In applications like IPTV, multicasting provides beneficial services. However, due to overhead and problems of multicast transmission, multicasting is not always profitable. In order to make well-justified decisions whether it is worthwhile to use multicasting or not, its efficiency must be quantified. Therefore, the metric of ‘multicast gain’ is introduced as a measure for the bandwidth reduction which can be expected when using multicast (instead of multiple unicast). Different definitions for multicast gain are given to cover different types of links. As an application of our metric, multicast transmission of live TV channels in WiMAX-based access networks is analyzed. WiMAX as one of the 4G candidates can transmit IPTV services to mobile subscribers because of salient features such as multicast support, wide coverage range and high bandwidth. In OFDMA-based WiMAX the smallest logical bandwidth allocation unit is a slot. In this article, we use the term slot to measure the efficiency of multicasting in WiMAX networks. We show that for unpopular TV channels, using unicast flows can be preferable.
