Two asynchronous multicasting techniques?patching and hierarchical merging?which optimize network bandwidth utilization are promising for on-demand video distribution. The hierarchical merging technique requires less network bandwidth than the patching technique but requires more frequent grafting of the multicast tree. This paper proposes a more optimal form of asynchronous multicasting which we call fragmented patching where even patch flows are sent in multicasting. This paper compares the required bandwidth and operational complexity on the network with the three techniques. It is the first to present mathematical models for the average usage of link bandwidth with the traffic intensity (Erlang) and the average frequency of tree grafting for multicasting. The mathematical models show that fragmented patching lessens the traffic intensity by 55% (trunk link) and by 75% and 76% (branch links which are branched to four and eight links respectively) compared with that of hierarchical merging when the request rate is 100 and the content length is 2. However the technique allows the rate of multicast tree grafting to rise. We allow broadcasting of the patch flows thus the rate of multicast tree grafting with fragmented patching remains the same as that with the patching technique. In this case fragmented patching reduces traffic by 27% (trunk) but adds traffic by 21% and 74% (branches) when the request rate is 20. However it reduces traffic by 55% (trunk link) and by 30% and 4% (branches) when the request rate is 100.

Two asynchronous multicasting techniques竏恥atching and hierarchical merging竏蜘hich optimize network bandwidth utilization are promising for on-demand video distribution. The hierarchical merging technique requires less network bandwidth than the patching technique, but requires more frequent grafting of the multicast tree. This paper proposes a more optimal form of asynchronous multicasting which we call fragmented patching, where even patch flows are sent in multicasting. This paper compares the required bandwidth and operational complexity on the network with the three techniques. It is the first to present mathematical models for the average usage of link bandwidth with the traffic intensity (Erlang) and the average frequency of tree grafting for multicasting. The mathematical models show that fragmented patching lessens the traffic intensity by 55% (trunk link) and by 75% and 76% (branch links which are branched to four and eight links, respectively), compared with that of hierarchical merging when the request rate is 100 and the content length is 2. However, the technique allows the rate of multicast tree grafting to rise. We allow broadcasting of the patch flows, thus, the rate of multicast tree grafting with fragmented patching remains the same as that with the patching technique. In this case, fragmented patching reduces traffic by 27% (trunk) but adds traffic by 21% and 74% (branches) when the request rate is 20. However, it reduces traffic by 55% (trunk link) and by 30% and 4% (branches) when the request rate is 100.