Presentation on theme: "T.Sharon-A.Frank 1 Multimedia Quality of Service (QoS)"— Presentation transcript:
T.Sharon-A.Frank 1 Multimedia Quality of Service (QoS)
2 T.Sharon-A.Frank Contents Why Quality of Service (QoS)? Introduction Streaming Multimedia on the Internet Is Internet Real-time? Internet QoS Models
3 T.Sharon-A.Frank 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.
4 T.Sharon-A.Frank Introduction QoS Parameters Why is QoS Hard? QoS Layering and Mapping
5 T.Sharon-A.Frank 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.
6 T.Sharon-A.Frank 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 router A B propagation transmission nodal processing queueing
7 T.Sharon-A.Frank 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 (~2x10 8 m/sec) propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!
8 T.Sharon-A.Frank 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
9 T.Sharon-A.Frank Example:VC QoS Throughput Los s Jitter Measured QoS Parameters
15 T.Sharon-A.Frank Why is QoS Hard? (3) 1. End-to-End vs. Local Node (control) 2. Global vs. Specific QoS (application) 3. Uniform vs. Distance Dependant 03 02
16 T.Sharon-A.Frank 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)
17 T.Sharon-A.Frank System (OS) Application NetworkDevice s Disk, MM devices Users QoS Layering
18 T.Sharon-A.Frank QoS Mapping Example TYPE VideoSource = INTERFACE BEGIN GetVideo : OPERATION = [ ] RETURNS [ VideoFrame ] WITH QOS “ StandardVideo ” ; END. Interface Specification Burst size: 100 Kbps Burst rate: 100 per sec Delay: 1 sec Jitter: 20 ms Priority: 10 Error profile: FEC Error rate: 2% Delivery rate: 25 frames/sec Permissible jitter: 10 ms Synch interval: 1 second Orchestration Transport
19 T.Sharon-A.Frank QoS for Networked Applications
20 T.Sharon-A.Frank 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.
22 T.Sharon-A.Frank 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!
23 T.Sharon-A.Frank 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.
24 T.Sharon-A.Frank 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.
25 T.Sharon-A.Frank 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).
26 T.Sharon-A.Frank End-device to End-device Streams Setting up a stream directly between two devices – i.e., no inter-networked processes
27 T.Sharon-A.Frank 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.
28 T.Sharon-A.Frank 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 …
29 T.Sharon-A.Frank Synchronization Mechanisms (1) The principle of explicit synchronization on the level data units
30 T.Sharon-A.Frank Synchronization Mechanisms (2) The principle of synchronization as supported by high-level interfaces
31 T.Sharon-A.Frank 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.
32 T.Sharon-A.Frank Data Stream A general architecture for streaming stored multimedia data over a network.
33 T.Sharon-A.Frank 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.
34 T.Sharon-A.Frank Enforcing QoS (1) Using a buffer to reduce jitter
35 T.Sharon-A.Frank Enforcing QoS (2) The effect of packet loss in (a) non interleaved transmission and (b) interleaved transmission