Improving application layer multicast forwarding performance by offloading multisend operations

摘要

Multicast is considered as an efficient mechanism to support group communication applications. Application Layer Multicast (ALM) has become an effective alternative to IP multicast across the Internet at present. In the traditional ALM forwarding, if end-host is to send data packets to N different receivers, then the N copies of each packet have to be sent from host memory to network interface card (NIC) buffer, marking poor use of the limited bandwidth and computing resource. Therefore, this paper proposes a high performance multicast forwarding scheme, in which NIC-based multisend approach is used to send multiple copies of ALM packet to different destinations with less CPU intermediation compared to the traditional Host-based multisend scheme. By adopting NIC-based multisend scheme, the CPU overhead and the number of times that data packets are copied from host memory to NIC buffer are reduced. Theoretical analysis indicates that the new scheme can notably decrease the multicast delay and enhance the service capability of ALM proxies by offloading multisend operations onto NIC. We have modified the NIC driver and added some corresponding APIs to network protocol stack to implement the proposed scheme. Experimental results illustrate that NIC-based multisend scheme can greatly improve forwarding performance for ALM.