User guide

August 2001 73
Handling Incoming and Outgoing Calls
Transferring Calls
You can transfer calls on digital lines if the equipment
connected to your system supports call transfers. Most COs do
not support call transfer if your application is emulating
another CO. However, if your application is emulating customer
equipment, the CO might allow call transfers if you have the
service enabled. In most cases, you can do call transfers if you
have Centrex lines or if your system is connected to a PBX that
supports digital lines as extensions. You will need support from
your PBX manufacturer, but you can transfer calls to any
destination your PBX supports. Loop Start and Ground Start
protocols are the only two that normally do call transfers.
Use RHT_HOOK_FLASH to transfer calls. This is the same
function used in analog lines. When you call
RHT_HOOK_FLASH, the driver uses the protocol file to send
the appropriate bit patterns and timings for the digital hook
flash.
To perform a hook flash, the channel must be off hook and
transmitting the appropriated bit pattern for that protocol. A
brief on hook pattern is transmitted for the duration specified
by RDG_LOCAL_FLASH_DUR, followed by the off hook
pattern again for the duration specified by
RDG_LOCAL_FLASH_GUARD_TIME.
The only requirements for a protocol to support a hook flash are
on hook and off hook bit patterns that differ from each other.
However, the flash signal might be ignored or interpreted as a
disconnect followed by a line seizure if the CO does not support
call transfer. The only protocols that cannot transmit a flash
hook signal are the CO versions of Loop Start and Ground Start.