Streaming, RTP, RTSP ITEM, 26feb02, Leif Arne Rnningen

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Streaming, RTP, RTSPITEM, 26feb02, Leif Arne
Rønningen
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Streaming from a Streaming Server to a Media
player
ITEM, 1nov00 Leif Arne Rønningen
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Media Player

• The Media Player shown is a plug-in to the
  browser (running native code) or a stand-alone
  application, and provides the following
• Decompression
• Jitter removal
• Error correction
• GUI Graphical User Interface

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Best-effort Quality of Service - QoS

• Internet today, best-effort delivery service
• No guarantee of
• End-to-end delay
• Delay jitter
• Packet loss
• Packet sequence
• No traffic control
• No admission control

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RTP - Real-time Transport Protocol

• One-way streaming, unicast or multicast of audio
  and video in general
• The media stream is sent as chunks of data, put
  into RTP packets
• Each RTP packet header includes stream
  identifier, time stamp and sequence number (error
  correction)
• On top of UDP/IP
• Application and transport layer
• Does not provide Quality of service guarantee

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RTCP RTP Control Protocol

• Used with RTP to monitor the Quality of Service
• Feedback information can be used for adaptive
  control of senders output data rates (adaptive
  scaling of service profile and level)
• On top of UDP/IP
• Does not provide Quality of Service guarantee

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RTSP - Real-time Streaming Protocol

• Application-level protocol for control over the
  delivery of data with real-time properties
• Media on-demand control, player-server
  interaction
• Requests and Responses, not memoryless,
  HTTP-friendly, supports most HTTP features
  new
• RTP used for the actual delivery of data (sound,
  video)
• On top of UDP/IP or TCP/IP
• Does not provide Quality of Service guarantee

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RTSP, example
HTTP GET
Web Browser
Web Server
Description file
SETUP
Media Player
Media Server
PLAY
Media stream
PAUSE
TEARDOWN
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RTSP, description file
lttitlegtTwister/titlegt ltsessiongt ltgroup
languageen lipsyncgt ltswitchgt lttrack
typeaudio ePCMU/8000/1 src
rtsp//audio.example.com/twister/
audio.en/lofigt lttrack typeaudio eDVI4
/16000/2 pt90 DVI4/8000/1 scrrtsp//audio
.example.com/twister/
audio.en/hifigt lt/switchgt lttrack
typevideo/jpeg scrrtsp//video.example.com/
twister/videogt lt/groupgt lt/sessiongt
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Explanation The RTSP Content Markup Language
document can be defined using an XML DTD
(Document Type Definition), and is HTML-like.
Most of it is self-explanatory. The group
includes two audio tracks and a video track, and
the group tag includes the language parameter
(en English) and a requirement that the sound
shall be lip-synchronised with the video. The
swich tag indicates that we can swich between
two sound tracks. The coding schemes for the
audio are given by the parameters e and pt.
To locate resources, RTSP defines a variant of
URL, see src. The parameter lofi indicates
low fidelity sound. The RTSP URL may include a
port number.
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RTSP, player-server interaction
Player SETUP rtsp//audio.example.com/twister/aud
io RTSP/1.0 Cseq 1 Transport rtp/udp
compression port3056 modePLAY Server RTSP/1.0
200 OK Cseq 1 Date 23 Jan 2001 174505
GMT Session 42311234 Transport rtp/udp
compression port3056 modePLAY P PLAY
rtsp//audio.example.com/twister/audio.en/lofi
RTSP/1.0 Cseq 2 Session 42311234 Range
npt0- S RTSP/1.0 200 OK Cseq 3 Date 23
Jan 2001 174605 GMT Range npt0-
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RTSP, player-server interaction
P PAUSE rtsp//audio.example.com/twister/audio.en
/lofi RTSP/1.0 Cseq 4 Session
42311234 Range npt37 S RTSP/1.0 200 OK Cseq
4 Date 23 Jan 2001 174705 GMT P TEARDOWN
rtsp//audio.example.com/twister/audio.en/
lofi RTSP/1.0 Cseq 10 Session
42311234 S RTSP/1.0 200 OK Cseq 10
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Explanation The request-response interaction
between Player and Server are HTTP-like, but not
memoryless. A setup has to be performed before
data transfer can take place. The SETUP method is
followed by the RTSP URL (universal resource
locator). Cseq is a sequence number that uniquely
identifies each request-response. The session
number identifies the setup session. The RTP
protocol shall be used, over UDP. The npt
parameter indicates the normal play time in
seconds. The rest should be self-explanatory.
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QuickTime streaming media

• QuickTime
• Browser plug-in, or stand-alone QuickTime Player
• Retrieve streams from QuckTime Streaming Server
• Handles multimedia components like
• video, sound, animation, graphics, text, music,
  360-degree virtual reality (VR) scenes
• stored in every major format
• Timecode tracks
• RTP and RTSP application protocols
• See www.apple.com/quicktime/ for more details
• QuckTime demo
• rtsp//129.241.26.182/stud/arne/ice_age_hint.mov

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RTSP Media Player-Server, Message Sequence Chart
User Interface
RTSP Player
RTSP Server
OpenURL
SETUP
response1
PLAY
Activate RTP
Activate RTP
response2
audio
PAUSE
response3
Quit
TEARDOWN
response10
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Media Player State-transition diagram
y
x
Wait S2
O
Passive
O
Response2 / Activate RTP
OpenURL / SETUP
Play, RTP
Wait S1
O
O
response1
/ PAUSE
Wait S3
Wait UI1
O
O
response3
/ PLAY
z
y
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Media Player State-transition diagram
z
Wait UI2
O
Quit / TEARDOWN
Wait S10
O
response10
Transition message in / message out, task
x
O other message continue
z
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State Machine Implementation
RTP
State descripton table
Task or method
Queue
State Interpreter
Message out
Message in
State
Software Process (entity)
Note RTP could be implementet as a separate
entity, not as a task
table
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State Interpreter behaviour

• waituntil (at least one message in queue)
• get message from queue
• check message name
• read present state
• read state table (state, message in)
• set next state
• send out message (state, message in)
• activate task or function

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State Description Table
State message in next state message
out task/function Wait UI2 Quit Wait
S10 TEARDOWN ,,, ,,, ,,, ,,, Wait
S2 response2 Play, RTP activate RTP
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Timeouts, retry-counters
Timer
RTSP Player

OpenURL(N3)
SETUP
Set-timer(2, N)
(response1 is lost)
2 sec.
Timeout(2,N)
SETUP
Set-timer(2, N)
(response1 delayed)
2 sec.
Timeout(2,N)
Countdown If N0 then begin N3
StatePassive end else NN-1
response1
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Extended state machine

State descripton table
xyz
xyz
Tasks or methods
Queue
State Interpreter
Message out
Message in
State, Variable N
Next state dependent on value of N
software
table
Note The Timer can be implemented as a task or
as a separate entity
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Other streaming media systems

• RealPlayer
• Sun Java Media Framework
• Microsoft Streaming Media
• MPEG-21 (coming)
• Other

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QoS guarantee

• Packets have to be classified in different
  traffic classes
• It is desireable to minimise interference between
  traffic flows
• Resources like link capacity, storage and
  processing units should be utilised efficiently
• Call admission control is needed. Admission
  requestes from flows have to include QoS
  requirements