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Transcript of 2 Multimedia Networking
8/11/2019 2 Multimedia Networking
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MultimediaNetworking
8/11/2019 2 Multimedia Networking
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Outline
The Internet Protocol Stack (Review)MM networking applications
Multimedia over “best effort” Internet
Evolving the Internet to supportmultimedia apps
Stored media streaming (in some detail)
What will we cover in this course?
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Internet protocol stack (Review 1/5)
application: supporting network applications FTP, SMTP, STTP
transport: host-host data transfer TCP, UDP
network: routing of datagrams from sourceto destination IP, routing protocols
link: data transfer between neighboringnetwork elements PPP, Ethernet
physical: bits “on the wire”
application
transport
network
link
physical
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The Network Layer (Review 2/5)
End systems inject datagrams in the networks A transmission path is determined for each packet
(routing)
A “best effort” service
Datagrams might be lost Datagrams might be arrive out of order
Jitter in arrival of datagrams from the same stream
Analogy: Postal system
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The Transport Layer (Review 3/5)
Concerned with end-to-end data transfer betweenend systems (hosts)
Transmission unit is called segment
TCP/IP networks such as the Internet provides
two types of services to applications “connection-oriented” service – Transmission Control
Protocol (TCP)
“connectionless” service - User Datagram Protocol (UDP)
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Connection-oriented Service (Review 4/5)
Handshaking between client & server programs Parameters for ensuing exchange Maintain connection-state
Packet switches do not maintain any connection-state; hence “connection-oriented”
Similar to a phone conversation TCP is bundled with reliability, congestion control,
and flow control.
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UDP: Connectionless Service (Review 5/5)
No handshaking Send whenever and however you want
A “best effort” service No reliability
No congestion & flow control services Why is it needed?
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Outline
The Internet Protocol Stack (Review)MM networking applications
Multimedia over “best effort” Internet
Evolving the Internet to supportmultimedia apps
Stored media streaming (in some detail)
What will we cover in this course?
8/11/2019 2 Multimedia Networking
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MM Networking Applications
Fundamentalcharacteristics:
Typically delay sensitive end-to-end delay
delay jitter But loss tolerant:
infrequent losses causeminor glitches
Antithesis of data,which are loss intolerantbut delay tolerant.
Classes of MM applications:1) Streaming stored audio
and video
2) Streaming live audio and
video3) Real-time interactive
audio and video
Jitter is the variabilityof packet delays withinthe same packet stream
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Streaming Stored Multimedia (1/2)
VCR-like functionality: client canpause, rewind, FF, push slider bar
10 sec initial delay OK
1-2 sec until command effect OK need a separate control protocol?
timing constraint for still-to-betransmitted data: in time for playout
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Streaming Stored Multimedia (2/2)
1. videorecorded
2. videosent
3. video received,played out at client
streaming: at this time, clientplaying out early part of video,while server still sending laterpart of video
networkdelay
time
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Streaming Live Multimedia
Examples: Internet radio talk show
Live sporting event
Streaming
playback buffer playback can lag tens of seconds after
transmission
still have timing constraint
Interactivity
fast forward impossible
rewind, pause possible!
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Interactive, Real-Time Multimedia
end-end delay requirements:
audio: < 150 msec good, < 400 msec OK• includes application-level (packetization) and network
delays
• higher delays noticeable, impair interactivity
session initialization
how does callee advertise its IP address, portnumber, encoding algorithms?
applications: IP telephony,video conference, distributedinteractive worlds
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Outline
The Internet Protocol Stack (Review)MM networking applications
Multimedia over “best effort” Internet
Evolving the Internet to supportmultimedia apps
Stored media streaming (in some detail)
What will we cover in this course?
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Multimedia Over “Best Effort” Internet
TCP/UDP/IP: no guarantees on delay, loss
Today’s Internet multimedia applicationsuse application-level techniques to mitigate
(as best possible) effects of delay, loss
But you said multimedia apps requiresQoS and level of performance to beeffective!
? ? ? ?
?
?
? ? ?
?
?
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Outline
The Internet Protocol Stack (Review)MM networking applications
Multimedia over “best effort” Internet
Evolving the Internet to supportmultimedia apps
Stored media streaming (in some detail)
What will we cover in this course?
