The frame frequency of 32 kHz has also been chosen as a 4x multiple of that of STM-1, so that one byte of frame corresponds to the transmission capacity of a 64 kbit/s channel. The first 36 bytes of each row of a frame (with the exception of row 16) contain a Section OverHead. The first 36 bytes of row 16 contain the AU pointer (payload address). The field consisting of 261X36 bytes is for payload transmission (The STM payload is known as the Virtual Container (VC) and consists of the actual payload, known as the Container (C) and additional overhead known as Path Over Head (POH), for path related information). The Virtual Container is not located rigidly in the frame but can move around freely in the payload section. The pointer indicates the position of the first byte of the VC (which is always the first byte of the POH). This allows a VC received in the multiplexer to be matched to a pre-specified frame phase of the STM-4. Synchronous optical networking