7.6 QoS ??

1
7? ??

• 7.1 ????? ???? ??
• 7.2 ???? ?? ??? ? ???
• 7.3 ??? ???? ??? ????
• 7.4 ??? ??? ???

• 7.5 ??? ??? ??? ??
• 7.6 QoS ??

2
???? ????? ???? ?? ??

• ?? ????? ?? ??
• client?? buffering
• encoding
• ??

Media Player

• ?? ??(jitter) ??
• ?? ??(decompression)
• ?? ???
• ??? ??? ?? GUI

3
??? ????? ??? ??

• ???/???? ??? ??
• ??? HTTP object?? ??
• client? ??? ?? ??? media player? ???

• audio/video? ???? ??
• play? ??? ? ??? ??

4
??? ????? ???? ??

• browser? HTTP GET?? metafile? ??
• Metafile? audio/video ??? URL? content type ???
  ?? ??.
• browser? media player? ????, metafile? ???
• media player? ? ??? ??
• ??? audio/video? player? ????? ????.

5
???? ??? ?? ????

• ???? ??? media player? HTTP? ?? ???? ??
• ??(3)?? UDP ?? TCP? ??

6
???? ????? client buffering
constant bit rate video transmission
Cumulative data
time

• Client?? ?? ?? ??? ??? ?? ??? playout? ????. ???
  ???? ??? ??? ? ?? ??? ??? ?? ?? ??? ??????.

7
???? ????? client buffering
constant drain rate, d
variable fill rate, x(t)
buffered video

• TCP? ?? ??? x(t)? ??? ?? ???.
• TCP? ??? ??? ?????? UDP ?? ? ?? ??? ??? ? ??? ???
  ? ? ???? play? ?? ??? ? ??.

8
???? ????? UDP or TCP?

• UDP
• ??? ?????? ??? ???? ??? ??(congestion? ???? ??)
• ?? send rate encoding rate constant rate
• ???, fill rate constant rate - packet loss
• Jitter? ???? ?? ?? playout ?? ?? (2-5 seconds) ??
• TCP
• TCP ?? ?? ????? ???? ?? ??? ??
• fill rate? TCP ?? ??? ??
• playout ?? ??? ?? ?? TCP ?? ??? ??? ?????.
• HTTP/TCP? ???? ?? ??? ? ??.

9
???? ????? client rate(s)
1.5 Mbps encoding
28.8 Kbps encoding

• Q ??? ?? ?? client? ?? ??? ??? ????
• 28.8 Kbps dialup modem
• 100 Mbps Ethernet

A ??? ?? ??? encoding? ??? copy? ???? client?
??? ??? ?? ??? copy? ????.
10
???? ???? ?? RTSP

• HTTP
• ????? ???? ???? ??? ??
• RTSP RFC 2326
• client-server ?? ?? ????
• ???? ??? ?? ???, ?? ??, ?? ??, ?

• RTSP? ???? ?
• audio/video? ??? encapsulation???? ??? ??
• streamed media? ?? ?? ?? ????? ??? ? ??? ?? (UDP
  ?? TCP ?? ??)
• media player? audio/video? ??? ???? ? ??? ??

11
RTSP out of band ??

• RTSP ???? out-of-band? ??
• RTSP ?? ???? ??? ????? ?? ?? ??? ??? ????.
• ?? ?? 554
• ??? ???? in-band? ??? ? ??.

12
RTSP ?

• ????
• Metafile? ? ????? ????.
• ????? media player? ?????.
• media player? ?? ??? ??? ?? ??? ??? ??? ?? ???
  ???? ??? ????.

13
Metafile ?

• lttitlegtTwisterlt/titlegt
• ltsessiongt
• ltgroup languageen lipsyncgt
• ltswitchgt
• lttrack typeaudio
• e"PCMU/8000/1"
• src
  "rtsp//audio.example.com/twister/audio.en/lofi"gt
  
• lttrack typeaudio
• e"DVI4/16000/2"
  pt"90 DVI4/8000/1"
• src"rtsp//audio.ex
  ample.com/twister/audio.en/hifi"gt
• lt/switchgt
• lttrack type"video/jpeg"
• src"rtsp//video.ex
  ample.com/twister/video"gt
• lt/groupgt
• lt/sessiongt

14
RTSP ??
15
RTSP ??? ?? ?

• C SETUP rtsp//audio.example.com/twister/audi
  o RTSP/1.0
• Transport rtp/udp compression
  port3056 modePLAY
• S RTSP/1.0 200 1 OK
• Session 4231
• C PLAY rtsp//audio.example.com/twister/audio
  .en/lofi RTSP/1.0
• Session 4231
• Range npt0-
• C PAUSE rtsp//audio.example.com/twister/audi
  o.en/lofi RTSP/1.0
• Session 4231
• Range npt37
• C TEARDOWN rtsp//audio.example.com/twister/a
  udio.en/lofi RTSP/1.0
• Session 4231
• S 200 3 OK