SDLC
Reference standard: IBM GA27-3093-2
SDLC frame structure: fields
| length |
field |
| 1 octet |
Address |
| 1 octet |
Control |
| n octets |
Optional information |
| 2 octets |
Frame Control Sequence |
Address field
Reference standard: ISO 3309
The address field identifies a frame as either a command or a response. A
command frame contains the address of a station to which the command is being
sent. A response frame contains the address of the station sending the frame.
| bits 1 _ _ _ _ _ _ 8 |
Address field basic mode |
| a a a a a a a a |
1 octet - value 0 to 255 |
Control field
The control field contains a command or a response, and sequence numbers
where applicable.
Three types of control field formats are used to perform:
- numbered information transfer
with I format,
- numbered supervisory
functions with S format,
- unnumbered control functions
with U format.
| - 1rst octet: |
|
| bit 1 |
0 |
|
| bits 2-4 |
N(S) |
Transmitter send sequence number |
| bit 5 |
P |
Poll bit (1 = Poll) |
| bits 6-8 |
N(R) |
Transmit. receive sequence number |
| bit 1 |
Command |
Response |
Frame designation |
| 0 |
I |
|
Information |
| - 1rst octet: |
|
| bits 1-2 |
1 0 |
|
| bits 3-4 |
S S |
S: supervisory function bit |
| bit 5 |
P/F |
Poll bit when issued as a command
Final bit when issued as a response
(1 = Poll/Final)
|
| bits 6-8 |
N(R) |
Transmit. receive sequence number |
| bits 3-4 = SS |
Command |
Response |
Frame designation |
| 0 0 |
RR |
RR |
Receive Ready |
| 0 1 |
RNR |
RNR |
Receive Not Ready |
| 1 0 |
REJ |
REJ |
Reject |
| 1 1 |
SREJ |
SREJ |
Selective Reject |
The encoding values of the two S bits included in the first octet of the
control field are listed and ordered according to their hexadecimal code:
| octet code |
Type |
C/R |
Frame designation |
| x1 |
RR |
C/R |
Receive Ready |
| x9 |
RNR |
C/R |
Receive Not Ready |
| x5 |
REJ |
C/R |
Reject |
| xD |
SREJ |
C/R |
Selective Reject |
Note : Hexadecimal code corresponds to b8-b1.
| - 1rst octet: |
|
| bits 1-2 |
1 1 |
|
| bits 3-4 |
M M |
M: modifier function bit |
| bit 5 |
P/F |
Poll bit when issued as a command Final bit when
issued as a response
(1 = Poll/Final)
|
| bits 6-8 |
M M M |
M: modifier function bit |
| |
|
|
| bits M : 34 - 678 |
Command |
Response |
Frame designation |
| 0 0 - 0 0 1 |
SNRM |
|
Set Normal Response Mode |
| 1 1 - 1 0 0 |
SARM |
|
Set Asynchronous Response Mode |
| 1 1 - 1 0 0 |
SABM |
|
Set Asynchronous Balanced Mode |
| 0 0 - 0 1 0 |
DISC |
|
Disconnect |
| 1 1 - 0 1 1 |
SNRME |
|
Set Normal Response Mode Extended |
| 1 1 - 0 1 0 |
SARME |
|
Set Asynchronous Response Mode Extended |
| 1 1 - 1 1 0 |
SABME |
|
Set Asynchronous Balanced Mode Extended |
| 1 0 - 0 1 0 |
SIM |
|
Set Initialization Mode |
| 0 0 - 1 0 0 |
UP |
|
Unnumberd Poll |
| 0 0 - 0 0 0 |
UI |
UI |
Unnumberd Information |
| 1 1 - 1 0 1 |
XID |
XID |
Exchange Identification |
| 1 1 - 0 0 1 |
RESET |
|
Reset |
| 0 0 - 1 1 1 |
TEST |
TEST |
Test |
| 1 0 - 0 1 1 |
CFGR |
|
Configure |
| 1 1 - 0 0 0 |
|
DM |
Disconnected Mode |
| 0 0 - 1 1 0 |
|
UA |
Unnumbered Acknowledgement |
| 1 0 - 0 0 1 |
|
FRMR |
Frame Reject |
| 0 0 - 0 1 0 |
|
RD |
Request Disconnect |
| 1 0 - 0 0 0 |
|
RIM |
Request Initialization Mode |
| 1 1 - 1 1 1 |
|
BCN |
Beacon |
The encoding values of the five M bits included in the first
octet of the control field can also be listed and ordered
according to their hexadecimal code
or their type.
