[LAU] Latency and jack parameters clarification

In trying to get support with this usb problem in kernel 3.8: https://bugs.launchpad.net/bugs/1191603 I have been asked to provide info on what the period size in jack is and how the round trip latency is calculated. The dev can't see how with a 1ms latency (which is what jack is using with a period size of 256 samples) the round trip latency is around 10ms. I have quoted bits of the jack manual page but he doesn't find this helpful and I have now reached the limits of my understanding of the matter and can't find any more detailed descriptions on the web. It would be great if someone with a more in-depth understanding could help out here! James