Institute of Electrical and Electronics Engineering (IEEE) 1394 devices that meet the following conditions may be unable to allocate the required bus bandwidth units through the Microsoft 1394 API if the device is connected to a four-port 1394 host controller on a Windows 2000-based computer:

•	Require more than 200 megabits per second (Mbps) physical speed
•	Use isochronous data transmission
•	Require the maximum isochronous payload for 400-Mbs bandwidth as specified in IEEE-1394-1995

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This problem can occur if the 1394 Open Host Controller Interface (OHCI) host controller contains four or more ports. The 1394bus.sys driver for Windows 2000 is not able to parse Self-ID packets properly if the 1394 host controller sends multiple Self-ID packets to the computer (which occurs if the controller contains four or more ports). Under this condition, the 1394 bus driver sets the controller speed capability to 200 Mbps instead of 400 Mbps. Any 1394 physical-layer unit (PHY) that contains more than three ports must send multiple Self-ID packets, because each 1394 Self-ID packet can describe a maximum of three ports.

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To resolve this problem, obtain the latest service pack for Windows 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

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Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows 2000 Service Pack 1.

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