difference b/w broadcasting and multicasting

hello!!
what is basically the difference between broadcasting & multicasting?In both the cases the CPU has to make a decision on the destination machines to be.Data packets are sent to multiple machines in both the transmission technologies.. I am not very clear on the above issue.

 

Hello Sanchita nice to know that you have got such a deep intrest in networking....
herez something that'll help u understand difference a lil better hope u like it....

Network interface cards r usually programmed to listen for three types of messages. They r messages sent to their specific address, messages broadcast to all NICs, and messages that qualify as a multicast for the specific card. There r three types of addressing:

Unicast - A transmission to a single interface card.
Multicast - A transmission to a group of interface cards on the network.
Broadcast - A transmission to all interface cards on the network. RFC 919 and 922 describe IP broadcast datagrams.
Limited Broadcast - Sent to all NICs on the some network segment as the source NIC. It is represented with the 255.255.255.255 TCP/IP address. This broadcast is not forwarded by routers so will only appear on one network segment.
Direct broadcast - Sent to all hosts on a network. Routers may be configured to forward directed broadcasts on large networks. For network 192.168.0.0, the broadcast is 192.168.255.255.
All other messages r filtered out by the NIC softwr unless the card is programmed to operate in promiscuous mode to perform network sniffing.

Broadcasting
The types of broadcasting uses on TCP/IP that I know abt r:

ARP on IP
DHCP on IP
Routing table updates. Broadcasts sent by routers with routing table updates to other routers.


The ethernet broadcast address in hexadecimal is FF:FF:FF:FF:FF:FF. There r several types of IP broadcasting:

The IP limited broadcast address is 255.255.255.255. This broadcast is not forwarded by a router.
A broadcast directed to a network has a form of x.255.255.255 where x is the address of a Class A network. This broadcast may be forwarded depending on the router program.
A broadcast sent to all subnetworks. If the broadcast is 10.1.255.255 on network 10.1.0.0 and the network is subnetted with multiple networks 10.1.x.0, then the broadcast is a broadcast to all subnetworks.
A broadcast sent to a subnet in the form 10.1.1.255 is a subnet broadcast if the subnet mask is 255.255.255.0.


Multicasting
Multicasting may be used for streaming multimedia, video conferencing, shrd white boards and more as the internet grows. Multicasting is still new to the internet and not widely supported by routers. New routing protocols r being developed to enable multicast traffic to be routed. Some of these routing protocols r:

Hierarchical Distance Vector Multicast Routing Protocol (HDVMRP)
Multicast Border Gateway
Protocol Independent Multicast
Since IP is not a reliable network protocol, a new reliable multicast protocol that works at the transport layer and uses IP at the network layer has been developed. It is called Multicast Transport Protocol (MTP)

Ethernet Addressing:
The internet assigned numbers authority (IANA) allocates ethernet addresses from 01:00:5E:00:00:00 through 01:00:5E:7F:FF:FF for multicasting. This means there r 23 bits available for the multicast group ID.

IP Addressing:
An IP multicast address is in the range 224.0.0.0 through 239.255.255.255. In hexadecimal that is E0.00.00.00 to EF.FF.FF.FF. To be a multicast address, the first three bits of the most significant byte must be set and the fourth bit must be clear. In the IP address, there r 28 bits for multicasting. Therefore there r 5 multicasting bits that cannot be mapped into an ethernet data packet. The 5 bits that r not mapped r the 5 most significant bits.

 

nice one !

 

The below link has more info :- http://www.comptechdoc.org/independent/networking/guide/netbroadcasting.html