Specifications

2-29
TOKEN RING OVERVIEW
Figure 2-6. Data Frame Structure
Start of Frame and End of Frame Sequences
The SD and AC fields are referred to as Start of Frame Sequence (SFS), and
the ED and FS fields as the End of Frame Sequence (EFS).
Frame Control (FC)
The Frame Control field shown in Figure 2-7 defines the type of frame and
certain MAC and information frame functions.
The eight bits are referenced as follows:
F F | Z Z Z Z Z Z
Where:
FF = 00 - MAC frame (Contains MAC PDU)
= 01 - LLC frame (Contains an LLC PDU)
= 1x - Undefined (Reserved for future use)
If the frame type is an LLC frame then the ZZZZZZ control bits are
designated as rrrYYY where rrr is reserved for future use and is
transmitted as 000 and the YYY bits may be used to carry the priority of
the Protocol Data Unit (PDU) from the source LLC to the destination LLC
entity.
SD AC FC DA SA INFO FCS ED FS
SFS
FCSC EFS
SFS = Start of Frame Sequence
FCSC = Frame Check Sequence Coverage
EFS = End of Frame Sequence