Methods for transmitting data

Abstract

A data transmission method quickly and reliably transfers data (e.g., a computer file) from a source to recipients. While the frames are being transmitted, negative acknowledgments from recipients are received by the source. These acknowledgments indicate which frames require retransmission. After all frames have been transmitted out, a retransmission is performed by the source for only those frames which the acknowledgments indicate require retransmission. Additional retransmissions can occur. This multi-pass data transfer technique requires only negative acknowledgements to be sent by the recipients. Features include the ability to set the transmission rate and to define multicast groups. Also, it is possible to determine the capacity of links of unknown capacity using a 'multicast network probe' feature of the invention, and to determine the frame error rates of known-capacity links by utilizing the same feature. A 'multicast ping' feature of the invention can be used to determine the connectivity between a source and members of a multicast group. 'Speed groups' can be set up after determining link capacities, or if they are already known, whereby the recipients connected to the source by the fastest links receive all of the data while slower-link recipients receive only a portion of the data, on the first pass. The number of recipients which can receive the data from the source can be greatly increased by using a 'negative acknowledgement collection' scheme whereby 'replication points' (preferably routers) collect individual negative acknowledgements and forward them as a unit to the next level.