. It is
(ABR). An ATM switch keeps this field reserved or sets it in accordance with the ITU recommendation.A SN cell is sent out periodically on all lines
(AIMUX) and indicates how many cells have been sent in the time
between the last SN cell and the one currently being transmitted. The SN cell is used to restore the sequence of the payload cells at the receiving location. In the Realtime Transport Protocol (RTP), the Sequence Number (SN) is a 1-byte data field.