t.sharon-a.frank 1 multimedia quality of service (qos)
TRANSCRIPT
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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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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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Application QoS Parameters
• Synchronization
• Orchestration
• Multicast Delivery
• Protection/Security
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Why is QoS Hard? (2)
1. End-to-End vs. Local Node (control)
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
1 10 250 statistical 10-2
MPEGVideo
10 1 250 deterministic 10-9
VoiceAudio
64 10 250 statistical 10-1
HiFiAudio
2 5 500 deterministic 10-5
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Why is QoS Hard? (3)
1. End-to-End vs. Local Node (control)
2. Global vs. Specific QoS (application)
3. Uniform vs. Distance Dependant
0302
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Why is QoS Hard? (4)
1. End-to-End vs. Local Node (control)
2. Global vs. Specific QoS (application)
3. Uniform vs. Distance Dependant
4. Higher-Level vs. Lower-Level (user/application/OS/network/device)
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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 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.