A question about issueisochtransfer in wince.net

Hello,Thanks for your attention!
i want to use issueisochtransfer on a pipe.this pipe's maxpacksize is
1023. A Transfer consist of 32 frames.
when i use the following codes:
///////////////////////////////////////////////////////////////////////////
for(i=0 ; i < 32 ; i++ ) dwFrameLen[i] = 1023;

GetFrameNumber( hUsbdevice, &dwFrameNumber );

for( i = 0; i < 5; i++)
{
IssueIsochTransfer( hPipe, UrbComplete, hEvent,
USB_IN_TRANSFER | USB_NO_WAIT,
dwFrameNumber+5 , 32 , dwFrameLen ,
&Buffer[i] , NULL);
dwFrameNumber=dwFrameNumber+32;
}
/////////////////////////////////////////////////////////////////////////////////
it come about following problems:
1. the framenumber i specified is sometimes can't satified the request
,but msdn says it only needs to delay 3 frames . So ,how should i confirm my
specified framenumber ?
2. when i finish one urb request,the second and the subsequent requests
can't not start normally, because it can't allocate enough memory. So how
can i schedule 5 urb request sequencely? is it need to allocate physical mem
? it's better to give Example .

Thanks !