Computer Networking: A Top Down Approach Featuring the Internet - Chapter 7 Multimedia Networking docx

Chapter 7
Multimedia Networking

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Computer Networking: A Top
Down Approach Featuring the
Internet,
3rd edition.
Jim Kurose, Keith Ross
Addison-Wesley, July 2004.

Thanks and enjoy! JFK / KWR
All material copyright 1996-2006
J.F Kurose and K.W. Ross, All Rights Reserved

7: Multimedia Networking 7-1


Multimedia, Quality of Service: What is it?
Multimedia applications:

network audio and video
(“continuous media”)

QoS
network provides
application with level of
performance needed for
application to function.
7: Multimedia Networking 7-2


Chapter 7: Goals
Principles
Ì Classify multimedia applications
Ì Identify the network services the apps need
Ì Making the best of best effort service
Ì Mechanisms for providing QoS

Protocols and Architectures
Ì Specific protocols for best-effort
Ì Architectures for QoS

7: Multimedia Networking 7-3


Chapter 7 outline
Ì 7.1 Multimedia

Networking Applications
Ì 7.2 Streaming stored

audio and video
Ì 7.3 Real-time
Multimedia: Internet
Phone study
Ì 7.4 Protocols for RealTime Interactive
Applications
r

RTP,RTCP,SIP

Ì 7.5 Distributing

Ì 7.6 Beyond Best

Effort
Ì 7.7 Scheduling
and Policing
Mechanisms
Ì 7.8 Integrated
Services and
Differentiated
Services
Ì 7.9 RSVP

Multimedia: content
distribution networks

7: Multimedia Networking 7-4

MM Networking Applications
Classes of MM
applications:
1) Streaming stored
audio and video
2) Streaming live
audio and video
3) Real-time
interactive audio
and video
Jitter is the variability
of packet delays within
the same packet stream

Fundamental
characteristics:
Ì Typically delay
sensitive
r
r

end-to-end delay
delay jitter

Ì But loss tolerant:

infrequent losses
cause minor glitches
Ì Antithesis of data,
which are loss

intolerant but delay
tolerant.

7: Multimedia Networking 7-5


Streaming Stored Multimedia

Streaming:
Ì media stored at source
Ì transmitted to client
Ì streaming: client playout begins
before all data has arrived
Ì timing constraint for still-to-be

transmitted data: in time for playout

7: Multimedia Networking 7-6


Cumulative data

Streaming Stored Multimedia:
What is it?

1. video
recorded

2. video
sent

network
delay

3. video received,
played out at client
time

streaming: at this time, client
playing out early part of video,
while server still sending later
part of video

7: Multimedia Networking 7-7


Streaming Stored Multimedia: Interactivity

Ì

VCR-like functionality: client can pause,
rewind, FF, push slider bar
r 10 sec initial delay OK
r 1-2 sec until command effect OK
r RTSP often used (more later)

Ì timing constraint for still-to-be

transmitted data: in time for playout

7: Multimedia Networking 7-8


Streaming Live Multimedia
Examples:
Ì Internet radio talk show
Ì Live sporting event

Streaming
Ì playback buffer
Ì playback can lag tens of seconds after

transmission
Ì still have timing constraint

Interactivity
Ì fast forward impossible
Ì rewind, pause possible!

7: Multimedia Networking 7-9


Interactive, Real-Time Multimedia

Ì applications: IP telephony, video

conference, distributed
interactive worlds

Ì end-end delay requirements:

r

audio: < 150 msec good, < 400 msec OK

• includes application-level (packetization) and network delays
• higher delays noticeable, impair interactivity
Ì session initialization
r

how does callee advertise its IP address, port number, encoding
algorithms?

7: Multimedia Networking 7-


Multimedia Over Today’s Internet
TCP/UDP/IP: “best-effort service”
Ì no guarantees on delay, loss

?

?

?

?

?

?

But you said multimedia apps requires ?
QoS and level of performance to be
?
? effective!
?

?

Today’s Internet multimedia applications
use application-level techniques to mitigate
(as best possible) effects of delay, loss
7: Multimedia Networking 7-


How should the Internet evolve to better
support multimedia?
Integrated services
philosophy:
Ì Fundamental changes in
Internet so that apps can
reserve end-to-end
bandwidth
Ì Requires new, complex
software in hosts &
routers
Laissez-faire
Ì no major changes
Ì more bandwidth when needed

Ì content distribution,
application-layer
multicast
r

application layer

Differentiated services
philosophy:
Ì Fewer changes to
Internet
infrastructure, yet
provide 1st and 2nd
class service.

