delay transmit

Buffer, Decompress, PlaybackAcquire signal, Digitize, Compress

If arrives late – useless/loss. Playback point: Signal generation time + Fixed offset delay.

Compute offset based on max delay:Offset delay can be adjusted

provided by network based on observed delays

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Internet QoS Models

• Adaptation Model– Adapt applications

• hide Internet service from the users – scaling

– Adapt Internet• Differentiated Services (DiffServ) – simple priority

• Extension Model• Integrated Services (IntServ) – resource reservation

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Adaptation Model

• Use network Feedback/Scaling• Adapt applications (Scaling)• Minimal changes to Internet (DiffServ)• No need for Resource Reservation:

– “Bandwidth will be infinite”When? Everywhere? Overload?

– “Applications can be adaptive”Too slow? Can users adapt?

– “Simple priority is sufficient”All high priority? Overload?

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Scaling

Transparent Scaling - usually by dropping some portion of the data

stream.

Non-transparent Scaling - usually by adjusting parameters in the coding

algorithm.

Means to sub-sample a data streamand only present a fraction of its original content.Scaling types:

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Scaling in Audio and Video

Audio– Transparent scaling is difficult because human ear is

sensitive– usually done by changing sampling rate

Video– Temporal scaling (drop frames)– Spatial scaling (reduce resolution)– Frequency scaling (reduce number of DCT coefficients)– Amplitude scaling (reduce color depth)– Color space scaling (reduce number of color entries or even

switch to gray scale)

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Audio Scaling

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Scaling Example: Videoconferencing

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Scaling Example:Videoconferencing (2)

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Stream Management

• Managing streams is all about managing bandwidth, buffers, processing capacity and scheduling priorities – which are all needed in order to realize QoS guarantees.

• This is not as simple as it sounds, and there’s no general agreement as to “how” it should be done.

• For instance: ATM’s QoS (which is very “rich”) has proven to be unworkable (difficult to implement).

• Another technique is the Internet’s RSVP.

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Improving QoS in IP Networks

• IETF groups are working on proposals to provide better QoS control in IP networks, i.e., going beyond best effort to provide some assurance for QoS.

• Work in Progress includes Differentiated Services (DiffServ), RSVP and Integrated Services (IntServ).

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Differentiated Services (DiffServ)

• Relatively simple, coarse-grained QoS mechanism.

• Deployed in networks without needing to change the operation of the end system application.

• Based around marking packets with a small-fixed bit-pattern, which maps to certain handling and forwarding criteria at each hop.

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Extension Model

• Single Service Model– Best-effort services

– Soft real-time services

• Keep Internet Philosophy– Downward compatible

– Common infrastructure

– Unified protocol stack

– Open/public access

– User usage-based pricing

Need New Integrated Services (IntServ) Model?

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Resource Reservation

• Pre-allocation of needed resources to guarantee deterministic QoS.

• Allocated resources are dedicated; if not used – remain idle.

• Example: Internet RSVP – Resource reSerVation Protocol.

• If resources cannot be reserved, scaling can be used.

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Internet RSVP QoS

The basic organization of RSVP for resource reservation in a distributed system – transport-level control protocol for enabling resource reservations in routers. Interesting characteristic: receiver initiated.

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Specifying QoS with Flow Specifications

A flow specification – one way of specifying QoS – a little complex, but it does work (but not via a user controlled interface).

Characteristics of the Input Service Required

• maximum data unit size (bytes)• Token bucket rate (bytes/sec)• Toke bucket size (bytes)• Maximum transmission rate (bytes/sec)

• Loss sensitivity (bytes)• Loss interval (sec)• Burst loss sensitivity (data units)• Minimum delay noticed (sec)• Maximum delay variation (sec)• Quality of guarantee

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An Approach to Implementing QoS

The principle of a token bucket algorithm – a “classic” technique for controlling the flow of data (and implementing QoS characteristics).

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Integrated Services (IntServ)

• An architecture for providing QOS guarantees in IP networks for individual application sessions.

• Relies on resource reservation.

• Routers need to maintain state info, maintaining records of allocated resources and responding to new Call setup requests on that basis.