Welltech Dialogic SS7 Protocols ISUP - Manual (Page 111)

Dialogic ® SS7 Protocols ISUP Programmer's Manual Issue 15
111
6.8.8 BICC Application Transport
If the ISUP module receives a message containing an application transport
parameter with the Application context set to BAT ASE and the segmentation
indicator not set to final segment, it starts timer TIM_REASS (wait for
segmentation message, if enabled – see treass in ISP_MSG_CNF_TIM). If
TIM_REASS expires, ISUP will send an Application Transport (APM) message
with the context identifier set to EUCEH ASE, the APM segmentation Indicator
(set to final segment(0)), the Segmentation local reference, and the
Origination Address to the user application indicating that the timer has
expired.
8 7 6 5 4 3 2 1
ext = 1 Application context identifier = 0x6 (EUCEH ASE) 1
ext = 1 0 SNI = 0 RCI = 0 2
ext = 0 SI = 0 APM segmentation indicator = 0 3
ext. Segmentation local reference 3a
Originating Address length 4
Originating Address 4a
Destination Address length = 0 5
ext = 1 APM-User context identifier = 5 6
ext = 1 Reason = Reassembly error = 2 7
An APM message will also be sent to the user application if another BICC
message is received in the same direction, for the same CIC, OPC, DPC and
SIO, before the APM segment or a SGM message was received. For example,
if the ISUP module received an ACM from the network containing a
segmented APP parameter and subsequently received an ANM before the
second segment of the APP parameter, the ISUP module would send ACM
followed by an APM before sending the ANM to the user application.
In this way, the ISUP module ensures that the user application will always
receive an APM message following a message with the segmentation indicator
set and will never receive a "stray" message segment. The user application
does not need to run timer TIM_REASS.
APM Segment validation can be disabled by setting the BICX1GOP_REASS bit
of the ext_1_options field of ISP_MSG_CNF_GRP to 0.
Whether the application stores the received message whilst awaiting the
segment or passes it to the other side of the call depends on the position in
the network.