MBone: The Multicasting Backbone

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MBone The Multicasting Backbone

• Rajendra Singh Chandrawat
• 04/24/07

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Topics to be covered

• Introduction and History
• MBone Architecture
• Multicast Networks
• Mrouted
• Bandwidth Constraints
• Pruning
• Bandwidth Protection

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Introduction

• Definition
• The MBone is a virtual network of hosts connected
  to the Internet communicating using a technique
  called Internet Protocol multicasting.
• Uses of MBone
• Video and audio conferencing .
• Internet Talk Radio.
• distance learning.
• Multimedia over high-speed networks offers
  attractive possibility to bring expertise
  together over long distances and so multiply
  training benefits.
• Goal
• Since most LAN hardware and software already
  support multicasting in local networks the
  challenge is to extend this feature to
  internetworks efficiently.

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MBone History

• Named by Steve Casner.
• Dates back to 1992.
• Due to IETFs efforts to multicast Audio and
  Video.

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MBone Architecture
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Multicast networks

• Multicasting existed for several years on local
  area networks.
• With IP multicast addressing at the network
  layer, group communication can be established
  across the Internet.
• Two things that make multimedia multicasting
  feasible on a worldwide scale
• (1) Installation of high bandwidth Internet
  backbone connections.
• (2) Widespread availability of workstations with
  adequate processing power and built-in
  audio/video capability

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mRouted

• A Network of routers that supports Multicasting.
• Upgraded commercial routers.
• Working
• Mrouted (multicast routing demon) forwards a
  multicast datagram along a shortest (reverse)
  path tree rooted at the subnet on which the
  datagram originates.
• It is a BROADCAST tree.
• Datagram will not be forwarded onto LEAF subnets
  of the tree if those subnets do not have members
  of the destination group.
• Furthermore, the IP time-to-live may prevent it
  from being forwarded along the entire tree.

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Tunneling

• A scheme to forward multicast packets among the
  islands of MBone subnets through Internet IP
  routers that typically do not support IP
  multicasting.
• Encapsulate multicast packets inside regular IP
  packets.
• In order to support multicasting mrouted includes
  support for "tunnels.
• -gt virtual point-to-point links between pairs of
  mrouteds located anywhere in the Internet.
• IP multicast packets are encapsulated for
  transmission through tunnels, so that they look
  like normal unicast datagrams to intervening
  routers and subnets.
• The encapsulation takes the form of an IP source
  route that is inserted on entry to a tunnel, and
  stripped out on exit from a tunnel.

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Bandwidth constraints

• The reason a multicast stream is
  bandwidth-efficient is that one packet can touch
  all workstations on a network.
• Multicast packets prevented from crossing
  network boundaries.
• Avoid Flooding or Network Saturation.
• Therefore, controls are necessary.
• MBone can control multicast packet distribution
  across the Internet in two ways
• (1) It can limit the lifetime of multicast
  packets, and
• (2) It can use sophisticated pruning algorithms
  to adaptively restrict multicast
• transmission.

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Pruning

• Pruning -
• A way to tell an upstream router that it should
  not send packets addressed to a certain multicast
  address, since nobody is listening to it anymore.
• Data distribution tree gets created.
• Routers may send prune or Grafts.
• If a member appears, send grafts.
• Grafts then "chase" the previous prunes upstream
  until they hit a point
• on the real distribution tree.
• Data starts getting forwarded and the tree gets
  recreated as before.

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Solution

• To protect the resources, per-tunnel rate
  limiting was introduced.
• Example will explain.
• Mrouted enables you to do it in the following
  way
• Set the rate limit to 192kps at the lowest.
• Keep the multicast traffic below 192kbps.

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Thanks !!!Any Queries ???