In the network level computer group-communication (one-to-many) technology, IP-multicast contributes significant roles in enhancing the physical network scalability by replicating identical packets at routers. However, since its initial proposal the IP-multicast has not been widely enabled due to the slow pace of its deployment. Hence, the application-level multicast (ALM) concept emerged to solve this deployment issue by shifting the multicast support from routers to end-systems. The article reviews the most important facts of the Application-Level Multicast and its proposed models. Furthermore, the article describes a novel concept of modeling relative density of members called bunched mode and a proposed host-end multicast transport protocol called shortest tunnel first (STF). The bunched mode is based on the thematic multicast concept (TMC), which means that it is a typical multicast scenario where there are a lot of interested hosts in certain institutes and these institutes are relatively far from each other. The developed analysis tool NetSim and the implementation of the TMC called PardedeCAST are also presented as the tools of this research.
Key Terms in this Chapter
Application-Level Network (ALN): The applications, which are running in the hosts, can create a virtual network from their logical connections. This is also called overlay network (see following term). The operations of such software entities are not able to understand without knowing their logical relations. The most cases this ALN software entities use the P2P model (see following term), not the client/server (see following term) one for the communication.
Autonomous System (AS): Network with common administration; it is a basic building element of the Internet. Each AS is independent from the others.
Peer-to-Peer (P2P): It is a communication way where each node has the same authority and communication capability. They create a virtual network, overlaid on the Internet. Its members organize themselves into a topology for data transmission.
Client/Server Model: A communicating way, where one host has more functionality than the other. It differs from the P2P model (see following term).
Local Area Network (LAN): Network, where inside of it there is not routing. There is in the LAN a router acting as gateway and the remained nodes are usually hosts without any routing functionality.
Ad Hoc Computer Network: Mobile devices that require base stations can create the ad hoc computer network if they do not need routing infrastructure.
Ad Hoc Network: A network which does not need any infrastructure. Such network is the Bluetooth.
Application-Layer Multicast (ALM): A novel multicast technology, which does not require any additional protocol in the network routers, since it uses the traditional unicast IP transmission. Its alternative name is application-level multicast.
Multicast Island: Multicast capable network, where all routers have multicast routing protocols and the IP-multicast is available. One of the main problems of the IP-multicast is to connect the multicast islands into an Internet-wide network.
Overlay Network: The applications, which create an ALN (see previous term), work together, and they usually follow the P2P communication model (see following term).