A technique in which a single copy of data is sent over a network to a specific group of computers. Multicasting is connectionless - clients receive multicast transmissions by “tuning in” to them, a process similar to tuning in to a radio station. Multicasting is essentially a point-to-multipoint communication mechanism.
Microsoft NetShow is an example of an application that uses multicasting technology to transmit streaming audio and video over the Internet and corporate intranets. Multicasting is unidirectional communication between a NetShow server and a NetShow client.
NetShow multicasts require two pieces of information:
The method used to inform the client of the destination IP address and port depends on the kind of stream being multicast. The types of streams are as follows:
Multicast IP addresses are class D addresses and fall in the range 188.8.131.52 through 184.108.40.206. For intranet use, addresses in the range 239.*.*.* are recommended. Port numbers can range from 1 through 65535, although ports below 1024 are reserved, as are some ports above 1024. Port numbers for RTP audio should be even numbers in the range 16384 through 32768.
In NetShow you set multicast scopes by specifying a Time to Live (TTL) value, which decrements each time packets pass through a router. NetShow default scope values are as follows:
These values can be customized to meet the needs of your network.