Transcript Multimedia Networking

Multimedia Networking
Sound, Video
Applications
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•
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Downloadable files
Streaming Video
Streaming Audio
VoIP (Voice over IP)
– Internet Phone
Problems for multimedia
• Best-effort-service
– No promises about delay
• Packet jitter
– Variable packet delays
• Dropped packets
– Time delay caused by out of sequence
packets
Fixes
• Faster internet ISPs
– More bandwidth for the Internet
• Content distribution networks (CDNs)
– Distribute the data over a wider area (edges
of the internet)
• Multicasting (multicast overlay network)
– Not IP multicast but a server based distributed
multicast.
Human Interface
• Hearing limitations
– Ear response 20 to 20,000 Hertz
– Networking speeds are up to
100,000,000,000 hertz
– Phonemes are from 5-100msec
– Ear does not respond to delays < 150msec
• Visual limitations
– The eye retention is about 60 msec.
– Any transfer faster than 16 frames per second
will not appear to flicker.
Data Preparation
• Audio and Video compression
– Sampling rate
– Quantization (rounding samples to finite values)
– Fit the quantization values into a fixed size
– Pulse Code Modulation (PCM)
• Sample rate * # of bits * 2 (if stereo)
– Compression
• GSM (Global System Mobile) or G.723.3 (ADPCM)
• MPEG 1 layer 3 or MP3
• Coding/Decoding
– Codecs
Video Compression
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MPEG1 CD-ROM quality
MPEG 2 for DVD quality
MPEG4 for object oriented
H.261
Proprietary
– Apple Quick Time
– Real Networks
Protocols
• RTP (Real Time Protocol)
• RTSP (Real Time Streaming Protocol)
• These are not IP protocols but are
accessed via help applications in browsers
• They provide:
– Decompression
– Jitter Removal
– Error Correction
Types of transfer
• Web server file access
– Download the multimedia file
– Play the file on Windows media player or your
favorite version of player.
– Requires local storage of the file
• Streaming
– Access the audio/video stream via web server
– Playback portions of the stream in real time
via the streaming server.
RTSP
• Real Time Streaming protocol
– Does not set compression schemes
– Does not define encapsulation
– Does not restrict the transport
– Does not restrict buffering
• Uses out-of-band signaling (separate port)
Internet Phone Example
• Packet Loss
• Packet Jitter
Packet Loss Recovery
• Forward Error Correction
– Piggybacking redundant information
– Utilizes lower bit rate chunks for redundancy
– Works well for harsh environments
• Interleaving
– Splitting the stream across several packets
– Increased latency (delays)
• Packet repetition
– Copies good packets to replace lost ones.
– Works well for small loss rates
End to End Delays
• The human ear smaller than 150msec are
indiscernible to the human ear
• If the delay exceeds 400msec then the
packet is lost.
Packet Jitter
• Delay fluctuations between packets.
• Removing Jitter
– Use sequence numbers, timestamps and:
– Fixed Playout Delay
• Delay before playing packet
• Phone system can handle 400 msecs of delay
– Adaptive Playout delay
• Adjust delay depending on the flow of data
Real Time Protocol
• Runs on top of UDP (for speed)
• Packet header includes:
– Payload type
– Sequence number
– Timestamp
– Sync source identification number
– Miscellaneous
• Defines which coding method is used and
timing to overcome jitter.
RTCP
• Real Tine Control Protocol
• Used to communicate information from
source to destination.
– Sync Source ID
– Packets lost
– Last sequence number
– Number of bytes in the stream
– Scaling parameters (packet size)
Session Initiation Protocol
• Internet Phone
• Sorta like Telnet for the phone system
Name Translation
• SIP Proxy
– Authenticates SIP invitations
• SIP registrar
– Keeps track of the users IP address
H.323
• Internet Phone to PSTN (Public Switched
Telephone Network)
– Defines how endpoints negotiate audio/visual
encodings
– Defines how to encapsulate data
– Defines how to communicate with
gatekeepers
– Defines how VoIP interfaces with ordinary
telephones.
Queuing Schemes
• FIFO (First In First Out)
– Every packet in order regardless of class
Queuing Schemes
• Priority Queuing
– Based on priority class in header
Queuing Schemes
• Round Robin/Weighted Fair Queuing
– Based on class of service
Reservation Protocol
• RSVP
– Provides for resource reservation in multicast
trees
– Receiver oriented, receiver initiates and
maintains resource reservations
• Handles the problem of different speed
receivers all following the same
video/audio stream
Tour of USU Network
Infrastructure
Borrowed Space in Telephone Switching Site
Surge Protectors
Cross-Connect Blocks
Wiring trays
above is typical
for telephone
locations
Telephone
Equipment
Now that’s a Ground!
10BaseT Hubs
10/100 switch
10/100 switch
with FDDI
FDDI
Concentrator
Media
Converters
Fiber
Optics
Router
Close up View
Media Converters
Computer Room in SER
Building
Servers, Building Network, and
Campus Networking
Internet Feed
Pix Fire Wall
Cisco Border
Router
Packeteer
Primary USU Cisco
Router
USU/UEN
Interface
180 Mbs
UEN
Internet
Feed
Salt Lake
Housing
Rest of USU Campus
Connections
for building
network
Other
Campus
Network
Equipment
Student
Housing
Front Side of Equipment Racks
Inside of Fiber Panels
Internet
gateway
router
Switch with
router card &
100BaseFX
connections
Misc. Novell
servers
VMS cluster
a.k.a.
cc.usu.edu
opie
barney
sneezy
sleepy
grumpy
Cluster Connections
Barney Grumpy Sleepy
.89
.86
.85
Sneezy
.87
Foundry Load Balancing
Switch
Opie
.150
129.123.1.1
cc.usu.edu
USU Backbone
Multimedia Networking