DSS1 LAYER2 - Address field format
MSB LSB
bit: 8 7 6 5 4 3 2 1
+----------------------+---+---+
octet | SAPI |C/R|EA |
2 | | | 0 |
+----------------------+---+---+
octet | TEI |EA |
3 | | 1 |
+--------------------------+---+
The elements of the address field:
EA Address field extension bit
C/R Command/response field bit
C/R
Command network -> user 1
Command user -> network 0
Response network -> user 0
Response user -> network 1
SAPI Service access port identifier
0 call control procedures
1 - 15 reserved for future
16 packet communication (X.25 3. layer)
17- 31 reserved for future
63 Layer 2 management procedures
all others Not available
TEI Terminal endpoint identifier
0 -63 non automatic TEI assignment user equipment
64-126 automatic TEI assignment user equipment
127 broadcast