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B 1.3 Coding of Control Field
Contents of field
high order           low order
8 7 6 5 4 3 2 1
I          Information frame
0
S          Supervisory frame
0 1
RR             Receiver Ready
0 0 0 1
RNR            Receiver Not Ready
0 1 0 1
REJ            Reject
1 0 0 1
U          Unnumbered frame
1 1
SARM           Set Asynchronous Response Mode
0  0 0       1  1 1  1
SABMSet        A synchronous Balanced Mode
0  0 1       1  1 1  1
DISC           Disconnect
0  1 0       0  0 1  1
UA             Unnumbered Acknowledgement
0  1 1       0  0 1  1
CMDR/FRMR Command/Frame Reject
1  0 0       0  1 1  1
• CMDR/FRMR choice is determined by whether Response mode or Balanced mode
is in effect
• The coding for the SARM command is the same as for the DM response
B 1.4  Information (I) Frame
The contents of the Control field for the I-frame are as follows:
Contents of field
high order            low order
8 7 6 5 4 3 2 1
R R R P S S S 0
Where— RRR         represents the N(R) value
represents the Poll bit
P
represents the N(S) value
SSS
The frame portion between the Control field and the FCS contains the layer three packet
information.

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