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ViewStation EX, ViewStation FX, and VS4000 API Guide
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• Pass-Thru Mode to Pass-Thru Mode: Both endpoints are set to
Pass-Thru Mode.
• Pass-Thru Mode to Control Mode: The near site is set to
Pass-Thru Mode and the far site is set to Control Mode.
Operational Modes: The following information describes
operational modes in more detail.
• Pass-Thru Mode to Pass-Thru Mode—Two stations set to
Pass-Thru Mode behave essentially as a null-modem between
their respective externally connected devices. These two
stations can be two ViewStation EX systems, two ViewStation
FX systems, two VS4000 systems, or one ViewStation EX
system and one ViewStation FX or VS4000 system.
The RS-232 port is used as a data channel over an H.320 video
call. Data received from the RS-232 port on the near-end
system is pushed through the call to the far-end endpoint and
then transmitted to the endpoint’s RS-232 port. Similarly, data
from the far-end endpoint is transmitted back to the near-end
system (through the H.320 call) and then transmitted to the
near-end RS-232 port.
The data channel speed is dynamically allocated. The maximum
data flow rate is based on the bandwidth of the call.
Because data throughput has priority over video throughput,
video bandwidth may be restricted to support data
requirements. Audio is not compromised.
Pass-Thru Mode is a proprietary feature that is only supported
when both endpoints are either ViewStation EX, ViewStation
FX, or VS4000 systems.
The RS-232 port only supports data Pass-Thru in H.320 mode
(ISDN or V.35/RS-449/RS-530/RS-366/RS-366). Data
Pass-Thru in an H.323 (IP) video call or multipoint call is not
supported, as alternative file transfer methods such as ftp or
Telnet are widely available.
Note In Pass-Thru mode, both local and remote stations
need to be set to the same data rate.
• Pass-Thru Mode to Control Mode—If the near site is set to
Pass-Thru Mode, but the far site is set to Control Mode, then the
device connected to the near site RS-232 port can be used to