Unicasting is a Two-way, point-to-point communication between stations on a network. This is in contrast to broadcasting, which is multipoint in nature and directs information to all accessible hosts on the network, and multicasting, which directs information only to hosts that request it. For a unicast packet to arrive at its destination host on the network, it must be configured with the specific destination address of that host, usually in the form of a logical address such as an IP address and a physical address, or MAC address.
Most user-initiated network traffic is unicast or directed traffic, while broadcast traffic is mostly for clients and services to announce themselves on the network and multicast traffic is for streaming multimedia communication. In the TCP/IP protocol suite, both the connection-oriented Transmission Control Protocol (TCP) and the connectionless User Datagram Protocol (UDP) support unicast transmission of Internet Protocol (IP) packets.
Graphic U-2. Comparison with multicasting and broadcasting.
Routers, which are network devices that can forward packets to other networks, are usually configured to forward unicast packets (packets directed to a specific host on a destination network) but not broadcast packets (packets directed to all users on a subnet, network, or internetwork). You can use a Microsoft Windows NT or Windows 2000 multihomed system for unicast IP routing by installing the Routing and Remote Access Service (RRAS), which turns the system into a dynamic router that supports both the Routing Information Protocol (RIP) and the Open Shortest Path First (OSPF) Protocol.
In addition to supporting streaming multicast traffic, Microsoft NetShow supports unicasting to transmit streaming audio and video over the Internet and corporate intranets directly from a NetShow server to a specific NetShow client.