Welltech Dialogic SS7 Protocols ISUP - Manual (Page 24)

Section 6 Interface to Application
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call_ref is used to identify the circuit or call to which the message refers.
Currently, when 32768 circuits or less are configured, the most significant bit
of the call_ref is ignored by the ISUP module, and the remaining bits map
directly to the Circuit Identifier cid so the valid range for call_ref is from 0 to
one less than the number of circuits supported. If more than 32768 circuits
are configured, then the call_ref is identical to the cid.
Note: Earlier revisions of the ISUP module required the most significant bit of the
call_ref to be set in all messages relating to outgoing calls.
6.2.2 Receive Indication
This primitive is used by the ISUP module to send a message to the
application module.
Primitive Indication From ISUP
Field Name Meaning
type ISP_MSG_RX_IND (0x8701)
id call_ref
src ISUP module ID
dst Application module ID
rsp_req 0x00
hclass 0x00
status 0x00
err_info 0x00
len Number of bytes of user data
parameters User data (Len bytes in length)
call_ref is used to identify the circuit or call to which the message refers.
Currently, when 32768 circuits or less are configured and the ISPF_16CID
flag is set to 0, the most significant bit of the call_ref is set to 1 by the ISUP
module for all messages relating to outgoing calls and the remaining bits map
directly to the Circuit Identifier cid. If 32768 circuits or less are configured
and the ISPF_16CID flag is set to 1, or if more than 32768 circuits are
configured, then the call_ref is identical to the cid.
Note: Earlier revisions of the ISUP module required the most significant bit of the
call_ref to be set in all messages relating to outgoing calls. To allow for
interworking with earlier application software which make use of this bit the ISUP
module continues to set the bit in all messages relating to outgoing calls for
configurations with 32768 circuits or less, when the ISPF_16CID flag has been set
to 0. It is recommended that existing applications be modified to ignore the
setting of the most significant bit.