Internet Based Media Communication

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Internet Based Media Communication

• Multicasting and Mobile ad-hoc networks

Mihály Orosz Budapest University of Technology
and Economics mihi_at_nimrud.eet.bme.hu
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Multicast Fundamentals

• The communication ways of the hosts
• IP multicast
• Application level multicast

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The Communication Ways of the Hosts
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Needs for Multicast

• Classic communication protocols (e.g. HTTP) are
  client-server oriented
• They resemble one-to-one connections
• a client sends a request and
• the server answers with his reply
• Although a web site directs its content to a mass
  audience,
• each connection is a connection between a single
  user's client and the website's server
• The same applies to the streaming protocols used
  by internet radios
• A web radio really runs into problems when it
  becomes popular
• it has to pay too much for its increasing
  upstream bandwidth
• No wonder that we do not see many web-TV stations
  until now
• the technology simply does not allow it
• Huge amounts of data directed to a mass audience
  must be distributed differently now
• TV programs are being broadcasted via satellite
  or cable
• movies are distributed physically on DVD

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IP Address Classes
Three fundamental types of IPv4 addresses
- Unicast - Broadcast - Multicast
1. Unicast is designed to transmit a packet
to a single destination
2. Broadcast is used to send a datagram to an
entire subnetwork
3. Multicast is designed to enable the
delivery of datagrams to
a set of hosts that have been configured as
members of Multicast group in
various scattered
subnetworks
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Broadcast/Unicast/Multicast/Concast

• Unicast a separate IP packet is sent from a
  source to a destination participating in a
  connection.
• Broadcast When a packet is broadcast the same
  packet is sent to all clients on the network.
• Multicast General idea behind multicast is to
  send single copy of an IP packet to all of those
  of clients that requested it, and not to send
  multiple copies of a packet over the same portion
  of the network.
• Basic idea in multicasting IP packets is to
  construct a tree structure data delivery path
  through the network.
• This tree is rooted at the source of the
  multicast traffic and its leaves are subnetworks
  containing receivers of that traffic
• ConcastIt has mainly theoretical importance
  only. It can be imagined as a reversed multicast.

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Broadcast

• BROADCAST
• Source transmits one stream of data for all the
  receivers without exception
• Replication happens inside routers and switches
• Broadcast is limited for LANs

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Unicast

• UNICAST
• With 4 receivers, sender must replicate the
  stream 4 times

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Multicast

• MULTICAST
• Source transmits one stream of data for n
  receivers
• Replication happens inside routers and switches
• WAN links only need one copy of the data, not n
  copies.

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Concast

• CONCAST
• Source recieves one stream of data from n
  receivers
• Aggregation happens inside routers and switches

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Concast
Aggregation of the data is necessary for
bandwidth saving
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Multicast application
ConferenceXP An Example of Multicast application
Distance Learning
Video Conference

• Further applications
• Audio conference
• IP TV, Video on Demand
• Advertisement, Stock
• Synchronizing of distributed database, websites

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The IP Multicast

• AnySource Multicast (ASM)
• STEVE DEERING estabilished in 1989 (RFC 1112)
• Group communication model
• Dynamic and anonym group membership
• The source does not know the places or addresses
  of destinations it send data packets to the
  group address only
• The care of the network is to perform the
  necessary routing and packet multiplication
• The client does not know from where the
  information comes, it joins only to a multicast
  group and then receives all data packets, which
  are sent to this address

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The IP Multicast

• Source Specific Multicast (SSM)
• In its case the explicit knowledge of the sources
  is necessary
• Source is identified by its unicast ip address
• All the sources (mainly only one) have to be
  known by the recievers
• Less trouble for the routing
• Source routed trees can be used easily based on
  unicast routing information

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The IP Multicast
Multicast Groups
Group Membership Protocol

• A group membership protocol is employed by
  routers to learn about the presence of group
  members on their directly attached subnetworks

Multicast Routing Protocol

• Multicast routers execute a Multicast routing
  protocol to define delivery paths that enable
  the forwarding of Multi- cast datagrams across
  an internetwork

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Multicast Group and Service Model I

• The key difference between a multicast IP packet
  and a unicast IP packet is the presence of a
  GROUP ADDRESS in the Destination Address field of
  the IP header of multicast IP packet.
• A multicast address is designed to enable a
  delivery of IP multicast packets to a set of
  clients that have been configured as members of a
  multicast group in various scattered subnetworks.
  
• Individual clients are free to join or leave
  multicast group at any time. A client may be a
  member of more than one multicast group at any
  given time and does not have to belong to a group
  to send message to members of a group.

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Multicast Group and Service Model II

• Multicast Address
• IP reserved class D addresses for multicast
  224.0.0.0239.255.255.255
• Base address 224.0.0.0 is reserved
• 224.0.0.1224.0.0.255 are devoted to multicast
  routing and group maintenance protocols
• Multicast addresses can only be used as
  destination

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Multicast Group and Service Model III

• Mapping IP Multicast to Ethernet Multicast Place
  the lower 23 bits of the IP multicast address
  into the lower 23 bits of special Ethernet
  multicast address 01.00.5E.00.00.00. 32 multicast
  groups may be mapped into the same address.
  Probability is small, but receivers should check
  the datagram

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Mapping the Multicast MAC- IP-Addresses
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Reserved Multicast Addresses
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Scope Control

• Distance-based scope control
• Distance (or time-to-live) based
• Additional meaning of the TTL comparing to the IP
  unicast
• Administrative scope control

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TTL Domains
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Administrative Scope-control

• Demand geographical and bandwidth limitations
  parallel
• The range 239.0.0.0 - 239.255.255.255 is reserved
  for administrative scoping
• Similar to the local unicast address ranges
  (192.168., 10. etc.)
• Reuse a multicast address used by an application
  inside a scope controlled region can be used by
  any application outside of the scope
• The applications can totally use the available
  bandwidth without the traffic flushing the
  smaller bandwidth connections and arising a
  glitch in the whole communication session

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Application Level Multicast

• The multicast communication session is possible
  in the application level, too
• Host applications forward data by unicast
• Disadvantages
• The propagation time is increased
• The hosts have not inherent responsibility in the
  internet (oppositely of the routers)
• Only sub-optimal bandwith usage (double or more
  on the last hop)
• Presently operating solutions
• System of network news (Usenet)
• Virus dissemination through the network
  (regrettable)