Isochronous data transfers fail when you attach a remote 1394A-compliant IEEE 1394 node to a Windows Vista-based or Windows Server 2008-based computer that does not support the IRM role
Consider the following scenario on a computer that is running Windows Vista or Windows Server 2008:
- You have an IEEE 1394 bus host controller installed on the computer.
- This IEEE 1394 bus host controller does not contain a physical layer (PHY) chip that complies with the IEEE 1394A (2000) specification.
- You attach a remote IEEE 1394 node that can function in the Isochronous Resource Manager (IRM) role. The node can be either of the following:
- Another computer on which there is an IEEE 1394 bus host controller that contains a 1394A PHY chip.
- Another IEEE 1394 device that supports the IRM role.
In this scenario, operations to support isochronous data transfers, such as querying for and allocating Isochronous Bandwidth and Channels, may fail. Additionally, isochronous data transfers may be impossible.
For example, when you issue a REQUEST_ISOCH_QUERY_RESOURCES request in an application, the request should be forwarded to the IRM on the remote node. Then, the request should return the channels and the bandwidth that are currently available according to the IRM’s registers. However, the request may be chained to the local IEEE 1394 host controller instead. Therefore, the request returns ’0′s for all available channels and the bandwidth.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB973414.