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How to provide better support forMultimedia? (2/4)
Concerns with Intserv: Scalability: signaling, maintaining per-flow router
state difficult with large number of flows
Flexible Service Models: Intserv has only two
classes. Desire “qualitative” service classes E.g., Courier, xPress, and normal mail
E.g., First, business, and cattle class
Diffserv approach:
simple functions in network core, relativelycomplex functions at edge routers (or hosts)
Don’t define define service classes, providefunctional components to build service classes
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How to provide better support forMultimedia? (3/4)
Content DistributionNetworks (CDNs) Challenging to stream large
files (e.g., video) from singleorigin server in real time
Solution: replicate content athundreds of serversthroughout Internet
content downloaded to CDNservers ahead of time
placing content “close” touser avoids impairments(loss, delay) of sendingcontent over long paths
CDN server typically in
edge/access network
origin serverin North America
CDN distribution node
CDN server
in S. America CDN server
in Europe
CDN server
in Asia
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How to provide better support forMultimedia? (4/4)
R1
R2
R3 R4
(a)
R1
R2
R3 R4
(b)
duplicate
creation/transmissionduplicate
duplicate
Source-duplication versus in-network duplication.
(a) source duplication, (b) in-network duplication
Multicast/Broadcast
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Outline
The Internet Protocol Stack (Review)
MM networking applications
Multimedia over “best effort” Internet
Evolving the Internet to support multimedia apps
Stored media streaming (in some detail) Streaming Architectures
Real Time Streaming Protocol
Packet Loss Recovery
What will we cover in this course?
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Internet multimedia: simplest approach
audio, video not streamed:
no, “pipelining,” long delays until playout!
audio or video stored in file files transferred as HTTP object
received in entirety at client
then passed to player
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Streaming vs. Download of Stored MultimediaContent
Download: Receive entirecontent before playback begins
High “start-up” delay as mediafile can be large
~ 4GB for a 2 hour MPEG IImovie
Streaming: Play the media filewhile it is being received Reasonable “start-up” delays
Reception Rate >= playbackrate. Why?
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Progressive Download
browser GETs metafile browser launches player, passing metafile
player contacts server
server downloads audio/video to player
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Streaming from a streaming server
This architecture allows for non-HTTP protocol betweenserver and media player
Can also use UDP instead of TCP.
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constant bitrate video
transmission
time
variable
networkdelay
client videoreception
constant bitrate video
playout at client
client playout
delay
b u f f e r e
d
v i d e o
Streaming Multimedia: Client Buffering
Client-side buffering, playout delay compensatefor network-added delay, delay jitter
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Streaming Multimedia: Client Buffering
Client-side buffering, playout delay compensatefor network-added delay, delay jitter
buffered
video
variable fill
rate, x(t)
constantdrain
rate, d
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Streaming Multimedia: UDP or TCP?
UDP server sends at rate appropriate for client (oblivious to
network congestion !)
often send rate = encoding rate = constant rate
then, fill rate = constant rate - packet loss
short playout delay (2-5 seconds) to compensate for networkdelay jitter
error recover: time permitting
TCP send at maximum possible rate under TCP
fill rate fluctuates due to TCP congestion control
larger playout delay: smooth TCP delivery rate
HTTP/TCP passes more easily through firewalls
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Outline
The Internet Protocol Stack (Review)
MM networking applications
Multimedia over “best effort” Internet
Evolving the Internet to support multimedia apps
Stored media streaming (in some detail) Streaming Architectures
Real Time Streaming Protocol
Packet Loss Recovery
What will we cover in this course?
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Real-Time Streaming Protocol (RTSP)
HTTP Does not target multimedia
content
No commands for fastforward, etc.
RTSP: RFC 2326 Client-server application
layer protocol.