| P=0 |
P=1 |
Type |
C/R |
Frame designation |
| 03 |
13 |
UI |
C/R |
Unnumberd Information |
| 07 |
17 |
RIM |
R |
Request Initialization Mode |
| 07 |
17 |
SIM |
C |
Set Initialization Mode |
| 0F |
1F |
DM |
R |
Disconnected Mode |
| 0F |
1F |
SARM |
C |
Set Asynchronous Response Mode |
| 13 |
23 |
SNRM |
C |
Set Normal Response Mode |
| 23 |
33 |
UP |
C |
Unnumberd Poll |
| 2F |
3F |
SABM |
C |
Set Asynchronous Balanced Mode |
| 43 |
53 |
DISC |
C |
Disconnect |
| 43 |
53 |
RD |
R |
Request Disconnect |
| 4F |
5F |
SARME |
C |
Set Asynch. Response Mode Extended |
| 63 |
73 |
UA |
R |
Unnumbered Acknowledgement |
| 6F |
7F |
SABME |
C |
Set Asynch. Balanced Mode Extended |
| 87 |
97 |
FRMR |
R |
Frame Reject |
| 87 |
97 |
RESET |
C |
Reset |
| AF |
BF |
XID |
C/R |
Exchange Identification |
| C7 |
D7 |
CFGR |
C |
Configure |
| CF |
DF |
SNRME |
C |
Set Normal Response Mode Extended |
| E3 |
F3 |
TEST |
C/R |
Test |
| EF |
FF |
BCN |
R |
Beacon |
Note : Hexadecimal code corresponds to b8-b1
with P/F bit=0 or P/F bit=1.
| Type |
P=0 |
P=1 |
C/R |
Frame designation |
| BCN |
EF |
FF |
R |
Beacon |
| CFGR |
C7 |
D7 |
C |
Configure |
| DISC |
43 |
53 |
C |
Disconnect |
| DM |
0F |
1F |
R |
Disconnected Mode |
| FRMR |
87 |
97 |
R |
Frame Reject |
| RD |
43 |
53 |
R |
Request Disconnect |
| RESET |
87 |
97 |
C |
Reset |
| RIM |
07 |
17 |
R |
Request Initialization Mode |
| SABM |
2F |
3F |
C |
Set Asynchronous Balanced Mode |
| SABME |
6F |
7F |
C |
Set Asynch. Balanced Mode Extended |
| SARM |
0F |
1F |
C |
Set Asynchronous Response Mode |
| SARME |
4F |
5F |
C |
Set Asynch. Response Mode Extended |
| SIM |
07 |
17 |
C |
Set Initialization Mode |
| SNRM |
13 |
23 |
C |
Set Normal Response Mode |
| SNRME |
CF |
DF |
C |
Set Normal Response Mode Extended |
| TEST |
E3 |
F3 |
C/R |
Test |
| UA |
63 |
73 |
R |
Unnumbered Acknowledgement |
| UI |
03 |
13 |
C/R |
Unnumberd Information |
| UP |
23 |
33 |
C |
Unnumberd Poll |
| XID |
AF |
BF |
C/R |
Exchange Identification |
Note : Hexadecimal code corresponds to b8-b1
with P/F bit=0 or P/F bit=1.
| 