T.Sharon-A.Frank 1 Multimedia Quality of Service (QoS)

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Multimedia

Quality of Service (QoS)

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Contents

• Why Quality of Service (QoS)?

• Introduction

• Streaming

• Multimedia on the Internet

• Is Internet Real-time?

• Internet QoS Models

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Why Quality of Service (QoS)?

Definition: QoS is the concept for specifying how “good” the offered services are.

Concept:• Quality of service is a concept based on the statement

that not all applications need the same performance from the system/network over which they run.

• Thus, applications may indicate their specific requirements to the network, including cost, before they actually start transmitting data.

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Introduction

• QoS Parameters

• Why is QoS Hard?

• QoS Layering and Mapping

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Major Parameters Defining QoS

• Throughput – the total amount of work completed during a specific time interval.

• Delay – the elapsed time from when a request is first submitted to when the desired result is produced.

• Jitter – the delays that occur during playback of a stream.

• Reliability – how errors are handled during transmission and processing of continuous media.

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Delay in packet-switched networks (1)

Packets experience delay on end-to-end path

• four sources of delay at each hop:

• nodal processing: – check bit errors– determine output link

• queuing– time waiting at output link

for transmission – depends on congestion level

of routerA

B

propagation

transmission

nodalprocessing queueing

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Delay in packet-switched networks (2)

Transmission delay:

• R = link bandwidth (bps)

• L = packet length (bits)

• time to send bits into link = L/R

Propagation delay:

• d = length of physical link

• s = propagation speed in medium (~2x108 m/sec)

• propagation delay = d/s

A

B

propagation

transmission

nodalprocessing queueing

Note: s and R are very different quantities!

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Communication QoS Parameters

• Average Throughput (bit rate, bandwidth) • Burstiness (average to peak ratio)• Minimum/Maximum transit (delay)

– Important for response time and RT perception

• Maximum Jitter (delay variance), – Important for synchronization

• Reliability– Acceptable bit error rate

– Acceptable packet error rate

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Example:VC QoS

Throughput

Loss

Jitter

Measured QoS Parameters

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Application QoS Parameters

• Synchronization

• Orchestration

• Multicast Delivery

• Protection/Security

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Why is QoS Hard? (1)

1. End-to-End vs. Local Node (control)

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Possible Network Bottlenecks

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2. Global vs. Specific QoS (application)

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Global/Standard Channel Types

ChannelType

Bandwidth(Mbps)

Jitter(ms)

Delay(ms)

Traffic Type Error

StandardVideo

25 10 250 statistical 10-3

SlowScanVideo


MPEGVideo

10 1 250 deterministic 10-9

VoiceAudio


HiFiAudio

2 5 500 deterministic 10-5

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3. Uniform vs. Distance Dependant

0302

02

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3. Uniform vs. Distance Dependant

4. Higher-Level vs. Lower-Level (user/application/OS/network/device)

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System (OS)

Application

NetworkDevices

Disk, MM devices

Users

QoS Layering

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QoS Mapping Example

TYPE VideoSource = INTERFACEBEGIN

GetVideo : OPERATION = [ ]RETURNS [ VideoFrame ]WITH QOS “StandardVideo”;

END.

Interface Specification

Burst size: 100 KbpsBurst rate: 100 per secDelay: 1 secJitter: 20 msPriority: 10Error profile: FECError rate: 2%

Delivery rate: 25 frames/secPermissible jitter: 10 msSynch interval: 1 second

Orchestration

Transport

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QoS for Networked Applications

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QoS Traffic Topics (1)

• Routing– Unicast (multi-hop network)– Multicast

• Congestion Control

• Traffic Topics

• Admission Control (on-line):– Systems often use an admission control algorithm

that admits a request for a service only if the server has sufficient resources to satisfy the request.

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QoS Traffic Topics (2)

• Traffic Classes (varied) – priorities

• Traffic Control (nodal)– packet classification/scheduling

• Traffic Shaping (per session)

• Traffic Monitoring

• Traffic Policing

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Streaming and QoS

• With text data, the effect that time has on correctness is of little consequence.

• However, audio and video are time-dependent data streams – if the timing is off, the resulting “output” from the system will be incorrect.

• Time-dependent information – known as “continuous media” communications:– Example: voice: PCM: 1/44100 sec intervals on playback.

– Example: video: 30 frames per second (30-40ms per image).

• KEY MESSAGE: Timing is crucial!

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Transmission Modes

• Asynchronous transmission mode – the data stream is transmitted in order, but there’s no timing constraints placed on the actual delivery (e.g., File Transfer).

• Synchronous transmission mode – the maximum end-to-end delay is defined (but data can travel faster).

• Isochronous transmission mode – data transferred “on time” – there’s a maximum and minimum end-to-end delay (known as “bounded jitter”).

• Known as “streams” – isochronous transmission mode is very useful for multimedia systems.

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Two Types of Streams

• Simple Streams – one single sequence of data, for example: voice.

• Complex Streams – several sequences of data (sub-streams) that are “related” by time. Think of a lip-synchronized movie, with sound and pictures, together with sub-titles …

• This leads to data synchronization problems … not at all easy to deal with.

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Components of a Stream

Two parts: a “source” and a “sink”.

The source and/or the sink may be a networked process (a) or an actual end-device (b).

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End-device to End-device Streams

Setting up a stream directly between two devices – i.e., no inter-networked processes.

2-35.2

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Multi-party Data Streams

An example of multicasting a stream to several receivers. This is “multiparty communications” – different delivery transfer rates may be required by different end-devices.

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Stream Synchronization

• A key question is:– “Where does the synchronization occur?”

• On the sending side?

• On the receiving side?

• Think about the advantages/disadvantages of each …

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Synchronization Mechanisms (1)

The principle of explicit synchronization on the level data units

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Synchronization Mechanisms (2)

The principle of synchronization as supported by high-level interfaces

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Streams and QoS (1)

• Definition: “ensuring that the temporal relationships in the stream can be preserved”.

• QoS is all about three things: 1. Timeliness

2. Volume

3. Reliability

• But, how is QoS actually specified?

• Unfortunately, most technologies do their own thing.

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Data Stream

A general architecture for streaming stored multimedia data over a network.

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Streams and QoS (2)

• Properties for Quality of Service (QoS):– The required bit rate at which data should

be transported.

– The maximum delay until a session has been set up.

– The maximum end-to-end delay.

– The maximum delay variance, or jitter.

– The maximum round-trip delay.

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Enforcing QoS (1)

Using a buffer to reduce jitter

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Enforcing QoS (2)

The effect of packet loss in (a) non interleaved transmission and (b) interleaved transmission

T.Sharon-A.Frank 1 Multimedia Quality of Service (QoS)

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