Functional Description
2.8
Layer-2 Functions for the ISDN Basic Access
LAPD, layer 2 of the D-channel protocol (CCITT I.441) includes functions for:
– Provision of one or more data link connections on a D channel (multiple LAP).
Discrimination between the data link connections is performed by means of a data link
connection identifier (DLCI = SAPI + TEI)
– HDLC-framing
– Application of a balanced class of procedure in point-multipoint configuration.
The simplified block diagram in figure 56 shows the functional blocks of the ISAC-S which
support the LAPD protocol.
Layer 1
R
IOM
Layer-1
Functions
HDLC
Receiver
HDLC
Transmitter
LAPD
Controller
S(D-Channel)
Status
Command
Registers
R-FIFO
2 x 32 byte
X-FIFO
2 x 32 byte
FIFO
Controller
Layer 2
µP-Interface
µC-System
Upper
Layers
ITS00861
Figure 56
D-Channel Processing of the ISAC®-S
Semiconductor Group
107
INFINEON [ Infineon ]
