Unit 9. Multimedia Applications

Transcription

1 nit 9 ultimedia pplications

2 xample of ulti edia pplications treaming video Podcasting P telephony nternet radio eleconferencing nteractive games Virtual worlds Distance learning

3 nicast and ulticast treaming

4 treaming pplications Delay ensitive - timing considerations are important because if more than a few milliseconds delay, the application is basically useless oss-tolerant packet loss only causes glitches in the audio/video playback which may be partially or fully concealed

5 General treaming lasses ive audio and video sent live using multicasting or can be unicast but usually can also be recorded on user s machine tored audio and video - an be indexed fast forwarded or rewound but once started should play continuously nteractive audio and video delays of less that 150 milliseconds are not noticed, more than 400 milliseconds are intolerable

6 Best ffort ervice Problems Packet oss no guarantee of delivery nd-to-end delay - o promises about the end-to-end delay for an individual Packet Packet Jitter - variation of packet delay within a packet stream equencing no guarantee of sequence of delivery unless a socket is used

7 urrent olutions Delay playback at the receiver by 100 ms or more to diminish i i the effects of networkinduced jitter. imestamp and equence umber packets at the sender so that the receiver knows when the packets should be played back tored audio/video we can prefetch data during playback when client storage and extra bandwidth are available end redundant information in order to mitigate the effects of network-induced packet loss

8 ompression ncompressed audio and video use a lot of memory and bandwidth ompression removes the inherent redundancies in the signal to reduce the amount of data that t needs to be stored and transmitted Process is to ample, Quantize and ompress P3 uses a a header less file format when broken up and put into packets ncoders typically compress to rates of 96 kbps, 18 kbps, and 160 kbps, and produce very little sound degradation. When Video is played at 4-30 frames per second PG can transmit at 1.5 to 6 bps

9 edia Players Helper applications that are running on the client computer to process the streamed data Decompression - decompress the audio/video on the fly during playback Jitter removal - buffer received packets for a short period of time to remove this jitter rror correction attempts to recover lost data

10 rror orrection Forward rror orrection - send a low resolution audio track as well as high h resolution track nterleaving using consistent t packet spacing to send redundant information if bandwidth available Retransmission - lient explicitly request retransmission of lost packets nd tation Repair - asking loss by interpolating the missing data from the received data

11 Web erver Playback Browser establishes a P connection with the Web server Browser requests the audio/video file with an HP request message Web server sends the audio/video meta file to the browser in an HP response message. ontent-type header identifies specific audio/video encoding Proper media player sets up P socket connection erver sends the actual audio/video file edia player renders the audio/video file

12 treaming erver Playback eparate server designed for media streaming ses buffers on user s machines to prefetch data and control the actual playback tart is delayed to eliminate jitter and get timing correct

13 RP Protocol RP Real ime treaming Protocol is considered an out-of-band protocol which means it is not part of the data stream ses P socket for control ctual data stream can be sent using either P or DP ontrols actions such as pause/resume, fast-forward, and rewind.

14 RP tatistics

15 Real ime nteractive Protocols RP can be used for transporting common formats such as P, G, and P3 for sound and PG and H.63 for video and used the RP for controls P is the wireless communication protocol that initiates and manages sessions H33 is completer suite of protocols used dfor real ltime audio and video conferencing over the internet

16 ontent Distribution etworks Ds are a system of computers networked together across the nternet that transparently deliver content with the fastest delivery time and lowest cost tore the most popular content at various location throughout the world to reduce transport t time content cluster or service node can be formed using a layer 4 switch to balance the load across several servers argest commercial Ds are kamai, imelight and Detworks

17 D etwork

18 Qo (Quality of ervice) ntserv developed to provide individualized Qo guarantees to individual application sessions by setting up the session and reserving resources Diffserv - provide the ability to handle different classes of traffic in different ways within the nternet. expedited forwarding traffic class guaranteed minimum bandwidth will equal or exceed configured amount regardless of other traffic assured forwarding - class is guaranteed to be provided with some minimum amount of bandwidth and also provides a drop preference for classes of traffic to alleviate congestion

19 ayer 4 Qo Queuing ethods FF queuing data processed in ordered that it arrived Priority queuing priority values assigned by type of traffic Weighted Fair queuing assigns priorities and a system of servicing each

20 Qo Packet Flow Policing verage rate - hese settings determine the maximum number of packets allowed so using a longer time period is usually more efficient in maintaining a better Qo For example using 6,000/minute is better than 100/sec Peak rate - limits the maximum number of packets that t can be sent over a given period of time. For example allowing 6,000/min while limiting the flow s peak rate to 1,500 /sec (based on buffer size) Burst size limits instantaneous number of packets (again based on equipment capabilities but not always used)

21 Qo

22 RVP (Resource Reservation Protocol) ignaling protocol that can reserve network resources for a specific application Requester makes a reservation for each requested service with all of the routers between the sender and the receiver

23 RVP Process