Abstract
For almost three decades the multicast communication has been a subject of a dynamic research. It came to the world of the packet switching networks rather late and still has not become a fist class citizen of the Internet, yet the demand for such services is growing and thus the relevant technologies evolve persistently providing increasing quality and availability of the means of the group communication. The overlay approach to the multicast is an application layer realization which came to life due to certain deficiencies at the lower layers. In general the gain from using multicast for group communication instead of duplicated unicast links is that we avoid sending the same data many times through a single link. Such gain may be achieved wit the use of the router level mulitcast solution. The overlay solutions tend to approach his level of efficiency with a different degree of success. Therefore one of the main characteristics that is interesting when evaluating a particular overlay protocol is how well does it achieve the aforementioned gain. There are several metrics that allow for objective comparison of protocols in this regard. However this is not the only point of view to provide a valuable evaluation of the multicast overlay solutions. One of the important aspects of the modern group communication such as the IPTV or teleconferencing is the dynamic nature of the users’ participation. A particular group may be joined and left by multiple users at a very frequent rate which is critical to the resources management as well as to maintaining the integrity of the abstract communication structure, e.g. a tree spanning all the participants. In such case two major classes of the evaluation criteria emerge: the statical and the dynamical ones. They’re both very important and interdependent, however the means to measure them may differ significantly. In this article a wide variety of the multicast overlay protocols have been analysed and two of them have been chosen to be compared. The stress of the evaluation has been put on the dynamic aspects of the multicast overlay protocols operation.
An overlay approach to data security in ad-hoc networks