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  1. 1. DeliveryCategories of Messaging
  2. 2. Messaging CategoriesUnicast: Messages are sent to a single,specific recipientMulticast: Messages are sent to a group ofrecipients Broadcast: Messages are sent to all recipients on the networkAnycast: Messages are sent to any memberof a group of recipients
  3. 3. UnicastThis is the normal, most common form ofmessagingUnicast messages are addressed using aspecific address of a recipient nodeNetwork routers choose the best path (onepath) for the message to travelEventually, the routers direct the message tothe correct node
  4. 4. Anycast Anycast messages also involve groups Anycast groups are groups of nodes where any node in the group can receive any of the messages intended for that group Anycast (rarely) is useful in situations such as sending a message to a router, which typically has several addresses  You don’t care which network port is used to receive the message by the router, as long as the router gets the message  Normally, the message is delivered to the node that has the shortest path from the sender
  5. 5. Broadcast Broadcasting can be considered a specific example of multicasting  All nodes on a network are the members of the multicast group  The big differences are that these nodes to not explicitly join the broadcast group, nor can they leave it Broadcasting is often implemented in hardware in LANs, which means broadcast messages use approximately the same bandwidth as a unicast message  In fact, most LANs use broadcast technology to implement multicasting also
  6. 6. LAN Broadcasting Most LANs use broadcast technology  All nodes on the network read all messages, and determine (by examining the address) if the message is intended for that node or not  Broadcasting uses a specific address to indicate that the node should keep the message  Broadcast-enabled NICs read messages addressed for the NIC (specifically) as well as messages addressed to the broadcast address  The only concern that must be taken, is that the message should be placed back onto the network after it has been read  Some LANs remove the message from the network medium when it has been received
  7. 7. LAN Broadcasting Broadcast LANs support broadcast delivery by transmitting a single packet  This packet is received by all nodes  e.g. Ethernet, Token Bus, Token Ring Daisy chain LANs send broadcast messages across the network sequentially  The sender transmits a broadcast packet, which is received by the next node  The next node transmits the broadcast packet again, and it is received by the next sequential node  e.g. FDDI
  8. 8. LAN Broadcasting: PhysicalThis is the messaging pattern in LANs that use broadcasttechnology Transmit M M M M M M M M
  9. 9. LAN Broadcast Addresses Most networks that use MAC addresses, use FF:FF:FF:FF:FF:FF for a broadcast address IP-based networks use for a broadcast address
  10. 10. LAN Broadcasting EfficiencyLANs that use broadcast technology The time to send a broadcast message is identical to the time to send a unicast messageE = O(1)LANs that use daisy-chaining The time to send a broadcast message is more than (or equal to) the time to send a unicast message The time to send a broadcast message is less than (or equal to) the time to send a unicast message to each node on the networkO(1) ≤ E ≤ O(N)
  11. 11. WAN BroadcastingIn WANs such as the Internet, a broadcastmessage would be received by millions ofmachines This is inefficient This is somewhat of an invasion of privacy This has no practical purposeOther WANs may choose to implement broadcastby sending a unicast or multicast message to allnodes on the network Even this is highly unlikely, but possible
  12. 12. MulticastMulticast messages are intended for a group ofrecipientsMulticast messages are not addressed to eachrecipient, but addressed to the group of recipientsMulticast groups are associated with specificaddresses, called multicast addresses In IP networks, these are Class D addresses
  13. 13. Multicast GroupsMessages sent to multicast group addressesare received by all members of the multicastgroup Therefore, in order to receive multicast group messages, a node must join the multicast groupMessages can be sent to a multicast groupwithout being a member The message is simply addressed to the multicast group’s address
  14. 14. LAN Multicasting LAN multicasting is often implemented in hardware Multicasting can be entirely implemented in the nodes  Each node’s NIC can be configured to accept packets addressed to a multicast address  Each multicast group is assigned a specific address (MAC, IP, etc…)  Since all nodes normally receive (in broadcast LANs) all messages, the nodes which are configured for a particular multicast address will accept packets sent to that address  Messages can be sent to a multicast group by addressing them with the multicast address for that group
  15. 15. LAN Multicasting In LANs that use broadcast technology, all messages are received by all nodes on a network  For multicast delivery to occur, the message must simply be addressed so that the multicast group members accept the packets and non-members reject them In LANs that do not use broadcast, messages are transmitted onto the network  The first multicast group member accepts the packet  The group member then retransmits the packet, where it is received by the next group member
  16. 16. LAN Multicast AddressesIn networks that use MAC addresses,multicast packets are addressed with: MAC addresses with the 8th bit set to 1  e.g. 01.5E. Unicast addresses have the 8th bit set to 0In IP-based networks, multicast packets areaddressed with Class D addresses: –  e.g.
  17. 17. LAN Multicast EfficiencyIn LANs that use broadcast technology: The time to transmit a multicast message is the same as the time to transmit a unicast messageE = O(1)In LANs that do not use broadcast: The time to transmit a multicast message is more than (or equal to) the time to transmit a unicast message The time to transmit a multicast message is less than (or equal to) the time to transmit a unicast message to each multicast group memberO(1) ≤ E ≤ O(N)
  18. 18. LAN Multicasting: PhysicalThis is the messaging pattern in LANs that use broadcasttechnology Transmit M M M M M Multicast Group A
  19. 19. WAN MulticastingWAN multicast cannot be implemented entirely atnode-level (as LAN multicast can) This is because routers must forward the multicast messages to other LANs Some LANs a router can access will not contain any multicast group members  It would be inefficient to send the multicast message to LANs such as these  Routers must know where (on which of its ports) there are members of each multicast group
  20. 20. Multicast TunnelingSome WANs do not support multicastWhen a multicast message is sent across a networkthat does not support multicast, it must tunnelthrough that network Multicast datagrams are encapsulated into a larger datagram which is transmitted (using unicast) from one part of the network, to another Assumedly, the second part of the network is connected to another network which supports multicast or else a network that should also use multicast tunneling
  21. 21. WAN Multicast EfficiencyLAN multicast is often identical (inefficiency) to LAN unicastWAN multicast, however, is typically lessefficient The total number of messages present on the network is typically more than one for WAN multicast