Ssap

Control

1 1 1-2 Variable

Fig. 11.26. Token ring format.

SD, AC and ED fields are already described. FC field is the Frame control (FC). In FC field, FF bits indicate the frame type. FF = 00 indicates MAC Frame, FF = 01 indicates LLC frame, and FF = 10 and 11 meant for reserved. RR set to 00 and they are reserved bits. ZZZZ = 0000 means a normal buffer and ZZZZ = 0001 indicates express buffer.

DA and SA are destination and source address fields respectively. DA uses the same address format of 802.3. Routing information (RI) is optional. If information field (IF) contains a MAC frame, the frame is called the MAC protocol data unit. If IF field contains an LLC frame, the field is called LLC protocol unit (LPDU). FCS is frame check sequence for error detection and Frame Status field (FS) have the field of 1 byte.

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