Introduction to Data Communications
Previous	45o. IEEE 802.5 Frames (cont'd)	Next

Frame Check Sequence (FCS)

The Frame Check Sequence (FCS) is used for error checking - uses 32 bit CRC (cyclic redundancy checking). It checks the FC, DA, SA and INFO fields. It is 4 bytes long.

End Delimiter (ED)

The End Delimiter is used to indicate the end of the frame. It consists of 8 bits in a "J K 1" sequence where J & K are Manchester coding violations.

		J K 1 J K 1 I E

Where:

• I = Intermediate bit, indicates that a frame is part of a multiframe transmission
• E = Error bit indicates that there is an error in the frame such as bad FCS, Manchester code violation, non-integral number of bytes.

Frame Status (FS)

The Frame Status (FS) field is used to indicate whether the address was recognized by the destination and if the frame was copied. This acts as an indication to the source that the destination station is present and accepting data. This FS field consists of 8 bits:

		A C r r A C r r

Where:

• A - address recognized bit
• C - Frame copied bit
• r - Reserved bit

Note: The A/C bits are provided twice for redundancy.

Introduction to Data Communications
Previous	Table of Contents	Next