# Sending LAPD messages

The NMS ISDN stack must be in LAPD stack mode to send LAPD messages.

To send a LAPD message, the application builds an ISDN_MESSAGE structure specifying the message primitive and other data, as follows:

ISDN_MESSAGE field | Value
--- | ---
nai | Specifies the network access identifier (NAI) of the destination trunk.
from_ent | ENT_APPLI Indicates that the message is sent from the application to the stack.
to_ent | ENT_DL_D Indicates that the message is sent to the data link layer.
to_sapi | DL_SAPI_SIG
conn_id | 1
code | Specifies the primitive of the LAPD message (for example DL_EST_RQ).
inf0, inf1, inf2, inf3, inf4 | Reserved for internal data relay.
data_size | Specifies the size of the message buffer containing data associated with the message, if any.
nfas_group | Specifies the NFAS group number for this network access identifier (NAI). Used only if duplicate NAI values are defined.
userid | Not used.

If necessary, the application also builds a message buffer containing data to send.