1. When the same message or packet needs to be sent to multiple destinations, multicasting is used.
2. Within campus and offices, using multicasting file distribution can be done.
3. System messages, news and videos can be sent at the same time.
4. More commonly used for audio and video streaming.

A public IP address allows equipment accessible to everyone on the internet. A private IP address is for private use within the network and allows many more PCs to be connected. If you are using a private IP and wants VOIP, you need to change to a public IP address.

Address Resolution Protocol ARP, is responsible for mapping an IP address to its corresponding physical network address.

Routing Protocol is the way to send routing information between any routers in an autonomous system.

Domain Name Server or DNS is used to resolve names into IP address. When a web address is entered into the browser, the DNS client sends a request to the DNS server to find the corresponding IP address for the name. The DNS server receives this request and searches for the corresponding IP address in the database. If at this point the resolution fails, this server sends this request to the parent server. The request keeps going up the hierarchy to the parent servers or the closest authoritive of the DNS server to resolve the address. If the request times out an error is returned to the client. if the server is able to resolve the name requested, it passes the information back to client. The next request sent by the client is to request for a web page for the IP address.