For user to control display:rewind, fast forward,
pause, resume,repositioning, etc…
What it doesn’t do: does not define how
audio/video is encapsulatedfor streaming over network
does not restrict how
streamed media istransported; it can betransported over UDP orTCP
does not specify how the
media player buffersaudio/video
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RTSP Example
Scenario: metafile communicated to web browser
browser launches player
player sets up an RTSP control connection, data
connection to streaming server
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Metafile Example
<title>Twister</title>
<session>
<group language=en lipsync>
<switch>
<track type=audio
e="PCMU/8000/1"src = "rtsp://audio.example.com/twister/audio.en/lofi">
<track type=audio
e="DVI4/16000/2" pt="90 DVI4/8000/1"src="rtsp://audio.example.com/twister/audio.en/hifi">
</switch>
<track type="video/jpeg"
src="rtsp://video.example.com/twister/video">
</group>
</session>
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RTSP Operation
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RTSP Exchange ExampleC: SETUP rtsp://audio.example.com/twister/audio RTSP/1.0
Transport: rtp/udp; compression; port=3056; mode=PLAY
S: RTSP/1.0 200 1 OKSession 4231
C: PLAY rtsp://audio.example.com/twister/audio.en/lofi RTSP/1.0
Session: 4231Range: npt=0-
C: PAUSE rtsp://audio.example.com/twister/audio.en/lofi RTSP/1.0Session: 4231Range: npt=37
C: TEARDOWN rtsp://audio.example.com/twister/audio.en/lofi RTSP/1.0Session: 4231
S: 200 3 OK
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Outline
The Internet Protocol Stack (Review)
MM networking applications
Multimedia over “best effort” Internet
Evolving the Internet to support multimedia apps
Stored media streaming (in some detail) Streaming Architectures
Real Time Streaming Protocol
Packet Loss Recovery
What will we cover in this course?
8/11/2019 2 Multimedia Networking
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Packet Loss
network loss: IP datagram lost due to networkcongestion (router buffer overflow)
delay loss: IP datagram arrives too late forplayout at receiver delays: processing, queueing in network; end-system
(sender, receiver) delays
Tolerable delay depends on the application
How can packet loss be handled? We will discuss this next …
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Receiver-based Packet Loss Recovery
Generate replacement packet Packet repetition
Interpolation
Other sophisticated schemes
Works when audio/video stream exhibits short-term self-similarity
Works for relatively low loss rates (e.g., < 5%)
Typically, breaks down on “bursty” losses
F d E C ti (FEC)
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Forward Error Correction (FEC)
for every group of n packets generate k redundant
packets send out n+k packets, increasing the bandwidth by factor
k/n.
can reconstruct the original n packets provided at most k
packets are lost from the group Works well at high loss rate (for a proper choice of k)
Handles “bursty” packet losses
Cost: increase in transmission cost (bandwidth)
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Interleaving: Recovery from packet loss
Interleaving
Re-sequence packets before transmission
Better handling of “burst” losses
Results in increased playout delay
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Summary: Internet Multimedia: bag of tricks
use UDP to avoid TCP congestion control (delays)for time-sensitive traffic
client-side adaptive playout delay: to compensatefor delay
server side matches stream bandwidth to availableclient-to-server path bandwidth chose among pre-encoded stream rates
dynamic server encoding rate
error recovery (on top of UDP) FEC, interleaving
retransmissions, time permitting
conceal errors: repeat nearby data
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What will we study in this course?
Empirical measurements
Multicast support IP Multicast, Application layer multicast
Content Distribution
Scalable streaming, CDNs Multimedia Rate Control
TCP overview, TCP Vegas, unicast and multicast ratecontrol protocol
Media streaming in wireless networks? Network Games?
Quality of Service Issues? … Any ideas?
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Example: Streaming Popular Content
Consider a popular media file Playback rate: 1 Mbps
Duration: 90 minutes
Request rate: once every minute
Can a video server handle such high loads? Approach 1: Start a new “stream” for each
request
Allocate server and disk I/O bandwidth for
each request Bandwidth required at server= 1 Mbps x 90
How to improve efficiency?
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Streaming Popular Content using Batching
Approach 2: Leverage the multipoint delivery
capability of modern networks Playback rate = 1 Mbps, duration = 90 minutes
Group requests in non-overlapping intervals of 30minutes:
Max. start-up delay = 30 minutes Bandwidth required = 3 channels = 3 Mbps
0 3
0
60 90 120 150 180 210 240
Time (minutes)
Channel 1
Channel 2
Channel 3
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Batching Issues
Bandwidth increases linearly with decreasein start-up delays
Can we reduce or eliminate “start-up”
delays? Periodic Broadcast Protocols
Stream Merging Protocols
CDNs
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Another Example: Streaming Live Multimedia
How to stream to large numbers of clients? Example: A popular sporting event
Use multicast/broadcast
What about client heterogeneity?
E.g., clients might have different available b/w Use layered/scalable video
Internet
Video Server
ADSL
Dial-up
High-speed
Access
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Multimedia Networking
Exciting, industry relevant research topicMultimedia is everywhere
Tons of open problems
Questions?