Method of determining whether to use preempt/resume or alternate protocol for data transmission

For use in a multi-system network in which data may be transmitted in either low-priority data packets or high-priority data packets, a method for determining whether to use a preempt/resume protocol or an alternate protocol for transmitting data packets from a local system to a remote system over a connecting communications link having a known line speed, said method being practiced at the local system and comprising steps of:

• a) sending a message to the remote system, said sent message containing fields indicating 1) whether the local system supports use of a preempt/resume protocol and 2) the size of the largest low-priority data packet the local system can send;
• b) receiving a message from the remote system, said received message indicating 1) whether the remote system supports use of a preempt/resume protocol and 2) the size of the largest low-priority data packet the remote system can receive;
• c) if the sent and received messages indicate that either or both of the local and remote systems do not support use of a preempt/resume protocol, then choosing an alternate protocol;
• and
• d) if the sent and received messages indicate that both of the system support use of a preempt/resume protocol
• 1) using field values in the sent and received messages, comparing the size of the largest low-priority data packet the local system can send to the size of the largest low-priority data packet the remote system can receive and selecting the lesser of the two sizes,
• 2) based on the known line speed and the selected size, determining whether transmission of a low-priority data packet of the selected size from the local system would delay transmission of a subsequent data packet by more than a predetermined amount of time, and
• 3) initiating use of a preempt/resume protocol only where the preceding step indicates transmission of a low-priority data packet of the selected size would delay transmission of a subsequent data packet by more than the predetermined amount of time.