DASS2 Layer2
Frame structure: fields
|
bits 8 _ _ _ _ _ _ 1 |
field |
|
octet 1 |
Address (High order octet) |
|
octet 2 |
Address (Low order octet) |
|
octet 3 |
Control |
|
octets 4-n |
Optional information |
Frame structure: address field
|
- Octet 1: |
|
|
bits 8-6 |
Signalling type |
|
bits 5-4 |
Channel type |
|
bit 3 |
Reserved (set to 1) |
|
bit 2 |
C/R: Command/Response |
|
bit 1 |
Address field extension (0) |
|
C/R value |
From network to user |
From user to network |
|
0 |
Response |
Command |
|
1 |
Command |
Response |
|
- Octet 2: |
|
|
bits 8-7 |
Reserved (set to 00) |
|
bits 6-2 |
Time-Slot |
|
bit 1 |
Address field extension (1) |
|
TS Value |
|
|
0 0 0 0 0 1 |
TS 1 |
|
0 0 0 0 1 0 |
TS 2 |
|
0 1 0 0 0 0 |
TS 16 |
|
1 1 1 1 1 1 |
TS 31 |
Frame structure: control field
The control field contains a command or a response.
U format
|
- Octet 3: |
|
|
|
bits 8-6 |
M M M |
M: modifier function bit |
|
bit 5 |
N |
Sequence Number of UI frame (modulo 2). |
|
bits 4-3 |
M M |
M: modifier function bit |
|
bits 2-1 |
1 1 |
|
The Sequence Number of each UI(Command) frame is defined as the Send Sequence Number N(P).
The Sequence Number of each UI(Response) frame is defined as the Received Sequence Number N(F).
|
bits M : 876 - 43 |
Command |
Response |
Frame designation |
|
1 1 1 - 1 1 |
SABMR |
|
Set Asynchronous Balanced Restricted Mode |
|
0 0 0 - 0 0 |
UI |
|
Unnumbered Information |
|
0 1 1 - 0 0 |
|
UA |
Unnumbered Acknowledgement |
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 (mnemonic):
M format : codes
|
N=0 |
N=1 |
Type |
C/R |
Frame designation |
|
03 |
13 |
UI |
C/R |
Unnumberd Information |
|
63 |
|
UA |
R |
Unnumbered Acknowledgement |
|
EF |
|
SABMR |
C |
Set Asynch. Balanced Mode Restricted |
Note : Hexadecimal code corresponds to b8-b1 with N bit=0 or N bit=1.
M format : types
|
Type |
N=0 |
N=1 |
C/R |
Frame designation |
|
SABMR |
EF |
|
C |
Set Asynch. Balanced Mode Restricted |
|
UA |
63 |
|
R |
Unnumbered Acknowledgement |
|
UI |
03 |
13 |
C/R |
Unnumberd Information |
Note : Hexadecimal code corresponds to b8-b1 with N bit=0 or N bit=1.
| 