Implementing Multicast

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Implementing Multicast

• Explaining Multicast

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Why Multicast?

• Used when sending same data to multiple receivers
• Better bandwidth utilization
• Less host/router processing
• Used when addresses of receivers unknown
• Used when simultaneous delivery for a group of
  receivers is required (simulcast)

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Unicast vs. Multicast
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Multicast Advantages

• Enhanced efficiency Controls network traffic and
  reduces server and CPU loads
• Optimized performance Eliminates traffic
  redundancy
• Distributed applications Makes multipoint
  applications possible

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Multicast Disadvantages

• Multicast is UDP-based.
• Best-effort delivery Drops are to be expected.
  Multicast applications must not expect reliable
  delivery of data and should be designed
  accordingly. Reliable multicast applications will
  address this issue.
• No congestion avoidance The lack of TCP
  windowing and slow-start mechanisms can result
  in network congestion. If possible, multicast
  applications should attempt to detect and avoid
  congestion conditions.
• Duplicates Some multicast protocol mechanisms
  result in the occasional generation of duplicate
  packets. Multicast applications should be
  designed to expect occasional duplicate packets.
• Out-of-sequence delivery Network topology
  changes affect the order of deliverythe
  application must properly address the issue.

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Types of Multicast Applications

• One to many A single host sending to two or more
  (n) receivers
• Many to many Any number of hosts sending to the
  same multicast group hosts are also members of
  the group (sender receiver)
• Many to one Any number of receivers sending data
  back to a source (via unicast or multicast)

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IP Multicast Applications
Corporate Broadcasts
Live TV and Radio Broadcast to the Desktop
Distance Learning
Multicast File Transfer Data and File Replication
Training
Videoconferencing
Video-on-Demand
Whiteboard/Collaboration
Real-Time Data DeliveryFinancial
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IP Multicast Basic Addressing

• IP group addresses
• Class D address (high-order three bits are set)
• Range from 224.0.0.0 through 239.255.255.255
• Well-known addresses assigned by IANA
• Reserved use 224.0.0.0 through 224.0.0.255
• 224.0.0.1 (all multicast systems on subnet)
• 224.0.0.2 (all routers on subnet)
• 224.0.0.4 (all DVMRP routers)
• 224.0.0.13 (all PIMv2 routers)
• 224.0.0.5, 224.0.0.6, 224.0.0.9, and 224.0.0.10
  used by unicast routing protocols

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IP Multicast Basic Addressing (Cont.)

• Transient addresses, assigned and reclaimed
  dynamically (within applications)
• Global range 224.0.1.0-238.255.255.255
• 224.2.X.X usually used in MBONE applications
• Limited (local) scope 239.0.0.0/8 for private IP
  multicast addresses (RFC-2365)
• Site-local scope 239.255.0.0/16
• Organization-local scope 239.192.0.0 to
  239.251.255.255
• Part of a global scope recently used for new
  protocols and temporary usage

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Layer 2 Multicast Addressing

• IP Multicast MAC Address Mapping Ethernet

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Learning About Multicast Sessions

• Potential receivers have to learn about multicast
  streams or sessions available before multicast
  application is launched. Possibilities
• Another multicast application sending to a
  well-known group whose members are all potential
  receivers
• Directory services
• Web page, e-mail
• Session Announcement Protocol

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A Cisco IP/TV Example

• Cisco IP/TV application
• Clients (viewers) use program listing
• Contact the server directly
• Listen to SAP announcements

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Summary

• IP multicast is a much more efficient means of
  delivering content where a single sender needs to
  deliver the content to multiple receivers. This
  task may be achieved through the use of multicast
  groups.
• IP multicasts are designated by the use of a
  specific Class D IP address range. This is
  achieved through global scope addresses, which
  are assigned dynamically, and administratively
  scoped, which are assigned locally and are
  reserved for use inside private domains.

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