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Global Call IP Technology Guide — November 2007 161
Dialogic Corporation
IP-Specific Operations
different from the current session properties, and to decide whether any proposed change is
acceptable.
The GC_PARM_BLOCK that is associated with the GCEV_REQ_MODIFY_CALL event may
contain any number of parameter elements which identify the supported media properties that were
proposed in the request. Each proposed media capability is handled as a parameter element of the
following type:
GCSET_CHAN_CAPABILITY
IPPARM_LOCAL_CAPABILITY
• value = IP_CAPABILITY data structure
The number of these parameter elements depends on the specifics of what change the re-INVITE is
requesting:
• If the SDP offer in the re-INVITE is proposing a full-duplex media session, there will be a pair
of GCSET_CHAN_CAPABILITY/IPPARM_LOCAL_CAPABILITY parameter elements for
each proposed media capability that is supported on the local platform, one element for each
direction. Within each parameter pair, all fields of the of the IP_CAPABILITY structure will
be the same except for the direction fields, one of which will be IP_CAP_DIR_LCLRECEIVE
and the other IP_CAP_DIR_LCLTRANSMIT.
• If the SDP offer in the re-INVITE is proposing a half-duplex media session, there may be only
a single GCSET_CHAN_CAPABILITY/ IPPARM_LOCAL_CAPABILITY element in the
parameter block, although multiple elements are possible if multiple coders are being
proposed. Within each parameter element, the IP_CAPABILITY.direction field will be either
IP_CAP_DIR_LCLRECVONLY or IP_CAP_DIR_LCLSENDONLY.
• If the SDP offer in the re-INVITE is seeking to suspend streaming (to place the call on hold,
for example), there may be only a single GCSET_CHAN_CAPABILITY/
IPPARM_LOCAL_CAPABILITY element in the parameter block, although multiple
elements are possible. When the re-INVITE is requesting to suspend streaming, the
IP_CAPABILITY.direction field will be set to either IP_CAP_DIR_LCLRTPINACTIVE or
IP_CAP_DIR_LCLRTPRTCPINACTIVE.
• If the SDP offer in the re-INVITE is proposing a change from audio mode to T.38 fax mode,
there will be only one GCSET_CHAN_CAPABILITY/ IPPARM_LOCAL_CAPABILITY
element in the parameter block. Within this element, the IP_CAPABILITY.capability field will
be GCCAP_DATA_t38UDPFax and the IP_CAPABILITY.direction field will be
IP_CAP_DIR_LCLTXRX.
Finally, The GC_PARM_BLK will include a parameter element that contains the remote RTP
transport address, which may be the same as the existing address or may be different. It is the
application’s responsibility to compare the address to determine whether it is different and whether
the proposed change is acceptable.
The RTP transport address is handled as a parameter element of the following type:
IPSET_RTP_ADDRESS
IPPARM_REMOTE
• value = RTP_ADDR data structure