A Method for Calculating Frame Check Sequences in Tagged Ethernet Frames

Abstract

Like other technologies such as Internet Protocol (IP) or Transmission Control Protocol (TCP), an Ethernet frame also has a field to detect some errors occurred on transmission. This field is referred to as frame check sequence (FCS). Usually, when an Ethernet frame conveys extra information on some feature such as VLAN (Virtual Local Area Network), a field called tagis inserted into the frame and FCS must be recalculated. In this paper we propose a method for calculating a frame check sequence in a tagged frame effectively. Our method utilizes the relationship between an Ethernet frame and its tagged Ethernet frame on FCS. And it is also shown that in most cases the FCS in a tagged Ethernet frame can be easily obtained by just adding the pre-calculated result to the FCS in an original Ethernet frame.