Delivery

Delivery

Categories of Messaging

Messaging Categories

Unicast: Messages are sent to a single, specific recipient

Multicast: Messages are sent to a group of recipients Broadcast: Messages are sent to all recipients

on the network

Anycast: Messages are sent to any member of a group of recipients

Unicast

This is the normal, most common form of messagingUnicast messages are addressed using a specific address of a recipient nodeNetwork routers choose the best path (one path) for the message to travelEventually, the routers direct the message to the correct node

AnycastAnycast messages also involve groupsAnycast groups are groups of nodes where any node in the group can receive any of the messages intended for that groupAnycast (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

BroadcastBroadcasting 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

LAN BroadcastingMost 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

LAN BroadcastingBroadcast 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

Transmit

LAN Broadcasting: Physical

M M

M

MMM

M

M

This is the messaging pattern in LANs that use broadcast technology

LAN Broadcast AddressesMost networks that use MAC addresses, use FF:FF:FF:FF:FF:FF for a broadcast address

IP-based networks use 255.255.255.255 for a broadcast address

LAN Broadcasting Efficiency

LANs 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 network

O(1) ≤ E ≤ O(N)

WAN Broadcasting

In WANs such as the Internet, a broadcast message would be received by millions of machines This is inefficient This is somewhat of an invasion of privacy This has no practical purpose

Other WANs may choose to implement broadcast by sending a unicast or multicast message to all nodes on the network Even this is highly unlikely, but possible

Multicast

Multicast messages are intended for a group of recipients

Multicast messages are not addressed to each recipient, but addressed to the group of recipients

Multicast groups are associated with specific addresses, called multicast addresses In IP networks, these are Class D addresses

Multicast Groups

Messages sent to multicast group addresses are received by all members of the multicast group Therefore, in order to receive multicast group

messages, a node must join the multicast group

Messages can be sent to a multicast group without being a member The message is simply addressed to the

multicast group’s address

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

LAN MulticastingIn 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

LAN Multicast Addresses

In networks that use MAC addresses, multicast packets are addressed with: MAC addresses with the 8th bit set to 1

e.g. 01.5E.00.00.00.01 Unicast addresses have the 8th bit set to 0

In IP-based networks, multicast packets are addressed with Class D addresses: 224.0.0.0 – 239.255.255.255

e.g. 229.201.35.82

LAN Multicast Efficiency

In 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 member

O(1) ≤ E ≤ O(N)

Transmit

LAN Multicasting: Physical

M

M

MM

M

This is the messaging pattern in LANs that use broadcast technology

Multicast Group A

WAN Multicasting

WAN multicast cannot be implemented entirely at node-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

Multicast Tunneling

Some WANs do not support multicastWhen a multicast message is sent across a network that does not support multicast, it must tunnel through 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

WAN Multicast Efficiency

LAN multicast is often identical (in efficiency) to LAN unicast

WAN multicast, however, is typically less efficient The total number of messages present on the

network is typically more than one for WAN multicast