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The Question is:
What is the maximum cable length for a serial cable from a VT520 terminal to a
serial port?
The Answer is :
The theoretical maximum distance is arguably limited by the speed of
light in the chosen communications medium and by signal interference
and by the speed of the data transfers required and is -- given the
appropriate hardware -- effectively limited to interplanetary distances
based solely on round-trip communications delays, though the general
baud rate for such long-distance connections will be fairly low and
the use of sliding-window-like or other protocols is recommended.
(Tachyon and faster-than-light discussions deliberately omitted.)
For information on the EIA-232 and EIA-423 requirements for traditional
serial wiring runs, please consult the associated EIA standards, or
please see the Boundless Technologies information, documentation, or
other materials on the Boundless Technologies VT520 terminal.
For network-based serial connections, please see the IEEE 802.3
network requirements. For VPN distances, planetary-scale connections
are common. For orbital connections, a network of several helical
antennas is recommended with specific sites based on the orbit.
Theoretical values aside, the practical limit is generally determined
locally and empirically, and this limit is heavily dependent on the
particular host controller UARTs, the terminal UARTs, the cable loss,
and the expected electromagnetic interference. (The performance and
the expections of various UARTs and other similar signalling devices
can and does vary (widely), of course.)
The OpenVMS Wizard has personally seen operational 9600 baud terminal
wiring runs over a kilometer in length, and has also seen other 9600
baud wire runs that will barely make three meters -- as an alternative
to traditional EIA-232 or EIA-432 serial communcations wiring, network
communications can potentially be supported over hundreds of kilometers
or more, using the appropriate network connection. Your mileage will
vary, of course.
For assistance with hardware and hardware questions, please contact
your hardware services organization, and please consult applicable
hardware specifications and standards documents.
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