USB Request Block & USB Protocol

5.1 Sync Field
Each USB packet starts with a SYNC field. This is basically used to synchronise the transmitter and the receiver so that the data can be transferred accurately.
In a USB slow / full speed system this SYNC field consists 3 KJ pairs followed by 2 K’s to make up 8 bits of data.
In a USB Hi-Speed system the synchronisation requires 15 KJ pairs followed by 2 K’s to make up 32 bits of data

Bus Hound 裏面有關 URB

USB Request Block 是定義在 Windows 或 Linux 中
跟實際的USB Protocol 沒有關係
URB 的定義在 usb.h 中
它是各種不同的定義的集合 ( union )
http://msdn.microsoft.com/en-us/library/ff538923(VS.85).aspx