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ITIS 1210
Introduction to Web-Based
Information Systems
Chapter 39
How Multicast IP and MBone Work
Introduction
 Internet content
 Originally it was just static content
 Download it, view it
 Branched out into other forms
 Sound
 Video
 Animations
 3D objects
 Now interactive content is prevalent
Introduction
 Problem:
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Providing a richer experience
Implies correspondingly larger files
That take longer to download
Causing massive congestion within the
Internet infrastructure
 Some content cannot be sent over Internet
at all because of capacity limitations
Introduction
 Example: telecast of a concert
 Assume a file size of 50MB
 Assume an audience of 10,000 people
 50MB must be sent individually to 10,000
subscribers
 This might not be possible without
seriously degrading the ability of local
sections of the Internet to continue to
service other customers
Introduction
 One solution is the experimental MBone
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Multicast Backbone
Virtual high-capacity backbone
Specifically designed to transmit broadcasts
Uses the IP multicast protocol
 Begins as a single transmission
 Instead of 10,000
 Included are all addresses of every
subscriber
Introduction
 As the file is sent across the Internet it
makes copies of itself
 Those copies are routed to individual
subscribers
Introduction
 Example:
 100 people want to see a broadcast of a 50MB file
 Under normal circumstances, 5GB of data would be
necessary
 50 are connected to the Internet via ISP X
 25 use ISP Y
 25 are on corporate network Z
 With multicast, the file is initially transmitted as a
single file
 Splits into three parts to X, Y, and Z
Introduction
 Each network delivers their copy on to
subscribers on that network alone
 Instead of 5GB being necessary
 Three 50MB files (150MB) are needed
 Normally the Internet is a unicast
environment
 One transmission goes to one destination
 Multicast enables simultaneous
destinations
Introduction
 MBone is a virtual network of host
computers that use the IP Multicast for
communications
 Process starts by digitizing and
compressing a video signal
 The compressed signal is sent using the
IP Multicast protocol
 Multiple destinations simultaneously
Introduction
 Major advantage is the single transmission
 TCP would require a transmission to each
recipient
 Information about the multiple destinations
goes into the packet
 Two major problems:
 Most networks and routers on the Internet do
not understand the multicast protocol
 Must still use standard Internet routes
Introduction
 Solution is called tunneling
 MBone data travels in tunnels built on top of
existing Internet networks and routers
 Ends of tunnel are workstations running a
multicast routing demon
 A demon (daemon) is a process that runs in the
background and performs some useful service
 The demon encloses the multicast packets
inside regular TCP packets
Introduction
 The now-standard TCP packets are sent
over the regular Internet to the other end
of the tunnel
 There the multicast packets are extracted
 Sent on via an MBone network that
understands the multicast protocol
Introduction
 Based on destination data in the multicast
packets
 The original data is sent to a number of
different hosts
 Individuals connected to these hosts can view
the content
 There are teleconferencing options that
enable interaction
 Audio and video
Introduction
 Multicast will probably become obsolete
 Hard to compute service charges for multicast
traffic
 Standard feature of IPV6