What’s your opinion?
7: Multimedia Networking 7-


A few words about audio compression
Ì Analog signal

sampled at constant
rate
r

r

telephone: 8,000
samples/sec

CD music: 44,100
samples/sec

Ì Each sample

quantized, i.e.,
rounded
r

e.g., 28=256 possible
quantized values

Ì Each quantized value

represented by bits
r

8 bits for 256 values

Ì Example: 8,000

samples/sec, 256
quantized values -->
64,000 bps
Ì Receiver converts it
back to analog
signal:
r

some quality reduction

Example rates
Ì CD: 1.411 Mbps
Ì MP3: 96, 128, 160
kbps
Ì Internet telephony:
5.3 - 13 kbps

7: Multimedia Networking 7-


A few words about video compression
Ì Video is sequence

of images displayed
at constant rate
r

e.g. 24 images/sec

Ì Digital image is

array of pixels
Ì Each pixel
represented by bits
Ì Redundancy
r
r

spatial

temporal

Examples:
Ì MPEG 1 (CD-ROM) 1.5
Mbps
Ì MPEG2 (DVD) 3-6 Mbps
Ì MPEG4 (often used in
Internet, < 1 Mbps)
Research:
Ì Layered (scalable)
video
r

adapt layers to available
bandwidth

7: Multimedia Networking 7-


Chapter 7 outline
Ì 7.1 Multimedia

Networking Applications
Ì 7.2 Streaming stored
audio and video
Ì 7.3 Real-time
Multimedia: Internet
Phone study
Ì 7.4 Protocols for RealTime Interactive
Applications

r

RTP,RTCP,SIP

Ì 7.5 Distributing

Ì 7.6 Beyond Best

Effort
Ì 7.7 Scheduling
and Policing
Mechanisms
Ì 7.8 Integrated
Services and
Differentiated
Services
Ì 7.9 RSVP

Multimedia: content
distribution networks

7: Multimedia Networking 7-


Streaming Stored Multimedia
Application-level
streaming techniques
for making the best
out of best effort
service:

r client side buffering
r use of UDP versus TCP
r multiple encodings of
multimedia

Media Player
Ì jitter removal
Ì decompression
Ì error concealment
Ì graphical user

interface
w/ controls for
interactivity

7: Multimedia Networking 7-


Internet multimedia: simplest approach

Ì audio or video stored in file
Ì files transferred as HTTP object

r

received in entirety at client

r

then passed to player

audio, video not streamed:
Ì no, “pipelining,” long delays until playout!
7: Multimedia Networking 7-


Internet multimedia: streaming approach

Ì browser GETs metafile
Ì browser launches player, passing metafile
Ì player contacts server
Ì server streams audio/video to player

7: Multimedia Networking 7-


Streaming from a streaming server

Ì This architecture allows for non-HTTP

protocol between server and media player
Ì Can also use UDP instead of TCP.

7: Multimedia Networking 7-


constant bit
rate video
transmission

variable
network
delay

client video
reception

constant bit
rate video
playout at client

buffered
video

Cumulative data

Streaming Multimedia: Client Buffering

time

client playout
delay

Ì Client-side buffering, playout delay compensate

for network-added delay, delay jitter

7: Multimedia Networking 7-

Streaming Multimedia: Client Buffering

constant
drain
rate, d

variable fill
rate, x(t)

buffered
video
Ì Client-side buffering, playout delay compensate

for network-added delay, delay jitter

7: Multimedia Networking 7-


Streaming Multimedia: UDP or TCP?
UDP
Ì server sends at rate appropriate for client (oblivious to network congestion !)

often send rate = encoding rate = constant rate
r then, fill rate = constant rate - packet loss
r

Ì
Ì

short playout delay (2-5 seconds) to compensate for network delay jitter

error recover: time permitting

TCP
Ì send at maximum possible rate under TCP
Ì fill rate fluctuates due to TCP congestion control
Ì larger playout delay: smooth TCP delivery rate
Ì HTTP/TCP passes more easily through firewalls

7: Multimedia Networking 7-


Streaming Multimedia: client rate(s)
1.5 Mbps encoding

28.8 Kbps encoding

Q: how to handle different client receive rate
capabilities?
r 28.8 Kbps dialup
r 100Mbps Ethernet
A: server stores, transmits multiple copies
of video, encoded at different rates
7: Multimedia Networking 7-


User Control of Streaming Media:
RTSP
HTTP
Ì Does not target
multimedia content

Ì No commands for fast
forward, etc.
RTSP: RFC 2326
Ì Client-server
application layer
protocol.
Ì For user to control
display: rewind, fast
forward, pause,
resume,
repositioning, etc…

What it doesn’t do:
Ì does not define how
audio/video is
encapsulated for
streaming over network
Ì does not restrict how
streamed media is
transported; it can be
transported over UDP
or TCP
Ì does not specify how
the media player
buffers audio/video

7: Multimedia Networking 7-


RTSP: out of band control

FTP uses an “out-ofband” control channel:
Ì A file is transferred
over one TCP
connection.
Ì Control information
(directory changes,
file deletion, file
renaming, etc.) is
sent over a separate
TCP connection.
Ì The “out-of-band” and
“in-band” channels use
different port
numbers.

RTSP messages are also
sent out-of-band:
Ì
RTSP control
messages use
different port
numbers than the
media stream: out-ofband.
r

Port 554

Ì The media stream is

considered “in-band”.

7: Multimedia Networking 7-