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February 09, 2005
CCIE Study memo2 : How is Multicast different from Unicast?
In my last entry, I said "if you use multicast, you’ll only need to send one stream of data to the switch or the router no matter how many clients wish to receive the multicast message."
But why is this? How is multicast different from unicast?
There can be many ways to explain the difference between multicast and unicast. In my view, the most important diffrence is:
Network devices like switches and routers copy the multicast packets whereas unicasts packets do not get copied by those devices.
MULTICAST:
When a switch receives multicast traffic, it creates the copies and flood them to all the hosts in the segment. (There is a way to food multicast traffic to a specific group of hosts instead of all the hosts. I will talk about it when I'm ready.
UNICAST
but this doesn't happen with unicast traffic.
Because the network can copy and flood the data to the recipients, the sender only has to send one data stream regardless of the number of the recipients.
So, multicast is pretty much the same as broadcast then?
Not really.
But there are two differences between multicast and broadcast. They are related with the following two questions.
1. who do you send the data to?
2. how far do you send the data to?
I will talk about these at my next CCIE study memo.
author aglogin : February 9, 2005 11:00 PM