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4.18.3 Composing Tunneled Signaling Messages
The process of sending a tunneled signaling message begins by composing a GC_PARM_BLK that
contains Global Call parameter elements for the message protocol, the message content, and any
nonstandard data.
The first parameter element identifies the message protocol. It must be one of the following two
forms:
IPSET_TUNNELEDSIGNALMSG
IPPARM_TUNNELEDSIGNALMSG_PROTOCOL_OBJECTID
• value = protocol object ID information in an IP_TUNNELPROTOCOL_OBJECTID data
structure and conforming to the appropriate ASN.1 format
IPSET_TUNNELEDSIGNALMSG
IPPARM_TUNNELEDSIGNALMSG_ALTERNATEID
• value = alternate protocol ID information in an IP_TUNNELPROTOCOL_ALTID data
structure
The second parameter element contains the actual message content. Applications should use the
gc_util_insert_parm_ref_ex( ) function to insert this parameter element because the parameter
data may exceed 255 bytes.
IPSET_TUNNELEDSIGNALMSG
IPPARM_TUNNELEDSIGNALMSG_CONTENT
• value = actual message content
max. length = max_parm_data_size (configured at library start-up)
In practice, applications may not be able to utilize the full maximum length of the TSM content
parameter element as configured in max_parm_data_size, particularly if the TSM also contains
non-standard data. The H.323 stack limits the overall size of messages to be max_parm_data_size
+ 512 bytes, and any messages that exceed this limit are truncated without any notification to the
application.
If the tunneled signal message includes optional nonstandard data, the GC_PARM_BLK needs to
contain two additional parameter elements. These parameters should only be inserted in the
GC_PARM_BLK if nonstandard data is being sent in the message. The first parameter element for
nonstandard data is:
IPSET_TUNNELEDSIGNALMSG
IPPARM_TUNNELEDSIGNALMSG_NSDATA_DATA
• value = actual nonstandard data, max. length = max_parm_data_size (configured at
library start-up)
Applications should use the gc_util_insert_parm_ref_ex( ) function to insert this parameter
element because the parameter data may exceed 255 bytes.
In practice, applications may not be able to utilize full maximum parameter length configured in
max_parm_data_size for nonstandard data content. The H.323 stack limits the overall size of
messages to be max_parm_data_size + 512 bytes, which must contain the tunneled signaling
message content as well as the nonstandard data.